i

Materials Science and

Engineering Laboratory

FY 2004 Programs and

Accomplishments

Materials

Reliability

Division

Alan F. Clark, Chief

Thomas A. Siewert, Deputy

NISTIR 7125

September 2004

National Institute of

Standards and Technology

Arden L. Bement, Jr.

Director

Technology

Administration

Phillip J. Bond

Undersecretary of

Commerce for Technology

U.S. Department

of Commerce

Donald L. Evans

Secretary
ii

Certain commercial entities, equipment, or materials may be identified in this document in order to

describe an experimental procedure or concept adequately. Such identification is not intended to imply

recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended

to imply that the entities, materials, or equipment are necessarily the best available for the purpose.
iii

Table of Contents

Table of Contents

Executive Summary ...................................................................................................................1

Technical Highlights...................................................................................................................3

Targeted Workshops: Developing Strategies for the Future ..............................................4

The Structural Steel of the World Trade Center Towers ....................................................6

Quantitative Nanomechanical Properties ...........................................................................8

Pediatric Pulmonary Hypertension ...................................................................................10

Nanometrology ........................................................................................................................13

Metrology for Nanoscale Properties

Metrology for Nanoscale Properties:

Brillouin Light Scattering ...................................................................................................14

Metrology for Nanoscale Properties:

X-ray Methods ..................................................................................................................15

Physical Properties of Thin Films and Nanostructures

Physical Properties of Thin Films and Nanostructures:

Grain Size Effects on Actuator Fatigue ............................................................................16

Physical Properties of Thin Films and Nanostructures:

Nanoporous Low-κ Dielectric Films ................................................................................ 17

Physical Properties of Thin Films and Nanostructures:

Green’s-Function Methods ................................................................................................18

Applications of Carbon Nanotubes

Applications of Carbon Nanotubes:

Carbon Nanotubes and Nanotube Contacts .....................................................................19

Applications of Carbon Nanotubes:

Cell Viability in Contact with Carbon Nanotubes .............................................................20

Applications of Carbon Nanotubes:

Electrochemical Characterization of In-Vivo Neuronal Probes .......................................21

Biomaterials .............................................................................................................................22

Biomaterials Metrology

Biomaterials Metrology:

Pediatric Pulmonary Hypertension ...................................................................................23

Biomaterials Metrology:

Mechanical Response of Tissue Engineering Constructs .................................................24
iv

Table of Contents

Biomaterials Metrology:

Cellular Level Measurements ........................................................................................... 25

Biomaterials Metrology:

Quantitative Ultrasonic Characterization ..........................................................................26

Materials for Electronics .........................................................................................................27

Electronic Packaging and Components

Electronic Packaging and Components:

Packaging Reliability .........................................................................................................28

Electronic Packaging and Components:

Acoustic Characterization .................................................................................................29

Micrometer-Scale Reliability

Micrometer-Scale Reliability:

Mechanical Behavior of Thin Films ..................................................................................30

Micrometer-Scale Reliability:

Chip-Level Interconnects..................................................................................................31

Micrometer-Scale Reliability:

Dynamic Imaging of Magnetic Domain Walls .................................................................. 32

Micrometer-Scale Reliability:

Bridging Length Scales .....................................................................................................33

Micrometer-Scale Reliability:

Molecular Dynamics .........................................................................................................34

Micrometer-Scale Reliability:

Solder Reliability................................................................................................................35

Safety and Reliability ...............................................................................................................36

Infrastructure Reliability:

Steel in the World Trade Center........................................................................................37

Infrastructure Reliability:

Test Methods for Fire-Resistant Steel .............................................................................. 38

Infrastructure Reliability:

Waveform-Based Acoustic Emission ................................................................................39

Infrastructure Reliability:

Charpy Impact Machine Verification ................................................................................40

Materials Reliability Division FY04 Annual Report Publication List .......................................41

Materials Reliability Division ...................................................................................................45

Research Staff.........................................................................................................................46

Organizational Charts ..............................................................................................................49
1

Executive Summary

The Materials Reliability Division’s mission is

to develop and disseminate measurement methods

and standards enhancing the quality and reliability of

materials for industry. We have changed our portfolio

of research projects slightly this past year as we have

found new, critical technology gaps that limit the

reliable use of materials. Yet we have maintained our

competence in our core areas. Much of our research

is concentrated in the NIST Strategic Focus Areas of

Nanotechnology, Health Care, and Homeland Security.

Our work covers a wide range of materials with

a dimension span that extends from nanometer-scale

devices, carbon nanotubes, and single cells, to tall

buildings, gas pipelines and bridges. For FY04, we

organized our research into the following focus areas:

Materials for Micro- and Optoelectronics

The U.S. microelectronics and related industries

continue to face fierce international competition. The

International Technology Roadmap for Semiconductors

(ITRS) has long recognized the importance of metrology

to the advancement of the industry by devoting an

entire chapter to the subject. The 2003 ITRS calls

specifically for solutions to the Interconnect Difficult

Challenge (through 2009) of achieving necessary

reliability due to the fact that “new materials, structures,

and processes create new chip reliability (electrical,

thermal, and mechanical) exposure. Detecting, testing,

modeling and control of failure mechanisms will be

key.” We continue to support the industry through the

following projects aimed at improved measurements,

modeling, and advanced materials science: measurement

of mechanical properties and micrometer-scale

reliability of thin films; improved understanding of

chip-level electrical and thermomechanical reliability

in metallic interconnects; improved measurements and

understanding of thermal flow and damage related

to packaging and thin film reliability; linking models

for structure and behavior of nanostructures from

interatomic, to nano-, to continuum length scales;

and molecular dynamics simulations of experimentally

observed thin-film structure and behavior.

Nanocharacterization

Metrology, the science of measurement, plays a

key role in the development and commercialization of

nanotechnology. Manufacturing commercially viable nanoscale products, so widely envisioned in the press, demands

vast improvements in our ability to measure material

dimensions, characteristics, and structures at the nanolevel. The overarching goal of our nanocharacterization

effort is to develop reliable and accurate measurement

techniques for a broad range of materials and material

properties at the nano-scale. We are applying a variety of

techniques to meet this challenge, such as atomic force

acoustic microscopy (AFAM), Brillouin light scattering,

Executive Summary

surface acoustic wave spectroscopy (SAWS), x-ray and

electron diffraction, and multiscale modeling. We continue

to explore synergies between these techniques as well

as application of these measurement tools to a wide range

of materials: ceramics, polymers, thin films, low-k

dielectrics, self-assembled structures and others.

Biomaterials Metrology

The medical research community has recognized a

burgeoning need to understand the role that the mechanical

behavior of biological materials plays in normal and

diseased tissues. This project addresses these needs

on multiple length scales: cellular, cell plus matrix, and

tissue levels. On the cellular level, we are using MEMS

(microelectromechanical systems) devices to apply and

measure loads and displacements on a single living cell.

Techniques to calibrate the MEMS devices are being

developed using an optical trap and the atomic force

microscope. A novel bioreactor was developed to apply

biaxial stress to tissue-engineered vascular grafts.

Functionality is substandard if the grafts are cultured in a

stress-free environment. Empirical models were identified

that predict the compressive response of a porous scaffold

used for tissue engineering. On the tissue level, work

is ongoing to use a rat model to predict the mechanical

response of arteries to the onset of pulmonary

hypertension. Two models for inducing hypertension were

compared. Complementary work was conducted using

quantitative ultrasonic techniques. These physical acoustic

techniques have also been applied to other tissue systems.

Strong and diverse collaborations are growing with

the University of Colorado, National Jewish Medical

Research Center, Children’s Hospital of Denver, and

the Colorado School of Mines.

Infrastructure

The projects in this group are designed to develop

measurement technology for determining a material’s

characteristics or for characterizing a measurement

system. In FY04, we reduced our activities in lead-free

solders, and transferred this effort to other infrastructure

issues. The Charpy SRM program had over 900 customers

in FY04, and we have shipped more than 1200 copies of

our new training video in the past two years. A three-year

international intercomparison of Charpy impact verification

specimens was completed, confirming the equivalence of

impact energy scales among the international producers

of reference specimens. We finished measuring properties

of steels used in the World Trade Center as part of the

NIST-led study (report to be published in December 2004)

and are looking at the issues that impede the use of fireresistant steel. A joint proposal (with Metallurgy Division)

on pipeline research was funded by DOT.

Al Clark, Chief

Tom Siewert, Deputy Chief
2

Executive Summary

Division Chief’s Commentary

Trying to advance our core science capabilities

during the unusually tight budget of the 2004 fiscal year

has been an extraordinary challenge for the Materials

Reliability Division. The technical staff has risen to

that challenge, and, in addition, they have reached out to

increase our visibility and exposure to the outside world.

This has taken the form of initiating and hosting several

workshops, bringing in outside expertise to assess our

program directions, and publishing in new journals and

giving many invited talks. These extra and successful

efforts are documented in this report along with the

usual, high-quality technical achievements.

In my short time as Division Chief, I have been

very impressed with the creativity and productivity

of the Division staff and am pleased to have had the

opportunity to work for them. “Reliability” has taken

on a whole new meaning for me.

Al Clark

Chief

Materials Reliability Division
3

Technical Highlights

Technical Highlights

The following Technical Highlights section includes

expanded descriptions of research projects that have

broad applicability and impact. These projects generally

continue for several years. The results are the product

of the efforts of several individuals. The Technical

Highlights include:

■ Targeted Workshops: Developing Strategies

for the Future

■ The Structural Steel of the World Trade

Center Towers

■ Quantitative Nanomechanical Properties

■ Pediatric Pulmonary Hypertension
4

Technical Highlights

Targeted Workshops: Developing Strategies for the Future

The Materials Reliability Division

hosted two workshops in August 2004:

Computational Tools for Modeling Acoustic

Propagation in Real World Materials.

Time-domain modeling of acoustic propagation is

of interest to scientists and engineers involved in

a range of disciplines such as medical ultrasound,

material characterization, underwater acoustics,

and geoacoustics. Real-world materials such

as tissue, textile composites, and suspensions

often exhibit properties that depend on the

frequency of the interrogating sound and also

lead to computationally intensive algorithms for

modeling its acoustic response. Wider availability

of high-performance computational tools will

permit simulations of higher fidelity that

benefit a range of industries involved in the

modeling of acoustic propagation.

Reliability Issues in Nanomaterials.

Nanomaterials, with their promise of control over

matter at the atomic level, are widely seen to offer

the possibility of breakthrough products in fields

from medicine to transportation to computers.

This workshop reports a roadmap indicating

metrology barriers, needs, and opportunities in

nanomaterial manufacturability and reliability.

Kendall R. Waters, David T. Read, and

Robert R. Keller

Acoustic Propagation

The Materials Science and Engineering Laboratory

sponsored a two-day workshop (August 9–10,

2004) that was organized by the Materials Reliability

Division with support from the Center for Theoretical

and Computational Materials Science in an effort

to propose collaborative investigations of problems

in materials theory, modeling, and evaluation. The

specific focus of the workshop was computational

tools for modeling acoustic propagation in real-world

materials with a broad goal of developing such tools

for a wide audience. Specific topics addressed during

the workshop included physical and mathematical

models, computational techniques, high-performance

computing (HPC) issues, and applications. Future

plans include the development of a working group for

HPC applications of acoustic propagation modeling.

Motivation

Many real-world materials exhibit acoustic

propagation properties of attenuation and phase

velocity that depend on the frequency of the sound.

These properties are not independent of one another

and are known to be linked by the principle of causality.

The consequences of causality for wave propagation

have long been considered. The standard approach to

this study is application of the Kramers–Krönig (K–K)

dispersion relations, which place restrictions on the

frequency response of a system. For the case of

acoustics, the K–K relations can be used to relate the

attenuation coefficient and the phase velocity.

More recently, interest has grown in the study of

the time-domain consequences of causality-imposed

restrictions. The basis for this approach is to consider

a time-domain equivalent of the K–K relations, known

as the time-causal relations. These relations are used

to modify a lossy wave equation to include effects

due to the frequency dependence of phase velocity,

commonly referred to as dispersion. The inclusion of

frequency-dependent attenuation in time-domain models

is straightforward. However, the effects of dispersion

depend on the history of the acoustic pressure field,

and its inclusion in time-domain models can be

computationally intensive.

A standard numerical approach for time-domain

modeling of acoustic propagation employs a finitedifference time-domain (FDTD) technique. FDTD

code has long been used for electromagnetic wave

propagation and is becoming more widely used for

acoustic wave propagation. Similar to analytical

modeling of acoustic propagation, numerical modeling

of materials with loss and dispersion is non-trivial.

At present, the availability of such a FDTD code

that accounts for loss and dispersion is limited.

Participation

The workshop was organized in collaboration with

colleagues Drs. J. Mobley and K. Wallace of the U.S.

Army Research Laboratory (ARL) and Washington

University in Saint Louis, respectively. Invited

speakers included Dr. D. Marlin of the U.S. ARL,

Dr. G. Norton of the U.S. Naval Research Laboratory,

Dr. M. Rielly of Philips Medical Systems, and

Dr. T. Szabo of Boston University. These speakers

provided reviews of the modeling and HPC aspects

of acoustic propagation in various acoustical systems.

Contributing speakers and other participants provided

discussions on specific applications such as surface

acoustic waves in thin films and medical ultrasound

contrast imaging. These participants came from an

equally diverse range of institutions including the

National Oceanic and Atmospheric Administration,

the University of Colorado, The Children’s Hospital in

Denver, and Weidlinger Associates Inc., as well as NIST.
5

Technical Highlights

In addition to presentations, break-out sessions

were held to discuss in more detail common aspects

of the physical and mathematical models for different

acoustic environments and issues related to HPC.

The establishment of a working group for continued

collaborations was discussed and is actively being

pursued. A summary of the workshop will be

prepared and distributed in the near future.

Nanomaterials Reliability

The Materials Reliability Division of NIST, the

University of Colorado, and the National Science

Foundation have teamed to offer the Workshop

on “Reliability Issues in Nanomaterials,” held

August 17–19, 2004.

Motivation

Nanomaterials, with their promise of control over

matter at the atomic level, are widely seen to offer

the possibility of breakthrough products in fields from

medicine to transportation to computers. NIST is a

participating agency in the National Nanotechnology

Initiative; one of NIST’s key roles is to develop

metrology and tools needed for the success of

nanotechnology. But NIST cannot do this alone;

the nation will be best served by a cooperative effort,

at a pre-competitive level, among all interested parties.

Goal

The goal of this workshop, inspired by the

success of the International Technology Roadmap

for Semi-conductors, was to produce a first version

of a roadmap including: (i) present state-of-the-art

in nano-mechanical reliability research, including

experimental, theoretical, and numerical approaches;

(ii) identification of measurement-related barriers to

improve reliability; and (iii) identification of possible

solutions or approaches to solutions, which overcome

such barriers. The report of the workshop, describing

our progress toward defining a nanomaterials reliability

roadmap, will be published as a NIST Special Publication.

Technical Focus

The nine plenary presentations were divided into

two main areas: fabrication and processing; and

characterization and testing. General topics of

interest included:

■ Nanomaterials processing and fabrication, and their

effects on mechanical reliability;

■ Methods and techniques for characterizing structure

of nanomaterials;

■ Methodologies for measuring mechanical properties

in nanomaterials;

■ Experimental and modeling approaches to

understanding effects of structure and dimensional

scaling on mechanical behavior of nanomaterials,

with emphasis on surface and interface issues;

■ Approaches to understanding what roles nanomechanics plays in other types of reliability; and

■ Structure, property, and lifetime prediction.

This workshop addressed some of the issues raised

during the Nanomechanics Breakout Track of the

NNI Interagency Workshop on Instrumentation and

Metrology, held January 2004 at NIST–Gaithersburg.

Namely, we addressed the following Grand Challenges:

■ Modeling of nanomechanical experiments;

■ Integration of multiple techniques for measurement

and characterization;

■ Experimentation/testing under real application

conditions;

■ Standardization and calibration;

■ Instrument development for nanomechanics;

■ High-throughput, automated nanomechanics

measurements.

Participation

The eight non-NIST plenary speakers were:

Susanne Arney (Lucent Technologies), John Randall

(Zyvex), Ken Rodbell (IBM), Rachel Goldman (Univ.

of Michigan), William Gerberich (Univ. of Minnesota),

Martin Dunn (Univ. of Colorado), Nancy Burnham

(Worcester Polytechnic Institute), and Neville Moody

(Sandia National Laboratories). Each was allotted

60 minutes for presentation and discussion. We invited

50 additional participants representing industry, national

laboratories, and universities. Breakout sessions

followed for in-depth discussion of metrology needs

for advancing the use of nanomaterials in practice.

The ninth plenary session featured a presentation of

ongoing nanomaterials research in the NIST Materials

Science and Engineering Laboratory by Doug Smith

(MSEL/Ceramics Division) and included discussion of

the role of NIST. This was followed by a summary of

the technical presentations and discussion of priorities

for future mechanics-related nanomaterials research

by all the organizations represented.

For More Information on this Topic

K.R. Waters, D.T. Read, R.R. Keller (Materials

Reliability Division, NIST)
6

Technical Highlights

The Structural Steel of the World Trade Center Towers

Figure 1: Enhanced image of the impact zone has allowed

determination of failure modes in the perimeter columns.

An outline of the plane is superimposed. Steel panels recovered

for the investigation are highlighted in color.

Task 2 — Categorize Failure Mechanisms

Based on Visual Evidence

The damage to the steel components of the buildings

represents an important check on the accuracy of the fire

and impact modeling, with the caveat that the recovered

steel could have been damaged before the collapse,

during the collapse, or during the salvage efforts.

Image enhancement techniques were used to

study photographs of the impact zones of the towers

to establish the failure mechanisms of the perimeter

columns. By making montages of many different

images, it was possible to produce a nearly smoke-free,

composite view of the columns that the aircraft struck.

The columns failed by several different mechanisms.

One important result was the demonstration that several

key impact-zone columns in the NIST inventory were

damaged primarily in the aircraft impact, and not in the

subsequent collapse or recovery efforts. Figure 1 is a

map of the impact zone of WTC 1 that illustrates the

nature of the damage to the individual columns.

Tasks 3 & 4 — Determine Steel

Properties to Support Airplane Impact

and Structure Performance Studies;

Correlate Properties with Those

Specified in the Construction

One important part of this task was to assess the

quality of steel and determine whether it met the original

specifications. In support of this goal, the group conducted

more than 200 room-temperature tensile tests on samples

from 39 different building components, which represented

In August of 2002, NIST took responsibility for the

investigation of the World Trade Center disaster. The

investigation objectives include determining: why

the buildings collapsed; the procedures and practices

used in the design, construction, operation and

maintenance of the buildings; and areas in codes

and practices that warrant revision. The eight

interdependent projects include Project 3 — Analysis

of Structural Steel, led by the Materials Science and

Engineering Laboratory. The objective of the project

is to determine and analyze the properties and

quality of the steel, weldments, and connections

from steel recovered from the World Trade Center.

Stephen W. Banovic, Richard J. Fields,

Timothy J. Foecke, William E. Luecke,

J. David McColskey, Christopher N. McCowan,

Thomas A. Siewert, and Frank W. Gayle

I

n terms of the steel used, the World Trade Center

was very complex. Plans called for steels of fourteen

different yield strengths between 36 ksi and 100 ksi.

Many of these steels were proprietary and were not

supplied to any existing ASTM specification. To further

complicate matters, four different fabricators provided

steel for the upper stories, and each used steel from

more than one supplier. Most of the records that

documented the steel actually used were either not

preserved or destroyed in the collapse.

The MSEL Metallurgy and Materials Reliability

Divisions have determined properties of the steel

recovered from the WTC site and characterized failure

modes associated with pre-collapse damage. This

information has been provided for use in models of the

building response to airplane impact and fire. In 2004,

all major tasks were completed.

Task 1 — Collect and Catalog

Physical Evidence

The Structural Engineers Association of New York

(SEAoNY), later supplemented by NIST personnel, spent

countless hours selecting steel in the New Jersey recycling

yards for later forensic analysis. After shipment to NIST,

the Metallurgy Division cataloged the 236 recovered steel

components. Since many pieces were stamped and painted

with unique serial numbers correlated with the building

plans, it was often possible to identify the exact original

location in the building.

As a second part of this task, we also researched

contemporaneous construction documents and steel

specifications. This task helped identify steel suppliers

and fabricators, as well as material substitutions.
7

Technical Highlights

Figure 2: Yield strength — measured vs. specified minimum.

The few anomalous data can be attributed to damage incurred

in the collapse that removed the yield point behavior, or to the

natural and accepted strength variability of structural steel.

all the steels relevant to the investigation. Tests indicate

that the steels generally met or exceeded the specified

minimum strengths (Figure 2).

Steel specifications also regulate the chemical

compositions. More than 350 different specimens,

representing nearly every relevant steel component in

the building, were analyzed for chemical composition

and all of the sections relevant to the investigation. The

chemical analysis helped confirm archival information

that an American steel mill supplied steel for parts of

the perimeter columns. The analyses also support the

conclusion that the steels in the buildings met the

specifications called for in the building plans.

The strength of steel increases as the deformation

rate increases. Accurately modeling these rate effects

is essential for estimating the energy and momentum of

the aircraft remnants which damaged the core columns.

To establish the strain rate sensitivity of the relevant

steels, we have conducted more than 100 tests on

specimens from both the perimeter and core columns

at rates up to 2000 s–1 (200,000 % deformation

per second).

Ultimately, the fires in the towers weakened the steel

structure leading to collapse. We conducted more than

100 high-temperature tensile and creep tests to provide

models of the deformation of structural steel at elevated

temperatures for use in models of the building response

to the fires.

Task 5 — Analyze Steel to

Estimate Temperature

Just as the nature of the deformation and failure

of the recovered steel reveals information about the

impact and collapse, the steel can also contain evidence

of its exposure to the elevated temperatures in the fire.

The situation is made more complex because much

of the steel was also exposed to extended fires in

the rubble before recovery. Several different methods,

both conventional and novel, were examined for

estimating high-temperature excursions seen by the

steel. Only one method proved to be robust and easy

to implement: paint on steels that reached temperatures

over 250 °C cracked from the difference in thermal

expansion between the paint and the steel.

Figure 3: Illustration of the method to establish the temperature

excursions of recovered steel. The segment of the column

protected by the floor slab remained at lower temperature.

From photographs showing fire in windows, all

recovered columns that may have been exposed to

pre-collapse fire were identified and characterized

using the paint crack technique. Figure 3 illustrates

one of the columns that showed evidence of having

exceeded 250 °C.

Outputs

Outputs for the project include parts of the

June 2004 Progress Report on the World Trade Center

Disaster (NIST SP 1000-5) and numerous memos for

contractors that explain how to employ Project 3 data

and deformation models. The final NIST investigation

report will be released in the spring of 2005.

For More Information on this Topic

T.A. Siewert (Materials Reliability Division, NIST);

F.W. Gayle (Metallurgy Division, NIST)
8

Technical Highlights

We are developing AFM-based metrology for

rapid, nondestructive measurement of mechanical

properties with true nanoscale spatial resolution.

Atomic force acoustic microscopy methods enable

elastic-modulus measurements at either a single

point or as a map of local property variations.

Complementary information obtained with

scanning electron microscopy provides insight

into structure-property relations and helps to

interpret nanoscale contact-mechanics behavior.

The information obtained furthers our understanding

of the nanomechanical properties of surfaces,

thin films, and nanoscale structures.

Donna C. Hurley

New measurement solutions are required to address

the rapidly burgeoning field of nanotechnology.

In particular, information about mechanical properties on

the nanoscale is needed. Knowledge of properties like

elastic modulus and interfacial quality (defects, strain,

adhesion, etc.) is critical to successful development of

new films and nanoscale assemblies. Such information

could also assess integrity or reliability in applications

from microelectronics to biotechnology. Existing

methods for mechanical-property measurements have

drawbacks: they are destructive, limited to specialized

test specimens, or not quantitative. Instrumented or

“nano-” indentation (NI), a current industry workhorse,

will have limited value as scales shrink well below

1 μm, and softer materials are more frequently used.

To meet this need, we are developing tools that

exploit the spatial resolution of atomic force microscopy

(AFM). Our approach, called atomic force acoustic

microscopy (AFAM), involves the vibrational resonance

of an AFM cantilever when its tip is in contact with a

sample. By comparing the cantilever’s contact-resonance

frequencies for an unknown material to those for a

reference sample with known properties, the indentation

modulus M of the unknown material can be determined.

[For an isotropic material M = E/(1–ν2), where E is

Young’s modulus and ν is Poisson’s ratio.] The small

tip radius (~5–50 nm) means that we can obtain in-situ

elastic stiffness images with nanoscale spatial resolution.

In FY04, we extended our quantitative AFAM

techniques in a variety of ways. In one effort, the

effect of film thickness on measurement accuracy

was investigated. We measured M for three nickel

(Ni) films approximately 50, 200 and 800 nm thick.

The values of M ranged from 220 GPa to 223 GPa,

significantly lower than that expected for bulk

Quantitative Nanomechanical Properties

polycrystalline Ni. Scanning electron microscopy (SEM)

revealed that the films were nanocrystalline (grain diameter

< 30 nm). The observed reduction in M may be attributed

to an increased volume fraction of grain boundaries in the

nanocrystalline films. More importantly, the average values

of M for all three films were the same within measurement

uncertainty (~10 %). Thus the AFAM results were not

influenced by the elastic properties of the silicon substrate,

even for a 50 nm film. This behavior is due to the fact

that the AFAM stress field extends less than 100 nm into

the sample and decreases rapidly with depth due to the

small applied static loads (0.3–3 μN) and small radius of

contact (5–25 nm). Our result contrasts sharply with

nanoindentation, in which substrate properties must be

included to accurately measure submicrometer films.

The elastic properties of the 800 nm Ni film were also

measured using NI, microtensile testing, and surface

acoustic wave spectroscopy (SAWS). Both AFAM and

NI measure the film’s out-of-plane indentation modulus.

The results were in excellent agreement, validating AFAM

as a quantitative method in spite of its relative newness.

Microtensile testing values for the in-plane Young’s

modulus of the film were not consistent with the AFAM

and NI results if the film was assumed to be elastically

isotropic. The apparently contradictory results were

reconciled by use of a transversely anisotropic model for

the film’s elastic properties. This model is consistent with

the strong <111> film texture observed by x-ray diffraction.

When analyzed with the same model, the SAWS results

indicated that the film density was only slightly lower

(< 5 %) than the bulk value. These results illustrate a

relatively straightforward way to interpret mechanicalproperty measurements of thin films that is based on a

more physically realistic model than the simple assumption

of elastic isotropy.

Another effort investigated the effects of relative

humidity (RH) on AFAM measurements. AFAM contact

Figure 1: a) AFM tapping-mode topography and b) AFAM

relative-stiffness images of Si with n-octyldimethylchlorosilane SAM.
9

Technical Highlights

stiffness measurements may be affected by a variable

water layer between the tip and sample, at least in some

cases. By refining our data analysis methods to include

the effects of such a layer, apparent correlations between

the measured values of M and the ambient RH were

eliminated. This year we also developed a RH-controlled

AFM chamber in order to systematically study

these effects. Samples for the experiments were

provided by the Polymers Division and consisted

of patterned self-assembled monolayers (SAM) of

n-octyldimethylchloro-silane on Si substrates.

Through controlled ultraviolet-ozone exposure, the

relative hydrophobic/hydrophilic nature of the SAM

was adjusted in different sample regions. Figure 1

shows an AFM topography image and an AFAM

relative-stiffness image for a SAM/Si sample. The

SAM stripes are virtually invisible in the topography

image, even at very high resolution (10 nm full scale

height). However, the AFAM image clearly reveals the

hydrophobic SAM stripes. The regions covered by the

SAM appear more compliant (lower contact stiffness)

due to AFAM’s sensitivity to local variations in the

tip-sample adhesion. We are currently performing

further experiments on similar samples in order to

quantify how humidity and adhesion effects can be

distinguished from true mechanical-property variations.

measurements were done at relatively low static loads;

the load was then successively increased up to several

micronewtons to try to break and/or plastically deform

the tip. High-magnification SEM images were obtained

before and after each AFAM measurement. As can be

seen in Figure 2, R increased with use, indicating tip

wear. Values of R measured from the SEM images

were compared to the values obtained from AFAM

data using a Hertzian contact-mechanics model.

The AFAM values of R were consistently smaller than

the SEM values. Further data analysis and additional

experiments are planned to clarify this issue. The

knowledge gained in this way will help us to refine

our understanding of AFAM contact mechanics,

beyond the Hertz approximation, in order to improve

measurement accuracy and repeatability.

In related work, we are performing finite-element

studies of the AFM cantilever. The finite-element mesh

is based on actual cantilever dimensions from SEM

images and includes elastic anisotropy. The predicted

free-space resonant frequencies are in excellent

agreement with those observed experimentally.

Work is underway to predict the vibrational behavior

in contact. These results will allow us to refine

our data analysis models and thus improve

measurement accuracy.

The research described above involves either

quantitative single-point measurements, or qualitative

imaging of relative stiffness. In FY04, we worked to

realize our ultimate goal of quantitative nanomechanical

mapping. Critical to our success is a new frequency

tracking circuit that can determine the contact-resonance

frequencies at each image pixel. The circuit is based on

digital signal processing architecture that enables rapid

data acquisition (typically < 30 min. for a 256 × 256

image). We have begun to obtain resonance-frequency

images for a variety of materials. Recent enhancements

to our AFM mean that we can acquire images from not

only the flexural modes, but also the torsional modes of

the cantilever. By combining information from flexural

and torsional images, it may be possible to determine

simultaneously both Young’s modulus and Poisson’s

ratio for an isotropic material. Work in upcoming

months will focus on issues related to quantitative

image interpretation such as calibration procedures,

cantilever selection, tip wear, and choice of

contact-mechanics model. Each of these elements

plays a role in attaining our goal of truly quantitative

nanomechanical imaging.

For More Information on this Topic

D.C. Hurley (Materials Reliability Division, NIST)

Figure 2: SEM images of AFM cantilever tip a) before use and

b) after repeated AFAM contact experiments. The circled regions

indicate the tip wear that occurred through use.

 AFAM contact-resonance frequencies depend not

only on elastic properties, but also on the value of the

tip radius R. Thus knowledge of R and how it changes

over time is essential for accurate measurements of

elastic properties. To address this issue, we performed

AFAM experiments with different AFM cantilevers

on a sample with known elastic properties. The first
10

Technical Highlights

Pulmonary hypertension is a potentially fatal

complication of congenital heart defects in

children who live at high altitudes. Discovering

the pathophysiology and expression of the disease

may open the way to finding new, more effective

diagnostics and treatments. Our contribution to

this goal is to investigate the differences in the

mechanical properties of the pulmonary artery

and its constituents between healthy and

diseased tissue.

Elizabeth S. Drexler

Members of the Biomaterials Metrology Project

are working in conjunction with researchers at the

University of Colorado and Children’s Hospital of Denver

to characterize the development and pathophysiology of

secondary pulmonary hypertension (PHT) in children.

The high elevation of the Rocky Mountain region causes

children born with heart defects to have a greater

propensity for developing PHT, so it is an area of great

concern for this region. Members of this collaborative

team are addressing the role of fluid mechanics,

biochemistry, pathology, histology, and the arterial wall

mechanics during development and at maturation of

the disease. It is our goal to develop new, less-invasive

diagnostics that might hasten treatment and mitigate

permanent damage. At the present time, diagnosis

is sometimes delayed by two factors: a variety of

conditions that can display similar clinical expression,

and the reluctance of physicians to subject a child to

catheterization unless it is clearly necessary.

The Pediatric Pulmonary Hypertension subproject is

focusing on the dual goals of quantizing the mechanical

properties and identifying the structural differences

between normotensive and hypertensive pulmonary

arteries (PAs). Our approach is to begin with a rat

model to determine whether we can detect differences

in the stress–strain and ultrasonic properties between

conditions. We have chosen the Long–Evans breed of

rats because they can be genetically modified so that

the endothelin B receptor is disabled (knock-out or KO).

The endothelin B receptor is responsible for activating

the vasodilators prostacyclin and nitric oxide.

 The test matrix includes testing controls (otherwise

referred to as untreated wilds), monocrotaline-treated

wilds, hypoxic wilds, hypoxic KOs, and perhaps

monocrotaline-treated KOs. Monocrotaline is a synthetic

chemical derived from a naturally occurring substance

that produces an inflammatory response in the lungs that

Pediatric Pulmonary Hypertension

typically degenerates into PHT. The rats are injected with

monocrotaline subcutaneously, and the disease is allowed

to develop over four weeks before the arterial tissue is

tested. To induce PHT with hypoxia, rats are held in a

hypobaric chamber that simulates oxygen conditions at

5200 m above sea level for three weeks before testing.

Specimens from the trunk, and the right and left main

branches are tested. It is thought that these proximal

arteries are likely to be used for clinical diagnosis as

they are more readily imaged non-invasively.

A bubble-test configuration is employed to obtain

stress–strain data (Figure 1). The specimen sits in a

reservoir and is pressurized in 1.4 kPa (10 mm Hg)

increments from the adventitial side with a physiological

solution. Images of the bubble profile are collected at

each pressure increment from six camera angles located

30° apart. These images are used to measure the changing

length of the extruded bubble to calculate strain. The

bubble is fitted as an ellipsoid to calculate the surface area

to determine stress. The various camera angles allow us

to account for anisotropic deformation. However, at this

point, we are using the formulation for the stress at the

apex of an ellipsoid of an isotropic material to approximate

the stress. Models are nearing completion that will

determine the elastic constants of the material from

the experimental measurements based on established

anisotropic constitutive relationships.

The results of the tests for each population are shown

in Figures 2a–d. All values for strain were relative to the

displacement measured at 1.4 kPa. Both the hypoxic wilds

and the hypoxic knock-outs showed less strain at a given

stress value than did the controls — the knock-outs more

so than the wilds. It should also be pointed out that, in

general, the hypoxic specimens were pressurized to

equivalent pressures to the controls and monocrotaline

treated specimens, and oftentimes 15–20 % higher.

The thickness of the hypoxic specimens had a dramatic

effect on the stress relationship. We found that the effect

of the monocrotaline treatment on the wild population was

Figure 1: Schematic of the bubble test fixture.
11

Technical Highlights

unclear on the stress–strain relationship. We are in the

process of identifying a reasonable mathematical model

for the data so that statistical analyses may determine

significance among the populations. Work has begun

to correlate general trends in our pressure-displacement

data to in vivo compliance data acquired by use of input

impedance measurements in the catheterization laboratory.

Ultrasonic measurements have been performed

and analyzed for three different rat populations

(six controls, four wild hypoxics, and six KO

hypoxics). We use a 50 MHz acoustic microscope

in double-transmission mode with insonification in

the radial direction of the PA wall. Thickness and

speed of sound are determined by measuring changes

in times-of-flight of ultrasonic signals through a

reference path of a nutritive solution and a path

substituted with the PA specimen. The slope of

attenuation is determined by spectral analysis of these

same ultrasonic signals. Current acoustic microscopy

results are not yet fully understood. Models from

the wild hypoxic rat exhibited an expected increase

Figure 2: Stress–strain results from the a) control, b) mono-crotaline-treated, c) hypoxic wild, and d) hypoxic knock-out rats.

in speed of sound (up to 10 %) in the PA trunk

compared with that of the controls, which is

indicative of stiffening as a result of remodeling

due to hypertension (see Figure 3a). However, the

speed of sound in the KO hypoxic PAs does not

appear to differ significantly from that of the controls.

More marked increases (up to 100 %) were observed

in slope of attenuation for the PA trunk for both hypoxic

models as compared with controls (see Figure 3b).

Smaller changes in the ultrasonic properties were

observed for either the left or right PA branches.

Continuing studies aim to investigate the effect of

loading of tissue to mimic in vivo arterial pressures

and to increase the population counts of the rat models

to reduce the large standard deviations.

The histology of the PAs is being evaluated to

determine relationships between the structure and

properties of the tissue, and to characterize remodeling

of structure associated with increases in stiffness

measured for patients with PHT. As shown in Figure 4,

the extrapulmonary arteries have complex structures
12

Technical Highlights

Figure 4: A cross-section of a pulmonary artery, taken just

adjacent to the heart in a hypoxic knockout rat, showing the three

major layers (endothelial, medial, and adventitial) characteristic

of extrapulmonary arteries. The lumen (cavity in which the

blood flows) is partially visible at the bottom edge of the figure.

The endothelial layer, which is in contact with the blood, is a very

thin layer adjacent to the lumen that ends at the first elastic lamella

(black bands). The medial layer in this particular artery has

about eight elastic lamella that separate it into about seven

sublayers of smooth muscle. The adventitial layer is the third

layer on the outside diameter of the artery. This layer is typically

a fibrous low-density layer compared with the medial layer.

that provide the strength and elasticity required for

the conduit function and environment.

Current observations indicate that the hypoxic

knockouts have collagen deposition and vascularization

in the adventitial layer adjacent to the medial layer.

In Figure 4, for example, there is a gradient of apparent

density through the adventitial layer, where control

samples tend to have a structure more like that

near the outside diameter of this example. Other

measurements, such as elastic lamina thickness,

sublayer thickness, and the size of the smooth

muscle cells, are also being evaluated.

One of the advantages to conducting this work

at NIST is our ability to apply different techniques

to the same problem or issue, thereby gleaning a

more complete understanding of the development

of the pathophysiology of PHT and its effect on the

pulmonary arterial mechanics. The elastic properties

generated by the acoustic microscope provide the best

opportunity for bridging the technical gap between

clinical in vivo ultrasonic measurements and in vitro

mechanical properties measured in the laboratory.

The complementary work on the histology will help

to corroborate the statistical significance in the

mechanical properties observed among the populations.

Moreover, the histological analysis can contribute to

future treatments of PHT directed at the specific cell

or biochemical expressions that result in reduced

compliance of the arterial wall.

For More Information on this Topic

E.S. Drexler, C.N. McCowan, T.P. Quinn,

A.J. Slifka, K.R. Waters (Materials Reliability Division,

NIST)

Figure 3: a) Comparison of the speed of sound and b) slope of

attenuation in pulmonary branches for controls (n= 6), hypoxic

wilds (n= 4), and hypoxic KO (n=6). Error bars represent

standard deviations among the specimens.
13

Program Overview

Nanometrology

in determining mechanical properties of thin films

and nanostructures, focuses on developing traceable

calibration methodologies and standard test methods.

We also use atomic force acoustic microscopy,

surface acoustic wave spectroscopy, and Brillouin light

scattering to measure the mechanical properties of

thin films. In addition, we are developing micro- and

nano-scale structures and test methods to measure

strength and fracture behavior of interfaces and

materials having very small volumes.

The chemical and structural characterization and

imaging utilize neutron and x-ray beam lines at three

facilities: the NCNR; the National Synchrotron Light

Source at Brookhaven National Laboratory; and

the Advanced Photon Source at Argonne National

Laboratory. Innovative scattering and spectroscopy

methods are advancing our ability to obtain a wide

range of chemical and structural information at the

nanoscale, including chemical bond identification and

orientation, polyelectrolyte dynamics, and equilibrium

structures. In collaboration with three other NIST

laboratories, we are developing electron microscopy

and spectroscopy instrumentation for quantitative,

3D chemical imaging at the nanoscale. Other

characterization projects include work on gradient

reference specimens for the calibration of advanced

scanning probe microscopy, and the application of

carbon nanotubes as physical probes of cell membranes.

Efforts in the fabrication and monitoring of

nanoscale processes and events include the study of

electrochemical and microfluidic methods for fabricating

nanostructures, novel approaches to nanocalorimetry

for the study of interfacial reactions, in situ observations

of nanoparticle and nanotube dispersion and alignment,

and advanced instrumentation for nanotribology

experiments.

Finally, we have extensive efforts in the theory,

modeling, and prediction of material properties and

behavior extending from nanoscale to macroscale

dimensions. Modeling efforts include large-scale finite

element methods, multiscale Green’s function methods,

classical atomistic simulations, first principles, and

quantum mechanical calculations using density

functional theory. Often, several modeling methods

must be combined into one study to accurately describe

the material behavior; thus, we pay great attention to

the correct interfacing between models operating at

different length scales, to ensure that our models

properly capture the physics of both components

and total systems.

Contact: Stephanie A. Hooker

The burgeoning field of nanomaterials extends

across the full range of traditional material classes,

including all forms of metals, polymers, and ceramics.

No previous materials technology has shown so

prodigiously a potential for concurrent advances in

research and industry as does the field of nanomaterials

in mechanical devices, electronic, magnetic, and optical

components, quantum computing, tissue engineering

and other biotechnologies, and as-yet unanticipated

exploitations of as-yet undiscovered novel properties

of nanoscale assemblies of particles. Already, there

is growing excitement surrounding the ability of

some molecules or particles to self-assemble at

the nanoscale to form new materials with unusual

properties. Nanometrology, i.e., the ability to conduct

measurements at these dimensions, to characterize the

materials, and to elucidate the structure and nature of

these new and novel assemblies, is a requisite and

fundamental cornerstone that must be established

securely if this technology is to flourish.

NIST is uniquely positioned to lead the development

of the measurement methods, instrumentation, standards,

and reference materials that, together, will form the

metrological infrastructure essential to the success

of nanotechnology.

The MSEL Nanometrology Program incorporates

basic measurement metrologies to determine material

properties, process monitoring at the nanoscale,

nanomanufacturing and fabrication techniques, and

structural characterization and analysis techniques

such as advanced imaging and multiscale modeling.

The Program comprises 22 projects in the Ceramics,

Materials Reliability, Metallurgy, and Polymers

Divisions, and includes structural characterization

using neutron scattering at the NIST Center for

Neutron Research (NCNR). The projects cover a

wide range of measurement and characterization

methods grouped into the areas of mechanical

property measurement, chemical and structural

characterization and imaging, fabrication and monitoring

of nanoprocesses and events, and modeling of nanoscale

properties. In each area, we work to advance basic

measurement capabilities and lead the intercomparison,

standardization, and calibration of test methods. The

newly completed Advanced Measurement Laboratory

at the NIST Gaithersburg site provides an incomparable

environment for accurate nanoscale metrology.

In the area of mechanical property measurement,

we are developing and standardizing techniques for

determining nanoscale elastic properties (elastic moduli,

Poison’s ratio, and internal stress), plastic deformation,

density, adhesion, friction, stiction, and tribological

behavior. Work in nanoindentation, used extensively
14

Nanometrology

Brillouin light scattering is being employed to

provide information on acoustic and magnetic

waves at gigahertz frequencies in thin-film

materials. Measurements and modeling in FY04

have focused primarily on interactions of spin

waves in ferromagnetic films, elastic constants of

nanoporous low-κ dielectrics, and propagation

of acoustic waves in nanopatterned polymers.

Ward Johnson, Sudook Kim, and

Colm Flannery

Technical Description

Brillouin light scattering (BLS) is an experimental

technique that measures the intensity of spectral

components of light that is inelastically scattered

by vibrational waves (phonons) or spin waves

(magnons) in a material. Fabry–Perot interferometric

techniques are used to acquire accumulated spectra

through repeated mechanical sweeping of the

etalon spacing.

BLS is the only laboratory technique that is

currently available for detecting magnons of finite

wavenumber. Because of this capability and because

of innovations in interferometric techniques, BLS has

been increasingly applied to problems in magnetics

over the past couple of decades.

For characterization of phonons in thin films,

BLS offers several advantages over other techniques.

Since it detects phonons in the gigahertz range, elastic

constants can be determined in films of submicron

thickness without the complication of vibrational

energy penetrating significantly into the substrate.

Modes localized in submicron structures can be

characterized. Spatial variations in elastic properties

and vibrational patterns can be measured with a lateral

resolution equal to the size of the laser focal spot on

the specimen (typically, ~50 micrometers).

In this division, techniques are being developed

for characterizing interactions of magnons in metallic

ferromagnetic thin films. Such interactions limit

the speed of magnetic-storage devices, spin-valve

sensors, and other thin-film magnetic devices.

BLS measurements and modeling of vibrational

modes are being pursued in several thin-film systems,

including nanoporous low-dielectric-constant (low-κ)

dielectrics, nanopatterned polymers, and arrays of

molecular rotors.

Metrology for Nanoscale Properties: Brillouin Light Scattering

Accomplishments

During FY04, we developed and applied methods

for measuring magnons that arise directly or indirectly

from microwave pumping of metallic ferromagnetic

films in a static magnetic field (Figure 1). BLS

spectra were studied as a function of scattering

angle, microwave power, and laser power to provide

information on magnon–magnon interactions in

Ni81Fe19. The results demonstrate, for the first time,

detection of nonzero-wavevector magnons arising

from the decay of pumped uniform-precession

magnons in metallic thin films.

Young’s modulus and Poisson’s ratio in

nanoporous low-κ dielectric films were measured

using conventional backscattering techniques. This

research is described elsewhere in this annual report.

Measurements and modeling of vibrational modes in

nanoimprinted polymers were pursued in collaboration

with the University of Akron and the NIST Polymers

Division. In addition to bulk and surface modes,

low-frequency modes were detected and found to

be consistent with vibrational localization in the

imprinted lines. This result suggests the possibility

of characterizing elastic properties on a scale of

tens of nanometers.

Contributors and Collaborators

P. Kabos (Radio-Frequency Technology Division,

NIST); S. Russek (Magnetic Technology Division,

NIST); A. Slavin (Oakland Univ.); J. Michl (Univ.

of Colorado, Chemistry Dept.); R. Horansky (Univ. of

Colorado, Physics Dept.); C. Soles (Polymers Division,

NIST); R.H. Hartschuh, A. Kisliuk, and A. Sokolov

(Univ. of Akron)

Figure 1: Scattering of light off waves in a thin film.
15

Metrology for Nanoscale Properties: X-ray Methods

Texture has a large influence on many properties

of thin films. XRD was the primary method for the

characterization of texture for many years. Recently,

alternative local techniques have been developed to

bring the measurements to the nanoscale. This year,

we compared measurements taken with conventional

XRD and EBSD on two thin films: sputtered aluminum

and electroplated copper. Both films had a thickness

of about 1 μm and were grown on [100] silicon

wafers. The inverse pole figures for both samples and

techniques are shown in Figure 1. It is obvious that

the agreement between XRD and EBSD in case of

aluminum film is very good, whereas it is rather poor

for copper film. This is a consequence of different

penetration depths of electrons and x-rays; while the

aluminum sample is homogeneous through the film

thickness, copper film is not. After sample preparation,

electroplated copper is likely to undergo self-annealing

at room temperature. This well-known phenomenon

yields a difference in grain size and orientation

between the surface and the bulk of the sample.

Contributors and Collaborators

Adriana Lita, Jens Müller, Roy H. Geiss,

Dave T. Read, M. Kopycinska–Müller, Robert Keller

(NIST); Laurna Kaatz, Amitendra Chaudhuri

(University of Denver)

Figure 1: EBSD (left) and XRD (right) inverse pole figures of

aluminum (top) and copper (bottom) thin films.

of the {321} lattice spacings (sin2ψ method) yielded the

total residual stress at ambient temperature. The values

obtained are about 0.7 GPa and higher, where the bulk

of the stress is due to the intrinsic (growth) component.

Nanometrology

Macroscopic properties of technologically

interesting materials originate from their

underlying micro-structure. To design and

understand improved materials, it is necessary

to characterize the microstructure and correlate

its changes to the macroscopic properties of

interest. We especially focus on x-ray diffraction

studies of biomedical, ferroelectric, optoelectronic,

photovoltaic, semi-conducting, and other materials

relevant to the health and microelectronics

industries. In particular, studies of microstructural

properties, such as strain and stress, crystalline

defects, and texture, complement the information

obtained by other techniques.

Thomas A. Siewert and Davor Balzar

I

n this report, we focus on two topics: the studies of

superconducting tungsten thin films and comparison

of the thin-film texture, as obtained by Electron Back

Scatter Diffraction (EBSD) and x-ray diffraction

(XRD). Tungsten superconducting transition-edge

sensors (TES) are used in different astrophysics and

astronomy applications, and as single-photon detectors

for the quantum computing experiments. Such

detectors comprise thin tungsten films and operate at

temperatures close to absolute zero and to the critical

superconducting transition temperature (Tc) of

tungsten. Thin films, in general, contain both hightemperature α-W phase (with Tc = 15 mK) and β-W

(A15 cubic structure with Tc = 1–4 K). Close to the

Tc, very small thermal changes, such as the absorption

of a single photon, increase the film electrical

resistance. The result is the production of an electrical

output signal that corresponds directly to the detection

of the absorbed photon energy. In general, residual

stress can influence the Tc of the thin film both directly

and by inducing the β→α phase transformation. Thus,

in order to control the Tc, it is necessary to measure

and control both the phase composition and residual

stresses. Residual stresses in films depend on the

preparation conditions, the thickness of the film, and

the difference in thermal expansion coefficient between

the film and the substrate. The total residual stress

results from both the intrinsic (growth) stress and

thermal stress. We measured the stress by XRD

at both ambient and cryogenic temperatures.

The sample was held in a continuous flow cryostat

that was capable of achieving temperatures as low

as 8 K. The cryostat was mounted on a goniometer

to enable the angle-dispersive XRD measurements.

The shift of the α-W {110} Bragg reflection was used

to estimate stress at 8 K, and directional measurement
16

Nanometrology

Several materials are now produced commercially

with particle sizes on the order of 10–100 nm.

The availability of ceramic materials in this size

classification is particularly important for the

electronic component industry. Nanopowders

can enable significant decreases in internal layer

thickness (for multilayer devices), minimize the

size and prevalence of processing defects, and

boost the overall performance of components

ranging from capacitors to resistive gas sensors.

Quantifying these performance enhancements

and their dependence on microstructure is a key

objective in the Materials Reliability Division.

Stephanie A. Hooker

Many multilayer ceramic devices can benefit from

the use of ultra-fine powders, including passive

electronic components, gas sensors, and miniature

actuators. However, fabrication issues associated

with processing these high-surface-area powders

have hindered their commercialization. Key challenges

have included nanopowder reproducibility, optimization

of processing slurries, and control of sintering

profiles to produce the desired micro/nanostructure

characteristics. Moreover, in many cases, predicting

the optimum microstructure features for maximum

performance is quite difficult, and extensive

experimentation remains necessary.

One specific component that can benefit from the

use of nanopowders is the multilayer piezoelectric

actuator. These devices generate precise, controlled

motion for translating optics, damping vibrations,

redirecting air flow, and dispensing fluids. Each

component consists of many active layers, the

thickness of which determines the device’s power

requirements. Layer thickness is typically on the

order of several hundred microns for conventional

actuators and is driven by the need for many individual

piezoelectric grains to span the active layer, thereby

reducing the chance for electrical failure. Reducing

grain sizes from micrometer to submicrometer scales

enables dramatic decreases in layer thickness, reducing

power needs and increasing applicability.

However, at issue is the piezoelectric response and,

in particular, the long-term fatigue resistance. Fatigue is

the change in polarization or displacement over time and

is a recognized problem for state-of-the-art actuators.

Because processing-induced defects tend to be on the

scale of the starting powder, nanopowders can improve

mechanical durability. However, a corresponding

Physical Properties of Thin Films and Nanostructures:

Grain Size Effects on Actuator Fatigue

decrease in ferroelectric response is also anticipated

as grain size reduces. Fatigue is affected by both

the mechanical and electrical responses, making its

prediction quite difficult for fine-grained components.

In FY04, we investigated the fatigue behavior of

14 microstructures obtained by controlled sintering

of 80-nm PZT-5A powders. The devices tested were

1206-sized (0.30 cm × 0.15 cm, or 0.12′′ × 0.06′′)

chips, each with 10 active layers (50 μm thick).

Characterization included dielectric, impedance, and

ferroelectric properties, as well as short- (< 1 million

cycles) and long-term (1–100 million cycles) degradation

under combined electrical and mechanical influences.

Figure 1: Effect of sintering temperature on ferroelectric fatigue.

The results clearly demonstrate the dependence of

fatigue on microstructure. Figure 1 compares changes

in remanent (i.e., permanent) polarization over time

when devices were cycled using a 35 Hz sinusoidal

wave with an amplitude of +/–75 V. The average

decrease in polarization for the finest-grained materials

(sintered at 1175 °C) was less than 20 % after

0.5 million cycles, compared to nearly 50 % for

larger-grained components.

In FY05, we will expand on this work and examine

the corresponding effects on displacement and domain

reorientation for devices with even thinner internal

layers. The resulting data will then be used to validate

the suitability of these components for biomedical and

smart structures applications, both of which demand

high performance and long operational lifetimes.

Contributors and Collaborators

R. Geiss (Materials Reliability Division, NIST);

C. Kostelecky, D. Deininger, K. Womer (Synkera

Technologies)
17

Nanoporous low-dielectric-constant (low-κ) films

present considerable implementation challenges for

the microelectronics industry and also raise new

scientific questions. We apply optical methods to

these films to evaluate such critical properties as

density/porosity, Young’s modulus, and Poisson’s

ratio. Our techniques allow measurement of

properties that are otherwise difficult to determine

and shed light on how the mechanical properties

depend on porosity.

Colm Flannery and Donna C. Hurley

Current miniaturization trends in microelectronics

require faster device switching. This need can be at

least partially met by lowering the resistance-capacitance

factor of the dielectric materials. One promising solution

is to introduce nanometer-sized pores that reduce the

dielectric constant κ. Unfortunately, introduction of

porosity may lead to a drastic reduction in stiffness

(Young’s modulus), adversely affecting the material’s

chances of surviving the fabrication process. In addition

to predicting and ensuring process reliability, accurate

values of a film’s mechanical properties are needed

to model the mechanical behavior of the resulting

microelectronics device. New tools are needed to

characterize these relevant thin-film properties

(e.g., Young’s modulus and Poisson’s ratio ν), as

well as to better define their dependence on porosity.

In FY04, we evaluated Poisson’s ratio ν in

methylsilsesquioxane (MSSQ) polymer films of varying

porosity with Brillouin light scattering. In this technique,

a Fabry–Perot interferometer detects frequency-shifted

photons scattered by ambient thermal phonons in

the material. The frequency shift of the photons is

characteristic of the acoustic phonon modes in the film.

Values of ν were determined from measurements of both

longitudinal and surface acoustic wave modes. Figure 1

reveals that ν decreases as porosity increases. The results

Physical Properties of Thin Films and Nanostructures:

Nanoporous Low-κ Dielectric Films

Figure 1: Measured Poisson’s ratio vs. porosity for MSSQ films.

Figure 2: Predicted dependence of Poisson’s ratio on porosity.

of an existing finite-element model, shown in Figure 2,

predict that ν will either decrease or increase depending

on the initial ν of the matrix material. In addition, ν tends

towards a constant value of 0.2 for all materials at high

porosity. Our measurements are consistent with the

model. However, they show a much larger rate of decrease

in ν, probably because a percolation threshold had

been reached. Quantitative results like these will prove

valuable for modeling of structures involving low-κ

films. The results also yield insight into the porosity

dependence of ν, about which very little is known.

A second method to determine thin-film properties

involves the frequency-dependent dispersion of lasergenerated surface acoustic waves (SAWs). In FY04,

efforts concentrated mainly on the development of a

standard SAW data analysis procedure. With careful

signal processing that minimizes sensitivity to noise and

maximizes the frequency range of the measured signals,

we can extend the frequency range of our measurements

by 20 %. The result is a significant reduction in the

uncertainty of the extracted film properties. The method

lends itself to automatation and has allowed us to inspect

films less than 300 nm thick. (Previously, films less than

500 nm thick were challenging.)

The improved measurement procedure, combined

with new multilayer Green’s function analysis software,

has allowed us to inspect multilayer structures.

With these capabilities, we have extracted properties

of thin (50–100 nm) capping layers of stiffer materials

on top of more compliant functional films. In addition,

the Young’s modulus, density, and thickness of

the underlying dielectric films were evaluated.

Contributors and Collaborators

S. Kim, V. Tewary (Materials Reliability Division,

NIST); Y. Liu (International Sematech); J. Wetzel

(Tokyo Electron America)

Nanometrology
18

Nanometrology

In the continuum model, we simulate free surfaces

and interfaces by applying the usual boundary conditions.

Accomplishments

We have carried out a detailed analysis of SAW

measurements in a thin TiN film on Si, calculated

stresses in a wide range of solids, and modeled Ge

clusters in Si containing a free surface and a vacancy.

The work is reported in six papers. A library of GFs

is available at www.ctcms.nist.gov/gf, which contains

downloadable teaching and tutorial material on

GFs and computer codes for calculation of GFs.

A GF group of about 50 international users has been

formed at CTCMS.

Contributors and Collaborators

D. Hurley, D.T. Read (Materials Reliability

Division, NIST); L. Bartlolo (Kent State University);

A. Powell (M.I.T.)

Precise knowledge of atomistic configuration

and strains in nanomaterials is needed for their

characterization and development of new devices.

We have developed computationally efficient

Green’s-function methods for calculation of lattice

distortion, elastic strains and displacements in

a variety of material systems. Our work is useful

for interpretation of data obtained by AFAM,

nanoindentation, and SAW experiments.

Vinod K. Tewary and Bo Yang

Technical Description

Green’s function (GF) provides a computationally

efficient tool for interpretation of data obtained by

nanoindentation and atomic force acoustic microscopy

(AFAM) which is useful for elastic characterization of

nanomaterials. The dynamic GF is used for modeling

propagation of surface acoustic waves (SAWs) in

solids and their phonon properties. The GF accounts

for interfaces and free surfaces in the solid and its

elastic anisotropy, which play relatively important roles

in the elastic response of nanomaterials as compared

to ordinary solids. We use GF to calculate the elastic

displacement fields, interaction energy between the

embedded nanostructure and other defects and free

surfaces. The displacement field, due to a force at

the surface, is used for interpretation of AFAM and

nanoindentation measurements. The interaction

energy of the nanostructures is an important factor

in the stability and growth of the nanostructure.

We have developed GF methods both at the discrete

atomistic and macro continuum scales. For a lattice

model containing N atoms, the GF is given by:

G = Φ–1

where G and Φ are 3N × 3N matrices of GF and

force constants respectively. The matrix inversion

is carried out by using the discrete Fourier transform

for a perfect lattice or numerically by computer

simulation for a model crystallite as in molecular

dynamics.

In order to model an embedded nanostructure

in a host solid, or a thin film on a substrate, we

define an initial GF for the host and the final GF.

The final GF is related to the initial GF through the

Dyson equation.

Physical Properties of Thin Films and Nanostructures:

Green’s-Function Methods

Figure 1: Stress distribution in Si due to a surface load.

Figure 2: Interaction energy of a cluster of 147 Ge atoms

with a vacancy and free surface in Si.
19

Applications of Carbon Nanotubes:

Carbon Nanotubes and Nanotube Contacts

A critical requirement for developing carbon

nanotube based electronics is determining the

mechanical and electrical characteristics of

the connection between the carbon nanotube

and its electrode. On this scale (nanometers),

the properties of both the nanotube and

the contact are not scaleable from larger

measurements. To address this issue we are

exploring a technique commonly used to

manipulate the nanotubes and attach them

to substrates inside the scanning electron

microscope. We are subsequently developing

the techniques to measure the small electrical

currents and test the small mechanical strength

associated with the contacts and nanotubes.

Paul Rice

We are developing techniques to measure the

mechanical and electrical properties of carbon

nanotube-based devices and also to image the

nanometer-scale structure within the nanotube and

their electrical contact. Shown in Figure 1 is a

test device that we have fabricated to measure the

electrical characteristics of an individual multiwalled

carbon nanotube. The nanotube was attached,

or welded, to the device in the scanning electron

microscope (SEM) using an accepted technique called

electron beam deposition (EBD). In this example,

a single tube extends from one electrode to another.

Understanding the mechanical properties of the weld

requires visualizing its structure on the atomic scale if

possible. Using high-resolution microscopy techniques

available within the division, we have seen some

interesting new structures of the weld. Previously,

it was assumed that the weld was a uniform material

composed of amorphous carbon. However, we have

seen, using atomic force microscopy (AFM) as well

as transmission electron microscopy (TEM), spurious

deposits of carbon far outside the weld. Figure 2

shows a nanotube welded to a chromium film.

The residual carbon is seen as a surface texture that

covers almost everything including the nanotube.

Figure 1: SEM image of carbon nanotube test device for

electrical measurements. The nanotube extends across a 2 μm

gap. A second accidental tube is hanging on the side and is not

connected to the electrodes.

Figure 2: AFM image of a multiwalled carbon nanotube welded

to a chromium film. The orange peel texture is residual carbon

left behind from the weld process.

This work is beginning to shed some light on the

properties and structure of these very small devices.

A paper has been submitted entitled, “Electron Beam

Deposition Welding: A Practical Application to Building

Carbon Nanotube Devices,” by P. Rice, R.H. Geiss,

S.E. Russek, A. Hartman and D. Finch, to the Journal

of Vacuum Science and Technology B. Further work is

planned to measure contact resistance within the weld

and resistance changes due to distortions caused by the

weld process.

Demonstrating the need for better standards for

nanotube device characterization, a new standards

committee was recently formed by IEEE, on which NIST

currently serves as a contributing member. Furthermore,

presentations have been given to the American Vacuum

Society, NASA Johnson Space Center, and the engineering

department of the University of Colorado.

Contributors and Collaborators

R. Geiss (Materials Reliability Division, NIST);

S.E. Russek, P. Kabos (EEEL, NIST); D. Finch,

A.B. Hartman (University of Colorado)

Nanometrology
20

Nanometrology

With the recent excitement about carbon

nanotubes and their biological applications,

preliminary studies are underway to determine the

biocompatibility of nanotubes with cell cultures

using our vascular smooth-muscle cell line. The

response of these cells will help us understand the

effects of cell proliferation or degradation due

to direct contact with nanotube mats or clusters.

Paul Rice and Tammy Oreskovic

Carbon nanotubes (CNTs) have great potential for

nanometer scale electronics, superior strength

composites, biological implants, and many other

applications where a well-organized nanometer scale

material is needed. One possible application is using

nanotubes as scaffold materials to support the growth

of transplanted cells and establish proper orientation to

grow artificial tissue. NASA has recently demonstrated

growing retinal cells on nanotube mats. Other possible

applications include sensors and probes for miniature

biological devices, and electrodes for detecting

biomolecules in solutions. However, many issues still

remain in assessing the biocompatibility of these

nanomaterial biosystems for in vivo applications.

In FY04, we explored the viability and proliferation

of cells in contact with carbon nanotubes and

dispersion techniques for compatible surfactants in

cellular environments. In preliminary experiments,

smooth muscle cells were exposed to both entangled

mats and suspensions of multi-walled CNTs by use of

surfactants for dispersion (Figure 1). Results of the

proliferation assay indicate that there is a reduction in

growth and metabolic activity for cells grown directly

on the nanotubes as compared to the controls. These

results indicate that cell attachment may not be as

strong in regions of high CNT density. However, if

the nanotubes are coated with a biologically compatible

surfactant and suspended in media, there appears

to be little effect when compared to the controls.

Figure 2 shows preliminary results of an Alamar

blue proliferation assay.

In FY05, we will continue to explore the

interactions of structure and the effects of clumping

of CNTs on cell growth and orientation. Other possible

directions may include surface modification to promote

cell adhesion and growth, tomography, and size

distribution of CNTs.

Contributors and Collaborators

Dr. N. Varaksa contributed the work on the

surfactant chemistry; Dr. E. Gruelky (University of

Kentucky) supplied carbon nanotubes.

Applications of Carbon Nanotubes:

Cell Viability in Contact with Carbon Nanotubes

Figure1: Vascular smooth muscle cell growing on a cluster

of multiwalled carbon nanotubes on a glass substrate.

Figure 2: Alamar blue assay, test for cell growth and

proliferation. As the cells grow and divide they metabolize

the Alamar blue compound, changing the medium in which the

cells are growing from a blue color to clear.
21

Instruments for in-vivo recording of neural activity

are critical for ongoing and future research aimed

at Alzheimer’s, Parkinson’s, epilepsy, stroke, and

spinal cord injuries. In addition, the development

of a human-brain-machine interface (HBMI) relies

on improved recording and processing of neuronal

signals. Future recording electrodes must be

small, stable, biocompatible, and robust. More

rugged test procedures are also needed for

evaluating and qualifying new electrode materials.

Stephanie A. Hooker and Dudley Finch

New tools are needed to better image and measure

signal transfer inside live cells. One conventional

approach to electrical measurements in cellular materials

involves a two-electrode glass micropipette that clamps

the cell membrane. The discovery of this device,

referred to as a patch clamp, in 1972 had widespread

impact, leading to a Nobel Prize in 1991. However, the

patch clamp is too large for many of today’s desired

measurements in neurobiology, due to the extent of

physical damage caused during its insertion and use.

Recently, silicon-based MEMS technology has been

explored as a method to produce smaller probes for

neuronal research. These devices typically consist of a

silicon shank (several hundred micrometers long) with

an array of microelectrode recording sites located along

its surface. In this manner, multiple neurons can be

studied simultaneously with a single insertion point.

While these devices show considerable promise,

many biologists continue to employ individual metallic

wires as their primary recording electrodes. These

wires are similar to those used inside the patch clamps

but are inserted directly into the brain. Polymer coatings

are often applied to increase impedance, enable better

handling, and improve biocompatibility. The wires are

typically tungsten or stainless steel with diameters on

the order of 50–100 microns. To date, few studies have

attempted to optimize the wire material, the coating,

or the insertion technique (applied force, speed, etc.).

In collaboration with the University of Colorado’s

Health Sciences Center and the Departments of

Chemistry, Electrical Engineering, and Mechanical

Engineering at the University of Colorado at Boulder,

we are developing measurements to help improve and

optimize in-vivo probes. In FY04, we completed

preliminary studies of wires (25 μm in diameter) coated

with thin (~ 60 nm) layers of aluminum oxide, Al2O3.

Atomic layer deposition (ALD) was used to precisely

Applications of Carbon Nanotubes:

Electrochemical Characterization of In-Vivo Neuronal Probes

control coating thickness, and seven different wires were

compared to determine metal effects on performance.

Figure 1: Electrochemical impedance of ALD-coated microwires

in Ringer’s solution as a function of applied voltage at 100 Hz.

A two-electrode configuration was used for testing

in a Ringer’s buffer solution. Several procedural

variables were evaluated, including the type and size

of the reference wire, the solution temperature and pH,

and the electrode placement. Impedance was measured

as a function of frequency, voltage (Figure 1), and time.

The latter indicates the stability and reliability during

extended recordings, a key requirement for long-term

studies. Stability measurements will continue during

the upcoming months in order to ensure that the ALD

coating is not degraded either chemically (by the

solution) or electrically (by the measurement itself).

However, it should be noted that 25 μm wires are still

too large for subcellular studies. As a result, we plan

to evaluate carbon nanotube (CNT) probes in FY05.

CNT-based AFM probes have already been developed

by other researchers in the Materials Reliability Division

for studying microelectronic films. Moreover, dielectric

coatings have recently been applied to individual tubes

(via ALD) to further enhance signal transfer. If successful

electrochemical measurements can be demonstrated,

CNT based in-vivo probes could have a significant impact

on neuroscience due to their small size (0.1 μm or less)

and anticipated long-term stability.

Contributors and Collaborators

D. Restrepo, A. Sharp (University of Colorado

Health Sciences Center); R. Artale, K. Gall, S. George,

R. Zane (University of Colorado at Boulder)

Nanometrology
22

Program Overview

and enamel. This approach will ultimately lead to

materials with improved durability, toughness, and

adhesion to contiguous tooth structure. We also

collaborate with the ADAF to develop metrology

for the biocompatibility of synthetic bone grafts.

In this era of interdisciplinary research,

we provide an added dimension. By taking a

physical/mechanical approach to how cells function,

respond, and remodel in interaction with synthetic

materials, we provide skill sets typically absent in the

biomedical community. Mechanical properties issues

also arise when considering synthetic bone grafts

and tissue engineering scaffolds. Complementing

traditional bulk mechanical property measurements,

combinatorial approaches are being developed to

identify compositions and surface features that

affect properties such as biocompatibility and

mechanical durability.

Our mechanical property metrology extends further

to biological systems that span the range from individual

neurons and muscle cells to complete pulmonary

arteries. This necessitates the development of unique

mechanical testing platforms and application of a

materials science approach to understanding integrated

properties. Recently, we have developed a bioreactor

capable of applying biaxial stresses and allowing

monitoring of the stress and strain of a two-dimensional

scaffold sheet during tissue growth.

Fundamental to the Biomaterials program is

recognition of the need for an integrated systems

approach. Collaborations among and between project

teams are critical to progress against the ambitious

goals of this program.

Contact: Elizabeth S. Drexler

New materials and devices are radically changing

the treatment of injury and disease, yet it is clear that

within this rapidly evolving segment of the materials

industry, a basic measurement infrastructure does

not exist. The Biomaterials Program develops

measurement methods, standards, and fundamental

scientific understanding at the interface between the

materials and biological sciences. For the health care

industry, we focus on dental and medical sectors that

apply synthetic materials for replacement, restoration,

and regeneration of damaged or diseased tissue.

Three primary foci exist within this program:

biocompatibility, biomaterials characterization, and

materials measurements applied to biological systems.

Whether the medical issue involves implanting

a hip- or knee-joint prosthesis, a synthetic bone graft,

or a tissue engineering scaffold into the human body,

one primary issue is biocompatibility. Using our

expertise in materials science, we have developed

suitable Reference Materials (RM) for investigating

biocompatibility and implant suitability. Research has

focused on measuring cellular response to powders

and bulk materials that are candidates for implants;

recently, we produced a realistic wear particle Standard

Reference Material (SRM® 2880) for bioactivity testing.

Work on quantitative methods of biomaterials

characterization includes assays for adhesion,

viability, proliferation, and differentiation of bone

cells, 3-dimensional structural/functional imaging

of tissue in-growth, and biochemical assays to

quantify inflammatory responses to synthetic materials.

The focus of this effort is bridging the gap between

fundamental knowledge and the product development

needs in industry. For example, in collaboration with

the Chemical Science and Technology Laboratory,

we are developing measurement methodologies and

reference materials to assess interactions in complex

systems of living cells with synthetic materials.

The expected outcome of this work includes reference

substrates that induce specific cellular responses,

and engineered DNA vectors to act as fluorescent

reporters of cellular responses.

Another example of our effort to bridge this gap

is our collaboration with the dental industry, which

is primarily composed of small manufacturers with

limited R&D capability. Collaborations with the

American Dental Association Foundation (ADAF)

develop improved materials and materials measurements

techniques, patent and license these inventions, and,

most importantly, provide a technical foundation.

Research focuses on improved understanding of the

synergistic interaction of the phases of polymer-based

composites and the mechanisms of adhesion to dentin

Biomaterials
23

Biomaterials

Pulmonary hypertension is a potentially fatal

complication of congenital heart defects in

children who live at high altitudes. Discovering

the pathophysiology and expression of the disease

may open the way to finding new, more effective

diagnostics and treatments. Our contribution to

this goal is to provide data on the mechanical

properties of the pulmonary artery and its

constituents in healthy and diseased tissue.

Elizabeth S. Drexler

Background

Children born with heart defects (~ 1.0 %) have

an increased risk of developing pulmonary

hypertension at the high altitudes of the Rocky

Mountain region. The mechanisms for developing

this potentially fatal complication are not clearly

understood. It is known that the heart becomes

enlarged while trying to maintain a constant flow

volume. A cyclic response whereby the heart increases

pressure to maintain flow volume and the pulmonary

arteries (PAs) remodel to compensate for the increased

stress on the walls will ultimately result in morbidity

or mortality if not treated.

Technical Strategy

The goal of the project is to determine the critical factors

in the development of pulmonary hypertension in children

so that we can prevent or mitigate the effects. The

strategy is to characterize the fluid dynamics of the system,

and identify how, where, why, and over what period the

tissue of the artery remodels. The “how” will be answered

through measurement of the mechanical properties; the

“where” through the histology of the artery; the “why”

through study of the biochemical signals that cause the

tissue to remodel; and the time frame by using input from

all the preceding. Our contribution will be to measure

and compare the mechanical properties and histology of

PAs using animal models. Our collaborators will perform

the clinical and biochemical studies. Tests are conducted

within 24 hours of excising the arteries, so that the cells

are still viable and responsive. A bubble test is used to

obtain stress–strain data, and an acoustic microscope is

used to obtain speed of sound and attenuation from the

PAs of control, monocrotaline-treated, and hypoxic rats.

An additional population of hypoxic rats (knockouts) that

are missing the endothelin B receptor (responsible for the

expression of vasodilators) has been tested.

Biomaterials Metrology:

Pediatric Pulmonary Hypertension

Figure 1: Comparison of hypoxic and control data from the

proximal arteries of rats.

We believe that monocrotaline may not be an effective

agent for inducing hypertension in the extrapulmonary

arteries. The PAs from the hypoxic normal rats also

exhibited stiffer behavior than did the controls, but not

to the extent of the knock-out hypoxics. The histology

indicates that the adventitial layer is thicker in the hypoxic

PAs due to collagen deposition, but no obvious differences

were observed between the PAs of the controls and the

monocrotaline-treated rats. Fixturing has been developed

and preliminary results from the acoustic microscope

have been generated and are being analyzed. Studies

continue to determine the differences in the remodeling

of the arterial walls and how those disparities influence

the mechanical properties. Analysis of the data in light

of general material thickening is being pursued.

Contributors and Collaborators

Chris McCowan, Tim Quinn, Andy Slifka, Kendall

Waters, Joyce Wright (Materials Reliability Division, MSEL,

NIST), D. Vecchia, J. Splett (Statistical Engineering

Division, ITL, NIST); R. Shandas (University of

Colorado); K. Colvin, D. Ivy (University of Colorado Health

Sciences Center and Children’s Hospital of Denver)

Accomplishments

Data from the PAs of 10 monocrotaline-treated

rats were reduced and analyzed in FY04. Additionally,

the PAs from 12 hypoxic knock-out rats, six hypoxic

normal rats, and 12 control rats were tested and analyzed.

Figure 1 shows the data from six rats each for the control

and hypoxic knockout conditions. It is clear that the

PAs from hypoxic rats demonstrated less strain at a

given stress than did the controls. The PAs from the

monocrotaline-treated rats did not display overtly different

stress–strain behavior as compared with the controls.
24

Tissue engineering offers the hope that

diseased or injured structures within the body

can be replaced by tissues grown on scaffolds.

To be effective, test methods for the mechanical

properties of the polymeric scaffold with and

without tissue ingrowth must be developed

and the properties themselves measured.

Timothy P. Quinn and Tammy L. Oreskovic

Background

Aproposed method for treating disease and injury in

the human body is to replace the diseased tissue

with tissue that is grown outside the body. Typically,

healthy tissue is cultured to grow into a synthetic or natural

scaffold. The scaffold supports the tissue and coaxes it

to grow into the proper geometrical shape. The scaffold

can be cultured with cells in vitro, or a bare (or initially

seeded) scaffold can be used. In both cases, the

mechanical properties of the scaffold or scaffold/tissue

construct must be known in order to ensure that it does

not fail mechanically after it is implanted. A typical

approach would be for the implant designer to use a finite

element model to predict the response of the implant to

in vivo loads. The mechanical quality of the scaffolds

must be assured before they are implanted as well.

Mechanical Models

In collaboration with the Polymers Division, an

unseeded poly(e-caprolactone) (PCL) scaffold was

mechanically tested in compression, and the resulting

stress–strain curves were fitted with empirical models.

The pore structure of the scaffold was varied by changing

the randomly distributed pore size. The models are

hyperbolic in form: The hyperbolic

model was compared to the secant modulus used for rigid

cellular plastics as recommended by ASTM (Table 1).

Biomaterials Metrology:

Mechanical Response of Tissue Engineering Constructs

Optical coherence microscopy (OCM) was used

to scan the interior of the scaffold samples, and the

pores were measured automatically with image analysis

software. The OCM images were also used to form

the basis of finite element (FE) models that were used

to predict the initial elastic modulus of the scaffold (E).

Each 4 μm pixel of the OCM image was represented

with a brick element and assigned the Young’s modulus

of bulk PCL, and a value of 0 for a pore. A compressive

strain was imposed on the model, and the resulting

stresses were calculated. The elastic constants of

scaffold were then calculated by use of Hooke’s law

for a linear-elastic, isotropic material.

The stress–strain curve of the porous PCL cannot easily

be approximated with a line up to 10 % strain. However,

the hyperbolic model has the drawback of having relatively

large standard deviations in its fitted parameters E and A

but is the best fit for the non-linear stress–strain curve.

The secant modulus offers a much lower variability and

could be used for quality control. The results from

the FE model are within one standard deviation of

the experimental values of E (the initial modulus).

Novel Bioreactors

Pore Size Area E Secant Modulus

(mm2) (MPa) A (MPa)

0.0014 89 ± 40 19 ± 10 30 ± 5*

0.0039 122 ± 60 21 ± 13 38 ± 6

0.0150 144 ± 58 31 ± 18 36 ± 5

*Significantly different (p < 0.05) from the secant modulus

of the other two pore size samples. No other parameters

showed significance.

Figure 1: The copper-colored load cells measure the applied

force in this biaxial bioreactor. The sample is held in the center

of the fixture and can be imaged from below to measure strain.

The sample is bathed in nutrients (not shown), and the nutrient is

also pumped across the surface of the scaffold through the grips.

A bioreactor capable of applying biaxial stresses

(Figure 1) has been developed. The applied stress and

strain of the two-dimensional scaffold sheet can be

monitored while the tissue is growing.

Contributors and Collaborators

J.D. McColskey, C.N. McCowan (Materials

Reliability Division, NIST), F.A. Landis, N.R. Washburn

(Polymers Division, NIST)

Table 1. Summary of results of model parameters

and pore size

Biomaterials

H

H

V

A

E

 1 . 
25

Techniques and tools that facilitate the exposure

of single cells (and arrays) to control and

quantify mechanical forces, and at the same

time allow for the characterization of other

biological phenomena, are needed for the

study of cardiovascular tissues and cells.

The development and evaluation of one of

these tools, an optical tweezer, is a focus

of this year’s effort.

Christopher N. McCowan and Andrew J. Slifka

Overall, the challenge is to develop mechanical test

platforms and tools that can be integrated with

currently used biological techniques for the evaluation

and measurement of cellular response (e.g., gene

expression, cell morphology, area of adhesion, etc.).

These types of studies are needed because the

development of vascular smooth muscle cells in

cardiovascular tissue, for example, depends on the

variations in the stress–strain environment that result

from the expansion and contraction of the vessel wall.

The importance of the environment becomes apparent

when one considers that engineered tissues have

mechanical properties inferior to those of naturally

grown tissues. This is possibly a bulk effect, but

is clearly related to processes at the cellular level.

Without a quantitative understanding of the mechanics

and functionality of the building blocks (cells and

fibers), the bulk properties of the tissues cannot be

fully understood and modeled.

The focus for this year was to build an optical

trapping system, including a force/displacement

measurement loop. This system will be used to

calibrate MEMS devices designed for testing single

cells, in addition to measuring cellular components.

To facilitate this effort, we are collaborating with

David Marr at CSM, who has two optical tweezers.

A fluid-flow channel for the calibration of the tweezers

has been built. This flow channel will allow us to

calibrate the tweezers using a drag force, or Stokes

method, and will be compared with methods of

calibration based on Brownian motion.

We have calibrated Bio-MEMS devices using the

atomic force microscope (AFM). Figure 1 shows one

of the devices and a 180 μm long AFM cantilever used

for force calibration. The central platform of such a

Biomaterials Metrology:

Cellular Level Measurements

Figure 1: A Bio-MEMS device used to apply controlled forces

to cells.

Our first application of the tools developed in this

program will be to measure mechanical properties

of leukocytes. This will be done in collaboration

with Dr. Worthen of National Jewish Medical and

Research Center, who has been studying the role of

polymorphonuclear leukocytes, or neutrophils, in

acute lung inflammation. The neutrophil is larger

than the capillaries in the vascular bed of the lung.

Therefore, details of the deformation of the neutrophil

and capillaries are important in determining the

mechanisms of pulmonary inflammatory response.

We plan to develop tools such as optical tweezers

and MEMS devices to apply and sense deforming

forces on cells such as neutrophils.

Contributors and Collaborators

D.S. Finch, T. Oreskovic, D. Lauria (Materials

Reliability Division, NIST); R. Rorrer (Mechanical

Engineering, CU Denver); D. Marr, J. Oakey (Chemical

Engineering, Colorado School of Mines); D. Serrell,

H. Panchawagh (Mechanical Engineering, CU Boulder)

device would hold a cell that would then be subjected

to a controlled, oscillating mechanical environment.

This device operates in a suitable fluidic environment

that keeps the cell viable and allows for biological

assay measurements.

Biomaterials
Quantitative ultrasonic characterization of

biological materials is the application of physical

acoustics techniques to biological and medical

problems. The mechanical vibrations of ultrasound

involve frequencies from below 1 MHz to over

100 MHz with corresponding length scales

from millimeters down to tens of micrometers.

Quantitative measurement of propagation and

scattering properties enables evaluation of

the health and quality of biological materials.

Kendall R. Waters

Background

The biological and medical research communities are

often interested in the health or quality of a biological

material. Measurement of the mechanical properties

of the material can provide information complementary

to that determined from biochemical measurements.

Furthermore, longitudinal studies monitor materials over

an extended length of time, often requiring measurements

to be performed nondestructively. Ultrasonic measurement

techniques permit nondestructive evaluation of the

mechanical properties of biological materials.

Materials can be characterized by their ultrasonic

propagation and scattering properties such as phase

velocity and attenuation coefficient. In quantitative

ultrasonic characterization of biological materials,

changes in ultrasonic properties can be correlated to

changes in structure and morphology, which then can

offer insight into a disease process, for example.

Technical Strategy

We are interested in several classes of biological

materials, including soft and hard tissues and engineered

biomaterial constructs. Ultrasonic measurements of

pulmonary arteries (PAs) from rat models are performed

to understand the mechanical effects of pulmonary

hypertension. A collaboration with Dr. B. Hoffmeister

investigates how ultrasonic properties of cancellous

bone depend on bone mineral density, a key factor

in the risk of fracture in osteoporotic patients.

Another collaboration, with Dr. K. Anseth, investigates

the propagation and scattering properties of a

tissue-engineered construct of bovine cartilage and

hydrogel seeded with chondrocytes (cartilage cells).

For the majority of measurements, we use an

acoustic microscope in double-transmission and

Biomaterials Metrology:

Quantitative Ultrasonic Characterization

Phase-spectroscopic analysis of measurements in

the medio–lateral (ML) and superior–inferior directions

of ten cancellous bone specimens (bovine tibia) has been

completed. Dispersion (frequency dependence of phase

velocity) correlated well with density for ML specimens,

as shown in Figure 1. Results indicate that dispersion

may be a useful parameter for assessing fracture risk.

Preliminary investigations of the ultrasonic

properties of a bovine cartilage-hydrogel construct have

been performed. Results indicate that the reflection

coefficient at the cartilage-hydrogel interface may provide

a useful measure of integration with the native tissue.

Contributors and Collaborators

A. Slifka (Materials Reliability Division, NIST);

K. Anseth (University of Colorado); B. Hoffmeister

(Rhodes College of Memphis, TN)

Figure 1: Relation between dispersion and density for bovine

cancellous bone in superior–inferior and medio–lateral directions.

backscatter modes to determine propagation and scattering

properties. Thickness and speed of sound are determined

by measuring changes in times-of-flight of ultrasonic

signals through a reference path and a path substituted

with the biological material. Attenuation is determined

by spectral analysis of the same ultrasonic signals.

Accomplishments

Measurements of PAs from three different rat models

(controls, hypoxics, and knock-out hypoxics) have been

performed. See the Technical Highlight on Pediatric

Pulmonary Hypertension for a summary of results.

Biomaterials

26
27

Program Overview

Materials for Electronics

The U.S. electronics industry faces strong

international competition in the manufacture of smaller,

faster, more functional, and more reliable products.

Many critical challenges facing the industry require

the continual development of advanced materials

and processes. The NIST Materials Science and

Engineering Laboratory (MSEL) works closely with

U.S. industry covering a broad spectrum of sectors

including semiconductor manufacturing, device

components, packaging, data storage, and assembly,

as well as complementary and emerging areas such as

optoelectronics and organic electronics. MSEL has a

multidivisional approach, committed to addressing the

most critical materials measurement and standards

issues for electronic materials. Our vision is to be

the key resource within the Federal Government for

materials metrology development and will be realized

through the following objectives:

■ Develop and deliver standard measurements and data;

■ Develop advanced measurement methods needed by

industry to address new problems that arise with the

development of new materials;

■ Develop and apply in situ as well as real-time, factory

floor measurements, for materials and devices having

micrometer- to nanometer-scale dimensions;

■ Develop combinatorial material methodologies for

the rapid optimization of industrially important

electronic materials;

■ Provide the fundamental understanding of the

divergence of thin film and nanoscale material

properties from their bulk values;

■ Provide the fundamental understanding of materials

needed for future nanoelectronic devices, including

first principles modeling of such materials.

The NIST/MSEL program consists of projects led

by the Metallurgy, Polymers, Materials Reliability, and

Ceramics Divisions. These projects are conducted in

collaboration with partners from industrial consortia

(e.g., International SEMATECH), individual companies,

academia, and other government agencies. The program

is strongly coupled with other microelectronics

programs within the government such as the National

Semiconductor Metrology Program (NSMP). Materials

metrology needs are also identified through the

International Technology Roadmap for Semiconductors

(ITRS), the IPC Lead-free Solder Roadmap, the

National Electronics Manufacturing Initiative (NEMI)

Roadmap, the Optoelectronics Industry Development

Association (OIDA) Roadmap, IPC (the International

Packaging Consortium), and the National [Magnetic

Data] Storage Industry Consortium (NSIC) Roadmap.

In each of these areas, MSEL researchers have made

substantial contributions to the most pressing technical

challenges facing industry, from new fabrication methods

and advanced materials in the semiconductor industry, to

advanced packaging materials, to magnetic data storage.

Below are just a few examples of MSEL contributions

over the past year.

Advanced Gate Dielectrics

To enable further device scaling, the capacitive

equivalent thickness (CET) of the gate stack thickness

must be 0.5 nm to 1.0 nm. This is not achievable with

existing SiO2/polcrystalline Si gate stacks. Given the

large number of possible choices for these new layers,

the only feasible approach to understanding the complex

materials interactions that result at the gate dielectric/

substrate and gate dielectric/metal gate electrode

interfaces is through the application of combinatorial

methodologies. This same methodology and apparatus

are applicable to a wide variety of problems in the

electronic materials field.

Sub-100 nm Nanofabrication

The continual decrease in feature size has been the

driving force for advances in the semiconductor industry.

Current structures have 90 nm dimensions with planned

nodes at 65 nm and 35 nm structures. Advanced

measurements of the patterning materials (photoresists),

are needed to enable future large scale manufacturing of

smaller devices. MSEL utilizes advanced x-ray and

neutron tools to provide insight into the feasibility

and optimization of these important processes.

Advanced Metallization

Electrodeposited copper is rapidly replacing aluminum

for on-chip “wiring” because of its lower electrical

resistivity, superior electromigration behavior, and the

ability to fill fine features without the formation of seams

or voids. As feature dimensions go below 100 nm,

difficulties in maintaining performance are anticipated.

These issues are addressed through a combination of

modeling and experimental efforts.

Test Methods for Embedded Passive Devices

Significant advantages arise if passive devices are

integrated directly into the circuit board as embedded

passive devices rather than discretely attached with

automated assembly. New metrology methods were

developed to address the needs of the electronic industry.

Two test methods were completed and have received

wide acceptance by industry as new methods to accelerate

the development of embedded passive device technology.

Contact: Robert R. Keller
28

Materials for Electronics

We are developing methods to examine materials and

interfaces in electronic packaging applications and

elucidate the damage mechanisms. Our current focus

is on advanced packaging structure, embedded

passive materials, and thin metal films by use of

thermal microscopy to measure heat flow and thermal

properties on increasingly smaller size scales.

Andrew J. Slifka

Technical Description

The microelectronics industry is moving toward

components of higher density and smaller size

that use less expensive materials. One result of this is

that reliability becomes an increasing concern due to

coefficient of thermal expansion (CTE) mismatch and

increased heat flow. As size decreases and functionality

increases, thermomechanical fatigue becomes a factor

in more areas of the microelectronics industry,

including lead-free solders and interconnects.

We are investigating the structural damage induced

from CTE mismatches between the various component

materials in electronic packages to determine initiation

of damage and the ultimate failure mechanisms.

Thermal microscopy is used to measure changes in

interfacial thermal resistance in order to detect the onset

and continuation of thermomechanical damage, leading

to electrical failure at interfaces.

We are developing new measurement methods

using scanned-probe microscopy (SPM) in order to

characterize packages and measure thermal conductivity

of thin films at increasingly smaller size scales.

Accomplishments

We have completed measurements on industrial

embedded resistors (see Figure 1), making comparative

measurements between the SPM thermal system and

the IR microscope.

We have made measurements of films by use

of thermal SPM in a mode that uses the probe tip

simultaneously as a point-source heater and a resistive

element in a Wheatstone bridge circuit. For example,

we have made preliminary measurements using various

thicknesses of gold films on different substrates,

and have compared a new theory, developed by our

collaborators, to our measurements. Figure 2 shows data

from a suite of these measurements. We will add interfacial

modifications to the samples and to the theory in order to

Electronic Packaging and Components:

Packaging Reliability

make the measurement method applicable to films used in

industry. In addition, we have been using this measurement

method on diamond-like-carbon (DLC) films. These

industrial films are made from a polymer precursor,

which allows easy and inexpensive coating onto various

substrates. The thermal conductivity of these films, and

how they compare to conventionally processed DLC films,

is being investigated.

Finally, we are also measuring thermal conductivity

of lead-free solder balls and interfacial thermal

resistance between alloys and intermetallics.

Contributors and Collaborators

J. Felten (DuPont Technologies, Research Triangle

Park, NC); R. Snogren (SAS Circuits, Inc., Littleton,

CO); K. Cole (University of Nebraska, Lincoln, NE);

S. Joray (Cenymer Corp., Longmont, CO); F. Hua,

(Intel Corp., Santa Clara, CA)

Figure 1: Results of thermal SPM measurements on embedded

resistor materials.

Figure 2: Thermal SPM measurement results on various

thicknesses of gold films on glass substrates.
29

Materials for Electronics

Bulk acoustic techniques have been developed

and applied to the characterization of a variety of

materials, with particular emphasis on piezoelectric

crystals for electronic oscillator and filter

applications. The research includes metrology of

mode-selective noncontacting resonant spectroscopy,

characterization of physical mechanisms that

degrade performance of piezoelectric compounds

with the structure of langasite, and determination

of elastic constants of body-centered-cubic Ti

and the shape-memory alloy NiTi.

Ward Johnson, Sudook Kim, and

Carlos Martino

Over the past several decades, the Materials

Reliability Division has established special

capabilities in a variety of resonant acoustic techniques,

including resonant ultrasound spectroscopy (RUS), timedomain resonance methods, noncontacting transduction,

Marx-oscillator measurements, and torsional-pendulum

measurements. The combined capability of these

resonance systems enables elastic constants and anelastic

damping to be measured from 4 K to 1100 K. The division

also has implemented several conventional pulse-echo

systems, including immersion scanning. During FY04,

research was focused primarily on noncontacting mode

selective metrology, analysis of anelastic damping in

piezoelectrics, measurements of the temperature

dependence of elastic constants of a shape-memory

alloy, and determination of elastic constants of Ti in

its high-temperature body-centered-cubic phase.

Langasite (La3Ga5SiO14) and several of its isomorphs,

including langatate (La3Ga5.5Ta0.5O14), have attracted

significant attention in recent years as piezoelectric

materials for improved electronic oscillators and filters.

Research in our lab over the past year has sought to identify

the dominant anelastic mechanisms that degrade the

performance of these materials. An algorithm has been

developed for fitting the measured temperature and

frequency dependences of the mechanical Q to a

superposition of loss mechanisms. For langasite, three

point-defect relaxations are shown to be superimposed

on a contribution that increased monotonically with

temperature. In langatate, very similar anelastic effects

appear, with distributions of activation energies that

apparently arise from variations in residual stress.

To enable robust measurement of elastic constants

of trigonal piezoelectric crystals, such as langasite,

Electronic Packaging and Components:

Acoustic Characterization

methods of selectively measuring and analyzing resonant

frequencies of modes with specified symmetry have

been developed. This approach overcomes errors in

analysis that can arise from misidentification of modes.

The research has included measurements and analysis

of quartz cylinders and sapphire disks. Noncontacting

piezoelectric coupling with switchable electrode

configurations and Ritz inversion algorithms including

full symmetry information have been developed.

In collaboration with Los Alamos National Lab,

analysis of resonance measurements on polycrystalline

Ti at 1270 K were performed. Polycrystalline elastic

constants were determined using the Ritz method. Then,

the Kröner model was used to estimate monocrystalline

constants from these polycrystalline constants.

Measurements of the temperature dependence of

the elastic constants of the shape-memory alloy NiTi

have been pursued in collaboration with the Mechanical

Engineering Department of the University of Colorado.

This study determined the effects of metallurgical

treatments on the martensitic transition temperature and

elastic constants. Pulse-echo measurements of elastic

constants were performed on cold-drawn and hot-rolled

specimens from 155 K to 300 K. Large Poisson ratios (> 0.4)

reflect the material’s superelasticity. Information was

obtained on the hysteresis in elastic constants arising from

the phase transition, which is a subject of controversy.

Contributors and Collaborators

P. Heyliger (Colorado State Univ.); M. Dunn,

K. Gall (Univ. of Colorado, Mechanical Engineering

Dept.); H. Ogi (Osaka Univ., Japan); H. Ledbetter

(Los Alamos National Lab); A.Teklu (Univ. of

Mississippi, Oxford)

Figure 1: Vibrational mode of a sapphire disk.
30

Measurement methods and materials data are

needed for the design of interconnect structures

in high-performance integrated circuits. These

micro- and nanometer-scale thin films are formed

by physical vapor deposition; their microstructures,

and hence their mechanical properties, are quite

different from those of bulk materials of the same

chemical composition. The ultimate goals of this

project are to characterize the exact materials

used in IC fabrication, at their proper size scale,

and to understand the relevant deformation and

failure mechanisms.

David T. Read

I

nterconnect structures in advanced integrated circuits

carry power, signals, and heat from the transistors to

the outside environment. These structures consist of

multiple layers of thin films of conductors and dielectrics

with barrier and adhesive layers. These thin films are an

essential component of all advanced electronic devices,

and similar materials are used in a variety of other

applications, such as reflective coatings. Industry is

aggressively pressing new materials into service, reducing

the size of the structures, and requiring more functionality,

including mechanical functionality, from all components

of their structures. Design of reliable structures relies on

quantitative numerical modeling, which requires accurate

material property data. Because the films are formed by

physical vapor deposition, their microstructures, and hence

their mechanical properties, are quite different from those

of bulk materials of the same chemical composition.

The objectives of this project are:

■ To develop experimental techniques to measure the

mechanical properties of thin films, in specimens

fabricated and sized like materials used in actual

commercial devices;

■ To relate thin-film mechanical behavior to

microstructure;

■ To extend test techniques from their present level

(1 μm thick, 10 μm wide) to smaller specimens that

are similar in size to the conductive traces used in

contemporary VLSI circuits (widths of 0.1 to 1 μm).

In previous years we reported properties of aluminum,

polyimide, and polysilicon films at room temperature.

We have now measured the tensile properties of aluminum

films from a commercial source, and lab-made

electrodeposited copper films from room temperatures

Micrometer-Scale Reliability:

Mechanical Behavior of Thin Films

Figure 1: TEM of fractured tether of aluminum contact metal

microtensile specimen. The dark lines on the left are dislocations;

note their absence toward the right, near the fracture edge.

up to 150 oC. The mechanical properties decline only

slightly with increasing temperature, in a pattern normal

for face-centered-cubic metals.

Microtensile Young’s (elastic) modulus data for nickel

were contributed to a comparison study. The microtensile

value was 177 ± 8 GPa (most probable uncertainty). Details

are given elsewhere, but the conclusion from the full set

of measurements is that both the modulus and the density

of this sputtered nickel film are lower than bulk values.

Microtensile modulus measurements, in particular, have

been suspect because the results are often lower, by

10 % or more, than bulk values. See the Molecular

Dynamics page of this report for more on this.

The transmission electron microscope (TEM)

micrograph in Figure 1 shows two different deformation

mechanisms for a thin aluminum film. Prismatic vacancy

loops, seen as circular features about 20 nm in diameter

on the right, are formed in the absence of dislocations in

the thinner part of the deformation zone near the fracture

edge (far right, lower). Dislocations are seen only in the

thicker regions, at the left in the image. The size and

density of the loops seems to be dependent on the speed

of the deformation, with smaller loops 5–10nm in diameter

seen in more slowly deformed material.

Contributors and Collaborators

Y-W. Cheng, J.D. McColskey, R.R. Keller, R. Geiss,

J. Wright (Materials Reliability Division, NIST);

MOSIS Service (specimen fabrication)

Materials for Electronics
31

Semiconductor manufacturers require increasingly

demanding thermal and electrical performance from

chip-level interconnects, as feature sizes continue

to shrink. Reliability of such small structures then

becomes compromised by failure modes unseen

by earlier generation interconnect systems.

Our studies address thermal and electrical behaviors

of interconnects under conditions of extreme

stressing. In particular, we concentrate on the

roles of localized stress and variations in micro

nanostructure in limiting interconnect performance

and lifetime. We performed basic studies on

aluminum-based structures undergoing AC stressing

at high current density (> 10 MA/cm2) as well as

measurements of electrical behavior in advanced

sub-100 nm copper and silver wires.

Robert R. Keller, Roy H. Geiss, and

Yi-Wen Cheng

A C stressing at high-current density and low frequencies

 is used to simulate the thermomechanical fatigue that

can occur during a microelectronic device’s operational

lifetime, due for example to power cycling, energy saving

modes, and to application-specific thermal fluctuations.

Cyclic Joule heating takes place, leading to differential

thermal expansion between metallic interconnects and

surrounding substrates or passivation layers. The resulting

damage is due to fatigue mechanisms known to operate

in bulk metals, but with the constraints associated with

thin films imposed. This year, we performed detailed

transmission electron microscope (TEM) studies of the

deformation mechanisms, supplementing last year’s

electron backscatter diffraction studies.

Figure 1 shows a pair of TEM images, bright field

(above) and weak beam dark field (below), taken from

the same region of a cross section of a severely stressed

aluminum interconnect. The image shows a high density

of dislocation loops, as indicated by arrows. Analysis of

diffraction contrast suggests these to be prismatic loops,

where the Burgers vector lies normal to the plane of the

loop. Such dislocations can be formed by the coalescence

of lattice vacancies into a platelike arrangement. Probable

sources of vacancies in thermomechanically deformed

metal films include grown-in vacancies or those formed

during cross-cutting of screw dislocations.

The existence of prismatic loops suggests a possible

means for estimating the local temperature rise during a

heating cycle. Such loops are known to disappear after

prolonged exposure to high temperatures, as vacancies

Figure 1: TEM images showing dislocations induced during

high-current density AC stressing in aluminum.

Micrometer-Scale Reliability:

Chip-Level Interconnects

diffuse out of the film. The observation of these loops

after two hours of testing suggests that there was little

sustained exposure above approximately 150 °C, which

is consistent with our estimates based on electrical

resistance measurements. Both a conference proceedings

and an archival manuscript are in progress.

We also completed, in collaboration with Metallurgy

Division, a study of linewidth effects on resistivity in

narrow (< 50 nm) silver interconnects fabricated by

patterned electrodeposition. We found that resistivity

increases could be attributed to electron scattering from

interconnect surfaces. More details are provided in the

Metallurgy Division Annual Report for fiscal year

2004. A manuscript is now in press for Journal of

Applied Physics.

Contributors and Collaborators

D. Josell (Metallurgy Division, NIST); C. Burkhard

(Clarkson University); C. Witt (Cookson Electronics–

Enthone)

Materials for Electronics
32

The purpose is the development of high-sensitivity,

low-noise magnetic sensors for use as metrological

tools in health care, homeland security and general

information technology. In health care, non-invasive

sensors are needed for medical evaluation in the

areas of magneto-cardiography and magnetic bead

tracking of blood flow and stem cells. In homeland

security, sensors are needed to detect low levels of

pathogens. In IT, sensors are needed for ND failure

analysis and magnetic data storage, among others.

Roy H. Geiss

The goal is to develop multi-level magnetic sensors

with a sensitivity better than 1 p-tesla/√Hz at 1 Hz

noise level that operate at room temperature and can

be easily integrated with standard silicon electronics.

This involves a many-faceted program that includes

materials development, sensor fabrication, sensor

characterization, modeling and nanomagnetodynamic

imaging. The component being studied here concerns

the dynamic observation of magnetic domain walls

using Lorentz microscopy in the transmission electron

microscope (TEM). Imaging of static magnetic domain

walls in the TEM is not new, but our focus is to study

the dynamics of domain wall-defect interactions and

changes in spin distributions associated with defects or

other discontinuities in nanodevices. The ultimate goal

is to associate the dynamical interactions with electrical

noise measurements in the same sensor.

The effort to image magnetic domain walls has just

started. A 200 kV TEM was obtained in 2003. A highresolution, high-speed CCD camera was installed, and highresolution, dynamic-magnetic imaging was successfully

demonstrated. A sample holder with multiple current feed

throughs was designed that allows the application of

magnetic fields for in-situ testing. Thus far, we have

obtained high-resolution images of domain walls at frame

rates up to 15 s–1. In particular, we have filmed the

formation and movement of Bloch lines and points in

cross-tie walls in Ni80Fe20 films 50 nm thick, and have

observed the pinning of cross-tie walls at small defects

in a noncrystalline CoFeNiSiB alloy film provided by

a U.S. magnetic sensor company. Both these dynamic

experiments were performed by slowly varying the small

local magnetic field in the neighborhood of the specimens

in the TEM. Movement of domain walls was possible

since the coercivity of both films was very small,

on the order of a few oersteds.

The observation of pinning of the domain walls

by small defects in the CoFeNiSiB film demonstrated

Micrometer-Scale Reliability:

Dynamic Imaging of Magnetic Domain Walls

Figure 1: Images a to d are from a video sequence showing

domain wall pinning. The cross-tie wall seen at the left-hand side

in a slowly moves to the right under the application of a small

magnetic field in b through d. In b the wall is pinned by defect 1.

With continued applied field, the wall breaks free from defect 1

and moves to defect 2, where it is again pinned, as suggested in c

and definitely in d. Defects 1 and 2 are 4 μm apart.

Figure 2: Images of the individual defects 1 and 2.

our capability to view interactions in real time.

Further, with frame-by-frame analysis of the video,

we determined which defects interacted with the

domain walls. A few frames from a video sequence

containing domain wall pinning are shown in Figure 1.

High magnification images of the noncrystalline defects

are given in Figure 2.

An abstract involving this work has been submitted to

the “2004 Magnetism and Magnetic Materials” conference.

Studies on smaller structures are the next phase.

Contributors and Collaborators

Steve Russek, Bill Rippard, David Pappas (Magnetic

Technology Division, NIST)

Materials for Electronics
33

We have developed a multiscale model for

nanostructures in solids. The model relates the

physical processes at the interatomic level to

measurable lattice distortions at the nanometer

level and macroscopic stresses and strains.

The model links the subnano (interatomic),

nano (nanostructures), and macro length scales

by integrating the powerful techniques of

molecular dynamics, lattice-statics Green’s

functions, and continuum Green’s functions.

David T. Read and Vinod K. Tewary

Technical Description

Mathematical modeling is a very important tool

for understanding the mechanical behavior of

nanomaterials and for research and design of devices

based upon nanostructures. A nanostructure needs to

be modeled at the following scales: (i) the core region

of the nanostructure (subnanometer), where the

nonlinear effects may be significant; (ii) the region of

the host solid around the nanostructure (nanometer);

and (iii) free surfaces and interfaces in the host solid

(macro). A nanostructure causes lattice distortion in the

host solid that manifests as strain throughout the solid.

The strain is essentially a continuum-model parameter,

whereas the lattice distortions are discrete variables that

must be calculated by use of a discrete lattice theory.

Hence, one needs a multiscale model that relates the

discrete lattice distortions at the microscopic scale to

a measurable macroscopic parameter such as strain.

Conventional models of nanostructures are based

upon either the continuum theory, which is not valid

close to the defect, or molecular dynamics (MD) which

is CPU intensive and usually limited to small crystallites,

which may introduce spurious size effects. We need a

computationally efficient multiscale model that links the

length scales from subnano to macro and that can be

used on an ordinary desktop. Such a model will be a

valuable tool for research and engineering designs.

 Our model is based upon the lattice-statics Green’s

function (LSGF) G that reduces asymptotically to the

continuum Green’s function (CGF). The displacement

field in this model containing N atoms is given by:

u(l) = (1/N) ΣkG(k) F(k) exp(ik.l),

where l is a lattice site, k is a reciprocal space vector,

and F(k) is the Kanzaki force, which is calculated by

using MD without making the linear approximation.

For small k, G(k) reduces to CGF. Thus, for large l,

the equation reduces to macroscopic continuum

theory while the discrete lattice effects are retained

in F(k). Thus our model is truly multiscale since it

seamlessly links the discrete atomistic effects in F(k)

to macroscopic scales through the GF. Even for a

million atom model, the calculation of GF takes only

a few CPU seconds on a standard 3 GHz desktop.

Accomplishments

Initial conference presentations and a journal paper

on this new approach, first reported at the end of

FY 2003 and during FY 2004, have been well received.

Figure 1: Section through Ge quantum dot in Si matrix after

partial relaxation. The red circles indicate the original positions

of the Si lattice sites; the atom in red is the center of the QD.

This year, we set out to apply the approach to a more

timely, but also more challenging, physical system, namely,

a germanium “quantum dot” (QD) in a silicon matrix.

On the GF side, the challenge was to treat the more

complex diamond-cubic lattice structure; on the MD

side, the more complex modified embedded atom model

potential, needed for silicon and germanium, had to be

coded and tested. As of this writing, the first iteration of

the Si-Ge quantum dot is in progress. The figure shows

the initial distortions of the diamond cubic lattice around a

QD with 281 Ge atoms; the method is capable of handling

much larger QD, even with a desktop computer.

Contributors and Collaborators

R.R. Keller, Bo Yang (Materials Reliability Division,

NIST); E. Pan (Akron University)

Micrometer-Scale Reliability:

Bridging Length Scales

Materials for Electronics
34

It is widely anticipated that applications of

nanomaterials will enable major advances

in technology in a variety of fields, including

sensors, high-strength materials, medicine, and

others. Computer simulations seem to offer a path

to quantitative understanding of the behavior of

nanoscale materials. The form and parameters of

the interatomic forces may turn out to be the most

concise and useful representation of materials

measurement results. Atomistic simulations are

widely used in interpreting nanoscale phenomena

at the boundary between mechanics and chemistry

and to support the plausibility of proposed

devices. We are developing the capability to

use molecular-dynamics simulations to interpret

our own measurements, and to assess the

accuracy of proposed interatomic potentials.

David T. Read

Various approaches to simulating atomic interactions

have been reported. The first-principles approach

uses quantum mechanical models of nuclei and electrons.

Even though this approach typically includes only the

valence electrons, it can handle only a few tens of atoms.

Recently, in an innovative study, the first principles

approach was used to search for new superalloys.

The molecular-mechanics approach, widely used

for organic molecules such as proteins, requires explicit

assumptions about atomic bonding, specifically, a list

of which atoms are bonded to which other atoms.

The bonds are represented by force laws, and the

configuration of complex molecules can be studied.

Different force laws may be used for certain types

of atoms, depending on the chemical environment.

For instance, the carbon–carbon force law in diamond

may be different from that in graphite, because of

the difference in local chemistry.

Molecular dynamics (MD) treats atoms or

molecules as particles that follow Newton’s laws of

mechanics. The particles interact with a prescribed

force law, which depends only on the chemical identity

of the interacting atoms. The force laws are derived

empirically, and the parameters are selected by fitting to

measured properties, such as the elastic constants, the

vacancy energy, the energy of sublimation, the phonon

frequencies, and others. This approach can treat solids,

liquids, or gases, and can model melting temperatures

and equilibrium crystal structures.

Micrometer-Scale Reliability:

Molecular Dynamics

Molecular-dynamics results obtained in the current

fiscal year may indicate a mechanism for the recurring

reports that the Young’s (elastic) modulus values of thin

films are lower than those of the corresponding (perfect)

bulk material by 10 % or more. Last year’s report showed

a high-resolution SEM micrograph of electrodeposited

copper with a morphology of agglomerated spheres. It’s

Young’s modulus was over 40 % lower than the bulk

value. This year, the elastic behavior of a simplified model

of such a solid was simulated by molecular dynamics.

Caution is in order. The size scale (number of atoms

per sphere) and time scale of the simulation were much

less than for the actual specimen. The results, averaged

over a random set of crystal directions for the spheres,

and for two sizes of spheres, produced a Young’s modulus

35 % below the bulk value. This was surprising because

continuum-mechanics calculations of the modulus

decrease produced by defects of like porosity show values

proportional to the volume loss. The present MD results

are much more dramatic because after the model was

brought to equilibrium, it had a density of about 95 %

of the bulk value.

Contributors and Collaborators

J. Rifkin (University of Connecticut, author of MD

program used)

Figure 1: Cross-section from the center of an array of spheres

(AS) model. Atoms shown in color have local fcc symmetry.

Atoms shown as black have a lower local symmetry. Because of

the periodic boundary conditions, this cell is effectively replicated

indefinitely in all 3 dimensions.

Materials for Electronics
35

The electronics industry is replacing lead–tin eutectic

solders with lead-free solders because of the

environmental hazards of lead. In doing so, they

have created a need for material property data of

the new lead-free solder compositions. A test method

has been developed to measure the mechanical

properties using specimens on the same size scale

as the solder structures used in industry.

Timothy P. Quinn

Background

I

ndustry groups have pointed out the need for material

property data for the new lead-free compositions of

solder; this includes pooling the data that already exist

and filling the critical holes in the data, especially at

low-strain rates.

Most of the data that are available for all solders come

from specimens that are very large (on the order of

millimeters) compared to the solder structures themselves

(on the order of hundreds of micrometers). As the solder

structures (solder balls for flip chip packages, for example)

become smaller (~ 150 μm), their dimensions approach

the dimensions of the phases in the solder itself. The

assumption of a homogeneous material used to analyze

the stresses in the structure is challenged. We have

therefore started testing samples that are on the same size

scale as current solder structures to study this interaction.

Accomplishments

A test method that used “miniature” specimens was

developed to mimic the size of typical soldered joints.

The purpose was to examine the effects of the size of

the specimens (and hence the typical structures found

in industry) and to fill in the gaps in the data for the

lead-free solders. Solder was cast in a Ti mold between

two copper blocks, and 300 μm specimens were cut

from the blocks. The usable gauge length of the

specimens was about 300 μm. We can consistently

make specimens with a known thermal cycle and

maintain well-defined microstructure. Because the

samples were sliced off a relatively large “loaf,” a large

number of samples could be made in a short time.

After determining the geometry of the gage section

using an optical microscope, the specimens were

imaged in an ultrasonic microscope with a beam diameter

of 45 μm at an operating frequency of 100 MHz.

Micrometer-Scale Reliability:

Solder Reliability

Measuring the time-of-flight from the front to the rear

of the sample allowed us to calculate Young’s modulus

knowing the density and Poisson’s ratio (Figure 1).

Figure 2: The measured stress–strain curve for a Sn-3.8Ag-0.7Cu

solder.

Figure 1: An ultrasound scan of a solder tensile specimen.

The image was made by mapping the amplitude of the reflection

off the front interface (white = larger amplitude).

The samples were then tested in uniaxial tension using

pin-style grips. The specimens were first painted white,

and then a dark line was painted on the specimen over the

gauge section. A video-microscope recorded images of

the gauge section at about 0.75 μm/pixel. The edges of

the gauge section were then tracked with an automated

algorithm and used to calculate strain. The stress–strain

curve was then plotted (for example see Figure 2). Note

that because of the small displacements in the elastic

region, the camera does not have enough resolution to

adequately predict Young’s modulus. The ultimate tensile

strength, yield strength and percent elongation were all

obtained using the camera data. Tests have been conducted

using Sn-3.8Ag-0.7Cu, Sn-3.7Ag, Sn-0.7Cu, Sn-5Sb,

and Sn-37Pb.

Contributors and Collaborators

Ilan Makover, T.P. Quinn, K.R. Waters (Materials

Reliability Division, NIST), Yair Rosenthal (Ben-Gurion

University, Israel)

Materials for Electronics
36

Program Overview

Safety and Reliability

While various structural failures have captured

national attention over the years, the events of

September 11, 2001 generated a greatly increased

awareness of vulnerabilities in our national

infrastructure. The extent of these vulnerabilities

depends to a large degree on the performance of

materials in situations outside of the original design

considerations. It is now recognized that a critical

and urgent national need exists to establish the

behavior of materials under such extreme loadings,

and to disseminate guidance and tools to assess and

reduce future vulnerabilities.

The goal of providing a technical basis for cost-effective

changes to national practices and standards, coupled with

a need for an integrated effort drawing on capabilities and

expertise of a broad collaborative team, has lead to the

development of the Safety and Reliability Program within

MSEL. This program draws on the expertise of several

divisions in MSEL and across NIST.

Project selection is guided by an identification and

assessment of the particular vulnerabilities within our

materials-based infrastructure, and focusing on those

issues which would benefit strongly by improved

measurements, standards, and materials data. Ultimately,

we intend to moderate the effects of acts of terrorism,

natural disasters, or other emergencies, all through

improved use of materials.

Our vision is to be the key resource within the Federal

Government for materials metrology development as

realized through the following objectives:

■ Identify and address vulnerabilities and needed

improvements in U.S. infrastructure

■ Develop and deliver standard measurements and data;

■ Develop advanced measurement methods needed by

industry to address new problems that arise with the

development of new materials;

■ Support other agency needs for materials expertise.

This program responds both to customer requests

(primarily other government agencies) and to the

Department of Commerce 2005 Strategic Goal of

“providing the information and framework to enable

the economy to operate efficiently and equitably.”

For example, engineering design can produce safe and

reliable structures only when the property data for the

materials is available and accurate. Equally importantly,

manufacturers and their suppliers need to agree on

how material properties should be measured.

The Safety and Reliability Program works toward

solutions to measurement problems on scales ranging

from the macro to the micro, in three of the Laboratory’s

Divisions (Materials Reliability, Metallurgy, and Polymers).

The scope of activities includes the development and

innovative use of state-of-the-art measurement systems;

leadership in the development of standardized test

procedures and traceability protocols; development of

an understanding of materials in novel conditions; and

development and certification of Standard Reference

Materials (SRMs). Many of the tests involve extreme

conditions, such as high rates of loading, high temperatures,

or unusual environments (e.g., deep underwater). These

extreme conditions often produce physical and mechanical

properties that differ significantly from the handbook

values for their bulk properties under traditional conditions.

These objectives will be realized through innovative

materials, property measurement and modeling.

The MSEL Safety and Reliability Program is

also contributing to the development of test method

standards through committee leadership roles in

standards development organizations such as the

ASTM International and the International Standards

Organization (ISO). In many cases, industry also

depends on measurements that can be traced to NIST

Standard Reference Materials (SRM®).

In addition to the activities above, all three divisions

provide assistance to various government agencies on

homeland security and infrastructural issues. Projects

include assessing the performance of structural steels

as part of the NIST World Trade Center Investigation,

advising the Bureau of Reclamation on metallurgical issues

involving pipelines and dams, advising the Department of

the Interior on the structural integrity of the U.S.S. Arizona

Memorial, and collaborating with both the Department

of Transportation and the Department of Energy on

pipeline safety issues.

Contact: Thomas A. Siewert or Frank W. Gayle
37

Safety and Reliability

Infrastructure Reliability:

Analysis of Structural Steel in the World Trade Center

In 2002 NIST became the lead agency in the

investigation of the World Trade Center collapse.

The investigation addresses many aspects of the

catastrophe, from occupant egress to factors

affecting how long the Twin Towers stood after being

hit by the airplanes, with a goal of gaining valuable

information for the future. A critical aspect of

the investigation is the metallurgical analysis of

structural steels from the Twin Towers. The analysis

includes characterization of properties, failure

modes, and temperature excursions seen by the steel.

Stephen W. Banovic, Richard J. Fields,

Timothy J. Foecke, William E. Luecke,

J. David McColskey, Christopher N. McCowan,

Thomas A. Siewert, and Frank W. Gayle

The collapse of the World Trade Center (WTC)

Towers on September 11, 2001, was the worst building

disaster in human history. Engineers, emergency

responders, and the nation were largely unprepared for

such a catastrophe. NIST is investigating the disaster

(see http://wtc.nist.gov/), and a primary objective is to

determine why and how the towers collapsed after the

initial impact of the aircraft. As part of this investigation,

the Metallurgy and Materials Reliability Divisions in

MSEL are studying recovered structural steel from

the WTC site. Progress in this study is outlined here.

Task 1 — Collect and catalog physical evidence:

236 structural pieces of the WTC towers have

been collected, brought to NIST and studied. Reports

have been issued documenting the steel, the as-built

locations, the structure of the towers based on design

documents, and the standards at the time of construction.

Figure 1: Enhanced image of the impact zone of WTC 2 has

allowed determination of failure modes in the perimeter columns.

Figure 2: Normalized yield strength and ultimate tensile strength

measured as function of temperature. Model curve is based on

historical data for WTC era steels.

Task 2 — Categorize failure mechanisms

based on visual evidence: Available photographic

evidence and recovered steel have been examined and

documented as to failure mechanisms (Figure 1).

Task 3 — Determine steel properties to

support structure performance and airplane

impact modeling studies: 29 different steels

have been characterized for room temperature

mechanical properties. High-temperature and

high-strain-rate tests are now complete. Creep, or

time–temperature-dependent behavior, has been

determined for floor truss and column steel.

Task 4 — Correlate determined steel properties

with specified properties: Most steel was found to

exceed the specified minimum values by 5 to 10 percent.

Task 5 — Analyze steel to estimate temperature

extremes: We have developed a technique of

paint characterization to provide a quick mapping of

temperature excursions seen by the steel. Challenges

included deciphering pre- and post-collapse exposure

(see related Highlight in this report).

Data on material properties have been provided to aid

in the modeling of plane impact and structural response

to the fires. A final draft of the investigation report will

be released for public comment in December 2004.

Contributors and Collaborators

R. Santoyo, L. Rodine (Materials Reliability Division,

MSEL, NIST); M. Williams, S. Claggett, M. Iadicola,

R. Jiggetts (Metallurgy Division, MSEL, NIST)
38

Infrastructure Reliability:

Standard Test Methods for Fire-Resistant Steel

Safety and Reliability

The fires in the World Trade Center and the

ensuing collapse focused attention on the

vulnerability of structural steel to fire. Recently,

steel mills in Europe and Japan have begun to

market steels designated as “fire-resistant.”

This project is developing a standard test method

for quantitatively evaluating and comparing

the resistance to high-temperature deformation

and failure of structural steels.

William E. Luecke, J. David McColskey,

Richard J. Fields, and Frank W. Gayle

At room temperature, the stress–strain behavior of

 structural steel is considered to be independent of

time. Above about 300 °C, structural steel begins to lose

strength. At still higher temperatures, about 500 °C,

creep, or time-dependent deformation, further reduces

the load-carrying capability. By 600 °C, most structural

steels have lost more than half their strength. For this

reason, structural steels in buildings are insulated to

minimize the temperature rise and resulting strength loss.

Fire resistant (FR) steels are intended to be drop-in

replacements for structural steel. They typically meet

the same specifications with similar welding properties

and cost only marginally more. Yet these steels retain

superior high-temperature strength, offering potential

for extra time for building occupants to escape a fire.

In Japan and Europe, FR steels are qualified

based on yield strength retention at high temperature.

This definition may not be the most appropriate since

retained yield strength is a short-time property, yet

fire-resistance is often measured in hours. Also, with

increasing temperature, strength becomes increasingly

sensitive to the strain rate. Current U.S. standards for

load-bearing components in fire are based on time to

reach a given temperature, so effectively all steels are

considered to have the same high-temperature strength

reduction, regardless of actual properties.

We are currently studying a hybrid of creep and

conventional tension tests. The test specimen is held

under constant load as the test temperature ramps

upward linearly. Over a narrow temperature range,

which can be approximated as a critical temperature,

the deformation rate increases dramatically, and the

specimen fails. This critical temperature can be used

as a measure of fire resistance.

One goal of this project is to refine this test

technique and offer it as a draft standard. Published

research has established that the temperature ramp test

Figure 1: Comparison of “run-away creep” deformation of

FR and ordinary construction steel.

can rank steels, but definitive studies comparing

ordinary and FR steels are lacking. Until a standard

test method is developed, it is difficult to confidently

compare results between laboratories. This research

will focus on understanding the limitations, repeatability,

and reproducibility of the method by characterizing

several different classes of construction steels.

Interlaboratory studies will be used to probe the

method’s limitations, precision and bias.

A second goal is to generate constitutive models

for modeling high-temperature deformation of steels.

If test results are not predictable from underlying

deformation behavior, a test cannot possibly indicate

real-world performance. A second benefit is that

much-needed data will be supplied for finite element

modeling of modern structural steel deformation in fire,

a prerequisite for performance-based fire resistant design.

Figure 1 illustrates the concept of critical

temperature for “run-away” creep for two FR steels

and one conventional construction steel. The results

demonstrate the potential performance advantage of

FR steel. Much more work is necessary, however, to

understand the variability in performance of ordinary

and FR steels.

During 2004, we also spearheaded the development

of an ASTM task group under committee A01 to evaluate

test methods for fire resistance of structural steel.

Contributors and Collaborators

M. Bykowski (SURF)
39

The major project objective is to develop the

scientific underpinnings necessary to enhance

acoustic emission (AE) technology through

increased, high-sensitivity bandwidth. Current

secondary objectives include: (1) developing for

many users the missing element of modeling AE

signals for multiple sources in specimens with

and without edge reflections; and (2) developing

rational approaches to analyze AE waveforms

to solve the real-world problems of reliable

identification and location of sources of AE signals.

Thomas A. Siewert and Marvin Hamstad

Technical Description

Acoustic emission (AE) refers to the generation of

 propagating elastic displacement waves as a result

of micro-sized transient-energy releases in a material.

Monitoring these waves can provide fundamental

information about the location and mechanism(s) of

the transient-energy release as well as the time/stress

history of such releases. The technical approach, which

is beyond that currently commercially offered for either

resonant or waveform-based AE technology, is to develop

all the key components relevant to a wideband application

of AE technology. These include development of

wideband high-sensitivity sensor/preamplifiers; high-speed

digital recording data-gathering systems of wide dynamic

range; finite-element modeling (FEM) to predict nearand far-field displacement waves from AE sources in

large and small specimens; wideband experimental AE

displacement waveforms from sources in materials of

interest; signal-processing techniques to accurately identify

source types and their locations; and experimental

characterizations of simulated AE wave propagation.

The scope in FY2004 covered studies on the effects

of electronic background noise on the identification of

AE source types through the use of modal amplitudes

obtained from wavelet-transform (WT) results.

Accomplishments

Previous work, with FEM-generated signals,

demonstrated a technique to identify AE sources by using

ratios of modal magnitudes in two different radiation

directions. The finite-element code modeled AE signals

for dipole-type sources in an aluminum plate 4.7 mm thick.

The plate had transverse dimensions sufficient that plate

edge reflections did not superimpose on direct signal

arrivals. The FEM signals were essentially noise free.

To examine how the presence of electronic noise (from

the sensor/preamplifier) alters the ability to correctly

identify AE source types, detailed analysis was carried

out by superimposing experimental wideband noise on

the FEM-based AE signals. Important discoveries were

made. The WTs of typical noise signals demonstrated

that the WT magnitudes of the noise at each frequency

vary with time in a random fashion. Hence, it was

necessary to do a statistical study of the effects of noise.

Fifty noise segments were prepared. The noise segments

were added to the noise-free FEM signals. At each signalto-noise (S/N) ratio, fifty FEM-plus-noise signals were

used for each source type (in-plane dipole, micro-crack

initiation, and shear without a moment). The S/N ratio

was calculated based on the peak signal amplitude in the

assumed direction of applied stress for the three source

types. Using the same successful technique for noise

free signals, the FEM-plus-noise signals were processed.

Figure 1 shows how the number of correct source

identifications depends on the S/N ratio. Clearly a S/N

ratio of at least six to one is needed to correctly identify a

large percentage of the source types. It is expected that

all modal amplitude techniques of source identification

will be similarly affected. Close examination of the WTs

of the noise and the AE signals revealed that the noise

signals inhabit the same frequency ranges as the AE signals;

hence it will not be straightforward to filter out the

noise signals.

Contributors and Collaborators

NIST participants: D. McColskey (Materials Reliability

Division, NIST); Cross OU collaborators: A. O’Gallagher,

J. Gary (Information Technology Laboratory, NIST);

W. Prosser (NASA Langley)

Infrastructure Reliability:

Waveform-Based Acoustic Emission

Figure 1: Percent of trials out of 50 with correct source identification

versus S/N ratio for the source types and depths listed.

Safety and Reliability
40

Safety and Reliability

We assist owners of Charpy impact machines in

achieving conformance with the requirements of

ASTM Standard E 23. We interact with the ASTM

Committee responsible for the Charpy impact

standard to improve the service and to maintain

a high-quality verification program. We also

participate in the activity in ISO Committee TC

164, so our specimens and procedures remain

compatible with the associated international

and regional standards.

Thomas A. Siewert

Technical Description

The Charpy impact test uses a swinging hammer to

assess the resistance of a material to brittle fracture.

The absorbed energy is measured from a calibrated

scale, encoder, and/or an instrumented striker. The low

cost and simple configuration of the test have made it a

common requirement in codes for critical structures

such as pressure vessels and bridges. This project is

handled jointly by the Standard Reference Materials

Program (of the Office of Measurement Services),

which oversees the administrative aspects of the

program, and the Materials Reliability Division, which

handles the technical and verification aspects. NIST

provides highly characterized standard reference

materials (SRMs) to machine owners and independent

calibration services, then evaluates the results of tests

of these specimens on their impact machines. Owners

of machines that meet the requirements of ASTM

Standard E 23 are given a letter of conformance,

while owners of nonconforming machines are given

recommendations on corrective actions. Our special

facilities include three master Charpy impact machines

(all 300 J to 400 J capacity). These three machines are

used to establish certified values for the NIST reference

materials sold through the Standard Reference Materials

Program Office. In addition, we have several more

machines (3 J to 400 J capacities) that are used for

research purposes.

Accomplishments

We expect about 950 customers for this service in

FY04, a number similar to the customer base in recent

years. The great majority of these machines were within

tolerances required by ASTM Standard E 23. As usual,

many customers took advantage of our support services,

as shown by over 674 emails, 730 faxes, and 500 phone

calls in the first 9 months of FY04. We immediately

contact the machine owner when it fails to meet the

verification criteria. In this contact (by phone, mail,

email, or fax), we suggest corrective measures.

One big change this year was that Dan Vigliotti

retired after serving as Charpy Coordinator for about

12 years. Ray Santoyo has completed his training for

this position and has taken over as Charpy Coordinator.

We have just completed a three-year test program that

is collecting data on “International Master Batches” of

Charpy impact verification specimens. A meaningful

harmonization (equivalency) of Charpy V-notch

standards around the world is unlikely until the

reference materials used for the verification of impact

machines in Europe, Japan, and the United States

(EN-10045-2, JIS B 7722, and ASTM E 23) share a

more common method of certification. The results

of this test program are being used to evaluate the

use of Master Specimens as a common control in the

certification procedure for CVN verification specimens

between the three countries’ National Measurement

Institutes. It will also evaluate machine variables,

offsets, uncertainty, and other factors relevant to

the harmonization of our respective systems. Initial

results indicate the equivalency of the energy scales

used to measure absorbed energy by the United States,

Europe, and Japan.

We are helping to organize another international

symposium, “Second Symposium on Pendulum Impact

Machines: Procedures and Specimens,” to be held in

conjunction with the November 2004 meeting of ASTM

Committee E 28 in Washington, D.C. Previous

symposia have provided valuable insight into

improvements in our program.

This year, we dedicated a previous Charpy master

machine to Izod impact testing, and expect to produce

a new SRM in FY05.

Chris McCowan serves as the Chairman of ISO

TC164 SC4 P, on pendulum impact and also as

the Chairman of ASTM Subcommittee E28.07 on

impact testing.

Contributors and Collaborators

NIST participants: Ray Santoyo (Charpy Program

Coordinator), C. McCowan, T. Siewert, J. Clark,

D. Cyr, C. Dewald, S. Vincent, N. Neumeyer, J. Percell;

External collaborators: IRMM (Europe), NRLM (Japan),

Members of ASTM Subcommittee E 28.07

Infrastructure Reliability:

Charpy Impact Machine Verification
41

Materials Reliability Division FY04 Annual Report Publication List

Materials Reliability Division FY04 Annual Report Publication List

Balzar, D., “Characterization of strain by diffraction

and its influence on the Curie–Weiss temperature in

ferroelectric thin films,” Computer Modeling in

Engineering and Sciences, in press.

Balzar, D., “Size-strain line-broadening analysis of

the Ceria round robin: Sample II. The results of the

round robin,” J. Appl. Crystallography, submitted.

Balzar, D., and N.C. Popa, “Elastic-strain tensor

and inhomogeneous strain in thin films by x-ray

diffraction,” Thin Solid Films 450, 29–33 (2004).

Balzar, D., and N.C. Popa, “Residual Strain/Stress

and Crystallite Size Modeling in Rietveld Refinement,”

Diffraction Analysis of the Microstructure of Materials,

edited by E.J. Mittemeijer and P. Scardi (Springer,

2004) pp. 125–145.

Balzar, D., and N.C. Popa, “Residual Stress

Determination by Diffraction: Modeling and

Applications,” Proceedings of the International

Conference on Computational and Experimental

Engineering and Sciences (ICCES’04), Tech Science

Press, in press.

Cheng, Y.W., D.T. Read, J.D. McColskey, and

J.E. Wright, “A tensile-testing technique for micrometersized free-standing thin films,” Thin Solid Films.

Downs, K.S., M.A. Hamstad, and A. O’Gallagher,

“Wavelet Transform Signal Processing to Distinguish

Different Acoustic Emission Sources,” J. of Acoustic

Emission 21, 52–69 (2003).

Drexler, E.S., J.E. Wright, A.J. Slifka, C.N. McCowan,

D.D. Ivy, and R. Shandas, “Stress-strain behavior of

rat pulmonary arteries,” J. Appl. Physiol.

Drexler, E.S., C.N. McCowan, J.E. Wright, A.J. Slifka,

D.D. Ivy, and R. Shandas, “Comparison of strength

properties of normotensive and hypertensive rat pulmonary

arteries,” Proc. Rocky Mountain Bioengineering Symp.

Flannery, C., and S. Kim, “Poisson ratio porosity

dependence of low k dielectric films,” Appl. Phys. Lett.

Flannery, C., S. Kim, and D. Hurley, “Opto-acoustic

inspection techniques on layered low dielectric constant

films for microelectronic interconnect,” Materials

Research Society.

Gall, K., Y. Liu, D. Routkevitch, and D. Finch,

“Instrumented microindentation of nanoporous alumina

films,” J. Mater. Res.

Gall, K., G. Stafanic, D. Balzar, M.L. Dunn, and

Y. Liu, “Internal stress storage in shape memory polymer

nanocomposites,” Appl. Phys. Lett. 85 290–292 (2004).

Hamstad, M.A., K.S. Downs, and A. O’Gallagher,

“Practical Aspects of Acoustic Emission Source

Location by a Wavelet Transform,” J. of Acoustic

Emission 21, 70–94, A1–A7 (2003).

Hartman, A.B., P. Rice, D.S. Finch, G.D. Skidmore,

and V.M. Bright, “Force-deflection characterization

of individual carbon nanotubes attached to MEMS

devices,” Proc. Actuators and Sensors, MEMS 2004

Conf.

Heyliger, P., S. Cook, W. Johnson, and S. Kim,

“Continuum-based free vibration of circular elastic

and piezoelectric trigonal plates,” J. of Sound and

Vibration.

Hurley, D.C., and J.A. Turner, “Humidity effects on

the determination of elastic properties by atomic force

acoustic microscopy,” J. Appl. Phys. 95, 2403 (2004).

Hurley, D.C., K. Shen, N.M. Jennett, and J.A. Turner,

“Atomic force acoustic microscopy methods to

determine thin-film elastic properties,” J. Appl. Phys.

94, 2347 (2003).

Johnson, W.L., S.A. Kim, and S. Uda, “Acoustic

loss in langasite and langanite,” Proceedings of the 2003

IEEE International Frequency Control Symposium,

p. 646 (2003).

Josell, D., C. Burkhard, Y. Li, Y.W. Cheng,

R.R. Keller, C.A. Witt, D.R. Kelley, J.E. Bonevich,

B.C. Baker, and T.P. Moffat, “Electrical properties

of superfilled sub-micrometer silver metallizations,”

Journal of Applied Physics 96 (1), July 2004.

Keller, R.R., R. Geiss, Y.W. Cheng, and D.T. Read,

“Microstructure evolution during alternatingcurrent-induced fatigue,” 2004 ASME International

Mechanical Engineering Congress, Nov. 13–19,

(2004) Anaheim, CA.

Ledbetter, H., H. Ogi, S. Kai, S. Kim, and M. Hirao,

“Titaniums b.c.c. monocrystal elastic constants,”

J. Appl. Phys.

Lomonosov, M., P. Hess, R.E. Kumon, and

M.F. Hamilton, “Laser-generated nonlinear surface

wave pulses in silicon crystals,” Phys. Rev. B 69,

035314 (2004).
42

Materials Reliability Division FY04 Annual Report Publication List

Miller, D., C. Hermann, K. Spark, D. Finch,

S. George, C. Stoldt, and K. Gall, “Thermomechanical

behavior and reliability of Au/SI MEMS structures,”

Intl. Reliability Phys. Forum.

Padilla, T.M., J.R. Berger, D.R. Munoz, T.P. Quinn,

and R.A.L. Rorrer, “Contact models of GMAW wire

liner friction: An inverse photoelastic solution,” Proc.

85th Annual AWS Convention and 2004 Welding Show.

Popa, N.C., D. Balzar, G. Stefanic, S. Vogel,

D. Brown, M. Bourke, and B. Clausen, “Residual-strain

determination by least-squares refinement of TOF

neutron-diffraction measurements of deformed

uranium,” Advances in X-Ray Analysis, 47 (2004)

CD-ROM.

Quinn, T.P., T.L. Oreskovic, C.N. McCowan,

and N.R. Washburn, “Material models for a

poly(e-caprolactone) scaffold,” Proc., 41st Ann.

Rocky Mountain Bioengineering Symp.

Read, D.T., “Atomistic simulation of modulus deficit

in thin film copper electrodeposits,” J. Appl. Phys.

Read, D.T., R. Geiss, and Y.W. Cheng, “Morphology,

microstructure, and mechanical properties of a copper

electrodeposit,” Microelectronic Engineering.

Read, D.T., R. Geiss, and Y.W. Cheng, “Mechanical

behavior of electrodeposited copper film at elevated

temperatures,” 2004 ASME International Mechanical

Engineering Congress, Nov. 13–19, 2004, Anaheim, CA.

Rice, P., R.H. Geiss, A.B. Hartman, and S.E. Russek,

“Practical application of electron beam deposition

welding to building carbon nanotube devices,” Proc.

Amer. Vacuum Soc. 5th Intl. Conf. on Microelectronics

and Interfaces.

Rice, P., R.H. Geiss, S.E. Russek, A.B. Hartman,

and D.S. Finch, “Electron Beam Deposition Welding:

A Practical Application to Building Carbon Nanotube

Devices,” Journal of Vacuum Science and

Technology B, submitted.

Rorrer, R.A.L., A.J. Slifka, H.V. Panchawaugh,

D.S. Finch, and R.L. Mahajan, “Calibration of

vertically actuated MEMS devices via the AFM,”

J. Microelectromechanical Systems.

Shen, K., D.C. Hurley, and J.A. Turner, “Dynamic

behavior of dagger-shaped atomic force microscope

cantilevers,” Nanotechnology, submitted.

Siewert, T.A., and W. Rippey, “Thirteenth

International Conference on Computer Technology

in Welding,” NIST SP 1008.

Siewert, T.A., and C.N. McCowan, “The

Development of Procedures for Impact Testing,”

Journal of ASTM International, submitted.

Slifka, A.J., H. Panchawagh, R.L. Mahajan,

D. Finch, and R.A.L. Rorrer, “Static and quasi-static

calibration of a bio-MEMS device,” Proc., 41st Ann.

Rocky Mountain Bioengineering Symp.

Slifka, A.J., E.S. Drexler, J.E. Wright, and

R. Shandas, “Bubble-test method for synthetic and

bovine vascular material,” J. Biomech.

Slifka, A.J., H.V. Panchawagh, R.A.L. Rorrer,

R.L. Mahajan, and D.S. Finch, “Force and

displacement calibration of a bio-MEMS device,”

J. Microelectromech. Syst.

Splett, J.D., and C.N. McCowan, “Summary of

Charpy Impact Verification Data: 1993–2003,” BERB

JULY XX).

Sundaram, V., R.L. Mahajan, D.S. Finch, and

S.A. Hooker, “Thermal, electrical, and mechanical

characterization of carbon nanotube-epoxy

composites,” Proceedings of ASME HT-FED 2004,

July 11–15, 2004, Charlotte, NC.

Tewary, V.K., and D.T. Read, “Integrated Green’s

function molecular dynamics method for multiscale

modeling of nanostructures: Application to Au

nanoisland in Cu,” CMES (Computer Modeling in

Engineering and Science).

Tewary, V.K., “Green’s function method for

modeling surface acoustic wave dispersion in

anisotropic material systems and determination of

material parameters,” Wave Motion.

Tewary, V.K., “Elastostatic Green’s function

for advanced materials subject to surface loading,”

J. Eng. Math.

Tewary, V.K., and D.T. Read, “Multiscale modeling

of quantum nanostructures using integrated Greens

function and molecular dynamics,” Pre-conf. Proc.

ICCES 04, July 26–29, 2004.

Tewary, V.K., and D.T. Read, “Multiscale

Green’s function method for modeling quantum

nanostructures” Proc. 12th International Workshop

on Physics of Semiconductor Devices, edited

by K.N. Bhat and A. Das Gupta, 1, 521–526

(2003).
43

Materials Reliability Division FY04 Annual Report Publication List

Tewary, V.K., “Multiscale Green’s-function

method for modeling point defects and extended

defects in anisotropic solids: application to a vacancy

and free surface in copper,” Physical Review B 69

094109 (2004).

Turner, J.A., and D.C. Hurley, “Ultrasonic

methods in contact atomic force microscopy,”

Ultrasonic Methods for Material Characterization,

edited by D. Placko and T. Kundu (Paris: Hermes

Science Publications, 2003), Chap. 5, 117–148.

Waters, K.R., J. Mobley, and J.G. Miller,

“Causality-imposed (Kramers–Krönic) relationships

between attenuation and dispersion: Historical

perspective,” IEEE Trans. Ultrason. Ferroelect.

Freq. Cont.

Wright, J.E., E.S. Drexler, A.J. Slifka,

C.N. McCowan, D.D. Ivy, and R. Shandas,

“Estimation of stress and strain in rat pulmonary

artery material during a biaxial bubble test,”

Proc. Rocky Mountain Bioengineering. Symp.,

April 23–25, (2004).

Yang, B., and V.K. Tewary, “Defect Greens

function analysis of an inhomogeneous quantum dot

in a half-space anisotropic substrate,” J. Appl. Phys.

Yang, B., E. Pan, and V.K. Tewary,

“Three-dimensional Green’s function of steady-state

motion in anisotropic half-space and bimaterials,”

Engineering Analysis with Boundary Elements, (2004).

Yang, B., and V.K. Tewary, “Continuum Dyson’s

equation and defect Green’s function in a heterogeneous

anisotropic solid,” Mechanics Research Communications

31, 405–414 (2004).

Yang, B., and V.K. Tewary, “Static responses of

a multilayered anisotropic piezoelectric structure to

point force and point charge,” Smart Materials and

Structures 13, 175–183 (2004).
44
45

Materials Reliability Division

Materials Reliability Division

Chief

Alan F. Clark

Phone: 303– 497–5202

E-mail: aclark@boulder.nist.gov

Deputy Chief

Thomas A. Siewert

Phone: 303– 497–3523

E-mail: siewert@boulder.nist.gov

Group Leaders

Microscale Measurements

Robert R. Keller

Phone: 303– 497–7651

E-mail: keller@boulder.nist.gov

Microstructure Sensing

Stephanie A. Hooker

Phone: 303– 497–4326

E-mail: shooker@boulder.nist.gov

Process Sensing & Modeling

Thomas A. Siewert

Phone: 303– 497–3523

E-mail: siewert@boulder.nist.gov
46

Research Staff

Research Staff

Cheng, Yi-Wen

cheng@boulder.nist.gov

Deformation and strain

Scanning electron microscopy

Microstructural characterization

Drexler, Elizabeth

drexler@boulder.nist.gov

Electron-beam moiré

Tissue mechanics

Metrology of biomaterials

Geiss, Roy

geiss@boulder.nist.gov

Electron microscopy

Microstructural characterization

Materials science

Hamstad, Marvin

hamstad@boulder.nist.gov

Acoustic emission

Composite materials

Nondestructive evaluation

Hooker, Stephanie

shooker@boulder.nist.gov

Nanomaterials and composites

Electromechanical characterization

Sensors and actuators

Hurley, Donna C.

hurley@boulder.nist.gov

Microscale elasticity

Nonlinear ultrasonics

Solid-state physics

Johnson, Ward

johnson@boulder.nist.gov

Ultrasonic measurements

Internal friction

Process sensing

Keller, Robert

keller@boulder.nist.gov

Materials science

Electron microscopy

Mechanical behavior

Kim, Sudook

sak430@boulder.nist.gov

Elastic properties

Low-temperature physical properties

Ultrasonic measurements

McColskey, J. David

mccolske@boulder.nist.gov

Crack propagation

Composite materials

Mechanical testing

McCowan, Christopher

mccowan@boulder.nist.gov

Charpy impact testing

Microscopy and failure analysis

Metrology of biomaterials

Oreskovic, Tammy

oreskov@boulder.nist.gov

Metrology of biomaterials

Scaffold materials

Mechanical measurements

Quinn, Timothy

quinn@boulder.nist.gov

Metrology of biomaterials

Modeling of biomaterials

Strength of lead-free solders

Read, David

read@boulder.nist.gov

Electronic packaging

Elastic-plastic fracture mechanics

Mechanical behavior of thin films

Rice, Paul

paulrice@boulder.nist.gov

Scanned probe microscopy

Magnetic force microscopy

Nanometer scale manipulation

Rodine, Lonn

rodine@boulder.nist.gov

Instrumentation

Data collection and reduction

Computer support

Santoyo, Raymond

santoyo@boulder.nist.gov

Instrumentation

Charpy impact testing

Computer support

Siewert, Thomas

siewert@boulder.nist.gov

Standard reference materials

X-ray sensing and diffraction

Weld sensing
47

Research Staff

Slifka, Andrew

slifka@boulder.nist.gov

Thermal conductivity

Thermal barrier coatings

Surface characterization

Tewary, Vinod

tewary@boulder.nist.gov

Solid-state physics

Green’s-function methods

Elastic-wave propagation

Waters, Kendall

krwaters@boulder.nist.gov

acoustic microscopy

ultrasonic biomaterial evaluation

wave propagation and scattering

Wright, Joyce

jewright@boulder.nist.gov

Modeling of material behavior

Finite-element analysis

Mechanical behavior of thin films
48
49

Organizational Charts

Organizational Charts

Materials Science and Engineering Laboratory

Polymers

E.J. Amis, Chief

C.R. Snyder, Deputy

Metallurgy

C.A. Handwerker, Chief

F.W. Gayle, Deputy

Ceramics

D.L. Kaiser, Chief

R.G. Munro, Deputy

Materials Reliability

A.F. Clark, Chief

T.A. Siewert, Deputy

NIST Center for

Neutron Research

P.D. Gallagher, Director

Director

Deputy Director

National Institute of Standards and Technology

Director

Boulder Laboratories

Baldrige National Quality

Program

Director for

Administration

& Chief Financial

Officer

Technology

Services

Advanced

Technology

Program

Manufacturing

Extension

Partnership

Manufacturing

Engineering

Laboratory

Chemical Science

and Technology

Laboratory

Materials Science

and Engineering

Laboratory

Electronics and

Electrical Engineering

Laboratory

Information

Technology

Laboratory

Physics

Laboratory

Building and

Fire Research

Laboratory

L.E. Smith, Director

S.W. Freiman, Deputy Director
50

Materials Reliability Division (853.00) Organization Chart — 2004

Organizational Charts

Guest Researchers and Contractors

— C. Martino — W. Grell

— T. Padilla

— S. Vincent

— T. Dvorak

— B. Goudy

— D. Serrell

Students

V.E. Ciaranello

Division Secretary

MATERIALS RELIABILITY

DIVISION

Alan F. Clark, Chief

Thomas A. Siewert, Deputy Chief

853.07 Process Sensing

and Modeling

Thomas A. Siewert

Supervisory Metallurgist

853.05 Microstructure

Sensing Group

Stephanie A. Hooker

Supervisory Physicist

853.08 Microscale

Measurements

Robert R. Keller

Supervisory Materials

Research Engineer

— J.H. Clark

— C.N. McCowan

— T.L. Oreskovic

— T.P. Quinn

— L.A. Rodine

— R.L. Santoyo

— D.C. Hurley

— W.L. Johnson

— S.A. Kim

— V. Povilus

— P.S. Rice

— V.K. Tewary

— K.R. Waters

— Y. Cheng

— E.S. Drexler

— R.H. Geiss

— J.D. McColskey

— D.T. Read

— A.J. Slifka

— J.E. Wright

A.M. Reidy

Administrative Officer

L.B. Vaughan, AO Trainee

— C. Flannery

— M. Kopycinska–Müller

— D. Lauria

— N. Varaska

— B. Yang

— H. Zheng

— D. Finch

— J. Kim

— J. Müller

— R. Rorrer

— D. Balzar

— A. Chyaudhuri

— C. Dewald

— M. Hamstad

— L. Kaatz

— I. Makover

— Y. Rosenthal

— L. Wcislak
51
52