CNST NEWS

SUMMER 2012

IMAGING SPIN POLARIZATION IN 

 A SUPERCONDUCTOR SANDWICH

LUMEDYNE BUILDS A TUNNELING INERTIAL SENSING TRANSDUCER 

USING DNA ORIGAMI TO MANUFACTURE 3D NANOSTRUCTURES

SIMPLIFYING AFM LATERAL FORCE CALIBRATION

THE

INSIDE

WWW.NIST.GOV/CNST
I

t is exciting to see the next generation of nanotechnologists filling our labs 

and hallways. This summer, fifteen students joined about forty full-time 

postdoctoral researchers working at the CNST doing cutting-edge research in our laboratories, with many 

working in the NanoFab and its cleanroom.

The CNST sponsors undergraduate science and engineering majors interested in nanotechnology through 

the highly-competitive Summer Undergraduate Research Fellowship (SURF) program, which offers the 

opportunity for students to spend eleven weeks during the summer performing hands-on research under 

the mentorship of a CNST project leader. Participants receive stipends along with housing and travel 

allotments. A complementary program for high school students, the Summer High School Intern Program 

(SHIP), provides unpaid research opportunities for students who have completed their junior or senior years; 

some of these students continue as interns throughout the year. Additional research opportunities for 

students and recent graduates will be offered through the new Pathways Program (see www.opm.gov/

hiringreform/pathways/). 

Supporting the development of the next generation of researchers is a responsibility that we at the CNST 

take very seriously. Our research programs are often a student’s first research experience. These programs 

provide opportunities for students to experience the possibility of a research career in nanoscale science 

and technology, and to appreciate the value and importance of fundamental research to tomorrow’s 

industrial applications. While our goal is to inspire a passion for research in our student researchers, we 

take particular pleasure when they inspire us to think about our research challenges in new ways.

This summer our undergraduate researchers came to us from universities in eleven states spread 

throughout the country. Reflecting an emerging academic trend as well as the interdisciplinary nature of 

nanotechnology, most of the students are double majors or are majoring in one discipline while minoring in 

another, including Physics, Electrical Engineering, Mechanical Engineering, Biology, Nanoscale Engineering, 

Mathematics, French, and Engineering Physics. The students work on a wide range of projects. For example, 

Anthony Gianfrancesco worked with CNST researchers Nikolai Zhitenev and Joseph Stroscio characterizing 

photovoltaic materials using thin film phosphors as a near-field optical source. Victoria Savikhin, who 

worked with Veronika Szalai, learned to prepare DNA oligonucleotides and to measure nanofiber assembly 

rates and morphologies using optical spectroscopy, gel electrophoresis, and atomic force microscopy. 

Sarice Barkley, a recent graduate from St. Olaf College with a B.S. in Physics who returned for a second 

summer in the SURF program, continued a line of research she started last summer with Rachel Cannara. 

Based on that work, Sarice was first author on a Review of Scientific Instruments publication evaluating a 

new lateral force calibration technique for atomic force microscopy (see the article on the next page of this 

newsletter). At the end of the summer, the SURF and SHIP students practice one of the most important 

skills for a research scientist—communicating results and analyses—by presenting their work at a threeday colloquium. 

I encourage interested students to start the process early (by winter break, or sooner!). Please visit the 

NIST student employment page to learn about opportunities NIST-wide at www.nist.gov/hrmd/staffing/

studentshome.cfm. 

DIRECTOR

From the Director | 2 FROM THE

Lumedyne Builds an Inertial 

Sensing Transducer | 3

Evaluating a Simpler Lateral 

Force Calibration Technique for 

Atomic Force Microscopy | 3

Characterizing Magnetic 

Media on the Nanoscale 

Using Rippling Spin Waves | 4

Imaging Complex Domain 

Wall Structures in 

Magnetic Nanostripes | 4

Spin Polarized 

Supercurrents Optimized 

with a Simple Flip | 5

Fabrication Process for Silicon 

Carbide Nanowire Arrays | 5

Researchers Quantify the 

Kinetics of Nanoscale 

Assembly with DNA Origami | 6

In-Situ Observations 

Reveal How Nanoparticle 

Catalysts Lower Operating 

Temperatures in Fuel Cells | 6

New ALD Process for 

Coating High Aspect 

Ratio Structures | 7

New Dry Plasma Etching 

Process is Available for 

Making Photomasks | 7

IN THIS ISSUE

EDITOR | 

ROBERT RUDNITSKY

GRAPHIC DESIGN | 

KRISTEN DILL

DISCLAIMER | Certain commercial 

equipment, and software, are identified in 

this documentation to describe the subject 

adequately. Such identification does not 

imply recommendation or endorsement 

by the National Institute of Standards 

and Technology, nor does it imply that the 

equipment identified is necessarily the 

best available for the purpose. 

Robert Celotta

2
L

umedyne Technologies, a San Diego-based 

microelectromechanical system (MEMS) 

development company, has built a proof of concept 

device for measuring inertial forces that integrates 

precision timing with the well-defined motion of a 

MEMS harmonic oscillator. The device can be used 

as a component in small, low-cost, low-power, 

navigation-grade gyroscopes and to provide force 

measurements for position recorders. 

Lumedyne’s MEMS force transducer consists of 

a simple diving board cantilever that oscillates 

at its mechanical resonance. As the cantilever 

vibrates, a tunneling tip on its edge passes a 

tunneling tip on a rigid substrate. The resulting 

tunneling current acts as a “triggering” event 

that precisely defines the cantilever’s location as 

a function of time. When the device is subjected 

to a force, the system measures the change in the 

oscillator’s amplitude and frequency. Three of 

these transducers placed in orthogonal directions 

in a single device can record forces in all three 

directions. The system promises to allow users to 

know the location of the device relative to an initial 

location with sub-meter accuracy in places where 

there is no GPS signal. 

The company used a commercial foundry to 

fabricate the wafer structure and to provide 

metallization for the circuitry and tunneling 

junction. Working with Process Engineer Joshua 

Schumacher in the NanoFab, they used a focused 

ion beam to cut separations of 10 nm to 40 nm 

between the two tunneling tips without damaging 

the tips. They are now experimenting with 

scaling up production by using a CMOS process 

to fabricate the gap. The researchers believe that 

their device will be useful for applications where 

a GPS signal is not available, including seismic 

imaging for oil and gas exploration, targeting for 

weapons systems, and for navigation use in cell 

phones within buildings. 

3

LUMEDYNE BUILDS AN INERTIAL SENSING TRANSDUCER

R esearchers from the CNST and NIST’s Material Measurement Laboratory (MML) 

have demonstrated that a simpler technique for 

calibrating lateral sensitivity in an atomic force 

microscope (AFM) agrees with a calibration 

method developed at NIST to within 5 %. The 

equivalence of these two independent methods 

represents an important step towards traceable 

accuracy in lateral force microscopy and will 

allow scientists to better understand the atomicscale origins of friction across a wide range 

of materials. The NIST “HammerHead” (HH) 

method relies on precise positioning of the arms 

of a specially-fabricated, tee-shaped cantilever 

over well-defined alignment marks in a surface; 

a torque is applied at different locations on the 

cantilever arm by pressing it against a small sphere 

attached to the edge of the surface. The ratio of 

the change in the normal (vertical) signal to the 

lateral signal can be used to calibrate sensitivity 

and extract friction forces corresponding to the 

lateral signals measured during an experiment. 

The new “Diamagnetic Lateral Force Calibrator” 

(D-LFC) method, developed at Brown University, 

requires fewer independent measurements. The 

AFM cantilever presses against the surface of a 

piece of graphite that levitates in a magnetic field. 

When the magnetic field is moved horizontally 

in the AFM, the levitating graphite behaves like 

a mass on a very weak spring. A lateral force 

is applied by the graphite to the tip of the AFM 

cantilever, causing the cantilever to twist. This 

twist leads to a change in the lateral signal in 

the AFM that can be used to calibrate friction 

directly, without the need for an independent 

measurement of the normal signal. While the 

D-LFC method is preferable for most circumstances 

because it uses fewer parameters and therefore 

has greater precision, the HH method can be 

advantageous if contact between the probe tip 

and the calibration surface must be avoided. The 

researchers believe that the overall accuracy and 

comparability of these two methods establishes 

the importance of the D-LFC method as a valuable 

tool for unifying quantitative measurements 

of friction at the nanoscale, and establishes a 

potential path towards the development of lateral 

force standards.

EVALUATING A SIMPLER LATERAL FORCE CALIBRATION 

TECHNIQUE FOR ATOMIC FORCE MICROSCOPY 

In the diamagnetic lateral force calibration method, an AFM 

cantilever (shown here is a NIST HammerHead cantilever) 

presses against the surface of a piece of graphite that 

levitates in a magnetic field. When the magnetic field is 

moved horizontally in the AFM, friction between the AFM 

tip and graphite surface causes the cantilever to twist. This 

twist leads to a change in the lateral signal in the AFM that 

is used to calibrate friction directly, based on the spring 

constant of the graphite in the magnetic field. 

Quantitative comparison of two independent lateral force calibration techniques for the atomic force microscope, S. S. Barkley, Z. Deng, R. 

S. Gates, M. G. Reitsma, and R. J. Cannara, Review of Scientific Instruments 83, 023707 (2012).

As the cantilever (microscope image, top) vibrates, a 

tunneling current passes between paired tips (scanning 

electron micrograph, bottom) on the cantilever and on the 

rigid substrate.  
CNST researchers in collaboration with 

the University of Maryland and the Royal 

Institute of Technology in Stockholm, Sweden have 

developed a new method to measure magnetic 

properties and defects in thin films with a spatial 

resolution of approximately 100 nm. Controlling 

variations and defects in thin films of magnetic 

materials is a key challenge to developing 

magnetic random access memory (MRAM), a 

new type of magnetic memory that promises 

to be faster, smaller, and more energy efficient 

than memory based on current semiconductor 

technology. Building on previous work at the Ohio 

State University, the new technique is designed 

to trap and image oscillating perturbations of the 

magnetization—known as “spin waves”—in a 

thin film. By trapping the spin waves at the location 

being measured, this approach overcomes the 

limitations usually associated with measurements 

of local magnetic properties, which are generally 

hindered by strong exchange and dipole-dipole 

interactions that make it difficult to separate the 

properties of one region from the next. An analogy 

to these localized spin waves is a frozen pond 

with a hole in the ice, where a breeze only excites 

ripples in the water filling the hole. In this new 

method, the frequency of a driving microwave field 

is tuned to a frequency below the band where spin 

waves can propagate, essentially preventing spin 

wave excitation by the microwaves and “freezing” 

the magnetization. The “hole” in the frozen spins 

is provided by a magnetic tip of a ferromagnetic 

resonance force microscope (FMRFM) held above 

the film surface on a cantilever. The magnetic tip 

changes the magnetic field under the tip, allowing 

spin wave “ripples” to form, and the tip can be 

scanned back and forth across the film to map out 

the film’s nanoscale properties. The ability to image 

these properties is expected to prove valuable in 

determining the limitations and failure modes of 

prototype nanomagnetic data storage devices.

CHARACTERIZING MAGNETIC MEDIA ON THE NANOSCALE 

USING RIPPLING SPIN WAVES

Researchers from the CNST and MIT have used the scanning electron microscopy with 

polarization analysis (SEMPA) technique to provide 

the first direct images of the magnetic structure of 

highly twisted domain walls in patterned thin film 

magnetic nanowires. This imaging method allows 

these complex and delicate structures to be easily 

compared to magnetic simulations, a useful step 

for developing technology that uses domain walls 

in nanowires for high density data storage and for 

field or current driven magnetic logic. A typical 

domain wall separates two opposite regions 

of magnetization, making it a “180° wall”. The 

researchers showed that several 180° walls could 

be injected into a nanowire, where they either

annihilated each other or they combined to 

form complex walls in which the magnetization 

rotated by up to 540°. The 360° walls were 

of particular interest, since their magnetic 

behavior is dramatically different from the 

180° walls currently used in prototype memory 

and logic devices. The researchers believe 

that, in addition to providing information about 

how 180° walls interact in domain wall-based 

nanowire memories, this work may lead to new 

magneto-electronic applications using 360° 

domain walls, such as manipulating bits using 

highly localized magnetic fields in magnetic 

logic circuits. 

IMAGING COMPLEX DOMAIN WALL STRUCTURES IN MAGNETIC NANOSTRIPES

As shown in the simulation above, spin waves of 

different frequencies trapped beneath the magnetic tip 

of a microscale cantilever produce varying magnetic 

force profiles which can be used to non-destructively 

probe the properties of magnetic materials. This 

technique can be used to search for nanoscale 

defects, especially in multilayer magnetic systems 

like typical hard drives, where defects can be buried 

beneath the surface.

4

Nanoscale spin wave localization using ferromagnetic resonance force microscopy, H.-J. Chia, F. Guo, L. M. Belova, and R. D. McMichael, 

Physical Review Letters 108, 087206 (2012).

Formation and structure of 360 and 540 degree domain walls in thin magnetic stripes, Y. Jang, S. R. Bowden, M. Mascaro, J. Unguris, and 

C. A. Ross, Applied Physics Letters 100, 062407 (2012).

SEMPA images of magnetic domain walls in a nanowire. 

The magnetization direction is given by the arrows and 

the background colors. Top: Two separate 180° domain 

walls. The most common domain walls, 180° domain 

walls, form when the magnetization reverses direction. 

Bottom: An unusual 360° domain wall can form when the 

two 180° walls are pushed together.
I

n collaboration with researchers from Michigan 

State University, the NIST Center for Neutron 

Research and the CNST have discovered the key 

to controlling and enhancing the lossless flow 

of a current with a single electron spin state in 

a standard superconducting device. Production 

of superconducting currents (“supercurrents”) 

that are also spin polarized opens up new 

possibilities in spintronics, an emerging field that 

integrates magnetic phenomena into conventional 

semiconductor electronics. The Michigan State 

researchers previously demonstrated that a 

spin-polarized super-current can be generated 

and sustained over a long range by passing a 

current through a carefully engineered stack 

of superconducting and magnetic thin films. 

However, they were surprised to discover that 

substantially larger currents can be created by 

exposing the device to a magnetic field. 

T

he mystery was solved by NIST scientists who 

determined the complex magnetic configuration 

of the layers in the stack using the complementary 

techniques of Polarized Neutron Reflectivity 

(PNR) and Scanning Electron Microscopy with 

Polarization Analysis (SEMPA). Together these 

measurements revealed that the magnetic field 

flips most of the magnetic layers to create a more 

ideal local environment for sustaining the polarized 

current. The researchers believe that combining 

spin polarized supercurrents and spintronics, such 

as spin transistors and spin filters, will eventually 

lead to novel applications similar to ones 

generated when superconducting devices were 

first combined with electronics.

A collaboration between scientists from the NIST Material Measurement Laboratory 

(MML), Mississippi State University, and GeneSiC 

Semiconductor, a world-leading provider of highperformance silicon carbide (SiC) based power 

semiconductor products headquartered in Dulles, 

VA, has demonstrated the ability to fabricate arrays 

of aligned SiC nanowires. This advance opens 

the possibility of developing three-dimensional 

device platforms with SiC nanoscale elements for 

electrical, biomedical, and sensor applications. 

Nanowires of SiC have been extensively studied 

because of their high thermal and mechanical 

robustness, radiation hardness, excellent 

biocompatibility, and low background electrical 

noise for sensor applications compared to silicon. 

However, typical bottom-up fabrication processes 

result in randomly oriented SiC nanowires, limiting 

their utility for device applications, which are 

expected to require densely-packed arrays of wellaligned nanowires grown in a specific orientation 

to a host substrate. 

The researchers grew SiC nanowires on the top 

surfaces and walls of mesas that they created 

using reactive ion etching of single-crystalline SiC 

wafers. Catalytic nickel nanodots were deposited 

on the SiC substrate surfaces using the electron 

beam deposition system in the NanoFab. The 

nanowires were later fabricated at Mississippi 

State University utilizing a metal-catalyzed chemical 

vapor deposition process. Using field-emission 

scanning electron microscopy, transmission 

electron microscopy, X-ray diffraction, and 

electron-back-scatter-diffraction, the researchers 

determined that different orientations of the 

crystallographic planes of the SiC mesas resulted 

in six distinct directions of nanowire growth. Of 

these, well-aligned nanowires grew on one 

particular set of crystallographic planes on the SiC 

mesas with lengths in the tens of micrometers, 

depending on their growth time, and diameters 

from 20 nm to 100 nm, depending on the diameter 

of the catalyst. According to GeneSiC’s Director 

of Technology, Siddarth Sundaresan, who is also a 

guest researcher in MML, GeneSiC has “developed 

highest-in-class performance SiC semiconductor 

devices and associated products for customers 

ranging from the Department of Defense and the 

Department of Energy to large commercial clients, 

such as Halliburton, Schlumberger, General 

Electric, and Boeing.” As with other projects that 

GeneSiC is undertaking at the CNST, they “could 

not have fabricated the nanowires without the 

NanoFab’s world-class cleanroom nanofabrication 

tools.” 

The researchers’ next step is to refine the process 

for fabricating large-area arrays of aligned SiC 

nanowires and to perform additional electrical 

characterization. They believe that the SiC 

nanowire arrays may enable the development of 

advanced electronic and biomedical devices. 

5

FABRICATION PROCESS FOR SILICON CARBIDE NANOWIRE ARRAYS

Scanning electron micrograph shows an array of aligned 

nanowires grown on the sidewall of SiC mesa.

Growth of SiC nanowires on different planes of 4H-SiC substrates, R. V. K. G. Thirumalai, B. Krishnan, I. Levin, A. V. Davydov, S. 

Sundaresan, J. N. Merrett, and Y. Koshka, Materials Science Forum 717-720, 1279-1282 (2012). 

Growth on differently oriented sidewalls of SiC mesas as a way of achieving well-aligned SiC nanowires, R. V. K. G. Thirumalai, B. 

Krishnan, A. V. Davydov, J. N. Merrett, and Y. Koshka, Crystal Growth & Design 12, 2221–2225 (2012).

SPIN POLARIZED SUPERCURRENTS OPTIMIZED WITH A SIMPLE FLIP

Using SEMPA, the magnetic structures in the top and 

bottom layers of a cobalt-ruthenium-cobalt sandwich 

contained within a superconducting device were imaged, 

both before (left) and after (right) applying a magnetic 

field, with the magnetization direction shown using a 

color wheel. The net magnetization in each layer was 

measured using PNR, and was shown to flip (gray arrows) 

after applying an appropriate magnetic field. These flips 

produce the local transport properties needed to sustain 

spin polarized supercurrents. The image layers shown 

above are 25 μm × 25 μm. 

Optimization of spin-triplet supercurrent in ferromagnetic Josephson junctions, C. Klose, T. S. Khaire, Y. Wang, W. P. Pratt, N. O. Birge, 

B. J. McMorran, T. P. Ginley, J. A. Borchers, B. J. Kirby, B. B. Maranville, and J. Unguris, Physical Review Letters 108, 127002 (2012).
6

Researchers from the CNST and Arizona State University have used environmental 

transmission electron microscopy (ETEM) to 

explain the role of nickel nanoparticles in lowering 

the operating temperature of praseodymium doped 

ceria (PDC) anodes in solid-oxide fuel cells (SOFCs). 

These fuel cells are a promising technology for 

efficiently converting chemical fuels into electricity, 

and PDC-based anodes have the potential to 

replace the more commonly used nickel and 

yttria-stabilized zirconia anodes, which operate 

at higher temperatures (typically in excess of 

1000 °C) that unfortunately cause the anodes to 

degrade. Nickel and PDC are being investigated 

as alternative anode materials because they 

operate at a lower temperature of 500 °C 

to 700 °C, making the anodes more stable. 

Using the ETEM, the researchers were able to

visualize nanometer-scale structural and chemical 

changes occurring at the interface between the 

nickel and the PDC as a function of temperature in 

an atmosphere of dry hydrogen at 130 Pa, mimicking 

the partial pressure of hydrogen in a SOFC. Using 

energy-loss spectra, the researchers showed that 

the introduction of nickel nanoparticles lowered 

the reduction temperature of the PDC in a 20 

nm-deep reduction zone around the interface 

between the two materials. The formation and 

size of the reduction zone is consistent with two 

possible mechanisms, each involving the spillover 

of ambient atomic hydrogen from the nickel to the 

PDC. The researchers believe that understanding 

and controlling how the nickel nanoparticles 

catalyze these lower-temperature reactions will 

enable the development of SOFCs that are both 

efficient and long-lived. 

IN-SITU OBSERVATIONS REVEAL HOW NANOPARTICLE CATALYSTS LOWER 

OPERATING TEMPERATURES IN FUEL CELLS

High resolution environmental transmission electron 

microscope image of a nickel–praseodymium (PDC) doped 

interface in a dry hydrogen environment. 

Direct observation of hydrogen spillover in Ni-loaded Pr-doped ceria, V. Sharma, P. A. Crozier, R. Sharma, and J. B. Adams, 

Catalysis Today 180, 2-8 (2012).

By varying the spacing and number of binding sites on DNA “origami”, CNST researchers 

have determined the rate constants for attaching 

functionalized quantum dots (QDs) and identified 

factors that can improve the attachment yield. Using 

the highly specific nature of DNA hybridization, 

DNA can be cross-linked into relatively rigid two or 

three dimensional shapes known as DNA origami. 

These shapes can be engineered to provide 

molecularly precise attachment points (such as 

biotin) at which nanostructures functionalized with 

biomolecular receptors (such as streptavidin) can 

bind, making DNA origami an ideal test platform 

for learning how to manufacture diverse types of 

nanostructures via self-assembly in a controlled 

fashion. However, in order to determine whether 

this approach might be useful for practical tasks 

such as constructing semiconductor devices, 

drug delivery systems, or sensors for specific 

proteins, it is necessary to learn the rate at which 

binding reactions occur, what kind of yields are 

possible, and what specific design considerations 

need to be taken into account. To answer these 

questions, the researchers created 100 nm x 70 

nm origami rectangles with different binding 

site configurations and mixed them with 20 nmdiameter, functionalized QDs. The results showed 

that the reactions between these objects—which 

are large compared to the typical molecular 

scale—are limited by diffusion and are therefore 

surprisingly slow, taking many hours to complete. 

Moreover, the large diameter of the QDs limits 

how closely the dots can be positioned relative to 

each other, reducing the yield of the desired, fullyoccupied QD-origami structures. Even with three 

QD binding sites at each attachment point, the 

yields are significantly below 100 %. The work 

shows that while this approach will be promising 

for biological applications such as sensing and drug 

delivery, it will be difficult to apply to areas such as 

semiconductor device manufacturing because the 

placement precision is too low and the error rate is 

too high.

RESEARCHERS QUANTIFY THE KINETICS OF NANOSCALE ASSEMBLY 

WITH DNA ORIGAMI

As shown in these atomic force microscope topographic 

images, NIST researchers made three DNA origami 

templates designed so that quantum dots would arrange 

themselves: in the corners (top), diagonally (middle), and 

in a line (middle). The researchers found that putting the 

quantum dots closer together caused them to interfere 

with one another, leading to higher error rates and lower 

binding probability.

Nanomanufacturing with DNA origami: factors affecting the kinetics and yield of quantum dot binding, S. H. Ko, G. M. Gallatin, and 

J. A. Liddle, Advanced Functional Materials 22, 1015–1023 (2012).
The NanoFab has set up a new dry etching 

process using a 125 mm (5 in) mask carrier and 

a ceramic ring clamp installed in one of the Oxford 

plasma etchers to make chromium (Cr) photomasks 

with significantly smaller feature resolution than 

the traditional wet chemical etching process. The 

wet chemical etching process limits photomask 

feature sizes to greater than one micrometer. 

Using the new process, NanoFab engineers 

have successfully patterned 150 nm half-pitch Cr 

gratings and 1 μm-diameter dots. 

The new dry Cr mask etching process also 

simplifies post-etch cleaning. The photoresist 

which was used as a Cr etching mask can 

now be cleaned by oxygen plasma in the same 

chamber that was used for etching the Cr. This 

dry cleaning process eliminates the solvent 

residual created by wet chemical cleaning 

and reduces the use of hazardous organic 

solvents. For more information, contact Lei Chen, 

301-975-2908, email: lei.chen@nist.gov. 

7

NEW DRY PLASMA ETCHING PROCESS 

IS AVAILABLE FOR MAKING PHOTOMASKS

Atomic force microscope image of a 150 nm half-pitch Cr 

grating (top) and an optical microscope image of 1 μmdiameter Cr dots (bottom), patterned using the NanoFab’s 

new dry plasma etching process.

An ASML engineer installs a lens in the NanoFab’s 

new stepper, which is now available for use. The 

stepper can expose 80 to 120 wafers per hour, and 

provides frontside and backside alignment with 

resolution down to 280 nm and overlay accuracy of 

40 nm. It can handle 200 mm-diameter wafers as well 

as small pieces. For more information, contact Liya Yu, 

301-975-4590, email: liya.yu@nist.gov. 

Process engineers in the CNST NanoFab have developed a new atomic layer deposition (ALD) 

process which can conformally coat platinum (Pt) 

on to high aspect ratio nanoscale structures. While 

physical vapor deposition (PVD) and chemical vapor 

deposition (CVD) have been used for decades to 

deposit thin films with accurate thickness control 

on to substrates, coating a thin film on to high 

aspect ratio nanoscale structures has remained a 

challenge. Unlike CVD and PVD, which coat thin 

films from the top of the structure, ALD uses a selflimiting, gas-phase surface chemical reaction to 

coat thin films from the bottom of the structure up, 

making it an excellent technique for coating high 

aspect ratio structures. The self-limiting reaction 

in ALD allows each deposition cycle to deposit 

only one monolayer of material. In principle, this 

advantage allows an operator to achieve excellent 

film conformity and desired thin film thickness by 

simply repeating the monolayer coating a desired 

number of times. 

In practice, during ALD processes both PVD 

and CVD can occur at the same time due to 

incomplete purges and physical adsorption of 

precursor compounds. To ensure that the ALD 

process is completely self-limiting and that the 

precursors can reach the bottom of the deep 

trench, the new process pauses the release of the 

precursor inside the reaction chamber and purges 

out the extra precursor completely. Precursor 

holding and purging times have been tested and 

optimized. Using high aspect ratio silicon gratings 

provided by Professor Jay Guo’s research group 

at the University of Michigan as a substrate, the 

engineers demonstrated that the new ALD coating 

process can conformally coat 30 nm-thick Pt on to a 

surface that has trenches that are 100 nm wide by 

2 μm deep. During ALD, the gap spacing decreases 

gradually. Scanning electron micrographs show 

that Pt can be coated uniformly from top to bottom 

leaving evenly-spaced 30 nm gaps. For more 

information, contact Lei Chen, 301-975-2908, 

email: lei.chen@nist.gov.

NEW ALD PROCESS FOR COATING HIGH ASPECT RATIO STRUCTURES

Scanning electron micrograph of a high-aspect-ratio 

silicon grating with 100 nm spacing and 2 μm trenches 

coated with 30 nm-thick platinum. 
CENTER FOR NANOSCALE 

SCIENCE AND TECHNOLOGY 

The CNST is a national user facility purposely designed to accelerate 

innovation in nanotechnology-based commerce. Its mission is to operate a 

national, shared resource for nanoscale fabrication and measurement and 

develop innovative nanoscale measurement and fabrication capabilities to 

support researchers from industry, academia, NIST, and other government 

agencies in advancing nanoscale technology from discovery to production. 

The Center, located in the Advanced Measurement Laboratory Complex 

on NIST’s Gaithersburg, MD campus, disseminates new nanoscale 

measurement methods by incorporating them into facility operations, 

collaborating and partnering with others, and providing international 

leadership in nanotechnology.

If you would like to subscribe to this newsletter, go to 

http://www.nist.gov/cnst/newsletters.cfm, enter your e-mail address, 

and follow the on-screen instructions. 

WWW.NIST.GOV/CNST

SUPPORTING THE 

DEVELOPMENT OF 

NANOTECHNOLOGY 

FROM DISCOVERY TO 

PRODUCTION 

Center for Nanoscale Science and Technology 

National Institute of Standards and Technology 

100 Bureau Drive, MS 6200 

Gaithersburg, MD 20899-6200 

Phone: 301-975-8001 

E-mail: cnst@nist.gov

NANOFAB USERS MEETING

THURSDAY, SEPTEMBER 6, 2012 | 2–4 PM

BUILDING 215/C103

Current and potential NanoFab researchers and others interested in NanoFab operations are invited to the quarterly NanoFab Users meeting. Topics typically 

include safety, policy changes, new equipment purchases or upgrades, research highlights, and new standard processes. Every meeting also includes an open 

discussion to allow users to bring ideas and suggestions to our attention. Anyone wishing to have an item added to the agenda should contact Vincent Luciani, 

301-975-2886, email: vincent.luciani@nist.gov.

ANNOUNCEMENTS

SECONDARY ION MASS 

SPECTROMETER ADDED TO 

NANOFAB ION MILL SYSTEM 

The CNST has purchased a secondary ion mass 

spectrometer (SIMS) which will be added to its ion 

milling system in the fall. It will be available to users 

beginning in November 2012. The module detects 

ion mill by-products for up to four materials at one 

time. The SIMS can reliably determine with better 

than 0.2 nm accuracy the endpoint for an etch that 

terminates at or near the interface of almost any 

two dissimilar materials. For more information, 

contact Gerard Henein, 301-975-5645, email: 

gerard.henein@nist.gov.

120809 

MATERIALS RESEARCH SOCIETY

FALL MEETING

Hynes Convention Center 

Boston, Massachusetts 

November 25 - 30, 2012

Visit the

 CNST Booth

 at the