Workshop Summary Report: 

Scanning Probe 

Nanolithography Workshop

A workshop sponsored by the 

Precision Engineering Division, 

Manufacturing Engineering 

Laboratory, NIST, under a Research 

Cooperation Agreement on 

advanced lithography of functional 

nanostructures signed in 2001 by 

the National Microelectronics 

Center of Spain (CNM), the National 

Institute of Advanced Industrial 

Science & Technology (AIST) of 

Japan, and NIST. 

held at 

NIST, Gaithersburg MD 20899 

on 

November 12 – 13, 2002 

NISTIR 7040 

John A. Dagata 

National Institute of Standards & 

Technology 

Hiroshi Yokoyama 

National Institute of Advanced 

Industrial Science & Technology of 

Japan 

Francesc Perez-Murano 

National Microelectronics Center of 

Spain 

U.S. DEPARTMENT OF COMMERCE 

Technology Administration 

National Institute of Standards & Technology 

Manufacturing Engineering Laboratory 

Gaithersburg MD 20899 

January 2003
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EXECUTIVE SUMMARY

A workshop on Scanning Probe Microscope (SPM)-based Nanolithography was held at NIST 

Gaithersburg on November 24-25, 2002. The meeting was sponsored by the Precision 

Engineering Division, Manufacturing Engineering Laboratory, NIST, under a Research 

Cooperation Agreement on advanced lithography of functional nanostructures signed in 2001 by 

the National Microelectronics Center of Spain (CNM), the National Institute of Advanced 

Industrial Science & Technology (AIST) of Japan, and NIST. 

The workshop program focused on fundamental studies in nanoscience, the kinetics and 

modeling of SPM oxidation, and applications to nanotechnology, Fundamental studies included 

discussions of current measurement during SPM oxidation, measurement of charge & density 

variation in SPM oxides, control & understanding of the meniscus shape, and 3-D multiphysics 

modeling of electrostatics, transport, and chemical reaction during SPM oxidation. Applications 

to nanotechnology included the fabrication of nano-electronics, nano-photonics, nanoelectromechanical, and microfluidic devices and systems. 

ACKNOWLEDGMENTS 

We thank Dennis Swyt and Michael Postek of the Precision Engineering Division of NIST for 

providing financial support for this workshop, Regenia McCloud of the Precision Engineering 

Division for expert assistance in coordinating visitors’ travel plans and conference preparations, 

and Steve Knight and Jack Martinez of the NIST Office of Microelectronic Programs for support 

of the nanoscale metrology group’s nanofabrication program. 
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ABSTRACT 

A workshop on Scanning Probe Microscope (SPM)-based Nanolithography was held at NIST 

Gaithersburg on November 24-25, 2002. The meeting was sponsored by the Precision 

Engineering Division, Manufacturing Engineering Laboratory, NIST, under a Research 

Cooperation Agreement on advanced lithography of functional nanostructures signed in 2001 by 

the National Microelectronics Center of Spain (CNM), the National Institute of Advanced 

Industrial Science & Technology (AIST) of Japan, and NIST. A dozen active collaborators of 

NIST, AIST, and CNM projects in this emerging field presented their most recent results on 

fundamental aspects of nanostructure fabrication and characterization and on the application of 

SPM nanostructures to nano-electronics, nano-optics, and nano-mechanical devices. 

 
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TABLE OF CONTENTS 

EXECUTIVE SUMMARY 3 

ACKNOWLEDGMENTS 3 

ABSTRACT 6 

WORKSHOP AGENDA 9 

EXTENDED ABSTRACTS 15 

PARTICIPANTS LIST 83 
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WORKSHOP AGENDA 
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SPM Nanolithography Workshop 

November 12 - 13, 2002 

National Institute of Standards and Technology 

Gaithersburg MD 20899 USA 

Sponsored by the Precision Engineering Division, Manufacturing Engineering Laboratory, NIST, 

under a Research Cooperation Agreement on advanced lithography of functional nanostructures 

signed in 2001 by the National Microelectronics Center of Spain (CNM), the National Institute 

of Advanced Industrial Science & Technology (AIST) of Japan, and NIST. 

Preliminary Agenda 

Tuesday, November 12, 2002

Room B-321, Metrology Building (220) NOTE ROOM CHANGE THIS DAY ONLY

8:00 - 8:30 A.M. 

Arrival and check-in 

8:30 - A.M.

Dale Hall, Director of the Manufacturing Engineering Laboratory, NIST: Welcome and 

Introduction to MEL and NIST 

John Dagata, NIST: History and scope of this workshop 

9:00 - A.M.

Hiroshi Yokoyama, AIST: Use of scanning probe nanofabrication for creating liquid-crystal 

nanostructures 

9:30 - A.M.

Francesc Perez-Murano, CNM: Non-contact AFM nano-oxidation: new experiments and 

application to thin aluminum films 

10:00 - A.M.

Hiromi Kuramochi, AIST: Current detection during Si nano-oxidation 

10:30 - 11:00 A.M 

BREAK 

11:00 - A.M.

Felix Gwo, N. Tsing-Hua U (Taiwan): Study of trapped charges in scanning-probe-induced 

oxides by electrostatic force microscopy 
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11:30 - A.M.

Jerry Young, U of Akron: Free boundaries in an electrochemical nanocell 

12:00 1:00 PM 

LUNCH (Cafeteria) 

1:00 - P.M.

Takashi Tokizaki, AIST:Application of SPM oxidation to nano-photonics and nano-spintronics 

1:30 - P.M.

Rex Ramsier, U of Akron: Nanoscale oxidation of zirconium surfaces: kinetics and mechanism 

2:00 - P.M.

Zach Davis, Danish Tech U (Denmark): Status of the EU NANOMASS Project 

2:30 - 3:00 P.M. 

BREAK 

3:30 - P.M.

Forest Chien, ITRI (Taiwan): Fabrication of Si nanostructures by Scanning Probe Oxidation and 

Anisotropic Wet Etching. 

4:00 - P.M.

Mike Fasolka, NIST: Overview of the NIST Combinatorial Methods Center 

4:30 - P.M.

Tony Schmitz, U of FL: Nanolithography and microfluidics: a manufacturing perspective 

5:00 - P.M.

John Dagata, NIST: Integration of SPM nanolithography, nanoimprint lithography, and 

microfluidics 

5:30- 6:00 P.M.

DISCUSSION & ADJOURN 

7:00 - P.M .

DINNER (TBD) 

November 13, 2002

Room B-111, Administration Building (101) 

9:00 A.M. 

Arrival 
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9:15 - 10:30 A.M.

Discussion 1 

Topic: Identifying and measuring experimental input parameters required for quantitative 

modeling of transport and reaction processes during SPM oxidation 

Francesc Perez-Murano & Jerry Young, discussion leaders 

10:30 - 11:00 A.M. 

BREAK 

11:00 A.M. 12:00 P.M.

Discussion 2 

Topic: Prospects for using SPM oxidation as a materials characterization technique 

Felix Gwo & Rex Ramsier, discussion leaders 

12:00 - 1:00 P.M. 

LUNCH (Cafeteria) 

1:00 - 2:15 P.M.

Discussion 3 

Topic: Nanostructured templates and self-organized chemistry 

Hiroshi Yokoyama & Mike Fasolka, discussion leaders 

2:15 - 3:15 P.M. 

BREAK 

3:15 - 4:30 

Discussion 4 

Topic: 

Designs and timelines for nanofluidic, photonic, and NEMS devices 

Zach Davis & Forest Chien, discussion leaders 

4:30 P.M . 

ADJOURN 
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EXTENDED ABSTRACTS 
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Welcome to the Manufacturing Engineering Laboratory at the 

National Institute of Standards and Technology 

Dale Hall, Director, Manufacturing Engineering Laboratory (MEL) 

NIST has a long history of involvement with scanning probe microscopy, from the pioneering 

work of Russell Young in the 1970’s, to its advancement as a metrology tool by Clayton Teague 

in the 1980’s & 1990’s. Since 1990, we’ve continued our scientific advancements in 

nanolithography and nanofabrication. 

NIST and MEL serve established industries, such as automotive and semiconductor, as well as 

nascent industries such a biotechnology and nanotechnology. Let me give you some background 

on NIST. NIST’s predecessor - the National Bureau of Standards, was established in 1901. In 

1988, Congress assigned several new and major responsibilities to the organization and renamed 

the agency the National Institute of Standards and Technology. NIST is part of the U.S. 

Department of Commerce and its mission is to strengthen the U.S. economy and improve the 

quality of life by working with industry to develop and apply technology, measurements, and 

standards. We carry out this mission through a portfolio of four major programs: 

• The Advanced Technology Partnership program is a unique co-funded partnership 

between NIST and private industry to accelerate the development of high-risk, enabling 

technologies with broad benefits for the entire economy and for society. 

• The Manufacturing Extension Partnership program is a nationwide network of locally 

managed extension centers offering technical assistance and best business practices to the 

Nation’s 385,000 smaller manufacturers in all 50 states, DC and Puerto Rico. 

• The Malcolm Baldridge National Quality Program is an outreach program that recognizes 

U.S. manufacturing, service, education, and health care organizations for their 

achievements in quality and performance and to raise awareness about the importance of 

quality and performance excellence as a competitive edge. 

• The NIST measurement and science laboratories are the Nation’s ultimate reference point 

for measurements, standards, and metrology research to support industry, science, health, 

safety and the environment. 

NIST maintains the U.S. national standards for all fundamental measurements (length, time, 

mass, electric current, etc.) and for dozens of derived measurements. The staff works with 

industry on measurement (methods, evaluated data, and test procedures) and standard issues. 

The U.S. economy depends upon NIST measurements. NIST measurements are used to make 

sure that our everyday life functions smoothly. For example, telecommunication devices, 

computer chips, pharmaceuticals, medical imaging, even gas pumps, rely on fundamental 

measurements to ensure proper operations. 

NIST has seven technical laboratories: Physics, Information Technology, Electronics and 

Electrical Engineering, Materials Science and Engineering, Chemical Science and Technology, 

Building and Fire Research, and my own lab –Manufacturing Engineering. 
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The laboratory programs cover a broad range of subjects and much of our work is 

multidisciplinary, with collaboration among the labs. The major U.S. effort in nanotechnology 

requires the kind of inter-laboratory and multidisciplinary collaboration that is in many instances 

unique to the NIST laboratories. 

Nanotechnology is the creation and utilization of materials, devices, and systems through the 

control of matter on the nanometer-length scale, that is, at the level of atoms, molecules, and 

supra-molecular structures. The U.S. National Nanotechnology Initiative (NNI) has spurred 

intense interest on the part of other nations and regions to begin programs of their own. Within 

the NNI, NIST’s involvement is in the development of measurement technologies and standards 

to assist U.S. industry at the nanometer-scale level. Although it is too early to know exactly 

when and how the critical components of nanotechnology will impact industrial products and 

services, it is crucial for NIST labs to gain the expertise required to provide measurements and 

standards at the nanoscale as demanded by industry. Our efforts are now focused on putting this 

infrastructure into place. 

This infrastructure will help NIST support opportunities to commercialize nanotechnology in the 

U.S. and facilitate international trade. NIST enables commercialization and international trade 

through: a) nanoscale measurement science, and b) nanoscale measurement standards. 

The NNI issued several “Grand Challenges” some of which directed specifically to U.S. 

government agencies to help them identify and begin working on the support infrastructure 

needed for commercializing nanotechnology. To build that infrastructure, we need to explore: a) 

New measurement tools and techniques - basic science needed; b) Facilities – unique 

instrumentation and specially designed measurements labs; and c) Standards and traceability for 

nanotechnology. 

Some examples of the technical challenges that we have are issues with: a) resolution - 

molecular to atomic spatial scales and high-speed temporal scales; b) sensitivity and specificity - 

i.e., molecular or atomic level sensitivity and specificity with simultaneous imaging and 

identification, and simultaneous multiple spectroscopy for chemical and physical properties, c) 

3-D characterization capability, and 4) automated databases. 

Within the U. S., MEL has primary responsibility for length- and mass-based standards. MEL’s 

length-based measurements range from 100’s of meters to picometers. The instruments that we 

use for dimensional metrology includes laser trackers, coordinate measuring machines, optical 

interferometers, scanning electron-beam microscopes, and -- of particular interest to you -- 

scanning probe microscopes. 

There are many ways to describe the type of work that MEL does. I’ve chosen to describe our 

technical agenda using four main themes: Measurements and Standards for Making Things...a) 

Right, b) Interoperable, c) Traceable, and d) Small. All of our programs can be mapped into 

these themes. While the connection between MEL’s technical theme of “Making Things Small” 

and the some of the NNI Grand Challenges are obvious, I do want to stress that, from the 

manufacturing perspective, many of the novel fabrication processes and measurement 
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technologies that make nanodevices and nanosystems feasible must evolve under the same 

requirements to which all successful manufacturing must conform - hardware and software 

elements of these devices and systems must be made ... right, interoperable, and traceable, not 

only small. 

It is amazing to thing that over four decades ago, Richard P. Feynman predicted the coming of 

the nanotechnology age in his famous talk “There’s Plenty of Room at the Bottom”. 

Nanotechnology will transform many of the technical devices as we know them, however, before 

we can get there, scientists need to perfect positional control at the atomic level and to keep the 

cost down, there needs to be a reliable and probably self replication manufacturing system. You 

need to be able to build a small basic unit at the atom level and then combine units to create the 

larger product. 

While it is clear that nanotechnology will revolutionize many industries, for practical realization 

of nanotechnology, we must be able to measure nanoscale properties accurately and 

reproducibly. NIST helps build the measurement infrastructure to support the development and 

application of nanotechnology. MEL’s metrology research encompasses optical, electron, and 

probe-based metrology. Here are some examples of our work. Optical instruments are used to 

calibrate and develop measurements and standards for pitch and linewidth used in many 

industries. Photomask overlay metrology is important for the semiconductor industry. Modelbased scanning electron-beam (SEM) metrology meets another a critical need of the 

semiconductor industry. Model-based SEM metrology methods developed here show that the 

technique is comparable to the traditional but more expensive destructive cross sectional 

technique. These differences are within the uncertainty attributable to line edge roughness. 

Within MEL, we have three unique scanning probe microscope systems that we use for 

dimensional metrology research. The Molecular Measuring Machine features a scanning 

tunneling microscope with a Michelson interferometry. Our goal is to maintain nanometer 

uncertainty for point-to-point measurements within the 50 mm x 50 mm measurement area. The 

Calibrated Atomic Force Microscope (C-AFM) is used to calibrate tools for measurements of 

surface structures or surface roughness where the measured height parameter is less than 1 nm. 

The C-AFM is used primarily for NIST measurements of the Si(111) single atom step height but 

can also be used to perform linewidth measurements in an intercomparison of different 

measurement techniques. The UHV STM/FIM (ultrahigh vacuum scanning tunneling 

microscope/field-ion microscope) is really a facility or system because it contains multiple UHV 

chambers: one for very leading-edge sample preparation, one for the FIM – used to accurately 

characterize at the atomic-level tip shapes, and the last for the STM - the tips characterized in the 

FIM are used in this chamber to measure and prepare atomically ordered substrates. The sample 

and tips used for measurements are prepared to atomically precise conditions in ultra-high 

vacuum (UHV) portion of the system. The system has a tunable diode laser-based, frequencytracking interferometer with picometer resolution. With this system, we can measure atomspacings directly rather than using the conventional fringe counting. Our current research is 

looking for ways to make samples in a reproducible manner anywhere from the 10 nm down to 

the atomic dimension level. 
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MEL is also exploring novel fabrication methods for nanostructures. Let me give you some 

examples of our own efforts to prototype nanoscale standards. The first example is a pitch 

calibration prototype designed and prepared here at NIST by scanning probe lithography and 

silicon etching. These prototypes demonstrate that 100-nm minimum pitch and sub-50-nm 

linewidth can be obtained. Pitch placement accuracy has been analyzed using statistical methods 

developed in the optical and SEM dimensional metrology projects. This work was performed in 

collaboration with a guest researcher from the Center for Measurement Standards in Taiwan, 

Forest Chien. Another example is a replica of a magnification artifact produced by the 'soft 

lithography' technique (casting a silicon mold using poly dimethyl siloxane, or PDMS). Since 

one of the manufacturing goals of nanotechnology is low unit-cost production, there is a great 

need for, and growing interest in, commercializing rapid and cheap prototyping methods. 

NIST partners with industrial consortia, individual companies, other government agencies, and 

universities. When NIST works on a technical issue with its partners, we tend to focus on issues 

that can benefit industry sectors in a broad sense. Our partnerships typically relate to 

measurements and standards issues. I would like to encourage further interactions among all of 

the workshop participants. 

Successfully bringing nanotechnology to industry will depend on meeting challenges in 

measurement, fundamental understanding, and control of dimensional and materials properties 

and processes that work at the nanometer level. Length, height, force, tribology, finish, and 

composition are just a few of the properties that we must deal with simultaneously in order that 

components of nanoscale devices and systems are made “right, interoperable, traceable, as well 

as small.” I encourage you to ask questions and follow up on any of our work that you find 

interesting. Descriptions of NIST’s or MEL’s technical programs can be found on website – 

www.nist.gov. 
SPM Nanolithography Workshop 

National Institute of Standards and Technology 

November 12-13, 2002 

History and scope of this workshop 

John A. Dagata 

Precision Engineering Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

Gaithersburg MD 20899 USA 

History of this workshop 

It is worth recording briefly how this workshop on scanning probe microscope (SPM)-based 

nanolithography evolved. New opportunities for US government scientists to collaborate directly 

with their counterparts in the Japanese government arose through the signing of the US-Japan 

Framework Agreement of 1993-1994. In particular, this agreement simplified processes for 

establishing collaboration between NIST and MITI’s Agency of Industrial Science & 

Technology (AIST). This prompted discussions in 1996 between myself and Hiroshi Yokoyama 

and Junji Itoh of AIST’s Electrotechnical Laboratory (ETL) on the possibility of establishing 

regular research visits aimed at integrating scanning probe lithography and electric force 

microscopy (EFM) for nanodevice applications. SPM oxidation, as everyone at this workshop 

knows, was a technique first demonstrated at NIST in 1990. The scanning Maxwell-stress 

approach to EFM was likewise formulated by Drs. Yokoyama and Itoh in 1992 at ETL. My first 

research visit to ETL occurred during Dec 1996-Jan 1997. 

During that visit we initiated two experimental 

directions which figure prominently in the range of 

topics that will be discussed at the present workshop. 

First, working with Alamgir Karim of the Polymers 

Division at NIST, we prepared thin-film samples of a 

conducting polymer, polythiophene, blended with 

polystyrene as a test system for subsurface EFM 

imaging. Because of the dielectric difference between 

these two organic components, we were able to observe 

the inhomogeneous distribution of the components in 

separated phases and follow subsurface annealingdependent reorganization for film thicknesses up to 100 

nm. A 

Figure 1 

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visualization of the subsurface polythiophene network near the silicon substrate within the 

polystyrene-rich phase appears in Figure 1. Materials characterization using EFM in combination 

with other SPM methods remains one of foundational approaches of our research. 

Second, we demonstrated the feasibility 

of producing SPM oxide features -- sub100-nm dots on silicon substrates, for 

example -- and then using EFM to image 

the potential signature of these features. 

This research indicated that dopingdependent trapped charge was present 

within the silicon oxide and therefore 

should tell us something about the 

underlying kinetics and mechanism of 

the oxidation reaction. Application of 

this integrated approach led to design 

and fabrication of a silicon device in 

collaboration with Kiyoshi Morimoto 

(Matsushita) as part of his involvement 

in MITI’s Quantum Functional Devices 

project. Figure 2 illustrates the integrated 

system for SPM lithography, EFM 

imaging, with simultaneous currentvoltage (I-V) device measurement 

capabilities along with the device. Dr. 

Morimoto spent 3 months as a visiting 

researcher at NIST in 1999 analyzing 

high-resolution cross-sectional 

transmission electron microscope results 

and drafting a manuscript. Internal I-V 

testing of the device has been compared 

with local EFM imaging to locate 

regions of inhomogeneous trapped 

charge at the buried Si/SiO2 interface. 

device

electrical probes

SPM tip

Integrated probe station and

scanned probe microscope

Figure 2 

105n Buried 

Substrate (back 

gate) 

65nm

2μ

Thinned p++-Si area 

Metal 

CVD 

SiO2

p++ p -Si ++-Si 

(S )

In 1997, Francesc Perez-Murano of the 

Univ. Autonoma Barcelona and I began 

collaboration with the intention of 

aligning the NIST-ETL integrated-oxide 

characterization effort with UAB’s 

studies of the meniscus control made 

possible by SPM oxidation performed in 

dynamic mode. This collaboration was 

initially supported in part by a Fulbright 

Commission grant for US-Spain 

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Cooperative Research. Publication of voltage modulation, density variation, and space-charge 

modeling studies of SPM oxidation were an outcome of this collaboration. 

After having met in Japan, Europe, and the US at various meetings and workshops1

, it became 

apparent to Hiroshi, Francesc, and I that a more formal agreement would facilitate regular 

exchange of information, help each of us to focus on new directions, and help to broaden our 

productive and ongoing discussions to include a wider circle of collaborators. In September 2001 

a Cooperative Research Agreement was signed by CNM of Spain, AIST of Japan, and NIST to 

promote advanced lithography of nanostructures and we agreed to hold this next workshop at 

NIST. 

Scope of this workshop 

The organization of this workshop follows a somewhat arbitrary distinction between 

fundamental studies in nanoscience – the kinetics and modeling of SPM oxidation -- and 

applications to nanotechnology, particularly fabrication of nano-electronics, nano-photonics, and 

nano-electromechanical devices and systems. Fundamental studies that promise to lead to a more 

complete understanding, predication, and application of SPM oxidation are covered in the 

following talks: 

• Current measurement during SPM oxidation (Francesc Perez-Murano, Hiromi 

Kuramochi) 

• Measurement of charge & density variation in SPM oxides (Felix Gwo) 

• Control & understanding of the meniscus shape (Francesc Perez-Murano) 

• 3-D multiphysics modeling of electrostatics, transport, and chemical reactions (Jerry 

Young). 

Hiroshi has long argued that reliable current measurements during SPM oxidation are required to 

complement our earlier EFM measurements of the resulting oxide charge and volume to gain 

complete understanding and control of the process. The measurements that Francesc and Hiromi 

Kuramochi (AIST) have made recently are extremely promising in this regard. These efforts 

represent essential input into the modeling efforts of Jerry Young and his colleagues at the Univ. 

of Akron in bringing a self-consistent method to solving the system of reaction-diffusion 

equations. These equations describe the chemical aspects of oxide film growth with the physical 

description of the electrostatic field that exists within the water meniscus and its dielectric/ionic 

character during exposure. The extent to which it is becoming possible to control the meniscus 

shape, and thereby the total current passing through the system, as Francesc discusses in his 

presentation, must be accounted for within the model. The composition of the resulting oxide 

1 SP-Nano I - Tsukuba 1997, QFD Society Meeting - Gaithersburg 1997, SP-Nano II - Tsukuba 

1999, Informal workshop on SPM lithography - Tsukuba 2000, Limits to miniaturization - 

Barcelona 2002, SPM Nanolithography workshop - Gaithersburg 2002. 
24

film must reflect the fact that considerable charge may be present within SPM oxide, a result first 

pointed out in the initial experiments that Hiroshi and I performed in 1996-7. In addition, a 

satisfactory model must account for the lower density of the oxide and its variability with 

exposure conditions, as discussed in the papers that Francesc, Dr. Morimoto, and I co-authored 

in recent years. 

Since then, Felix Gwo and his group at National Tsing-hua Univ. have adopted a strategy of 

using in-situ EFM to gain detailed understanding of charge trapping within silicon and silicon 

nitride films. Using a low-vacuum system for environment and temperature control, they have 

performed systematic identification of electronic and ionic species and lifetimes. Sustained 

progress will provide essential input and consistency checks on emerging models. 

Applications to nanotechnology are described in the following talks: 

• Materials characterization (Felix Gwo, Rex Ramsier) 

• Nanoelectronic devices (Takashi Tokizaki) 

• Nanoelectromechanical systems (Zach Davis) 

• Optics and photonics (Hiroshi Yokoyama, Forest Chien, Takashi Tokizaki) 

• Microfluidic systems (Tony Schmitz, Mike Fasolka) 

A basic tenet of nanotechnology – at least in my view – is that fabrication and characterization 

become inextricably intertwined at the nanoscale. Prototyping efforts that provide value-added 

information about dimensional and materials properties are a unique aspect of SPM methods. 

Felix extends the use of EFM to characterization of charge deposited within oxide and nitride 

films for data storage. Similarly, Rex Ramsier and his group are applying SPM oxide growth 

kinetics to augment their surface science studies of Zr and ZrN thin films. A significant portion 

of the data for Zr and ZrN thin films was obtained by Natalia Farkas, a graduate student at Univ 

of Akron, during a 6-week research visit to NIST in 2001. Of particular interest are the rich and 

complicated chemical reactions between surface and subsurface oxygen, nitrogen, and hydrogen 

species that they have catalogued using thermal and e-beam activation. Coupled with Felix’s 

evidence for complete conversion of Si3N4 to SiOx by SPM oxidation, it will be very satisfying 

to understand the details of the corresponding conversion in the ZrN system. 

A compelling aspect of SPM oxidation is that almost every material oxidizes under the extreme 

electric-field conditions that exist between the tip and substrate during SPM oxidation. Examples 

of SPM oxide patterning of device-related materials that have appeared in the literature recently 

include diamond, superconducting materials, magnetic, and 2-D electron gas in III-V 

semiconductors. Spintronic devices are being studied with great interest currently and Takashi 

Tokizaki (AIST) reports on his efforts to pattern such materials. Zach Davis (Danish Tech. 

Univ.) provides a status report on fabricating a nanomechanical resonator using SPM oxidation. 

SPM oxidation is combined with laser lithography of an aluminum film to pattern the mask 
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defining the resonator structure by reactive ion etching. A key aspect of this joint research 

activity between the Danish Microelectronic Center and the National Microelectronics Center of 

Spain is that the processing sequence is integrated with standard CMOS technology. This work is 

being funded under a European Union research grant now in Phase II. 

Optics and photonics applications of SPM lithography are underway and a number of ideas and 

directions will be presented. Hiroshi is also the leader of an ERATO project in Japan and in this 

role discusses the use of SPM lithography for patterning liquid-crystals with elegant control of 

domains at the sub-micrometer scale. Forest Chien of the Industrial Technology Research 

Institute of Taiwan discusses fabrication of 2-D silicon nanoarrays using SPM oxidation and 

anisotropic wet etching for potential use as photonic crystals. Forest spent 6 months as a visiting 

researcher at NIST extending his PhD-thesis work on KOH etching to tetra-methyl ammonium 

hydroxide etchants and Si(100) and silicon-on-insulator (SOI) substrates, providing a significant 

database for the optimum production of sub-micrometer silicon nanostructures. Takashi Tokizaki 

also reviews his unique work using an Al-coated near-field scanning optical microscope 

(NSOM) tip to simultaneously perform SPM oxidation of a sub-wavelength optical waveguide 

and measure the resulting optical transmission characteristics. 

Finally, Mike Fasolka (NIST) describes the mission and capabilities of the NIST Combinatorial 

Methods Center. During the past year Mike and I have identified several opportunities for 

combining dimensional and chemical patterning with the gradient methods being developed by 

the Center. In his presentation, Tony Schmitz (Univ. of FL) summarizes our collaboration during 

the past year aimed at gaining basic expertise in microfluidic device fabrication and nanoimprint 

lithography using hot embossing techniques. Our initial results suggest that microfluidic devices 

provide a significant platform for incorporating SPM-fabricated nanostructures in the near future. 
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Tri-stable nematic liquid-crystal device using orientationally 

frustrated surface patterns fabricated by the atomic force 

microscopy nanorubbing 

Hiroshi Yokoyama*†, Jong-Hyun Kim* and Makoto Yoneya* 

*

Yokoyama Nano-structured Liquid Crystal Project, ERATO, Japan Science and Technology 

Corporation, TRC 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan, †Nanotechnology Research 

Institute, National Institute of Advanced Industrial Science and Technology 1-1-1 Umezono, 

Tsukuba, Ibaraki 305-8568, Japan 

Multi-stable liquid-crystal (LC) devices are known for many years to be desirable for 

realizing drastically reduced power consumption needed for high information content 

mobile displays. However, no industrially feasible multi-stable nematic liquid-crystal 

(NLC) device has ever been realized due to their inherent uniaxial symmetry1-7. Recently 

we demonstrated a robust surface-alignment bistability on micro-fabricated orientational 

checkerboard pattern, in which neighbouring unit square domains are so treated as to 

enforce mutually orthogonal alignment8,9. The four-fold symmetry of the pattern 

automatically allowed the two diagonal axes of the checkerboard to become equally stable 

macroscopic orientations. Here we report the first tri-stable surface alignment of NLCs 

tailored by extending the symmetry approach. A six-fold symmetrical orientational micro 

pattern was inscribed on polyimide surface by nano-rubbing using the stylus of atomic 

force microscope (AFM). The surface is tiled with 60-degree rotated nano-rubbed 

parallelograms. The hexagonal symmetry ensures the three local rubbing directions to give 

stable macroscopic LC orientations in the bulk, which are mutually switchable by an inplane electric field. The new LC mode is surface-driven and hence essentially compatible 

with ever demanding flexible display applications. The present result also illustrates how a 

nanotechnology tool can be useful in prototyping a cutting edge LC device. 

It has long been known that, on a fresh surface of a cleaved single crystal such as NaCl, 

mica, etc., NLCs can assume multiply stable orientations, faithfully reflecting the 

crystallographic axes10-12. Given the microscopic uniformity of the cleavage surface, the ordinary 

anchoring energy coefficient, which is generally represented by a second rank tensor1, should be 

isotropic for surfaces with four-fold or higher-order symmetries. This implies that the multistability observed on single crystal surfaces is a higher-order anchoring effect that makes it 

susceptible to external contaminants and disturbances leading to the first-order anchoring 

effect13. 

Borrowing the concept of symmetry on single crystals while retaining the first-order 

robustness of our frustrated micro-patterning, we devised a higher symmetry surface patterns to 
realize artificial multi-stability of NLCs. As an example of this approach, we demonstrate here a 

tri-stability on a hexagonally symmetric pattern consisting of locally rubbed parallelograms as 

shown in Fig.1. The shape of the parallelogram was designed to have the corner angles of 

and so that three of them, mutually rotated by 

60°

120° ± 60°, make a hexagon. The infinitely 

extended pattern tiled with the hexagons (Fig1a) has a six-fold rotational symmetry. 

For the purpose of examining the aligning characteristics of the orientational pattern, we 

fabricated a structure comprised of unit domains as large as 10μm (Fig.1b). We carried out the 

nano-rubbing on a polyimide-coated glass slide14-17, the details of which have been described 

elsewhere8,9,17. In brief, the precursory polyamic acid (SE-150, Nissan Chemical Co.) was spun 

on the glass slide and was baked. For the nano-rubbing, an AFM ( SPA-500, Seiko Instruments 

Inc.) was used in the contact mode. The nano-rubbed polyimide surface acquired the ability to 

align LC in parallel to the surface along the symmetrically scanned direction, giving a zero tilt 

bias angle17. A room temperature NLC, 4-n-pentyl-4’-cyanobiphenyl (5CB), was applied onto 

the patterned surface to an appropriate thickness without a cover slide. 

Since the size of the unit domain is large here, LC orientations on individual domains and 

at the domain boundaries are clearly resolved in the micrographs (Fig1b). The contrast changes 

under a rotating analyzer confirm that the alignment inside the unit domain is along the local 

rubbing direction. The domain boundaries also have a distinct brightness, reflecting the 

alignment transition from one domain to the next. As indicated by the director symbols in Fig1c, 

two of the three boundaries meeting at a corner are associated with in-plane rotation from 

one domain to the next (π/3-wall), whereas the remaining one is associated with rotation 

(2π/3-wall). This combination of walls corresponds to the lowest free-energy configuration that 

can cover the entire surface without introduction of point defects. Depending on the position of 

the 2π/3-wall boundary, there appear three orientationally distinct, yet energetically equivalent 

states as depicted in Fig.2. These states are mutually convertible by way of rotation of the 

director in an appropriate one of the three constituent parallelograms, and are the basis of the 

present tri-stability. The global configuration of the director for a given surface orientation is 

determined in such a way as to minimize orientational distortions described by the Frank elastic 

energy

60°

120°

180°

18. Consequently, the inhomogeneous LC orientation imposed by the patterned surface 

relaxes rapidly into a uniform bulk alignment, which bears three stable axes depending on the 

relative arrangement of π/3- and 2π/3-walls. More quantitatively, if we assume the one-constant 

approximation, the equilibrium configuration of the director azimuth φ satisfies the Laplace 

equation 18 =φΔ 0 . It follows that the laterally inhomogeneous component of φ with the wave 

vector k decays exponentially as − k z)exp( with the distance along the surface normal into 

the bulk LC. Therefore, the director profile at a point away from the surface by a distance larger 

than the unit domain size d becomes virtually uniform with the orientation 

z

( )z = φφ )0( , where 

 denotes the average over the surface. This shows that one stable bulk orientation is identical 

with the local orientation on the unit domain located between the two π 3/ -walls. The remaining 

two stable states are generated from this configuration by the natural symmetry operation of 

28
NLCs to flip the surface director by over any particular subset of parallelograms (Fig.2), 

giving rise to a shift of 

180°

60° φ )0( . 

To confirm the tri-stabile alignment, the hexagonal pattern was scaled down to the quarter 

of the aforementioned pattern to be of 2.4μm side length. As the size of the unit domain 

approaches the wavelength of visible light, the optical uniformity of the patterned area rapidly 

improves for the decrease of the orientational relaxation length /1 k and the increase of the 

optical diffraction angle beyond the numerical aperture of the observation optics. By combining 

the patterned substrate with a counter polyimide-coated glass slide that was conventionally 

rubbed, a 50μm –thick sandwich-type LC cell was fabricated (Fig3a). On the glass substrate also 

fabricated were three pair of electrodes to apply in-plane electric fields, concentrically arranged 

with shift as shown in Fig3a. The AFM nano-rubbing was conducted in the central space 

between electrodes. Nano-rubbing directions were set parallel with the electric field directions. 

The vacant cell was injected with the NLC. Sinusoidal electric field of 1kHz was used for 

electro-optical switching experiments. 

60°

As shown in Figs.3b and 3c, the hexagonally patterned area clearly showed three stable 

states that were mutually switchable by the electric field. The stable states were found resistant 

to mechanical disturbances for no-disruption of alignment in prolonged experimentation. This 

appears reasonable in that the effective anchoring energy of the tri-stable cell is reduced only by 

1/3 of a uniform cell, because the switching is associated with the flip of local director on 1/3 of 

the unit parallelograms. As the field is increased along the destination direction, the LC in bulk 

starts to reorient along the field. Up to a certain threshold field ≈ /V6 μm , the alignment relaxes 

back to the original state as the field is turned off. When the field strength exceeds the threshold 

field, the switching begins locally by the domain nucleation and growth. Due to various 

inhomogeneities associated with LC injection, non-uniform electric and director field 

distributions on the pattern boundary, the switching cannot be ideally abrupt, but the field should 

be a little increased before the entire area is switched. While the three different states switched 

reversibly between each other, the field strength necessary to drive the a-a’ switching was found 

to be larger than those for others (b-b’ and c-c’). The difference might reflect the persistent effect 

of flow alignment during LC injection19, which took place nearly perpendicular to the a-a’. The 

optical transmission measurements revealed that the contrast ratio was about 5 for all states 

(Fig3c). This ratio has been improved to ca. 20 for a tri-stable device with 1.2μm unit domain. 

The angle differences between the stable states were not exactly , but they were about 

symmetrically about the LC injection direction. 

60° 50°

The switching behaviour can be readily analyzed for the extreme cases of small and large 

unit domains relative to the anchoring extrapolation length 022 ; here, and W0 are the 

twist elastic constant and anchoring energy, respectively. In the limit of small unit domains 

e , the elastic force overwhelms the surface anchoring, thereby making the alignment 

microscopically uniform

/WKde = K22

<< dd

8

. For large unit domains , on the other hand, we can treat the >> dd e

29
system as a uniform planar structure subjected to an in-plain field and obtain the threshold field 

as K/WCE Δε Mth 0 22 = 2 for Rapini-Papoular anchoring1

. Δε is the dielectric anisotropy and 

( ( )) M Ee C += −φφ 2 31 tanarctan2cos31 is a symmetry factor depending on the relative 

azimuthal angle of the field φ E and the easy direction on the parallelogram φe . For the tristability φφ Ee 60°=− , one obtains ≅ 05.1 CM , which shows that the threshold field remains 

only 5% higher than that for the bistability. The observed Eth V/6~ μm is consistent with this 

estimate, given Eth V/5~ μm and for the bistability 2-4

0 W ≈ J/m10 8

. It follows that the angle, 

( || ) ± − φφ Ee

31 tanarctan , by which the surface director should rotate before the switching slightly 

increases from 45°(bistability) to (tri-stability). 2.50 °

As in the ordinary NLC devices, the cell thickness is a critical parameter determining the 

electro-optic response. Due to the patterned nature of the tri-stable surface, there appears a lower 

bound for the cell thickness t , set by the condition that the surface inhomogeneity should 

sufficiently relax inside the cell, i.e., 

d

t >> dd 2/ π , to give uniform LC alignment to assure 

quasi-homogeneous optical and elastic behaviours. Only under this condition, the surface 

switching can be initiated by the in-plane Freedericksz transition in bulk as required by the 

switching mechanism8

. For a domain size of d ≈ 1μm, one may safely adopt a thickness 

dt ≈ μm5 , indicating that the response speed of the tri-stable device can at least be comparable 

with that of existing NLC devices. The thickness dt ≈ 50μm used in the present study is 

obviously an overly safe choice, solely taken for demonstration purposes. 

In conclusion, we demonstrated for the first time the orientational tri-stability, which could 

be switched by an in-plane electric field. The present approach is believed to be generic, based 

only on the frustration of the periodically aligned LC, not relying on any delicate balance of 

multi-directional forces, and may be extendable to even higher degree of stabilities. 

Consequently, the property of the tri-stability is not sensitive to the material or fabrication 

parameters. The anisotropic LC properties coupled with the symmetry of the substrate will open 

up a rich new area of electro-optical applications and interfacial sciences of liquid crystals. 

References 

1. Yokoyama, H. in Handbook of Liquid Crystal Research (ed. Collings, P. J. & Patel, J. S.) Ch. 

6 (Oxford Univ. Press, New York, 1997). 

2. Boyd, G. D, Cheng, J. & Ngo, P. D. T. Liquid-crystal orientational bistability and nematic 

storage effects. Appl. Phys. Lett. 36, 556-558 (1980). 

3. Berreman, D. W. & Heffner, W. R. New bistable liquid-crystal twist cell. J. Appl. Phys. 52, 

3032-3039 (1981). 

4. Scheffer, T. J. & Nehring, J. A new, highly multiplexable liquid crystal display. Appl. Phys. 

Lett. 22, 1021-1023 (1984). 

30
31

5. Yang, K. H. Weak boundary storage effect in homogeneous liquid crystal cells. Jpn. J. Appl. 

Phys. 22, 389-393 (1983). 

6. Ong, H., Meyer, R. B. & Hurd, A. J. Multistable orientation in a nematic liquid-crystal cell 

induced by external-field and interfacial interaction. J. Appl. Phys. 55, 2809-2815 (1984). 

7. Barberi, R., Boix, M. & Durand, G. Electrically controlled surface bistability in nematic liquid 

crystals. Appl. Phys. Lett. 55, 2506-2508 (1989). 

8. Kim, J. H., Yoneya, M., Yamamoto, J. & Yokoyama, H. Surface alignment bistability of 

nematic liquid crystals by orientationally frustrated surface patterns. Appl. Phys. Lett. 78, 3055-

3057 (2001). 

9. Kim, J. H., Yoneya, M., Yamamoto, J. & Yokoyama, H. Controlling surface alignment on 

nanoscopically tailored competing domains. Mol. Cryst. Liq. Cryst. 367, 151-158 (2001). 

10. Blinov, L. M. & Sonin, A. A. The interaction of nematic liquid crystals with anisotropic 

substrates. Mol. Cryst. Liq. Cryst. 179, 13-25 (1990). 

11. Schuddeboom, P. C. & Jerome, B. Azimuthal anchoring of liquid crystals on surfaces with 

high symmetry. Phys. Rev. E. 56, 4294-4305 (1997). 

12. Schuddeboom, P. C. & Jerome, B. Multistable bulk orientation induced by highly symmetric 

liquid-crystal monolayer. Europhys. Lett. 39, 515-520 (1997). 

13. Yoneya, M., Kim, J. H. & Yokoyama, H. Simple model for patterned bidirectional anchoring 

of nematic liquid crystal and its bistability. Appl. Phys. Lett. 80, 374-376 (2002). 

14. Ruestschim, M., Grutter, P., Funfschilling, J. & Guntherodt, H. J. Creation of liquid crystal 

waveguides with scanning force microscopy. Science, 265, 512-514 (1994). 

15. Pidduck, A. J., Haslam, S. D., Bryan-Brown, G. P., Bannister, R. & Kitely, I. D. Control of 

liquid crystal alignment by polyimide surface modification using atomic force microscopy. Appl. 

Phys. Lett. 71, 2907-2909 (1997). 

16. Rastegar, A., Skarabot, M., Blij, B. & Rasing, Th. Mechanism of liquid crystal alignment on 

submicron patterned surfaces. J. Appl. Phys. 89, 960-964 (2001). 

17. Kim, J. H., Yoneya, M., Yamamoto, J. & Yokoyama, H. Nano-rubbing of a liquid crystal 

alignment layer by an atomic force microscope: a detailed characterization. Nanotechnology 13, 

133-137 (2002). 

18. de Gennes, P. G. & Prost, J. The Physics of Liquid Crystals, (Oxford Univ. Press, New York, 

1993).

19. Yamaguchi, R. & Sato, S. Determination of nematic liquid crystal (NLC) orientation by 

observing NLC droplets on alignment surfaces. Jpn. J. Appl. Phys. 35, L117-L119 (1996).

 
a b

c

Figure 1. Schematic diagram of the alignment pattern and texture of NLC on the surface. (a) The 

pattern is an array of identical hexagons, which consist of three elemental parallelograms. Each 

parallelogram has a shifted local rubbing direction, which is expressed by the solid lines. (b) The 

LC texture on the patterned alignment layer under a rotating analyzer in the optical polarizing microscope. 

Outside of the patterned area was left as-coated. The slight contrast of brightness in the figure indicates

that the patterned region is divided globally into two regions of different macroscopic orientations. Black

and white arrows indicate the directions of polarizer and analyzer. The side of the unit parallelogram is 

10μm-long. (c) Orientations of surface directors in individual domains and at boundaries. Green 

arrows indicate the macroscopic orientations of two regions. Blue ‘T’ symbols correspond to the director

inside the domains and at the boundaries associated with 60° in-plane twist (π/3-wall). Red ‘T’ symbols 

are the directors at the 120° in-plane twist boundaries (2π/3-wall).

32
120

0

60 60 degree

-60

0

60 0 degree 

-60

-120

0

-60 degree

Average 

orientation

Figure 2. Three possible macroscopic orientations of NLC on the hexagonal pattern. The lines inside the

pattern indicate the local rubbing direction, in which the LC is locally aligned. The NLC and local

rubbing are invariant to 180° rotation. The three types of hexagons on the right illustrate the

energetically degenerate ground states, which differ from each other in terms of the position of the 120°

in-plane twist boundary. Starting from any one of the hexagons, the LC orientations on the remaining two

types of hexagons can be obtained by flipping the director by 180° in one of the three unit

parallelograms. The macroscopic LC alignment, appearing sufficiently inside the bulk LC, is simply given

by averaging the director orientation over the surface, and is 0°, − 60° and + 60° from top to bottom.

Thick blue and red lines show the π/3- and 2π/3-walls, respectively. Black arrows are the macroscopic LC

alignment orientations. The exact match between the macroscopic alignment and either one of the local

rubbing directions is valid only when the elastic anisotropy is negligible and/or the inscribed pattern is not

chiral. The present hexagonal pattern is chiral in the sense that its mirror image cannot overlap itself. In

general, therefore, the macroscopic alignment could be slightly shifted from the local rubbing direction,

although the 60° difference among three stable states remains the same owing to its symmetry origin.

33
c θ

-90 -45 0 45 90

6

12

18

24

Intensity (a.u.)

 (degree)

a b

a’ a

Pol

bc

-20

30

80

a-a’ b-b` c-c’ θ 

Electric 

Field 

b’ c’

Ana

Figure 3. Structure of the LC cell and tri-stable switching behaviours. (a) The size of the

pattern was about 90μm by 90μm. The in-plane electric field was applied along a-a’, b-b’, and c-c’ for

switching. The cell was placed under a polarizing optical microscope for texture observations and for

light transmission measurements. Conventional rubbing on the covering substrate and the polarizer

were set parallel to each other, and one of the local nano-rubbing was adjusted perpendicular to it. The

θ is the angle of the analyzer from the crossed analyzer direction. (b) The LC textures of the

switched states in the absence of electric field; the applied electric field was : 10.0Vrms/μm along aa’, 7.8Vrms/μm along b-b’ and 8.6Vrms/μm along c-c’. The field difference may reflect the

inhomogeneity of the cell. The analyzer directions were adjusted near the minimum brightness of each

state. Most of the area could be switched at lower field strength than these values. Schematic drawings

on the bottom are the three dimensional director profile for each switched state over the patterned

surface into the bulk. As shown in Figure 2, the red lines are 2π/3-walls and the blue lines are π/3-

walls. The black arrows indicate the macroscopic orientation in each switched state. (c) Transmission

as a function of the analyzer angle for each switched state in the absence of the electric field. : aa’ direction, : b-b’ direction and : c-c’ direction. 

34
35

Non contact AFM nano-oxidation: Recent experiments and 

application to thin aluminum layers 

Francesc Pérez Murano 

Institut de Microelectrònica de Barcelona (IMB-CNM-CSIC) 

Abstract 

Despite that many examples of nanostructure and device fabrication using SPM nano-oxidation have 

been reported, a deep study of the oxidation mechanism and kinetics is still missing. In this presentation, I 

will review some of the most relevant results that have been published for the understanding of the 

mechanism and kinetics. This information is related with the role of the meniscus when the AFM oxidation 

is performed at a finite tip-sample distance, and with the electrical current detection during oxidation. 

Finally, the advantage of using non-contact AFM for nano-oxidation of thin aluminum layers is described 

1.- Recent results of AFM nano-oxidation. 

Figure 1 shows the general concept of the SPM oxidation mechanism on silicon: the oxidation reaction 

takes place at the silicon/oxide interface; as a product of the reaction H+

 is created, which contribute to 

the creation of defects in the oxide. In addition to this, the water meniscus connecting tip and surface 

provides the adequate conditions (OH-

 concentration) for the oxidation to proceed. The most direct 

evidence of the consequent space charge build-up on the oxide is provided from SMM measurements 

performed in ref. [1]. 

Space charge build-up in the oxide is a clue factor for understanding oxidation kinetics. This has been 

analyzed in reference 2, where a model for the kinetics of oxide growth has been elaborated, which 

predicts the temporal evolution of defect and intermediate species creation [2]. A way to show up the 

effect of space charge in the oxide growth kinetics consists on performing the oxidation under AC voltage. 

Figure 2 shows some examples of how the kinetics is changed under AC voltage, both in height vs. time 

and width vs. time [3]. An additional consequence of space charge build-up in the oxide is the low density 

of the SPM oxide compared to thermally grown oxide. After an annealing, the density of the oxide 

increases as it has been determined from the XTEM analysis [4]. 

The kinetics of the oxide growth can be also modified by manipulating the water meniscus, i.e., by 

changing the tip-sample distance when doing the oxidation in non-contact mode. Figure 3 shows the 

effect of changing the tip sample distance while inducing the oxidation. Environmental SEM images of the 

meniscus provide a nice representation of the role of the meniscus. 

The interplay between water meniscus and space charge build-up in the oxide can be further analyzed by 

detecting the current during the SPM oxidation. Figures 4 and 5 show preliminary measurements of 

current detection during oxidation (figure 4) and meniscus conductivity. For all the data, stiff cantilevers 

(k=40 N/m) with n-doped silicon tips have been used. Current acquisition is performed simultaneously to 

the acquisition of a force vs. distance curve, so that the dependence of current vs. tip-sample distance 

(as well as the current evolution with time) can be established. 
36

2.- AFM nano-oxidation of thin aluminum layers 

Figure 6 shows AFM images of the aluminum surface used in the experiments. Although surface is very 

rough compared to the surface of a silicon wafer, it is good enough for serving as a template for AFM 

oxidation experiments. Al thin films (thickness of 8 nm) have been deposited by sputtering at CNM. The 

motivation for using aluminum is that it is a widely used material in Microelectronics, and it is a very good 

mask for reactive ion etching in terms of selectivity against silicon. We are currently using AFM oxidation 

of aluminum for the fabrication of nanomechanical devices [5]. 

AFM oxidation of aluminum requires application of high voltages because of the high insulating 

characteristics of the aluminum oxide. Application of high voltages under contact mode AFM produces 

undesirable breakdown effects, i.e., damage on surface and tip. By inducing the oxidation at finite tipsample distance, the breakdown effect disappears. Figure 7 shows a set of lines made at different values 

of tip-sample distance and voltage. It is remarkable that for the last line, oxidation is performed at high 

voltage (56 V) and large tip-sample separation (32 nm). By choosing the adequate values for voltage, tip 

sample separation and scanning speed, line width can be optimized, as it is shown in the right image of 

figure 7. 

References 

[1] J.A. Dagata, T. Inoue, J. Itoh, K. Matsumoto and H. Yokoyama. Appl.Phys.Lett. 73, 271 (1998) 

[2] J.A. Dagata, F. Pérez-Murano, G. Abadal K. morimoto, T. Inoue, J. Itoh, H. yokoyama. 

Appl.Phys.Lett. 76, 2710 (1998) 

[3] F. Pérez-Murano, K. Birkelund, K. Morimoto, J.A. Dagata. Appl.Phys.Lett. 75, 199 (1999) 

[4] K. Morimoto, F. Pérez-Murano, J.A. Dagata. Appl.Surf.Science 158, 205 (2000) 

[5] See presentation of Z. Davies in this workshop. 
Si + 4h+

+2OHÆ SiO2 + 2H+

Silici

SiOx

Tip

 H+ + OHÆ H2O

 H2O Æ H+ + OH-

 OH- OH- OH- 

 H H + + H+ H+ H+ H+

Oxidation mechanism and effect of space charge in the oxide

J.A. Dagata, T. Inoue, J. Itoh, K. Matsumoto and H. Yokoyama

Applied Physics Letters 73, 271 (1998)

Figure 1. Oxidation mechanism and role of space charge 

37

1500 nm

0.1 s

5 s

10 s

100 s

50 s

0.5 s 1 s

800 nm

1400 nm

10 s 100 s 50 s

f=10 Hz Vox=10 V Vres = -10 V

Vox=10 V

F. Pérez-Murano, K. Birkelund, K. Morimoto, J.A. Dagata

Appl.Phys.Lett. 75, 199 (1999)

SPM oxidation under voltage modulation

Figure 2. Oxidation under AC voltage 
1.0μm

+ +

– –

2.0μm

Non contact SPM nano-oxidation

Environmental SEM images of the meniscus:

M. Schenk, M. Futing, and R. Reichelt. J. Appl. Phys. 84, 4880 (1998)

Figure 3. When performing the oxidation in non-contact, varying the tip-sample 

distance can control the width of the oxidation 

Preliminary measurements of current detection

-5 0 5 10 15 20 25 30 35 40 45

-25

-20

-15

-10

-5

0

5

Deflection (nm)

Z displacement (nm)

0 10 20 30 40

0

5

10

15

Current (pA)

Z displacement (nm)

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

1E-3

0.01

0.1

1

10

100

6.1V

 6.4V

 6.9V

 7.3V

 7.85V

 9.3V

Current (pA)

time (s)

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

-10

0

10

20

30

40

50

60

70

80

90

100

110

6.1V

 6.4V

 6.9V

 7.3V

 7.85V

 9.3V

Current (pA)

Time (s)

Cur11

0 500 1000

1E-3

0.01

0.1

1

10 cur12-13 5.9V

 cur11-44 6.1V

 cur11-50 6.9V

 cur12-15 6.4V

current (pA)

time(ms)

0 200 400 600 800 1000 1E-3

0.01

0.1

1

10

Cur12-13

5.9V

current (pA)

time(ms) 0 200 400 600 800 1000 1E-3

0.01

0.1

1

10

Cur12-15

6.4V

current (pA)

time(ms)

Figure 4. Current detection during oxidation

38
Preliminary results of meniscus conductivity

0 10 20 30 40

-17.199

-16.585

-15.971

-15.356

-14.742

-14.128

-13.514

-12.899

 25.2 V approach 25.2 V retract 

 27 V approach 27 V retract

 28.8 V approach 28.8 V retract

 30.6 V approach 30.6 V retract

 0 V approach 0V retract 

Deflection (nm)

Z displacement 0 10 20 30 40

-1

0

1

2

3

4 25.2 V approach

 25.2 V Retract

 27 V Retract

 28.8 V approach

 28.8 V Retract

 30.6 V approach

 30.6 V Retract

current (pA)

Z displacement (nm)

Current is detected before arriving to the repulsive force regime:

Meniscus conductivity can be studied

Figure 4. Meniscus conductivity at finite tip-sample distance

AFM nano-oxidation of thin aluminum layers

• Sputtered Al thin film (8 nm) on oxidized

silicon wafer

• Surface roughness >0.5 nm rms

• Native oxide: need of high voltage

• Al is used in Microelectronics for the

fabrication of integrated circuits

Figure 5. AFM images of the surfaces of a thin (~ 8 nm) aluminum layer 

deposited on oxidized silicon

39
44 V

12 nm

56 V

32 nm

AFM nano-oxidation on thin Al layers

Procedure for linewidth optimization:

Selection of optimal tip-surface separation

and voltage

10 nm width lines on Al

Figure 6. Oxide lines fabricated on thin aluminum layer 

40
In-situ current measurement during dot formation on Hpassivated p-Si(001) 

Hiromi Kuramochi and Hiroshi Yokoyama* 

Research Consortium for Synthetic Nano-Function Materials Project (SYNAF)-SII, 1-1-1 Higashi, Tsukuba, 

Ibaraki 305-8562, Japan 

*SYNAF- National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-

8568, Japan 

Nanometer-scale oxidation by atomic force microscope (AFM) -based method has been 

established in this decade and now it is a popular technique to fabricate nanostructures. The size 

of the structures decreased, the pattern became complicated and various materials have been used 

as objects. Understanding the nano-oxidation process is increased by development of study on 

kinetics and mechanism, such as the kinetic oxide growth model [1], steady-state model based on 

in situ electrical force characterization by scanning Maxwell stress microscopy [2] and water 

meniscus model for noncontact-AFM [3]. It is clear that direct monitoring of oxidation process 

is necessary for achieving further understanding of kinetics and precise control. Here, in situ

current detection during nano-oxidation in contact mode will be reported. 

 The sample was p-Si(001) with a resistivity of 1-10 Ω·cm and it was passivated by hydrogen 

using HF solution. Experiments were carried out at room temperature using an environmental 

control AFM (SII, SPA-300HV) which is combined with a humidity regulator. The humidity in 

the AFM chamber is controllable from 30-80 % with an accuracy of 1 %. The AFM based on 

the optical lever system [4] to measure the deflection of the cantilever. The conductive cantilever 

with microfabricated Si tip is coated with Rh. 

Soft cantilevers with the nominal spring constants of 

0.2N/m were used for current detection during dot 

fabrication and a bit stiffer ones (1.6 N/m) were current 

detection during force curve measurements. 

41

40

30

20

10

cu nt (pA) rre

 A conductive cantilever is kept at a position in contact 

with the Si surface, when a certain voltage is applied to 

the sample for a certain duration, a dot was fabricated by 

local oxidation. The threshold of bias voltage for 

oxidation is varied due to duration and humidity. Figure 

1 shows an example of topographic (a) and current 

image (b) of a fabricated oxide dot by applying a sample 

bias voltage of 6 V for 10 s at a humidity of 70 %. The 

diameter of this dot is 280 nm and the height is 3.5 nm. 

From the current image, the fabricated oxide is less 

conductive than substrate surface. The diameter of a dot in 

the current image is always larger than that in the 

topographic image. It indicates the actual oxide growth 

area. During oxidation, ionic current flows from the images 

of an oxide dot. 

Fig. 1 Simultaneous (a) topographic and 

(b) current images. 

2 4 6 8

10 V

50 %

60 %

40 %

70 %

0

time (s)

Fig. 2 Current vs. time as a function of 

relative humidity. 
Si surface to the tip. In situ current detection during oxidation was carried out at various sample 

bias voltage and humidity. Figure 2 shows detected current during dot fabrication by applying a 

sample bias voltage of 10 V for 10 s at various humidity. Current flew immediately after the bias 

voltage applied, and it decreased with time according to oxide growth. The initial value of the 

become large in sequence at higher humidity. The same experiments were performed in the 

sample bias voltage range of 8-10 V and humidity range of 40-70 %. The shape of current curve 

is not changed when the applied voltage and/or humidity are varied. It indicates the detected 

current curves well reflect the essential oxidation reaction. For quantitative analysis, the area 

between detected current curve and I=0 are calculated by integration. 

The relations between total current and oxidation conditions are shown in figure 3. Lines 

between data points in the graph are only conspicuous guides. Larger current was detected at 

higher voltage and higher humidity in order. The epitome of current behaviour to oxidation 

conditions could be led from figure 3, but further data points are required for precise modelling. 

It is possible to estimate the actual ionic current from the volume of fabricated dots. The volume 

above the surface was cubed geometrically from shape, diameter and height using line profiles. 

Total volume ought to include the volume of oxide under the surface. It is considered in the way 

of multiplication the volume above the surface by a ratio from previous paper [5]. Then using 

the expansion coefficient of 2 (SiO2/Si) and according to the reaction equation, the expected 

current for fabrication the observed dot is calculated as shown in figure 4. Comparing it to figure 

3, total current and expected current coincide well, but total detected current is slightly larger 

than the expected current. The difference between detected total current and expected current is 

caused from electronic current and error in volume estimation, because of the current noise was 

negligible as in figure 2. Such a small 

Fig. 3 Relation between total current for oxidation Fig. 4 Expected current from volume of 

(10 s) and applied voltage at various humidity. fabricated dots (10 s). 

difference between total current and expected current suggests that ionic current has the main 

proportion of detected current. 

 To estimate the effects of tip-sample distance to the meniscus dynamics, current detection 

was carried out in parallel with force curve measurement. In the course of force curve 

measurement, sample was moved in z as much as setting range; approaching to the tip then 

pulling off after contact. The setting range is from 200 nm to -20 nm and it takes 60 s to measure 

a whole force curve. Figures 5 show a part of a force curve measured at a sample bias voltage of 

10 V and corresponding current curve as an example set. When the force fell down to negative 

42
value on the approach route, the current jumped up. It means the meniscus formation and the tip 

jumped to contact. The current decreased as time due to oxide growth during tip was in contact 

to the surface. Then force and current returned to zero suddenly when the meniscus broke up. 

The same experiments were performed at various sample bias voltage (0-10 V). The number of 

data is still not enough, but it is possible to say the pattern of detected current is the same if the 

bias voltage is above the threshold. Thus this experiment is useful to know the behaviour of 

meniscus that more detail experiments will be required at various bias voltage and humidity. 

 

200

150

100

50

0

-50

Force (nN)

-20 0 20 40 60 80 100

z Displacement (nm)

0.6

0.4

0.2

0.0

Current (pA)

-20 0 20 40 60 80 100

z Displacement (nm)

Figs. 5 (a) A part of force curve at a bias voltage of 10 V and a humidity of 50 %. Measurement takes 33 s for this 

part. (b) Corresponding detected current. The spring constant of the cantilever is 1.6 N/m. 

 

 As a summary, in situ current detection during nano oxidation and force curve measurement 

were successfully started. The effectiveness of current detection on the study of meniscus is 

proved. The direction of further experiments on current detection is clarified and pointed out. 

This work was partly supported by NEDO under the Nanotechnology Materials Program. 

[1] P. Avouris et al., Appl. Phys. Lett 71, 285 (1997). 

[2] J. A. Dagata et al., Appl. Phys. Lett. 73, 271 (1998); J. Appl. Phys. 84, 6891 (1998); Appl. 

Phys. Lett. 76, 2710 (2000). 

[3] R. Garcia et al., J. Appl. Phys. 86, 1898 (1999). 

[4] G. Mayer and N. M. Amer, Appl. Phys. Lett. 53, 1045 (1988). 

[5] K. Morimoto et al., Appl. Surf. Sci. 158, 205 (2000). 

43
44
45

 

Charge imaging and manipulation using carbon nanotube 

probes 

S.-D. Tzeng, C.-L. Wu, Y.-C. You, T. T. Chen, and S. Gwoa)

Department of Physics, National Tsing-Hua University, Hsinchu 300, Taiwan 

H. Tokumoto 

Nanotechnology Research Institute 

National Institute of Advanced Industrial Science and Technology (AIST) 

Central-4, Higashi 1-1-1, Tsukuba, Ibaraki 305-8562, Japan 

Abstract 

Due to their high aspect ratio, well-defined cylindrical structure, good electrical conductivity, 

and the possibility to encapsulate magnetic materials, carbon nanotubes (CNTs) are ideal probes 

for “true” local imaging of electric and magnetic domain structures at the nanoscale. By 

performing force-distance measurements and tip-shape profiling with a uniformly charged oxide 

square, we clearly demonstrate the local nature of the CNT tip for electrostatic force microscopy. 

We show that CNTs can be used to probe long-range electrostatic forces with a lateral resolution 

better than 5 nm. In addition, CNT can be applied to manipulate charges on the charge-trapping 

media with an areal density greater than 60 Gbit/in2

. 

PACS Numbers: 81.07.De, 68.37.Ps, 77.84.Bw, 81.16.Pr 

Direct imaging and manipulation of electric and magnetic domain structures 

(spontaneously or artificially formed) at the nanoscale has become increasingly important 

because of the recent developments in ultrahigh-areal-density storage devices using chargetrapping1

, ferroelectric2, or ferromagnetic3 materials. Electrostatic force microscopy (EFM) and 

magnetic force microscopy (MFM), variations of scanning force microscopy (SFM), are two of 

the most widely used techniques for this purpose. To date, the major difficulty related to the 

long-range force imaging is to decouple the short-range interactions without degrading the 

spatial resolution. This problem is especially severe for the conventional micromachined EFM 

and MFM probes with conical or pyramidal shaped tips. Carbon nanotubes (CNTs), consisting of 

one or several graphene sheets rolled into tubes, have great potential to be used as the probing 

tips for the scanning probe techniques. Several groups have already reported experimental 

approaches to attach a single CNT to a conventional SFM tip.4-6 Both high-resolution imaging7,8

and lithography9,10 applications of CNT probes have been reported. Since CNTs are electrically 

conducting, mechanically robust, and having a perfect cylindrical geometry with very large 

aspect ratio, they are also very suitable for imaging long-range forces.11,12 In this letter, we show 

that CNT is an ideal tip material for “true” local probing and manipulation of charges trapped in 

nitride films. 

We used a specially designed field emission scanning electron microscope (FE-SEM) to 

attach individual multi-wall carbon nanotubes to PtIr-coated Si tips of commercial EFM probes 

a) Electronic mail: gwo@phys.nthu.edu.tw 
46

(~70 kHz resonance frequency and ~2.8 N/m force constant, and ~10-15 μm tip length). To 

separate the electrostatic force information from the total interaction of probe and sample, we 

used a dual-modulation scheme (operating in the dynamic mode), where a near-resonant 

mechanical modulation (ωm ≈ ω0 ≈ 70 kHz) was applied to the cantilever and a non-resonant 

electric modulation (ωe, ≈ 20 kHz) was applied to the sample bias voltage. The average tipsample separation (dynamic mode) used in this study was ~15-30 nm. Two types of chargestorage media were used in this work for EFM imaging. One type consists of a Si3N4/SiO2

bilayer (4-nm/3-nm thickness); and the other is a single Si3N4 layer (3.5-nm thickness), both 

grown on p-type Si(001) substrates. For both types of samples, the nitride layer was used as the 

charge-trapping layer and was deposited by conventional low-pressure chemical vapor 

deposition. 

Figure 1(a) shows dynamic force-distance curves of PtIr-coated Si tip and CNT-attached 

tip measured by the same type of EFM probes on a gold film in air. And, Fig. 1(b) shows 

quasistatic force-displacement curves used to determine the closest tip-sample distances before 

the tip snap-in. The drastic difference in the contact force (surface adhesion due to the absorbed 

humidity layer) between these two types of tips can be directly observed in Fig. 1(b). From the 

measurement shown in Fig 1(a), we can confirm that the force-distance relationship of a 

conventional EFM probe with a metal-coated Si tip is in qualitative agreement with the results 

simulated by S. Belaidi et al.

13 We can use a sphere/cone/cantilever probe geometry to 

understand the measurement results of a conventional EFM probe. In the large-distance regime 

(tip-sample distance >10 μm), the detected electrostatic force is mainly a long-range capacitive 

force resulting from the cantilever and the Au sample. In the intermediate regime (<10 μm), the 

electrostatic force between the tip cone and the Au sample begins to contribute significantly to 

the detected force. Only in the proximate regime (<40 nm), the main detected electrostatic force 

is from the interaction between the tip apex and the sample. However, in this regime, van der 

Waals and various chemical interactions also become dominant. Therefore, to separate these 

interactions between the sample and the conventional Si tip, the conventional approach is to 

“lift” the tip above the sample some tens of nanometers. However, in this case, reduction in 

lateral resolution would occur due to the increase in the tip-to-sample distance and the 

occurrence of electrostatic interaction between the sample and the cone structure of Si tip. By 

contrast, the force-distance curve of CNT-attached tip shows much less contribution from the Si 

cone structure in a wide range of tip-sample distance. This is the main reason why CNT probes 

enable “true” local sensing of electrostatic interactions under typical noncontact or intermittentcontact operating conditions. Two dotted lines in the CNT force curve of Fig. 1(a) shows the 

regions of interaction transition. The actual CNT length (~380 nm) acquired by FE-SEM 

imaging is also indicated in the curve. The measured power-law exponents for force versus tipsample distance are: –1 (∝ 1/d) for the spherical tip apex of the conventional probe and –0.45 for 

the nanotube, while the exponent for the common tip cone structure is –0.25, which are 

consistent with the expected sphere-like, rod-like, and cone-like behaviour, respectively. 

For nitride charging experiments performed on nitride films in air, we have previously 

discovered14 that anodic oxidation could occur in the proximity of the local probe due to the 

intense electric field built between the grounded probe and the humidity-layer-covered nitride 

film on top of a positively biased Si substrate. We have found that the main oxidation by-product 
47

ions (positive charge state) could be trapped at the anodic-oxide/nitride interface with a long 

retention time. Therefore, a well-prepared oxide pattern on nitride can be used as a uniformly 

charged “mirror” for imaging the tip shapes of EFM probes. Figure 2 shows an example of such 

experiments on an oxide-nitride-oxide-silicon (ONOS) structure with two types of probes. A 

positively charged oxide square was prepared by locally oxidizing the Si3N4/SiO2 bilayer film 

using a conducting probe under ambient conditions. Instead of the centre-protruded EFM image 

taken with a conventional EFM probe, using a CNT probe, we can resolve the sharp boundary of 

the charged and uncharged regions and the electrostatic force signal is quite uniform within the 

charged region. 

To obtain the information of optimum resolution for EFM imaging with a CNT-probe, an 

array of alternative positively and negatively charged regions was written in a Si3N4 film with 

±10 V voltage pulses (1-ms-width for the PtIr-coated Si tip and 1-s-width for the CNT tip) 

applied between the conducting tip and the p-type Si substrate, as shown in Fig. 3. In order to 

avoid the complication of field-induced oxidation and charge trapping occurred in ambient air, 

the local charging experiments were performed in high vacuum (~10-6 Torr) with an 

environment-controlled SFM system (SPA300HV, Seiko Instruments) such that field-induced 

anodic oxidation did not occur during the charging and subsequent imaging process. We found 

that the topographic images taken with the CNT probe displays much finer topographic features 

of the nitride surface with small feature sizes of the order of ~5-nm. Since the Z-feedback of the 

probe position is controlled by the surface topography and the electrostatic force signal 

corresponds to the interaction of the tip with the bulk charge trapping sites within the nitride 

film, the “true” local sensing of electrostatic force should reflect the local surface topography 

because that the tip moves conformably with the surface topography during simultaneous EFM 

imaging and the effective probed volume of bulk charged sites should change accordingly. This 

is observed only with the EFM image using the CNT probe because of its local probing 

capability. By comparing the fine features displayed in Figs. 3(d) and 3(e), the achievable EFM 

resolution using a CNT probe is determined to be better than 5 nm. In contrast to the much 

improved lateral resolution, the EFM signal obtained with the CNT probe is weaker due to the 

effective probed sample volume is much smaller than that of the conventional probe. This is 

consistent with the line profiles of EFM images shown in Fig. 2(e). 

The areal bit density of the charged array demonstrated here is ~64 Gbit/in2

 and the 

charged regions are erasable and rewritable by applying reverse voltages. From the known trap 

density of electron or hole in Si3N4 film, we estimate that each charged bit contains a few tens of 

electrons or holes. It is interesting to note that although CNT probes can provide an extremely 

high lateral resolution for EFM imaging, the charged dot diameter induced by the CNT tip is not 

significantly smaller than that induced by the tip of a conventional EFM probe (45-50 nm vs. 60-

65 nm). The reason might be that, during the writing process, the intensive charging field causes 

significant lateral relaxation of the trapped charges similar to the known phenomenon of electricfield-induced thermal excitation of trapped charge carriers at room temperature.15 Although we 

demonstrate only the capabilities of imaging and manipulation of charges on insulating films, the 

drastic improved spatial resolution of EFM imaging with single CNT tips can open up new 

applications of nanometer-scale surface potential measurements. This is especially important for 

studying individual nanomaterials such as nanocrystals,16 CNTs,17 or even biological samples. 
48

We thank the National Science Council (NSC) in Taiwan and the Program for Promoting 

Academic Excellence of Universities, the Ministry of Education (MOE) in Taiwan for 

supporting this research and J. A. Dagata for enlightening discussions. The SEM manipulation 

work performed in AIST, Tsukuba was partially supported by the New Energy and Industrial 

Technology Development Organization (NEDO), Japan. 
49

References:

1. R. C. Barrett and C. F. Quate, J. Appl. Phys. 70, 2725 (1991). 

2. C. H. Ahn, T. Tybell, L. Antognazza, K. Char, R. H. Hammond, M. R. Beasley, Ø. Fischer, 

J.-M. Triscone, Science 276, 1100 (1997). 

3. D. Weller and A. Moser, IEEE Trans. Magn. 35, 4423 (1999). 

4. H. Dai, J. H. Hafner, A. G. Rinzler, D. T. Colbert, and R. E. Smalley, Nature 384, 147 

(1996). 

5. H. Nishijima, S. Kamo, S. Akita, Y. Nakayama, K. I. Hohmura, S. H. Yoshimura, and K. 

Takeyasu, Appl. Phys. Lett. 74, 4061 (1999). 

6. J. H. Hafner, C. L. Cheung, T. H. Oosterkamp, and C. M. Lieber, J. Phys. Chem. B 105, 743 

(2001). 

7. S. S. Wong, E. Joselevich, A. T. Woolley, C. L. Cheung, and C. M. Lieber, Nature 394, 52 

(1998); J. H. Hafner, C. L. Cheung, A. T. Woolley and C. M. Lieber, Prog. Biophys. Mol. 

Biol. 77, 73 (2001). 

8. T. Uchihashi, N. Choi, M. Tanigawa, M. Ashino, Y. Sugawara, H. Nishijima, S. Akita, Y. 

Nakayama, H. Tokumoto, K. Yokoyama, S. Morita, and M. Ishikawa Jpn. J. Appl. Phys., 

Part 2 39, L887 (2000). 

9. H. Dai, N. Franklin, and J. Han, Appl. Phys. Lett. 73, 1508 (1998). 

10. E. B. Cooper, S. R. Manalis, H. Fang, H. Dai, K. Matsumoto, S. C. Minne, T. Hunt, and C. F. 

Quate, Appl. Phys. Lett. 75, 3566 (1999). 

11. S. B. Arnason, A. G. Rinzler, Q. Hudspeth, and A. F. Hebard, Appl. Phys. Lett. 75, 2842 

(1999). 

12. J. A. Dagata, F. S. S. Chien, S. Gwo, K. Morimoto, T. Inoue, J. Itoh, and H. Yokoyama, 

Proc. SPIE 4344, 58 (2001). 

13. S. Belaidi, P. Girard, and G. Leveque, Appl. Phys. 81, 1023 (1997). 

14. F. S.-S. Chien, J.-W. Chang, S.-W. Lin, Y. C. Chou, T. T. Chen, S. Gwo, T.-S. Chao, and 

W.-F. Hsieh, Appl. Phys. Lett. 76, 360 (2000); S. Gwo, J. of Phys. and Chem. of Sol. 62, 

1673 (2001). 

15. S. M. Sze, J. Appl. Phys. 38, 2951 (1967). 

16. T. D. Krauss and L. E. Brus, Phys. Rev. Lett. 83, 4840 (1999). 

17. A. Bachtold, M. S. Fuhrer, S. Polyasunov, M. Forero, E. H. Anderson, A. Zettle, and P. L. 

McEuen, Phys. Rev. Lett. 84, 6082 (2000). 
Figure 1. (a) Dynamic force-distance curves of PtIr-coated Si tip and CNT-attached tip measured by the same type 

of commercial Si probes on a gold film. Inset shows an FE-SEM image of the CNT probe. The scale bar is 100 nm. 

The upper curve is vertically shifted for clarity. To measure the electrostatic force vs. distance relationship, the 

cantilevers were excited electrically with a voltage modulation technique (without mechanical modulation). The ac 

component of the bias voltage was 2 V (peak to peak) and the dc component was 1 V (with respect to the surface 

potential of Au film). The EFM 1ω signal was acquired by using a lock-in amplifier. (b) Quasistatic forcedisplacement curves. The force-displacement hysteresis curve consists of the approach (right to left) part and the 

withdrawal (left to right) part. Discontinuities aa’ and bb’ indicate the onsets of tip jump-to-contact and jump-offcontact with the sample. 

50
Figure 2. Simultaneous images of surface topography (a and b) and EFM 1ω signal (c and d) of a uniformly charged 

oxide square on top of the scanning-probe-patterned ONOS structure. All images were taken in air. Both mechanical 

and electrical excitations of the probe were applied. The ac component of the bias voltage was 4 V (peak to peak) 

and the dc component was 0 V (with respect to the flat band voltage). First harmonic signals of ωm and ωe were used 

as Z-position feedback and EFM data signal, respectively. (e) Line profiles of EFM images shown in (c) and (d). 

51
Figure 3. Simultaneous images of surface topography (a and d) and EFM 1ω signal (b, c, e, f) of a charged dot array 

on a thin nitride film. The scale bars are 50 nm in all images. Images (a), (b), and (c) were obtained with a PtIrcoated Si tip, while Images (d), (e), and (f) were acquired with a CNT-attached tip (the corresponding image sizes 

are the same). All images were taken in high vacuum with imaging conditions similar to that used in Fig. 2 except 

that the ac component of the bias voltage was 2 V (peak to peak). From Figs. 3(d) and 3(e), the EFM resolution 

using the CNT-probe is determined to be better than 5 nm (the arrows in images point some sub-5-nm features for 

comparison). 

52
53

Free boundaries in an electrochemical nanocell 

Gerald W. Young, Curtis Clemons, Dmitry Golovaty, Rex Ramsier, D. Dane Quinn 

And S.I. Hariharan, The University of Akron 

John Dagata, NIST 

OVERVIEW 

The central goal of this modeling effort is to couple mathematical modeling and analysis to study 

lithographic patterning techniques based on scanned probe oxidation. At the nanometer length 

scale this process leads to the formation of a self-sustaining three-dimensional electrochemical 

nanocell that is not present in macroscopic anodic deposition processes. This nanocell is defined 

within four free boundaries: a fluctuating atomic-force microscope (AFM) tip, and the liquid/gas, 

liquid/oxide, and oxide/substrate interfaces. Further, there are moving contact lines at the 

junction of the interfaces and at the AFM tip. The complexity of this nanocell system presents 

significant mathematical challenges for the solution of the model equations and leads to a 

significant number of problems for analysis. 

PROPOSED MODEL 

A comprehensive mathematical model of the scanned probe oxidation process does not exist. As 

such our model includes the meniscus, hyper-thermal surface chemistry, reaction-diffusion 

mechanisms within the oxide and substrate, the electrical, morphological, thermal and wetting 

characteristics of the substrate, the electric field, and the thermal and mechanical oscillations 

within the system. The model consists of free boundaries separating regions of substrate, oxide 

and fluid. Coupling between the regions will be included since this influences the mechanical 

and reactive mechanisms, ion transport and electromagnetic fields in the system. The goals of 

the modeling effort are to explain experimental observations that are not well understood and 

identify the range of parameters that is optimal for high-aspect ratio nanoscale growth of oxide 

lines. 

 

For illustrative purposes we present a preliminary formulation that assumes oxyanions move 

through the oxide layer and react at the oxide/substrate interface. The substrate is taken to be a 

single material. Figure 1 describes the geometry of the system. We assume an axisymmetric 

configuration with zero scan speed so that we can investigate the formation of an oxide dot 

beneath a tip. Modifications to this formulation for other reaction models (mobile substrate ions 

and recombination within the oxide) and more complicated composite substrate systems can be 

included. 

AFM TIP DYNAMICS. The AFM tip location, z = F(r, t), is a free surface. The tip location 

responds primarily to an electrostatic force, but the capillary force exerted by the meniscus, r = 

R(z, t), may also be important. Thus, we assume the tip dynamics can be modeled as a forced 

oscillator (with known mass, damping and spring constant). The motion of the tip will influence 

the shape of the meniscus through the contact line conditions. 
Figure 1: Schematic of the nanocell geometry 

BOUNDARY CONDITIONS AT THE MENISCUS/AFM TIP CONTACT LINE. Let r = 

B(t) denote the location of the contact line. The simplest contact condition is the fixed type that 

assumes B(t) is a known quantity. We shall also consider a mobile contact line at the tip and 

pose a fixed contact angle condition where φ 0 is the equilibrium contact angle. This sets the 

slope of the meniscus at the contact line and causes B(t) to adjust to achieve this slope. 

DEFINITION OF THE MENISCUS. The determination of the meniscus shape is important 

since this shape influences the electric field lines. The shape of the meniscus will be governed 

by the hydrostatic equation balancing pressure with the curvature of the meniscus. Three 

conditions will be needed to determine the integration constants and the pressure. One of these 

conditions is the contact condition at the AFM tip. Another is the contact condition at the oxide 

that will be discussed below. The third condition is a mass balance. The rate of change of the 

volume of the bridge is equal to the increase in water volume due to transport of water from the 

substrate surface minus the amount of water leaving the system due to ion transport across the 

oxide layer. 

ION TRANSPORT WITHIN THE LIQUID BRIDGE. The basic model accounts for water 

hydrolysis and formation of OH-

 ions at the tip, transport through the liquid bridge and transport 

across the liquid/oxide interface z = h(r, t). Due to the high electric field in the z direction of the 

system, augmented drift diffusion equations are used to describe the transport of OH-

 and H+. 

These equations couple to the Poisson equation for the potential VL in the water bridge. 

Important parameters in these equations are the diffusion coefficients of the ions, and the ionic 

mobilities. These quantities can be functions of the electric field. Boundary conditions at the 

AFM tip define the tip region as the source of ions due to hydrolysis. 

54
Finally, at the liquid/oxide interface z = h(r, t) we develop boundary conditions that relate the 

concentration of OH-

 and H+ ions in the liquid bridge to that in the oxide. These expressions 

relate the motion of the oxide/liquid interface to the current densities at this location. There is a 

possibility that a buildup of OH- ions occurs in the liquid bridge ahead of this interface. Perhaps 

this buildup leads to significant reduction of ionic transport within the nanocell. 

ION TRANSPORT IN THE OXIDE LAYER. The governing equations are similar to the 

above. Further, if the substrate ions are included in the oxide layer then we must add a transport 

equation to the above set to track the concentration of these ions. 

REACTIONS AT THE OXIDE/SUBSTRATE INTERFACE. First we assume that the rate 

of growth of the oxide/substrate front z = -f(r, t) is proportional to the rate of the reaction at this 

front. Information about the reaction rate constant is needed. Other boundary conditions relate 

the motion of the oxide/substrate interface to the current density at the front. Finally, due to the 

reactions at the substrate surface, H+

 ions are released as the oxide is formed. Hence, the 

reaction serves as a source of these ions and provides the boundary condition for H+

. 

BOUNDARY CONDITIONS AT THE MENISCUS/OXIDE JUNCTION. First we have the 

conditions of contact that require the oxide/liquid, oxide/substrate, substrate, and meniscus to 

meet at A(t), the unknown location of the contact line or edge of the oxide layer. We also 

assume a contact-line mobility condition based upon deviations of the contact angle θ from the 

equilibrium contact angle of the meniscus at the oxide. This equation will be applied provided θ

> θ equil. In this case the contact line will move radially outward. If this condition is not 

satisfied, then the contact line remains fixed. The latter condition is imposed so that the oxide 

edge does not recede. 

We complete the system of equations by requiring that the mass consumption of the substrate 

equal the mass increase of the oxide. 

Each of the physical phenomena described above is coupled to one or more of the others through 

free boundaries and reaction terms. The tip dynamics influence the meniscus region, which 

determines the ion transport, which finally drives the reactions at the oxidation interface. In 

addition, this problem is fully coupled, so that we may not simply solve for one effect to be used 

as a "forcing" for the next. The resulting analysis must therefore account for this two-way 

coupling, which is expected to play a significant role in the resulting performance of this system. 

SOLUTION AND ANALYSIS STRATEGIES. To understand the complex process depicted 

in Figure 1 it is essential to understand the dynamics in one dimension. This model will help to 

identify the nonlinear coupling between various physical entities, and guide the analysis of the 

more complex axisymmetric configuration. The multi-dimensional structure of the scanned lines 

has received relatively little attention in the literature as the focus has been on explaining the 

55
56

self-limited vertical growth. We shall develop quasi-steady and thin-domain two-dimensional 

models for the system. A second axisymmetric strategy is to suppose that the oxide layer is 

modeled as a thin cylindrical disk beneath a cylindrical column of liquid. 

Throughout the model development and simulation we plan to continually revisit the models 

after comparing model predictions with experimental observations. The experimental 

investigations for current measurement within the nanocell are of particular interest for 

investigating the transport mechanisms and self-limited vertical growth of the oxide. 
Application of SPM oxidation to nano-photonics and nanospintronics 

Takashi Tokizaki 

National Institute of Advanced Industrial Science and Technology (AIST), Japan 

1. Introduction 

 The recent progress of the SPM oxidation allows us to fabricate nanometer-scaled structures. 

The method has been widely used to produce small electronic devices, such as a single-electron 

transistor [1], because narrow oxide structures are suitable for separating small electrodes. 

However, nanometer-sized oxides can be widely utilized for the other purposes. Since lots of 

metal oxides are optically transparent, they will be applicable in optical devises. Moreover, the 

oxidation changes the magnetism of materials. In this paper, the SPM oxidation of several 

materials is reported with the aim of the development of nano-photonic and nano-magnetic 

devices. 

2. Fabrication of nano-waveguides and evaluation 

 In waveguides with a metal core or clad, the surface plasmon polariton (SPP) is excited on the 

metal surface. The SPP can be propagated in waveguides, even if the cross-section size of the 

core is much smaller than the light wavelength [2]. Using the SPM oxidation, optically 

transparent metal-oxide structures are partially embedded in metal films, and we can excite the 

SPP at the interface between a small oxide core and a metal clad [3]. In order to improve the 

SPP propagation length, Ti-Ag composite films were used here. A portion of the upper Ti layer 

is oxidized, and the bottom of the Ti oxide contacts the lower Ag layer. In this structure, the SPP 

is excited on the Ag surface, so that we expect the propagation length of several microns, which 

is hundred times longer than that for the SPP on Ti surfaces. 

 Figure 1(a) shows the topographic images of waveguides, which were fabricated using a 

scanning near-field microscope (SNOM) with the bias voltage of 35 V. The width and the 

thickness of Ti oxide cores are 300 nm and 70 nm, respectively. The lower waveguide 

(waveguide A) has a dot-like structure at the left end of the waveguide. The dot was fabricated 

by raising the bias voltage up to 45 V, and a 

portion of Ag was oxidized. From the bias 

voltage dependence of the height and the 

transparency for oxides, the production of 

optically transparent Ag oxides was 

confirmed [4]. 

 Figure 1(b) shows the transmission SNOM 

images using light with the wavelength of 830 

nm. For the upper waveguide without a dot 

(waveguide B), a constant increase of the 

signal on the waveguide is observed. Since the Ti 

layer at waveguides is thinner than unoxidized 

films, the intensity of light transmitted directly 

through the metal layers is slightly stronger, but 

the signal is not caused by the SPP on the 

A

B

dot

B

A

3 μm

(a) (b)

Fig.1 (a) Topographic and (b) SNOM 

images of nano-waveguides fabricated on 

a Ti-Ag composite film. Waveguide A 

has a dot-like structure 

57
waveguide. On the other hand, the intensity for the waveguide A is much stronger, and increases 

toward the dot structure. When the probe is positioned on the waveguide A, the SPP is excited 

by the near field at the probe apex, and propagates toward the dot. The SPP is transformed to 

light at the dot, so that the scattered light is additionally measured as the signal. From the 

decrease of the signal apart from the dot, we can estimate the SPP propagation length of 6 μm. 

These results confirm the optical transparency of Ti oxides and the SPP propagation in nanowaveguides. 

1μm

0nm

60nm

Fig.2 (a) Topographic image of the oxide 

structure fabricated on a MnSb thin film. 

Fig.3 Temporal change of the bias voltage 

(dot line) and the height (solid line). The 

height of the oxide decreases with 

applying the negative bias voltages.

3. Nano-oxidation of magnetic materials 

 The local control of the magnetism of magnetic materials using the SPM oxidation will be 

applied to higher-density storage devices and smaller-sized magnetic-sensor devices. In this 

paper, the oxidation of a typical ferromagnetic material of MnSb is reported. For MnSb thin 

films, it is known that paramagnetic MnO2 layers are produced by the thermal oxidation [5]. 

 Figure 2 shows the topographic image of an oxide structure, which was fabricated using the 

bias voltage of 20 V for a 30-nm thick MnSb film on a GaAs substrate. The height and the 

diameter are 45 nm and 300 nm, respectively. We can oxidize MnSb using bias voltages beyond 

7 V, and control the height based on the bias dependence with the constant of 3.4 nm/V. 

However, the diameter is determined by the apex size of the probe in the experiments. Next, we 

applied negative bias voltages to oxides fabricated with positive voltages. Figure 3 shows in situ

observation of the process. An oxide structure grows during the increase of the bias voltage, and 

the height of 80 nm is not changed after reaching at the maximum voltage of 20 V and even for 

the zero bias. After that, the height of the oxide starts to decrease at the bias voltage below -10 

V, and reaches to 30 nm at the bias voltage of -20 V. 

 While many types of oxides of Mn and Sb are known, the stoichiometry of oxides produced by 

the SPM oxidation has not been determined. From our results, it is guessed that the complex of 

these oxides is produced and that the valence number and the complex ratio are changed by the 

bias including the negative region. In future, we should determine the stoichiometry, and 

understand the process of the SPM oxidation for compound materials. 

58
59

4. Summary 

 The SPM oxidation was applied to several materials. For making optical nano-waveguides, the 

thickness of Ti oxides was controlled up to 100 nm, and also Ag layers under Ti oxides were 

oxidized. The propagation of the SPP in nano-waveguides was confirmed based on a near-field 

optical technique. Next, the oxidation of a ferromagnetic material of MnSb was reported. While 

the magnetism and the stoichiometry of oxides have not been determined, the phenomenon 

which is understood as the deoxidation was found. 

References 

[1] Y..Gotoh et al., Jpn. J. Appl. Phys., 41 (2002) 2578. 

[2] J.Takahara et al., Opt. Lett., 22 (1997) 321. 

[3] T.Onuki et al., Appl. Phys. Lett., 80 (2002) 4629. 

[4] T.Onuki et al., Jpn. J. Appl. Phys., 41 (2002) 6256 

[5] H.Akinaga et al., Jpn. J. Appl. Phys., 35 (1996) L897.
60
Nanoscale oxidation of zirconium surfaces: kinetics and 

mechanisms 

Rex D. Ramsier 

Departments of Physics, Chemistry, and Chemical Engineering 

The University of Akron 

Akron, OH 44325-4001 USA 

rex@uakron.edu 

Zirconium and zirconium alloys have been used as structural materials in nuclear and chemical engineering 

applications for many years, and are now beginning to appear in the biomedical and dielectric arenas. Although 

metallic Zr is itself chemically very active, the environmental resistance that this class of materials exhibits in 

practice is attributable to a chemically passive and mechanically stable oxide layer on its surfaces. For the past 

several years, our group has been involved in studying this class of materials from both the fundamental and applied 

surface science standpoints. This involves approaches ranging from ultra-high vacuum single crystal studies of 

electron-induced surface chemistry to the thermal annealing of alloy sheet stock under ambient conditions. Our 

primary concern in all of these efforts has been the kinetics of Zr surface oxidation and the role and fate of O, H, and 

N species in this process. Since we have an understanding of the kinetics and mechanisms of zirconium surface 

reactions from our macroscopic studies, the opportunity to use SPM nanolithography to study similar processes at 

the nanoscale is very welcome. This endeavor has the potential to deepen our understanding of surface 

reactions in the Zr materials system while at the same time helping us better comprehend the complex synergy of 

physics and chemistry occurring during nanoscale surface patterning. A summary illustration of our understanding 

of the thermally-activated chemistry of zirconium surfaces is shown in Figure 1. 

Subsurface

Potential Energy

Distance

High Adsorption Temperature

Surface

Subsurface

Potential Energy

Distance

Low Adsorption Temperature

Surface

E(sr)

E(sb)

Figure 1. Illustration of the energetics of surface-subsurface transport 

that play a role in the surface chemistry of zirconium. 

61
62

Zirconium has the ability to hold large weight percentages of O and H in solid solution, and the 

diffusivity of both species through the Zr lattice is quite high. We have been able to show that 

these species are kinetically mobile and chemically reactive, and that they participate in surface 

chemistry depending on the conditions. Nitrogen species strongly perturb the resulting thermal 

behavior of these surfaces, and there is evidence for mixing of surface and subsurface species. 

This rich kinetic behavior makes the Zr materials system very interesting to study, and our 

results lend insight into the mechanisms responsible for the environmental resistance exhibited 

by this class of materials. 

SPM nanolithography, made possible by our collaboration with Dr. John Dagata at NIST, is 

another way in which we can study the kinetics of Zr surface oxidation and the role of nitrogen 

in this process. Our initial efforts have been very successful, and we anticipate expanding the 

role of SPM in our kinetic studies. We have shown that AFM-induced oxide features can be 

reproducibly formed on both Zr and ZrN surfaces, and that the growth rate decreases rapidly 

with increasing time. There is an increase in oxide-feature height with humidity for both 

systems, and an approximately linear dependence of the height of the structures on the applied 

voltage for all films for short exposure times. As the anodization time increases, the thinnest 

films show a large enhancement in oxide-feature height whereas the behavior of the other films 

is unchanged, demonstrating the role of the film/substrate interface. Under the same conditions, 

the height of features grown on ZrN films is greater than for those grown on Zr films, indicating 

that nitrogen plays a role in the oxidation process. 

As an example of the power of SPM nanolithography in kinetic studies, Figure 2 demonstrates 

that both the vertical and lateral growth rates of the oxides formed on Zr and ZrN films with 

AFM decrease rapidly with increasing time. Power-law relationships of height versus AFM 

anodization time are also found for AFM oxidation of Ti, TiN, Si, and Si3N4 surfaces. This type 

of power-law behavior is due in part to the space charge built up in the early period of local 

oxidation using dc voltages. Space charge is a consequence of unbalanced ionic reactants and 

products, mainly O- and H-containing species, generated during oxidation. This in turn leads to 

oxides with a lower density than expected. 

We also find that the height of the oxide features for the Zr and ZrN systems increases linearly 

with humidity at long anodization times (t > 200 s), which is also observed for the anodic 

oxidation of Ti films. For a given tip-surface distance and AFM tip geometry, the equilibrium 

shape of the meniscus depends on the humidity and the applied voltage. Since the local reaction 

volume is defined by the meniscus, it is important to distinguish material-dependent factors that 

contribute to the growth rate from those depending solely on the meniscus. To demonstrate this 

distinction, we take the long-time height and width data of Figure 2 and re-plot these in Figure 3 

versus relative humidity. Clearly, material dependence can be observed in the height data in the 

top of Figure 3, whereas the bottom of Figure 3 demonstrates that the width data are independent 

of film composition or thickness. 
Time (s)

0 100 200 300 400 500

Height (nm)

0

2

4

6

8

10

12

14

16

ZrN 20 nm, 81%

ZrN 20 nm, 55%

ZrN 20 nm, 21%

Zr 6 nm, 43%

Zr 6 nm, 37%

Zr 36 nm, 76%

Zr 36 nm, 60%

Zr 36 nm, 32%

Time (s)

0 100 200 300 400 500

Width (nm)

50

100

150

200

250

300

ZrN 20 nm, 81%

ZrN 20 nm, 55%

ZrN 20 nm, 21%

Zr 6 nm, 43%

Zr 6 nm, 37%

Zr 36 nm, 76%

Zr 36 nm, 60%

Zr 36 nm, 32%

Figure 2. Time dependence of nano-structure growth on Zr and ZrN films 

during DC oxidation at 8 V. 

Although the overall behavior of the growth curve is similar for Zr and ZrN, we see in Figure 3 

that the height of the features grown on ZrN films is consistently greater than those on Zr films, 

roughly by a factor of 2. Previous work with nitrogen-containing species on single crystal 

zirconium indicates that nitrogen atoms can readily displace subsurface oxygen, known to be 

intrinsic to crystalline zirconium, effectively forcing oxygen to the surface where it combines 

with hydrogen during thermal desorption experiments to form water. This desorption of water is 

accompanied by ammonia as well, but disproportionately leaves strongly-bound residual 

nitrogen behind at the surface. We believe that this displacement and water-formation reaction is 

in some sense the reverse reaction of what we observe during AFM nanolithography, where 

oxyanions, driven by an applied electric field, oxidize the zirconium nitride surface. 

Our interpretation is that the presence of nitrogen, even in a relatively strongly-bound state, 

enhances the oxidation of zirconium films because it is able to react efficiently with hydrogen 

and leave the system as a by-product. Evidence for this conjecture is based on our previous 

electric potential imaging of AFM oxides on silicon that demonstrate positive charge buildup 

during oxidation and doping-dependent differences. We attribute this effect to H+

 ions liberated 

from hydroxyl species during oxide growth at the silicon-oxide interface. 

As we progress toward more comprehensive models of AFM-induced oxidation, we find not 

only observations common to many materials systems but also system-specific behavior. It is 

known that Ti films can be oxidized using scanning probe techniques, and our use of chemically 

similar Zr allows us to compare which surface chemical properties of the substrate are most 

important for nanolithography of metals. We see that humidity is important as expected, with an 

increase in feature height with humidity for all Zr and ZrN surfaces studied. We also find that 

very small surface roughness and good control over the applied voltage sequence is critical for 

reproducible results, as our initial attempts to study growth kinetics on lower-quality Zr surfaces 

without a computer-controlled voltage source proved unsuccessful. 

63
Relative Humidity (%)

20 30 40 50 60 70 80

Height (nm)

0

2

4

6

8

10

12

14

16

ZrN 20 nm

Zr 6 nm

Zr 36 nm

Relative Humidity (%)

20 30 40 50 60 70 80

Width (nm)

120

160

200

240

280

320

Data From All Samples

In The Upper Panel 

Figure 3. Humidity dependence of nano-structure growth on Zr and ZrN films 

 during DC oxidation at 8 V. 

Our results for AFM-induced oxide growth on Zr and ZrN surfaces show kinetics similar to 

those seen in other metal and semiconductor systems, with generally similar feature dimensions 

and time/voltage characteristics. This would seem to indicate that the major factors influencing 

the growth are inherent to the method itself, and not to the details of the surface chemistry. This 

strengthens arguments that the AFM-based technique is transferable across materials systems, 

which greatly enhances its potential role in nano-fabrication technology. However, it also leads 

to fundamental questions as to why the results are somewhat insensitive to the surface chemistry 

which we know strongly depends on the material system in other contexts. The answer to these 

questions may lie in the presence of very high electric fields and a resulting dominance by 

hyperthermally-driven surface reactions involving ionic and radical species during AFM 

oxidation. Such species are not present during standard surface kinetic studies, and their 

concentration and flux at the surface even in normal electrochemical measurements is certainly 

much lower than in the nanolithography process. 

Recent Papers Related to AFM and Zirconium Surface Chemistry 

"Ultra-High Vacuum Investigation of the Surface Chemistry of Zirconium", 

Y.C. Kang, M.M. Milovancev, D.A. Clauss, M.A. Lange and R.D. Ramsier, 

J. Nucl. Mater. 281, 57 (2000). 

"SPM Tip-Sample Interactions in Primary Alcohols of Varying Chain Length", 

R.M. Ralich, Y. Wu, R.D. Ramsier and P.N. Henriksen, 

J. Vac. Sci. Technol. A 18, 1345 (2000). 

"The Behavior of Zirconium Surfaces in the Presence of Oxygen, Nitrogen, and 

Hydrogen Containing Adsorbates", 

Y.C. Kang, D.A. Clauss and R.D. Ramsier, 

J. Vac. Sci. Technol. A 19, 1996 (2001). 

64
65

"Nanolithography of Silicon: An Approach for Investigating Tip-Surface Interactions 

During Writing", 

R.D Ramsier, R.M. Ralich and S.F. Lyuksyutov, 

Appl. Phys. Lett. 79, 2820 (2001). 

"The Adsorption of Ammonia on Zirconium Surfaces: Effect of Adsorption Temperature 

on the Thermal Desorption of Water", 

Y.C. Kang and R.D. Ramsier, Vacuum 64, 113 (2002). 

 

"Measuring and Modeling Thermal Fluctuations at Nanometer Length Scales", 

R.M. Ralich, R.D. Ramsier, D.D. Quinn, C.B. Clemons, and G.W. Young, 

Phys. Rev. E 65, 057601 (2002). 

"Optical and Structural Studies of Films Grown Thermally on Zirconium Surfaces", 

J.M. Morgan, J.S. McNatt, M.J. Shepard, N. Farkas and R.D. Ramsier, 

J. Appl. Phys. 91, 9375 (2002). 

"Investigation of Nitric Oxide Adsorption on Zr(0001)", 

Y.C. Kang and R.D. Ramsier, 

J. Nucl. Mater. 303, 125 (2002). 

"The Influence of Subsurface Species on Desorption Kinetics: 18O2/Zr(0001)", 

Y.C. Kang and R.D. Ramsier, 

Appl. Surf. Sci. 195, 196 (2002). 

"Non-destructive Characterization of Films Grown on Zircaloy-2 by Annealing in Air", 

J.S. McNatt, M.J. Shepard, N. Farkas, J.M. Morgan and R.D. Ramsier, 

J. Phys. D: Appl. Phys. 35, 1855 (2002). 

 

"Kinetic Effects of Subsurface Species on Zr(0001) Surface Chemistry", 

Y.C. Kang and R.D. Ramsier, 

Surf. Sci., 519, 229 (2002). 

"Ammonia Adsorption on Zr(0001): The Effect of Electron Bombardment 

on Hydrogen Production", 

N. Stojilovic, Y.C. Kang and R.D. Ramsier, 

Surf. Interface. Anal., Accepted (2002). 

"Electron Bombardment of Water Adsorbed on Zr(0001) Surfaces", 

S. Ankrah, Y.C. Kang and R.D. Ramsier, 

J. Phys. C: Cond. Mater., Under Consideration. 

"Nanoscale Oxidation of Zirconium Surfaces: Kinetics and Mechanisms", 

N. Farkas, G. Zhang, E.A. Evans, R.D. Ramsier and J.A. Dagata, 

J. Vac. Sci. Technol., Under Consideration. 
66

Recent Students Working with AFM and Zirconium Surface Chemistry 

Zr(0001) Thermal Surface Chemistry 

Yong-Cheol Kang – Ph.D. Chemistry 

Mike Milovancev – M.S. Physics 

Doug Clauss – B.S. Natural Sciences 

Matt Lange – B.S. Physics 

Electron Bombardment Effects: NH3/Zr(0001)

Nenad Stojilovic – M.S. Physics 

Electron Bombardment Effects: D2O/Zr(0001)

Seth Ankrah – M.S. Physics 

SPM Nanolithography of Zr and ZrN 

Guanghai Zhang – Ph.D. Chemical Engineering 

Natalia Farkas – M.S. Physics 

Kevin Donnelly – B.S. Biomedical Engineering and Physics 

Zircaloy Oxidation and Phosphonate Adsorption 

Matt Shepard – B.S. Physics (Honors) 

Jeff Comer – B.S. Physics (Honors) 

Jeremiah McNatt – B.S. Physics (Honors) 

Jess Morgan – B.S. Physics (Honors) 

 

Zircaloy Oxidation and Bacterial Adhesion 

Tracie Kittinger – B.S. Microbiology 

Brad Buczinsky – B.S. Microbiology (Honors) 

Applications of AFM 

Mike Ralich – M.S. Physics 

Yue Wu – M.S. Physics 
67

Status of the EU NANOMASS Project 

Zachary James Davis*

, Gabriel Abadal**, Esko Forsén*, Ole Hansen*, F. Campabadal***, E. Figueras***, J. 

Esteve***, J. Verd**, Francesc Pérez-Murano***, Xevi Borrisé**, Sara G. Nilsson , Ivan Maximov** **, Lars 

Montelius , Núria Barniol**  and Anja Boisen* 

Mikroelektronik Centret, Denmark Technical University, 2800 Lyngby, Denmark*

Dept. Enginyeria Electrònica, Universitat Autònoma Barcelona, E- 08193 Bellaterra, Spain**

Institut de Microelectrònica Barcelona (IMB-CNM), Campus UAB, 08193 Bellaterra, Spain***

Solid State Physics & The Nanometer Consortium, University of Lund, Sweden****

The growing need for faster, cheaper and more sensitive sensors is pushing the world of MEMS into the nano 

regime (NEMS). This paper presents the fabrication and characterization of a mass sensor, which consists of a 

nano-sized cantilever fully integrated with standard CMOS circuitry. The cantilever is electrostatically excited 

laterally into resonance and the cantilever’s vibrational amplitude is monitored by measuring the capacitance change 

between the vibrating cantilever and a fixed parallel electrode with integrated CMOS circuitry. The concept of the 

sensor can be seen in figure 1. By monitoring the change in the cantilever’s resonant frequency, a mass change of 

the cantilever can be measured. Compared to other groups [1,2] this device is very compact, due to the integrated 

readout, and well suited for both vacuum and gas measurements. 

The EU NANOMASS project is a joint collaboration between four European research institutes, MIC in Denmark, 

UAB and CNM located in Barcelona, Spain and Lund University in Sweden. The design, fabrication and testing of 

the CMOS circuitry is performed by UAB and CNM while the nanofabrication technologies are provided by MIC 

and Lund. One of the main objectives of the project is to compare AFM and e-beam lithography techniques. 

The fabrication process is seen in figure 2. The fabrication of the cantilever is performed as a post process module 

on pre-fabricated CMOS chips. The CMOS technology is a standard twin well, 2-poly, 2-metal technology. The 

cantilever is fabricated using the bottom poly0 layer, which is highly doped. The first step of the fabrication is 

opening a hole in the CMOS passivation layer and dry etching through the top poly1 layer (figure 2a). Then a mask 

definition step is performed (Figure 2b). Three different lithography techniques are being investigated, which are 

laser, e-beam and AFM lithography. Results of cantilever fabrication with laser lithography have been presented at 

Transducers ’01 [3]. With e-beam lithography a 30nm thick Al mask is defined using lift-off technique. With AFM 

lithography a 10nm thick Al layer is locally oxidized with the AFM tip, whereafter the non-oxidized Al is etched 

chemically leaving the Al oxide mask. After the mask definition, the cantilever and parallel electrode are transferred 

to the poly0 by dry etching (figure 2c). Finally, the structures are released in BHF, which etches the underlying 

1μm thick SiO2 layer (figure 2d). In figure 3 images are shown of cantilevers fabricated with (a) laser and (b) ebeam lithography. With laser lithography the width of the cantilever is approximately 800nm and with e-beam the 

width is approximately 400nm. 

Due to the roughness of the poly0 surface AFM nanolithography has unsuccessful on the CMOS chips. However, 

AFM nanolithography has been performed on SOI substrates. In figure 4(a) an AFM image of an AFM oxidized 

etch mask is seen. This pattern was written using non-contact mode nanolithography. The width of the cantilever is 

easily controlled by controlling the tip/sample separation and in this case is approximately 50nm. The gap size here 

is approximately 500nm and the length is 2μm. In figure 4(b) a finished nanocantilever is shown. First the AFM 

written mask is developed by etching the non-oxidized Al away is a wet Al etch. Then the top Si layer is 

anisotropically etched down to the oxide with reactive ion etching (RIE). And finally the Si structure is released by 

wet etching the oxide in BFH. As seen in the SEM image, the tip of the cantilever is sticking to the surface of the 

underlying substrate. This is a major problem and we are working on a solution based on encapsulating the 

cantilever in resist directly after underetching and then releasing the cantilever in a dry O2 etch. The theoretical 

mass sensitivity, for the nanocantilever shown in figure 4(b), is approximately 10-18g/Hz. 

The characterization of the cantilever was performed by wire bonding the chip to a chip holder and mounting it onto 

an AFM microscope. The AFM microscope is used to image the cantilever during excitation and for unsticking the 
68

cantilever if it sticks to either the parallel electrode or the bottom substrate. Figure 5(a) shows an AFM image of an 

e-beam lithography defined cantilever on a CMOS chip. In figure5(b) is an AFM image of the oscillation amplitude 

of a laser defined cantilever on a CMOS chip. The image is made by scanning the same line across the cantilever 

and sweeping the driving frequency of the AC voltage. It is seen that the oscillation amplitude is approximately 

200nm at the peak resonance. In figure 6 the readout circuitry’s voltage output is shown as a function of the AC 

voltage frequency. The curves are measured with an AC voltage of 7Vpp and a DC voltage of either 18V or 20V. 

For the 20V curve the resonant peak is larger and shifted to a lower frequency. When applying a higher DC voltage 

the force between the static electrode and cantilever increases, increasing the oscillation amplitude and thereby the 

voltage output. Also, the increase in electrostatic force decreases the effective spring constant of the cantilever and 

thus decreases the cantilever’s resonant frequency. For the investigated device a mass sensitivity of approximately 

10-16g/Hz is expected. Presently, applications of the mass sensor as a gas sensor are being pursued. 

 

REFERENCES 

[1] A.N. Cleland and M.L. Roukes, Appl. Phys. Lett., 69 (1996) 2653-2655. 

[2] J. Yang, T. Ono and M. Esashi, Sensors and Actuators, 82 (2000) 102-107. 

[3] Z. J. Davis, G. Abadal, B. Helbo, O. Hansen, F. Campabadal, F. Pérez-Murano, J. Esteve, E. 

Figueras, R. Ruiz, N. Barniol, A. Boisen, Proceedings of Transducers 01, pp. 72-75 (Munich 

2001). 
69

 

Figure 1: Schematic drawing of the mass sensor 

device, based on a laterally vibrating cantilever

Figure 3: Optical and SEM images of devices 

fabricated using (a) laser lithography and (b) ebeam lithography. 

Figure 2: Process sequence for the 

Figure 4: (a) An AFM image of a dry etching mask patterned by AFM 

nanolithography on an SOI substrate. The width of the cantilever is 
 

600 610 620 630 640 650 660 670 680

50

60

70

80

90

100

110

120

130

140

 Vin = 20 VDC + 7 VppAC

 Vin = 18 VDC + 7 VppAC

Vout (mV)

Frequency (kHz)

Figure 6: Electrical readout of the cantilever’s 

oscillation amplitude. 

Figure 5: (a) AFM image of a cantilever device. 

(b) x-scan as function of driving frequency 

showing the resonant peak. 

 

70
 Fabrication of Si nanostuctures by scanning probe oxidation 

and anisotropic wet etching

Forest S.-S. Chien 

Center for Measurement Standards, ITRI, Taiwan 

 This presentation focused on the fabrication of Si nanostructures by scanning probe 

oxidation and anisotropic wet etching, which have a high potential to the applications of nano 

photonic devices. 

 We applied contact mode atomic force microscope (AFM) to produce SiOx on Si 

substrates, where the sample bias is ~8-12 V and the writing speed is ~1-2 μm/s. By taking 

advantage of the material contrast between probe-induced oxide and Si substrate, Si 

nanostructures are made with subsequent wet etching. We used potassium hydroxide (KOH) and 

tetra-methyl ammonium hydroxide (TMAH) solutions for anisotropic wet etching. Both 

solutions have very good Si/SiO2 etch selectivity, and (110)/(111) and (100)/(111) etch 

anisotropy. Note that TMAH is less aggressive to Si, more suitable to make nanostructures. 

 A variety of Si nanostructures were made on different substrates, including isolated Si 

grid of 500 nm x 500 nm pitch on (100)-oriented silicon on insulator (SOI), Fig. 1, grating of 

vertical ridge on bare Si(100), Fig. 2.a, grating of vertical trench on Si3N4/Si(100), Fig. 2.b, and 

grating of vertical ridge on bare Si(110). With the 1D pitch pattern composed of two sets of 

markers (one with a nominal 8 μm pitch, Fig. 3, and the other of 100 nm to 2 μm pitch, Fig. 4), 

we demonstrated the uniformity and placement linearity of probe oxidation on large scale 

patterning over 80 μm × 20 μm. Analyzed by the optical microscope and scanning electron 

microscope at NIST, the linearity is less than 2% for the pitch of 100 nm to 8 μm. The Si ridges 

of 40 nm linewidth and 100 nm pitch was achieved to prove the capability of ultra-high 

resolution of this method, comparable to the existing electron beam lithography. 

 We observed the evolution of hexagonal pits on Si(110) with a oxide grid mask and the 

dependence of hexagonal pits on the shape and orientation of oxide grids. It indicated that the 

etching anisotropy at nano scale is different from its typical behavior at larger scale. The etching 

is preferential at the direction where the oxide pattern and the slow-etched (111) plane are less 

correlated. 

(a) (b)

 To make a device composed of micron scale and nano scale structures, it is necessary to 

combine the probe oxidation and photolithography. A multilevel Si structure is made to 

demonstrate the possibility of such a combination, which is meaningful to fabricate a functional 

photonic devices, Fig. 5. For instance, a waveguide grating can be made, where the waveguide is 

defined by photolithography and the fine grating is defined by probe oxidation. 

 Scanning probe oxidation cooperated with anisotropic wet etching is a promising 

approach for prototyping photonic devices, since it delivers the uniformity and smoothness and 

positioning accuracy, which are essential to the function of photonic devices. On the other hand, 

it is a low-cost and rapid-turnaround method for developing Si nanostructures. 

71
240 nm

150 nm

Fig. 2. (a) vertical ridge on

Si(100) and (b) vertical trench on

Si3N4/Si(100). 

500 nm

500 nm

Fig. 1. Si grid on SOI. 

Fig. 3. Markers of a nominal 8 μm pitch. 

80 μm

20 μm

8 μm

Fig. 4. Fine markers. 

1 μm

Fig. 5. Multilevel structures 

72
Overview of the NIST Combinatorial Methods Center (NCMC) 

Michael J. Fasolka, Polymers Division, NIST 

Combinatorial techniques offer a highly parallel, automated, and often miniaturized route for 

experimentation that allows hundreds or thousand of specimens to be fabricated and analyzed in 

a rapid and efficient fashion. Such techniques provide opportunities to significantly boost 

productivity, increase the scope of parameter-space exploration and enhance the understanding 

of complex systems in a variety of scientific and technological disciplines. Indeed, in recent 

years the unmitigated success of combinatorial and high-throughput methods in the 

pharmaceutical industry and the worldwide genomics effort has spurred researchers in the 

materials science and chemical industries to reconsider their reliance on traditional “one-at-atime” experimental approaches to product and knowledge discovery. However, several 

challenges impede the successful adaptation of combinatorial methods in these arenas. For 

example, pharmaceutical combi models, which emphasize product discovery, often do not 

provide insight into the structure/property/processing relationships that are central to materials 

research. In addition, techniques and instrumentation explicitly suited to the high-throughput 

fabrication and analysis of combinatorial libraries of interest to materials scientists need to be 

developed. Moreover, many institutions interested in acquiring combinatorial methods require 

information on how to incorporate such strategies into their research program. 

In response to these technical and educational needs, the NIST Combinatorial Methods Center 

(NCMC) was formally established in January 2002. A NIST-wide effort centered in the 

Polymers Division, the NCMC includes contributions from throughout MSEL and several other 

laboratories including MEL, BFRL, Physics, and CSTL. The NCMC’s mission is twofold. As a 

research program focused upon the creation of novel specimen libraries and instrumentation, the 

NCMC advances the state-of-the-art in combinatorial methods geared towards materials research 

and discovery. A complimentary effort is the NCMC’s outreach program, which serves to 

disseminate NCMC research products, instrument design, best protocols and practices and other 

information relevant to the combi method. This organization also provides an effective means 

by which industrial needs are gauged. 

NCMC Gradient Research and Nanotechnology 

NCMC combinatorial methods research is rooted in the socalled gradient approach. The core of gradient combi is the 

gradient specimen. These samples continuously vary in one 

property (e.g. film thickness) along a spatial coordinate over a 

prescribed range. By arranging two such gradients (e.g. 

thickness and temperature) in an orthogonal manner, a gradient 

library is created that exhibits every possible combination of 

properties within the scope of the constituent gradient 

specimens. Gradient libraries are particularly useful to 

materials scientists because they offer a convenient and 

thorough way in which to map parameter space. In addition, 

Scheme 1: Gradient 

73 combinatorial library 
74

gradient libraries are especially amenable to examination via microscopy and micro-analysis, 

which facilitates the illumination of structure-property relationships. Finally, as opposed to 

many robotics-oriented discrete approaches, gradient techniques can offer a cost effective way 

of performing combinatorial studies, making them attractive to a wider range of institutions. 

As they are the basic unit of gradient libraries, many NCMC research efforts concentrate upon 

the development of novel gradient specimens and processes, with polymer science being a 

focus in recent years. NCMC methods for producing gradients in film thickness (20 nm to 

250 nm range), composition (dilute solutions, including nanoparticles) and temperature (-5 °C 

to 250 °C) provide a foundation for combinatorial studies of materials properties and 

processing. This year, several new techniques were added to the NCMC repertoire. New 

instrumentation for generating gradients in UV-radiation exposure was central to this effort. 

Here, a UV slit-source is accelerated across a planar specimen. When this source is held in 

close proximity (< 5 mm) to the sample UV-generated ozone can chemically modify SAM 

treated sample surfaces, resulting in a gradient in surface energy and/or chemical 

functionality. Depending upon the SAM employed, such surface energy gradients can span 

70° in water contact angle (20 J/m2

 to 78 J/m2). Larger source/sample distances are effective 

in producing gradients in light-induced crosslinking, polymerization and degradation. Since 

the degree of UV exposure is controlled through stage motion, this instrument is particularly 

versatile. Gradient profile, depth and steepness are easily tuned for a wide range of 

applications. One of these is a gradient specimen useful for gauging the chemical sensitivity 

of Chemical Force Microscopy (CFM). Here, a hydrophobic SAM is microcontact printed 

onto the substrate to form mm-scale lines. Subsequent filling with a hydrophilic SAM results 

in a chemically heterogeneous surface. When a gradient in UV exposure is applied to this 

specimen, the chemical contrast between the hydrophilic and hydrophobic domains is reduced 

along the gradient direction, i.e. the hydrophobic SAM is gradually converted into hydrophilic 

species. Performing CFM along this gradient, which can be calibrated with spectroscopic 

techniques or water contact angle, gives a measure of the probe sensitivity and a more 

quantitative aspect to CFM images. 

In another new technique, gradients in the height of topographic surface features can be 

created. Here, topographic gratings are lithographically etched into wedges of silsesquioxane 

“spin-on” oxides created via flow-coating. The resulting patterns, with heights ranging from 

30 nm to 150 nm, provide a combi strategy for examining topography-mediated templating of 

film properties, for example the self-assembly of block copolymers and photonic colloids. 

Given their scope, many NCMC techniques are well geared to advance nanotechnology, 

MEMS and other thin next-generation devices. In order to best harness these techniques for 

higher-tech aims, during the past year, the NCMC has been collaborating with MEL to 

produce a host of tools, including lithographic masks and imprinting approaches, that 

combine the precision and manufacturing expertise found in MEL with the combi- approach 

to experimentation. For more information about the NIST Combinatorial Methods Center, 

including a list of NCMC publications relevant to this article, please visit our web site at 

http://www.nist.gov/combi. 
75

Nanolithography and Microfluidics: A Manufacturing Perspective 

T.L. Schmitz1

, J.A. Dagata2 , B. Dutterer2 

1

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, USA 2

National Institute of Standards and Technology, Gaithersburg, MD, USA 

Abstract 

Microfluidic systems for analytical, medical, and sensing applications integrate optical or electrical 

readouts in low-cost, low-volume consumption systems. Embedding chemically functionalized 

templates with nanoscale topography within these devices links the scale at which molecular 

recognition and self-organization occurs and the macroscopic layout of fluid channels, mixing 

volumes, and detection regions. This paper addresses a path toward standardization of 

manufacturing procedures for microfluidic devices through: 1) scanning probe lithography to 

produce sub-50-nm scale features in a silicon master; 2) master replication in plastics by hot 

embossing; and 3) the development of a generic microfluidic experimental platform that orients 125 

micrometer channels embossed in a poly(vinyl chloride) gasket to an array of high-speed machined 

channels and a silicon substrate. 

Introduction 

The use of microfluidic systems in biological, analytical, medical, and sensing applications is 

continually growing. Applications include, for example, studies of synergistic/antagonistic 

interactions between two drug substances and DNA analysis. To this point, many research efforts 

have focused on the ability to either produce sub-micrometer scale features or replicate these 

features in polymers [e.g., 1-7]. However, the manufacture of the platforms where the 

microfluidic experiments are completed and results evaluated has remained primarily a benchtop 

activity with little thought given to standardization. In this paper, we describe initial efforts in the 

development of a suite of manufacturing procedures for the production and rapid replication of 

microfluidic testing platforms. These manufacturing methods include 1) scanning probe 

lithography to produce sub-50-nm scale features on a standard sized silicon master; 2) hot 

embossing for replication of the silicon master, or other larger-scale features (≥100 μm), in 

polymers; and 3) high-speed machining for the production of the microfluidic experimental 

platform, as well as any hot embossing tooling required for larger-scale features. 

MANUFACTURING METHODS 

Prior to providing a description of the standardized microfluidic experimental platform, we 

present an overview of the production methods applied in this research. However, it is expected 

that other capabilities will be added in the future. 
Scanning probe lithography (SPL) 

In this method, an electrical bias is applied between the 

silicon substrate and an atomic force microscope (AFM) 

cantilever tip [8-9]. In the presence of water (as vapor in the 

air or condensation on the silicon surface), an 

electrochemical cell is formed in which the AFM tip serves 

as the cathode, the silicon substrate as the anode, and the 

liquid column as a ‘dielectric bridge’ as shown in Figure 1. 

Anodic oxidation proceeds as the silicon gives up electrons to 

become positively charged and these electrons serve to 

reduce gaseous oxygen in the presence of water to form 

oxyanions (OH-

). The combination of the silicon cations, 

gaseous oxygen, and water yields silicon dioxide and 

AFM 

tip

silicon

oxide

liquid

v(t column

) +

-

Figure 1: SPL 

AFM 

tip

silicon

oxide

liquid

v(t column

) +

-

Figure 1: SPL 

 hydrogen anions. By translating the AFM tip relative to the silicon surface, nanometer scale 

oxide patterns can be formed on the surface of the substrate. SPL therefore serves as a directwriting and resistless prototyping method for nanometer scale devices [10-11]. 

Hot embossing 

Although SPL is useful for producing nanometer scale devices, it is also a slow process. 

Therefore, efficient replication of the features produced on the silicon master in low-cost 

materials is necessary when completing multiple test cycles in a short period of time with one or 

more control variables in, for example, chemical analysis. Traditionally, the replication materials 

have been polymers (e.g., poly(dimethylsiloxane) (PDMS) and poly(methyl methacrylate) 

(PMMA)) because they are generally inexpensive, mechanically robust, and optically transparent 

(to allow in-process viewing). Typical replication methods include casting, injection molding, 

and hot embossing [12]. In this work, we focus on hot embossing of poly(vinyl chloride) (PVC). 

In this technique, the PVC is first heated to its glass transition temperature, and then the desired 

features are forced into the plastic and held for a short time. Our setup included a vacuum 

hotplate to heat and hold the PVC and gravitational mass loading to apply the force. 

High-speed machining 

Significant advancements in high-speed machining (HSM) technology, including new spindle 

designs for higher rotational speed, torque, and power, increased slide speeds and accelerations, 

new machine designs for lower moving mass, and tool material/coating developments, have 

made HSM a viable alternative to other manufacturing processes in many applications. For 

example, HSM has been used extensively in the aerospace industry, where the dramatic increases 

in material removal rates have allowed designers to replace assembly-intensive sheet metal 

build-ups with monolithic aluminum components [13]. HSM has been applied in this research 

due to its inherent flexibility; it can produce features in a number of materials over the full size 

range required for this research (∼100 μm to 10 cm, or roughly 3 orders of magnitude). 

76
STANDARD PLATFORM DEVELOPMENT 

The fundamental requirements for a standardized microfluidic experimental platform include 1) 

the ability to align fluid inputs and outputs to a (patterned) gasket and silicon master; 2) optical 

transparency of the individual components for in-process evaluation; and 3) minimum 

manufacturing cost, time, and difficulty. Figure 2 shows our concept for a prototype flexurebased platform that positions the inlet/outlet flow tubes (FT), fixed with epoxy into holes drilled 

into the PMMA cover, relative to the base using a parallelogram leaf-type flexure arrangement. 

A patterned 1 cm x 2 cm PVC gasket (G) is captured in a well machined into the base. For initial 

testing of laminar flow in micromachined channels, 125 μm wide by 50 μm deep channels (C) 

were machined in the bottom of the well and no silicon master was used, although the design will 

be upgraded and the master added in future iterations. In the following paragraphs, we present 

the details for the prototype platform including critical dimensions, flexure design, surface 

roughness measurements, laminar flow characteristics, and preliminary hot embossing results. 

Flexure

FT G

C

Figure 2: Prototype platform

Flexure design 

The parallelogram leaf-type flexure design was selected to clamp the cover/gasket/base assembly 

due to its ability to provide repeatable, nearly linear motion and its ease of manufacture. The 

flexure dimensions are shown in Figure 3. A zero slope condition at the free end of the flexure 

was obtained by applying the actuation force at a distance of one-half the flexure length from the 

fixed end. Following the analysis of Smith [14], the minimum leaf flexure length to avoid plastic 

deformation, Lmin, parasitic deflection, δx, and actuation force, Fy, were calculated according to 

Equations 1-3, where E is the PMMA modulus (3x109

 Pa), Y is the yield strength (6.7x107 Pa), δy

is the required deflection (0.5 mm), t is the leaf flexure thickness (0.4 mm), w is the total width 

of the two flexure arms (4.0 mm), and L is the length (7.5 mm). The predicted δx value was 

incorporated into the platform design to minimize positioning errors between the flow tubes and 

base. 

mm5.2

3 2

1

Y

δ tE

L y

min = ⎥

⎦

⎤ ⎢

⎣

⎡ = (1) 

mm0.02

5

3

L

δ

δ

2

y

x −= − = (2) 

77
== N 1 3

y

3

y L

wt Eδ

F (3) 

2.0 

mm

2.0 mm x 0.4 mm x 

7.5 mm

Fy

20 

mm

50 mm

2.5 mm

Figure 3: Flexure 

x

y 2.0 

mm

2.0 mm x 0.4 mm x 

7.5 mm

Fy

20 

mm

50 mm

2.5 mm

Figure 3: Flexure 

x

y

Platform surface roughness measurements 

Once the platform cover and base were machined, surface roughness measurements were 

performed using a scanning white light interferometer (5x objective, 1.2 mm x 1 mm field of 

view). Microscopic images of the 125 μm wide by 75 μm deep channels and 800 μm diameter by 

200 μm deep holes machined into the well located in the base are shown in Figure 4. An example 

roughness measurement for a channel bottom is shown in Figure 5 (average roughness for this 

plot is 0.31 μm). 

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.2 0.4 0.6 0.8 1 1.2

Trace length (mm)

Surface height (

μm)

Figure 5: Channel roughness

20x 5x

Figure 4: Microscope images.

78
79

out

B-Green flow 

out

Y flow in B flow in

Y-Green flow

Laminar flow measurements 

To observe flow characteristics in the milled channels, water mixed with yellow (Y) and blue (B) 

dye, respectively, was introduced to the assembled platform via the flow tubes as shown 

schematically in Figure 6 (other flow patterns were also evaluated). The 10x microscope images 

included in this figure show laminar behavior with very little boundary diffusional mixing over 

the short length scales of 12 mm or less used in this research (see the sharp corner at the top T 

junction, for example). The low Reynolds numbers, and subsequent laminar flows, in typical 

microchannels can, in fact, be problematic in situations where mixing is required, such as the 

homogenization of reagents in chemical reactions [3]. An important area of future research for 

SPL is, therefore, the fabrication of structured features that lead to efficient mixing over short 

distances. 

Hot embossing results 

Replication of features in 1 mm thick PVC sheet by hot embossing from both silicon masters and 

larger machined tooling was completed. Macro-pressures of 7x103

 Pa to 14x103 Pa (localized 

pressures under the actual features were much higher, but unknown) were applied at 

temperatures of 90°C to 160°C. 

Microscope images and AFM measurements for 10 μm wide wells in a silicon master and 

corresponding anti-wells in PVC indicate that the lateral dimensions were accurately reproduced 

in the PVC, while the heights were not, i.e., 1100 nm silicon well depths versus 620 nm PVC 

anti-well heights. This is due to the visco-elastic behavior of the PVC and will be the subject of 

Y B

Y B

B

Y

B

Y

Mass

Syring

ee

Figure 6: Laminar flow 

Y flow in B flow in

Y-Green flow 

out

B-Green flow 

out

Y

Y B

Y B

B

B

Y

Mass

Syring

ee

Figure 6: Laminar flow 
future investigations. Figure 8 shows microscope images and AFM measurements for silicon 

posts. Again, it is seen that the heights were not reproduced with high fidelity, i.e., 1080 nm high 

silicon posts versus 740 nm deep PVC anti-posts. Additionally, there was substantial relaxation 

of the PVC within the embossed cavities so that the flat tops of the silicon posts were not 

accurately replicated. 

Distance (μm)

0

325

650

975

00 nm

0 2.66 5.32 7.98 10.64 1

1080

10 μm

Silicon posts

0

25

50

75

0 2 68 5 36 8 04 10 72 13 4

PVC anti- 740 nm

Figure 7: Hot embossed

To test the feasibility of combining hot embossed channels in PVC with high-speed machined 

channels in the platform base to achieve more complicated, multi-level flow patterns, a highspeed machined copper tool was used to emboss a PVC gasket with the geometry. The scanning 

white light interferometer measurements show the tool (80 μm high walls separated by 1 mm) 

and embossed PVC (13 μm deep channels); the PVC relaxation at the larger scale is clearly quite 

severe. This patterned gasket was then sealed against the platform base and fluid flow was 

introduced (again using syringes as demonstrated in Figure 6) to the crossed pattern shown in 

Figure 8. In the left two microscope images, yellow fluid flow was coupled into both inputs and 

yellow fluid flow was observed at both outputs. In the right two images, yellow was input to the 

left hand port and blue to the right hand port. In this case, yellow flow was seen at the left hand 

output and blue-green flow was observed from the right hand output. 

summary 

In this paper, we described initial efforts toward the development of a suite of manufacturing 

methods for the production and rapid replication of microfluidic testing platforms. We presented 

experimental results for the production of patterned silicon masters using scanning probe 

lithography (SPL) and the replication of these features in thin PVC sheet using hot embossing. 

We also showed embossing results for larger features reproduced from high-speed machined 

copper tooling. In both situations, it was seen that visco-elastic relaxation of the PVC sheet led 

80
Embossed 

gasket 

channels

4.5 

mm

Machined 

channels in 

Y base

input

Y 

input

Y 

input

B 

input

Figure 10: Gasket/machined 

channel flows

Embossed 

gasket 

channels

4.5 

mm

Machined 

channels in 

Y base

input

Y 

input

Y 

input

B 

input

Figure 10: Gasket/machined 

channel flows

8

Embossed 

gasket 

channels

4.5 

mm

Machined 

channels in 

Y base

input

Y 

input

Y 

input

B 

input

Figure 10: Gasket/machined 

channel flows

Embossed 

gasket 

channels

4.5 

mm

Machined 

channels in 

Y base

input

Y 

input

Y 

input

B 

input

Figure 10: Gasket/machined 

channel flows

8

to low fidelity reproduction of feature heights, although it was more severe for the larger 

structures. We also showed laminar flow characteristics in high-speed machined 125 μm wide 

channels using a prototype microfluidic testing platform. Finally, we demonstrated flow through 

a combination of embossed channels in a PVC gasket and machined channels in the platform 

base. 

acknowledgments 

T.L. Schmitz gratefully acknowledges partial financial support for this research through a grant 

from the National Institute of Standards and Technology. 

81
82

references 

[1] Dasgupta, P., Surowiec, K., Berg, J., 2002, Flow of Multiple Fluids in a Small Dimension, Analytical Chemistry,

74/7: 208A-213A. 

[2] McDonald, J., Chabinyc, M., Metallo, S., Anderson, J., Stroock, A., Whitesides, G., 2002, Prototyping of 

Microfluidic Devices in Poly(dimethylsiloxane) Using Solid-Object Printing, Analytical Chemistry, 74/7: 1537-

1545. 

[3] Stroock, A., Dertinger, S., Ajdari, A., Mezić, I., Stone, H., Whitesides, G., 2002, Chaotic Mixer for Microchannels, 

Science, 295: 647-651. 

[4] Tamanaha, C., Whitman, L., Colton, R., 2002, Hybrid Macro-micro Fluidics System for a Chip-based Biosensor, 

Journal of Micromechanics and Microengineering, 12: N7-N17. 

[5] Lin, L., Cheng, Y.T., Chiu, C.J., 1998, Comparative Study of Hot Embossed Micro Structures Fabricated by 

Laboratory and Commercial Environments, Microsystem Technologies, 4: 113-116. 

[6] Tan, H., Gilbertson, A., Chou, S., 1998, Roller Nanoimprint Lithography, Journal of Vacuum Science and 

Technology B, 16/6: 3926-3928. 

[7] Stix, G., 2002, Soft Manufacturing, Scientific American, 287/2: 30-31. 

[8] Chien, F.S., Hsieh, W.F., Gwo, S., Vladar, A.E., Dagata, J.A., 2002, Silicon Nanostructures Fabricated by 

Scanning Probe Oxidation and Tetra-methyl Ammonium Hydroxide Etching, Journal of Applied Physics, 91: 

10044. 

[9] Matsumoto, K., Gotoh, Y., Maeda, T., Dagata, J.A., Harris, J., 2000, Room-temperature Single-electron Memory 

Made by Pulse-Mode Atomic Force Microscopy Nano Oxidation Process on Atomically Flat α-Alumina 

Substrate, Applied Physics Letters, 76/2: 239-241. 

[10] Dagata, J.A., 1995, Device Fabrication by Scanned Probe Oxidation, Science, 270: 1625-1626. 

[11] Dagata, J.A., Schneir, J., Harary, H.H., Evans, C.J., Postek, M.T., Bennett, J., 1990, Modification of HydrogenPassivated Silicon by a Scanning Tunneling Microscope Operating in Air, Applied Physics Letters, 56: 2001-

2003. 

[12] Gale, M.T., 1997, Replication, in Micro-optics, Elements, Systems, and Applications, H.P. Herzig, Ed., Taylor 

and Francis, London. 

[13] Halley, J., Helvey, A., Smith, K.S., Winfough, W.R., 1999, The Impact of High-Speed Machining on the Design 

and Fabrication of Aircraft Components, Proceedings of the 17th Biennial Conference on Mechanical Vibration 

and Noise, 1999 ASME Design and Technical Conferences, September 12-16, Las Vegas, Nevada. 

[14] Smith, S.T., 2000, Flexures, Gordon and Breach Science Publishers, London. 
83

 PARTICIPANTS LIST 
84
85

PARTICIPANTS LIST 

Francesc Perez-Murano 

Institut de Microelectronica de Barcelona (IMB) 

Centro Nacional Microelectrónica (CNM) 

Campus Universitat Autonoma de Barcelona 

E-08193 Bellaterra. SPAIN 

Phone: (34)93 594 77 00 (ext. 1206, 1054) 

Fax: (34) 93 580 14 96 

e-mail: Francesc.Perez@cnm.es 

Zachary Davis 

Mikroelektronik Centret 

Technical University of Denmark, Bldg. 345e 

Dk-2800 Lyngby, Denmark 

Tel. direct: +45 4525 5733 

Fax: +45 4588 7762 

e-mail: zd@mic.dtu.dk 

Hiroshi Yokoyama 

Nanotechnology Research Institute 

National Institute of Advanced Industrial Science and 

Technology (AIST) 

1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan 

Phone: +81-298-61-5538, FAX: +81-298-61-5548 

E-mail: yokoyama-hiroshi@aist.go.jp 

Kuramochi Hiromi 

Nanotechnology Research Institute 

National Institute of Advanced Industrial Science and 

Technology 

Research Consortium for Synthetic Nano-Function 

Materials Project 

Tsukuba Central 4, 1-1-1 Higashi, Tsukuba, Ibaraki 

305-8562, Japan 

TEL: +81-(0)298-61-5080 ex.55014 

FAX: +81-(0)298-61-2786 

Email: hiromi.kuramochi@aist.go.jp 

Dr. Takashi TOKIZAKI 

Near-Field Nano-Engineering Group 

Nanotechnology Research Institute 

National Institute of Advanced Industrial Science and 

Technology 

AIST Tsukuba Central 2, Tsukuba, Ibaraki 305-8568, 

JAPAN 

Phone: +81-298-61-5395 

Fax: +81-298-61-5400 

e-mail: t-tokizaki@aist.go.jp 

Forest Chien 

Center for Measurement Standards 

Industrial Technology Research Institute 

E200 Bldg 16 321 Kuang Fu Rd Sec 2 

Hsinchu Taiwan 300 

TEL: 886-3-5743730 

FAX: 886-3-5724952 

Email: forestchien@itri.org.tw 

Shangjr Gwo, 

Department of Physics 

National Tsing-Hua University 

Hsinchu 300, Taiwan 

886-3-5742636 

886-3-5723052 

gwo@phys.nthu.edu.tw 

Gerald W. Young 

Department of Mathematics & Computer Science 

Ayer Hall 230 University of Akron 

Akron OH 44325-4002 

330-972-5731 tel 

330-374-8630 fax 

gwyoung@uakron.edu

Rex D. Ramsier 

Departments of Physics, Chemistry, and Chemical 

Engineering 

Ayer Hall Room 111 

250 Buchtel Commons 

The University of Akron 

Akron, OH 44325-4001 

USA 

ph: 330-972-4936 

fax: 330-972-6918 

e-mail: rex@uakron.edu 

Tony Schmitz 

University of Florida 

Department of Mechanical and Aerospace 

Engineering 

237 MEB 

Gainesville, FL 32611 

Phone: (352) 392-8909 

Fax: (352) 392-1071 

Email: tschmitz@ufl.edu
86

John A. Dagata 

Precision Engineering Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (8212) 

Gaithersburg MD 20899-8212 

Phone: 301-975-3597 

Email: john.dagata@nist.gov

Michael Fasolka 

NIST Combinatorial Methods Center 

Polymers Division (854) 

National Institute of Standards and Technology 

100 Bureau Drive, Stop 8542 

Gaithersburg MD 20899-8212 

Phone: 301-975-8526 

Email: Michael.fasolka@nist.gov

Joseph Fu 

Precision Engineering Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (8212) 

Gaithersburg MD 20899-8212 

Phone: 301-975-3495 

Email: joseph.fu@nist.gov

Dale Hall, Director 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (8200) 

Gaithersburg MD 20899-8200 

Phone: 301-975-3400 

Email: dale.hall@nist.gov

John Kramar 

Precision Engineering Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (8212) 

Gaithersburg MD 20899-8212 

Phone: 301-975-3447 

Email: john.kramar@nist.gov 

Kevin Lyons 

Manufacturing Systems Integration Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (8263) 

Gaithersburg MD 20899-8263 

Phone: 301-975-6550 

Email: Kevin.lyons@nist.gov

Michael Postek 

Nanoscale Metrology Group 

Precision Engineering Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (8212) 

Gaithersburg MD 20899-8212 

Phone: 301-975-2299 

Email: michael.postek@nist.gov 

Richard Silver 

Precision Engineering Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (8212) 

Gaithersburg MD 20899-8212 

Phone: 301-975-5609 

Email: Richard.silver@nist.gov

John Suehle 

Semiconductor Electronics Division 

Electrical and Electronics Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (812) 

Gaithersburg MD 20899-812 

Phone: 301-975-2247 

Email: john.suehle@nist.gov

Dennis Swyt, Chief 

Precision Engineering Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (8210) 

Gaithersburg MD 20899-8210 

Phone: 301-975-3463 

Email: dennis.swyt@nist.gov

Xianfan Xu, Associate Professor 

School of Mechanical Engineering 

Purdue University 

West Lafayette, IN 47907 

Phone: (765) 494-5639 

Fax: (765) 494-0539 

URL: http://widget.ecn.purdue.edu/~xxu

Clayton Teague, Chief 

Manufacturing Metrology Division 

Manufacturing Engineering Laboratory 

National Institute of Standards and Technology 

100 Bureau Drive Stop (8220) 

Gaithersburg MD 20899-8220 

Phone: 301-975-6600 

Email: clayton.teague@nist.gov