IN THIS ISSUE
 

From the Director | 2 

A First: Metal-Organic 

Frameworks that are 

Electrically Conducting | 3 

Frequency Conversion to the 

Telecommunications Band 

using a Nanophotonics 

Interface | 4 

Review of Atomic-Level 

Stick-Slip Behavior | 4 

Now You See It: Electromagnetically Induced 

Transparency in a Silicon 

Nitride Optomechanical Crystal | 5 

Explaining Interactions in Silicon 

Photonic Microresonators | 6 

Characterizing Solar Cells using 

a Low-Energy Electron Beam | 7 

Tests Explore the Safety of 

Nanotubes in Modern Plastics | 8 

A Framework for Understanding 

Current-Switched Magnetic 

Devices | 9 

Using Domain Wall Chirality 

for Storing Information | 10 

Lloyd Whitman serving as 

Interim Director of NNCO | 10 

Coming Soon: New Tools in 

the NanoFab | 11 

Organizational News | 12 

EDITOR | 

ROBERT RUDNITSKY 

ADDITIONAL CONTRIBUTORS | 

MARK ESSER 

CHAD BOUTIN 

GRAPHIC DESIGN | 

KRISTEN DILL 

DISCLAIMER | Certain commercial equipment, 

and software, are identified in this documentation 

to describe the subject adequately. Such 

identification does not imply recommendation 

or endorsement by the National Institute of 

Standards and Technology, nor does it imply that 

the equipment identified is necessarily the best 

available for the purpose. 

FROM THE 

DIRECTOR 

This issue, I’d like to devote my column to answering the most common
 

questions we get asked about the CNST. Then, I’ll have a few
 

questions of my own!
 

Question: I do not have any ongoing collaborations or projects at NIST 

and have never worked there. I don’t even know anyone at NIST. Can I still use the NanoFab? 

Answer: This is probably our most frequently asked question and I understand why it comes about. 

A common motivation for collaboration is gaining access to needed instrumentation. But the whole 

purpose of the NanoFab is to allow seamless access without any requirement for collaboration. 

Our state-of-the-art equipment is there for your use; just contact the NanoFab Manager (Vincent 

Luciani, nanofab@nist.gov) or user office (nanofabuseroffice@nist.gov) to get started. 

Question: Great! So access to the NanoFab is easy! How can the other part of CNST, the NanoLab, 

help me? 

Answer: In the NanoLab, the CNST research staff develops next generation instruments and fabrication 

processes that go beyond the commercial state-of-the-art tool set available in the NanoFab. Think 

of the NanoFab as being akin to a world-class hospital, where elaborate and expensive equipment 

is available and where the support staff is top-flight. The NanoLab would then be closer to 

a clinical trial, where you work hand-in-hand with our multidisciplinary researchers trying to 

advance the state-of-the-art. Generally, NanoLab interactions are done on a collaborative, no-fee 

basis. 

Question: So, if I collaborate with somebody in the NanoLab, then I get free access to the NanoFab, right? 

Answer: Nope. In order to be fair and to keep the costs for users as low as possible, everybody pays the 

same rates for accessing the NanoFab, including our own NanoLab researchers. 

Question: How hard is it to get access to the NanoFab? How long will it take me? 

Answer: We try to make it as easy as possible, requiring only a short form to be submitted. Generally 

access is within two weeks and we have done it faster when necessary. 

Okay, now for you! 

Question: How are we doing? 

Question: If you have used our facilities, was your experience positive? If we could do better, what would 

you suggest? What capability or tool do you need that we lack? 

Question: If you thought about using our facilities but haven’t yet, is there a barrier that we need to know 

about? 

I’d love to hear any comments you might have, positive or negative. Please drop me a note at 

Robert.Celotta@NIST.gov. 

Robert Celotta 

2 
3 

 

 

BREAKTHROUGH: METAL-ORGANIC FRAMEWORKS THAT ARE ELECTRICALLY 

CONDUCTING 

Scientists from the CNST and Sandia National 

Laboratories have added something new to a 

family of engineered, high-tech materials called 

metal-organic frameworks (MOFs): the ability to 

conduct electricity. This breakthrough—conductive 

MOFs—has the potential to make these already 

remarkable materials even more useful, particularly 

for detecting gases and toxic substances. 

MOFs are three-dimensional crystalline materials 

with nanoscale pores made up of metal ions linked 

by various organic molecules. MOFs have huge 

surface areas, and scientists can easily control 

the size of their pores and how the pores interact 

with molecules by tinkering with their chemistries. 

These characteristics make them ideal for use as 

catalysts, membranes, or sponges for gas storage 

or for drug delivery, among other applications. 

Thousands of new MOF structures are discovered 

and characterized each year. While they come in a 

dizzying array of chemistries and structures, none 

of them conducts electricity well. The CNST/Sandia 

team developed a method to modify the electrical 

conductivity of MOF thin films and to control it over 

six orders of magnitude. Their findings appear in 

the journal Science. 

“MOFs are typically extremely poor electrical 

conductors because their constituent building 

blocks, the organic linkers and the metal ions, 

don’t really talk to each other in terms of electrical 

conduction,” says Andrea Centrone, a project 

leader in the CNST Energy Research Group (ERG). 

“Our work points to a way of controlling and 

Credit: M. Foster/Sandia National Labs

Schematic showing electron-sharing tetracyanoquinododimethane molecules bound to copper ions in 

the framework, enabling electrical conductivity in MOF materials. The dotted white arrows illustrate the 

increasing their conductivity.” 

The group accomplished this by “infiltrating the 

insulating MOF with redox-active, conjugated guest 

molecules.” They infused and bound electronsharing molecules into MOF thin films to create a 

material that is stable in air and approximately a 

million times more conductive than the unaltered 

MOF. 

“Based on several spectroscopic experiments, 

we believe that the guest molecules serve two 

important purposes: they create additional bridges 

between the metal ions—copper, in this case— 

mechanism of electrical conductivity in these materials. 

and they accept electrical charge,” says ERG 

project leader Veronika Szalai. 

According to Paul Haney, an ERG project leader 

who provided some modeling for the experimental 

data, the arrangement of the guest molecules in 

the MOF creates a unique conductivity mechanism 

while preserving the benefits of the porous MOF 

crystalline structure. 

These porous and conductive MOFs may be the 

first in an entirely new class of materials that 

could be used for sensing, conformal electronics 

(electronics that can bend and conform to 

unusual shapes), and other as-yet-unknown 

applications. 

“Our discovery gives chemists and engineers 

a whole new degree of freedom to tailor these 

materials for their technological applications,” 

says Centrone. “I would not be surprised if 

solar cells could be made using this new class 

of materials.” 

Tunable electrical conductivity in metal-organic framework thin-film devices, A. A. Talin, A. Centrone, A. C. Ford, M. E. Foster, V. Stavila, P. Haney, R. A. Kinney, V. Szalai, F. E. Gabaly, H. P. Yoon, F. Léonard, and 

M. D. Allendorf, Science 343, 66–69 (2014). 
 

 

 

 

 

FREQUENCY CONVERSION TO THE TELECOMMUNICATIONS BAND USING
 

A NANOPHOTONICS INTERFACE
 

Using nanofabricated waveguides in a siliconbased platform, CNST researchers have 

developed a frequency conversion interface 

between the telecommunications wavelength band 

and the optical transition wavelengths found both 

in quantum dots and in naturally occurring atoms. 

Optical frequency conversion is an important 

resource for applications in both classical and 

quantum information processing, where it can link 

components of a system that perform optimally 

at their specific tasks, but operate at different 

wavelengths. 

In this work, the researchers focused on an 

interface between near-infrared wavelengths 

below 1000 nm, where systems like semiconductor 

quantum dots and neutral alkali atoms have their 

optical transitions, and the telecommunications 

band of 1550 nm, which is the lowest loss 

wavelength through which light propagates in 

an optical fiber. To develop this interface, they 

built upon previous work (see the Fall 2012 issue 

of The CNST News) in which they demonstrated 

that a low-noise frequency conversion process 

called four-wave-mixing Bragg scattering 

could be realized in silicon nitride waveguides 

fabricated on a silicon substrate. While that 

work focused on demonstrating conversion over 

a range of a few nanometers with conversion 

efficiencies reaching a few percent, here the 

authors extended the conversion range to nearly 

600 nm. This improvement was made possible 

by the nature of the four-wave-mixing process, in 

which the locations of the two pump fields, input 

signal, and converted signal can be re-arranged 

while preserving the requirements of energy and 

momentum conservation. 

The authors demonstrated that the process was bidirectional (signals can be converted from 980 nm 

to 1550 nm and back), and developed designs to 

interface light at wavelengths all the way down to 

637 nm — characteristic of the nitrogen vacancy 

center in diamond — with the 1550 nm band. All 

samples were fabricated using CNST NanoFab’s 

thermal oxidation, low pressure chemical vapor 

deposition, electron beam lithography, and reactive 

ion etching capabilities. 

Future work will be focused on significantly 

increasing the conversion efficiency levels of these 

devices by optimizing the geometries and using 

resonant cavities. 

Left: Scanning electron micrograph of the crosssection of a silicon nitride waveguide designed 

for the frequency conversion with a simulation 

of the device’s optical field profile superimposed. 

Right: As shown in the schematic, in frequency 

downconversion, an input signal at 980 nm is 

frequency shifted to the 1550 nm wavelength band 

through the application of two strong pump lasers. 

The reverse process of upconversion (shifting 

an input signal from 1550 nm to 980 nm) was also 

demonstrated. 

A chip-scale, telecommunications-band frequency conversion interface for quantum emitters, I. Agha, S. Ates, M. Davanço, and K. Srinivasan, Optics Express 21, 21628–21638 (2013). 

CNST RESEARCHERS PUBLISH REVIEW OF ATOMIC-LEVEL STICK-SLIP
 

BEHAVIOR IN THE ENCYCLOPEDIA OF TRIBOLOGY
 

Researchers from the University of 

Pennsylvania, the University of California, 

Merced, and the CNST have recently published a 

review chapter on stick-slip behavior at the atomiclevel in the Encyclopedia of Tribology. In their 

review, the collaborators describe the present-day 

understanding of the atomic-level process by which 

nanoscale objects interact at sliding contacts. 

Atomic-level stick-slip refers to the behavior 

of a sliding interface, usually an atomic force 

microscope (AFM) tip sliding along a crystalline 

surface, where the tip sticks and then slips 

laterally with respect to the surface. These stickslip events repeat with the periodicity of the 

surface’s atomic lattice. The stick-slip behavior 

of both insulating and conducting materials have 

been studied to reveal interfacial properties, 

including the degree of commensurability (how 

well the two surfaces “fit” together at the atomic 

scale), temperature and load dependencies, and 

variations in contact stiffness. The chapter 

provides a brief overview of related experiments 

and theories and of the different mechanisms that 

contribute to the stick-slip effect. 

The authors end the chapter by describing the 

potential for stick-slip behavior to be used 

in applications that enable highly precise 

manipulation and control of surface or interfacial 

forces, that allow nanoscale friction to be 

switched off and on, and that employ stick-slip as 

a ratcheting mechanism for nanoscale positioning. 

Atomic-level stick-slip, R. W. Carpick, A. Martini, and R. J. Cannara, in Encyclopedia of Tribology, edited by Q. J. Wang and Y.-W. Chung (Springer, New York; London, 2013), p. 140–148. 

4 
 

 

 

 

NOW YOU SEE IT: ELECTROMAGNETICALLY INDUCED TRANSPARENCY IN A
 

SILICON NITRIDE OPTOMECHANICAL CRYSTAL
 

Researchers from the CNST have observed 

electromagnetically induced transparency 

at room temperature and atmospheric pressure 

in a silicon nitride optomechanical system. This 

work highlights the potential of silicon nitride as a 

material for producing integrated devices in which 

mechanical vibrations can be used to manipulate 

and modify optical signals. The ability to 

harness the radiation-pressure-based interaction 

between light and mechanical vibrations in these 

devices could lead to applications in optical 

communications and information processing such 

as optical wavelength conversion and optical 

signal storage. 

Using the electron beam lithography system 

and reactive ion etcher available to users at the 

CNST NanoFab, the researchers produced a line 

of oval holes with dimensions of a few hundred 

nanometers on a 700 nm wide, 350 nm thick 

suspended silicon nitride beam. The finished 

structure is called a nanobeam optomechanical 

crystal, and is designed to have complementary 

mechanical and optical properties. 

When near-infrared laser light is injected into 

the optomechanical crystal, it becomes confined 

within the etched, suspended beam, within a 

micrometer-scale region halfway along its length. 

The sidewalls of the optical confinement region 

mechanically expand and contract, vibrating 

at microwave frequencies, forming a so-called 

breathing mechanical mode. Energy from this 

breathing mode is added to the stored light, 

resulting in the generation of a new light signal 

with a slightly different color (called the anti-Stokes 

wavelength). This new light signal is also confined 

within the nanobeam. If an additional probe 

laser light, now at the anti-Stokes wavelength, 

is also injected into the crystal, it interferes with 

the generated optical signal. This interference 

causes the optomechanical crystal, which 

originally reflects back light at the anti-Stokes 

wavelength, to become transparent at that color. 

This phenomenon, called electromagnetically 

induced transparency (EIT), has recently been 

observed in a handful of cavity optomechanical 

systems at telecom and visible wavelengths. For 

the first time, the researchers demonstrated the 

phenomenon at a near-infrared wavelength with 

the system operating at room temperature and 

atmospheric pressure and using only moderate 

optical power. 

This result was made possible by designing the 

system to use radiation pressure to achieve a 

strong interaction between the stored light and 

mechanical vibrations of the nanobeam, and 

by fabricating the device from silicon nitride, a 

common material in chip-scale devices which 

is optically transparent over a broad range 

of wavelengths. 

The device demonstrates that optics and 

mechanics can interact within the silicon nitride 

platform. It is a first step towards applications that 

leverage this interaction, including wavelength 

conversion in which widely spaced optical 

wavelengths are connected through interaction 

with the mechanical system. Future work will 

focus on such wavelength conversion, connecting 

near-infrared wavelengths planned for quantum 

information applications, infrared wavelengths 

used for telecommunications, and possibly even 

microwave frequencies used in superconducting 

quantum circuits. 

The team included researchers from the CNST, 

the University of Maryland, and the California 

Institute of Technology. 

Top: Schematic of the crystal geometry, overlaid with a simulation of an optical resonance. Middle: Schematic showing a mechanical breathing mode. Bottom: Scanning electron micrograph of 

a silicon optomechanical crystal. 

Si3N4 optomechanical crystals in the resolved-sideband regime, M. Davanço, S. Ates, Y. Liu, and K. Srinivasan, Applied Physics Letters, 104 041101 (2014). 

5 
 

 

 

 

 

 

EXPLAINING INTERACTIONS BETWEEN LIGHT, HEAT, AND CHARGE 

CARRIERS IN SILICON PHOTONIC MICRORESONATORS 

I

n the March 28th issue of Physical Review Letters, 

researchers from Northwestern University working 

with researchers from the CNST have presented a 

new analysis that accurately describes the behavior 

of silicon photon microresonators in the nonlinear 

regime, where the amount of light exiting the system 

is not directly proportional to the amount of light 

entering it. Their work includes simple equations to 

provide physical intuition and scaling rules that can 

be used to design new chip-scale photonic devices, 

including optically-driven oscillators and switches 

with potential applications as optical components in 

computing and communication systems. 

The researchers studied a 260 nm thick, 10 μm 

diameter silicon microdisk resonator fabricated in 

the CNST NanoFab and optically probed with a 

continuous infrared laser. When the laser light 

entering the device is at low intensity, the fraction 

of that light exiting the device remains constant over 

time. However, as predicted by the researchers’ 

theory, when the incoming laser intensity is increased 

past a certain threshold, the exiting light begins to 

oscillate. Its intensity varies periodically in time. 

Its frequencies spread across several hundred 

megahertz and consist of narrow spectral lines which 

are called a “frequency comb spectrum” because of 

their resemblance on a graph to the teeth of a comb. 

The system’s behavior is driven by two-photon 

absorption, a process by which light is absorbed in 

the silicon with a strength that depends on the square 

of the incoming light’s intensity. This absorption 

heats the silicon, changes its refractive index, and 

generates free charge carriers (e.g., electrons), which 

further change the refractive index of the silicon and 

cause additional absorption. This overall interplay 

between light, heat, and the free charge carriers 

in the disk leads to a range of interesting behavior, 

including the experimentally observed oscillations 

and frequency comb spectrum. 

The authors’ new theoretical analysis of this 

behavior combines detailed numerical simulations 

with a combination of semi-analytic techniques 

that use approximations to simplify the equations 

describing the system. This analysis yields simple, 

yet experimentally verified, expressions for critical 

quantities such as the frequency comb spacing. 

According to the researchers, future work will 

focus on experimentally studying other regimes 

of device behavior predicted by the theory and 

exploring the potential role of such devices in 

metrology applications. 

Top: Scanning electron micrograph of a silicon photonic microdisk resonator 

which was fabricated in the CNST NanoFab. The researchers studied the 

nonlinear dynamical behavior caused by the interplay between injected 

light, heat, and free charge carriers inside the resonator. Middle: Frequency 

spectrum of light exiting the microdisk resonator, exhibiting a “comb” of 

equally spaced spectral components. Bottom: Image plot showing a series 

of frequency spectra plotted against the detuning, which is the difference 

between the input laser wavelength and the optical cavity wavelength. The 

researchers’ theoretical analysis accurately models the frequency spacing of 

the comb lines and how the spacing changes as a function of detuning. 

Nonlinear oscillations and bifurcations in silicon photonic microresonators, D. M. Abrams, A. Slawik, and K. Srinivasan, Physical Review Letters 112, 123901 (2014). 

6 
7 

 

 

 

CHARACTERIZING SOLAR CELLS WITH NANOSCALE PRECISION USING 

A LOW-ENERGY ELECTRON BEAM 

CNST researchers have demonstrated a new 

low energy electron beam technique and used 

it to probe the nanoscale electronic properties of 

grain boundaries and grain interiors in cadmium 

telluride (CdTe) solar cells. Their results suggest 

that controlling material properties near the grain 

boundaries could provide a path for increasing the 

efficiency of such solar cells. 

Among thin film photovoltaic solar cells, those 

made from CdTe are among the most successful on 

the market. However, the efficiency of commercial 

cells is still less than half of the theoretical 

maximum, and the underlying mechanisms for the 

deficiency are not well understood. CdTe cells 

are believed to lose current at their material grain 

boundaries; however, it has also been suggested 

these grain boundaries have properties that could 

actually improve carrier collection if they were 

better understood. 

Characterization techniques using focused electron 

beams to induce currents are increasingly used for 

investigating the properties of thin film solar cells. 

The measurements are easier using high energy 

electrons, but the higher energy reduces the spatial 

resolution. The researchers extended traditional 

electron-beam-induced current measurements by 

using low energy beams to locally excite the CdTe 

and create current. These beams have a spatial 

resolution of about 20 nm, small enough to map 

the photocurrent response inside the grain interiors 

or at the grain boundaries. The measurements 

were performed on fragments extracted from 

a commercial thin film solar cell. Nanoscale 

electrical contacts were prepared with sizes 

comparable to a single or a few grains, confining 

the current path to sizes relevant for understanding 

current production and loss. 

The measurements show that a large fraction 

of grain boundaries display higher current 

collection than the grain interiors, seemingly 

enhancing device performance. However, using 

2D finite element simulations, the researchers 

demonstrated that these grain boundaries also 

create a large pathway for leakage current, which 

Electron beam induced current (red) superimposed on a scanning electron micrograph (gray). Bright contrast in the vicinity 

of grain boundaries indicates that these regions have higher carrier collection efficiency than the grain interiors. The use of 

electron beam induced current to visualize the behavior of photovoltaic cells at these length scales provides a valuable tool for 

understanding both loss mechanisms within photovoltaic materials as well as internal structures within these materials that may 

lead to higher overall cell efficiencies. 

completely negates the efficiency gains from the 

enhanced photocurrent collection. 

The researchers believe that their technique 

provides a valuable tool for visualizing the 

behavior of photovoltaic cells at the length scales 

needed to understand both loss mechanisms within 

photovoltaic materials as well as internal structures 

within these materials that may lead to higher 

overall cell efficiencies. 

Local electrical characterization of cadmium telluride solar cells using low-energy electron beam, H. P. Yoon, P. M. Haney, D. Ruzmetov, H. Xu, M. S. Leite, B. H. Hamadani, A. A. Talin, and N. B. Zhitenev, 

Solar Energy Materials and Solar Cells 117, 499–504 (2013). 
NEW TESTS EXPLORE SAFETY OF NANOTUBES IN MODERN PLASTICS
 

OVER TIME
 

Who cares about old plastic? Researchers 

at the NIST Material Measurement 

Laboratory (MML) and the CNST do, so that you 

won’t have to years down the road, when today’s 

plastics start to break down and disintegrate from 

weather exposure. They are working to devise 

better tests to make sure aging plastics won’t 

turn into environmental or health hazards as time 

goes by. 

Tests like these are more important now than 

ever, because plastics aren’t what they used to be. 

Modern epoxies are increasingly made stronger, 

lighter and more resilient with the addition of 

multiwalled carbon nanotubes (MWCNTs). These 

nanotubes already enhance plastics used in 

baseball bats, tennis rackets, bikes and airplanes, 

and though the tiny tubes appear to be long-lasting, 

no comprehensive set of tests exists to determine 

what happens to them over the long haul. A NIST 

team took steps to change that. 

“Some studies have been done about the effect 

of ultraviolet (UV) light, but not with a large 

number of analytical methods,” says MML’s Elijah 

Petersen. “We wanted to begin developing a suite 

of tests for evaluating the performance of these 

nanocomposite materials, so that we can examine 

their potential risks, if any, during usage.” 

The team needed a way to simulate the degrading 

effect of years of high temperature, humidity and 

sunlight, but without waiting that long for results. 

They created samples of epoxy with 3.5 percent 

MWCNTs—a fairly typical mixture quantity— 

and put them into a NIST-developed device 

called SPHERE (Simulated Photodegradation 

via High Energy Radiant Exposure), which pours 

out powerful UV light into a chamber kept at 

50 degrees Celsius and 75 percent humidity. 

Keeping the samples there for 100 days “was the 

equivalent of four years in the bright Florida sun,” 

Petersen says. 

After exposing the samples to this artificial Florida, 

the team ran a set of six different tests that 

Exposed to intense ultraviolet light and high temperatures, samples of epoxy containing multiwalled carbon nanotubes 

deteriorated. Exposure tended to destroy the epoxy, but on the surface remained a network of nanotubes, which NIST tests 

indicated were less damaged than the epoxy over time. 

analyzed changes ranging from mass to 

appearance to surface chemistry. One major 

discovery was that the UV light tended to 

destroy the epoxy, but on the surface remained 

a spaghetti-like network of nanotubes, which the 

group of tests indicated were less damaged by 

SPHERE exposure than the epoxy matrix. 

So are these nancomposite materials stable 

forevermore? Petersen says the study did not 

answer every question, but that it should help 

researchers determine answers more effectively 

than was possible before by development and 

optimization of multiple analytical methods. 

“We got a lot of new information from the test 

suite about how nanocomposites degrade,” says 

Petersen, “and the most encouraging thing is that 

the results of the different tests generally back 

one another up. We hope the test suite allows for 

better analysis of the stability of these new plastics, 

which are growing more common in everyday life.” 

Methods to assess the impact of UV irradiation on the surface chemistry and structure of multiwall carbon nanotube epoxy nanocomposites, E. J. Petersen, T. Lam, J. M. Gorham, K. C. Scott, C. J. Long, D. Stanley, 

R. Sharma, J. Alexander Liddle, B. Pellegrin, and T. Nguyen, Carbon 69, 194–205 (2014). 

8 
 

 

 

 

CNST RESEARCHERS DEVELOP FRAMEWORK FOR UNDERSTANDING 

CURRENT-SWITCHED MAGNETIC DEVICES 

An international collaboration led by 

researchers from the CNST has made 

significant progress in modeling how electric 

currents affect the magnetization in some 

current-switched magnetic devices. While a 

number of such devices hold promise as low 

energy electronics, progress on some of the 

latest ideas has been impeded because different 

and contradictory models have been proposed 

to understand how they work and how to best 

optimize their performance. 

Electronic devices based on magnetic materials 

have the potential to significantly reduce energy 

consumption below that of CMOS devices because 

they retain their state even after current has been 

removed. However, devices that use magnetic 

fields to switch their magnetization do not scale 

well to smaller sizes. An alternate approach 

that scales well has recently been developed. It 

uses spin currents rather than magnetic fields 

to transfer information between the electrical 

current and the magnetization. One promising 

device is spin-transfer-torque switch magnetic 

random access memory (STT-MRAM), which is in 

development in several leading integrated circuit 

manufacturers. Device designers are searching for 

ways to reduce the current required to switch the 

magnetization in order to reduce both device size 

and energy consumption. One possible mechanism 

for reducing current is to incorporate materials 

with strong spin-orbit coupling, where the spin of 

the particle strongly affects its motion. Several 

experimental groups have shown remarkable 

results for switching magnetic bits and for moving 

domain walls in magnetic nanowires, which have 

strong spin-orbit coupling. 

Common factors in these devices are their reliance 

on strong spin-orbit coupling and the presence of 

an interface between different materials. To test 

the existing theories for explaining their measured 

behavior, the researchers have taken a variety of 

approaches with the goals of unifying the disparate 

models and connecting the models’ results to 

the experimental systems. In one approach, 

they compute all of the relevant experimental 

quantities predicted by a widely used theoretical 

model. They find that this single model cannot 

consistently explain all of the data, indicating that 

other important physics is at play in these systems. 

In a complementary approach, they compute the 

interfacial spin-orbit coupling and its consequences 

using first principles techniques. They show that 

the ability to switch the magnetization by current 

flow is determined by the extent to which the 

material with strong spin-orbit coupling induces 

large spin-orbit splitting, or changes in the electron 

energy levels, in the ferromagnetic material. 

The researchers believe that these analyses form 

a framework that can help experimentalists select 

materials to optimize the spin-orbit splitting needed 

for successful current-switched magnetic devices. 

The collaboration included researchers from the 

CNST; Pohang University of Science and Technology, 

Korea; Korea University, Korea; and King Abdullah 

University of Science and Technology, Saudi Arabia. 

Chirality from interfacial spin-orbit coupling effects in magnetic bilayers, K. -W. Kim, H. -W. Lee, K. -J. Lee, and M. D. Stiles, Physical Review Letters 111, 216601 (2013). 

Current-induced torques and interfacial spin-orbit coupling, K. J. Lee, H. W. Lee, A. Manchon, P. M. Haney, and M. D. Stiles, Physical Review B 88, 214417 (2013). 

A VIEW FROM 

THE INSIDE 

Scanning electron micrograph of the inside 

of one of the NanoFab’s two FEI Helios 650 

microscopes. Each dual-beam microscope 

combines a monochromated field emission 

scanning electron microscope with an 

advanced focused ion beam column for 

fast, precise nanomachining and nanoscale 

structural characterization. The first microscope’s enhanced capabilities include 

nanoscale positioning and in situ electrical 

measurements using a Kleindiek four-probe 

system with rotating grippers (inset) and a 

dedicated low-noise vacuum feed through 

to take electrical signals from the substrate 

to a parametric tester located outside of the 

vacuum chamber. The second microscope 

includes capabilities for simultaneous 

chemical characterization using energy 

dispersive x-ray spectroscopy and material 

crystallographic characterization using 

electron backscatter diffraction. 

9 
 

 

 

 

CNST RESEARCHERS DEMONSTRATE FEASIBILITY OF USING DOMAIN 

WALL CHIRALITY FOR STORING INFORMATION 

CNST researchers have found that the chirality 

of a magnetic domain wall in a nanowire can 

be used to store information. Recently there has 

been a great deal of interest in devices that can 

potentially store information by reading and writing 

domain walls in nanowire structures. Magnetic 

domain walls, which separate regions of opposite 

magnetization, can be moved along the wire using 

magnetic fields or electrical currents, and they can 

be detected by magnetic sensors along the wire. 

In thin nanoscale stripes such as nanowires, the 

magnetization within a domain wall can either 

rotate in a clockwise or a counterclockwise 

direction. The researchers found that, like the 

presence of the domain wall itself, this domain 

wall chirality can be sensed using magnetic 

nanostructures that are patterned near the wires, 

providing an additional way to store binary data. 

Using various magnetic nanostripes and sensing 

elements that were custom-made in the CNST 

NanoFab, the researchers systematically explored 

the sensitivity and reliability of chirality sensing 

to various geometries. The researchers found 

that they were able to sense domain wall chirality 

when triangular elements were placed within 

50 nm of the stripe edge. As domain walls of 

different chiralities pass these triangles, the 

magnetization in the triangles changes. In 

a device, the magnetization changes in the 

triangular elements could be read using either 

conventional giant magnetoresistance, a 

method used in commercial hard drives, or other 

established techniques. 

The motion of the domain walls and their 

interactions with the sensing elements are directly 

imaged using CNST’s scanning electron microscopy 

with polarization (SEMPA) microscope. The 

domain wall interactions with the sensor elements 

were also simulated using NIST’s Object Oriented 

MicroMagnetic Framework (OOMMF) modelling 

software The experiments and modelling show 

that changes as small as 10 nm in the dimensions 

of the elements can affect the reliability of 

the switching. 

This work demonstrates both the feasibility of 

using domain wall chirality for storing information 

or for manipulating logic, and the sensitivity of 

chirality-based device operation to the quality of 

the nanoscale lithography and the elimination of 

structural defects during fabrication. 

Domain wall chirality can be sensed when triangular elements are placed within 50 nm of the edge a magnetic nanostripe. 

Left to right: as a domain wall (shown as a boundary between white and black regions) in the center stripe passes the triangles, 

the magnetization in the lower triangles changes. 

Field-driven sense elements for chirality-dependent domain wall detection and storage, S. R. Bowden and J. Unguris, Journal of Applied Physics 114, 223904 (2013). 

CNST DEPUTY DIRECTOR LLOYD WHITMAN SERVING AS INTERIM 

DIRECTOR OF THE NATIONAL NANOTECHNOLOGY COORDINATION OFFICE 

CNST Deputy Director Lloyd Whitman has been detailed to the National Science 

and Technology Council (NSTC) to serve as the 

Interim Director of the National Nanotechnology 

Coordination Office (NNCO). He is leading the 

coordination and integration of the scientific 

research components of the National 

Nanotechnology Initiative and he assists the 

co-Chairs of the Nanoscale Science, Engineering 

and Technology Subcommittee under the NSTC in 

long-range planning, coordinating with agencies 

and other NSTC groups and coordination offices. 

Lloyd will lead the NNCO until a new Director is 

in place (which is expected to be within 6 months). 

His appointment follows the recent retirement of 

NNCO Director Dr. Robert Pohanka. 

“Lloyd’s broad background in nanotechnology 

and long involvement with the National 

Nanotechnology Initiative will help to maintain 

the Initiative’s important work in this economically 

important domain of science and technology, and 

will ensure a smooth transition while we conduct 

a national search for the next NNCO Director,” 

said Dr. Altaf (Tof) Carim, Assistant Director for 

Nanotechnology at the Office of Science and 

Technology Policy. 

Dr. Whitman has been a representative for both 

the Department of Defense and for NIST on 

the National Science and Technology Council, 

Subcommittee on Nanoscale Science, Engineering 

and Technology (NSET), and since December 2012 

has served as Co-Chair of the NSET. 

10 
 

COMING SOON: NEW TOOLS IN THE NANOFAB
 

The CNST has acquired a range of new tools 

which will become available to NanoFab users 

in the coming months. 

Sputtering Cluster System 

The CNST has purchased a 4Wave Sputtering 

Cluster System (SCS) which will be available to 

users in fall 2014. The new SCS can deposit a 

variety of high quality thin films with 12 readyto-deposit materials using ion beam deposition 

technology. Its cassette-to-cassette and robot 

wafer handling allow for largely unattended 24/7 

deposition capability along with the densest thin 

films available via physical vapor deposition at 

room temperature. 

The SCS will be able to deposit the following 

materials: Cr, Au, Fe, Ni, Ti, Pt, Ta, Al, 

Co, SiO2

, ITO, TiO2, Ta2O5, and Permalloy. 

For additional information, please contact Gerard 

Henein, 301-975-5645, gerard.henein@nist.gov. 

Lithography Coater System 

A new SUSS MicroTec ASC200 Gen 3 automated 

resist coater, which will be available to users in 

summer 2014, can spray and spin resist coating 

and has automated wafer handling and resist 

baking. The device can apply high quality resist 

films on wide range of substrate shapes, sizes and 

topologies with consistent and uniform results. 

This new resist coater will enhance the quality, 

repeatability and throughput of NanoFab precision 

lithographic imaging. For more information, 

contact Liya Yu, 301-975-4590, liya.yu@nist.gov. 

Direct Write E-Beam Lithography 

System 

A second JEOL JBX-6300FS direct write 

electron beam lithography system is going to be 

installed in the cleanroom in summer 2014. The 

new state-of-the-art system is used to pattern 

electron sensitive materials or resists during the 

fabrication of nanoscale structures and devices. It 

lithographically defines the nanoscale structures 

on resist coated substrates using an electron beam 

focused to nanometer-diameter spot size. The 

system allows high resolution exposure capability 

and provides automated substrate processing with 

batch handling. For more information, contact 

Rich Kasica, 301-975-2693, rkasica@nist.gov. 

Deep Silicon Etcher 

The CNST has purchased a new SPTS 

Omega c2L Rapier deep silicon etcher (DSE) which 

will be available to users at the end of June. The 

new DSE etches silicon wafers up to 200 mm in 

diameter faster than the NanoFab’s current deep 

silicon etcher while providing both smoother 

sidewalls and better end point detection. The 

tool can fabricate three-dimensional structures 

in silicon with very high aspect ratio (greater 

than 50 to 1) vertical sidewalls. Applications 

include fabricating microelectromechanical and 

nanoelectromechanical systems (MEMS and 

NEMS) such as accelerometers, ink jet heads, 

pressure sensors, gyroscopes, microphones, 

microactuators, and lab-on-a-chip devices. For 

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

lei.chen@nist.gov. 

Hydrofluoric Acid Vapor Etcher 

A new SPTS μEtch stand-alone hydrofluoric 

acid (HF) vapor etcher has been installed 

in the cleanroom in room 215/B102 and is 

available for reservations through the NEMO 

system. This tool uses a combination of 

hydrofluoric acid vapor and alcohol to create a 

vapor that isotropically etches silicon dioxide 

without etching silicon. Applications include 

fabricating microelectromechanical and 

nanoelectromechanical systems (MEMS and 

NEMS) such as accelerometers, ink jet heads 

and pressure sensors. The tool can release 

microscale and nanoscale silicon structures 

by etching a sacrificial layer of silicon dioxide 

underneath a silicon device layer, leaving the 

silicon structures freely suspended. For more 

information, contact Rich Kasica, 301-975-2693, 

rkasica@nist.gov. 

NanoFab Engineer Marc Cangemi testing the CNST’s new SPTS Omega c2L Rapier deep silicon etcher (DSE). The new 

DSE etches silicon wafers up to 200 mm in diameter faster than the NanoFab’s current deep silicon etcher while providing both 

smoother sidewalls and better end point detection. 

11 
CENTER FOR NANOSCALE 

SCIENCE AND TECHNOLOGY 

The CNST is a national user facility purposely designed to accelerate 

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

national, shared resource for nanoscale fabrication and measurement and 

develop innovative nanoscale measurement and fabrication capabilities to 

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

agencies in advancing nanoscale technology from discovery to production. 

The Center, located in the Advanced Measurement Laboratory Complex 

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

measurement methods by incorporating them into facility operations, 

collaborating and partnering with others, and providing international 

leadership in nanotechnology. 

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

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

and follow the on-screen instructions. Alternately, you may request 

a subscription via email or phone. 

SUPPORTING THE 

DEVELOPMENT OF 

NANOTECHNOLOGY 

FROM DISCOVERY TO 

PRODUCTION 

Center for Nanoscale Science and Technology 

National Institute of Standards and Technology 

100 Bureau Drive, MS 6200 

Gaithersburg, MD 20899-6200 

Phone: 301-975-8001 

E-mail: cnst@nist.gov 

VISIT THE CNST BOOTH AT THE 

OPTICS AND PHOTONICS 

CONFERENCE 

JULY 13 TO 17, 2014 

SAN DIEGO, CA 

World

Innovation Conference & Expo 

TECHCONNECT WORLD 

INNOVATION 

CONFERENCE & EXPO 

JUNE 15 TO 18, 2014 

WASHINGTON, DC 

NEW NANOFAB TOOL RESERVATION RULES 

I

n an effort to ensure that tools are available number of adjacent reservations that a user can over time, based on efficiency data and on input 

to users when they need them, the CNST is schedule for each tool. The rules will be customized that we receive from our users. Once the system 

implementing new tool reservation rules for the for every tool and will be listed on the NEMO tool is in place, we ask users to send comments and 

NanoFab. Users will soon see the new rules when pages. Beginning in July, the reservation rules for feedback to nemo@nist.gov. 

using the NEMO tool reservation system. These every tool will also be listed on the NanoFab web 

tool rules will limit the amount of time and the site. These rules will be modified and optimized 

WWW.NIST.GOV/CNST 140528