After several trips back to the drawing board, scientists

finally came up with the right recipe for a glue that works

on a specialized class of ceramic materials.

Mercury contamination is a huge problem at sites throughout the DOE complex. Read how an Ames Lab scientist is

responding to this problem with the development of a

mercury continuous emission monitor.

Since 1990 when they theoretically demonstrated the

existence of the first photonic bandgap crystal, Ames Lab

scientists have steadily been moving the research forward.

Now they are on the verge of achieving their goal: fully

three-dimensional optical photonic crystals.

Dan Barnard wants to solve a mystery that may have

significant implications for a relatively new technique

known as acoustic harmonic generation.

Sam Houk has speeded up the process of identifying

ultratrace metals in biological systems. Allowing measurements at parts-per-trillion levels, his innovative technique is more sensitive and selective than traditional

methods.

Cheuk Ng’s basic research in vacuum ultraviolet chemistry provides chemists with some of the most fundamental

scientific measurements – those that help them better

determine whether a reaction will go or not.

STICKING WITH IT Susan Dieterle

2

5

8

13

17

20

Look in on some more Ames Lab success stories.

INtouch

12

16

24

Inquiry is published annually by the

Ames Laboratory Office of Public

Affairs and Information. Iowa State

University operates the Laboratory for

the U. S. Department of Energy under

contract W-7405-Eng-82. Located on

the ISU campus, the Ames Laboratory

is a member of the university’s

Institute for Physical Research and

Technology, a consortium of research

and technology development and

transfer centers.

Editor

Steve Karsjen

Managing Editor

Saren Johnston

Art Director

Michael Marti

Photographer

Mark Davitt

Contributing Photographer

Dennis Sailsbury

Copyright 1999 by Ames Laboratory.

All rights reserved. For additional

information about the Ames

Laboratory or any of the topics

covered in this publication, please

contact:

Editor, Inquiry

Ames Laboratory

111 TASF

Ames, Iowa 50011-3020

515-294-9557

http://www.external.ameslab.gov

Features

THE RIGHT STUFF Steve Karsjen

PHOTONIC FRENZY Saren Johnston

BASIC NEEDS Saren Johnston

ANEW TWIST FOR TRACKING TRACE ELEMENTS Saren Johnston

GRAPPLING WITH THE HOOK Susan Dieterle

Kai-Ming Ho totes this colorful plexiglass model with him when

presenting invited talks throughout the world. It provides the perfect

example of his original layered lattice design for three-dimensional

photonic bandgap crystals. (see story page 8)

(back cover) A single crystal of copper sits in a sample holder while scientists prepare

to conduct tests using a technique known as acoustic harmonic generation.

The technique may provide the earliest information about cracks and fatigue

in materials. (see story page 13)
Welcome to the 1999 issue of Inquiry

 magazine – our annual mechanism for

providing a sampling of the unique and creative

research being conducted by scientists at Ames

Laboratory.

As this issue is arriving at your office, we are

preparing for a significant event in the life of

Ames Lab – one that plays a key role in every

piece of research featured in Inquiry – the

signing of our new five-year

contract with the Department of

Energy. In the strongest way

possible, this agreement will

provide the foundation from

which we will continue to advance the world-class research

that has become the hallmark of

Ames Laboratory throughout its

52-year existence.

As we prepare to embark upon

the exciting and challenging

scientific journey the next century

will no doubt provide, we look forward to those

research opportunities that have yet to present themselves. Key to our ability to address those opportunities is the synergistic approach we take in accomplishing our research. Examples of that synergy are

prevalent in the stories featured in this issue of

Inquiry.

I invite you to turn the page and witness our scientists’ substantial

efforts to help solve our nation’s energy problems. It is an endeavor that is as exciting today as it has been at any time throughout the history of Ames Laboratory.

 Director Greetings from the

Inquiry 1

1999

AMES LABORATORY

As we prepare to

embark upon the

exciting and challenging scientific journey

the next century will

no doubt provide, we

look forward to those

research opportunities

that have yet to

present themselves.
By Susan Dieterle

The extreme stickiness of a new

glue for ceramic composite materials

is nothing compared to the stick-toitiveness of its inventors.

The group of Ames Laboratory

researchers went back to the drawing

board repeatedly while trying to

develop a glue that would hold

together parts made of a rugged class

of ceramic materials known as silicon

carbide composites.

Undeterred by the setbacks, they

now have an easy-to-use glue that

produces strong joints without the

expensive, high-temperature curing

process associated with other types of

ceramic glues. They hope that this

simple, effective joining method will

prompt industry to make greater use

of ceramic composites in hightemperature settings.

The composites have properties

that, in some applications, make them

superior to steel and superalloys

because they can withstand higher

temperatures, do not melt and are less

susceptible to corrosion. That makes

them ideal candidates for such

products as industrial furnace fans

and turbines in hot, corrosive environments.

“If we had turbine engines that

allowed fuel to burn hotter and

industrial furnaces that could operate

After several trips back to the drawing

board, scientists finally came up with the

right recipe for a glue that works on a specialized class of ceramic materials

Inquiry1999 2

(From left) Sina

Maghsoodi,

Mohammad Nosrati

and Iver Anderson

 stand atop a

 board supported

 by small platforms

 made with the

 glue they

 invented.
A micrograph shows the joint made between two pieces of silicon

carbide composite. The joint area runs through the middle of the

image, as denoted by the red line to the left.

at uniform, constant temperatures, we

would increase their efficiency immensely,” says Iver Anderson, director

of the Lab’s Metallurgy and Ceramics

Program. “Ceramic composites could

make that possible and would result in

a substantial reduction in energy costs

for many industries.”

Brittle material

Silicon carbide itself is a brittle

material that lacks the strength needed

for load-bearing applications. So some

industries have turned to a composite

in which silicon carbide fibers are

woven together like a mat and then

encased in a silicon carbide matrix.

Just as steel rebar strengthens concrete,

the fibers strengthen the matrix

material. Silicon carbide composites

are considered the most developed of

the various types of ceramic composite

materials and are closest to large-scale

commercialization.

But there has always been a

drawback associated with their use –

the lack of a satisfactory way to join

parts made of the material. “If you

want to make a fan, you have to join

blades to a hub and a hub to a shaft,”

Anderson says.

“And nobody had a

convenient, robust

method for doing

that.”

The problem

has been difficult to

solve because,

although silicon

carbide itself can

withstand temperatures of up to 2000 C

(3600 F), the fibers

in the composite

material begin to

degrade at 1200 C

(2200 F). Traditional ceramic-joining methods don’t

work well because they involve curing

the joints at temperatures of at least

1600 C (2900 F), usually in furnaces

with inert atmospheres.

Three years ago, the Department

of Energy asked its scientists to come

up with possible solutions to the

joining problem. Ames Lab Director

Tom Barton, whose background is in

materials chemistry, participated in

phone conferences regarding the issue

and then paired up Anderson and

materials chemist Sina Maghsoodi to

attend a Salt Lake City workshop

where it would be discussed.

Airport chat

During a long layover in

Denver on the way back, the two

scientists came up with a promising

concept. What if they used

Maghsoodi’s silicon-bearing

preceramic polymers along with

Anderson’s aluminum-silicon metal

powder? The idea intrigued both

the chemist and the metallurgist.

Preceramic polymers have

several unique properties,

Maghsoodi says. They are easily

processed into a variety of shapes

and forms and bind easily with

metal alloy powders. This would

give the glue adhesive properties in

its “green state” while allowing it to

convert to nanocrystalline ceramics at

higher temperatures to form a strong

joint, he says.

Anderson notes that the aluminumsilicon powder also had several

purposes. “Aluminum readily forms a

eutectic alloy with silicon; that is, a

relatively ductile alloy that has a

melting point lower than either

aluminum or silicon alone,” Anderson

says. In addition to lowering the

melting point of silicon, the aluminum

in the powder would bond with the

oxygen that enters the joint when the

polymer was heated in air. The result,

they believed, would be a joint filled

with small islands of aluminum oxide,

making it as strong or stronger than

the parts themselves.

But getting their concept to work

was simpler in theory than in actual

practice.

First, a student couldn’t make the

long-chained polymers Maghsoodi

wanted. The scientist ended up using

intermediate-length polymers, called

oligomers. Fortunately, the honeylike

consistency of the oligomers proved

preferable to the stiffness of longchained polymers.

Then, the scientists determined

that the alloy powder had too much

aluminum and too little silicon, so

they had to change the composition of

the metal alloy powder.

“It wasn’t working very well at

2 Inquiry 3

1999

The small platforms consist of three pieces of silicon

carbide composites that were glued together, with plastic

discs at the ends. Seven such platforms supported the

weight of the three researchers in the photo at left.
one night and needed to use a furnace

that heats to 1500 C, but it wasn’t

working,” Maghsoodi recounts. “He

checked it and saw that the heating

element was broken.”

So, Nosrati smeared some of the

glue on the broken ends of the

heating element, heated it with a

propane torch and then placed it back

in the furnace. “It worked,”

Maghsoodi says, noting that he

shows the heating element to

interested companies to

demonstrate how easily

the glue can be used.

To keep the

sticky glue

from getting

on their

hands,

researchers

prefer to

apply it

with a

syringe.

Growing interest

The glue, which already has two

patents with a third in the works, is

attracting attention from companies

throughout the world. One of those

is Amercom, A Synterials Company,

a Virginia-based enterprise that

conducts research and development

work on ceramic-matrix and metalmatrix materials.

Bill Bustamante, Amercom’s

vice president of business developfirst,” Maghsoodi remembers with a

rueful laugh.

Getting it right

The two scientists, who continued

gathering input and direction from

Barton, added another member to the

team – Mohammad Nosrati, a graduate student in ceramics. Nosrati began

experiments to work out the kinks in

the glue. He added a pinch of boron

to the mixture, strengthening the

bonds between the glue’s

components.

When they

came up with

a compound

that worked

well at

room

temperatures, they

turned to

ceramist

Ozer Unal

to measure

the strength of

the glue at high

temperatures. The

results were disappointing. “The joints had

only 10 percent of their roomtemperature strength at 1200 C,”

Maghsoodi says. “So, we had to go

back to the drawing board and find a

new formulation.”

More adjustments followed. In

the end, the group had a sticky,

grayish paste that could be applied to

the joint area with a syringe. From

there, the joint can be heated and

cured in a regular air atmosphere

without clamping pressure. The glue

makes a strong joint that can withstand pressures of up to 14,500

pounds per square inch, the equivalent

of 100 megapascals.

The source for heating the joints

can be something as simple and

portable as a propane torch, as Nosrati

discovered one evening. “Mohammad

was working in a lab on campus late

ment, is interested in the glue largely

because it is air-stable and can be

easily used in the field. “That’s

especially attractive for some of the

military applications and for the

aerospace industry,” he says.

Some of the ceramic composite

materials are used in the hot sections

of gas turbine engines, Bustamante

says. Because the engines are big

enough to walk around in, the ceramic

parts can be damaged through a

worker’s carelessness. “The possibility of using this glue to patch or repair

a damaged component is very, very

attractive,” he says.

Maghsoodi has also been approached by companies wanting to

know if the glue can be adapted for

use with materials other than silicon

carbide composites. “We’re working

with them on small projects to try to

help them solve their problems,” he

says. “So what started as a project for

DOE has now increased 100 times

through involvement with companies

trying to solve their own problems.”

The level of interest in the glue

makes the scientists glad that, despite

the initial setbacks, they stuck with

the work. ✤

For more information:

Sina Maghsoodi, (515) 294-1110

ijadi@ameslab.gov

Iver Anderson, (515) 294-4446

andersoni@ameslab.gov

Current research funded by:

DOE Office of Basic Energy Sciences

Inquiry1999 4

Maghsoodi uses this repaired heating

element to demonstrate how easily the

glue can be applied in the field.
Inquiry 5

1999

This was no ordinary bake-off.

 There were no apron-clad chefs

standing around taste testing entries

in the chocolate chip cookie contest.

In this bake-off, as it was affectionately called by participants, the

"recipe" being judged was for the

best continuous emission monitor, or

CEM, and the prize was the enviable

status of being judged the company

with the best the CEM industry had

to offer.

No small distinction, this honor

would not only carry with it bragging

rights but an opportunity to impact

the way mixed wastes are monitored

during the incineration process.

Mixed wastes are those containing

both hazardous and radioactive

constituents. Disposing of mixed

waste is an enormous problem for

government agencies like the

Department of Energy. “It’s estimated the United States has in excess

of 165,000 cubic meters of mixed

waste,” says Bill Haas, a senior

scientist at Ames Laboratory and a

technical consultant to DOE’s

Characterization, Monitoring, and

Sensor Technology Crosscutting

Program, the program that along with

the Environmental Protection Agency

organized the bake-off. “That

translates into approximately 800,000

55-gallon barrels of waste needing to

be destroyed.”

Mixed waste can be anything

from tubing to hoses to paper

products. Its common denominator is

that the waste is hazardous and

radioactive, mostly low-level and

mostly the byproduct of government

research or weapons production.

Currently, the only EPA-approved

process for treatment of mixed waste

is incineration. As the largest

operator of mixed waste incinerators

nationwide – with two sites at Idaho

National Engineering and Environmental Laboratory, one at the

Savannah River Site and another at

Oak Ridge National Laboratory – it’s

easy to see why the DOE would place

importance on finding a safe way to

dispose of mixed waste.

Key to operating a successful

mixed-waste incinerator is the ability

to monitor the materials, or feedstock, that are fed into the incinerator

in order to ensure the heavy metal

emissions coming out of the

incinerator’s smokestack are within

limits set by the EPA. Incinerator

operators can monitor the feedstock

two ways: by taking samples and

sending them to a laboratory for

analysis, which is laborious and time

consuming, or by performing periodic

trial burns every three to five years to

verify that the facility meets EPA

emission standards.

During a trial burn, the incinerator is run under a range of conditions,

 Right Stuff

Bill Haas (left) and David Baldwin stand in front of the mercury CEM. Their collaboration

helped produce the spark that got the mercury CEM to the development stage.

by Steve Karsjen

and measurements are made based on

EPA standards. “As long as you’re

able to operate with emissions that

are less than what the regulation says,

you’re OK,” says Haas. “However,

three to five years is a long time

between measurements.” The

beauty of CEMs, he says, is their

“continuous” operation. “In fact, if

everything works out as planned and

CEMs are a mandatory piece of

The
An ordinary pen lamp is a key

piece of equipment in the

mercury CEM.

mercury to minimize exposure and

danger.”

Fortunately, elemental analysis is

an area that has been at the forefront

of Baldwin’s work at Ames Lab,

going back several years to when he

and his colleagues used an inductively coupled plasma-atomic

emission spectrometer to conduct onsite uranium analysis of soil at DOE

facilities like the Fernald Plant in

Ohio. When that work dried up due to

a DOE shift in emphasis from on-site

characterization and treatment of

contaminated soil to bulk removal

and transport to disposal facilities,

Baldwin turned his attention to

developing systems to support a

new DOE thrust, which was

analyzing air emissions

resulting from incineration

of mixed wastes.

“In order to do this,

we needed to be able to

draw material from air

and then be able to

analyze it with a

smaller ICP than the

one-ton spectrometer

we had used for soil

characterization,” says

Baldwin, who set

about the task of

developing a spectrometer system based

on acousto-optic

tunable filter and

echelle grating

technologies that

would be smaller and

provide higher

resolution than past

spectrometers. At the

same time, Baldwin looked at

combining this system with a portable

air-plasma ICP-AES system, which

was being developed at Mississippi

State University, to provide the realtime sensitivity and resolution

capabilities necessary to perform

multi-element analysis in smokestacks.

“That’s how we got to where we

are – from dirt to building a highresolution spectrometer that can be

placed on a smokestack along with an

air plasma and can measure emissions

from those stacks,” says Baldwin.

From there it was a natural progression to Baldwin’s current effort to

develop a mercury monitor. “Since

mercury was an area in which we

Inquiry1999 6

hardware on every incinerator,

incinerators will not be able to burn

waste if the CEM is not working,”

notes Haas. “What this will provide

is a much higher level of protection to

the neighbors related to the air they’re

going to be breathing – air that’s not

been assaulted, even temporarily,

above emission limits.”

To determine the state-of-the-art

in CEM development, Haas and other

partners on the DOE/EPA bake-off

team conducted a test in September

1997 at the Rotary Kiln Incinerator

Simulator at EPA’s National Risk

Management Research Laboratory in

Research Triangle Park, N.C. Results

of the test were expected to help the

EPA establish standards for smokestack emissions of six toxic metals –

arsenic, beryllium, cadmium, chromium, lead and mercury – under the

draft EPA Maximum Achievable

Control Technology (MACT) rules for

hazardous waste combustors.

During the demonstration, seven

multimetal CEMs at various stages of

development were tested, and results

were compared to EPA’s reference

method for metals emission measurements. “A number of characteristics

were taken into consideration in the

test, such as sensitivity, speed and

data quality, but the most important

performance issue was whether the

CEMs could quantitatively measure

all six metals,” says Haas. In the test,

the six metals were injected along

with fly ash from a coal-fired utility

boiler into the afterburner of the

EPA’s incinerator simulator, and the

relative accuracy of each multimetal

CEM was calculated. According to

Haas, the results of the tests were

“disappointing.” None of the CEMs

tested met performance specifications

for sensitivity and data quality in

EPA’s draft MACT rule for hazardous

waste incinerators. Only one of the

CEMs tested was able to measure all

six metals at the concentrations tested,

but the relative accuracy of that CEM

varied between 35 and 100 percent,

not 20 percent or less as required in

the EPA performance specification.

So what did the test accomplish?

“Our findings were significant

because they helped prevent the EPA

from putting in place incinerator

emission standards as part of its

MACT rules based on the abilities of

some monitors that weren’t up to

standards,” says Haas. “Ultimately,

we’re not there yet in terms of

satisfactory CEMs, but through our

trials we’re moving the process along

by providing data from which

regulators can make reasonable

judgements about standards.”

Developing a mercury CEM

The North Carolina test did not

go unnoticed by David Baldwin,

Ames Lab chemist and program

director for the Lab’s Environmental

and Protection Sciences Program.

Baldwin had provided a prototype

high-resolution optical spectrometer

as part of an inductively coupled

plasma-atomic emission system

for use by one of the groups

involved in the test.

Following completion of

the tests, Baldwin and

Haas began talking

about the need to

develop an effective

CEM specifically for

mercury.

Why mercury?

“Mercury is near the

top of the list of

elements that EPA

wants much better

knowledge and

control of,” says

Haas. “Mercury has

a much greater

importance than the

other five elements

simply because it’s

more common, more

easily volatilized and

has many pathways to

human exposure.”

 Baldwin adds, “Mercury is a

huge problem throughout the DOE.”

Measuring mercury in the waste feed

is costly and difficult, especially for

heterogeneous waste. Representative

sampling is nearly impossible, and

mercury is notorious for not being

evenly distributed in the waste. Add

to that the toxicity of mercury, which

increases the risk of personnel being

exposed to hazardous chemicals, and

you have a major challenge facing the

DOE. “DOE is laden with tons of

mercury that was used as part of the

process to produce uranium at Oak

Ridge National Lab,” Baldwin says.

“In order to decontaminate and

decommission places like that, you’re

going to have to be able to monitor
Inquiry 7

1999

were doing exploratory work already,

we decided to do experiments to see

whether the instrument we built to

monitor other metals could also be

used as a mercury monitor,” he says.

Going beyond conventional CEMs

The mercury CEM begins with

an ordinary pen lamp, which shows

the many colors that result from

excited mercury. The color, or line, of

importance to the scientists is the 253

nanometer emission line because it is

the one that’s absorbed by mercury.

“In order to measure the amount of

mercury in a cell, you need to be able

to measure how much absorption of

light is occurring as a result of

mercury vapor in the cell absorbing

light,” says Baldwin. The process

sounds simple but it isn’t because of

two outside influences: interference

and scattering.

For the mercury CEM to work

effectively, it had to solve the

interference and scattering problems.

For example, Baldwin says when you

burn hazardous materials in an

incinerator, you often have molecular

gases like sulfur dioxide (SO2) in the

stream. This presents

a problem for current

CEMs because SO2

absorbs the same

wavelength as mercury, which can throw

off the measurement

process. “If you’re

measuring mercury

based on absorption of

a single wavelength,

you may also be seeing

a lot of SO2, which

you might think was

mercury, but it isn’t,”

says Baldwin.

The mercury

CEM also overcomes

the second problem,

scattering. When

chemical or mixed

waste is being burned

in an incinerator,

particulate matter, such

as fly ash, is naturally

present. “Particles, of

course, scatter light

which creates another

type of interference,

this one being scattering rather than absorption as in the

case of SO2,” Baldwin says. “Essentially, we do a background correction

for molecular interferences, such as

SO2, and for scattering.”

Baldwin says a third problem

with conventional CEMs is that

they’re not “hardened” for field use.

Typically, the light has to go through

the incinerator smokestack and out

the other side and into a detector. “It

could be 100 degrees with 100

percent humidity in this environment,

and the likely result will be that those

adverse conditions will cause the

monitors to clog or fail to calibrate

properly,” Baldwin says. “They just

don’t handle the harsh environment

well.” Baldwin says what is needed

is a high-resolution spectrometer that

can measure multiple wavelengths

simultaneously and is not prohibitive

in size. The mercury CEM addresses

both those issues by bringing a highresolution echelle spectrometer into

the equation. “With an echelle

spectrometer, you can accomplish

both tasks,” he says.

The future is bright*

Building on the collaborative

efforts already existing between

Baldwin and Haas, another Ames Lab

scientist will soon become involved

in helping test the mercury CEM.

Glenn Norton, an Ames Lab associate

chemist, has funding from DOE to

look at commercial mercury analyzers

for combustion gases. “He has quite

an extensive testing system set up for

this type of analysis,” says Baldwin,

who plans to use Norton’s testing

facilities and test the mercury CEM

being built in the laboratory. “We

need to concentrate on making a

system that will survive these hostile

environments, and then build a

fieldable system.”

Baldwin’s goal is to be ready the

next time DOE and EPA conduct

another bake-off. “Bill has mentioned there’s going to be another

mercury test next fiscal year,” says

Baldwin. “We hope to be there with

a system that meets the EPA’s

performance requirements.” ✤

For more information:

David Baldwin, (515) 294-2069

dbaldwin@ameslab.gov

Bill Haas, (515) 294-4986

haas@ameslab.gov

Current research funded by:

DOE Office of Environmental

Management

Ames Lab assistant chemist Dan Zamzow makes adjustments to the

echelle spectrometer of the mercury CEM.
that is an electrical insulator or in

which an electric field can be

perpetuated with a minimum loss in

power. Scientists must arrange the

photonic material in a lattice structure

that repeats itself identically and at

regular intervals. If the assemblage is

precisely made, the resulting crystal

can have a photonic bandgap, a range

of forbidden frequencies within

which a specific wavelength is

blocked, and light is reflected.

With the exception of the

bandgap, a properly constructed

photonic crystal will transmit

wavelengths of light up and down the

electromagnetic spectrum. Now

scientists can predetermine the

bandgap by engineering the lattice

spacing of the photonic material to

match the wavelengths they wish to

block. This fortunate circumstance

has given them the ability to control

and manipulate light, sending it down

assigned routes and around loops and

bends.

The push is on

to produce

3-D structures

that control light

at visible wavelengths

Inquiry1999 8

PHOTONIC

by Saren Johnston

Photonic crystals don’t occur

naturally. If you want one, you have

to make it – not an altogether easy

job. But scientists are aggressively

pursuing this task, manipulating

photons to control electromagnetic

radiation for potential applications

that include optical switches, microfabricated lasers, waveguides, lightemitting diodes and telecommunications.

Building a photonic crystal

requires creating a periodic structure

from dielectric material – material
Kai-Ming Ho (left) and Rana Biswas examine the

computer image of a photonic crystal built by

researchers at Sandia National Laboratories

using Ames Lab’s original layered lattice design.

that still didn’t solve the problem of

getting the bandgap into the optical

region.”

The collaboration begins

When Biswas was giving a talk at

a 1997 American Physical Society

meeting, it was not by chance that

Shawn Lin from Sandia National

Laboratories was in the audience. Lin

had been corresponding with Ho and

knew that Biswas would be at the APS

meeting. “After the session, Shawn

came up to me and said he’d like to

try to make the Ames structure in his

lab at Sandia,” says Biswas. “They

have a state-of-the-art processing lab

at Sandia, probably one of the leading

facilities anywhere in the world.”

In 1998, Lin’s team built the

Ames group’s structure using bars

made of silicon. But instead of

leaving an inner air space, they filled

the region inside the bars with silicon

dioxide to give the structure more

strength. Where other groups had

Proving the gap

A good deal of the credit for light

control belongs to an inspired group

of Ames Laboratory researchers led by

senior physicist Kai-Ming Ho. Ho

knows his way around photonic

crystals. In 1990, he and Costas

Soukoulis, senior physicist, and

Che-Ting Chan, a former Ames Lab

physicist now at the University of

Science and Technology in Hong

Kong, theoretically demonstrated the

existence of the first photonic

bandgap crystal.

“While exploring a number of

structures, we discovered that the

diamond structure had a bonafide

three-dimensional photonic band

gap,” says Ho. “We were just doing

the calculations, so the structure

existed only on the computer at that

time.”

However, it wouldn’t be long

before the diamond lattice structure

that Ho and his fellow theorists

developed through computer simulations would become a tangible object.

Their design led to the construction of

the first successful photonic crystal,

which was built later in 1990 by Eli

Yablonovitch, a scientist at Bellcore

Labs in Red Bank, N.J.

The crystal Yablonovitch fabricated from the Ames Lab design had a

bandgap in the microwave region of

the electromagnetic spectrum and was

produced by drilling a series of

carefully positioned holes in a

dielectric material. However, drilling

holes small enough and precisely

enough to position the diamond lattice

bandgap in the infrared or visible

range of the spectrum where more

potential applications exist turned out

to be extremely difficult.

After seeing the problem that

plagued Yablonovitch, Ho, Soukoulis

and Chan started looking for a

different way to construct the diamond

lattice structure. Ho came up with a

variation of the structure that could be

built in a layer-by-layer fashion. “The

idea was that instead of trying to drill

holes, we’d stack alumina rods in

alternating layers that ran perpendicular to one another, and we’d position

the rods in every layer halfway

between the rods two layers away,”

says Ho. The researchers received a

patent for their novel design, which

was fabricated in 1992 by former

Ames Lab associate physicist Ekmel

Ozbay and Gary Tuttle, an Iowa State

University associate professor of

electrical and computer engineering.

From rods to wafers

Between 1992 and 1994,

experimentalists Ozbay and Tuttle

built a number of three-dimensional

diamond lattice bandgap structures to

work in the microwave and millimeter-wave regions.

“Then Ekmel came up with the

idea of making the structures

smaller,” says Ho. “Building the

crystal with alumina rods takes quite

a bit of time because you have to lay

out all the rods and glue them

together, stick by stick. So the idea

was to make use of wafer technology.

Ekmel and Gary would fabricate a

whole layer at a time on a wafer and

then stack it. That approach was

quite successful.”

Rana Biswas, a physicist and

a member of the photonic

crystal theoretical team

with Ho, Soukoulis and

associate scientist

Mihail Sigalas,

explains the push to

make smaller

structures. “We

wanted to make

these structures

work at optical

wavelengths, or at

least work at

infrared wavelengths so there

would be applications

for lasers and telecommunications.

“Since 1994, we have

been working with Gary Tuttle

at Iowa State University’s

Microelectronics Research Center

and Ekmel Ozbay, now of Bilkent

University in Turkey, to make the

structures smaller and smaller,”

Biswas continues. “We had some

success with structures made from

metal strips deposited on plastic, but

Inquiry 9

1999
structure of gallium arsenide rods

with a bandgap layer in the infrared.

“They use a different technique

involving wafer bonding and ion

etching, and now they have a sample

with eight layers,” says Ho.

Colloidal crystals

While the Sandia researchers

investigate ways to improve the

emission rate for silicon photonic

crystals, researchers on Ho’s Ames

Lab team are turning their attention

from rods to spheres.

Kristen Constant, an Ames Lab

associate and an ISU associate

professor of materials science and

engineering, came up with a novel

ceramic technique for making

photonic crystals from a nontoxic

mixture of polystyrene microspheres

and titania. She explains that polystyrene spheres can be purchased in

dimensions less than 1 micron in size

and can self-assemble into periodic,

close-packed structures at optical

wavelengths. “This makes them very

attractive candidates for fabricating

optical photonic crystals,” she says.

Graduate student Ganesh

Subramania knows just how good a

mold the microspheres provide for

fabricating photonic crystals. He’s

the person who makes the crystals,

and he does it with surprisingly lowtech and inexpensive equipment.

Subramania begins the crystalconstruction process by spreading a

few drops of a slurry of titania

suspension and polystyrene spheres

on a glass substrate. The sample

failed with this “back-filling” procedure, Sandia succeeded because of

their capability to planarize, or flatten,

each successive layer of the stacked

crystal so well that, as Ho describes

the process, “adding another layer was

just like starting anew with the initial

flat substrate on which the first layer

of the structure was readily built.” In

the final step, the Sandia researchers

immersed the whole structure in acid

to etch away the silicon dioxide. The

resulting three-dimensional diamond

lattice structure had a bandgap of

about 12 microns. “That’s an

important region because the carbon

dioxide laser operates around 10

microns,” Ho explains. “There are

lots of interesting uses you can apply

these structures to if you can hit the

CO2 laser wavelength.”

Later in 1998, Lin’s group

succeeded in fabricating an even

smaller version of Ames Lab’s layered

lattice design, bringing the bandgap

into the region of 1.35-1.95 microns

in the near-infrared, a significant

achievement because the wavelength

used for transmission of telecommunications by optical fibers is 1.5

microns. Photonic crystals with

bandgaps at that wavelength could be

used to improve the efficiency of

optical switches for fiber optic

communications.

The combined efforts of Ames

Lab and Sandia researchers in

designing and fabricating threedimensional photonic crystals with

bandgaps in the near-infrared range of

the electromagnetic spectrum was a

major step made even more noteworthy because the fabrication

method is economical and lends itself

to mass production. However, the

silicon photonic crystal presents a

problem in that it has an indirect

bandgap, which lowers spontaneous

emission. But Lin thinks he can

overcome this problem with certain

doping measures.

Further testimony to the success

of the Ames structure is the fact that

Susumu Noda and Noritsugu

Yamamoto, researchers at Kyoto

University in Japan, have also used

Ho’s design to fabricate a layered

Inquiry1999 10

spends 24 hours drying in a humidity

chamber and is then taken to be

“squished,” as Constant refers to its

fate, in a cold isostatic press. Five

minutes of compression helps thin the

sample and reduces stress cracks in

the heat-treatment process that

follows.

Slow baking is the final step.

Subramania heats the sample to 520 C

(968 F) over five hours, during which

time the mold of polystyrene spheres

is burned off, leaving behind air

spheres in a titania matrix. Shiny

regions are visibly apparent in the

remaining photonic crystals. These

regions have characteristic

colors that depend on the size of the

polystyrene spheres used. The

crystals made with smaller spheres

(395 nanometers) have bright green

regions, and those made with larger

spheres (479 nanometers) are

salmon-red in color.

“The color indicates that the

structure that’s present is what we’re

looking for – basically, a periodic

structure at a certain length scale,”

says Constant. “If we don’t see

color, either the scale is wrong or the

structure is wrong. It’s nice because

we can visually inspect some of

these to see if they have the right

structure. Then Ganesh does scanning

electron microscopy on the good

samples to see the detailed, periodic

structure.”

Colloidal crystals begin “life” on a glass

substrate. A few drops of a slurry of

titania suspension and polystyrene

spheres is all it takes.

Ganesh Subramania places the

colloidal crystal samples in a

humidity chamber to dry for 24

hours.
And the beat goes on

Constant hopes they will eventually be able to make large-area

optical photonic crystals using the

economical and reproducible ceramic

technique. Such an achievement

would greatly enhance the efforts of

scientists to find out more about the

control of light emission and propagation in these materials. But there is

still work to be done.

Biswas and Sigalas note that

although they have now achieved

This scanning electron microscope image

of a photonic colloidal crystal shows the

close packing of the air spheres.

Following compression, the sample

undergoes a five-hour baking process

to burn off the mold of polystyrene

spheres, leaving only air spaces

in a titania matrix. Kristen

Constant visually inspects

the resulting colloidal

crystal sample for the

shiny regions of green

or salmon-red that

indicate a periodic

structure is

present.

The crystals are

protected from the

oily compression

of the cold

isostatic press by

being placed

inside a condom

in a wire basket. Condoms are

used instead of standard laboratory bags because they are

cheaper and easier to obtain.

optical photonic crystals with

colloidal systems, the structures don’t

have a fully three-dimensional

bandgap like the ones the Sandia

team has produced using Ho’s

original stacked crystal design. On

the other hand, the Sandia team is still

trying to reach the optical region.

There’s plenty of work to be

done, but there’s also plenty of work

that’s come out of the photonic

crystal research to date. And Biswas

says both the theorists and the

experimentalists are involved in

efforts to expand that work. “One of

the next steps we have to focus on is

finding new uses for all the research

that is coming out,” says Biswas.

“We also want to partner with

industry, and we’ve had some good

feelers.” ✤

For more information:

Kai-Ming Ho, (515) 294-1960

kmh@ameslab.gov

Rana Biswas, (515) 294-6987

biswasr@ameslab.gov

Mihail Sigalas, (515) 294-7245

sigalas@ameslab.gov

Kristen Constant, (515) 294-3337

constant@iastate.edu

Current research funded by:

DOE Office of Basic Energy Sciences

Inquiry 11

1999
IBM workstations are helping advance cluster

computing research at Ames Laboratory.

DOE Labs Unite to Advance 

Computational Materials Science

Ames Laboratory Deputy Director Bruce Harmon recognizes the key role computational modeling has

to play in the design, processing and production of better

materials with more desirable properties. To advance that

effort, Harmon, also the director of the Lab’s Condensed

Matter Physics Program, helped create and now serves as

one of the coordinators for

the new Computational

Materials Sciences Network.

 CMSN is funded through

DOE’s Basic Energy Sciences Office and came about

as a result of interactions

between Harmon and Iran

Thomas, director of the BES

Division of Materials

Sciences, as well as the other

CMSN coordinators: Chuck

Henager of Pacific Northwest Laboratories, Malcolm

Stocks of Oak Ridge

National Laboratory and

Ellen Stechel of Ford Motor

Co.

The coordinators planned a series of CMSN workshops that brought together scientists from DOE labs,

academia, industry and other government labs to formulate challenging materials science projects that could best

be pursued through broad cooperative efforts. Seven

broad subject categories were identified:

▼ Polymers at Interfaces

▼ Understanding Ductile and Brittle Behavior in

 Fracture

▼ Excited-state Electronic Structure and Response

 Functions

▼ Microstructural Evolution Based on Fundamental

 Interfacial Properties

▼ Bridging Basic and Applied Science in Magnetic

 Materials

▼ Oxidation

▼ Microstructural Effects on the Mechanics of

 Materials

“CMSN focuses on relevant, interesting and important science,” says Harmon. “Larger, more complex

problems require interdisciplinary teams, and CMSN

provides a means for the DOE materials science community to work together where there’s mutual interest in

solving significant problems.”

Access CMSN at:

 http://cmpweb109.ameslab.gov/cmp/ccms.

Intouch

IT TAKES A TEAM IBM Grant 

Gives Huge Boost

to Cluster Computing

When IBM officials visited Ames Laboratory and Iowa State University last April, they brought

their checkbook with them – figuratively speaking. The

visit was to formally announce the company’s selection of

ISU’s chemistry department as the recipient of a Shared

University Research grant.

The chemistry department and Ames Lab’s Scalable

Computing Lab and Condensed Matter Physics Program

all benefit from the

$665,000 SUR grant

that provided 15 dualprocessor, top-of-theline IBM Power3 RS/

6000 43P Model 260

workstations. Housed

in the SCL where one

of the primary objectives is to develop new

methods for doing

scalable computing,

the workstations are

helping to advance

cluster computing.

Cluster computing

involves networking

groups of highperformance workstations to create clusters

that operate at

supercomputer speed and at a very economical cost.

“ The SUR grant is highly competitive,” said Mark

Gordon, director of Ames Lab’s Applied Mathematics and

Computational Sciences Program and an ISU distinguished professor of chemistry. “ The fact that we

received it says that Ames Lab’s and ISU’s combined

expertise is very attractive to IBM, and that they see great

promise in our collaborative efforts.”

Jeff VerHeul, vice president of Server and Workstation Development, IBM Server Group, said the SUR grant

allows IBM, Ames Lab and ISU to work closely to explore

the performance of clustered systems. “All three organizations will benefit from the discovery and shared learning

currently underway,” said VerHeul. “Professor Gordon’s

team has built a world-class learning laboratory using this

new technology to solve real-world scientific problems.”

Inquiry1999 12

Bruce Harmon
“It’s always fun to be one of the

first to find something new.”

Two years ago, Ames Lab assistant scientist Dan Barnard uncovered

a scientific riddle that has yet to be

solved.

Barnard and Otto Buck, former

director of the Metallurgy and

Ceramics Program, were conducting

experiments with acoustic harmonic

generation, a

technique in

which ultrasound

frequencies

provide information about a

material’s strength

and other characteristics. As Barnard

plotted the data from his experiments,

he noticed a pronounced downward

curve as the amplitude of the frequency decreased. He showed the

graph to Buck, who asked in his thick,

German accent, “Vat’s dat hook?”

Inquiry 13

1999

Grappling

With

the

By Susan Dieterle

Dan Barnard (foreground) and Jim Foley use acoustic harmonic generation techniques on a single crystal of copper that sits in the middle of the three-tiered

apparatus.

don’t have any preference as far as the

real source of the hook,” he says. “I’d

just like to know what’s causing it.”

 The debate is difficult to resolve

because researchers are still trying to

understand acoustic harmonic

generation. The technique comes

from the realm of nondestructive

evaluation in which the reliability of

materials is studied without the use of

invasive procedures. Ultrasonic

testing, which involves transmitting

high-frequency sound waves into a

material to detect imperfections and

microstructural changes, is a standard

evaluation method. It is often used in

a linear fashion, which involves

pumping sound energy

into one end of a

material and then

measuring how much

energy comes out the

other end.

But there is a

growing interest in nonlinear acoustic

techniques like harmonic generation,

Barnard says. While the approach is

similar, scientists also measure the

faint frequencies emanating from the

microstructure itself at double, triple

and even quadruple the rate of the

— Dan Barnard

Thus was born

“the hook” – and the controversy

about whether it even exists.

As Barnard and other scientists

have grappled with what the hook

means, two schools of thought have

emerged. One side thinks the

sensitive testing equipment is picking

up noise from the instrumentation

itself, and that the hook doesn’t really

exist. The other side believes the

hook may indicate something new

about the microstructure of the

materials being tested.

Which camp is Barnard in? “I
original frequency.

“For example, we put in energy

at a fundamental frequency of 10

megahertz and then we look at the

energy in the harmonics, usually at

20 and 30 megahertz,” Barnard says,

noting that the harmonics are usually

1/100th or 1/1,000th the strength of the

fundamental frequency.

Cracks, dislocations and fatigue

in the material produce the second

harmonics, but no one fully understands how or why. “We don’t have a

complete understanding of the

sources of harmonic generation and

we don’t know how they relate to

each other,” Barnard says. “We want

to find out how each source affects

harmonic generation, and how they

affect it when they’re combined.”

 What they do know is that

harmonic generation is more sensitive than linear methods and can

detect cracks that aren’t visible –

even through the most powerful

optical microscope. “There are

limitations on what kind of information you can get out of the materials

with linear acoustic techniques,”

Barnard says. “Harmonic generation

is a lot more sensitive to very fine

changes that can occur at the microstructural level and even at the atomic

level.”

That kind of information could be

crucial in settings such as power

plants, where high temperatures and

radiation can make materials brittle.

“You don’t ever want a brittle material

when you have lots of power or

pressure or temperature behind it,”

Barnard says. “Theoretically, they

could use harmonic generation to

determine the state of a material and

know when to retire it and put in new

material.”

First, though, scientists need a

better understanding of harmonic

generation, and they need to adapt the

technique for use in the field. Currently, the procedure requires painstaking, time-consuming measurements that wouldn’t be possible in

industrial settings (see sidebar next

page).

The experiments that Barnard and

Buck began two years ago were part

of a collaboration with Oak Ridge

National Laboratory to establish a

deeper understanding of the phenomenon by measuring samples of

copper-aluminum alloys.

Theory predicted that the data

from the experiments would move in

a straight line until reaching the

“noise floor,” or the level of background noise, which would then cause

the data to shoot upward. That’s why

the emergence of the downward hook

at low amplitudes was so puzzling.

“We’d never seen it go down and

then go back up, and we couldn’t

think of any experimental reason why

it would do that,” Barnard says,

adding that he has also seen the hook

with samples of pure aluminum. In

his tests with fused silica, however,

there was no hook.

So far, Barnard and others have

been unable to provide a definitive

answer about the nature of the hook.

Scientists at Oak Ridge produced an

equation in support of their belief that

the hook came from instrument noise,

but Barnard says their

equation doesn’t fit all of

the data.

Also, researchers at

NASA’s Langley Research

Center have found curved

deviations – some upward,

some downward – at low

amplitudes in aluminum

alloys. John Cantrell,

senior materials physicist in

the Nondestructive Evaluation Sciences Branch at

Langley, says that much of

the curvature in his data

appears to be linked to

instrument noise. When

corrected for that factor, the

curves disappear – almost.

“If we go down to

sufficiently low amplitudes,

we still see some variation,”

Cantrell says. “But we’re

not sure whether that’s due

to an instrument offset or

whether that’s real.”

Inquiry1999 14

The graphic illustrates the emergence of the downward "hook" at low amplitudes in tests

involving four copper-aluminum alloys. Barnard is trying to determine whether the hook is

caused by the material itself or by equipment noise.

0

2

4

6

8

10

12

14

16

18

20

Nonlinearity Parameter, 

β

0 2 4 6 8 10 12 14 16 18 20 22 24

Fundamental Amplitude, A1 (Angstroms)

Cu-2 at% Al

Cu-4 at% Al

Cu-6 at% Al

Cu-8 at% Al
Inquiry 15

1999

Cantrell, who uses different

harmonic-generation techniques and

equipment, says he plans to test the

Ames Lab copper-aluminum samples

to corroborate Barnard’s findings.

“If it turns out that the hook, or at

least part of the hook, is real and not

due to instrumentation offset, that

would give us some insight into the

material physics going on at low

acoustic amplitudes,” Cantrell says.

“But even if it isn’t a physical process

in the material, the very fact that

there’s an instrumentation situation

has to be recognized. In some cases,

you’re going to be publishing data

from low-amplitude tests, and you

have to make sure you don’t have

instrument offset giving you false

positive readings.

“Either way, Dan has made the

nondestructive evaluation community

aware of a very important situation,”

he adds.

Notes Jim Foley, who now serves

as Barnard’s Ames Lab group leader,

“The hook is a result – not that we

understand that result, but it’s a result.

Now we have to see what we can do

to critically evaluate whether it’s a

real phenomena or an instrumental

phenomena.”

Since Buck’s death in November

1997, Barnard has continued working

with Oak Ridge to better understand

the nature of harmonic generation and

its contributing sources. In addition,

Ames Lab has received funding from

the Department of Energy to research

ways of adapting the technology for

use in the field.

“I think this technique has a

definite use in the real world,” he

says. “And there aren’t a whole lot of

other people doing this kind of

research. It’s always fun to be one of

the first to find something new.”

The Lab recently purchased a

more sensitive amplifier system that

Barnard hopes will give him new

insights into harmonic generation.

And it may also help him solve the

perplexing riddle of the hook. If it

turns out to be a true material phenomenon, Barnard would like to call

it the Otto Buck Hook in memory of

his mentor.

“If it’s an instrumental effect,

then I’d like to know what it is and

develop a correction for it,” Barnard

says. “But if it’s a material effect,

then that’s something new, and we

want to know what’s going on.”

And although much of Barnard’s

time is spent on other research, the

hook remains firmly embedded in his

thoughts. “When I have time, I go

back and do some measurements to

see if the hook is still there,” he says

with a smile. “And it’s always there.” ✤

For more information:

Dan Barnard, (515) 294-9998

dbarnard@ameslab.gov

Current research funded by:

DOE Office of Basic Energy Sciences

How does it work How does it work

requires patience and precision.

How does it work

Using acoustic harmonic generation ?

Researchers like Dan Barnard hope to find

ways of making the technique easier to use in

the field. If they can do that, they’ll give

industries a powerful new tool that will

provide the earliest possible information about

cracks and fatigue within a material.

But for now, harmonic generation is used

only in research laboratory settings. “Right

now, the techniques take so much time that

they could never really be applied to industry,”

Barnard says. “For some tests, we have to

polish the surfaces of the material until they’re

mirror-smooth. On a factory floor, that’s just

not easy to do.”

It usually takes Barnard at least three hours

to set up and conduct a single series of tests.

After putting the material in the sample holder,

he must let it sit for an hour to make sure that

it’s absolutely still. Then he uses mineral oil to

couple the receiving transducer to one side of

the sample. Because the transducer is loaded

on a spring and rests slightly against the

sample to pick up the vibrations during the

test, Barnard must let the sample sit for

several minutes until the oil “squeezes out” to

the thinnest possible layer before taking a

calibration measurement. Then he must repeat

the process on the other side of the sample

with the transmitting transducer.

During the test, ultrasonic pulses are sent

into one side of the 1- to 3-inch sample. The

pulses must be short enough that they finish

going in one side of the sample before they

come out of the other. “We’re talking about

millionths of a second,” Barnard says.

A complex network of amplifiers and

recorders measures the original signal as it

goes into and out of the sample, as well as the

“second harmonic” frequency generated by the

microstructure at double the original rate.

In addition, Barnard must take a variety of

measurements from the equipment itself to

ensure the greatest possible accuracy. “If one

of those measurements is off, it can skew the

results,” he notes.

The process isn’t easy, but Barnard thinks

it’s worth it. “Because of the high sensitivity

of this technique, I think it has real promise,”

he says.

As short pulses are shot into the copper crystal, the

frequencies generated by the microstructure are shown on

the oscilloscope behind the sample holder.
Tom Barton

“This is a challenging time for

federal laboratories, and I look

forward to working closely with the

FLC as it helps its members

strengthen ties with industry,” Barton

said.

Barton became director of the

Ames Laboratory in 1988. Since

April 1998, he has also served as

director of the Institute for Physical

Research and Technology, a consortium of 11 research and technologytransfer centers on the Iowa State

University campus. Ames Lab is the

largest of the IPRT centers. Barton is

also an ISU distinguished professor of

chemistry.

Ames Laboratory scientists are hoping to convert some of their analytical expertise into techniques that

may help local and national forensic investigators.

Representatives from

both the FBI Laboratories

and the Iowa Criminalistics

Laboratory are searching

for rapid, more accurate

methods of assessing

crime-scene evidence.

Forensic investigators

often use various types of

chemical and materials

analysis as they search for

clues from evidence such

as firearm residues,

fingerprints and fragments

left by explosive devices.

Because Ames Lab

scientists use some of the

latest analytical techniques

available in these fields,

law-enforcement agencies are interested in finding ways

of adapting these techniques for use in forensic investigations.

Five research projects for the FBI Laboratories – the

Intouch

Barton Will Help Chart Course for Barton Will Help Chart Course for

National Laboratory Organization National Laboratory Organization

Inquiry1999 16

Lab Scientists Apply Analytical Expertise to

Forensic Techniques

Ames Lab director Tom Barton has

 been appointed to the National

Advisors Group for the Federal

Laboratory Consortium.

The FLC is a quasi-governmental

organization involving 711 federal

laboratories. Its primary focus is

moving laboratory research and

technology into the marketplace. The

National Advisors Group is a select

panel of approximately 15 people

who provide guidance to the FLC in

pursuing its technology-transfer goals

and making the organization more

effective. The group includes senior

agency officials, laboratory administrators and industry leaders.

nation’s largest forensic laboratory – are already underway. Along with counterparts from the Iowa State

University campus, Ames Lab scientists are investigating

techniques that would enable criminal

investigators to:

▼ Restore stamped or engraved serial

 numbers that had been obliterated

 from guns and stolen automobiles

▼ Characterize various types of

 explosive devices and understand

 blast effects upon detonation

▼ Use analytical tools to determine

 the sources of metal fragments

 found at crime scenes

▼ Develop criteria for comparing

 pieces of trace evidence

▼ Access an electronic database of

 facilities and veterinarians through-

 out the country who could rapidly

 determine the presence of animal

 pathogens that could be used as

 biological warfare agents

Meanwhile, Lab officials are still discussing possible

research projects with the Iowa Criminalistics Laboratory,

which serves local and state law-enforcement agencies in

Iowa.
For good or for bad – the jury is

still out – tiny amounts of various

metals in our bodies give up their

freedom for a chance to cozy up to

our DNA. In fact, trace metals can

get pretty friendly with all kinds of

biological systems, abandoning their

freedom in the ecosphere to attach

and bind themselves to proteins and

other biomolecules. And whether

this circumstance is good or bad

depends on the element.

“The basic phenomena responsible for the toxicity of trace elements

are complex,” says Sam Houk, senior

chemist. “Some elements like

cadmium and lead can replace

essential elements like copper and

zinc in enzymes, thus interfering with

the biological activity of the enzyme.

Radioactive elements like uranium,

thorium and other actinides are toxic

chemically. They can also bind to

DNA and cause mutations when they

decay. Since the Department of

Energy has large amounts of such

elements in storage, monitoring their

binding to proteins and DNA at very

low concentrations is of great

environmental importance.”

Measuring the metal

 Using a novel extension of

inductively coupled plasma-mass

spectrometry, a well-established

analytical technique pioneered at

Inquiry 17

1999

A novel use of an old method is

speeding identification of trace

metals in biological systems

ANew

Twist

for

Tracking

Trace

Elements

Using his innovative technique that combines ICPMS with chromatography, Sam Houk can identify

ultratrace metals in biological systems at parts-pertrillion levels. As his office decor suggests, the

scientist is also a dedicated student of history, and

he relishes the opportunity to take an interested

“pupil” back in time.

by Saren Johnston
Ames Laboratory, Houk can determine the total amounts of ultratrace

metals in biological specimens. His

method is faster and more sensitive

and selective than conventional

schemes. Allowing measurements at

parts-per-trillion levels, the ICP-MS

technique relies on a special type of

chromatographic separation called

size exclusion chromatography in

connection with a state-of-the-art

magnetic sector mass spectrometer

and an inductively coupled plasma –

a very hot argon gas.

In Houk’s new method, chromatographic separation of the

compounds of interest provides

chemical information, in particular

the molecular weights of the proteins.

Jin Wang, who recently received his

Ph.D. with Houk and is now a

postdoctoral fellow at Baylor College

of Medicine in Houston, did much of

the chromatography work. “It’s his

specialty,” says Houk. “He did

almost all of the experiments. He’s

good at both chromatography and

ICP-MS.”

The chromatography work is

crucial because it reveals the percentage of a trace element in a sample that

is bound to particular biomolecules.

“If we just put the entire sample in the

ICP, it would only measure the total

amounts of the individual elements

present,” says Houk. “It would not

tell us that, say, 90 percent of an

element is in a particular molecular

weight range, and 10 percent is in a

different fraction.”

Once the chromatography is

completed, the sample is automatically injected into a nebulizer that

produces a mist of fine droplets. The

droplets dry into aerosol particles and

pass into a hot argon inductively

coupled plasma. In the ICP, they are

converted to atomic ions that are

measured by the mass spectrometer.

The resulting measurements provide

data that allow scientists to better

comprehend the effects of unusual

elements in

biology and

environmental

sciences.

Houk is

quick to point

out that his

development of

the new ICPMS method for

trace metal

identification

was facilitated

by interactions

with instrument

manufacturers

Transgenomic

CETAC Technologies and Finnigan

MAT and Micromass Ltd. CETAC

provided personnel, nebulizers and

supplies, while Finnigan MAT loaned

the mass spectrometer on which Houk

ran his experiments. And Dan

Wiederin, a former Ph.D. student of

Houk’s and now the president of

Elemental Scientific in Omaha, has

served as the primary collaborator on

the research.

Few limits

Houk’s experiment is applicable

to almost any element in practically

any kind of biological system. “The

main exceptions are the common

elements that are always present:

carbon, nitrogen, oxygen and hydrogen – we don’t measure those,” he

says.

Just as there are few limits

regarding the elements to which Houk

can apply his methodology, there is

also a seemingly endless array of

potential applications. Work for the

Department of Energy deals with

determining the fate of radionuclides

in the ecosphere, a major concern in

the cleanup of nuclear facilities. The

conversion of radioactive elements to

atomic ions in the ICP considerably

reduces the time required for measuring nuclides with long half-lives from

that required by conventional techInquiry1999

18

niques.

“There are also important medical

applications,” says Houk. “For

example, there’s a lot of interest in

selenium compounds, which are being

marketed as health foods and as

preventive treatments for cancer and

are touted to delay the onset of AIDS

symptoms. But there have been few

direct measurements of the role of

selenium in this regard.”

Agricultural applications could

involve extracting proteins or other

macromolecules from grains and

measuring the binding of trace

elements. Similarly, researchers could

measure the binding of metal ions to

environmental compounds, such as

humic acids, large polymeric compounds with many carboxylate groups

attached.

Houk says his experiment could

An open view of the inductively coupled plasma

chamber (top photo) looks drab compared to the

brilliant emission from the hot argon ICP.

bottom photo courtesy of Varian Corporation
What the ICP does is give us an

extremely sensitive and selective way

to find unique inorganic elements.”

To more precisely identify the

proteins, Houk says they would

probably start with size exclusion

chromatography, collect a fraction of

the liquid coming out of the chromatographic column and inject it into

another kind of chromatographic

column that would provide better

resolution.

“We might also try capillary

electrophoresis, which is an effective

way to separate proteins. And we

could use different variations of mass

spectrometry, such as electrospray

MS, which can measure molecular

weights and also the sequences of

amino acids but is much less sensitive

to whether there are small levels of

inorganic elements present. These are

some of the things we have in mind

for the future.” ✤

For more information:

Sam Houk, (515) 294-9462

rshouk@iastate.edu

Current research funded by:

DOE Office of Basic Energy Sciences

weight,” he says. “A chromatographic fraction for an element could

include many different proteins that

contain that element. We want to

separate those proteins more effectively and also develop mass spectrometric measurements that will be

sensitive to the particular molecule.

You see, we get information on the

identity of the molecule only from the

chromatography, not from the ICP.

Inquiry 19

1999

also be used to measure trace metals

in synthetic polymers if they could be

brought into solution. “There is

some interest in this since the

processing procedures for polymers

usually involve exposing the material

to metals,” he explains. “There’s a

question about where the metals wind

up in the final product.”

More selectivity

Houk’s experiment can accommodate just about any organic sample

as long as it has an inorganic element

in it. But now his goal is to improve

selectivity in identifying the biological compounds. “Currently, all we

get in this particular experiment is a

kind of crude separation of compounds based on their molecular

Houk’s experiment is applicable to

almost any element in practically any

kind of biological system.

Jin Wang observes the fine droplets of mist created when a sample is injected into the

nebulizer following the chromatography process.
W

hen chemists try to predict

 whether the chemicals they want

 to combine will create a reaction,

they must first know if the reaction is

energetically possible – if there’s

enough “oomph” in the atoms to make

the reaction go.

Knowing the ionization and bond

dissociation energies for the molecules under investigation is critical to

accurately predicting reactions, such

as electron transfer or oxidationreduction processes. And Cheuk Ng,

an Ames Laboratory senior chemist

and an Iowa State University distinguished professor of chemistry, has

helped many a chemist make some

successful and more accurate predictions. His research in vacuum

ultraviolet (VUV) chemistry has

provided some of the most accurate

ionization and bond dissociation

energy data for many molecular

species.

Ng considers himself fortunate

because he has a dual “playground”

in which to investigate molecular

dissociation (separation into two or

more fragments, creating atoms, ions

or radicals) and ionization processes

in the VUV range of the spectrum –

photon energies in the 6-30 electronvolt region. There, in principle, any

molecule can be ionized, a process in

which a molecule or atom loses an

electron, acquiring a net charge and

making the transformation to an ion.

To perform his experiments, Ng takes

advantage of the third-generation

synchrotron radiation source at the

Chemical Dynamics Beam Line

associated with the Advanced Light

Source (ALS) at the Department of

Energy’s Lawrence Berkeley National

Laboratory. Or, he may use the stateof-the-art high-resolution VUV laser

apparatus at Ames Laboratory.

To be sure, Ng’s research sounds

weighty and complicated, but he

would argue unequivocally that it is a

fundamental thing of beauty. “When

I look at the data and understand it, I

feel unified with the universe and in

harmony with nature,” he says. “It’s

very basic research, but I’m excited

about it because every day I learn

something new. How much energy

does it take to ionize or dissociate a

specific molecule? This is a parameter that is fundamental to chemists.

Once they know the energetics, they

can use them to predict reaction rates.

Those rates are needed for modeling

problems in atmospheric, plasma and

combustion chemistry.”

The Berkeley playground

Ng’s work at the Advanced Light

Source centers around the highresolution VUV facility he designed

for the Chemical Dynamics Beam

Line. Specialized instrumentation at

the VUV facility allows him to make

both photoionization and photoelectron measurements. The spectroscopy he performs provides informa-

“Whether it’s basic research or applied

research, they are both very useful –

it’s a matter of time scale, but basic

research is always useful.” — Cheuk Ng

Inquiry1999 20

By Saren Johnston

This ion gauge monitors the quality of the vacuum in the high-

 resolution vacuum ultraviolet laser system used to measure

 photoions and photoelectrons.
“When I look at the data and understand it, I feel unified with the

universe and in harmony with nature.”

— Cheuk Ng

tion on the ionization and dissociation energetics of specific molecules

of interest. Photoionization spectroscopy involves detecting the ion(s)

produced when

one or more

electrons are

removed from an

atom or molecule

by absorption of

a VUV photon.

Photoelectron

spectroscopy offers a means of

detecting the electron(s) liberated by

photon-molecule interaction.

To design the VUV facility, a

unique user facility that today serves

chemical physics researchers

throughout the world, Ng went back

in time, in a manner of speaking. “I

started to design our experimental

station at Berkeley in the summer of

1993,” he says. “I went back to live

in a graduate student dorm, and I

worked like a graduate student.

Everybody asked me which group I

was working in at Berkeley, and I

told them I had graduated years

ago,” he says with a laugh,

recalling his brief return to

graduate school days.

In 1994, Ng sent graduate

students Chia-Wei Hsu and

Matt Evans to Berkeley to

assemble the photoelectron/

photoion apparatus he had

designed for the experimental station. “These two

students put the whole thing

together. I only put together

the mechanical design,” says

Ng modestly. “In 1995,

everything was up and working.

Chia-Wei and Matt did all the

performance checks for the apparatus,

so whenever I traveled from Ames to

visit the Berkeley experimental

station, I only had to ask, ‘How are

things going?’ I feel I’ve become a

theoretical experimentalist,” Ng

jokes, but with a certain

measure of seriousness. “I design

a scheme

and ask

the

students to try it and report the results

to me.”

The VUV facility is considered

the best in the world for doing ion

chemistry. “The photon energy

resolution and energy range we can

cover is unprecedented,” says Ng.

“Due to the development of several

novel experimental schemes, the

resolution we can achieve is at least

10 times better than what was

available in previous synchrotronbased studies before the VUV facility

existed.” Ng notes that they can

measure the dissociation threshold

Inquiry 21

1999

"We scientists live in an obscure corner that may not be related to daily life,"

says Ng, who often works day and night. "My research inspires me – that's not a

feeling you can easily explain. You have to experience it. And as I get older, the

teaching becomes more significant. Maybe that's more important than the

research," he muses. "My son tells me, 'Daddy, you don't have enough sleep; go

back to sleep.' But I cannot explain to him that I can't wait to wake up, see my

students and renew."
and thus the bond dissociation energy

of a molecular ion to the accuracy of

less than 0.001 electron volts. “Many

of the things we are doing now can be

considered as breakthroughs in the

field of VUV chemistry, and the

facility coaxes us to do more,” he

says.

Eyes on the ions and radicals

Some of Ng’s work includes

looking at radicals, or unstable

molecules, to explore the energetics

of combustion species for the

Department of Energy. “Combustion

is almost impossible to understand

because it’s a radical chain reaction,”

he says. “When one radical is formed,

it initiates another reaction, so there

are many, many intermediate species

that have not even been detected and

for which the energetics and structures are not known.”

An aspect of Ng’s research

important to plasma chemistry

involves looking at the reactivities of

ions and radicals, which depend on

their internal energy states. The state

of a molecule is related to how the

electrons and nuclei arrange in the

molecule. Because of the high

resolution capability of the VUV

facility, Ng is able to select a given

state of a molecular ion and then react

it and look at how the internal

excitation influences chemical

reactivity.

“A molecule can move around –

that’s what we call translational

energy,” says Ng. “A molecule can

also vibrate – vibrational energy, and

rotate – rotational energy. Electrons

can also arrange differently with

respect to the nuclei,” he adds. “This

arrangement gives rise to the specific

electronic state of the molecule. So

all of these things can influence the

chemical reactivity of the molecular

species. The study and ultimately the

control of molecular reactivity are of

great interest to chemists. So the

VUV facility has opened up opportunities for future investigations in

which scientists can really

control the internal energy of a

molecular ion to a very high

degree. For VUV chemistry, I

can confidently say that this

facility is the best in the world.

Many users have come here

and told me the same thing. So

it’s better that they tell me than

I say so,” Ng notes with a

smile.

His research is also helping

advance knowledge in the field

of atmospheric chemistry. The

ionosphere, the outermost

shield of the earth’s atmosphere, is ionized and dissociated by solar ultraviolet and

VUV radiation. In order to

understand and model the chain

reactions that follow the

ionization and dissociation

processes and cause such

phenomena as the aurora

borealis, Ng says scientists

must first measure the reaction

rates and determine how the

ions are initially formed. “A lot

of research work is needed,” he

says with conviction.

The home turf

As remarkable as the VUV

facility is, Ng can’t spend all his

time at the ALS. So, with the

assistance of fellow chemist

Chung-Lin Liao and postdoctoral

fellow Yuxiang Mo, he also runs

experiments on the high-resolution VUV laser instrumentation at

Ames Laboratory.

“The VUV laser has an established resolution better than that we

can achieve at the ALS, but it’s very

difficult to tune,” says Ng. “For

example, if you want to tune about .2

electron volts, it would take a few

weeks for two students to work on it.

At the ALS, we can tune through

more than 10 times that range in one

week, so the throughput or productivity comparison is no match at all. I

don’t think the laser can win in this

case. The resolution is slightly worse

at the ALS, but you don’t lose that

much chemistry and physics. It’s

really the ease of tunability that

makes the synchrotron so attractive.”

Ng explains that many of the

techniques they have now developed

for the ALS facility were previously

laser-based. “Now that we have

tapped into the synchrotron, I think

the laser is gradually losing ground,”

he says. “But for optical resolution,

the laser is still the best. Furthermore, some experiments are easier

using VUV lasers.”

Inquiry1999 22

This time-lapse photo shows Chung-Lin Liao (right) and Yuxing Mo

at home in their Ames Lab research space where they use the

high-resolution vacuum ultraviolet laser system to perform

detailed ionization studies.
Ng and Liao have many ongoing

projects in their Ames Lab research

quarters. They are focusing on VUV

mass spectrometry, VUV and ionetching reactions, and photoelectron

spectroscopy of radicals. “For the

studies of radicals, the VUV laser is

expected to do a better job than

synchrotron radiation because most

radicals can be prepared with high

specificity by pulsed laser dissociation,” explains Ng. “This pulsed

radical source matches the pulsed

nature of the VUV laser system.”

Ng on impress vs. inspire

Two students from Ng’s group,

Evans and Stephanie Stimson,

finished their Ph.D. theses working at

the VUV facility at the ALS, and Ng

will soon be sending three or

four more students to work

there. “It’s a tremendous

educational instrument for our

group,” he says. “Many

people in the world who are

known to be experts in VUV

chemistry come to the ALS,

so these students have the

opportunity to interact with

them and learn from them, not

just from me. Then, after

spending four or five years

working at the VUV facility,

the students will already have

connections with well-known

scientists.”

Ng says there is no better

avenue for training students

than basic research and that as

he gets older the teaching part

of his job becomes more

significant. “I often have

students ask me why they

have to learn certain things,”

he says. “To me, it’s very

obvious – understanding is

really the fulfillment in life. I

tell my students, ‘There are

two ways to make you work

hard – one is to impress and

one is to inspire. To impress

means you apply yourself – if

I do this and work hard, I’ll get a

million bucks in maybe a year or so.

Inspire means you don’t talk about

money – you work night and day.

That’s a higher level of learning.’

“If I work night and day on a

project, it must be fun,” says Ng.

“Fun is actually the key to being

inspired. I would like my students to

be inspired. The most important

mission to me is not to produce a

commercial product but to train

students.”

No boundaries

As Ng’s research matures, the

molecules he investigates at the VUV

facility are becoming more complex.

“We’ve been working on small

molecules because we have to test the

techniques we develop,” he says.

“But we’re moving on to more

complicated molecules related to

combustion.

“The VUV is a user facility, so

my job is to convince people that this

research is exciting,” he adds. “It has

been quite a venture in the last year.

People come from the United States,

Japan, Germany and France because

the chemistry is completely different

compared to working in a lab.

Everybody has his or her own

expertise, and I pick up many ideas

from users when they come. So to

me, the whole world is like a playground. I don’t feel the boundaries

anymore.” ✤

For more information:

Cheuk Ng, (515) 294-4225

cyng@ameslab.gov

Current research funded by:

DOE Office of Basic Energy Sciences

Inquiry 23

1999
Ateam of Ames Laboratory scientists has earned

 national recognition for its work with quasicrystals,

relatively new materials with potential as highly effective

coatings for automotive and mechanical parts and frying

pans.

The group received the U.S. Department of Energy’s

1998 Materials Sciences Award for “Outstanding Scientific Accomplishment in Materials Chemistry” for its work

in understanding the surface properties of quasicrystals.

The annual

awards

recognize

scientists at

DOE laboratories for their

research

accomplishments.

In the late

1980s,

scientists

discovered

that

quasicrystal

materials were

highly

resistant to

wear and

corrosion, and that they had low coefficients of friction –

highly desirable properties for coatings on mechanical and

automotive parts.

What was lacking, though, was an understanding of

why the materials exhibited these surface properties – a

shortcoming that Ames Lab researchers wanted to address.

“Five years ago, there were almost no papers in the

literature concerning surface properties of quasicrystals,”

said Pat Thiel, director of the Lab’s Materials Chemistry

Program. “The Ames group has begun to lay a foundation

for understanding this topic and is now internationally

recognized for its efforts.”

In addition to Thiel, the group includes Dan Sordelet,

James Anderegg, Matt Besser, Tamara Bloomer, Alan

Goldman, Cynthia Jenks, Matt Kramer and Tom Lograsso.

Other collaborators include Martin Gierer from Ludwig

Maximilians University in Munich, Germany, and Michel

Van Hove of DOE’s Lawrence Berkeley National Laboratory.

(from left) Ames Lab researchers Karl

Gschneidner Jr., Vitalij Pecharsky and David Jiles

Scientists at Ames Laboratory have begun working on a prototype cooling unit based on magnetic-refrigeration

technology.

Researchers Karl Gschneidner Jr., Vitalij Pecharsky

and David Jiles expect the prototype to demonstrate that

magnetic refrigeration is a reliable source of cooling

power, and is more energy-efficient and environmentally

safe than the vapor-cycle systems now used in refrigerators and air conditioners. They will be working with

Milwaukee-based Astronautics Corp. of America, the

Lab’s industrial partner in the project.

If successful, the prototype would be the first magnetic refrigerator capable of sustained operation and

generating enough cooling power for commercial applications.

Magnetic refrigeration is based on the magnetocaloric

effect – the ability of some materials to heat when magnetized and cool when removed from the magnetic field.

Using these materials as refrigerants would provide an

environmentally friendly alternative to the volatile liquid

chemicals, such as chlorofluorocarbons and

hydrochlorofluorocarbons,

used in traditional vapor-cycle

cooling systems.

In April, Ames

Laboratory and

Astronautics signed an

agreement to develop a

rotary prototype

magnetic-refrigeration

unit. The U.S. Department of Energy will

provide $750,000 in

funding over the next

three years toward the

project, and Astronautics will provide a

matching amount

through in-kind

contributions of personnel, research, services and facilities.

Ames Lab is concentrating on optimizing the refrigerant materials and developing a source for the magnetic

field that is more convenient and cost-effective than

superconducting magnets. Astronautics will design, build

and test the prototype.

“When these pieces of the puzzle are properly put

together, it will create a benchmark for all future developments of this new, emerging technology,” Pecharsky said.

Inquiry1999 24

Intouch

Scientists Nationally Scientists Nationally

Recognized for Recognized for

Quasicrystal Research Quasicrystal Research

Work Begins on Prototype

Magnetic Refrigeration Unit

This single-grain quasicrystal shows the pentagonal

facets that are characteristic of quasicrystal materials.

photo courtesy of P. C. Canfield and I. R. Fisher
Ankeny High Trio Ankeny High Trio

Triumphs at 1999 Triumphs at 1999

Ames Lab/ISU Ames Lab/ISU

Science Bowl Science Bowl Science Bowl

I

t was a battle of experience versus quantity in the

 championship match at this year’s Ames Laboratory/

ISU Regional Science Bowl. And experience won out.

Ankeny High School defeated Pleasant Valley High

School for the title, becoming the first three-member

team to win the annual Ames Lab/ISU event. The

competition drew 200 students who demonstrated their

academic skills in answering questions from a broad

range of science and math topics.

While most of the 40 participating schools had four

or five students on their teams, Ankeny decided to field

a team of only three players when a fourth student

withdrew because of another commitment.

“These three students are seniors who have

played together on Science Bowl teams since they

were sophomores,” said Ankeny coach Mark Maffett.

“They decided they knew each other so well that

they didn’t want to add someone new.”

Ankeny went on to participate in DOE’s

National Science Bowl along with 52 other regional

winners. Nationwide, more

than 9,000 students from

1,800 schools took part in

Science Bowl competitions.