A MATERIAL WORLD Tailoring Materials for the Future

WINTER• 2000-2001

A MATERIAL WORLDTailoring Materialsfor the Future

A QUARTERLY RESEARCH & DEVELOPMENT JOURNALVOLUME 2, NO. 4

ALSO:

New Materials for Microsystems

Predictive Modeling Meets the Challenge

S A N D I A T E C H N O L O G Y

ON THE COVER:Bonnie Mckenzie operates a dual beam Focused Ion Beam/Scanning ElectronMicroscope (FIB/SEM). The image on the computer screen shows a crosssection of a radiation-hardened device. The cross section was renderedwith the FIB/SEM and allowed the observation of stress voids that couldresult in device failure. The background image is a spectrum image of atwo-phase steel taken in a Scanning Electron Microscope. The image wasanalyzed using Sandia's newly developed information-extraction software.

Sandia Technology is a quarterly journal published bySandia National Laboratories. Sandia is a multiprogramengineering and science laboratory operated by SandiaCorporation, a Lockheed Martin company, for theDepartment of Energy. With main facilities in Albuquerque,New Mexico, and Livermore, California, Sandia has broad-based research and development responsibilities for nuclearweapons, arms control, energy, the environment, economiccompetitiveness, and other areas of importance to the needsof the nation. The Laboratories’ principal mission is tosupport national defense policies, by ensuring that thenuclear weapon stockpile meets the highest standards ofsafety, reliability, security, use control, and militaryperformance. For more information on Sandia, see ourWeb site at http://www.sandia.gov.

To request additional copies or to subscribe, contact:Connie MyersMarketing Communications Dept.MS 0129Sandia National LaboratoriesP.O. Box 5800Albuquerque, NM 87185-0129Voice: (505) 844-4902Fax: (505) 844-1392e-mail: [email protected]

Sandia Technology Staff:Laboratory Directed Research & Development ProgramManager: Chuck Meyers, Sandia National LaboratoriesEditor: Chris Miller, Sandia National LaboratoriesWriting: Katharine Beebe, Technically WriteDesign: Douglas Prout, Technically Write

Officials of FIRCO and CONAE (the Mexican National Commission for EnergySavings) discuss the recent installation of Sandia’s photovoltaic water-pumpingstation on Rancho Sagitario in Baja California Sur, just outside of La Paz,Mexico. The ranch manager is standing in the background (in the hat). (Fromleft: Oscar Sandoval, Regional Director of CONAE in Chihuahua; ranch manager,name not known; Jesús Parada, FIRCO, Chihuahua; and Simón Ortiz, FIRCO,Baja California Sur.)

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Dear Readers:

Materials science—always a vitalresearch area at Sandia NationalLaboratories—is taking on even greaterimportance as the nation’s nuclearweapons stockpile ages. Materialsscience is the study of the properties ofsolid materials and how those propertiesare determined by a material’scomposition and structure. Materialsscience can’t be understood within thecontext of any single discipline andtherefore combines an amalgam ofmany fields including solid-statephysics, metallurgy, and chemistry. Byunderstanding the origins of properties,materials can be selected or designedfor an enormous variety of applications,ranging from steel and lightweightpolymer components to silicon for themanufacture of integrated circuits andmicrosystems. Sandia’s work in materials scienceis critical to stockpile stewardship, orensuring our nation’s aging nucleararsenal remains safe, secure, andreliable. The nuclear arsenal is gettingolder than its design life, and withnuclear testing suspended, we must relyon fundamental science to ensureweapon components will continue tofunction and yet remain safe and secureas they remain in the stockpile. Sandia’s research in materials sciencecontinues to break new ground,particularly as we broach the relativelynew areas of nano- and biotechnology.What has become immediatelyappreciable is that much of our work inmaterials science—while focused onthe weapons program—has applicationsin many different areas that will benefitAmericans for years to come.

Chris MillerEditor

FROM THEE d i t o r

TABLE OFC o n t e n t s

A Material WorldTailoring materials for the future

New Materialsfor Microsystems

FAA Partnershipsto Reduce Alloy Defects

A Great IDEAfor Materials Analysis

Predictive ModelingMeets the Challenge

Affordable Hydrogen Getter

One Wafer, Many Tests

Solving a MysteryCould Lead to New Material Properties

Sandia’s PETL Facility:Where Materials Science Happens

Russian Cold Spray TechnologyComes to Sandia

Polymer GelsUsed as Actuators on a Microscale

I N S I G H T SBy V.S. Arunachalam, DistinguishedService Professor in the Department ofMaterials Science & Engineering,Engineering & Public Policy, and TheRobotics Institute of Carnegie MellonUniversity in Pittsburgh, Pennsylvania.

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Since thedawn of

civilization,materials have

been central to

our growth,

prosperity,

security, and

quality of life.

Nevertheless,

materials

research as an

identified field of

A Material Worldintellectual pursuit

is less than 50

years old. Its

emergence

coincides with

significant

expansion of the

field and its

growing contri-

butions to society.

Tailoring materials for the future

Sandia researcher Jeff Brinker observes the structures of a variety of submicroscopic spherescreated by his team at the nanometer scale.

New materials, or ways to make materials, are gaining greater use because of

their improved properties. These properties result from the materials’ composition

and structure at all levels, down to their atomic or

molecular structure and arrangement.

The field of materials research isdefined by the strong interrelationshipsamong materials’ properties, structureand composition, synthesis andprocessing, and performance. Indeveloping new materials, discoveryand application, and therefore scienceand engineering, are closelyinterrelated. Materials researchers study thestructure and composition of materialson scales ranging from the electronicand atomic through the microscopic tothe macroscopic. They develop newmaterials, improve establishedmaterials, and formulate methods to

produce materials reliably andeconomically. Researchers seek tounderstand phenomena and to measurematerials properties of all kinds. Theyalso predict and evaluate theperformance of materials as structuralor functional elements in engineeringsystems. This diversity of interests isreflected in the fields of materialsresearchers, who represent a broadrange of academic departments anddisciplines. Materials researchers are foundthroughout industry, academia, andgovernment. Their work can be limitedto one or two researchers at a small

start-up company or may involveseveral hundred staff at a majormaterials research center such asSandia. [See PETL Facility, page 14]Materials research also is aninternational endeavor. The MaterialsResearch Society, one of the majorprofessional societies in the field, hasmembers from more than 60 countries. Without new materials and theiradditional capabilities, many of thethings that we take for granted at thedawn of the 21st century—modern carsand airplanes, telecommunications,medicine, and computers—couldnot exist.

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Sandia has discovered a stress-free amorphous diamond thin film material that has many of the properties of crystalline diamond. The films as deposited have high stress, but a Sandia-discovered process allows for the complete tailoring of the final film stress state, from highly compressive through zero stress to tensile, depending on the need. The absence of film

stress eliminates the old problem with film de-adherence and now enables thick coatings to be applied to components to impart wear-resistance and hardness.

Sandia research has practicalapplications

Sandia’s materials science andtechnology (MS&T) organizationsundertake key research that forms thescientific basis for sound technicaldecisions about materials used in non-nuclear components for the nuclearweapons stockpile. These decisionsrange from materials choices, to themeans of manufacturing componentsand estimating component lifetimes.MS&T staff research the synthesisand processing of materials andmethods to determine their resultingstructure, properties, and performance.Staff apply insights gained from theseactivities to studies of materialsproperties that have technologicalimportance. Sandia’s three majorthemes of materials research arescientifically tailored materials,materials processing, and materialsaging and reliability.

Our work in scientifically tailoredmaterials addresses the need formaterials with specific properties orperformance characteristics. Projectsemphasize achieving scientificunderstanding of how the materialsproperties depend on composition,microstructure, and preparationconditions. We use this understanding

to develop materials with newproperties or combinations ofproperties. This capability allows usto identify replacements for materialsin the stockpile that are no longeravailable. We also develop newmaterials that simplify production,improve performance, or increasereliability and surety. [See AffordableHydrogen Getter, page 11] The materials processing effortdevelops a fundamental understandingof new and existing materials pro-cessing methods that are critical fordefense and other needs. We are de-veloping ways to fabricate parts faster,with fewer defects, and at lower cost.[See Materials Researchers BringRussian Cold Spray Technology toSandia, page 15] Our effort in materials aging andreliability addresses the chemical andphysical mechanisms that cause ma-terials properties to change with time.We must understand important mech-anisms involving both phenomena


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[Ron Brightwell examines the motherboard of one ofSandia’s Cplant (Computational plant) computers.Cplant integrates hundreds of off-the-shelf computersand ranks among the world’s fastest computers.

[

This Swiss cheese-like micrograph shows the precision of a lacework pattern that emerges on a film ofsilver one atom thick and sprinkled with sulfur. The phenomenon is one of many that scientists witness asthey study nanotechnology—the creation and manipulation of materials and devices built on a scale ofnanometers. Scientists are studying what drives this process, which could enable new generations ofrevolutionary nanostructures or materials.

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intrinsic to the materials themselvesand those associated with the environ-ments in which the materials are used.The scientific results from this workbecome the basis for quantitativepredictions of component reliabilityover time in the stockpile. [See OneWafer, Many Tests, page 12] Themethodology is equally applicable tomaterials reliability predictions in otherhigh-consequence applications. [SeeFAA Partnership, page 8] Modeling and simulation of materialsand processes are critical to achievingadvances in any of the three researchareas. The people who develop andimplement the models collaborateclosely with the researchers whoperform the experiments that validatethe model results. Sandia has theexpertise to simulate and predict thestructures and properties of metal,ceramic, and polymer materials atlength scales ranging from the macro-scopic to atomic level. As we developand validate materials models on someof the world’s fastest computers, weare able to simulate the structures ofsurfaces, interfaces, and bulk materials;determine how the microscopic-scalestructure of the material evolves duringprocessing or use; and analyzematerials properties and performance.[See Solving a Mystery, page 13]

New MESA Facility

Materials issues lie at the heart ofMESA (Microsystems and EngineeringSciences Applications), a major newthrust at Sandia. MESA is a proposedstate-of-the-art facility at SandiaNational Laboratories that will providethe capabilities essential to maintain asafe, secure, and reliable stockpile. Thefacility will provide a single locationfor the design, integration, prototypefabrication, and qualification ofintegrated microsystems into weaponcomponents, subsystems, and systems

for the U.S. nuclear weapon stockpile. Microsystems are not miniatureversions of larger devices. Differentphysical mechanisms becomeimportant. For example, microsystemshave a much higher percentage ofatoms and molecules at surfaces andinterfaces between materials than dolarger devices. [See New Materialsfor Microsystems, page 7] Materials research occurs at theinterface between long-establishedfields, such as physics and chemistry.This inherent interdisciplinarity leadsmaterials researchers to reach out toother fields in search of new connect-ions and insights.

[Sandia’s Jerry Floro (left) and John Hunter examine an atomic force micrograph image ofsemiconductor quantum dots.

[

The proposed MESA facility at Sandia.

Researchers at Sandia are pursuingthrusts at two new interfaces that weexpect to be very fruitful. The firststems from Sandia’s cutting-edge workin multivariate analysis of spectral data.Recently, we have generalized andexpanded these capabilities into thebroader area of information discovery,extraction, and analysis (IDEA) ofmultivariate data from any source. Thislink to the information sciences isalready being applied to materialsanalysis, biotechnology, satellite imageanalysis, seismic analysis, and processmonitoring. [See A Great IDEA,page 9] Another particularly successful areaof research is at the interface betweenmaterials science and biology. Bio-logical systems produce complexstructures without a drawing of thefinal product. Instead, they self-assemble using information pro-grammed into individual buildingblocks. The encoded informationdictates structural patterns, hierarchy,length scales, function, response, andoverall size by self-limiting. The endstructure is typically an order of

magnitude or more larger than theindividual components. Understandingthe design rules for self-assemblyshould allow us not only to imitatesome of the complexities of biologicalsystems but also to intentionally design

materials and materials systems ofunheard of complexity on thenanoscale. [See New Materials forMicrosystems, page 7] Materials scientists and engineersat Sandia will continue to be at theforefront of these and other areas ofscience and engineering in the serviceof society as they achieve new levelsof understanding and control of thebasic building blocks of materials:atoms, molecules, crystals, andnoncrystalline arrays. Today’s researchwill be the basis for new materialsadvances that will improve our livesfor generations to come.


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[ [Materials scientists at Sandia are combining nanofabrication and surface characterizationtechniques to study the fundamental mechanisms of structural metal corrosion.

Technical Contact: Julia M. Phillips(505) [email protected]

Pauline Ho at Sandia’s Plasma Processing Research Lab, where plasmas, or hot gases, are used toclean the surfaces of weapon components to enhance adhesion. They also are used to etch circuitson microchips.

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Sandia is pursingresearch and developmentto expand the range ofmaterials available forapplication in micro-systems to beyond justsilicon. Extending the rangeof materials is particularlyimportant for the sensingand acting elements ofintegrated microsystems.Sandia also is studying thematerial properties ofsilicon when it is used notjust for integrated circuits,but in devices that are tiny,functioning machines. Research in materialsscience to extend thematerials choices formicrosystems includesdeveloping new processingtechniques. A techniquecalled LIGA, an acronymfor the German words forlithography, electroplating,and molding, provides aplatform for our research in micro-systems materials. This technique relieson creating precise metal parts using X-ray synchrotron lithography andsubsequent electroplating. The uniqueand rather valuable metal parts madeusing this technique can be used directly

in applications, or the wafer full of metalstructures can be used as a mold forreplication. The most common methodof replicating a metal master mold relieson an injection molding techniquesimilar to the method used to makecompact disks. The inexpensive plastic

replicates can then beused as individual plasticmicroparts, oralternatively the full waferplastic replicate can beused again as a mold. Theplastic mold can be filledwith nanoparticles ofceramics, metals, or metalalloys that have uniqueproperties. In a sense, thisplastic mold can bethought of as a lost moldsimilar to that used inmany macroscale ma-terials processing tech-nologies such as casting.Sandia has active pro-grams in nanoparticlesynthesis, LIGA process-ing, and microscalemolding to explore thisexciting area. LIGA research anddevelopment is beingextended to other pro-cessing techniques that

also allow precision mold fabrication.Sandia researchers are developing newresists and materials that allow the useof thick ultraviolet processing and deepreactive ion etching to create more cost-effective molds or to further extend thecapability of the process.

Microsystems—small devices that sense, think, and act—have been

heralded as one of the major new technology revolutions. At Sandia,

we view microsystems as one of the future’s most important

technologies, both for increased surety of weapon systems as

well as for U.S. economic competitiveness.

Precision microcomponents fabricated with Sandia’s LIGA technology.


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Sandia has licensed the LIGA-processing know-how to AXSUNTechnologies, a U.S. telecommunica-tions company. AXSUN is using LIGAmetal microstructures in agile photonicsubsystems (See Sandia TechnologyFall 2000, p. 12). We are also workingwith several commercial partnersinterested in the technique for plasticand ceramic micropart fabrication.

Other materials science initiativesthat support microsystemsdevelopment include:

• Manipulation of metal and siliconnanostructures and development ofnew diamond morphologies.

• Experimental and modeling effortsto assess the performance andreliability of materials interfaces.

• Exploratory science supporting futuresystems, namely nanosystems andmolecular integrated microsystems.

• Studies on defect production and

reduction in optical materials foradvanced components andphotosensitive materials for weak-link applications.

• Plasma-control research to supportmicroelectronics fabrication andmodeling.

Technical Contact: Jill Hruby(925) [email protected]

Research in materialsscience to extend thematerials choices for

microsystems includesdeveloping new

processing techniques. Atechnique called LIGA,

an acronym for theGerman words for

lithography,electroplating, andmolding, provides a

platform for our researchin microsystems

materials.

Sandia andthe Federal Aviation

Administration (FAA) willteam up soon to researchmelting technology that

eliminates melt-relateddefects in alloys for rotatingengine components. The FAA

will provide $1.5 million forthe project.

Continuing a 12-year partnership,Sandia will be working with the Specialty

Metals Processing Consortium (SMPC). SMPC is a group of13 U.S. specialty-metals producers and aerospace-alloy userscollaborating to study specialty-metals production, processing,quality, and performance.

The partnership has developed expertise and a variety ofresources including diagnostic tools, process models, advancedprocess controls, and melting facilities. These resources areavailable for research on defect reduction in alloys used foraircraft propulsion systems. The FAA has recognized that an important asset of thispartnership is the close working relationship Sandia has withthe staff and management of member companies. This resultsin full communication of technical needs and ensures that newtechnology is rapidly incorporated into industrial practice. Benefits to the Department of Energy include the applicationof melting science and technology to the melting of uraniumalloys, and methods to decontaminate radioactive scrap-metalwaste using liquid-metal processing.

FAA Partnership to Reduce Alloy Defects

Technical Contact: Dick Salzbrenner(505) [email protected]

Sandians Doug Chinn, Craig Henderson, and Michael Winter display a chrome mask for LIGAfabrication. Photo courtesy of East Bay (California) Business Times.

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The Information Detection,Extraction, and Analysis(IDEA) program expandsSandia’s capabilities inmultivariate analysis (the studyof random variables that are multi-dimensional). At the Materials andProcess Sciences Center our expertiseand facilities for infrared spectroscopy,mass spectroscopy, and chromatographicmethods are combined with calibrationand classification methods to solveproblems surrounding materials analysis,aging, and characterization.

Multivariate analysis: Ourcalibration and classification capabilitiescan be applied to spectral data frommid- and near-infrared, visible, Raman,Auger, atomic emission, electronmicroscopy and ion mobility spectro-scopies. We have improved quantitativeand qualitative analyses and havedeveloped new calibration methods forprocess monitoring and quality control. In support of national security, ourmultivariate methods were developedto analyze seismic data to detect buriedequipment, conduct remote satelliteimaging, study the aging of nuclearweapons components, and ensure thenuclear weapons stockpile is safe, secure,and reliable. We license software that hasapplications in process monitoring,materials aging, and noninvasivebiomedical analysis and cellclassification, as well as kinetics,corrosion, and quality control.

Hyperspectral imaging: Anew FT-IR (Fourier Transform Infrared)spectrometer can generate detailedinfrared hyperspectral images in minutesand provide them in a choice of macro- and microscopic scale. Algorithms canmap the chemicals in samples. These

tools can be applied to remote-sensingsatellite imaging as well as to scanning-electron microscope imaging.

Weapon atmospheres:Nuclear weapons surveillance requiressampling of the atmosphere inside theweapon and conducting quantitativeanalyses of these samples. The resultingdata provide information on materialsdegradation and aging that may beoccurring within the weapon. The normalgas composition (called the signature)of each weapon system is computed bycombining new and existing methods.Resulting gas analyses are compared tothe signature. Weapons with abnormalcompositions are studied to determinethe cause.

FT-ICR mass spectrometry:This technology can measure massprecisely. (FT-ICR stands for FourierTransform Ion Cyclotron Resonance.)It can distinguish between differentelements by analyzing their mass. FT-ICR can also study ion-moleculereactions and kinetics.

Polychromator: A MEMS(microelectromechanical system)-basedtechnology, the polychromator performsreal-time detection and analysis of gasesand does so safely from a remotelocation. The polychromator works bypassing a sample gas through infraredradiation. The gas sample registers aspectral pattern. To identify the sample,its spectral pattern is then compared tothe spectrum of a reference gas.Polychromator development is a jointeffort with Sandia and the MassachusettsInstitute of Technology designing theMEMS device, and Honeywellfabricating it. A prototype is expectedthis year.

Technical Contact: Nancy Jackson(505) [email protected]

Sandia’s Mike Sinclair (left) and Mike Butler prepare to put the dime-sized polychromatorremote sensor chip into a testing unit.

A Great IDEA for Materials Analysis


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Sandia's materials and processcomputation and modelingeffort develops computer modelsof materials and processes.These models help us under-stand the microstructures thatlink processing to performance.We study manufacturingprocess, materials aging, new-materials properties, and theeffects of chemical and physicalstresses.

Using mathematical models to predictmaterials behavior is called materialsmodeling. This method is expected tobecome an important tool for materialsdevelopment and evaluation. Modelsrange from simple to complex computersimulations. During the past decade, materialsmodeling has become increasinglypredictive. Previous materials modelingwas qualitative. Advances in computingpower and in computational algorithmshave improved predictive capabilities.Useful across the spectrum of materialsactivities, this tool is part of a broadertrend in science and engineering. Today,computer modeling and simulationsupports most areas of scientific inquiry.Broad interest has developed in thesemethods, in part because fields outsideof materials research have used thesemodeling capabilities successfully. Anexample is pharmaceutical design. The challenge for materials modelingis to simulate and comprehend com-plexity. In recent years, materialsresearchers have used multi-scalemodeling, an approach with a hierarchyof detail to describe materials. Thecoarsest level of modeling, used forengineering design, relies on knowledgegained from the finer-level models.Intermediate, or mesoscale, modelssimulate and predict structures andproperties of materials, or the mannerin which materials interface with othermaterials, how microstructures change

during processing, and how thesematerials perform. Fine-scale modelsfocus on the atomic-level behavior ofindividual defects. Scientists need tounderstand materials in more detailthan the level at which they work. Ifthey work on a macro-level, they needto understand materials properties atthe micro-level. If they work at themicro-level, they need to understandproperties at the nano-level.

Materials modeling assists the threematerials research areas at Sandia:materials processing, scientificallytailored materials, and materials aging-and-reliability studies. For materials processing, researcherscan create a detailed model of a process,then computer simulations can test themodification. For scientifically tailored materials,modeling helps find materials withdesired properties. Models provideinsight into the origins of desiredproperties and provide a basis tosuggest advantageous modifications.Computer simulations can "test" thesemodifications before the fabricationprocess, thus often saving time andmoney. For materials-aging studies, computermodels are required to find out howlong a part will last. In accelerated-aging experiments, the researcherplaces the material in an environment,such as an elevated temperature thatages the part. However, a model isneeded to compare the failure timeunder the accelerated conditions to thefailure time under service conditions.The better the model is, the moreaccurate the predictions of materialsaging and reliability are.

Technical Contact: Huei Eliot Fang(505) [email protected]

PredictiveModelingMeets the

Challenge ofUnderstanding

Complexity

The challenge formaterials modeling is to

simulate andcomprehend complexity.

The hardness of a weld varies (false color) and canbe related to the details of its microstructure.

New patented hydrogen gettersare made from commercial chemicalsthat are nontoxic and can be recycledso precious metals can be reclaimed.The new getters use polymers withdouble bonds that act like chemicalhooks to catch hydrogen atoms. Thenew getter can be used in variousapplications, and has been com-mercialized for industrial use. Itlengthens the life of heat exchangers(installations as big as buildings),maintains a vacuum for insulation,and is used in chemical processing.

Hydrogen build-up inside sealedchambers of the heat exchangerprevents correct operation. Thehydrogen getters remove thehydrogen and the problem. “This allows heat exchangers tolast years longer,” said Sandian TimShepodd. Power plants and chemicalrefineries around the world now usehydrogen getters based on theSandia design. A patented spin-off technologyremoves explosive hydrogen build-up

in sealed consumer productspowered by batteries. “In a waterproof radio (forexample) that could detonate andblow your hand off, we can bringhydrogen down to a safe level,”Shepodd said.

Technical Contact: Tim Shepodd(925) [email protected]

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AffordableHydrogen Getter

Gets Good Marks

Sandia's patented hydrogen-getter material can be processed into a variety of forms so it can be used as a powder, a pellet,an adhesive, or a coating. The rubbery polymer is similar to what you might find in a tire, says co-inventor Tim Shepodd.


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Atmospheric corrosion can be the bane ofelectronic performance. Copper, a conductor,is a key material used in electronics. Corrosion can cause a componentto fail. Understanding how corrosionoccurs helps researchers to prevent itand predict the lifespan of electroniccomponents. Sandia’s LaboratoryDirected Research and Development(LDRD) program has provided fundsto develop analytical tools that predictcorrosion behavior on both copperand aluminum. Several Sandians are using LDRDfunds to study how and why coppercorrodes. Charles Barbour and JeffBraithwaite are combining multiple

corrosion experiments on a singlesilicon wafer. This microlaboratory,called combinatorial experimentation,ensures all experiments are runsimultaneously under identicalconditions. This eliminates the problemof trying to reproduce the experiment.Used in biomedical research, themethod is new to corrosion studies. “In the past when we did coppercorrosion tests,” Barbour said, “wewould put a piece of copper in anatmospheric chamber, add con-taminants at very low levels, and runthe experiment. But this serial approachis very time-intensive, and we wereunsure that the environment was the

same experiment to experiment. It wasdifficult to compare results.” In one kind of combinatorialexperiment, researchers used anelectron beam to evaporate a thincopper film onto silicon wafers. Thenportions of film were etched usingphotolithography and leaving thin,meandering lines of copper. The linesformed electrical resistors to monitorthe extent of corrosion as a function oftime. Impurities were implanted in theresistors. While the wafer was exposedto hydrogen sulfide, researchers usedthe change in resistance to calculatethe copper-sulfide corrosion thicknesson the meander lines. The study showedthat indium slows corrosion, butdeuterium accelerates it. “These experiments show it’spossible to use microcombinatorialtechniques to efficiently characterizecopper corrosion,” said JeffBraithwaite. “The small samples provedbeneficial because the extent ofcorrosion could be easily monitored asa function of time and because all theexperiments could be simultaneouslyperformed.”One Wafer,

Many Tests

Initiation of localized corrosion in aluminum is being studied with a novel microelectrochemicalcell. Nano-engineering techniques are used to control the aluminum microstructure andconcentration of defects.

Technical Contacts: Jeff Braithwaite(505) [email protected]

J. Charles Barbour(505) [email protected]

Charles Barbour (left) and Jeff Braithwaite prepare acombinatorial experiment.

A Sandia materialsresearcher has solved acentury-old mysterysurrounding a type of metalthat doesn't expand whenheated. Known as invar,shorthand for temperatureinvariant, these fewmaterials have physicalproperties that do notchange with temperaturevariations.

This is unusual because nearly allsolids, liquids, and gases expand whenheated. A hot can of soda pop is a goodexample. When heated, atoms jostle

about and push other atoms away moreaggressively. In a typical solid, theindividual atoms are constrained frommoving too much because the forcesthat pin the atoms to their crystallinepositions are strong. (This is why theexpansion in a solid is less dramaticthan in a gas). Each individual atommoves back and forth around itsequilibrium position (like a swingingpendulum). The restoring force lies inthe attraction between the positivelycharged nuclei and the negativelycharged electrons. This attractioncauses the atoms to assemble into asolid in the first place. At very low temperatures thevibrations have small amplitude, and

the motion is symmetric around thecenter. At higher temperatures, thevibrations become increasinglyasymmetric because the restoring forceis weaker when the atoms are fartherapart. Thus each atom spends slightlymore time farther away from itsneighbors than close to them. However, invar is different. Therestoring forces remain symmetrical,so the atoms maintain a symmetricalmotion around the center. The causewas thought to be some anomalousproperty of the electronic structure.Scientists have known that invar iscorrelated with magnetism, but theprecise mechanism has eludeddescription.

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Calculated magnetic spin configurations of atoms in an iron-nickel invar alloy at two different volumes. Red and blue arrows show the magneticmoments on iron and nickel atoms, respectively. The sizes of the arrows indicate the size of the local magnetic moment. The spins of the nickel atomsare always oriented in the same direction (vertically in the figure), while the orientation of the spins of the iron atoms varies.

Solving a MysteryCould Lead to NewMaterial Properties

Sandian Mark van Schilfgaarde whoco-authored the cover story in Nature,July 1999, showed that an iron-nickelalloy (the first and best-known invarmaterial) underwent a transition to acurious noncollinear state. (This meansthe tiny, atom-sized spins do not alignparallel to one another even in theirequilibrium state at low temperature.) Usually magnetic atoms in a materialalign themselves in parallel, like treesgrowing upward in a forest. Temperaturecauses the atoms to gyrate somewhat,analogous to the wind causing the treesto sway. But with invar, van Schilfgaardefound that the magnetic spins behavedifferently. Nickel and iron spins tendto align with each other in the usualway, and similarly nickel atoms alignwith other nickel atoms. But iron atomstry not to align with other iron atoms.Thus begins a curious dance where theiron atoms try to align with nickel whileat the same time trying to avoid oneanother. This unusual magnetic statealters the electronic restoring force andnearly cancels (or even reverses slightly)the asymmetry in the restoring force.This observation explains why invardoes not significantly change propertieswhen heated. Indeed, if the reversalcould be enhanced, it could be possibleto have a material that contracts as itis heated.

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Usually magnetic atomsin a material align

themselves in parallel,like trees growingupward in a forest.

Temperature causes theatoms to gyrate

somewhat, analogous tothe wind causing the

trees to sway.

Sandia’s PETL Facility:Where Materials Science Happens

Sandia’s Materialsand Process Sciences

Center has opened a $45.9million Processing and

Environmental TechnologyLaboratory (PETL).

Research at the facility reinforcesSandia’s mission of nuclearstockpile stewardship. The labopened last summer and wasdedicated in November. Materials-science research conducted atPETL supports nuclear weaponsdesign, manufacture, surveillance,maintenance, and dismantlement. Designed for teamwork andcreativity, the 151,000-square footfacility offers new labs for agingand reliability studies, fordeveloping scientifically tailoredmaterials, process exploration,materials characterization, andmodeling. To support research atthe nanoscale, the building hasfloors that eliminate vibration. Toensure safe working conditions,the layout separates workers fromchemicals, and air is not recircu-lated. The PETL building has twovideo conference rooms, seatingareas for informal gatherings,small conference rooms, and amultipurpose room.

“PETL is an extraordinaryresource that provides newopportunities for Sandians toexercise creativity,” said DirectorKay Hays of the Materials andProcess Sciences Center. The building offers plenty ofnatural lighting and easy accessto staff and managerial offices. “What’s essential in our workis not just good research, butcreativity,” said Deputy DirectorJim Jellison. The PETL project won aProgram and Project ManagementAward 2000 from the Departmentof Energy, the 1999 Excellence inConcrete Award (from the NewMexico chapter of the AmericanConcrete Institute) for its structureand precast exterior, and theEnergy Project of the Year (fromthe New Mexico chapter of theAssociation of Energy Engineers)for the chilled water thermal-energy storage system.

Technical Contact: Mark van Schilfgaarde(925) [email protected]

Integrated microsystems for defense, for chemicalsensing, and for medical applications of the futurewill rely on fast, efficient microactuators (smallmechanical devices that respond to electrical signals)to serve as valves and pumps. Sandia’s µChemLabTM on a chip is an example of analyticalequipment that is scaled down in size. A microlaboratorymounted on a computer chip, µChemLabTM can detect andanalyze chemicals. Correspondingly small micromechanicalstructures, such as pumps and valves, must be developed.However, conventionally engineered mechanisms, such aselectromechanical actuators, often cannot be scaled downand still function acceptably. Conductive polymer gels show

promise for microactuation because they use motion on amolecular scale to generate a macroscopic response (valveclosure, for example). Conductive polymer gels expand and contract whenexposed to a small electrical stimulation. This dimensionalchange results from the diffusion of ions and electrolytemoving into or out of the gel. Pressure resulting from thisinflow/outflow provides the activating force that could drivea valve, while the expansion and contraction can be usedto pump fluids.

Cold-spray technology is one method ofcoating a surface to enhance wear andcorrosion resistance. The cold-spraytechnique accelerates solid powderparticles, which are at or near roomtemperature, to velocities of 500 to 1500meters per second in a supersonic gas jet.The particles deform on impact and bondwith the underlying surface. The process compares to explosivewelding on a much smaller scale. Coldspray can deposit metals and other ductilematerials at a high rate. Steel and otheralloys can be sprayed onto aluminum orother low-melting materials to increasehardness and wear resistance. Copper,aluminum, and other reactive metals canbe cold-sprayed in open air with little orno oxidation. Cold spraying produces ahigher thermal and electrical conductivitythan traditional thermal spraying.

Developed in the Former Soviet Union,cold-spray technology was transferred tothe United States by Sandia’s Materialsand Process Sciences staff, who thencreated a 10-member industrialconsortium to research and commercializethis technology. The cold spray initiative is a new partof the spray-coatings program, whichincludes thermal sprays. Some programaccomplishments include:• Development by Sandia and General

Motors of a wear-resistant sprayedcoating for cylinder walls in aluminumengines and a new process-controlsystem for high-volume, highly reliableautomotive spray coating. The resultingprocess diagnostics and modelingdoubled production throughput andcut equipment costs by 50-percent.

• Development—with the Institute ofPaper Science and Technology plusThermal Spray Technologies—of anenergy-management coating to fostera new papermaking process that uses30-percent less energy than standardmethods.

• Restoration of a scrap satellite part(worth $150,000) using cold-spraydeposition.

• Construction of a production spray-process control system to monitor andcontrol velocity and temperature ofthe spray.

15


Materials ResearchersBring Russian Cold SprayTechnology to Sandia

Polymer Gels are Being Developed for Useas Actuators on a Microscale

Technical Contact: Mark F. Smith(505) [email protected]

Technical Contact: LeRoy Whinnery(925) [email protected]

16


INSIGHTS by V.S. Arunachalam

Materials Challengesfor the Next Century

By V. S. Arunachalam

The cliché "we live in a materialworld" seems so true. Even a cursorycataloguing of materials around us addsup to an impressive list. There are somany to choose from—and almost allof them new—that we now enjoy theluxury of choice, a privilege denied toour ancestors. More materials havecome into being in this century thanall past centuries combined. MichaelAshby,* in one of his schematicdiagrams, elegantly depicts the roadtraveled: from stones, flints, and potteryto tough engineering ceramics; fromwood, skins, and fibers to polymersand plastics; from alluvial gold andcopper to compound semiconductors.The list is truly grand.

History signposts periods ofhuman achievement by the materialsthat made them possible: neolithic, toremind us of artisans who molded clayto pottery; and chalcolithic, whenmetals were smelted and shaped. TheBronze Age. The Iron Age. And thusthe list goes on. What materials shouldrepresent this century? The sheernumber of possibilities and lack of ahistorical distance make this a difficultchoice. The spectacular growth ofmaterials science and technology inthis century has made its impact onmaterials development. Scientific rigorand technological competence havetransformed the profession to becomemore deliberate and purposeful. Thehunter has become the tiller.

As overtures for the nextmillennium begin to sound, we aretempted to speculate on materials thatwill persevere into the coming decadesand beyond. In the midst of ourdiscoveries, it was comforting toimagine that research and developmentdetermined the materials, the products,and even the market. But we now knowthat, more than ever, the marketdetermines what the products will be.Good materials have floundered whenthere has been no market for them. Theeconomist Joseph Schumpeter'sargument that societal demands drivedevelopment and even research, is seento be true in practically every exampleof technology. But for the market'sdemands for faster air travel—freeingone from long, turbulent, andclaustrophobic intercontinentaljourneys—and faster and more agilemilitary fighters, there would have beenno jet engines or high-temperaturesuperalloys. It is therefore prudent tospeculate on what our society's longingsare, and whether they are realizable at

all with our current repertoire ofknowledge and the materials requiredfor the short term and for the decadesbeyond our current horizon. The needfor new materials will emerge fromsuch projections.

V.S. Arunachalam is a Disting-uished Service Professor in theDepartment of Materials Science &Engineering, Engineering & PublicPolicy, and The Robotics Institute ofCarnegie Mellon University inPittsburgh, Pennsylvania. His currentresearch interests are in integratedmaterials design, issues on thedevelopment of infrastructuretechnologies, and lightwavecommunications. He is a formerpresident and a Fellow of the IndianNational Academy of Engineering anda Foreign Member of the RoyalAcademy of Engineering (UnitedKingdom). He has a Ph.D. degree fromthe University of Wales and honorarydoctorates from a number ofuniversities.

* See M.F. Ashby, Phil. Trans. R. Soc.Lond. A 322 (1987) p. 393.

Historysignposts periods

of humanachievement by

the materials thatmade thempossible.

The following is excerpted, with permission, from the January 2000 (Vol. 25,No. 1) issue of the MRS (Material Research Society) Bulletin.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a LockheedMartin Company, for the United States Department of Energy

under contract DE-AC04-94AL85000

SAND xxxxxxx

Marketing Communications Dept.MS 0129Sandia National LaboratoriesP.O. Box 5800Albuquerque, NM 87185-0129

Bulk RateU.S. PostagePAID

Albuquerque, NMPermit No. 232

“As overtures for the nextmillennium begin to sound,we are tempted to speculate

on materials that willpersevere into the coming

decades and beyond.”

V.S. ArunachalamDistinguished Service Professor in the Department of Materials Science& Engineering, Engineering & Public Policy, and The Robotics Institute

of Carnegie Mellon University in Pittsburgh, Pennsylvania

Documents

A MATERIAL WORLD Tailoring Materials for the Future