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IntroductionFrom the earliest work on laser interac-

tions with materials, direct-write processeshave been important and relevant tech-niques to modify, add, and subtract mate-rials for a wide variety of systems and forapplications such as metal cutting andwelding. In general, direct-write process-ing refers to any technique that is able tocreate a pattern on a surface or volume ina serial or spot-by-spot fashion. This isin contrast to lithography, stamping, di-rected self-assembly, or other patterningapproaches that require masks or preexist-ing patterns. At first glance, one may thinkthat direct-write processes are slower orless important than these parallelized ap-proaches. However, direct-write allowsfor precise control of material propertieswith high resolution and enables struc-tures that are either impossible or imprac-tical to make with traditional paralleltechniques. Furthermore, with continuingdevelopments in laser technology provid-ing a decrease in cost and an increase inrepetition rates, there is a plethora of ap-

plications for which laser direct-write(LDW) methods are a fast and competitive

way to produce novel structures and de-vices. This issue ofMRS Bulletin seeks toassess the current status and future op-portunities of LDW processes in the con-text of emerging applications.

There are many types of direct-writetechniques used in science and engineer-ing.1 For instance, previous MRS Bulletinissues discussed topics such as inkjetprinting (November 2003) and focusedion-beam processing (February 2000, July2001, and December 2005). In the mostclassical sense, engraving or milling can

be considered a direct-write process, sincea tool or stylus makes contact with a sur-face and is moved in a desired pattern toproduce a feature. The coupling of a high-powered laser with direct-write pro-cessing enables similar features to beproduced without requiring physicalcontact between a tool and the materialof interest. Because of this, few tech-niques share the versatility of LDW inadding, subtracting, and modifying differ-ent types of materials over many different

length scales, from the nanometer to themillimeter scale.

In LDW, the beam is typically focusedor collimated to a small spot (in industrialprocesses, this small spot can be severalmillimeters in diameter). Patterning is

achieved by either rastering the beamabove a fixed surface or by moving thesubstrate or part within a fixed beam. Animportant feature of LDW is that the de-sired patterns can be constructed in bothtwo and three dimensions on arbitrarilyshaped surfaces, limited only by the de-grees of freedom and resolution of themotion-control apparatus. In this manner,LDW can be considered a rapid prototyp-ing24 tool, because designs and patternscan be changed and immediately appliedwithout the need to fabricate new masksor molds.

The key elements of any LDW system

can be divided into three subsystems:(1) laser source, (2) beam delivery system,and (3) substrate/target mounting system(see Figure 1). At the heart of any LDWprocess is the laser source. Typical experi-ments and applications use anywherefrom ultrafast femtosecond-pulsed systemsto continuous-wave systems employingsolid-state, gas, fiber, semiconductor, orother lasing media. In choosing an appro-priate source, one must consider the fun-damental interactions of lasers with thematerial of interest. This requires knowl-edge of the pulse duration, wavelength,

divergence, and other spatial and temporalcharacteristics that determine the energyabsorption and the material response. In

beam delivery, there are a variety of waysto generate a laser spot, including fixed fo-cusing objectives and mirrors, galvano-metric scanners, optical fibers, or evenfluidic methods such as liquid-core wave-guides5 or water jets.6 The choice dependson the application demands, for instance,the required working distances, the focusspot size, or the energy required. The ulti-mate beam properties will be determined

by the combination of laser and beamdelivery optics. Finally, the substrate mount-ing is done in accordance with experimentalor industrial requirements and can be ma-nipulated in multiple directions to achievea desired result. Robotics and active feed-

back control, on either the substrate or beamdelivery optics, can add further design flex-ibility to the technique.

There is a vast range of LDW processes.For the purposes of this issue, we categorizethem into three main classes: laser direct-write subtraction (LDW), where materialis removed by ablation; laser direct-writemodification (LDWM), where material ismodified to produce a desired effect; and

laser direct-write addition (LDW),where material is added by the laser.

MRS BULLETIN VOLUME 32 JANUARY 2007 www.mrs.org/bulletin 9

Laser Direct-WriteProcessing

Craig B. Arnold and Alberto Piqu,Guest Editors

AbstractDirect-write techniques enable computer-controlled two- and three-dimensional

pattern formation in a serial fashion. Among these techniques, the versatility offered by

laser-based direct-write methods is unique, given their ability to add, remove, and

modify different types of materials without physical contact between a tool or nozzleand the material of interest. Laser pulses used to generate the patterns can be

manipulated to control the composition, structure, and even properties of individual

three-dimensional volumes of materials across length scales spanning six orders of

magnitude, from nanometers to millimeters. Such resolution, combined with the ability

to process complex or delicate material systems, enables laser direct-write tools to

fabricate structures that are not possible to generate using other serial or parallel

fabrication techniques. The goal of the articles in this issue of MRS Bulletin is to illustrate

the range of materials processing capabilities, fundamental research opportunities, and

commercially viable applications that can be achieved using recently developed laser

direct-write techniques. We hope that the articles provide the reader with a fresh

perspective on the challenges and opportunities that these powerful techniques offer

for the fabrication of novel devices and structures.

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Laser Direct-Write Subtraction(LDW)

LDW is the most common type oflaser direct-write. In general, this entailsprocesses that result in photochemical,photothermal, or photophysical ablationon a substrate or target surface, directlyleading to the features of interest.7 Com-

mon processes include laser scribing, cut-ting, drilling, or etching to produce reliefstructures or holes in materials in ambientor controlled atmospheres.8 Industrialapplications using this technique rangefrom high-throughput steel fabrication, toinkjet and fuel-injection nozzle fabrica-tion,9,10 to high-resolution manufacturingand texturing of stents or other im-plantable biomaterials.11 At a smaller scale,inexpensive benchtop laser cutting and en-graving systems can be purchased by thehobbyist or small company for artistic andarchitectural renderings. More recent de-velopments in LDW include chemicallyassisted techniques such as laser-drillingceramics or biomaterials and laser-induced

backside wet etching (LIBWE) of glass.12,13In fact, one may also consider laser clean-ing to be a controlled LDW process.14

The fundamental interactions leadingto material removal can be thermal orathermal, depending primarily on the ma-terial/environment characteristics and thepulse duration of the laser. These interac-tions have a direct effect on the quality ofthe resulting features. For instance, a heat-affected zone (HAZ) tends to occur in thevicinity of thermally removed material.

This region has structures and propertiesthat can differ from the bulk material and

can exhibit additional surface relief. Eitherof these effects may be beneficial or detri-mental, depending on the application. Incontrast, athermal and multiphoton ab-sorption processes caused by ultrafastlasers can reduce the formation of a HAZand enable features smaller than the dif-fraction limit.15,16

Laser Direct-Write Modification(LDWM)

In LDWM, the incident laser energy isusually not sufficient to cause ablative ef-fects but is sufficient to cause a permanentchange in the material properties. Typi-cally, these processes rely on thermalmodifications that cause a structural orchemical change in the material. A com-mon example of such processes is therewritable compact disc, in which a diodelaser induces a phase transition betweencrystalline and amorphous material.17 Inindustrial applications, one may considerlaser cladding, where a surface layer dif-ferent from the bulk material is producedthrough melting and resolidification,18or solid free-form fabrication (SFF) ap-proaches such as selective laser sintering(SLS),19 as important modifying processesthat would fall under the umbrella ofLDWM.

Many LDWM applications require aspecific optical response in the material ofinterest beyond simple thermal effects.Optically induced defects or changes inmechanical properties can lead to manynon-ablative material modifications. For

instance, photoresists respond to light bybreaking or reforming bonds, leading to

pattern formation in the material. Alterna-tively, LDW can cause defects in photo-etchable glass ceramics20 or other opticalmaterials through single- and multiphotonmechanisms,21 enabling novel applications

in optical storage,

22

photonic devices,

23,24

and microfluidics.25

Laser Direct-Write Addition(LDW)

LDW is perhaps the most recent of thelaser direct-write processes. In this tech-nique, material is added to a substrateusing various laser-induced processes.Many techniques are derived from laser-induced forward transfer (LIFT), where asacrificial substrate of solid metal is posi-tioned in close proximity to a second sub-strate to receive the removed material.26The incident laser is absorbed by the ma-

terial of interest, causing local evapora-tion. This vapor is propelled toward thewaiting substrate, where it recondenses asan individual three-dimensional pixel, orvoxel, of solid material. Such an approachhas found important use in circuit andmask repair and other small-scale applica-tions where one needs to deposit materiallocally to add value to an existing structure.This general technique has significant ad-vantages over other additive direct-writeprocesses, in that these laser approachesdo not require contact between the de-positing material and a nozzle, and can en-

able a broad range of materials to be trans-ferred. Variations on the general LIFTprinciple allow liquids, inks, and multi-phase solutions to be patterned withcomputer-controlled accuracy for use in avariety of applications such as passiveelectronics or sensors.27,28

Alternatively, LDW techniques canrely on optical forces to push particles orclusters into precise positions,29 or on chem-ical changes in liquids and gases to pro-duce patterns. For instance, laser-inducedchemical vapor deposition,30 or multipho-ton polymerization schemes of liquidphotoresists,31 can be used to fabricatethree-dimensional stereographic patterns.Examples of this have been demonstratedand show promise for many applicationssuch as fabricating photonic structures or

biological scaffolding.

Highlights of Articles in This IssueThe breadth of LDW processing makes

it impossible to cover the entire topic in asingleMRS Bulletin issue. The situation isfurther complicated by the fact that manyLDW processes have either grown intomature fields in and of themselves (lasercutting, welding, etc.) or provide ample

topical material for an independent MRSBulletin issue (solid free-form fabrication,

10 MRS BULLETIN VOLUME 32 JANUARY 2007 www.mrs.org/bulletin

Laser Direct-Write Processing

Figure 1. Schematic illustration of a laser direct-write system. The basic components of anLDW system are (left to right) a substrate mounting system, a beam delivery system, and alaser source. Motion control of either the beam delivery system or the substrate mountingsystem is typically accomplished using computer-assisted design and manufacturing(CAD/CAM) integrated with the laser source.

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laser cleaning, fiber laser development,etc.). Therefore, we restrict ourselves toLDW processes developed in the past fewyears that provide opportunities forgrowth beyond the traditional industrial

applications. Clearly, this coverage is notexhaustive, and there are many other LDWapproaches that could be discussed. How-ever, the reader of this issue should get agood sense of the possibilities of LDW.

We have purposely avoided focusingon femtosecond laser techniques becausethe August 2006 issue ofMRS Bulletin onUltrafast Lasers in Materials Sciencecovered this topic in detail, includingsome LDW approaches. Femtosecondlasers are very important in many of thenewer LDW approaches, as they enablehigher-resolution features, detailed controlover structures, and unique nonthermal

processing capabilities. The reader is re-ferred to the earlierMRS Bulletin for moreinformation.

In the first article in this issue, byGrigoropoulos et al., we look at ap-proaches for LDW that can produce fea-tures significantly smaller than thediffraction limit of light. In this approach,a near-field phenomenon is utilized thatradiates the electromagnetic field to the re-gion directly below an atomic force micro-scope (AFM) tip, removing material in anarea as small as 10 nm. Rastering is con-trolled by the motion of the AFM stage,

and various features can be produced. Bycoating the tip with metal, deposition onthe nanoscale by LDW can also beaccomplished.

Two articles on LDW follow. In thefirst, by Arnold et al., we look at LDW ofcomplex materials, including biologicalmaterials such as cells and proteins, elec-trochemical materials for energy storage,and even complete semiconductor devices.The approach relies on laser forwardtransfer of multicomponent suspensionscomposed of different liquid and/or solidmaterials, which allows for depositionwithout harming sensitive material prop-erties. This technique can be further com-

bined with LDWM or LDW to performpostdeposition processing with the sametool. Next, Stuke et al. turn our atten-tion to the LDW fabrication of three-dimensional structures such as cages fortrapping particles and photonic structuresfor guiding light. In this technique, a laser-

based chemical vapor deposition methodproduces highly conductive, freestandingmetal features. One particularly interest-ing application is the production of carbonnanotubes and wires in an LDW fashion.

One of the key advantages of LDWMfor material modification, in contrast tomany parallel approaches, is the ability toapply a unique photon flux at each laserspot. Livingston and Helvajian discuss a

real-time sequencing approach that pro-grams the incident laser pulses to enabledistinctive, site-selective processes. Thiscan be applied to photomodifiable glassesand glass ceramics to produce complexfeatures that would be difficult or impos-sible to make by other methods.

Finally, we look toward the future ofLDW with Sugioka et al., who discuss theglobal industrial aspects of LDW process-ing. Cutting-edge applications in Europe,the United States, and Japan are discussed,with implications for long-term growth.

Summary

One of the unique attributes of laserdirect-write processes is that the generalmethodology enables a complete range ofmaterials processing in order to fabricatedevices and structures. These techniquesmake it possible for a single tool, locatedin the research lab or on the factory floor,to design and build an entire part withprecise control over the composition,structure, and properties on each laserpulse.

Although that vision of LDW has notbeen reached, the articles in this issue ofMRS Bulletin cover additive, subtractive,

and modification methods and demon-strate a commercially viable technologywith abundant opportunities for funda-mental research that will continue to pushadvancements in the field. Ideally, theseapproaches lend themselves to rapid proto-typing and small-scale production whereunique features are needed for a desiredapplication. However, they also find im-portant implementation in commercialventures where high-repetition-rate, multi-

beam laser systems allow LDW to competewith parallel processing in speed and cost.The impact of LDW processes in ad-vanced applications will continue to growas new methods and technologies becomeavailable and the demands for more precisecontrol over material structures and prop-erties are met.

References1. See for instance, D.B. Chrisey, Science 289(2000) p. 879; A. Piqu and D.B. Chrisey, eds.,Direct-Write Technologies for Rapid Prototyp-ing Applications (Academic Press, San Diego,2002).2. C.C. Kai, L.K. Fai, and L.C. Sing, Rapid Proto-typing: Principles and Applications (World Scien-tific, London, 2004).

3. P.K. Venuvinod and W. Ma, Rapid Prototyp-ing: Laser-Based and Other Technologies (KluwerAcademic, Norwell, MA, 2003).4. A. Piqu and D.B. Chrisey, eds., Direct-WriteTechnologies for Rapid Prototyping Applications(Academic Press, San Diego, 2002).

5. K.W. Gregory and R.R. Anderson, IEEEJ. Quant. Elect. 26 (1990) p. 2289.6. P. Couty, F. Wagner, and P. Hoffmann, Opt.Eng. 44 068001 (2005).7. D. Buerle, Laser Processing and Chemistry, 3rdEd. (Springer, Berlin, 2000).8. W.M. Steen and K. Watkins, Laser MaterialsProcessing, 3rd Ed. (Springer, Berlin, 2003).9. H. Endert, R. Patzel, and D. Basting, Opt.Quant. Elect. 27 (1995) p. 1319.10. M.C. Gower, Opt. Exp. 7 (2000) p. 56.11. A. Kureil and N.B. Dahotre,J. Biomed. Appl.5 (2005) p. 5.12. X. Ding, Y. Kawaguchi, H. Niino, and A.Yabe,Appl. Phys. A 75 (2002) p. 641.13. G. Kopitkovas, T. Lippert, C. David, A.

Wokaun, and J. Gobrecht,Microelectron. Eng. 67(2003) p. 438.14. V. Tornari, V. Zafiropulos, A. Bonarou, N.A.Vainos, and C. Fotakis, Opt. Lasers Eng. 34(2000) p. 309.15. P.P. Pronko, S.K. Dutta, J. Squier, J.V. Rudd,D. Du, and G. Mourou, Opt. Commun. 114(1995) p. 106.16. M. Lenzner, J. Kruger, W. Kautek, and F.Krausz,Appl. Phys. A 68 (1999) p. 369.17. J. Feinleib, J. deNeufville, S.C. Moss, andS.R. Ovshinsky,Appl. Phys. Lett.18 (1971) p. 254.18. R. Vilar,J. Laser App. 11 (1999) p. 64.19. D.L. Bourell, H.L. Marcus, J.W. Barlow, and

J.J. Beaman, Int. J. Powder Metall. 28 (1992)p. 369.

20. T.R. Dietrich, W. Ehrfeld, M. Lacher, M.Kramer, and B. Speit, Microelectron. Eng. 30(1996) p. 497.21. K. Itoh, W. Watanabe, S. Nolte, and C.B.Schaffer,MRS Bull. 31 (8) (2006) p. 620.22. E.N. Glezer, M. Milosavljevic, L. Huang,R.J. Finlay, T.H. Her, J.P. Callan, and E. Mazur,Opt. Lett. 21 (1996) p. 2023.23. P.R. Herman, R.S. Marjoribanks, A. Oettl, K.Chen, I. Konovalov, and S. Ness,Appl. Surf. Sci.154 (2000) p. 577.24. A. Zoubir, M. Richardson, C. Rivero, A.Schulte, C. Lopez, K. Richardson, N. Ho, and R.Vallee, Opt. Lett. 29 (2004) p. 748.25. Y. Cheng, K. Sugioka, and K. Midorikawa,Opt. Lett. 29 (2004) p. 2007.

26. J. Bohandy, B.F. Kim, and F.J. Adrian,J. Appl. Phys. 60 (1986) p. 1538.27. D.B. Chrisey, A. Piqu, J. Fitz-Gerald, R.C.Y.Auyeung, R.A. McGill, H.D. Wu, and M. Duig-nan,Appl. Surf. Sci. 154 (2000) p. 593.28. A. Pique, R.C.Y. Auyeung, J.L. Stepnowski,D.W. Weir, C.B. Arnold, R.A. McGill, and D.B.Chrisey, Surf. Coat. Technol. 163 (2003) p. 293.29. M.J. Renn and R. Pastel,J. Vac. Sci. Tech. B 16(1998) p. 3859.30. S.D. Allen, J. Appl. Phys. 52 (1981) p. 6501.31. J. Serbin, A. Egbert, A. Ovsianikov, B.N.Chichkov, R. Houbertz, G. Domann, J. Schulz,C. Cronauer, L. Frohlich, and M. Popall, Opt.Lett. 28 (2003) p. 301.

Laser Direct-Write Processing

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Craig B. Arnold, GuestEditor for this issue of

MRS Bulletin, is an assis-tant professor of me-chanical and aerospace

engineering at PrincetonUniversity with a jointappointment in thePrinceton Institute forScience and Technologyof Materials (PRISM)and affiliations in elec-trical engineering andthe Princeton Environ-mental Institute. He re-ceived his BS degreein physics and mathfrom Haverford Collegein 1994, his PhD degree

in physics from HarvardUniversity in 2000, andworked as a NationalResearch Council post-doctoral associate priorto joining the faculty ofPrinceton in 2003. Hiscurrent research focuseson laser processing andtransport in materials,with a particular focuson energy storage, bio-materials, and photonicmaterials.

Arnold received aYoung InvestigatorAward from the Officeof Naval Research in2005 and a NationalScience FoundationCAREER Award in 2006.He currently serves aschair of the MRS Acade-mic Affairs Committeeand as an associate edi-tor of theJournal of Laser

Micro/Nanoengineering.Arnold can be reached

at Princeton University,

Department of Mechani-cal and Aerospace

Engineering, Engineer-ing Quadrangle,1 Olden St., Princeton,NJ 08544 USA; tel.609-258-0250 and e-mail

cbarnold@princeton.edu.

Alberto Piqu, GuestEditor for this issue of

MRS Bulletin, is head ofthe Electronic and Opti-cal Materials and De-vices Section in theMaterials Science Divi-sion at the U.S. NavalResearch Laboratory(NRL). Piqu holds BSand MS degrees inphysics from Rutgers

University and a PhDdegree in materials sci-ence and engineeringfrom the University ofMaryland. His group atthe NRL pioneeredthe use of laser-baseddirect-write techniquesfor rapid prototyping ofelectronic, sensor, andmicropower generationdevices. His research in-terests include the studyof processes involvinglasermaterial interac-tions, particularly thoserelevant to pulsed laserdeposition and laser for-ward transfer as appliedto the fabrication of thinfilms, multilayers, andembedded structures.

In addition to co-editing the book Direct-Write Technologies forRapid Prototyping Appli-cations, Piqu has morethan 130 scientific publi-cations and holds 15 U.S.

patents in laser materi-als processing. He is also

an associate editor fortheJournal of Laser Micro/Nanoengineering.

Piqu can be reachedat the Naval Research

Laboratory, Code 6364,4555 Overlook Ave. SW,Washington, DC 20375USA; tel. 202-767-5653and e-mail pique@nrl.navy.mil.

Anant Chimmalgi is asystem design engineerat KLA Tencor Corp. Hereceived his BE degreefrom the National Insti-tute of Technology inSurathkal, India, and his

MS and PhD degreesfrom the Department ofMechanical Engineeringat the University of Cali-fornia, Berkeley (2003and 2005, respectively).Chimmalgis currentresearch interests in-clude bright-field waferinspection technologies,semiconductor yieldmanagement, nanofabri-cation technologies,nanoscale heat transfer,nanoparticle manipula-tion, scanning probe mi-croscopy, and ultrashortlaser phenomena.

Chimmalgi can bereached at 5144 Etch-everry Hall, Universityof California, Berkeley,CA 94720-1740 USA; tel.510-642-1006 and e-mailanchip@ocf.berkeley.edu.

Gnter Fuhr is execu-tive director of theFraunhofer-Institut fr

Biomedizinische Technik(IBMT) in St. Ingbert,

Germany. He earned hisDipl.-Ing. degree inelectrical engineering atTechnische UniversittDresden in 1975. Fuhr

received his Dr. rer.nat. degree in bio-physics in the field ofplant physiology fromHumboldt-Universittzu Berlin (HUB) in 1981.He also earned his Ha-

bilitation degree in thefield of cell biology and

biophysics from HUBin 1985.

Fuhr became a fullprofessor at the Instituteof Biology at HUB in

1993. From 1994 to 1996,he was vice dean of thefaculty of Mathematicsand Natural Sciences Iat HUB. In 2000, Fuhr be-came the founding di-rector of the Center ofBiophysics and Bio-informatics at HUB. He

became a full profes-sor and chair of theBiotechnology and Med-ical Technology Depart-ment at the MedicalFaculty of the Univer-sitt des Saarlandesin 2001 and executivedirector of branchesin Sulzbach/Saar, Pots-dam, Berlin, and Shen-zhen, China, that sameyear. In 2003, Fuhr wasthe founding director ofthe Research Cryobankwithin the Center forCryobiotechnology(EUROCRYOSaar) inSulzbach/Saar.

Fuhr can be reached

at Fraunhofer-Institutfr Biomedizinische

Technik, EnsheimerStrasse 48, D-66386 St.Ingbert, Germany; tel.49-6894-980-100, fax 49-6894-980-110, and e-mail

guenter.fuhr@ibmt.fraunhofer.de.

Costas P. Grigoropoulosis a professor in the De-partment of MechanicalEngineering at the Uni-versity of California,Berkeley, and on thematerials science/engi-neering faculty of theEnvironmental EnergyTechnologies Division atLawrence Berkeley Na-

tional Laboratory.Grigoropoulos re-ceived Diploma degreesin naval architectureand marine engineeringand in mechanical engi-neering from the Na-tional Technical Univer-sity of Athens, Greece.He holds MSc and PhDdegrees in mechanicalengineering fromColumbia University.

His current researchinterests are in micro/nanoengineering, lasermaterials processingand micro/nanomachin-ing, microscale andnanoscale diagnosticsfor chemical analysis,phase transformationsin semiconductors andelectronic materials,laser-driven thin-filmcrystal growth forapplications in micro-electronic devices,nanofluidics, microscale

fuel cells, catalytic mi-croreactors, hydrogen

12 MRS BULLETIN VOLUME 32 JANUARY 2007 www.mrs.org/bulletin

Laser Direct-Write Processing

Anant Chimmalgi Gnter Fuhr Costas P. GrigoropoulosCraig B. Arnold Alberto Piqu

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Laser Direct-Write Processing

MRS BULLETIN VOLUME 32 JANUARY 2007 www.mrs.org/bulletin 13

storage, thermal man-agement in microde-vices, and transportdiagnostics in MEMS.Grigoropoulos is a fel-

low of ASME.Grigoropoulos can be

reached at the Univer-sity of California, Berke-ley, Department ofMechanical Engineering,6177 Etcheverry Hall,Berkeley, CA 94720-1740USA; tel. 510-642-2525,fax 510-642-6163, ande-mail cgrigoro@me.berkeley.edu.

Bo Gu is senior princi-

pal scientist at GSIGroup Inc. He has beenworking in the fields oflasers and laser applica-tions in industry formore than 20 years.

In the early 1990s, Guworked on developingexcimer lasers for semi-conductor lithography.Gus group was the firstto develop a CO2 lasersystem for microviadrilling for the micro-electronics industry. Hehas studied and devel-oped many industrialmicromachining appli-cations using diodepumped solid-state, ex-cimer, and CO2 lasers.His current interests in-clude the developmentand industrial applica-tions of new types oflasers. Gu has publishedmany papers on lasersand laser applications,organized and chaired

various conferences,and has more than

20 patents or pendingpatents.

Gu can be reached atGSI Group, 60 FordhamRoad, Wilmington, MA

01887 USA; tel. 978-661-4568, fax 978-988-8798,and e-mail bgu@gsig.com.

Henry Helvajian is asenior scientist at Aero-space Corp., a nonprofitorganization created bythe U.S. Congress withthe goal of providing re-search and developmentin the area of space sys-tems development. He

has worked on researchproblems in the area ofgas-phase photochem-istry and kinetics of acti-vated radical speciesand on photophysicalprocesses of low-fluencelasermaterial interac-tion phenomena. Helva-

jians present researchinterest is in the area ofcontrolled fluence laserprocessing for selectiveactivation of materialsproperty changes withsite-selective control. Hehas been working ondeveloping a materialsprocessing technique fornon-ablative and true3D patterning of photo-structurable glass ce-ramic materials. Hisresearch group is focusedon developing materialsprocessing techniquesthat will enable themass-producibleand mass-customizable

manufacturing ofnanosatellites primarily

composed of glass ce-ramic materials.

Helvajian can bereached at the Micro/Nanotechnology Depart-

ment, Space MaterialsLaboratory, AerospaceCorp., 2350 E. El SegundoBlvd., El Segundo, CA90245 USA; tel. 310-336-7621, fax 310-563-3175,and e-mail henry.helvajian@aero.org.

Andrew Holmes is areader in microelectro-mechanical systems(MEMS) in the Depart-ment of Electrical &

Electronic Engineeringat Imperial CollegeLondon. He receivedhis BA degree in naturalsciences from the Uni-versity of Cambridge in1987 and his PhD de-gree in electrical engi-neering from ImperialCollege London in 1992.

Holmes has workedon a wide range oftopics in optical signalprocessing, integratedoptics, and MEMS, andhas published approxi-mately 90 papers inthese areas. He is a co-founder and director ofMicrosaic Systems Ltd.,an Imperial College spin-out company started in2001 to exploit the col-leges MEMS research.His current research in-terests lie in the areas ofmicropower generation,MEMS devices for mi-crowave applications,

and laser processing forMEMS manufacturing.

Holmes can bereached at the Depart-ment of Electrical andElectronic Engineering,Imperial College

London, ExhibitionRoad, London SW72AZ, UK; tel. 44-20-7594-6239, fax 44-20-7594-6308, ande-mail a.holmes@imperial.ac.uk.

David J. Hwang is apostdoctoral researchassociate in the Mechan-ical Engineering Depart-ment at the Universityof California, Berkeley.

He received his BSE andMSE degrees in mechan-ical engineering fromSeoul National Univer-sity in 1995 and 1997,respectively, and his PhDdegree in mechanicalengineering fromUCBerkeley in 2005.

Hwang worked forthe Samsung AdvancedInstitute of Technology(SAIT) in South Koreafrom 1997 to 2000,where he was involvedin automotive enginecontrol, superconductor-related cryogenics, andmicrojetting devices. Hismajor research interestis in micro/nanoscaleprocessing of electronicmaterials based onpulsed lasers coupledthrough high-magnifica-tion objective lensesand/or optical near-field probes.

Hwang can be reached

at 5144 Etcheverry Hall,University of California,

Berkeley, CA 94720-1740USA; tel. 510-642-1006and e-mail djhmech@me.berkeley.edu.

Frank E. Livingston is aresearch scientist in theMicro/NanotechnologyDepartment of the SpaceMaterials Laboratory atAerospace Corp. Hereceived his BA degreefrom ClaremontMcKenna College andhis MS degree from Cal-ifornia State Universityat Fullerton, both inchemistry. At Cal StateFullerton, he worked

with B.J. Finlayson-Pitts,studying the kineticsand mechanisms of het-erogeneous processesrelevant to the tropo-spheric chemistry ofpolluted marine regionsand ozone destructionin the Arctic.

Livingston earned hisPhD degree in chemistryfrom the University ofCalifornia, Los Angeles,where he studied micro-scopic surface chemistryand photoionizationspectroscopy of alkalihalide clusters andnanocrystals under thedirection of R.L. Whetten.He then accepted asenior postdoctoral re-search fellowship withS.M. George at the Uni-versity of Colorado,Boulder, where he de-veloped several novellaser-based techniquesto study kinetic diffu-

sion processes on molec-ular solids.

Bo Gu Henry Helvajian Andrew Holmes David J. Hwang Frank E. Livingston

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Livingstons currentresearch focuses on thephotophysics and chem-istry of lasermaterialinteractions, laser

processing of photosen-sitive glass ceramics andprotean materials, ultra-fast optical spectroscopyof lasersurface phe-nomena, and opticaltrapping and nanoparti-cle ensemble assemblyfor nanostructured ma-terials development. Hehas a keen interest in thelaser-induced transfor-mation of materials, forexample, phase and

chemical transforma-tions of multimetallicperovskite and galliumoxide nanoparticle thinfilms for the develop-ment of improved-sensitivity uncooled IRdetectors and electro-luminescent phosphorsfor flexible displays.He has authored 45peer-reviewed papersand book chapters.

Livingston can bereached at the Micro/Nanotechnology De-partment, Space Materi-als Laboratory, AerospaceCorp., 2350 E. El SegundoBlvd., El Segundo, CA90245 USA; tel. 310-336-0056, fax 310-336-5846,and e-mail frank.e.livingston@aero.org.

Kurt Mueller is a mem-ber of the technical staffat Max-Planck-Institutfr Biophysikalische

Chemie. He can bereached at MPI fr

BiophysikalischeChemie, Am Fassberg11, D-37077 Gttingen,Germany; and by e-mailvia mstuke@gwdg.de.

Torsten Mueller earnedhis PhD degree in bio-physics at HumboldtUniversity in Berlin. Hecan be reached at EvotecAG, c/o Humboldt-Universitt zu Berlin,Invalidenstrasse 42,D-10115 Berlin, Ger-many; and by e-mail viamstuke@gwdg.de.

Doug A.A. Ohlberg is a

member of the Quan-tum Structures ResearchInitiative group atHewlett-Packard (HP)Laboratories. He re-ceived his BS degree inchemistry in 1989 fromCalifornia State Univer-sity, Fresno. OhlbergsMS degree in chemistrywas earned in 1995 atthe University of Cali-fornia, Los Angeles,with R. Stanley Williamsas his advisor. From1994 to 1996, Ohlbergworked as a graduatefellow for Sandia Na-tional Laboratories intheir Flat-Panel DisplayInitiative group.Ohlberg joined HPLaboratories in 1996.

His early research ef-forts at HP involved theformation of self-assembled nanostruc-tures, includinggermanium silicide

nanodots and rare-earthsilicide nanowires. He is

currently investigatingthe growth and electri-cal behavior of variousmaterials systems forimplementation as

switching elements inthe crossbar architecturethat HP is developingfor nanoscale logic andmemory circuitry.

Ohlberg can bereached at Hewlett-Packard Labs, 1501 PageMill Rd., MS1123, PaloAlto, CA94304; tel. 650-857-8487, fax 650-236-9885, and e-maildoug_ohlberg@hp.com.

Rachel Oliver is a re-search fellow in theDepartment of MaterialsScience and Metallurgyat the University ofCambridge. She ob-tained her doctoratefrom Oxford Universityin 2003. Her doctoraltraining included peri-ods as an intern atHewlett-Packard Labo-ratories in Palo Alto,California. Olivers re-search interests centeron nanoscale structuresin optoelectronicmaterials.

Oliver can be reachedat the University ofCambridge, Departmentof Materials Science andMetallurgy, New Muse-ums Site, PembrokeStreet, Cambridge, CB23QZ, UK; e-mailrao28@cam.ac.uk.

Pere Serra is an associ-

ate professor at the Uni-versity of Barcelona. He

obtained his PhD degreeat the university in 1997,where he investigatedthe expansion dynam-ics of laser-generated

plasmas of diversematerials. In particular,Serra devoted much ofhis work to the study of

bioactive ceramics forthe production of med-ical implants throughpulsed laser deposition.This research motivatedhim to turn his attentionto another laser-based ap-proach to the processingof materials for biomed-ical applicationslaser

surface treatment ofbiocompatible metalsand ceramics. He is nowengaged in the develop-ment of laser microfabri-cation techniques for thepreparation of miniatur-ized biosensors andlab-on-a-chip systems.

Serra can be reachedat the University ofBarcelona, AppliedPhysics and Optics De-partment, Mart i Fran-qus 1, E-08028Barcelona, Spain; e-mailpserra@ub.edu.

Michael Stuke is asenior scientist at theMax Planck Institute forBiophysical Chemistryin Gttingen, Germany,and professor of physics.He studied at the Uni-versity of Marburg,Technische UniversittMunich, and the Uni-versity of Heidelberg.

After receiving hisPhD degree in physical

chemistry, he became astaff member at MPIGttingen, where heheads the Laser Chemi-cal Processing of

Materials group. He hasworked at the Univer-sity of Southern Califor-nia, ENEA Frascati inItaly, RIKEN in Japan,and Hewlett-PackardLaboratories in PaloAlto, California. Stukereceived the Otto HahnMedal from the MaxPlanck Society and iseditor in chief ofAppliedPhysics A, Materials:Science and Processing.

Stuke can be reachedat Max-Planck-Institutfr BiophysikalischeChemie, PO Box 2841,D-37018 Gttingen,Germany; e-mailmstuke@gwdg.de.

Koji Sugioka is a seniorresearch scientist atRIKEN (the Institute ofPhysical and ChemicalResearch) and a guestprofessor at Tokyo Uni-versity of Science andTokyo Denki University.He received BE, ME,and PhD degrees inelectronics from WasedaUniversity in 1984,1986, and 1993, respec-tively. He joinedRIKEN in 1986.

At RIKEN, he hasworked on doping, etch-ing, and deposition ofsemiconductors and sur-face modification of me-tals using excimer lasers.

Sugioka also studied themicrofabrication of hard

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materials such as glassby using VUV andultrafast lasers. Hiscurrent interests centeron the development of

advanced laser micro-processing techniquesfor performing surfaceand 3D microstruc-turing of transparentmaterials, with appli-cations to lab-on-a-chip and photonicdevices.

Sugioka has receivedseveral awards for his

research and inventionsin the area of laser mi-croprocessing. He haspublished more than100 articles, given more

than 40 invited talks atinternational confer-ences and more than 50invited talks at domesticconferences, and holdsover 20 patents or pend-ing patents. He hasserved as a conferencechair, co-chair, and com-mittee member for nu-merous international

conferences. He is alsoeditor in chief of the

Journal of Laser Micro/Nanoengineering.

Sugioka can bereached at Laser Tech-nology Laboratory,RIKEN, Wako, Saitama351-0198, Japan; tel. 81-48-467-9495, fax 81-48-462-4682, and e-mailksugioka@riken.jp.

Kirk Williams is seniorR&D engineer and partowner of Free FormFibers LLC in Platts-

burgh, New York. Hereceived his BSc degreein mechanical engineer-

ing in 1998 and MScdegree in manufactur-ing systems engineer-ing in 2000 fromLouisiana Tech Univer-sity. In March 2006, hereceived his PhD degreein microsystems engi-neering from thengstrm Space Tech-nology Center at Upp-

sala University in Swe-den. He took briefpauses from hisacademic studies towork in the Departmentof Materials Chemistryat Uppsala in 1998 andat the Max Planck Insti-tute for BiophysicalChemistry in Gttingen,Germany, in 2000.

His research is fo-cused on the productionand characterization ofLCVD-deposited mi-crostructures such asfibers, microcoil heatersfor microthrusters inspace, and mass spec-trometry. At Free Form

Fibers, Williams work isfocused on using LCVDto deposit exotic andspecialty material fibersfor commercial use.

Williams can bereached by e-mail atkirk@kirk-williams.nu.

R. Stanley Williams is asenior HP fellow at

Hewlett-Packard Labo-ratories and foundingdirector (since 1995) ofthe Quantum ScienceResearch group. He re-ceived a BA degree inchemical physics in1974 from Rice Univer-sity and his PhD de-gree in physicalchemistry in 1978 fromthe University of Cali-fornia, Berkeley.Williams was a facultymember of the Chem-istry Department atUCLAfrom 1980 to1995. His primary sci-entific research duringthe past 20 years has

been in the areas ofsolid-state chemistryand physics.

Williams can bereached at QuantumStructures Research,Hewlett-Packard Labo-ratories, 1501 Page MillRd., Palo Alto, CA 94304USA; e-mail stan.williams@hp.com.

Kirk Williams R. Stanley Williams

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