vol 2 no. 3 jan. Œ mar. 2008 | issn 1793-3609 outlook-vol2no3-final.pdf · it instituted gold...

To spread information and knowledge and to promote collaboration in the area of Materials Research, Engineeringand Technology amongst the members of MRS-S

Vol 2 w No. 3 w Jan. – Mar. 2008 | ISSN 1793-3609

Ø MRS-S Activities: Past, Present and Future

The Materials Research Society of Singapore (MRS-S) organized four International andtwo National Conferences in Singapore since 2001. The biennial “InternationalConference on Materials for Advanced Technologies (ICMAT)” series were held in 2001,2003, 2005, and 2007. The biennial National Conferences were held in 2004 and 2006.MRS-S also sponsored/supported several other conferences, workshops, symposia andpublic lectures. It instituted gold medals for the best outgoing students in MaterialsScience at the National University of Singapore (NUS) and Nanyang TechnologicalUniversity (NTU). It instituted the “MRS Singapore Student Bursary Fund” at theNational University of Singapore.

To reach out to the public, MRS-S has organized number of public lectures by NobelLaureates and also an Astronaut.

The Institute of Materials Research and Engineering (IMRE), Singapore conductedthe “Postgraduate Student Poster Competition” on August 27, 2007 in which 27 Posterswere presented from all the “clusters” of IMRE. A panel of judges evaluated the Postersand selected the winners.

The “Prize of MRS-S” sponsored by MRS-S for the “2nd Best Poster”, was won by Mr. Li Zhipeng, with the title, 'Kinetically constraint zero- and one-dimensional het-eroepitaxial island growth’. The prize will enable him to participate in a Conference inSingapore on or before August, 2009.

MRS-S will be organizing the third “National Conference on Advanced Materials”,(incorporating MRS-S and MRS-I Mumbai-Chapter Joint Indo-Singapore Meeting) dur-ing 25–27 February 2008.

ICMAT 2009 will be held in July, 2009 in Singapore.

Ø Highlights of Previous ICMAT Conferences

Year 2001 w 1–6 July 200116 Symposia10 Plenary Lectures4 Public Lectures by

Nobel Laureates1400 Delegates18 Best Poster Awards36 Exhibitors

Year 2005 w 3–8 July 200525 Symposia9 Plenary Lectures2 Theme Lectures3 Public Lectures by


C O N T E N T SC O N T E N T SMRS-S MRS-S Activities: Past, PresentActivities: Past, Presentand Future and Future

ppage 60...age 60...

HighlightHighlights of Previous ICMAs of Previous ICMATTConferencesConferences


MRS-S Executive CommitteeMRS-S Executive Committeeppage 61...age 61...

HighlightHighlights of Previous Nationals of Previous NationalConferencesConferences

ppage 61...age 61...HighlightHighlights of the Recents of the RecentLiterature Literature


Recent BooksRecent Booksppage 63...age 63...

Materials Education &Materials Education &Research in Singapore Research in Singapore


Theme Theme Article Article ppage 68...age 68...

Conference Report Conference Report ppage 82...age 82...

Forthcoming ConferencesForthcoming Conferencesppage 83...age 83...

‘Theme ‘Theme Articles’Articles’ appeared inappeared inVVol. 1 Nos. 1–4 & Vol. 1 Nos. 1–4 & Vol. 2ol. 2Nos. 1–2 Nos. 1–2


MRS-S MembershipMRS-S Membershipppage 86...age 86...

InvitInvitation to MRS-S Membersation to MRS-S Membersppage 87...age 87...

©2008 MRS-S, Singapore. All rights reserved.

Year 2003 w 7–12 December 200316 Symposia9 Plenary Lectures2 Public Lectures by


Year 2007 w 1–6 July 200718 Symposia9 Plenary Lectures2 Theme Lectures2 Public Lectures by


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MRS-S OUTLOOK Volume 2 • No.3 • Jan.–March, 2008

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MRS-S Executive Committee(For 2006–08)

PresidentB.V.R. Chowdari, NUS

Founding PresidentShih Choon Fong, NUS

Vice PresidentsLim Seh Chun, NUSFreddy Boey, NTU

SecretaryLam Yeng Ming, NTU

Joint SecretaryChia Ching-Kean, IMRE

TreasurerRamam Akkipeddi, IMRE

Joint TreasurerFeng Yuan Ping, NUS

MembersDing Jun, NUS

Liu Ai Qun, NTULiu Bin, NUS

Lu Chun, IHPCPatrick Poa Chun Hwa, IMRE

Shen Ze Xiang, NTUG.V. Subba Rao, NUSTeo Kie Leong, NUS

Tim White, NTUJ.J. Vittal, NUS

Honorary AuditorsAjay Agarwal, IMEGregory Goh, IMRE

NUS: National University of SingaporeNTU: Nanyang Technological University, SingaporeIMRE: Institute of Materials Research & Engineering, SingaporeIHPC: Institute of High Performance Computing, SingaporeIME: Institute of Microelectronics, Singapore

Highlights of Previous National Conferences

Year 2004: 6 August 2004; 20 Invited Talks; 130Poster Papers; 4 Best Poster Awards .

Year 2006: 18–20 January 2006; Includes the Sym-posium on ‘Physics and Mechanic of AdvancedMaterials’; 60 Invited Talks; 200 Poster Papers; 1Public Lecture; 5 Best Poster Awards.

Highlights of the Recent Literature

(Contributed by the Editor)

Ultrastrong and Stiff Layered PolymerNanocomposites

Recently, Podsiadlo et al. [1] employed thebottom-up, layer-by-layer (LBL) assembly of amontmorillonite (MTM)-clay/poly (vinylalcohol(PVA)-polymer nanocomposite, and furtherstrengthened by cross-linking with glutaralde-hyde (GA), for the preparation of a homoge-neous, optically transparent material with planarorientation of the alumosilicate nanosheets. Typ-ically, the nanocomposite consisted of 200–300bilayer films with an average thickness of ∼5 nmper bilayer. The stiffness and tensile strength ofthese multilayer composites were found to be oneorder of magnitude greater than those of anal-ogous nanocomposites at a processing temper-ature that is much lower than those of ceramicor polymer materials with similar characteristics.Thus, the nanocomposite with MTM/PVA withGA showed a tensile strength (σUTS) of 400 (± 40)

MRS-S OUTLOOK (ISSN 1793-3609) is published quarterly by the Materials Research Society of Singapore(MRS-S), c/o Institute of Materials Research & Engineering, 3, Research Link, Singapore 117 602.Editor: G.V. Subba Rao. Disclaimer: Statements and opinions expressed in ‘MRS-S OUTLOOK’ are solely thoseof the authors, and do not reflect those of MRS-S, nor the editor and staff. Permissions: The subject matter con-tained in ‘MRS-S OUTLOOK’ can be freely reproduced for not-for-profit use by the readers; however, a word ofacknowledgement will be appreciated.

A Quarterly publication by the Materials Research Society of Singapore page 61


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ure MPa and a modulus (E’) of 106 (± 11) GPa, and an

exceptional stability under humid conditions. Theauthors state that “a high level of ordering of thenanoscale building blocks, combined with densecovalent and hydrogen bonding and stiffening ofthe polymer chains, leads to highly effective loadtransfer between nanosheets (of the MTM) andthe polymer (PVA with GA)”.

References

[1] P. Podsiadlo, A. K. Kaushik, E. M. Arruda,A. M. Waas, B. S. Shim, J. Xu, H. Nandivada,B. G. Pumplin, J. Lahann, A. Ramamoorthy, andN. A. Kotov, Science (2007) 318, 80–83 (Oct., 5 Issue).

Microfluidic Adhesion Induced bySubsurface Microstructures

The extraordinary ability of naturally occurringadhesives of climbing and jumping animals andinsects, like lizards, tree frogs and grasshoppers,is in part related to the complex and hierar-chical structural morphologies of their attach-ment pads, which use mechanisms of adhesionother than viscoelasticity (such as, friction, suc-tion, and molecular interactions). Several stud-ies in the literature on model textured surfaceshave shown that surface patterning can enhanceadhesive strength remarkably. However, the roleof subsurface structures such as the network ofmicrochannels has not been studied.

Recently, Majumder et al. [1] succeeded ingenerating cross-linked elastomeric adhesive lay-ers, with embedded air- or silicone oil-filledmicrochannels, bonded to a rigid substrate, andfound remarkable enhancement of adhesion,∼ 30 times, which results from the crack-arrestingproperties of the microchannels, together with thesurface stresses caused by the capillary force. Theauthors also examined the effect of the thicknessof the adhesive layer, channel diameter, inter-channel spacing, and vertical position within theadhesive. These findings can help in developingan optimal design for this type of microfluidicadhesive.

References

[1] A. Majumder, A. Ghatak, and A. Sharma, Science(2007) 318, 258–261 (Oct., 12 Issue).

Mussel-Inspired Surface Chemistry forMultifunctional Coatings

Inspired by the composition of adhesive proteinsin mussels, Lee et al. [1] recently reported a facileapproach to surface modification, by dip-coating,in which self-polymerization of dopamine(3,4-dihydroxy-phenethylamine, also known as,3-hydroxytyramine: ((OH)2C6H3CH2CH2NH2))produced an adherent polydopamine coating ona wide variety of inorganic and organic mate-rials. The latter include noble metals, metalswith native oxide surfaces (Cu, Stainless steel,Ni-Ti alloy), metal oxides (TiO2, non-crystallineSiO2, Al2O3), semiconductors (GaAs, Si3N4),ceramics (glass and hydroxyapatite (HAp)), andlarge number of synthetic polymers, includ-ing the classically adhesion-resistant materi-als like, poly(tetrafluoroethylene) (PTFE). Thethickness of these thin- and adherent -filmsranged from 5–50 nm depending on the dippingtime.

The authors found the polydopamine coat-ing to be an extremely versatile platform forsecondary surface-mediated reactions, leadingultimately to metal, self assembled monolayers(SAMs) and grafted polymer coatings, therebytailoring of the coatings for diverse functionaluses. Thus, for example, formation of adher-ent and uniform metal coatings onto substratesby electroless metallization was demonstratedthrough deposition of silver and copper metalfilms via dip-coating of polydopamine-coatedobjects into silver nitrate and copper(II) chlo-ride solutions, respectively. Grafting of poly-mer ad-layers onto polydopamine coatings wasaccomplished through the use of thiol- oramine-functionalized polymers in the secondaryreaction step, giving rise to bioresistant and/orbiointeractive surfaces. The authors state, “Thistwo-step method of surface modification isdistinctive in its ease of application, use of

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simple ingredients and mild reaction condi-tions, applicability to many types of materialsof complex shape, and capacity for multipleend-uses”.

References

[1] H. Lee, S. M. Dellatore, W. M. Miller, andP. B. Messersmith, Science (2007) 318, 426–430 (Oct.,19 Issue).

Coaxial Silicon Nanowires as Solar Cellsand Nanoelectronic Power Sources

Recently, Tian et al. [1] reported the fabricationand performance testing of p-type/intrinsic/n-type (p-i-n) coaxial silicon nanowire solar cells.These tiny devices with physical dimensions of∼300 nm in diameter and 3–22 μm in lengthshowed, under air mass 1.5 global (AM1.5G)simulated solar irradiation, an open-circuit volt-age Voc of 0.260 V, a short-circuit current Isc of0.503 nA and a fill factor Ff ill of 55.0%. The maxi-mum power output Pmax for the nanowire deviceat one solar equivalent (1-sun) illumination, was

∼72 pW. The above values were found to be con-stant for measurements made over a seven-monthperiod, thus demonstrating excellent stability.The apparent photovoltaic conversion efficiency(η) was 3.4% (upper bound) and 2.3% (lowerbound). Scaling of the output characteristics, likeVoc and Isc was also demonstrated in the inter-connected nanowire solar cells, as well as theimprovements in η at higher light intensity.

The authors demonstrated that individualand interconnected nanowire photovoltaic ele-ments can serve as robust power sources todrive functional nanoelectronic sensors (e.g., sil-icon nanowire pH sensor) and logic gates (e.g.,nanowire-based AND logic gate). They also sug-gested ways to improve the performance of thenanowire solar cells, such as by surface passiva-tion and, better coupling of light in to the devicesby vertical integration or multilayer stacking.

References

[1] B. Tian, X. Zheng, T. J. Kempa, Y. Fang, N. Yu,G. Yu, J. Huang, and C. M. Lieber, Nature (2007) 449,885–889 (Oct., 18 Issue).

Recent Books and Review Articles in the Area of Materials Science,

Engineering and Technology

(Contributed by the Editor)

Books• Handbook of Magnetism and Advanced Mag-

netic Materials, Edited by H. Kronmuller, andS. Parkin, July 2007, 5 Volumes, 3064 pp., Hard-cover, ISBN 978-0-470-02217-7. 1299. Hand-book/Reference Book.

• Liquid Phase Epitaxy of Electronic, Optical andOptoelectronic Materials, Edited by P. Capperand M. Mauk, July 2007, 464 pp., Hardcover.ISBN 978-0-470-85290-3. 205.

• Plasma-Aided Nanofabrication: From PlasmaSources to Nanoassembly, By K. Ostrikov andS. Ken, July 2007, XIV, 301 pp., Hardcover. ISBN978-3-527-40633-3. 89. Monograph.

• Computational Materials Engineering: AnIntroduction to Microstructure Evolution. ByKoenraad George Frans Janssens, Dierk Raabe,Ernest Kozeschnik, and Mark A. Miodownik,Academic (Elsevier Science), San Diego, 2007,357 pp., illus., Hardback, ISBN 9780123694683.$99.95.

• Biomaterials: An Introduction, 3rd ed., By JoonPark and R. S. Lakes. 3rd Edition. Springer,New York, 2007, 573 pp., illus., Hardback, ISBN9780387378794. $89.95.

• Materials Chemistry, By Bradley D. Fahlman,Springer, Dordrecht, Netherlands, 2007,497 pp., illus., Hardback, ISBN 9781402061196.$89.95.



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• Nanotechnology: Understanding Small Sys-tems, By Sumita Pennathur and Jesse Adams,CRC Press, 2007, 328 pp., ISBN 9780849382079.$89.95.

Review Articles

• Multiphoton Fabrication, by C. N. LaFratta,J. T. Fourkas, T. Baldacchini, and R. A. Farrer,Angew. Chem. Int. Ed., 46 (33) 6238–6258(2007).

AbstractChemical and physical processes driven by mul-tiphoton absorption make possible the fabricationof complex, 3D structures with feature sizes assmall as 100 nm. Since its inception less than adecade ago, the field of multiphoton fabricationhas progressed rapidly, and multiphoton tech-niques are now being used to create functionalmicrodevices.

This review discusses the techniques andmaterials used for multiphoton fabrication, theapplications that have been demonstrated, as wellas those being pursued. Also included is the out-look for this field, both in the laboratory and inindustrial settings. 173 References.

• From One-to Three-Dimensional Organic Semi-conductors: In Search of the Organic Silicon?,by J. Roncali, P. Leriche and A. Cravino, Adv.Mater., 19 (16), 2045–2060 (2007).

AbstractOrganic semiconductors (OSCs) based onp-conjugated systems are the focus of consider-able interest in the emerging area of soft or flexi-ble photonics and electronics. In recent years, theperformances of devices such as organic light-emitting diodes (OLEDs), organic field-effecttransistors (OFETs), or solar cells have under-gone considerable progress. However, a numberof technical and fundamental problems relatedto the low dimensionality of OSCs based on lin-ear p-conjugated systems remain to be satisfac-torily solved. This low dimensionality results inan anisotropy of the optical and charge-transportproperties, which in turn implies a control of the

material organization/molecular orientation dur-ing or after device fabrication.

This review illustrates possible alternativestrategies based on the development of OSCswith higher dimensionality which are capableof exhibiting isotropic electronic properties. 78References.

• Click Chemistry: Versatility and Controlin the Hands of Materials Scientists, byH. Nandivada, X. Jiang and J. Lahann, Adv.Mater., 19(17), 2197–2208 (2007).

AbstractThe increasing need for materials with tightlycontrolled structures will continue to fuel theinduction of synthetic organic concepts intomaterials science. One powerful example is theembracement of “click chemistry” by the mate-rials science community. Because of their highselectivity, near-perfect reliability, high yields,and exceptional tolerance towards a wide rangeof functional groups and reaction conditions,“click reactions” have recently attracted increasedattention, specifically for use in polymer synthe-sis as well as for the modification of surfaces andnanometer- and mesoscale -structures.

In this Review, examples of “click chem-istry”, such as the Cu (I)-catalyzed Huisgen 1,3-dipolar cycloaddition and the Diels–Alder reac-tion are shown to present a synthetic concept thatlends itself superbly to the controlled preparationof multifunctional materials. Thus for instance,incorporation of iridium complexes by “clickchemistry” resulted in functional polymericmaterials with potential applications in organiclight-emitting diodes (OLEDs), whereas fluo-ropolymers synthesized by poly(cycloaddition)showed good thermal stability and solubility incommon organic solvents. 123 References.

• Evolution of Ceramics with Medical Applica-tions, by A. J. Salinas and M. Vallet-Regı, Z.norg. Allgem. Chem., 633 (11–12), 1762–1773(2007)




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AbstractBioceramics can be defined as those ceramicsdesigned to be implanted into the human body.In the last fifty years these materials experiencedan enormous evolution: Initially, the objectivewas bio-inertness (minimum interaction with theliving organism). These bioceramics are nowa-days called first generation. The second genera-tion bioceramics were widely investigated in the1980s with the goal of a positive interaction withliving tissues. This group collects bioactive- andresorbable- bioceramics. At the beginning of thisdecade it was clear that the medical paradigmof tissue substitution must be replaced withtissue regeneration. Thus, bioceramics must besupplemented with cells and biologically activemolecules. The investigation in third generationbioceramics has just started.

This review presents a description of the mainsecond generation ceramics, and new advancedceramics currently under investigation at theAuthors’ laboratory aimed to be used as scaffoldsand templates in third generation biomaterials.174 References.

• Carbon-based electronics, by P. Avouris,Z. Chen, and V. Perebeinos, Nature Nanotech-nology, 2 (10), 605–615 (2007).

AbstractIn this review article, the authors examine theelectronic structure, electrical transport and opto-electronic properties of carbon nanotubes (CNTs)with a focus on the associated physical phe-nomena. The emerging area of study involvingtwo-dimensional graphene layers and narrowgraphene nanoribbons (GNRs) has been dis-cussed. The switching mechanism and character-istics of single-CNT field-effect transistors (FETs),GNR FETs, and efforts towards device integrationwere critically analysed. Also described are theprinciples of simple CNT optoelectronic devicessuch as electroluminescent light emitters andphotodetectors. The authors are highly optimisticof the emergence of the carbon-based electronics.98 References.

Materials Education & Research in Singapore

There are two Universities and several Research Institutes in Singapore involved in teaching,research and development in the broad area of Materials Science, Engineering and Technology.These are listed below along with the Websites and provide information on the available coursesand opportunities for undergraduate, graduate and post doctoral research. They also entertainqueries regarding openings for Research Scientists and Faculty positions.

National University of Singapore: www.nus.edu.sgNanyang Technological University: www.ntu.edu.sg

Institute of Materials Research and Engineering (IMRE): www.imre.a-star.edu.sg

Institute of Microelectronics (IME): www.ime.a-star.edu.sg

Data Storage Institute: www.dsi.a-star.edu.sg

Institute of Chemical & Engineering Sciences: www.ices.a-star.edu.sg

Institute of High Performance Computing: www.ihpc.a-star.edu.sgSingapore Institute of Manufacturing Technology: www.SIMTech.a-star.edu.sg

Institute of Bioengineering and Nanotechnology (IBN): www.ibn.a-star.edu.sg



Volume 2 • No.3 • Jan.–March, 2008 MRS-S OUTLOOK

About the Theme Article Authors

Dr. Akkipeddi RamamHead, SERC Nanofabrication and Characterization,Institute of Materials Research and Engineering (IMRE),A*STAR (Agency for Science, Technology and Research),3 Research Link, Singapore 117602

Dr. Ramam has been in the field of semiconductors for the last over20 years. He started his career with the Defense R & D labs in Indiaworking on GaAs based millimeter wave (mmW) devices and Mono-lithic Microwave Integrated Circuits (MMICs). He was awarded the“Young Scientist” award for developing the multi-mask process forbeam lead Schottky diodes and latter sent to Plessey III-V in UK to getinvolved in the technology development of MMICs. He then movedto SGS-Thompson Microelectronics, Singapore as a senior manufactur-

ing engineer before joining the National University of Singapore. Here, he specialized on the growthof arsenide based ternary/quaternary epitaxial materials by MBE and their optical/structural charac-terization for optoelectronic devices. For the last nine years he has been with IMRE, involved in thefabrication aspects of GaN based LEDs/Lasers and other III-V based opto-electronic devices, specifi-cally in the integration of InP based photonic devices with MEMS concepts. He is a senior member ofIEEE and has organized and chaired a number of symposia in international conferences. He is currentlya senior scientist and manages the nanofabrication and characterization group at the institute.

Dr. J. ArokiarajSenior Research Engineer,Institute of Materials Research and Engineering,A*STAR (Agency for Science, Technology and Research),3 Research Link Singapore 117602

Dr. J. Arokiaraj is a Senior Research Engineer with the Institute of Mate-rials Research and Engineering (IMRE), Singapore since year 2004. Heis specializing on wafer bonding techniques for III-V and III-N deviceswith Si substrates. Presently he is developing modified CNT’s as ther-mal interface materials and has a keen interest to develop new Tech-nologies for heat dissipation for GaN devices using wafer bondingschemes. Prior to IMRE, he had worked at Nangyang TechnologicalUniversity/School of EEE for two years on Widely Tunable InP lasers

using quantum well intermixing. He has worked at Nagoya Institute of Technology, Japan after his PhDfrom India (Anna University) for a period of five years. He was involved in the development of highefficiency GaAs solar cells on Si substrate. He has won the Young scientist researcher award from theJapanese Physical Society in the year 1999 and has published over 40 research papers in referred journalsand conferences.




Mr. Vicknesh ShanmuganSenior Research Officer, Temasek Laboratories @ NTUResearch TechnoPlaza,8 th & 9 th Storey, BorderX Block,50 Nanyang Drive, Singapore 637553

Mr. Vicknesh is presently working in the area of compoundsemiconductor-based, Monolithic Microwave Integrated Circuit (MMIC).His expertise include, device fabrication related to thin film depositionand plasma etching of various compound semiconductor materials torealize opto and microelectronic devices. He holds a Masters degreein Photonics from School of Electronics and Electrical Engineering ofNanyang Technological University (NTU). He is currently employedwith the MMIC Design Centre (MDC) at the Temasek Laboratories atNTU, Singapore.

Mr. Mithilesh Ashok Shah4552 Rue Drolet,Montreal H2T 2G4, Canada

Mr. Mithilesh A. Shah has worked in the area of microfluidic switchesand III-V semiconductor MEMS. He has investigated fluid behavior athigh pressure pulses for microfluidics, thermal behavior of polymersfor adhesive-bonding of dissimilar ceramic substrates and conductedfailure analysis of AlGaAs based LEDs. His work on thin film heaterreliability has resulted in 100-fold increase in the average life-cyclesto failure for thin-film resistance heaters on ceramic substrates. Hisexpertise includes microfabrication, failure analysis, surface microma-chining, and sublimation drying technique for MEMS, finite elementmodeling (FEM) of MEMS, optical characterization techniques in thin

films. He has authored 9 publications in international journals and conferences. He holds a mastersdegree in “Advanced Materials for Micro and Nano Systems” from Singapore-MIT Alliance program ofNational University of Singapore.



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Indium Phosphide Based MEMS for Tunable DevicesRamam Akkipeddi, J. Arokiaraj, S. Vicknesh and S. MithileshInstitute of Materials Research and Engineering, Agency for Science Technology and Research (A*STAR),3 Research Link, Singapore 117602

The article is organized in the following form:The introduction part discusses the motiva-tion and importance of III-V based MEMSstructures in WDM applications. The FiniteElement Analysis (FEA) modeling of variousarchitectures for a membrane structure is thendiscussed. The simulation work encompassesa new filter design and an investigation ofelectro-mechanical response. The consequentevolution of a criterion while trying to opti-mize the dimensions of a filter (based onmechanical/optical considerations) has led tofour filter designs. The branched beam typenovel filter design has a lower compliance ascompared to other filter designs, and is theone used for fabricating into a Electro-static(E-S) actuator. The fabrication schemes, theiroptimization and release of InP membranesusing an improvised freeze-dry technique ispresented next. Side-wall protection for theInP membrane structures was introduced bydepositing SiO2 layer and etching it selec-tively over the beam regions thus avoidingthe undercutting for the support regions. Thefabricated actuators were characterized underDC and quasi-static conditions, with a deflec-tion of about 350 nm, pull in voltage of 7 V andwith a response time of about 100 μsec.

1 Introduction

The increasing demand for more and more datatransmission capacity has driven the telecom-munications to seek answers in WDM (Wave-length Division Multiplexing) technology. Usingthis technology, different closely spaced wave-length channels are able to carry optical signalsfrom different sources, simultaneously througha common fiber. The implementation of thistechnology requires devices in the fiber opticnetwork to combine and/or separate the various

wavelength channels. A WDM network typicallyconsists of a number of channels each of whichis related to a different wavelength. Chan-nel manipulations especially channel selectionand detection of bit-stream on selected chan-nel/wavelength is an important function in suchoptical data transmission networks. There exist afew competing technologies for the wavelengthfiltering component of the tunable receiver how-ever each one has its own disadvantages. A filter-ing mechanism in tunable photo-receiver shouldessentially possess the following important fea-tures: low insertion loss, narrow bandwidth, highside lobe suppression, simple control mechanism,small size, and cost effectiveness. A diffractiongrating type of filter, for example, is capable ofwide tunable range but high polarization is aproblem.

Another widely used configuration in pho-tonic applications is Mach-Zehnder (MZ) inter-ferometer [1, 2]. In a typical MZ type filter anincident beam is split in two ways and recom-bined after a short distance. The combining lightfields interfere according to the phase differencebetween the two fields. If a time delay is intro-duced in one arm, e.g. by a phase modulator, aperiodic frequency dependent phase difference isformed according to which the fields get com-bined. Hence the intensity of the output is peri-odic function on optical frequency, usually witha small Free Spectral Range (FSR). Losses are amajor disadvantage of MZ type filters. MZ filterssuffer from low finesse and are therefore usuallycombined with additional wavelength selectiveelements.

Another class of filters, include, Acousto-Optic Tunable Filter (AOTF) and Electro-OpticTunable Filter (EOTF). In Acousto-Optic Tunable




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iclefilters, a light wave and a surface acoustic wave

(SAW) interact and cause a polarization shift ofthe Electromagnetic (EM) wave only at frequen-cies that satisfy the following phase matchingconditions [3].

|βTE−βTM| = |kac| (1)

where, ßTE, ßTM and kac are the wave num-bers of the light wave at TE and TM polariza-tions and the SAW respectively. This mechanismcombined with two TE/TM polarization split-ters, forms an efficient filter by selecting only thewavelengths that satisfy the phase-matching con-dition. By applying several SAWs in different fre-quencies, the AOTF can simultaneously filter outseveral channels. There are numerous problemsthat plague AOTF which include high insertionloss (∼5 dB), strong side lobes of the transfer func-tion that damage the filtering efficiency, somepolarization sensitivity and some frequency shiftdue to non linearity in the device; also their band-width is not very narrow. An Electro Optic Tun-able Filter (EOTF) works on very similar principleas AOTF i.e. by using the TE-TM mode coupling.However instead of a SAW, here the perturbationin incident band of light is introduced by electro-optic effect using electrodes positioned in equalspaces along the waveguide. Tuning is achievedby a uniform electric field that changes the aver-age refractive index. The EOTF like AOTF suf-fers from the wide bandwidth and strong sidelobes [4]. Arrayed Waveguide Gratings (AWGs)are also used for wavelength filtering applica-tions. AWGs basically utilize an integrated arrayof waveguides as a grating to produce an interfer-ence pattern. However, an AWG by itself is not atunable device and needs other components suchas a thermo-optic switch to achieve tunability.

The micro-machined Fabry–Perot Interferom-eter type filter is increasingly becoming a viablealternative. A Fabry–Perot filter comprises of anoptical cavity confined between two Bragg mir-rors. Of the several constituent wavelengths in theincident multiplexed signal, the filter transmitsonly the wavelength that satisfies the resonancecondition [5] for a given cavity length (Lcavity)

ncavityLcavity = mλ (2)

where, ncavity is the refractive index of cavitymedium i.e. air, m is an integer and λ is theresonant wavelength. In a tunable type Fabry–Perot filter the optical cavity consists of an air-gap and one of the mirrors is suspended bymicromechanical structures to enable verticaltranslation of suspended mirror by electrostaticactuation. The optical cavity length can thus bevaried resulting in a corresponding change in res-onant wavelength and thus wavelength tuning isachieved.

2 III-V materials in MEMS

Material systems like AlGaAs/GaAs andInGaAsP/InP have shown great promise formicro-machined Fabry–Perot type filters. Since,devices such as photodiodes, LEDs, and lasersare fabricated out of III-V materials systems themicro-machined filters are preferentially fabri-cated from the same materials system for theease of integration. Besides this, there are severaladvantages of micromachining in III-V semicon-ductor system. Intrinsic properties, viz. piezoelec-tricity, optical band gap, high mobility, hetero-structure based quantum effect have not beenfully exploited in the MEMS arena for novelapplications. Additionally, the epitaxial toolsfor growing III-V materials offer very sharpinterfaces (mono-layers), excellent compositionselectivity for creating very thin smooth opticalgrade beams or membranes (<0.1 μm), which arefavorable for MEMS devices. A wide variety ofetchants, with orientation dependent etch pro-files are also available to execute the sacrificiallayer etchings. The hetero-epitaxial layers in thesematerial systems can be etched by wet or drymeans with an excellent compositional selectivity[6]. These reasons make the GaAs and InP basedheterostructure systems very suitable for micro-machining of Fabry–Perot type tunable receivers.There is interest for WDM systems operating at1550 nm wavelength and the photo-detectors for1550 nm are typically based on InP/InGaAs mate-rials system. Major work has been done on bothGaAs based and InP based micromachined FPfilters, tunable VCSELs and tunable detectors[7–9]. Strassner et al. demonstrated a tunable




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3 Modeling and Simulation

Compound semiconductor substrates and theirhetero-structures are generally much more expen-sive to process. It was envisaged that the priorsimulation of the devices would help reduce costsby shifting trial and error on computing plat-form and minimizing the same on actual MOCVDgrown samples. In keeping with this cost effectivestrategy, finite element modeling, and simulationswere conducted for various designs and designparameters were optimized using the ANSYSsoftware.

A device incorporating a monolithically inte-grated photo-detector and a micromechanicallytunable Fabry–Perot filter is described here. TheFabry–Perot filter acts as a wavelength selectivecomponent while the integrated photo-detectorgives electrical response corresponding to theselected wavelength. The Fabry–Perot filter com-prises of two distributed Bragg reflector mirrorsseparated by an air cavity, created by microma-chining of a sacrificial layer. Wavelength tuningis achieved by varying the air cavity spacingbetween the two mirrors for which purpose oneof the mirrors is kept fixed while the other mirroris made movable. The movable mirror is mountedon top of a membrane supported by beams which

in turn are supported by a fixed platform allof which are micro-machined out of a semicon-ductor layer. The membranes and the support-ing beams are actuated on electrostatic actuationprinciple. This however, is an example of “stand-alone” Fabry–Perot filters with no integrated pho-todiode. A simplified schematic of such a deviceis depicted in the Fig. 1 below.

The Fabry–Perot filter comprises of two Braggmirrors with a cavity defined between them.Of the several constituent wavelengths in theincident multiplexed signal (normal incidence,θ =00), the filter transmits only the wavelengththat satisfies the resonance condition [5] for agiven Fabry–Perot Cavity length (Lcavity). Thewavelength thus transmitted forms the input tothe integrated photo-detector. A filter with fixedcavity length is able to select only the correspond-ing single wavelength. For a filter to be tunable,the cavity length should be variable which can beachieved by making one mirror movable whilethe other remains fixed. By varying the cavitylength i.e. by displacing movable Bragg mirrorwith respect to the fixed mirror, using electrostaticactuation mechanism, it is possible to select differ-ent wavelength channels contained in the incom-ing multiplexed signal. For separation of differentwavelength channels, finesse of Fabry–Perot filteris required to be high which in turn depends onplanarity of mirrors [12]. The maximum tolera-ble slope of movable top Bragg mirror is 0.0060

and hence for a spot size of 20 μm of light ontop mirror, the maximum allowed center to edgedeflection is 1 nm [13]. In the simulation work,four different filter designs have been investi-gated for their electro-mechanical response tothe tuning voltage and the effective tuning range

Fig. 1. A diagonally cut section schematically depicting the various parts of a tunable filter.




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In0.47Ga0.53AsPost

Si3N4/SiO2

DBR

Undercut

InP

L

L1 L2

Fig. 2. One quarter of a filter with mirror suspended diagonally with branching beams. Due to its four-fold symmetry only onequarter is modeled with appropriate symmetry boundary conditions.

when limited by Bragg mirror flatness. The mod-eling has been done using finite element analy-sis using sequentially coupled-field technique. Insequential coupling, the electrostatic model andthe mechanical model feedback to each other inan iterative manner to better simulate the non-linear nature of electrostatic actuation.

a) Design of Membranes

The Fabry–Perot filter consists of two Bragg mir-rors, one movable at the top and one fixed, atthe bottom. The bottom Bragg mirror consists ofalternating layers of InP and InGaAs of thick-ness λ/4 grown epitaxially over InP wafer sub-strate. On the top of bottom Bragg mirror there isa sacrificial InGaAs layer of thickness 1.55 μm. Itis this sacrificial layer, which upon etching formsan air-gap for the Fabry–Perot cavity. Above thissacrificial layer, there is a structural layer of p-doped InP. This structural layer is patterned toform membranes and cantilevers which deflectupon electrostatic actuation. The membrane pat-terned out of this structural layer carries the topBragg mirror at its center. The top mirror con-sists of alternating Si and SiO2 layers of λ/4 thick-nesses. There are different ways of suspendingthe top mirror. Using FEM we investigated, fourdifferent types of filter designs, three of whichhave been reported in the literature cited here andthe fourth type is a novel filter design introducedby the authors. The first design is the simplest andconsists of a square mirror at the free end of a

cantilever [14]. The second design is of a bridgetype with a square mirror at its center [6, 14].Third design is a square mirror suspended diago-nally by four cantilever type beams [6].

The fourth design is a novel configurationcomprising of a diagonal beam (length L1, <110>direction) splitting into two mutually perpendic-ular beams (length L2, <010> and <100> direc-tions) and the length of the mother beam (L1) isequal to length of branch beam (L2). The equiv-alent diagonal beam length for branched beamdesign is L (L=L1+

√2 L2 ). A symmetric quarter

of this type of, structure is shown in Fig. 2.

b) Finite Element Model

The investigation of all the four models describedin the design section was done to determine thefilter’s mechanical response to applied electricfield. When the device structure is comprised ofone movable and one fixed Bragg mirror, onlythe movable part and the adjacent support onwhich rigid constraints apply are considered. Sothe region under consideration includes the topSi/SiO2 mirror the membrane supporting the topmirror, the beam(s) supporting the membrane, theplatform anchor to which the beams are fixedand the under-etched region of InGaAs sacrifi-cial layer that supports the platform. A 3D finiteelement analysis of this model was done usingANSYS software package.

The rigid boundary constraints were appliedat the base of InGaAs post supporting the




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Fig. 3. Schematic illustrating the bending within the mirror (δ) due to mechanical deflection (y) of the membrane-beam structureunder excitation by an applied voltage.

platform. In doing so, even the compliance ofthe post supporting the structural layer has beentaken into account. During the sacrificial layerwet etching to release the structure, there isalways some under-etching below the platformsupporting the beams. Due to this reason, neitherthe root of the beams nor the entire base of theplatform can be considered as fixed. The mini-mum expected under-etching is at least half thedimension of the widest free standing structure.The square membrane is 30×30 μm2 therefore theundercut below the platform is taken as 15 μm.

For separation of different channels, finesseof the Fabry–Perot filter is required to be highwhich in turn depends on planarity of mirrors. Asexplained before, the maximum allowed center toedge deflection for the top mirror is 1 nm. Here wedefine a term Mirror Bending Limited Deflection(MBLD) as the least deflection (of the movablemirror) for which the bending within the mirrorhas reached 1 nm. This is schematically illustratedin Fig. 3.

From mechanical point of view, the maxi-mum achievable deflection in the filter is equalto one-third of the cavity length, because beyondthis, the structure “pulls-in”. But the opticalconsiderations ordain that the deflection in thefilter should not exceed the Mirror BendingLimited Deflection. The mechanical limit (pull-indistance) cannot be extended but the MBLD canbe extended and made equal to pull-in deflection.When this happens, the filter is utilized to its max-imum deflection capability without violating the

optical limits. This can be done if the beams sus-pending the mirror are made longer. In such acase the beams become more compliant and bend-ing is localized to the beams thereby keeping themirror relatively flat.

For the cantilever type filter, as shown (with ascale factor of 100) in Fig. 4, the MBLD increasesinitially with increase in beam length, reachesa maximum of 1.86 nm at 80 μm beam lengthand then drops with further increment in beamlength until it finally becomes zero. The MirrorBending Limited Deflection (MBLD) is zero forbeam lengths 180 μm and above because evenin the absence of applied voltage the displace-ment under self-weight is so large that the mirrorbending exceeds 1 nm. For bridge type filter(Fig. 4), the MBLD increases with beam length(of each of the two beams) up to 70 μm lengthand thereafter it becomes constant (∼500 nm).Below 70 μm length, the mirror curvature limitis reached before pull-in phenomena but beyond70 μm length, the structure pulls-in before mir-ror bending limit is reached and the pull-indistance is constant, therefore MBLD is con-stant. For the diagonal suspension type filter, theMBLD increases with increase in beam lengthup to 90 μm beyond which it becomes constant∼550 nm (Fig. 4).

To conclude, a bridge design with each ofthe two beams 70 μm long, a diagonal suspen-sion design with each of the four beams 90 μmlong and a branched beam design with effectivediagonal length of 110 μm for beams are suitable




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Fig. 4. Variation of Mirror Bending Limited Deflection (MBLD) of different types of filters with the change in length of the beamssuspending the DBR mirror.

for micro-machined Fabry–Perot filter applica-tion. Out of these three designs, the bridge typeachieves the same maximum deflection as theother two with lower actuation voltage and istherefore the most favorable design. Using thesurface micromachining technology, the designsunder investigation here have been practicallyrealized. The structures are released by sacrificialetching of InGaAs layer with H2SO4:H2O2:H2O(1:1:8). The released structures are rinsed with DIwater until the solution reaches a neutral pH. Thesolution is frozen and the freestanding structuresare obtained by sublimation drying from frozenDI water. The yields of the freestanding struc-tures with branched beam design are generallyobserved to be higher than other structures dueto lower compliance and robust suspension. Themicro-machined Fabry–Perot filters incorporatinga movable mirror based on MEMS technologyhave applications in tunable photodetectors andalso for adding tunability to VCSELs which canenhance the existing optical networks.

4 Simulation of Dielectric Based Mirrorsand Filters

A highly selective photodetector is required todetect only one wavelength ignoring all others foruse in Wavelength-Division Multiplexing (WDM)systems, spectroscopy etc. Since bare p–n or p–i–nphotodetectors absorb continuous band of wave-lengths, these detectors alone cannot be used todetect different wavelengths separately in WDMscheme. The conventional p–i–n photodiode isnot suited to high-speed optical systems whichrequire both high quantum efficiency and highspeed of response [15–16].

One solution to address at this trade-off incor-porating wavelength selectivity is to place a p–i–ndiode inside a Fabry–Perot (FP) cavity and usedistributed Bragg reflectors (DBR) as mirrors,which is popularly known as resonant cavityenhanced (RCE) p–i–n photodetectors [16]. TheDBR mirrors are usually made of quarter wavestacks with a periodic modulation of refractiveindices [17–19].

Single wavelength, selective optical filtersplay important roles in communication networks,optical source and detectors etc. The additionof tunability, in addition to the filtering of the




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1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 20

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0.9

1

Wavelength (μm)

Cav

itytra

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ittan

ce,T

SimulationExperimental

Peak T ≈≈≈≈ 80%

Fig. 5. Transmittance of dielectric based optical filter operating at C-band. Peak transmission of 80% has been obtained on fabri-cated filters.

optical waves, reduces the inventory cost in opti-cal networks. Moreover, the center wavelengthmight shift due to the environmental conditions(e.g., temperature fluctuation, humidity etc.),and electronic properties of materials duringthe operation of the opto-electronic devices. Thedesired wavelength can be tuned to correct thisproblem, only if the detector or filter can be madetunable. These two aspects form the motivation toconduct research and to fabricate tunable opticalfilter/photo-detector.

a) Single Wavelength Selective Filter at 1550 nm

Low-cost dielectric based optical filter for opera-tion at C-band (1550 nm) has been designed andoptimized. SiO2 cavity is sandwiched betweentwo highly reflective mirrors and capped bySi3N4 layer for passivation. The reflectance Rand transmittance T of the filter has been sim-ulated using transfer matrix method (TMM) andthe fabricated filter measured using spectropho-tometer. Figure 5 depicts the transmittance alongwith the simulation result. This filter has appli-cations in optical channel add/drop multiplexing(OADM), spectroscopy (identification of atmo-spheric gases, e.g., CH4), optical sources, detec-tors. The filter specifications are with a centerwavelength tolerance of ±5 nm, Full Width HalfMaximum (FWHM) of 2 nm, peak transmissionof 80% and quality factor of 100.

b) Tunable RC Filter at 1550 nm

A tunable resonant cavity filter using epitaxialdistributed Bragg reflector (DBR) material anddielectric based DBR has been designed. The sim-ulated filter transmission at various wavelengthsis plotted in Fig. 6 by changing the cavity spacing.c) Dielectric Based DBR Mirrors

High reflectivity Distributed Bragg Reflector(DBR) mirrors comprising of quarter wavelengthstacks of semiconductors [20] and dielectric [20–22] periodic structures are utilized in both activeand passive opto-electronic devices. These highlyreflective DBR mirrors are used to enhance deviceperformance by filtering (i.e. transmit what itdoes not reflect) [22] or “recycling” of opticalsignals. Fabrication of Bragg mirrors in resonantcavity filters is a key process in the realizationof highly efficient devices resulting in narrowwavelength selection [23] and high speed opera-tion. Examples of devices that have successfullydemonstrated Bragg mirrors for enhanced per-formance are, Vertical Cavity Surface EmittingLasers (VCSELs) [24] exhibiting low threshold-current densities [25], Resonant Cavity Pho-todetectors (RECAP’s) [26] exhibiting narrowline widths, high quantum efficiencies and highspeeds, Fabry–Perot filters [27] and reflectionmodulators [28]. These devices benefit from twopossible effects, first the intensity enhancement ofelectromagnetic waves within the active medium




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1.45 1.5 1.55 1.6 1.650

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0.6

0.7

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1

wavelength (μm)

filte

rtra

nsm

issi

on

1550 nm1530 nm1510 nm1490 nm

Fig. 6. Simulation plot of filter transmission as cavity spacing is varied by electro-static actuation. Wavelength tunability rangeis 100 nm.

of the resonator formed by both the Bragg mir-rors while the second being, the resonators sup-porting only certain wavelengths (cavity modes)so that they act as spectral and spatial filters. Suchdevices have promising future in high speed andwavelength-division-mulitplexing applications.

The highly reflective DBR mirrors are mul-tilayer structures consisting of alternating pairsof two materials with different or large refrac-tive indices. They (i.e. DBR mirrors) can be tai-lored to obtain any reflectivity between 0% andalmost 100% for a specific operating wavelength,λ depending finally on the application require-ments. The effect of refractive index contrastavailable at each interface, the number of pairsin the mirror and the polarization of the inci-dent light determines the net reflectivity. Thusto increase the net reflectivity, one has to eitherincrease the number of pairs or select materi-als of large refractive indices as the polarizationand the angle of incidence are usually limitedby the applications. Murtaza et al.. [20] has men-tioned that the reason for high peak reflectivityin a classical λ/4 stack is that, all the reflectionsare perfectly in phase with each other and band-widths are large. Also, as the wavelength sep-aration from the center wavelength increases,the phases in the reflected beams get in phase.Since most available optoelectronics devices arefabricated using III-V semiconductor materialsfor the visible and near infrared spectral range,

epitaxial Bragg mirrors, grown by sequentialMolecular Beam Epitaxy (MBE) or Metal OrganicVapor Phase Epitaxy (MOVPE), of single crys-talline quality are most popular and have beendiscussed extensively in the literature [20, 24, 28,29, 30]. In contrast, all dielectric-based high reflec-tive DBR mirrors, comprising of quarter wave-length stacks, uniformly deposited by plasmaenhanced chemical vapor deposition (PECVD)onto a novel tunable resonant cavity device inMEMS configuration is introduced. Reflectivity ofmore than 99% is achieved through the optimizedprocess comprising of 10.5 periods of alternatingquarter wavelength stacks of Si3N4 and SiO2. Interms of reflectivity, the dielectric-based mirrorsare equivalent to those obtained in epitaxial Braggmirrors. As such, the advantage of using dielectricbased DBR mirrors would be in the lower numberof pairs to achieve high reflectivity thus saving inthe cost of mirror formation.

Individual dielectric pairs (i.e. 5.5, 7.5 and 10.5stacks) deposited in a continuous cycle without,venting the chamber to atmosphere in betweendeposition of materials is reported. For example,in the case of 5.5 pairs of Si3N4/SiO2 DBR stacks,the sample is not removed until all 11 layers,including Si3N4 capping layer is deposited on InPsubstrate and similarly for 7.5 and 10.5 pairs ofSi3N4/SiO2.

Upon characterizing these highly reflectingDBR mirrors, we utilized them to realize in two




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Inset 1

InP

In

DBRstack

InP

InGaAs

ICP etching of 7.5pairsSi3N4/SiO2 with CHF3

Fig. 7. SEM image of 7.5 pairs of Si3N4/SiO2, etched using ICP showing highly anisotropic walls. (Inset 1 shows microscopeimage of patterned 7.5 pairs of Si3 N4/SiO2).

forms of applications, namely, as DBR mirrors onInP freestanding membrane and in a fixed cavityfilter with SiO2 material as the cavity. 7.5 pairsof highly reflecting DBR layers are deposited onInP based epitaxial layer sample used in realiz-ing electro-static (ES) actuation. Using lithogra-phy and plasma etching, we are able to patternthese 7.5 pairs of Si3N4/SiO2 onto an InP basedmembrane, which is shown in Fig. 7. Microscopeimage of 7.5 pairs of Si3N4/SiO2 residing on themembrane is shown as inset 1. In conclusion,3 different stacks (5.5. 7.5 and 10.5) have beendeposited on InP using PECVD and the reflec-tivity was measured to be 99.8% for 10.5 pairs ofSi3N4/SiO2 pairs, which is fairly near to the sim-ulated results.

d) Dielectric Based Optical Filters

A dielectric based fixed cavity optical filter, usingSiO2 layer as the cavity, sandwiched betweentwo highly reflecting mirrors was fabricated tofilter a single wavelength. At first 8.5 pairs ofSi3N4/SiO2 bottom mirror was first depositedfollowed by a SiO2 cavity layer, determining

the filtered wavelength and finally 8.5 pairs ofSi3N4/SiO2 top mirror, as shown in Fig. 8b.Characterization of the fixed cavity filter is doneusing spectrophotometer in transmission mode,where the sample is placed with the top mir-ror facing the light input (refer to Fig. 8b) but inFig. 8a, reflectance is plotted to highlight the fil-tering mechanism observed for 3 different cavitythickness.

The SiO2 cavity thickness is varied from0.51 μm to 0.63 μm with a variation of ± 0.02 μm,and a single wavelength filtering is assured foreach cavity, starting at 1473 nm to 1532 nm withinthe broad pass-band. The intensity of filteredsignal is not high and as it is suspected thatto absorption within the glass slide, could haveaffected it.

5 Releasing Technique for InP BasedFreestanding Structures

One of the major challenges in MEMS micro-fabrication is overcoming the problems ofadhesive failures popularly known as ‘stiction’.When the released microstructures are dried, they




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1473nm

Single wavelength dipobserved for variousthickness of SiO2 cavity.

(a)

8.5pairs

Cavity length

Light Input

Glass Substrate

SiN

SiO2

SiO2

SiN

SiO2

SiN

SiN

SiO2

SiO2

SiN

SiN

8.5pairs

(b)

Bottom

Top Mirror

Fig. 8. (a) Reflectivity measurement of a SiO2 cavity. Cavity thickness ranging from 0.51 μm to 0.63 μm, sandwiched between two8.5 pairs SiN/SiO2 highly reflecting mirrors. (b) Layers structure with SiO2 as a cavity between two 8.5 pairs of highly reflectingmirrors.

usually stick to the substrate or to the adjacentmicrostructures. This common problem known asstiction is attributed to the surface tension forcesarising from the drying of water in the narrowgaps between microstructure and substrate. Fromthe post rinsing stage at which the microstruc-tures are in released state but submerged underpure DI water with no residual etchant, there areseveral divergent ways to render the freestandingmicrostructures.

One such technique is sublimation drying inwhich, the microstructures are obtained as free-standing by freezing and subliming the liquid.In another approach described by Mulhern et al.[31], the problem of capillary forces is circum-vented by transfer of microstructures to CO2 insupercritical state where there is no meniscusseparating the liquid and vapor state and there-fore no capillary forces. In practice the DI wateris generally replaced by another liquid with alower surface tension than water from whichthese different approaches can be implemented.In supercritical drying the general approach asreported in the literature is to replace the DI watercompletely with methanol over several rinsingcycles. This methanol itself is then replaced in apressure, vessel equipment by liquefied CO2 for

subsequent drying of the microstructures by turn-ing the liquid CO2 into a supercritical state. Incase of sublimation drying, there are a numberof liquids that replace and substitute for the DIwater. One of them is tertiary-butyl alcohol. How-ever in our case we used the sublimation of frozenDI water to dry the microstructures.

Since in this case water itself was to be frozen,extreme care was taken to ensure that there wereno residues of the residual etchant from the etch-ing step. It is necessary to do so since the freez-ing point of water lowers due to presence of eventrace impurities. Bearing in mind the requirementof doing all processing from etching to rinsing tosolvent substitution while maintaining specimenin a submerged condition a special processing sta-tion referred to as surface micromachining work-station was set-up. The specimen is placed in aperforated bed vessel which is a module detach-able from the main station. The solvent inflowand outflow to this vessel is manually synchro-nized by two flow regulators. This balance in theinflow and outflow maintains a constant level ofsolvent in the vessel thereby ensuring that speci-men is submerged at all times.

After the rinsing is complete the specimenlies in the neutral solution. The vessel then




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DBRStack

Fig. 9. Topography of the freestanding structure generated using a white light interferometer. 3D plot is shown wherein thebending in the beams is quite evident.

containing the specimen is detached from themicromachining station and placed in the pre-freezer. The vessel is maintained in the pre-freezerfor a time long enough to freeze all the water. Toensure complete freezing the water confined sam-ple is frozen to 20 to 30 degrees below the freez-ing point. Once the sample is frozen it is quicklytransferred to the sublimation dryer. The trans-ferred sample is immediately subjected to highvacuum. It is imperative that the transfer fromfreezer to the vacuum chamber be fast enoughto prevent any melting. Once inside the vac-uum chamber, the vacuum itself maintains thespecimen in the frozen state. The sublimationunder vacuum is endothermic process whereinthe latent heat of vaporization is extracted fromthe sample itself thereby keeping it frozen atall times without any in-situ cooling in the vac-uum chamber. Using this process it was possi-ble to obtain freestanding structures. The samplewhen observed under SEM showed freestandingstructures with air gaps below the membranesand beams. White Light Interferometer is able toshow heights of various features, based on inter-ference pattern and is thus possible to make outa collapsed membrane at a lower height fromthe freestanding one. It was also discovered fromthe 3D Interferometer plots that the freestandingmicrostructures are deformed out of plane asshown in Fig. 9.

The passive microstructures that were realizedusing this technique used to have deep under-cuts below the platforms supporting them caus-ing the platforms to have freely bending edgeswhich contributed to additional overall bendingin the beams and membranes structures. There-fore, to prevent this, a protective dielectric (SiO2/SixNy) layer was added to the sample to protectthe sidewalls against the etchant. The releasedfreestanding structure is shown in Fig. 10.

Stiction and adhesive failures pose a signif-icant threat to yield and reliability of micro-machined freestanding structures. Problemsowing to stiction could arise either at the firststage during drying of the released microstruc-tures or during the operation. Even thoughthe microstructures may be rendered freestand-ing with aid of techniques such as sublimationdrying, supercritical CO2 drying or SAM (SelfAssembled Monolayer) technique, the structuresare still susceptible to adhesion to nearby surfacesduring operation or storage. Adhesive failurescan occur and cause surfaces of microstructuresto bond permanently if (a) during the physicalhandling or transportation, the surfaces acciden-tally come in contact (b) during the operationbuilt-up electrostatic potential between the freesurfaces exceeds a certain threshold value (pull-involtage) (c) condensation of humidity from theambient during the device operation.




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Beams

Membrane

Air-gap

DBR mirror

Fig. 10. SEM micrograph of a freestanding membrane of InP released by etching the underneath InGaAs epilayer with FeCl3:H2O(1:3).

6 Fabrication of MEMS Structures

The MEMS structures are formed by the typicalmicro-fabrication techniques, but with an extrachallenge of forming lattice matched epitaxiallayers with sharp interfaces. InP-based epitaxiallayers (InP/InGaAs/InP) were grown by metal-organic-chemical-vapor-deposition (MOCVD) ona 2-inch n+ InP substrate. The samples were ini-tially treated with the conventional organic sol-vents cleaning process. This was followed by aseries of patterning and etching steps to form themembrane structures. A sidewall protection layerwas formed by depositing silicon nitride (Si3N4)which was optimized in our previous work [33]to protect the undercutting below the supportstructure. The metal contacts were made byevaporating AuGe/Ni/Au metals, followed bya lift-off process. The membranes patterns weresubjected to etching in the sacrificial layer etchant[H2SO4:H2O2:H2O (1:1:8)] and finally released bythe sublimation method. Figures 11 (a)–(g) showthe sequence of masking layers formed on theactive sample to realize the final E-S actuatordevice.

Figures 12 (b)–(d) show SEM images of theundercut protection defined on the sidewalls ofthe support structures. It is easily seen that thenitride layer is protecting the support structureand does not flow over the beams, which wouldeventually be subjected to sacrificial etching forforming free standing structures. As the nitridefilm is impervious to the sacrificial etchant, it

would restrict the amount of etchant flowingunder the support structure and result in strongsupport structures.

The resulting device in the form of a freestanding membrane structure is similar to apin-diode formed by the InP/InGaAs/InP lay-ers. The two metal contacts placed on p and ntype of InP serve as anode and cathode elec-trodes for the E-S action. The junction capaci-tance is small providing a faster response andlarger impedance thus becoming more effectiveas an open circuit. This is ideal for actuating III-Vbased (p)InP-(i)InGaAs-(n)InP capacitive tunableplatforms that are formed in parallel with thepin-diode. The movable platform was manuallyremoved to “reveal” only the pin diode configu-ration without the capacitance contribution fromthe tunable platform. The movable platform wasconfirmed to be free-standing from earlier inspec-tion of the device using the ZYGO optical pro-filer. A reverse voltage was applied and slowlyincreased while making measurements at discretepoints, typically in an interval of 0.2 V. A displace-ment of about 300 nm was achieved at a reversevoltage of 7 V, before the pull-in finally took over.

7 Conclusions

The potential of combining novel movablestructures based on MEMS understanding withInP photonic devices is explored for tuningand coupling applications. Tunable devices haveadvantages in photonics industry especially




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InP

InP

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Si3N4

(c)

(e)

Si3N4

Si3N4

PR PR

n-InP

p-InP

(f)

Fig. 11. (a) – (g) Microscope pictures taken at 10x magnification, starting from structural definition to final device with both p-and n-metals defined.

In

Si3N4

InP

Si3N4

Complete Si3N4 coverageon sidewalls of support

(a)(b)

(c) (d)

Fig. 12. (a) Microscope picture taken at 10x magnification after Si3N4 etching using CHF3 plasma and PR removal, (b)–(d) SEMimages showing Si3N4 undercut protection over the beams and edges.

in optical communication for saving on theinventory of devices. The techniques of microma-chining of III-V materials and processes like freedrying, selective etching, dielectric based filters,metal contacts, etc, can be extended to other

photonic devices. There are however, issues ofrepeatability and reliability of certain free strand-ing structures formed out of InP material. III–Vmaterials would primarily have applications indevices/systems where light emission/detection,




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Dis

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]Fig. 13. Displacement versus applied reverse bias voltage in a E-S actuated device. The pull in voltage sets in at about 7 voltsand makes the membrane collapse.

high speed, high power and mechanical move-ment can be integrated.

Using finite element modeling and simu-lation work, a new filter design and electro-mechanical response of filter designs has beenrealized. The fabrication scheme adopted animprovised freeze-dry release technique for InPmembranes and side-wall protection was intro-duced by depositing SiO2 layer and etching itselectively over the beam regions. The fabri-cated actuators were characterized under DC andquasi-static conditions, with a deflection of about300 nm and pull in voltage of 7 volts.

References

[1] Ref: L. Wooten et al., J. Lightwave Tech., Vol. 14,No. 11, Nov 1996 pp. 2530–2536.

[2] B. H. Verbeek et al., J. Lightwave Tech., Vol. 6, June1988, pp. 1011–1015.

[3] Dan Sadot and Efraim Boimovich, IEEE Commu-nications Mag., December 1998, pp. 50–55.

[4] D. Brooks, and S. Ruschin, J. Lightwave Tech.Vol. 13, No. 7, July 1995, pp. 1508–1513.

[5] A. Yariv, Optical Electronics, Holt Reinhardt andWinston, New York, pp. 87–515 (1985).

[6] C. Seassal, J. L. Leclercq, and P. Viktorovitch,J. Micromechanics Microengg. 6 (1996) pp. 261.

[7] M. S. Wu, E. C. Vail, G. S. Li, W. Yuen, andC. J. Chang-Hasnain, IEEE Photonics TechnologyLetters 8 (1996) 98.

[8] M. C. Larson, A. R. Massengale, and J. S. Harris,Electron Letter 32 (1996) 330.

[9] M. Y. Li, W. Yuen, and C. J. Chang-Hasnain, Elec-tron. Lett. 33 (1997) 1122–1124.

[10] M. Strassner, J. Daleiden, N. Chitica, D. Keiper,

B. Stalnacke, S. Greek, and K. Hjort, Sensors andActuators 85 (2000) pp. 249–255.

[11] A. Spisser, R. Ledantec, C. Seassal, J. L. Leclercq,T. Benyattou, D. Rondi, R. Blondeau, G. Guillot,and P. Viktorovitch, IEEE photonics TechnologyLetters, Vol. 10, No. 9, September 1998, pp. 1259–1261.

[12] J. Peerlings, A. Dehe, A. Vogt, M. Tilsch,C. Hebeler, F. Langenhan, P. Meissner, andH. L. Hartnagel, IEEE Photonics Technology Letters,9 (9), 1235–1237 (1997).

[13] S. Greek, R. Gupta, and K. Hjort, Journal ofMicroelectromechanical Systems, 8 (3), 328–334(1999).

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[15] A. Ramam, G. K. Chowdhury, and S. J. Chua,Appl. Phys. Lett. 86, 171104 (2005).

[16] J. A. Jervase, and B. Hadj, IEEE J. QuantumElectron, 36 (3), 325 (2000).

[17] M. S. Unlu, and S. Samuel, J. Appl. Phys, 78 (2), 607(1995).

[18] B. Hadj, and A. J. Joseph, Semicond. Sci. Technol.,16, 581 (2001).

[19] S. O. Kasap, Optoelectronics and Photonics:Principles and Practices (Prentice Hall, UpperSaddle River, NJ, 2001).

[20] S. S. Murtaza, K. A. Anselm, A. Srinivasan,B. G. Streetman, J. C. Campbell, J. C. Bean, andL. Peticolas, IEEE Journal of Quantum Electronics,Vol. 31, No. 10, pp. 1819–1825, 1995.

[21] D. I. Babic, and S. W. Corzine, IEEE Journal ofQuantum Electronics, Vol. 28, No. 2, pp. 514–524,1992.

[22] H. A. Macleod, Thin-Film Optical Filters, Instituteof Physics Publishing, London, 2001.

[23] Y. Fink, J. N. Winn, S. Fan, C. Chen, J. Michel,J. D. Joannopoulos, and E. L. Thomas, SCIENCE,Vol. 282, pp. 1679–1982, 1998.




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Conference Report

IUMRS–ICAM 2007

8–13 October 2007, Bangalore, India

The International Conference on Advanced Mate-rials (ICAM) is one of the prestigious conferencesof the International Union of Materials ResearchSocieties (IUMRS) and is held in alternate years.The earlier conferences in this series were heldin Beijing, China (1999), Cancun, Mexico (2001),Yokohama, Japan (2003), and Singapore (2005).

The IUMRS-ICAM 2007, organized by theMaterials Research Society of India (MRSI)was held during 8–13 October 2007 inBangalore, India, under the Chairmanship ofProf S. B. Krupanidhi (Co-chair: Prof. K. T. Jacob).It consisted of 23 Technical symposia and 8Plenary lectures, and an Exhibition. Each sym-posium had invited talks, contributed oral andposter presentations. A range of topics of con-temporary importance for science, engineeringand technology of materials were highlighted.Around 1100 delegates from various countriesattended.

The list of Symposia are: (A) Intelligent Mate-rials,(B) MEMS, (C) Functional Materials, (D)Self Assembly and Nanomaterials, (E) Magneticand Spintronics Materials, (F) Semiconductorsfor Optoelectronics, (G) Materials for BiomedicalApplications, (H) Soft Condensed Matter, (I)

Polymer Materials, (J) Sensor Materials, (K) Pho-tonic Materials / Active Organic Materials, (L)Multilayered Materials, (M) Hybrid Materials,(N) Energy Materials, (O) Composite Materials,(P) High Performance Structural Materials, (Q)Computational Materials Science, (R) Materialsfor Catalysis, (S) Characterization of Materials,(T) Microscopy of Materials, (U) Materials Syn-thesis: Novel Approaches, (V) Nanomaterials andDevices, and (W) Materials Education.

“Meeting Scene Highlights” were providedon all the days of the Conference by Dr. GopalRao, Dr. Michael Driver, and Dr. Betsy Fleischer(MRS, USA). Consisting of salient features ofthe presentations, along with impressive pho-tographs of the selected topics and people, theseevery-day “Highlights” of the Conference werepromptly e-mailed to all the delegates, and allthe IUMRS members world-wide. No doubt the“Highlights” were received excellently well by allthe members of the Materials community.

For online archives of the “Meeting scenehighlights” of IUMRS-ICAM 2007,see: http://www.mrs.org/s mrs/sec.asp?CID=11254& DID=202229




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Forthcoming Conferences

3rd MRS-S Conference on Advanced Materials

(incorporating MRS-S and MRS-I Mumbai-Chapter Joint Indo-Singapore Meeting)25 – 27 February 2008, Singapore

For further information and correspondence:

Prof. B. V. R. Chowdari, Conference ChairPhysics Department, NUS, Singapore.Email: [email protected]

The 2nd IEEE International Nanoelectronics Conference (INEC 2008)

in conjunction with

Shanghai Nanophotonics & Electronics Forum

24–27 March 2008, Shanghai, China

For further information and Abstract submission, see:www.ieeenec.org

International Symposium on Integrated Ferroelectrics (ISIF2008)

9–12 June 2008, Singapore

The ISIF2008 is organized by the Institute of Materials of Research and Engineering (IMRE) and Agencyfor Science, Technology, and Research (A*Star), Singapore.

The science and technology of ferroelectric thin films and their applications have attracted manyresearchers and experienced tremendous progress in the past 20 years. The recent worldwide increasein commercial applications of ferroelectric devices is a symbol of both the maturity and the acceptanceof the technology.

ISIF2008 explores all the aspects of ferroelectric, piezoelectric and high K dielectric materials, partic-ularly ferroelectric thin films and other ferroelectrics of small sizes, including materials theories andmodeling, materials processing, properties, characterization techniques, materials integration issues,ferroelectric devices and their various applications. In addition, the ISIF2008 will feature discussionsof alternative non-volatile memory concepts and materials, such as phase change memories, researchon multiferroics and magnetoelectric materials, and new directions on the science of perovskites suchas biomolecular/polarizable interfaces.

The conference program includes tutorial lectures, plenary presentations, parallel sessions of oralpresentations and poster sessions.

The following topics will be covered in 12 Technical Sessions: Materials Theory and Modeling; Small-Dimensional Ferroelectrics, Interface and Size effects; Device Integration and Reliability; FerroelectricPolymers, Composites and Liquid Crystals; Ferroelectric and Alternative Memories; Multiferroics andMagnetoelectrics; High K Dielectrics and Capacitors; Ferroelectrics for RF Applications; Compositionsand Processing of Ferroelectric Materials; Piezoelectrics and Opto-Electrics for Sensors, Actuators andTransducers; Functional Mechanisms and Emerging Applications of Ferroics; Ferroelectrics and Inor-ganics in Medicines and Health Care.



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ISIF2008 General Chairs:

Carlos Paz de Araujo, Univ. of Colorado at Colorado Springs, and Symetrix Corp., USAOrlando Auciello, Argonne National Laboratory, USARudy Panholzer, Naval Postgraduate School, USA

ISIF2008 Program Chairs:

K. Yao, IMRE, SingaporeM. Alexe, Max Planck Institute, GermanyM. Shimizu, University of Hyogo, Japan

ISIF2008 Local Organizing Committee:

Kui YAO (Chair), IMREWeiguang ZHU (Co-Chair), Nanyang Technological UniversityJofelyn LYE Mei Lian (Secretary), IMRE

Details about the plenary talks and tutorial lectures are available in the conference websiteat: www.isif.net

Abstract submission deadline: 12 January 2008Acceptance of abstract: 12 February 2008

11th Asian Conference on Solid State Ionics (ACSSI-11)

9–13 June 2008, Coimbatore, India

The ACSSI-11 is organized by the BU-DRDO centre for Life sciences, Bharathiar University, Coimbatore,India for the Asian Society for Solid State Ionics (ASSSIS).

Solid State Ionics is a growing interdisciplinary branch of science and technology. It deals with ioni-cally conducting materials in the form of inorganic solids, ceramics, glasses, polymers, and composites,and nanostructures with applications in a wide variety of solid state devices.

Specific topics to be covered at the ACSSI-11 are: Cathode/anode materials and interfaces; Elec-tronically conducting polymers; Ion dynamics and theoretical modeling; Nanomaterials and devices;Advanced biomaterials; Electrochemical devices: Batteries, Fuel cells, Sensors, Solar cells, Supercapaci-tors, Electrchromic displays and Molecular electronic devices.

The Conference will provide an international forum for scientists, engineers and technologists todiscuss the latest developments and share knowledge in the discipline of Solid State Ionics, encourageyoung research scholars, and promote the collaboration among the Solid State Ionicists.Important dates:Abstracts due: 30 January 2008, to be sent by Email to: [email protected] of acceptance: 10 February 2008Manuscripts due: 15 March 2008Registration due: 1 April 2008Late Registration due: 30 April 2008

For further information, contact:Prof. S. Selvasekarapandian (Convener), ACSSI-11Email: [email protected]




The 4th International Conference on Technological Advances of Thin Films &

Surface Coatings (ThinFilms2008)a in conjunction with

The 1st International Conference on nanoManufacturing (nanoMan2008)b

14–16 July 2008, Singapore

For further information and Abstract submissionsee: www.thinfilms-Singapore.org; www.tju.edu.cn/nanoMan2008

aChair: Sam Zhang; Co-Chair: Frank F. S. ShieubChair: Fengzhou Fang; Co-Chair: Jack Luo

‘Theme Articles’ appeared in ‘MRS-S OUTLOOK’, Vol. 1 (Nos.1–4) &

Vol. 2 (Nos.1–2)

• “Perovskite structure: A versatile and perennial host for oxide functional materials”, by G. V. Subba Rao andB. V. R. Chowdari (Department of Physics, National University of Singapore), MRS-S OUTLOOK,1 (1) 8–14 (2006).Abstract: Presents a brief review of the perovskite-structure adopted by a large number and wide vari-ety of mixed-oxides and their importance as functional materials for applications in devices.

• “Drug eluting biodegradable polymers for biomedical stent implants”, by Xiong Ying, Subbu Venkatraman,Loo Say Chye and Freddy Boey (School of Materials Science & Engineering, Nanyang TechnologicalUniversity, Singapore), MRS-S OUTLOOK, 1 (2) 40–51 (2006).Abstract: After a brief review of the area and its importance for biomedical applications, this paperpresents some of the results of the work carried out by the authors in recent years.

• “The National University of Singapore Nanoscience and Nanotechnology Initiative (NUSNNI)”, byTeik-Cheng Lim, Xian-Ning Xie, Andrew Thye Shen Wee and Seeram Ramakrishna, (NationalUniversity of Singapore (NUS), Singapore), MRS-S OUTLOOK, 1 (3) 80–100 (2007).Abstract: This paper highlights some of the nanomaterials-related research work carried out by vari-ous Project Investigators under the NUSNNI.

• “Spin engineering: Ferromagnetic antidot mesostructures”, by C. C. Wang, N. Singh and A. O. Adeyeye(Department of Electrical and Computer Engineering, National University of Singapore, and Instituteof Microelectronics, Singapore), MRS-S OUTLOOK, 1 (4) 114–131(2007).Abstract: This paper presents a study of the magnetic and spin dependent transport properties oflithographically defined antidot mesostructures using a combination of characterization techniquesand simulation tools. Potential practical applications are also highlighted.

• “From Applied Science to Commercial Application – Synchrotron Radiation as a Broad R&D Platform: Part I”,by H. O. Moser1, K. Banas1, B. D. F. Casse1,5, A. Chen1, M. Cholewa1,6, C. Z. Diao1, X. Y. Gao2,S. P. Heussler1, L. K. Jian1, S. M. P. Kalaiselvi1, Z. J. Li1, G. Liu1, T. Liu2, Shahrain bin Mahmood1,S. K. Maniam1, A. T. S. Wee2, P. Yang1, Y. Adam Yuan3,4, MRS-S OUTLOOK, 2 (1) 11–23(2007).1Singapore Synchrotron Light Source, National University of Singapore, Singapore.2Department of Physics, National University of Singapore, Singapore.3Department of Biological Sciences, National University of Singapore, Singapore.4Temasek Life Sciences Laboratory, National University of Singapore and Nanyang TechnologicalUniversity, Singapore.



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hip 5Electronic Materials Research Institute, Northeastern University, Boston, USA

6 ANKA, Forschungszentrum Karlsruhe, Germany.

Abstract: In this Part I of theme article are illustrated the capabilities and scope of synchrotron radia-

tion applications using the example of the Singapore Synchrotron Light Source (SSLS) with selected

sections on micro/nanofabrication.

Applications in the areas of X-ray diffraction, reflectometry, absorption fine structure spectroscopy,

photoemission spectroscopy, phase contrast imaging, and the development of new sources will be

described and discussed in the near future.

• “From applied science to commercial application – synchrotron radiation as a broad R&D platform: Part II”,

by H. O. Moser1, K. Banas1, M. Cholewa1, C. Z. Diao1, X.Y. Gao2, L. K. Jian1, S. M. P. Kalaiselvi1, Z. J.

Li1, G. Liu1, T. Liu2, S. K. Maniam1, A. T. S. Wee2, P. Yang1 and Y. Adam Yuan3,4, MRS-S OUTLOOK,

2 (2) 42–52(2007).1Singapore Synchrotron Light Source, National University of Singapore, Singapore2Department of Physics, National University of Singapore, Singapore3Department of Biological Sciences, National University of Singapore, Singapore4Temasek Life Sciences Laboratory, National University of Singapore and Nanyang Technological

University, Singapore

Abstract: Applications of Synchrotron radiation in the following areas of materials science are dis-

cussed with illustrative examples: High resolution X-ray diffractometry; Rietveld refinement of the

X-ray powder data; Structure of La10−xNax(SiO4)6O3−x from resonant diffraction; Super-structure in

(GaIn)P2 epi-layer; Mapping in reciprocal space – epi-layer inclination, Mapping in reciprocal space

–clarification of crystal structure, and X-ray topography -surface inclusion in Si wafer.

The above can be accessed through the website: http://www.mrs.org.sg/outlook/

MRS-S Membership

Readers are invited to become members of the Materials Research Society of Singapore (MRS-S).

Professional Membership is open to any person engaged in activities associated with materials science,

engineering and technology.

Student Membership is open to any bonafide student of a tertiary institution genuinely interested in

the practice of materials science, engineering and technology.

Corporate Membership is open to any organisation, government or private, commercial or otherwise,

that is in any way engaged in any activities that deal with any aspect of material science, engineering

and technology. A Corporate Membership is entitled to nominate two of its employees as its official

representatives and to change its nominees from time to time provided the Committee has no objection

to any such nomination.

Annual Subscription Fee:

Professional Membership: S$50

Student Membership: S$5

Corporate Membership: S$500

For details and application form, please visit: www.mrs.org.sg




Invi

tati

onINVITATION

MRS-S members are welcome tocontribute to ‘MRS-S OUTLOOK’

• To suggest topics and prospective author(s) for ‘thematic’ articles pertaining tothe areas of materials science, engineering and technology. These will be ofgeneral interest to the students, teachers as well as active researchers. Thesecan be 10–15 pages (A4-size, single spaced) with figures, tables and selectreferences.

• To contribute reports on the recently held conferences and information on theforthcoming conferences.

• To contribute ‘Highlights from Recent Literature’ in the areas of materialsscience, engineering and technology. These must pertain to the years 2007and 2008, and be of general interest to non-specialists, students, teachers aswell as active researchers. Each ‘Highlight’ must not exceed 250–300 words,including reference(s). Contributing author(s) and e-mail address(es) will beincluded under each ‘Highlight’.

• To contribute information about the recent awards and distinctions conferredon the MRS-S members.

• To contribute ‘Letters to the Editor’. They may be edited for brevity, clarity andavailable space, and the author(s) will be informed.

Information on the above aspects may be communicated to the Editor:

Dr. G.V. Subba RaoE-mail: [email protected]

The Editorial Board of ‘MRS-S OUTLOOK’ reserves the right to include or not any of the submitted contributions.

Design & Typeset by Research Publishing ServicesE-mail:[email protected]


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