shape-controlled synthesis and surface plasmonic properties of metallic nanostructures

338 MRS BULLETIN • VOLUME 30 • MAY 2005

IntroductionNanostructures—structures with at least

one dimension between 1 nm and 100 nm—have attracted steadily growing interestdue to fascinating properties and intrigu-ing applications that are complementaryor superior to those of bulk materials.1Much of this interest is powered by thegrowing expertise in fabrication methodsthat allow more and more ways of realiz-ing nanostructures with well-controlledcomposition, size, and shape. The develop-ment of synthetic methodologies has alsoadvanced to a level where nanostructurescan be produced from many kinds of ma-terials with the quality, quantity, and yieldrequired for the systematic investigationof their peculiar properties (see Figure 1).The fundamental study of phenomena

that occur in nanostructured materials hasalready evolved into a new field of re-search that is often referred to asnanoscience. In addition to their indispens-able roles in nanoscience, nanostructuresare central to the development of a broadrange of emerging and exciting applica-tions such as more powerful computer chipsand higher-density information storage. Itis anticipated that nanotechnology willchange the way we live, just as microtech-nology has done in the last century.

This issue of MRS Bulletin is focused onthe shape-controlled synthesis and surfaceplasmonic properties of nanostructuresmade of two metals: gold and silver. Sincethe pioneering work by Gustav Mie in1908,2 it has been recognized for almost a

century that the interaction of light with freeelectrons in a gold or silver nanoparticlecan give rise to collective oscillations com-monly known as surface plasmons (SPs).Peaks appear in the extinction spectra (ex-tinction � scattering � absorption) when-ever SPs are excited by the electric field ofincident light under the resonance condi-tion. Such extinction peaks are responsiblefor the brilliant red color displayed in me-dieval stained glass windows, which arisesfrom the presence of gold nanoparticles inthe glass. The attractions of SPs lie in theirpotential to confine light to the metal/di-electric interface, which in turn generatesintense local electromagnetic fields andgreatly amplifies the weak signal typicalof Raman scattering or second-harmonicgeneration. The spatial confinement of lightto a structure of subwavelength dimen-sions also makes it possible to circumventthe optical diffraction limit, which arisesbecause the resolution of an optical lensequals the wavelength divided by the numerical aperture, enabling the realiza-tion of nanoscale photonics.

Surface PlasmonsPlasmonic behavior is a physical concept

that describes the collective oscillation ofconduction electrons in a metal (or a dopedsemiconductor).3 Many metals (e.g., alkalimetals, Mg, Al, and to some extent noblemetals such as Au and Ag) can be treatedas free-electron systems whose electronicand optical properties are determined bythe conduction electrons alone. In theDrude–Lorentz model, such a metal is de-noted as a plasma, because it containsequal numbers of positive ions (fixed inposition) and conduction electrons (freeand highly mobile). Under the irradiationof an electromagnetic wave, the free elec-trons are driven by the electric field to co-herently oscillate at a plasma frequency of�p relative to the lattice of positive ions.For a bulk metal with infinite sizes in allthree dimensions, �p can be expressed as

, (1)

where N is the number density of elec-trons, 0 is the dielectric constant of a vac-uum, and e and me are the charge andeffective mass of an electron, respectively.Quantized plasma oscillations are calledplasmons.

In reality, we have to deal with metallicstructures of finite dimensions that aresurrounded by materials with different di-electric properties. Since an electromagneticwave impinging on a metal surface onlyhas a certain penetration depth (�50 nmfor Ag and Au), just the electrons on thesurface are the most significant. Their

ε

�p � �Ne 2�ε0me�1�2

Shape-ControlledSynthesis andSurface PlasmonicProperties of MetallicNanostructures

Younan Xia and Naomi J. Halas, Guest Editors

AbstractThe interaction of light with free electrons in a gold or silver nanostructure can give

rise to collective excitations commonly known as surface plasmons. Plasmons provide apowerful means of confining light to metal/dielectric interfaces, which in turn cangenerate intense local electromagnetic fields and significantly amplify the signal derivedfrom analytical techniques that rely on light, such as Raman scattering. With plasmons,photonic signals can be manipulated on the nanoscale, enabling integration withelectronics (which is now moving into the nano regime). However, to benefit from theirinteresting plasmonic properties, metal structures of controlled shape (and size) must befabricated on the nanoscale.This issue of MRS Bulletin examines how gold and silvernanostructures can be prepared with controllable shapes to tailor their surface plasmonresonances and highlights some of the unique applications that result, includingenhancement of electromagnetic fields, optical imaging, light transmission, colorimetricsensing, and nanoscale waveguiding.

Keywords: field enhancement, gold nanoparticles, metallic nanostructures, shape-controlled synthesis, silver nanoparticles, surface plasmons.

www.mrs.org/publications/bulletin

Shape-Controlled Synthesis and Surface Plasmonic Properties of Metallic Nanostructures

MRS BULLETIN • VOLUME 30 • MAY 2005 339

collective oscillations are properly termedsurface plasmon polaritons (SPPs), but areoften referred to as surface plasmons(SPs).3–6 For a metal–vacuum interface,application of the boundary condition re-sults in an SP mode of in fre-quency. As depicted in Figure 2a, such anSP mode represents a longitudinal surfacecharge density wave that can travel acrossthe surface. For this reason, these SPs arealso widely known as propagating SPs (orPSPs), which can be excited through a reso-nant mechanism by passing an electronthrough a thin metallic film or by reflect-ing an electron or a photon from the surfaceof a metallic film. By resonance, we mean acondition in which the frequencies and wavevectors of both incident and SP waves areapproximately the same, leading to construc-tive interference and a stronger signal.

Another type of SP (localized SPs, or LSPs)corresponds to collective excitations offree electrons confined to a finite volume. Atypical example is shown in Figure 2b,where the conduction electrons of a spheri-cal gold colloid oscillate coherently in response to the electric field of incidentlight.4–6 When this process occurs in a vac-uum, the resonant frequency becomes

. For nearly a century, it has been known

that the number, location, and intensity ofSP bands of a gold or silver nanoparticleare strongly correlated with both the

�p��3

�p��2

shape and size of the particle. The goldand silver systems are unique because theirdensities of free electrons are in the properrange to give their nanoparticles SP peaks inthe visible regime. For spherical gold andsilver particles of relatively small size(��, the wavelength of light, with diameters in the range of 1–20 nm), only dipole plasmon resonance is in-volved; their suspensions display a strongSP peak around 510 nm and 400 nm, respectively.

Fabrication of NanostructuresMany techniques are available for fabri-

cating metallic nanostructures on solid sup-ports.7 The best-established, most versatiletool is probably electron-beam lithography(EBL), which has the capability of extremelyhigh resolution as a result of the short wave-lengths associated with high-energy elec-trons (e.g., �0.005 nm for an acceleratingvoltage of 50 kV).8 EBL is also a featurethat can be readily added onto most conven-tional scanning electron microscopy (SEM)systems.

In typical e-beam writing, a tightly fo-cused beam of electrons is scanned acrossthe surface of a layer of resist such aspoly(methyl methacrylate). The interac-tion of electrons with the resist causes localchanges to the polymer chains, makingthe material more or less soluble in a de-veloping solution. When combined with

masked evaporation and liftoff, relief patterns in the resist film can be readilytransformed into patterned metallic nano-structures with well-controlled dimensionsand separations.

In practice, the resolution of e-beamwriting is mainly determined by the scat-tering of both primary and secondary elec-trons in the resist film and the substrate.Structures with lateral dimensions as smallas �30 nm can be routinely generated usingEBL. Features as fine as �2 nm have alsobeen demonstrated,8 using thin membranesas substrates to reduce the scattering ofelectrons.

A related technique, focused ion-beam(FIB) lithography, provides another attrac-tive route to metallic nanostructures.9 It hasbeen shown that structures as small as�6 nm can be fabricated by using a 50 kV Ga� two-lens system, which usesmagnetic lenses like those in electronmicroscopes to focus a Ga� ion beam.9 Asan advantage over EBL, this technique canbe used to directly deposit metals as pat-terned nanostructures by decomposingsuitable precursors. However, this tech-nique is less popular in the scientific com-munity because it requires an expensive,more dedicated instrument system. Al-though attaining high-throughput fabrica-

Figure 1. Schematic illustration of nanostructure shapes.The shapes in the top row aresingle crystals, in the second row are particles with twin defects or stacking faults, and inthe third row are gold shells. All twinned and single-crystal shapes shown, with theexception of the octahedron, can be synthesized in solution. Control of shape allows controlof optical and catalytic properties, as well as suitability for electronic applications in the caseof wires, tubes, and possibly rods. Dark facets are (100) planes, light gray are (111) planes,and {111} twin planes are shown in red. Gold shapes represent gold particles, and grayshapes represent silver particles, although spheres, twinned rods, icosahedrons, and cubescan also be made from gold.

Figure 2. Schematic illustration of thecollective oscillations of free electronsfor (a) a metal–dielectric interface and(b) a spherical gold colloid. Excited bythe electric field of incident light, the freeelectrons can be collectively displacedfrom the lattice of positive ions (consistingof nuclei and core electrons). While theplasmon shown in (a) can propagateacross the surface as a charge densitywave, the plasmon depicted in (b) islocalized to each particle. (Courtesy ofR.Van Duyne and T. Schatz,Northwestern University.)



tion continues to be a major challengewith these two techniques, they have be-come the tools of choice for producing arbi-trary patterns for many technological andscientific applications.

A variety of unconventional approacheshave also been demonstrated for low-costfabrication of metallic nanostructures. Oneexample is nanosphere lithography (NSL),illustrated in the article by Haes et al. in thisissue. This technique relies on monodispersespherical colloids that readily assemble ona flat surface to form a close-packed mono-layer with hexagonal symmetry. The mono-layer can serve as a physical mask in thesubsequent step. For most demonstrations,a metal is evaporated through the mono-layer to fill the void spaces among adjacentcolloids in the monolayer lattice. Uponliftoff of the colloids, a periodic array ofnanometer-sized, pyramidal islands of the metal is left behind on the substrate. Thelateral dimensions of these islands and theseparation between them are determinedby the size of the spherical colloids, whilethe vertical dimension mainly depends onthe amount of deposited material. When adouble layer of spherical colloids is used,hexagonal dots corresponding to the smallopenings that remain in the close-packedlattice are formed.10 Most recently, amonolayer of spherical colloids was alsoused to direct the spreading of alkanethiolson a gold substrate to generate nanoscalerings of gold.11

Although NSL can be used to patternlarge areas in parallel, this technique re-mains sensitive to defects, distortions, anddomain boundaries that naturally appearwhen spherical colloids assemble on flatsubstrates. The structures and patterns thatcan be generated using this approach arelimited in terms of design and complexity.In this regard, unconventional approachesbased on soft lithography12 and dip-pennanolithography (DPN)13 might providesome immediate advantages.

Chemical Synthesis of Gold andSilver Nanostructures

The first documented synthesis of metal-lic nanostructures can be traced back to1856 when Michael Faraday demonstratedthe preparation of gold colloids by reduc-ing an aqueous solution of gold chloridewith phosphorus. His samples displayeda stable, ruby-red color, and some of themare still preserved today in the FaradayMuseum in London.14

In the past 150 years, a wealth of method-ologies has been developed for processingmetals such as gold and silver into nano-scale structures. However, most of the prod-ucts are characterized by problems such asirregular shapes, polydispersed sizes, and

poorly defined structures. Only within thelast decade have chemical methods beenestablished for generating high-quality goldand silver nanostructures in quantity, withthe reproducibility required for a system-atic study of the dependence of surface plas-monic resonance (SPR) properties on size,shape, and structure.15 Some of these developments are briefly covered in thearticles by Murphy et al., Wiley et al., andHalas in this issue.

Murphy and co-workers review thechemical synthesis of one-dimensionalnanostructures of gold and silver viasurfactant-directed routes. In a typical pro-cess, a precursor such as HAuCl4 or AgNO3is reduced to atomic species by chemical,electrochemical, or photochemical meansin the presence of ionic surfactants at highconcentrations. The aspect ratios (ratio oflength to width) of resultant nanostructurescan be easily varied over a wide range (up to 23) by adjusting the experimentalparameters.

These authors also discuss the surfaceplasmonic properties associated with gold orsilver nanorods.16 When a spherical particleis elongated, the SP band is split into two:the transverse band (along the short axis)and longitudinal band (along the longaxis). While the transverse band is located atroughly the same position as that of thespherical particle, the longitudinal bandcan be continuously shifted into the near-infrared region by increasing the aspectratio. Such control allows one to fine-tunethe resonance wavelength at which theelectromagnetic field will be enhanced.

Wiley et al. discuss a different approach,based on polyol reduction, to the large-scalesynthesis of silver nanostructures with avariety of well-defined shapes. The seedsformed in the nucleation step are eithertwinned or single-crystalline, dependingon the absence or presence of an oxidativeetchant. In the presence of a suitable cappingagent, the seeds can be directed to growinto nanostructures in the form of cubes,wires, quasi-spheres, or triangular plates.These authors also describe the use of agalvanic replacement reaction between sil-ver nanostructures and HAuCl4 in anaqueous medium as a powerful route tomaking gold nanocages—colloidal par-ticles having hollow interiors and porouswalls. It is worth noting that the SPRpeaks of gold nanocages can be continu-ously shifted from blue (425 nm) to near-infrared (1200 nm) by simply adjustingthe molar ratio between Ag and HAuCl4 (ina fashion similar to titration).

Halas discusses the synthesis and uniqueSP properties of gold/silver nanoshells—concentric nanoparticles consisting of di-electric cores and metallic shells. In contrast

to gold or silver solid colloids, the SPbands of such core–shell nanoparticlescan be continuously shifted from the visibleto the near-infrared region (where bloodand soft tissues are optically transparent) bycontrolling the diameter or wall thicknessof the nanoshells. Such a tuning capabilityhas enabled a variety of biomedical appli-cations, including optical sensing, imaging,and drug delivery. The author also discussesa model—plasmon hybridization—thather group has recently proposed to under-stand the optical resonant properties of goldnanoshells. In this new model, the couplingof plasmons follows a mesoscale analogueof molecular orbital theory, hybridizing in precisely the same manner as the indi-vidual atomic wave functions in simplemolecules. This model can be used to effec-tively predict SP properties of metallicnanostructures and is expected to play animportant role in the design and synthesisof structures with specific plasmonic features.

Light-Scattering and AbsorptionUnderstanding the extinction spectra of

gold and silver nanoparticles has long beenof interest to the scientific community, dat-ing back at least to Faraday’s investiga-tions of gold colloids in the middle of the19th century. In 1908, Gustav Mie solvedMaxwell’s equations and presented theexact formula for calculating both scatter-ing and absorption cross sections of aspherical particle of arbitrary size.2 Mie’ssolution remains of great interest and valueto this day, although it can only be appliedto spherical particles. In the past decade, anumber of numerical methods have beendeveloped to calculate the optical proper-ties of small particles of arbitrary shapes; a notable example includes the discrete dipole approximation (DDA) method.

Thanks to the efforts of several groups,the DDA method has emerged as a pow-erful tool for calculating the scattering/absorption cross sections of small particles.17

In this method, the particle is approximatedas an array of polarizable cubic elements,with the array being large enough for thecalculation to converge. The scattering andabsorption cross sections of the particlecan be obtained once the location and polarizability of each element have beenspecified. Figures 3a and 3b show thespectra calculated using this method forspherical gold colloids of 20 nm and50 nm in radius, respectively. In general,light absorption dominates the extinctionspectrum for particles of relatively smallradius (�20 nm), and light-scattering be-comes the dominant process for large par-ticles. As the particles increase in size, theSP peaks are usually shifted toward the



red wavelengths. New peaks may also appear in the extinction spectra due to theexcitation of quadrupole modes.

When compared with molecular speciessuch as organic chromophores, the absorp-tion and scattering cross sections of goldand silver nanoparticles are 5–6 orders in magnitude higher. As a result, thesenanoparticles have recently been exploredas a class of therapeutic and contrast agentsfor photothermal treatment and opticalimaging of tumors, respectively.18,19 The useof gold and silver makes it straightforwardto derivatize their surfaces with variousfunctional groups by taking advantage ofthe well-established monolayer chemistrybased on alkanethiols. It has also becomeincreasingly apparent that one can preciselycontrol the wavelengths at which goldand silver nanoparticles absorb and scatterlight by controlling their shapes, dimensions,and structures (e.g., solid versus hollow).In addition, it is possible to tailor the magnitude of absorption and scatteringcoefficients by engineering their geomet-ric parameters. All of these advances willgreatly boost the use of gold and silver

nanostructures in biomedical applicationssuch as optical imaging and the treatmentof cancer.

Colorimetric SensingThe sensitive response of SP peaks to

environmental changes can be exploited tooptically detect and monitor binding eventson the gold or silver surface. The mostpopular detection scheme is based on theexcitation of propagating SPs in a metallicthin film deposited on a transparent sub-strate.20 Commercial instruments are avail-able from a number of companies such asBiacore and Texas Instruments.

In addition to thin films, the localizedSPs of gold or silver colloids have beenwidely explored for optical sensing in twodifferent configurations. The first configu-ration involves the use of individual nano-particles and is discussed by Haes et al. in this issue. According to the scatteringtheory, any variation in the refractive indexof the surface layer will lead to somechanges in the intensity and/or positionfor the LSP peak, and an increase in the re-fractive index often causes the LSP peak toshift to the red.

Based on this mechanism, gold nanopar-ticles supported on substrates or suspendedin solutions have been used by severalgroups to demonstrate label-free opticalsensing.21 The sensitivity of such an opticalprobe is strongly dependent on the size,shape, composition, and structure of thenanoparticles. For example, the sensitivityfactor (i.e., the shift in peak position perunit change in the refractive index of thesurrounding medium) was reported to be76.4 nm per refractive index unit (RIU),defined as a change of 1 in the refractiveindex, and 191 nm/RIU, respectively, for a submonolayer of gold solid colloids (diameter, 13.4 nm) and a hexagonal arrayof silver islands (in-plane width, 100 nm;out-of-plane height, 50 nm) fabricatedusing NSL. The sensitivity factor could beincreased to 408.8 nm/RIU for gold nano-shells of 50 nm in diameter and 4.5 nm inwall thickness.22 In general, the spectralshift is relatively insignificant (�20 nm inwavelength), and a spectrometer is neededto detect the change in peak position.

Thaxton et al. discuss the second detec-tion configuration, which relies on the red-shift of the SP peak accompanying theaggregation of gold or silver particles dueto the coupling between their LSP modes.This configuration is distinguished from thefirst detection configuration by the presenceof an analyte that can be visually detectedby the naked eye, as long as the analytemolecules can selectively induce the col-loids to aggregate into larger particles. Thisapproach has been employed by the Mirkin

group to qualitatively detect DNA andsingle-base mismatches in DNA hybridiza-tion, and by the Rosenzweig group for immunoassays to probe the presence ofproteins.23

Aggregation-induced color changes dueto the formation of sandwich complexeshave also been explored by the Huppgroup to measure the concentration ofmetal ions such as K�, Pb2�, Cd2�, andHg2� through an ion-templated chelatingprocess.24 Because the surface of gold andsilver nanoparticles can be readily bioconju-gated to a number of binding groups, in-cluding oligonucleotides, proteins, andother biologically relevant ligands, it is fea-sible to design and synthesize optically andchemically encoded nanoparticle probesthat can support biomolecular assays withnumerous advantages over conventionalmethods, such as low cost and high sensi-tivity. It is believed that bioconjugated goldand silver nanoparticles will become thecenterpiece for a variety of detectionstrategies.

Enhancement of LightTransmission

When light is transmitted through anaperture with lateral dimensions muchsmaller than the wavelength of the light,the efficiency is extremely low (�10�3 fora 150-nm-diameter hole), because the pho-tons have to use an inefficient mechanismto tunnel through.

This picture may change completely if thehole is fabricated in a thin film of silver orgold. In this case, propagating surfaceplasmons can be activated in the metallicfilm to substantially enhance the transmit-tance of light at resonance wavelengths.29

Dintinger et al. review the current under-standing of this phenomenon and illus-trate how it can be applied to greatlyimprove the performance of various typesof photonic devices.

In a typical experiment, an aperture(hole or slit) is fabricated in a silver or goldthin film suspended or supported on atransparent substrate, and transmissionspectra are recorded. It is critical to havethe aperture surrounded by a periodiccorrugation in order to facilitate couplingbetween the incident light and the SPmodes.

For a periodic array of holes fabricatedin a suspended film, the light couples tothe SP modes at the input interface and ex-ponentially decays across the film. Thispropagation causes an energy transfer to-ward the output interface where SP modesare excited and then decoupled into freelypropagating light. The transmission spec-tra display peaks at wavelengths where theSP modes are excited.

Figure 3. Optical coefficients calculatedusing the discrete dipole approximationmethod for a spherical gold colloid with(a) radius r � 20 nm and (b) r � 50 nm(ext. stands for extinction, abs. forabsorption, and sca. for scattering).Water was taken as the surroundingmedium. In plotting the spectra, thecalculated cross sections were dividedby �r2 to obtain the dimensionlessoptical coefficients (Q). The calculationswere performed by Z.-Y. Li at theInstitute of Physics, Chinese Academyof Sciences.



The transmittance normalized to theaperture area can be orders of magnitudegreater than that predicted by classic dif-fraction theory. For systems with asym-metric interfaces (e.g., a silver filmsupported on a quartz substrate), the SPmodes at the input and output sides aredifferent in frequency. As a result, thetransmission spectrum contains two seriesof maxima associated with each interfacethat are offset by the difference in refrac-tive index for the media in contact withthe metal surfaces. In addition to the en-hancement of transmission, it is feasible toconcentrate the transmitted light into anarrow beam with an angular divergenceof less than a few degrees by surroundingthe aperture with an appropriate gratingon the exit side of the metallic film. Thesedemonstrations illustrate how surfaceplasmons can be exploited to control andmanipulate light at the subwavelengthscale.

Nanoscale WaveguidingIt has been demonstrated both theoreti-

cally and experimentally that a linear chainof gold or silver nanoparticles can channelthe flow of electromagnetic energy over dis-tances of hundreds of nanometers withoutsignificant loss.25 The major requirement isthat these nanoparticles are separated bygaps narrow enough (�1 nm) to enablenear-field coupling between the SPR modesassociated with individual nanoparticles.

In general, there is a tradeoff between energy loss and spatial localization in plas-monic waveguides, but for important vis-ible and near-infrared wavelengths, itshould be feasible to achieve centimeter-scale propagation. In practice, the metallicplasmonic structures can serve as inter-connects and can be potentially adoptedto create chip-scale integrated photonicsand nanoscale all-optical networks. It is an-ticipated that SPR coupling will become asimportant as p–n junctions, enabling therealization of nanoscale photonics, whereoptical devices can be scaled down to di-mensions of less than 10% of the free spacewavelength.

Atwater and co-workers describe thefabrication of nanoscale optical waveguidesby taking advantage of the SPR couplingbetween adjacent metallic nanostructures.In such waveguiding structures, the electro-magnetic wave can transport with a spatialconfinement well below the diffraction limit(�100 nm). A number of methods havebeen explored for fabricating plasmonicwaveguides, including e-beam lithogra-phy, high-energy ion irradiation, and self-assembly. Although e-beam writing canroutinely generate ordered arrays of metallicnanoparticles with well-controlled dimen-

sions and spatial separations, the develop-ment of this technique into a practicalmethod for producing large numbers of suchnanostructures rapidly and at low coststill requires great ingenuity. It is also non-trivial to control the gap between adjacentnanoparticles below a few nanometers.

In contrast, self-assembly provides a num-ber of attractive features in organizing metal-lic nanoparticles into ordered arrays. Asillustrated in the articles by Murphy et al.and Wiley et al. in this issue, both the sizeand shape of the building blocks (i.e.,nanoparticles) can be readily altered to tai-lor their SPR features, and the spacing be-tween adjacent nanoparticles can also becontrolled by coating their surfaces withthin dielectric shells.

Enhancement of ElectromagneticFields

In addition to the scattering and absorp-tion of light, gold or silver nanostructurescan be used to substantially enhance localelectromagnetic fields. Upon excitation ofSPs, charges will be concentrated at themetal–dielectric interface, resulting in verystrong amplification of the electric field (E).For colloidal particles 10–200 nm in sizewhere LSPs are excited, the |E|2 can be 100to 10,000 times greater in magnitude thanthe incident field. The distribution of field has a spatial range on the order of10–50 nm and is strongly dependent onthe size, shape, and local dielectric envi-ronment of the particle. For smooth thinfilms with thicknesses in the range of10–200 nm, the excitation of PSPs onlyleads to field enhancements (|E|2) on theorder of 10–100, although the field can ex-tend over a longer spatial range (�1000 nm).

The ability of gold and silver nanostruc-tures to enhance the local electric fieldshas led to the development of a new fieldknown as surface-enhanced spectroscopy.Haes et al. present an overview of someexciting developments in this area. Halasand Murphy et al. also provide some brief discussions on this subject in their articles.

Atypical example can be found in surface-enhanced Raman scattering (SERS),26 aphenomenon that was discovered almost30 years ago. SERS is a complicated processwhose operational mechanism can be attri-buted to at least two factors: electromag-netic enhancement and chemical enhance-ment. Electromagnetic enhancement occurswhen the incident light is in resonance withthe SP modes of a metallic thin film or nano-particle. In this case, it is crucial to fine-tunethe spectral positions of SPs to achieve theresonance condition. Gold and silver nano-structures with controllable shapes are ex-cellent candidates for this application.

Chemical enhancement is related to thepossible chemical interactions, includingcharge transfer and polarization, that mayoccur between adsorbed molecules andthe surface. In addition to SERS, surface-enhanced fluorescence has also been re-ported for chromophores near the surfacesof metallic nanoparticles.27 When the molecules are placed within �5 nm of themetal nanoparticle surface, fluorescence isquenched. However, the fluorescence canbe enhanced up to 100-fold by the local-ized electric field if the molecules are sep-arated from the metal surface by �10 nmor more. Furthermore, the enhancement oflocal field has also been used to amplifythe weak signals from nonlinear optical pro-cesses such as second-harmonic generation(SHG).28 It is expected that surface-enhanced spectroscopy will play an im-portant role in single-molecule detection.

Summary and OutlookSurface plasmons clearly have a broad

range of technological applications. Theyprovide a powerful tool for controlling,manipulating, and amplifying light on thesubwavelength scale, enabling the realiza-tion of highly complex nanoscale devicessuch as sensors, light sources, filters, po-larizers, and waveguides. For this technol-ogy to reach its paramount potential, activeplasmonic devices such as switches andmodulators still need to be demonstrated.In recent work by Andrew and Barnes, animportant step forward was made inshowing that SPs could be used to effec-tively transfer energy from donor to ac-ceptor molecules separated by silver filmsup to 120 nm thick.30 Such a molecularplasmonic device might lead to the fabri-cation of more efficient light-emittingdiodes and photovoltaics.

For most of the applications associatedwith SPs, generating metallic nanostruc-tures with controllable sizes, shapes, andstructures represents the first and one of themost significant challenges to their real-ization. Compared with nanofabricationtechniques, chemical synthetic methods arestill in a rudimentary stage of development.There are many fundamental issues thatneed to be solved before they can becomethe methods of choice for industrial appli-cations. For example, the exact nucleationand growth mechanisms involved in mostof the synthetic methods for creating metal-lic nanoparticles remain mysterious becauseof the length and time scales on whichthey occur. Although nuclei or seeds mayplay the most important role in determin-ing the morphology of final products, it isextremely difficult to probe their struc-tures experimentally. In fact, they mightassume crystal structures different from



Younan Xia, Guest Editorfor this issue of MRSBulletin, is a professor ofchemistry at the Univer-sity of Washington. Hereceived his BS degree inchemical physics fromthe University of Scienceand Technology of China(USTC) in 1987 and thenworked as a graduatestudent on inorganic non-linear optical crystals atthe Fujian Institute of Re-search on the Structure ofMatter, Academia Sinica.He earned his MS degreein inorganic chemistryfrom the University ofPennsylvania (with AlanG. MacDiarmid) in 1993and his PhD degree inphysical chemistry fromHarvard University (withGeorge M. Whitesides)in 1996. He then stayedat Harvard and workedas a postdoctoral fellowwith both Whitesides andMara Prentiss. He beganas an assistant professorof chemistry at the Uni-versity of Washington in1997.

Xia’s research interestsinclude nanostructuredmaterials, self-assembly,photonic crystals, col-loidal chemistry, micro-fabrication, surfacemodification, electrospin-ning, conducting poly-mers, microfluidics, andnovel devices for pho-tonics, optoelectronics,and displays.

He has received manyawards, including a National Science Founda-tion CAREER Award,the Camille DreyfusTeacher–Scholar Award,and the Victor K. LaMerAward from the AmericanChemical Society. He hasbeen an Alfred P. SloanResearch Fellow and aDavid and LucilePackard Fellow. Xia is theco-author of more than200 peer-reviewed pub-lications and has edited anumber of special issuesand books on nanostruc-tured materials. He cur-rently serves as anassociate editor for NanoLetters.

Xia can be reached bye-mail at [email protected].

Naomi J. Halas, GuestEditor for this issue ofMRS Bulletin, is theStanley C. Moore Pro-fessor of Electrical andComputer Engineeringand a professor ofchemistry at Rice Uni-versity. She received herundergraduate degreein chemistry from LaSalle University inPhiladelphia, and herMS and PhD degrees inphysics from BrynMawr College, the latterwhile she was a graduatefellow at IBM’s T.J. WatsonResearch Center. Follow-ing her postdoctoral re-search at AT&T BellLaboratories, she joinedthe faculty at Rice. She isbest known for her inven-tion of nanoshells, a newtype of nanoparticlewith tunable optical prop-erties especially suitedfor biotechnology appli-cations. She has been

honored with the NSFYoung InvestigatorAward, three HershelRich Invention Awards,the 2003 Cancer Innova-tor Award from theCongressionally DirectedMedical Research Pro-grams of the Departmentof Defense, and the 2000CRS–Cygnus Award forOutstanding Work inDrug Delivery. She wasalso awarded “Best Dis-covery of 2003” by Nano-technology Now and was afinalist for the Small Times2004 NanotechnologyResearcher of the Year.

She has published morethan 100 peer-reviewedpapers, has presentedover 150 invited talks, andholds nine issued patents.Halas is a fellow of theAmerican Physical Societyand of the Optical Societyof America. She is alsothe founder and directorof the Rice UniversityLaboratory for Nano-photonics (LANP), amultidisciplinary researchnetwork whose missionis the design, invention,and application of nanoscale optical components.

the bulk solids, and their catalytic activi-ties might strongly depend on their sizeand shape. All of these unknowns make itdifficult to decipher the mechanism re-sponsible for shape-controlled synthesis.

Our goal with this issue is to providereaders with some representative and ex-citing snapshots of the new developmentsoccurring in the field of surface plasmons.Due to the highly dynamic nature of thisfast-evolving area, it is impossible to coverevery aspect of the subject. There is no doubtthat research on fabrication and syntheticstrategies will continue to develop strongly,with contributions coming from chemists,physicists, materials scientists, and engi-neers. We sincerely hope that readers willnot only enjoy the topics presented here,but perhaps also find the inspiration topush this field to the next level of success.

References1. M. Di Ventra, S. Evoy, and J.R. Heflin Jr.,

eds., Introduction to Nanoscale Science and Technology (Kluwer Academic Publishers,Boston, 2004).2. G. Mie, Ann. Phys. 25 (1908) p. 377.3. C. Kittel, Introduction to Solid State Physics, 6th ed. (John Wiley & Sons, New York,1986).

4. C.F. Bohren and D.R. Huffman, Absorptionand Scattering of Light by Small Particles (JohnWiley & Sons, New York, 1983).5. U. Kreibig and M. Vollmer, Optical Properties ofMetal Clusters (Springer-Verlag, New York, 1995).6. E. Hunter and J.H. Fendler, Adv. Mater. 16(2004) p. 1685.7. M. Geissler and Y. Xia, Adv. Mater. 16 (2004)p. 1249.8. J.M. Gibson, Phys. Today (October 1997) p. 56.9. D. Brambley, B. Martin, and P.D. Prewett,Adv. Mater. Opt. Electron. 4 (1994) p. 55.10. C.L. Haynes and R.P. Van Duyne, J. Phys.Chem. B 105 (2001) p. 5559.11. J. McLellan, M. Geissler and Y. Xia, J. Am.Chem. Soc. 126 (2004) p. 10830.12. Y. Xia and G.M. Whitesides, Angew. Chem.Int. Ed. Engl. 37 (1998) p. 550.13. D.S. Ginger, H. Zhang, and C.A. Mirkin,Angew. Chem. Int. Ed. Engl. 43 (2004) p. 30.14. “Heritage: Faraday page,” the Royal Insti-tution of Great Britain, http://www.rigb.org/rimain/heritage/faradaypage.jsp (accessedMarch 2005).15. B. Wiley, Y. Sun, B. Mayers, and Y. Xia,Chem. Euro. J. 11 (2005) p. 455.16. M.A. El-Sayed, Acc. Chem. Res. 34 (2001)p. 257.17. K.L. Kelly, E. Coronado, L.L. Zhao, and G.C. Schatz, J. Phys. Chem. B 107 (2003)p. 668.18. L. Hirsch, R. Stafford, J. Bankson, S. Sershen, B. Rivera, R. Price, J. Hazle, N. Halas,

and J. West, Proc. Natl. Acad. Sci. U.S.A. 100(2003) p. 13549.19. J.G. Fujimoto, Nature Biotechnol. 21 (2003)p. 1361.18. I.O. Sosa, C. Noguez, and R.G. Barrera,J. Phys. Chem. B 107 (2003) p. 6269.20. J.M. Brockman, B.P. Nelson, and R.M. Corn,Annu. Rev. Phys. Chem. 51 (2000) p. 41.21. N. Nath and A. Chilkoti, Anal. Chem. 74(2002) p. 504.22. Y. Sun and Y. Xia, Anal. Chem. 74 (2002)p. 5297.23. N.T.K. Thanh and Z. Rosenzweig, Anal.Chem. 74 (2002) p. 1624.24. Y. Kim, R.C. Johnson, and J.T. Hupp, NanoLett. 1 (2001) p. 165.25. S.A. Maier, P.G. Kik, H.A. Atwater, S.Melyzer, E. Harel, B. Koel, and A.A.G. Requicha, Nature Mater. 2 (2003) p. 229.26. K. Kneipp, H. Kneipp, I. Itzkan, R.R. Dasari, and M.S. Feld, Chem. Rev. 99 (1999)p. 2957.27. A. Parfenov, I. Gryczynksi, J. Malicka, C.D.Geddes, and J.R. Lakowicz, J. Phys. Chem. B 107(2003) p. 8829.28. Y. Shen, C.S. Friend, Y. Jiang, D. Jakubczyk,J. Swiatkiewicz, and P.N. Prasad, J. Phys. Chem. B 104 (2000) p. 7577.29. W.L. Barnes, A. Dereux, and T.W. Ebbesen,Nature 424 (2003) p. 824.30. P. Andrew and W.L. Barnes, Science 306(2004) p. 1002. ■■

Younan Xia Naomi J. Halas

Xingde Li Zhi-Yuan Li Stefan Maier



Halas can be reached by e-mail at [email protected].

Harry A. Atwater is theHoward Hughes Profes-sor and a professor ofapplied physics and materials science at theCalifornia Institute ofTechnology. His researchinterests center on syn-thesis, properties, andprocessing of materialsfor use in electronic,photonic, and opto/mechanical devices andcircuits. His current re-search efforts are focusedon plasmonic and nano-crystal optoelectronicdevices; thin-film photo-voltaic materials and de-vices, including thin-filmsilicon, III–V compoundphotovoltaic heterostruc-tures, and nanostructurephotovoltaics; and ferro-electric and piezoelectricthin-film materials.

He has co-authoredover 150 refereed journalpublications in the fieldsof electronic and photo-tonic materials.

Atwater received hisPhD degree in electricalengineering from MIT in1987. He is a recipient ofthe NSF Presidential Investigator Award andthe AT&T FoundationAward and is a memberof the Böhmische Physi-cal Society and a JoopLoos Fellow of the FOMInstitute, Amsterdam. Hecurrently serves as the di-rector of Caltech’s Centerfor Science and Engi-neering of Materials (an

NSF MRSEC) and is amember of the board ofdirectors of the GordonResearch Conferences.He is founder and chieftechnical advisor forAonex Corporation.

He has consulted ex-tensively for industryand government andhas also actively servedthe materials commun-ity as a meeting chair(1997) and as president(2000) of the MaterialsReaserch Society and asa Gordon Research Con-ference chair (2001).

Atwater can bereached at the CaliforniaInstitute of Technology,Thomas J. Watson Labo-ratories of AppliedPhysics, Mail Code 128-95, Pasadena, CA 91125,USA; tel. 626-395-2197,fax 626-844-9320, and e-mail [email protected].

Hu Cang is a postdoctoralresearcher working withYounan Xia and XingdeLi at the University ofWashington. He receivedhis BS degree in chemicalphysics from the Univer-sity of Science and Tech-nology of China (USTC)in 1998, his MS degreein electrical engineeringfrom Stanford Universityin 2003, and his PhD degree in chemistryfrom Stanford (withMichael D. Fayer) in2004. His research inter-ests include nonlinearoptical spectroscopy, dynamics of complexliquids, glass transitions,

and optical coherencetomography.

Cang can be reachedby e-mail at [email protected].

Jingyi Chen is a graduatestudent in the Depart-ment of Chemistry at theUniversity of Washington,where she works on thesynthesis of nanostruc-tured materials and func-tionalization of theirsurfaces. She received herBS degree in chemistryin 1997 from Zhong-ShanUniversity in Guangzhou,China; her MS degree inchemistry in 2000 fromthe Guangzhou Instituteof Chemistry, AcademiaSinica; and her MS degreein biochemistry in 2002from Buffalo State College. She is a recipientof the NanotechnologyFellowship StudentAward (2003–2005) fromthe Center for Nanotech-nology at the Universityof Washington and anMRS poster award (2005).

Chen can be reachedby e-mail at [email protected].

Aloyse Degiron is apostdoctoral researcherat Duke University inNorth Carolina, in thegroup of David Smith.He completed both hisundergraduate andgraduate studies atLouis Pasteur Univer-sity in Strasbourg,France, receiving hisPhD degree in physicsin 2004. His current re-search is focused on avariety of phenomenaassociated with surface-plasmon-enhancedtransmission of sub-wavelength apertures.

Degiron can be reachedat the Department ofElectrical and ComputerEngineering, Duke University, 130 HudsonHall, Box 90291,Durham, NC 27708,USA, and by e-mail [email protected].

José Dintinger is a PhDstudent in physical chem-istry at Louis PasteurUniversity in Strasbourg,France, where he alsocompleted his under-graduate studies. His

research interests includesurface-plasmon–molecule interactions,strong coupling phe-nomena, and opticalproperties of nanostruc-tured materials.

Dintinger can bereached at ISIS, UniversitéLouis Pasteur, 8 alléeMonge, 67000 Strasbourg,France, and by e-mail [email protected].

Jennifer A. Dionne is adoctoral candidate in theApplied Physics Depart-ment at the CaliforniaInstitute of Technology.She graduated fromWashington Universityin St. Louis in 2003, receiv-ing BS degrees in physicsand systems science andengineering. Since joiningthe applied physics pro-gram at CalTech, her re-search has focused onunderstandinglight–matter interactionson the nano-scale, em-phasizing the analysisand design of plasmonwaveguides for deviceand sensor applications.She is a National Science

Harry A. Atwater Hu Cang Jingyi Chen Aloyse Degiron José Dintinger


Foundation GraduateResearch Fellow and a recipient of the NationalDefense Science and En-gineering Graduate Fel-lowship.

Dionne can bereached at the CaliforniaInstitute of Technology,Watson Laboratories ofApplied Physics, MailCode 128-95, Pasadena,CA 91125, USA; tel. 626-395-2380, fax 626-844-9320, and [email protected].

Thomas W. Ebbesen isa professor of chemistry atLouis Pasteur Universityin Strasbourg, France, anddirector of the Institutefor Supramolecular Science and Engineering(ISIS). He received hisBA degree from OberlinCollege in Ohio (1976)and his PhD degree inphysical chemistry fromPierre & Marie CurieUniversity in Paris (1980).He then spent an extend-ed period in the UnitedStates and Japan, work-ing, among other places,at the NEC Fundamental

Laboratory in Tsukubaand the NEC ResearchInstitute in Princeton be-fore returning to Francein 1999. His researchcurrently focuses onnanostructured materialswith a particular empha-sis on surface plasmonoptics.

Ebbesen can bereached at ISIS, Univer-sité Louis Pasteur, 8allée Monge, 67000Strasbourg, France, andby e-mail [email protected].

Anand Gole has been apostdoctoral researchfellow in the Departmentof Chemistry and Bio-chemistry at the Univer-sity of South Carolinasince November 2003.He recieved his PhD de-gree from the NationalChemical Laboratory inPune, India, where heconcentrated on problemsrelated to protein–lipidand protein–gold colloidbiocomposite materials.He also was a postdoc-toral fellow at the Labo-ratoire de Physique des

Solides in Orsay, France,where he focused onpolymer–surfactant andnanoparticle–lipid inter-actions at the air–waterinterface. His current re-search activities includethe synthesis, characteri-zation, and surfacemodification of one-dimensional nanostruc-tures and their subse-quent assembly ontoplanar surfaces for pos-sible sensing applica-tions, nanoparticle cytotoxicity studies, andthe formation ofnano/bio assemblies.

Gole can be reachedby e-mail at [email protected].

Amanda J. Haes is a National Research Councilpostdoctoral fellow at theU.S. Naval Research Lab-oratory in Washington,D.C. She received herBA degree in chemistryand physics from Wartburg College in 1999and her MS and PhD de-grees in chemistry fromNorthwestern Universityin 2001 and 2004, respec-

tively. Her research in-terests include nano-science, plasmonics, surface-enhanced spec-troscopy, and the inte-gration of lithographic,microscopic, and spec-troscopic techniques forbiological and chemicalsensor development.She is a recipient of theNorthwestern UniversityChemistry DepartmentAward for Excellence inGraduate Research(2004), a Materials Re-search Society GraduateStudent Gold Award(2003), an AmericanChemical Society Divisionof Analytical Chemistryand Dupont ResearchFellowship (2003), and aKirkbright BursaryAward from the Associ-ation of British Spectro-scopists (2004).

Haes can be reachedby e-mail at [email protected].

Christy L. Haynes iscurrently a National Institutes of Health post-doctoral fellow in R. MarkWightman’s laboratoryat the University of NorthCarolina, Chapel Hill, andwill join the Universityof Minnesota in fall 2005as an assistant professorof chemistry. She receivedher BA degree in chem-istry from MacalesterCollege in 1998, and herMS and PhD degrees inchemistry from North-western University in1999 and 2003, respec-tively. Her research interests include nano-

science, plasmonics, sur-face-enhanced spec-troscopy, electrochemistry,neurochemistry, and theapplication of Ramanspectroscopy to problemsin neurobiology.

Haynes is the recipientof a Nobel Laureate Signature Award forGraduate Education fromthe American ChemicalSociety (2005), a North-western UniversityChemistry DepartmentAward for Excellence inGraduate Research(2003), a NorthwesternUniversity PresidentialFellowship (2002), aKirkbright BursaryAward from the Associ-ation of British Spectro-scopists (2002), aGraduate Student GoldAward from the MaterialsResearch Society (2002),and an American Chem-ical Society AnalyticalChemistry Division Fellowship (2001).

Haynes can bereached by e-mail at [email protected].

Xingde Li is an assistantprofessor of bioengineer-ing at the University ofWashington. He receivedhis BS degree in appliednuclear physics from theUniversity of Science andTechnology of China(USTC) in 1990. He thenearned his PhD degreein condensed-matterphysics and biomedicaloptics from the Universityof Pennsylvania in 1998(with Arjun G. Yodh


Jennifer A. Dionne Thomas W. Ebbesen Anand Gole Amanda J. Haes Christy L. Haynes

Adam D. McFarland Chad A. Mirkin Catherine J. Murphy

C. Shad Thaxton Richard P. Van Duyne



and Britton Chance), atwhich point he joinedthe Research Laboratoryof Electronics at MIT for postdoctoral train-ing (with James G. Fujimoto).

Li’s research centerson low-coherence inter-ferometry, high-resolutionoptical coherence tomo-graphy, light scattering,photon diffusion, light–tissue interactions, bio-logical tissue absorptionand scattering spec-troscopy, optical molec-ular contrast agents, andoptically based novelminiature biomedicaldevices. He has receiveda National ScienceFoundation CAREERAward and has authoredor co-authored morethan 30 peer-reviewedpublications.

Li can be reached bye-mail at [email protected].

Zhi-Yuan Li is a professorof physics in the Instituteof Physics at the ChineseAcademy of Sciences inBeijing. He received hisBS degree in optoelectron-ics from the Universityof Science and Technologyof China (USTC) in 1994 and then workedas a graduate student onphotonic crystals andnear-field optics at the In-stitute of Physics, Chi-nese Academy ofSciences. After obtaininghis PhD degree in 1999,he worked as a postdoc-toral fellow at the HongKong University of Science and Technology,the University of Washington, and AmesNational Laboratory. Hisresearch interests includephotonic crystals,nanophotonics, near-fieldoptics, and integratedoptics.

Li is the co-author of more than 60 peer-reviewed publications.He currently serves as aregular referee for severalprominent physics and

optics journals, includ-ing Physical Review Letters, Applied PhysicsLetters, Physical Review Band E, and OpticsLetters.

Li can be reached bye-mail at [email protected].

Stefan Maier is a lecturerin the Department ofPhysics at the Universityof Bath in the UnitedKingdom. His researchinterests include plas-monic nanostructures forenergy guiding, confining,and biological sensing,and the interface betweenmicro- and nano-optics.His work on plasmonwaveguides has beenrecognized by numerousinvitations to interna-tional conferences. He isalso a frequent contribu-tor to Spektrum der Wissenschaft.

Maier can be reachedby e-mail at [email protected].

Adam D. McFarlandis a postdoctoral re-searcher in the Depart-ment of Materials Scienceand Engineering atNorthwestern University.He received his BS degreein chemistry from theUniversity of Dayton in1999 and his MS and PhDdegrees in chemistryfrom Northwestern Uni-versity in 2001 and 2004,respectively. His researchinterests focus on thedevelopment of analyti-cal techniques and in-

strumentation for thecharacterization of nano-scale materials. His pastresearch includes theutilization of single nano-particles as chemicalsensing platforms and themechanistic study ofsurface-enhanced Ramanspectroscopy. He is currently designing andconstructing a low-temperature scanningtunneling microscope forthe study of nanoscalematerials and molecularelectronics.

McFarland can bereached by e-mail at [email protected].

Chad A. Mirkin is theGeorge B. RathmannProfessor of Chemistryand a professor of medi-cine and materials scienceand engineering atNorthwestern University.He is also director ofNorthwestern’s Institutefor Nanotechnology.Mirkin is known for hisinvention and develop-ment of nanoparticle-based biodetectionschemes, dip-pen nano-lithography, and theweak-link approach tosupramolecular coordi-nation chemistry. He hasauthored more than 220manuscripts and holds 50patents. He is the founderof Nanosphere and Nano-Ink, two companies thatare commercializingnanotechnology applica-tions in the bio andsemiconductor industries.

He is a three-time winnerof the National InventorsHall of Fame CollegiateInventors Award (1998,2002, 2004), and most re-cently, he was recognizedwith the 2004 NIH Director’s Pioneer Award.

Mirkin can be reachedby e-mail at [email protected].

Catherine J. Murphy isthe Guy F. LipscombProfessor of Chemistry atthe University of SouthCarolina. She receivedBS degrees in chemistryand biochemistry in1986 from the Universityof Illinois at Urbana-Champaign, and she re-ceived her PhD degree in inorganicchemistry from the Uni-versity of Wisconsin in1990. She was then anNSF and NIH postdoc-toral fellow at the Cali-fornia Institute ofTechnology from 1990 to1993. Her research inter-ests include the synthe-sis, characterization, andoptical applications ofinorganic nano-materials, coordination

compounds for opticalsensing, and opticalprobes of local DNAstruc-ture and dynamics. Shehas received a CAREERAward and a SpecialCreativity Award fromthe National ScienceFoundation and has beena Research CorporationCottrell Scholar, an Alfred P. Sloan Founda-tion Research Fellow,and a Camille DreyfusTeacher–Scholar. She isalso an invited memberof the NanotechnologyTechnical AdvisoryGroup, which reports tothe President’s Councilof Advisors on Scienceand Technology, and sheserves on the editorialadvisory boards forseven journals.

Murphy can bereached by e-mail [email protected].

Christopher J. Orendorffis a postdoctoral fellow inthe Department of Chem-istry and Biochemistry atthe University of SouthCarolina. He earned hisPhD degree in analytical

Christopher J. Orendorff

Albert Polman Nathaniel L. Rosi Tapan K. Sau


chemistry from the Uni-versity of Arizona in 2003.His research focuses onusing primarily metallicnanorods/wires forchemical and biologicalanalysis and the rationalmanipulation ofnanorods/wires in solu-tion and on substrates.Currently, he is workingon patterning nano-spheres and nanorodson solid supports usingspecific biological andchemical interactions,studying elastic light-scattering from nano-particles of variousshapes, studying the self-assembly and controllingthe orientation of nano-rods in different media,and developing the useof nanorods as sensors todetermine physical stressand strain in polymersand biological tissues.

Orendorff can bereached by e-mail [email protected].

Albert Polman is thehead of the Center forNanophotonics at theFOM Institute for Atomic

and Molecular Physics(AMOLF) in Amsterdam.His main research interestis nanophotonics, thestudy of optical interac-tions in materials madeusing nanoscale fabrica-tion technologies. Hisgroup’s research programincludes the study of energy transfer in metallo-dielectric plasmonic struc-tures, control of opticalmodes and spontaneousemission in photonic crys-tals and microresonators,and light emission fromsilicon using rare-earthions or silicon nanostruc-tures. He has publishedover 150 journal articleson optical phenomena inphotonic nanomaterials.

Polman’s Web site iswww.erbium.nl; he canbe reached by e-mail [email protected].

Nathaniel L. Rosi isworking on postdoctoralstudies as a member ofChad A. Mirkin’s groupat Northwestern Uni-versity. He earned hisBA degree at GrinnellCollege in 1999 and hisPhD degree from the

University of Michiganin 2003, where he studiedthe design, synthesis, andgas storage applicationsof metalorganic frame-works under the guidanceof Omar M. Yaghi. Hiscurrent research focuseson the rational assemblyof DNA-modified nano-structures into larger-scalematerials.

Rosi can be reachedby e-mail at [email protected].

Tapan K. Sau is an assistant professor in theDepartment of Chemistryat Panjab University inChandigarh, India, andis currently on a leave ofabsence working as apostdoctoral fellow withC.J. Murphy in the Department of Chemistryat the University of SouthCarolina. He obtainedhis PhD degree from theDepartment of Chemistryat the Indian Institute ofTechnology in Kharagpur.

Sau can be reached bye-mail at [email protected].

George C. Schatz is theCharles E. and Emma H.Morrison Professor ofChemistry at North-western University. He isa theoretician who stud-ies the optical, structural,and energetic propertiesof nanomaterials, and hehas contributed to theoriesof dynamical processesimportant in chemistry,including gas-phase andcondensed-phase reac-tions, energy transferprocesses, transport

phenomena, and photo-chemistry. In the field of nanoscience, he has specialized in computa-tional electrodynamicstudies of noble metalnanoparticles, nano-holes, and other nano-structured materials. Hehas contributed to theoriesof DNA melting andnanoparticle aggregates,and he has studied themechanical properties ofnanotubes and thin films.

Schatz is a member ofthe American Academyof Arts and Sciences(2002), the InternationalAcademy of QuantumMolecular Sciences (2001),and is editor in chief ofthe Journal of PhysicalChemistry.

Schatz can be reachedby e-mail at [email protected].

Yugang Sun is a researchassociate at the Universityof Illinois at Urbana-Champaign workingwith John Rogers. He received his BS and PhDdegrees in chemistryfrom the University ofScience and Technologyof China (USTC) in 1996and 2001, respectively.After graduating fromUSTC, he worked as apostdoctoral researchassociate with YounanXia at the University ofWashington until the endof 2003. His research interests include thesynthesis and characteri-zation of nanostructures,micro- and nanofabrica-tion, bioanalysis, anddevices for photonicsand electronics.

Sun can be reached bye-mail at [email protected].

Luke Sweatlock is adoctoral candidate in theApplied Physics Depart-ment at the CaliforniaInstitute of Technology.He obtained his BS degreein engineering physicsat Cornell Universityand enrolled at Caltech

following employmentat Agere Systems’ opto-electronics center. His re-search focus is on opticalinteractions in nanostruc-tured metal compositesand enabling the designand characterization of novel plasmonic devices.

Sweatlock can bereached at Caltech, MC128-95, Pasadena, CA91125 USA; tel. 626-395-3826 and e-mail [email protected].

C. Shad Thaxton is pursuing a career in academic urology atNorthwestern University.He earned his BA degreeat the University of Colorado in 1998 and hisMD degree from North-western University’sFeinberg School of Med-icine in 2004. A HowardHughes Medical Institutefellowship for medicalstudents brought him tothe Mirkin laboratory atNorthwestern, where heworked on biomoleculardetection using goldnanoparticle probes. Hisfellowship experienceculminated with the re-porting of the bio-barcodeassay, for which he washonored with the NationalInventors Hall of FameCollegiate InventorsCompetition graduateprize. He returned to theMirkin lab to completehis PhD degree, wherehe continued to work onbiomolecular detectionand the use of goldnanoparticles for novelapplications in the lifesciences until beginninghis current pursuit in academic urology.

Thaxton can be reachedby e-mail at [email protected].

Richard P. Van Duyneis the Charles E. andEmma H. Morrison Professor of Chemistry atNorthwestern University.He is credited with thediscovery of surface-


Yugang Sun Luke Sweatlock

Benjamin Wiley Shengli Zou

George C. Schatz



enhanced Raman spec-troscopy (SERS) and theinvention of nanospherelithography (NSL); he alsodeveloped ultrasensitivenanosensors based onlocalized surface plasmonresonance (LSPR) spec-troscopy. His researchinterests include surface-enhanced spectroscopy,

nanofabrication, nano-particle optics, combinedscanning probe micros-copy/Raman micros-copy, Raman spec-troscopy of mass-selected clusters, ultra-high-vacuum surfacescience, structure andfunction of biomoleculeson surfaces, and surface-

enhanced spectroscopicmethods for chemicaland biological sensing.

Van Duyne is the re-cipient of several awards,including the NobelLaureate SignatureAward for Graduate Education from theAmerican Chemical Society (2005), election to

the American Academyof Arts and Sciences(2004), and the Earle K.Plyler Prize for MolecularSpectroscopy from theAmerican Physical Society (2004).

Van Duyne can bereached by e-mail [email protected].

Benjamin Wiley is agraduate student in thechemical engineeringprogram at the Universityof Washington. He re-ceived a BS degree inchemical engineeringfrom the University ofMinnesota in 2003. As amember of Younan Xia’sgroup at the Universityof Washington, his workfocuses on the synthesisof metallic nanostructureswith controllable shapesand understanding theirnucleation/growthmechanisms. He is a recipient of the IGERTFellowship Award (sup-ported by the NationalScience Foundation) fromthe Center of Nanotech-nology at the Universityof Washington, and aGraduate Student GoldAward from MRS(2005).

Wiley can be reachedby e-mail at [email protected].

Shengli Zou received hisBS and MS degrees inphysical chemistry fromShandong University inChina and a PhD degreein physical chemistryfrom Emory University(with Joel M. Bowman)in 2003. He has been apostdoctoral fellow inGeorge C. Schatz’s lab at Northwestern Univer-sity since December2002. His research interests include the op-tical properties of nano-particles, nanoparticle arrays, and nanopar-ticles for biological sensing. He is also inter-ested in the self-assemblyof biomolecules.

Zou can be reached by e-mail [email protected]. ■■

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shape-controlled synthesis and surface plasmonic properties of metallic nanostructures

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