Molecular Transport ...

376 MRS BULLETIN/JUNE 2004

Molecular Electronics: Definitionand History

Molecular electronics is most simply defined as electronics whose behavior isdictated by the chemical, physical, and elec-tronic structures of molecules. This defini-tion is very broad; it includes conductivepolymers and even the insulating poly-mer layers on metal wiring. In commonuse, molecular electronics refers to molec-ular structures whose characteristic fea-tures are on the nanoscale and that containbetween one and a few thousand molecules.The simplest challenge involves determin-ing the structure/function relationshipsfor electronic transport (intra- or intermol-ecular) through a junction containing oneor a few molecules as the transport mediumand with either two (source/drain) or three(source/gate/drain) electrodes. Suchtransport structures are a dominant themeof contemporary molecular electronics andare the focus of this issue of MRS Bulletin.

The history of molecular electronics isbrief. Some of the earliest work was per-formed at the laboratory of Hans Kuhn,working with Mann, Polymeropoulos, andSagiv.1 Using organic adlayers on solidsubstrates, this group reported some ofthe earliest (1971) reproducible electricaltransport measurements through organic

molecules. They also developed some ofthe first effective self-assembly techniquesfor preparing structures in which mole-cules adhere to surfaces not by simple dis-persion forces, but by molecular bondformation.

Following Kuhn’s work, there were anumber of important follow-up measure-ments.2 In addition, there were some vi-sionary (if perhaps premature) papers3

suggesting the use of single molecules asrectifiers and extensive device ideas involv-ing molecular logic structures.4

The great step forward came in 1983,with the development of scanning probemicroscopy (SPM).5 The capability to bothmanipulate and measure molecular struc-tures topologically and spectroscopicallyprompted a renewed focus on the possi-bilities of molecular electronics. Continu-ing advances in synthesizing organicmolecules with possible device applicabil-ity, and in their assembly and measure-ment, have led to increasing interest in thefield and to substantial advances in ourunderstanding.6

Starting roughly a decade after the in-vention of SPM, applications to molecularstructures and their transport behavior ap-

peared. Important early work includedthe use of C60 as an electromechanical gatedevice,7 transport measurements on or-ganic molecules with thiol end groups as-sembled between a gold surface and goldnanocrystals,8 and the introduction of breakjunction9 measurements to characterizecurrents in one (or a few) molecules.

Theoretical ideas for interpreting thecurrent/voltage characteristics in molecu-lar junctions began to appear in the 1990s.Some early approaches used the Landauerformulation,10 originally developed for semi-conductor devices. In this simple picture,transport through molecular junctions is in-terpreted in terms of elastic scattering, andthe conductance is given as the product ofthe quantized unit of conductance (12.9 k�)-1

and a transmission coefficient describinghow effective a molecule is in scatteringthe incoming electron from the upstreamlead into the downstream lead. Morepowerful formulations, including the non-equilibrium Green’s function (NEGF) ap-proach, were also introduced in themid-1990s.11 Integrating a proper descrip-tion of the molecule with an appropriatedescription of the leads is the challengethat these formulations face; the NEGFseems capable of including elastic and in-elastic effects as well as vibronic (vibra-tional electron) coupling and system/bathinteraction.

In this issue of MRS Bulletin, leading re-searchers provide a quick tour of some ofthe thematic areas of interest. In the firstarticle, Hersam and Reifenberger discusscharge transport through molecular junc-tions and provide a brief description of howto measure and interpret such transportbehavior.

Ghosh et al. provide a theoretical overviewof molecular charge transport structures.They introduce the different theoreticalformulations, and provide guidance bothfor building understanding and interpret-ing experiments.

In the third article, Kushmerick et al.discuss conductance with different test bedsand inelastic tunneling measurements.

In the last article, Avouris provides anintroduction to carbon nanotube junctions,structures, transport, and devices.

Synthesis, Interpretation, andDevice Aspects

In order to understand molecular struc-ture/function relationships, it is necessaryto synthesize appropriate molecules, fab-ricate (incorporate) them into a certainstructure (junctions), and probe their be-havior. Questions of structure and stabilityare crucial.

Both nature and synthetic chemistry haveexploited the unique bonding character of

Molecular TransportJunctions: AnIntroduction

Cherie R. Kagan and Mark A. Ratner,Guest Editors

AbstractThis issue of MRS Bulletin on molecular transport junctions highlights the current

experimental and theoretical understanding of molecular charge transport and itsextension to the rapidly growing areas of molecular and carbon nanotube electronics.This introduction will outline the progress that has been made in understanding themechanisms of molecular junction transport and the challenges and future directions inexploring charge transport on the molecular scale. In spite of the substantial challenges,molecular charge transport is of great interest for its intrinsic importance to potentialsingle-molecule electronic, thin-film electronic, and optoelectronic applications.

Keywords: carbon nanotubes, charge transport, molecular electronics, molecularjunctions, optoelectronics, self-assembly.

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Molecular Transport Junctions: An Introduction

MRS BULLETIN/JUNE 2004 377

the carbon atom and a range of metal co-ordination environments to prepare a vastnumber of molecular systems. Routinebench-scale chemical synthesis produces1023 molecules at a time, and each mole-cule is identical. Chemical functionaliza-tion of the molecules and van der Waals,�–�, covalent, and hydrogen bondingforces enable self-assembly of single mole-cules and molecular monolayers on sur-faces. The diversity of molecular systemssuggests the use of molecular materials ina wide range of applications (due to theirstructural and optical properties and proc-essability) in packaging, mechanical, dye,passive and active optical, and resist tech-nologies, and promises applications (arisingfrom their electronic properties) in electri-cal and optoelectronic devices.

Carbon nanotubes (CNTs), discovered byIijima in 1991, are frequently classified as“molecular” systems since their electronicstructure is discrete. CNTs possess re-markable mechanical, electrical, optoelec-tronic, and thermal properties, as detailedin the following paragraphs. They are alsothermally stable, making them compatiblewith Si processing and therefore particu-larly exciting for potential electronic andoptoelectronic devices.

Understanding the correlation betweenmolecular junction structure and electricalproperties is of fundamental and techno-logical interest. Fabricating molecularjunctions less than �10 nm in size presentsa tremendous challenge and has made it dif-ficult to compare reported measurementswith theoretical work carried out to de-scribe current flow in molecular junctions(see article in this issue by Ghosh et al.).Because CNTs can be much longer thansmall molecules, junctions with lengthsranging from the nanometer to the mil-limeter scales can be fabricated by stan-dard lithographic techniques, and devicestructures can be studied to provide feed-back between experimental and theoreti-cal work. Since molecules and CNTs havemany similarities, theoretical modeling ofcurrent flow in both molecule- and CNT-based junctions follows a generalized formof the Landauer theory. Insight into theelectrical characteristics of molecular andCNT junctions and the influence of struc-ture, conformation, interfaces with sub-strates or contacts, and environment is thefirst step in the pursuit of molecular-scaleand CNT devices and is important to theimprovement of thin-film organic elec-tronic and optoelectronic devices.

The chemical diversity of molecular sys-tems and the ability to synthetically tailormolecular structure has generated interest inmolecular analogues of insulators, intercon-nects (wires), rectifiers, switches (transis-

tors), memory elements, and sensors. Simi-larly, metallic and semiconducting CNTs areexciting as potential interconnects, diodes,switches, memory elements, and sensors.More recently, molecular-scale and CNTelectronic devices have received enormousattention, driven by the anticipation thatconventional Si technology is running everfaster toward its scaling limits as the channel length of transistors has shrunk to the nanometer (�100 nm) size regime.Molecular-scale devices are expected torepresent the ultimate in device scaling, asmolecular lengths can be as small as �1 nm,although limitations of tunneling andelectrostatics, as in Si devices, set a lowerbound on device dimensions (for the ex-ample of a molecular transistor, �3 nm).

The simplicity of solution- or gas-phaseself-assembly of molecular systems offers anopportunity for low-cost fabrication. Func-tionality that can be chemically tailoredmay provide for complexity in moleculardevices that is not found in Si devices. Forexample, while scaling in Si devices isgoverned by pushing device dimensionsever smaller, in molecular devices it maybe better to make larger molecules toachieve functionality and performancenot found in Si devices. In CNT field-effecttransistors (CNTFETs), the ballistic trans-port at small dimensions, reduced dimen-sionality, and the lack of dangling bonds thatprovides flexibility in interface/device design have led to promising demonstra-tions of device performance (see the articleby Avouris in this issue).

Charge transport in molecular junctionsis also important to the progress of thin-filmorganic devices such as light-emittingdiodes (LEDs), photovoltaics (PVs), thin-filmtransistors (TFTs), and memory cells. Themetal–molecule and metal–semiconductorjunctions in each of these applications sig-nificantly limit the performance of thin-filmmolecular devices. Organic LEDs (OLEDs)have recently been commercialized in carradio displays and indicator lights and arebeing developed by many manufacturersfor large-area displays. In OLEDs, chargeinjection across the molecule–metal inter-face requires high-voltage and, therefore,high-power operation and limits the sta-bility and lifetime of devices. In organic andorganic–inorganic PVs, recombinationlosses at metal–molecule and metal–semi-conductor interfaces represent one of thebiggest challenges to device efficiency.Similarly, in organic TFTs the molecule–contact interface presents electronic barriersto charge injection that give rise to currentcrowding at low voltage, measured assublinear I–V characteristics in the trioderegion, and that necessitate higher deviceoperating voltages.

Structure/Function RelationshipsMolecular electronics entails at least two

entities, the molecule and the electrode.From an energetic viewpoint, the molecu-lar states are discrete molecular orbitals,while the electrodes (metallic or semicon-ducting) consist of bands characterized bycontinuous densities of states. The mix ofdiscrete and continuous structures repre-sents much of the challenge in understand-ing molecular electronic transport.

As indicated earlier, formulating thetransport through the discrete structurerequires a molecular Hamiltonian descrip-tion and a Green’s function description ofthe interaction of that molecule with themacroscopic leads.

When voltage is placed across the mole-cule, the electronic structure of the molec-ular species is no longer in equilibrium,although it can be in a steady state. Themolecule tries to adjust to an electrochem-ical potential of one magnitude at thecathode side and another magnitude atthe anode side; this causes some polariza-tion within the molecule, which acts effec-tively as a polarized capacitor.

One of the reasons that CNTs are the mostadvanced areas of molecular electronics isthat the community has a reasonably goodunderstanding of their structure. BecauseCNTs can be prepared with lengths far ex-ceeding a few nanometers, measurementscan be (and have been, see Figure 1) madeof the nature of the electrostatic potentialacross the CNT, and of the approximateCNT geometries. For junctions containingorganic molecules—in particular, the verypopular thiol/gold structural motif—wehave no direct structural evidence con-cerning the geometry. This makes calcula-tions and mechanistic deduction quitecomplex. Indeed, understanding thestructure will be crucial if the kinds ofstructure/function relationships that areof primary interest in molecular electronicjunctions are to be compared directly toexperiment. Although the structures aregenerally only crudely understood, therehave been some major advances in ourunderstanding of how molecular behav-ior influences transport in junctions. High-lights of these advances include thefollowing:1. The comparison between the rate constant(the rate at which electrons would transferfrom a donor at one end of a molecularbridge to an acceptor at the other end) and the conductance through that samemolecular bridge has been clarified.12 Thispermits interesting aspects of the mechanism—such as the transition betweencoherent and incoherent transport as afunction of either length or temperature—to be compared.



2. The importance of covalent interactionsat the molecule/metal interface (effectivelyreducing the Schottky barriers and per-mitting more control of the molecular levelsby the applied voltage) has been clarified.13

In nanotubes, true ohmic junctions (for p-type transport) apparently can be pre-pared14 using palladium as the electrodematerial.3. The importance of molecular recognitionbehavior in the construction of junctionsand in preparing both adlayers and specificquantum dot junctions is now understood.4. Dynamical stereochemistry of moleculeshas been used as the basis for both model-ing15 and experimental demonstration16 ofmemory and switching applications. Thisstereochemical variation is one of theunique properties of molecules that moststrongly differentiates molecular from moretraditional semiconductor electronics.5. Acomparison has been made of transportthrough junctions containing single mole-cules with transport through those based onmolecular adlayer films; once again, theresults highlight the crucial role that con-tacts play in molecular junction transport.In particular, a substantial reduction in con-tact resistance has been demonstratedusing covalent interactions at carbon elec-trodes;17 less effective mixing occurs throughLewis interactions at metal/thiol or iso-cyano links.

6. The importance of the electrostatic po-tential and its control has been demon-strated clearly, both in measurements andmodels.7. Gating due to molecular geometricchange is going to be general at ambienttemperature, simply because molecules domove at room temperature. Such gating cancompletely dominate the measured I–Vbehavior. If controlled, such gating may leadto interesting device applications,15,16,18

both in two-electrode and three-electrodeconfigurations.8. Specific device applications, both in simplemolecular transport junctions and in suchareas as molecular sensing and molecularoptoelectronics, have been widespread andimpressive. The great sensitivity of trans-port through molecular junctions to theelectrostatic potential suggests that sens-ing using transport modification is effec-tive and powerful.

Elegant recent work by Ho and his col-laborators,19 discussed in the article byHersam and Reifenberger, demonstratesthe capability of current techniques to as-semble junctions on an atom-by-atom basisand then characterize the local densities ofstates using transport perpendicular to themolecular axis. Extending this understand-ing to the charge transport behavior, andproviding comparably detailed structure/function relationships, represents perhaps

the greatest challenge to our understand-ing of molecular junctions.

CNT and Molecular BehaviorsDeveloping a further understanding of the

electronic characteristics and fabrication ofmolecular- and CNT-based junctions anddevices presents unique challenges.

The electronic properties of CNTs havebeen studied by scanning probe micros-copies and optical spectroscopies. Figure 1shows a CNTFET in which the lithograph-ically defined 1.2 �m channel length islarge enough for a conductive AFM probeto measure the channel length dependenceof the device characteristics, electrostatics,and contacts.20 CNTs are being aggres-sively explored to understand the charac-teristics of different species of nanotubes,their contact physics, and environmentalinfluences, and to engineer high-qualityCNT devices.

Present synthesis routes typically preparebatches of CNTs containing both semicon-ducting and metallic tubes (determinedby their chirality) with a range of diame-ters. Work has proceeded on functionaliz-ing CNTs with organic molecules in an effortto solubilize them, to separate differentspecies of CNTs, to place the tubes on sur-faces, and to electronically manipulate ordope them. While considerable progresshas been made in regard to chemical ma-nipulation and synthetic routes, processingto separate and position CNTs presentsmajor challenges to the integration andfabrication of CNT junctions and devices.

In contrast to CNTs, while molecules canbe synthesized and self-assembled from so-lution onto surfaces, the nanometer lengthscale of molecules makes the study anddevice fabrication of molecular junctions very challenging. SPM (see Hersam andReifenberger) offers the resolution and con-trol to characterize single molecules andmolecular monolayers on surfaces. SPMhas been used to probe the dynamics ofmolecular conductance on surfaces. De-rivatives of 2,5-di(phenylethynyl-4’,4”-thio)benzene (the nitro/amine derivativeshowed negative differential resistance invertical structures)21 and, more recently,alkanedithiol molecules (Figure 2)22 showstochastic switching. Researchers are usingSPM to close in on the origin of conduc-tance modulations of molecules on surfaces.Both recent observation of switching inalkanedithiols and computations of theenergetics and transport properties of dif-fering junction geometries suggest thatthe thiol-Au contact may be responsiblefor the observed fluctuations.

While SPM provides well-controlled junc-tions and measurements of electron den-sity and density of states, the junctions

Figure 1. (a) A carbon nanotube transistor (channel length, 1.2 �m; nanotube diameter,2 nm; t � gate oxide thickness; Vg is the applied gate voltage). A conductive atomic forcemicroscope (AFM) probe is positioned over the device to study the channel length dependenceof the device characteristics and the electrostatics and contacts of the device. Electrodes,marked (1) and (2), and the AFM tip (3) can serve as the voltage source, current probe, orvoltage probe in the measurements. (b) The measured channel-length-dependentconductance (in units of the quantum conductance), as a function of Vg, where x is thechannel length, Vtip � 100 mV, and t � 500 nm.20 VSD is the source–drain voltage.Similarly (inset), the characteristics of a second device are plotted on a log scale, where t � 200 nm. (Reprinted with permission from Reference 20.)



consist of one chemical contact and one tun-neling contact, so SPM does not directlymeasure junction conductance. Mechani-cally controllable break (MCB) junctions, asshown in Figure 3,23 have been used9 to maketwo chemical contacts to a single moleculeand measure transfer in molecular junctions.MCB junctions are formed using piezo-electrics to push on the fabricated metalstructure, controllably breaking the junction,and to vary the separation between the metal tips. The I–V characteristics of somemolecular MCB junctions are similar totheoretical calculations and are molecule-specific. The I–V characteristics are stablefor many voltage sweeps, but are unstableover longer times, as seen by the differentfeatures in the two sets of characteristicscollected on the same sample. In effect, thetwo sets of characteristics represent differ-ent molecular junctions, as the junction isbroken and remade at the contacts, creatinga different spectral density for the mole-cule in the junction.

Scanning probe microscopy and MCBjunctions cannot be integrated into devicegeometries. Two-terminal vertical sandwichstructures, as shown in Figure 4, were firstused to fabricate molecular monolayerjunctions and can be fabricated in a crossbargeometry. Monolayer junctions are pre-pared by assembling the molecules onto abottom electrode and depositing a top metalelectrode, where in principle the mono-layer height defines the electrode separa-tion. Molecular monolayer junctions in thisgeometry have shown low leakage for in-sulating molecules, rectification in donor–acceptor molecules (Figure 4),23 and negativedifferential resistance/switching in someconjugated molecules. The clear drawbackof vertical sandwich structures is that thetop metal electrode is deposited on the molecules and may partially or completelypenetrate or react with the monolayer, de-pending on the choice of metal. For metal–molecule–metal structures, this often resultsin junctions with I–V characteristics thatare shorted or that have been misinter-preted. For metal–molecule–semiconductorjunctions, length-dependent electrical char-acteristics have been measured for denselypacked alkyl monolayers, suggesting thatthe monolayer coverage is sufficiently denseto mask direct metal-Si pathways.24

Concern over top metal deposition andthe limitation of providing only two ter-minal measurements has led to the pursuitof lateral junction geometries. Recently,electromigration has been used25 to openup �1 nm spacing at the constriction inmetal lines, as shown in Figure 5. Thesemiconductor support provides a third,although distant (relative to the source–drain spacing) and therefore weakly cou-

pled, gate electrode. Organometallic andorganic molecules and small metal clustershave been measured in these junctions.Low-temperature I–V characteristics arehighly non-ohmic, consistent with Coulombblockade (conductance gaps dominatedby single-particle charging energy), andKondo resonance (zero bias conductance,believed to originate from the spin and orbital degrees of freedom in the metalcenters). The junctions formed by electro-migration or electrochemistry provide anew platform with �1 nm gaps for study-ing the electrical behavior of single small-molecule systems.

Instead of pushing the dimensions ofthe channels to �1 nm separations, recentwork26 has used e-beam lithography toprepare reproducible junctions and chem-istry to bridge the separation between the electrodes, as shown in Figure 6. This

Figure 3. (a) Scanning electronmicrograph of a mechanically controllablebreak junction used to measure theconductance of 1,4-bis(2 -para-mercaptophenyl)-ethinyl-2-acetyl-amino-5-nitro-benzene. (b) Chemical structure.(c), (d) The I–V characteristics (rightaxis) and the numerically differentiateddI/dU (left axis) values are shown for(c) a junction repeatedly scanned and(d) a subsequent junction afterreconfiguration of the moleculesbetween the metal electrodes.(Reprinted with permission fromReference 23.)

�

Figure 2. (a), (b) Scanning probemicrographs of alkanedithiols insertedin an alkanethiol monolayer assembledon Au (c).The size bar is 10 nm.Stochastic switching is observed as theoctanedithiols blink on (a) and off (b).(Reprinted with permission fromReference 22.)



approach also allows a gate to be placed inproximity to the junction, allowing pene-tration of the gate field in the channel. Thisapproach was demonstrated for metal–metal coordination compounds by tem-plating the assembly of the compoundsoff the electrodes, using thiol chemistry,and adding molecules layer-by-layer tobridge the channel. I–V characteristicsshow consistent reversible traces at lowvoltage and a single, irreversible negativedifferential resistance at high voltage.

These examples illustrate the many ap-proaches being pursued to understandmolecular junctions and highlight someimportant future directions. Thiol chem-istry on Au or carboxylic acids and silaneson SiO2 have been the most heavily stud-ied systems, largely for historical reasons.Many studies suggest that instability in the Au–thiol contact may give rise to observed I–V characteristics, pointing tothe importance of controlling the self-assembly using the many functionalitiesprovided by chemistry. Nearly allschemes to create molecular junctions lackinformation regarding the geometry of themolecule(s) in the junctions, making it almost impossible to correlate the molecule–junction structure with its I–Vcharacteristics. Overcoming this limitationrequires new tools to address the molecular-scale geometry, as well as continued im-provement and new ideas to fabricatereproducible and reliable molecular-scalejunctions.

The fields of molecular and carbon nano-tube junctions, while presenting differentresearch challenges, are yielding an excit-ing fundamental understanding of their

Figure 5. (a) Schematic illustration and enlarged scanning electron micrograph (inset) of a transistor structure (channel length, �1 nm) formedby electromigration of Au electrodes deposited on a 3 nm Al2O3 gate dielectric with an Al gate. (b) Differential conductance ranges from zero(dark red) to 1.55 e2/h (bright yellow) as a function of bias and gate voltages. I and II indicate two conductance gap regions, and the diagramsillustrate the corresponding charge and spin states of the divanadium molecule in each region. (Reprinted with permission from Reference 25.)

Figure 4. (a) Schematic illustration of a two-terminal vertically fabricated junction. (b) I–Vcharacteristics showing rectification of a thiophene-terminated oct-7-en-1-trichlorosilaneself-assembled monolayer (triangles), and phenyl-terminated (squares) and thiophene-terminated(diamonds) heptadec-16-en-1-trichlorosilane self-assembled monolayers, in a molecularjunction between Al and n+ Si electrodes. The top graph shows the graphical determinationof the threshold voltage.VT is taken as the intercept of the linear extrapolation of the I–Vcurve and the zero of the y axis. (Reprinted with permission from Reference 24.)



Cherie R. Kagan, GuestEditor for this issue ofMRS Bulletin, is a re-search scientist in Physical Sciences at the IBM T.J. Watson Research Center. Shehas been with IBM since 1998, working on organic and organic–inorganic hybrid materials forthin-film devices. More recently, she hasfocused her work onmolecular assembly

and molecular-scale electronics.

Kagan received a BSEdegree in materials sci-ence and engineeringand a BA degree inmathematics from theUniversity of Pennsyl-vania in 1991. Sheearned her PhD degreein electronic materials atthe Massachusetts Insti-tute of Technology in1996. While at MIT, sheinvestigated the opticaland optoelectronic prop-

erties of nanocrystal assemblies. She thenworked as a postdoc-toral member of techni-cal staff at LucentTechnologies, Bell Labs,building a scanning con-focal Raman microscopeto study holographicphotopolymers.

Kagan can be reachedat the IBM Corporation,1101 Kitchawan Road,Yorktown Heights, NY10598, USA; and by e-mailat [email protected].

Mark A. Ratner, GuestEditor for this issue of

MRS Bulletin, is a mate-rials chemist and the

properties. While the science of these systems must come first, molecular andCNT junctions promise intriguing future applications.

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Figure 6. (a) Layer-by-layer assembly ofmetal–metal bonded coordinationcompounds templated from source anddrain electrodes. (b) Schematicillustration of a metal–metal bondedcoordination compound spanning Auelectrodes. (c) Measured I–Vcharacteristics after the assemblybridges the �80 nm channel. Arrowsindicate the measured current for the upand down swing in applied voltage.(Reprinted with permission fromReference 26.)

Cherie R. Kagan Mark A. Ratner



Morrison Professor ofChemistry at North-western University. Hiswork focuses on the in-terplay between molec-ular structure andmolecular properties, including molecularelectronics and optoelec-tronics, molecular sys-tems design, andbiomolecular behavior,as well quantum andclassical methodologiesfor understanding andpredicting molecularstructure and response.The major focus of hisresearch for the lastthree decades has beenthe understanding ofcharge transfer andcharge transportprocesses based on mo-lecular structures.

Ratner’s professionalhistory includes under-graduate work at Harvard University, graduate work at North-western, postdoctoralwork at the Universityof Aarhus and the Techni-cal University of Munich,and faculty positions at New York University

and Northwestern. Hehas active internationalcollaborations, particu-larly in Denmark, Israel,and the Netherlands. He has been awardedthe Feynman Prize inNanotechnology fromthe Foresight Instituteand the Irving Langmuir Award inChemical Physics fromthe American ChemicalSociety and is a memberof the National Acad-emy of Sciences, theAmerican Academy of Arts and Sciences,and the InternationalAcademy of QuantumMolecular Sciences.

Ratner can reached bye-mail at [email protected].

David L. Allara is a pro-fessor of materials scienceand chemistry at thePennsylvania State Uni-versity. His scientificprogram is focused onsurface chemistry andmaterials physics involv-ing the preparation,properties, and charac-terization of molecular

and polymeric thin films,modified surfaces, ma-terials interfaces, and self-assembly of nano-materials. His currentwork includes molecularelectronics, quantumcomputing, bio/chemsensors, and biointerfaces.

He received his BS(1959) and PhD (1964)degrees in chemistry(1964) from the Univer-sity of California atBerkeley and UCLA, re-spectively. After a 17-year career at AT&T BellLaboratories, where hewas a DistinguishedMember of the TechnicalStaff, he joined the facultyat Penn State in 1987.He is a AAAS fellowand the recipient of theAmerican Chemical So-ciety SpectroanalyticalChemistry Award(1998), the ACS Adam-son Award for distin-guished achievementsin surface chemistry(2003), and an honorarydoctorate of sciencefrom Lingkoping Uni-versity, Sweden (2003).His work in molecular

self-assembly is widelyrecognized, with morethan 4500 cites for the fivemost-cited publications.

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

Phaedon Avouris is anIBM Fellow and man-ager of Nanometer-ScaleScience and Technologyat the IBM T.J. WatsonResearch Center. He re-ceived his BS degree fromthe Aristotelian Univer-sity in Greece, and hisPhD degree in physicalchemistry from Michi-gan State University in1974. After postdoctoralwork at UCLA and AT&TBell Laboratories, hejoined the Research Di-vision of IBM in 1978.

His research interestshave ranged from laserstudies of fast phenom-ena to surface physicsand chemistry, scanningtunneling microscopy,and atom manipulation.His current research isfocused on experimentaland theoretical studiesof the electrical proper-

ties and transport mech-anisms of carbon nan-otubes, molecules, andother nanostructures.This work includes thedesign, fabrication, andstudy of model carbonnanotube and molecularelectronic devices andcircuits.

Avouris has published300 scientific papers. Heis a fellow of the Ameri-can Academy of Artsand Sciences, the Ameri-can Physical Society, theAmerican Association forthe Advancement of Sci-ence, the American Vac-uum Society, and theNew York Academy ofSciences. He received theIrving Langmuir Prizefrom the AmericanPhysical Society, theMedard W. WelchAward from the Ameri-can Vacuum Society, theFeynman Prize for Mol-ecular Nanotechnology,the ACSIN NanosciencePrize, the DistinguishedAlumnus Award fromMichigan State Univer-sity, and a number ofIBM Outstanding Tech-

David L. Allara Phaedon Avouris Prashant S. Damle Supriyo Datta Avik W. Ghosh

Mark C. Hersam James G. Kushmerick Thomas E. Mallouk Abraham NitzanTheresa S. Mayer



nical Achievementawards. He is co-editorof the Springer-Verlagbook series onnanoscience and cur-rently serves on the advisory editorialboards of Nano Letters,Nanotechnology, the International Journal of Nanoscience, the Journal of Computationaland TheoreticalNanoscience, Surface Review and Letters, andthe Journal of ElectronSpectroscopy.

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

Prashant S. Damle iscurrently working onthe development of 90 nm Flash memorytechnology at IntelCorp. in Santa Clara,Calif. He received aBTech degree in electricalengineering in 1997 fromthe Indian Institute ofTechnology, Bombay,and MS and PhD degreesfrom Purdue Universityin 1999 and 2003, respec-tively. His PhD researchfocus was on the model-ing of nonequilibrium electron transport innanoscale electronic de-vices such as ballisticnano-MOSFETs andatomic and molecularwires.

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

Supriyo Datta is theThomas Duncan Distin-guished Professor in theSchool of Electrical andComputer Engineeringat Purdue University,where he has been on the faculty since 1981.His current research in-terests are centered onthe physics of nano-structures, includingmolecular electronics,nanoscale devicephysics, spin electronics,and mesoscopic super-conductivity.

Datta earned a BTechdegree at the Indian In-stitute of Technology,Kharagpur, in 1975 andhis PhD degree from theUniversity of Illinois atUrbana-Champaign in1979. He received anNSF Presidential YoungInvestigator Award andan IEEE Centennial Keyto the Future Award in1984, the Frederick Em-mons Terman Awardfrom the ASEE in 1994,and shared the SRCTechnical ExcellenceAward (2001) and theIEEE Cledo BrunettiAward (2002) with MarkLundstrom. He is a fel-low of the IEEE, theAmerican Physical Soci-ety, and the Institute ofPhysics and has au-thored three books, Sur-face Acoustic WaveDevices, Quantum Phe-nomena, and ElectronicTransport in MesoscopicSystems.

Datta can be reachedby e-mail at [email protected] and URLhttp://dynamo.ecn.purdue.edu/~datta.

Avik W. Ghosh is a re-search scientist at Pur-due University, wherehe works on electrontransport in nanoscaledevices, includingatomic and molecularwires, nanoscale siliconMOSFETs, hybrid siliconmolecular devices, andcarbon nanotubes.Among his other re-search activities are ul-trafast opticalphenomena in semicon-ductor heterostructuresand noise-inducedtransport in Brownianenvironments. Ghosh re-ceived his MS degree inphysics from the IndianInstitute of Technology,Kanpur, in 1994 and hisPhD degree in physicsfrom the Ohio State Uni-versity in 1999, where hereceived the Ohio StateUniversity Presidential

Fellowship. He thenjoined Purdue Univer-sity as a postdoctoral research fellow in Elec-trical Engineering andwas appointed to hiscurrent position in 2001.

Ghosh can be reachedby e-mail at [email protected] and URLhttp://dynamo.ecn.purdue.edu/~ghosha.

Mark C. Hersam is anassistant professor in theDepartment of MaterialsScience and Engineeringat Northwestern Uni-versity. His research in-terests includesingle-molecule devicesand sensors, nanofabri-cation, scanning probemicroscopy and spec-troscopy, semiconductorsurfaces, and carbonnanotubes. He holds aBS degree in electricalengineering from theUniversity of Illinois atUrbana-Champaign; aMPhil degree in micro-electronic engineeringand semiconductorphysics from the Uni-versity of Cambridge,completed under aBritish Marshall scholar-ship; and a PhD degreein electrical engineeringfrom UIUC, completedwith the support of aNational Science Foun-dation Graduate Fellow-ship and an IBMDistinguished Fellowship.

Before joining North-western, Hersamworked for ArgonneNational Laboratoryand the IBM T.J. WatsonResearch Center, wherehe performed researchon surface acousticwave sensors and electrical properties ofcarbon nanotubes, respectively.

Since joining North-western in 2000, Hersamhas been named anArnold and Mabel Beck-man Young Investigator,a National ScienceFoundation CAREER

Award recipient, and aJunior Fellow of theSearle Center for Teach-ing Excellence. He is amember of the Ameri-can Vacuum Society, the American PhysicalSociety, the AmericanChemical Society, theMaterials Research Society, the AmericanSociety of EngineeringEducation, and the Institute of Electricaland Electronics Engineers.

Hersam can bereached by e-mail at [email protected] and atURL www.hersam-group.northwestern.edu.

James G. Kushmerick isa staff scientist at theU.S. Naval ResearchLaboratory in the Centerfor Bio/Molecular Sci-ence and Engineering.His current research isfocused on nanoscaleelectronics, encompass-ing both molecular andbio-organic electronics.Kushmerick earned hisPhD degree in physicalchemistry from thePennsylvania State Uni-versity. Before taking his current position at the NRL, he spent twoyears as a postdoctoralfellow at Sandia Na-tional Laboratories inthe Biomolecular Materials and InterfacesDepartment.

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

Thomas E. Mallouk isthe DuPont Professor ofMaterials Chemistry atthe Pennsylvania StateUniversity. He is bestknown for his work oninorganic self-assemblyand the chemistry oflayered, porous, andnanoscale materials. Hisresearch has focused onapplications of inorganicmaterials to differentchemical problems, in-

cluding nanoscale andmolecular electronics,fuel-cell electrochem-istry, photochemical energy conversion,chemical sensing, andenvironmental chem-istry. Mallouk receivedan ScB degree fromBrown University. Hewas a graduate studentat the University of Cali-fornia, Berkeley, and apostdoctoral fellow atMIT. In 1985, he joinedthe chemistry faculty atthe University of Texasat Austin, and moved toPenn State in 1993.

Mallouk is the authorof about 220 scientificpublications and hasalso edited four bookson chemical sensing andsolid-state chemistry. Heis currently associate editor of the Journal ofthe American ChemicalSociety.

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

Theresa S. Mayer is anassociate professor inthe Department of Elec-trical Engineering at thePennsylvania State Uni-versity. Her current re-search interests are innanoscale device fabri-cation, integration, andcharacterization for ap-plications in logic, mem-ory, and sensing circuits.The primary focus ofthese activities is study-ing molecular electronicand semiconductornanowire-based elec-tronic devices and metallo-dielectric photonic-bandgap materials and devices.

Mayer received herBS degree in electricalengineering from Vir-ginia Tech (1988) andher MS (1989) and PhD(1993) degrees in electri-cal engineering fromPurdue University,where she was a Kodakfellow. She is the recipi-ent of a National Science

Foundation CAREERAward and the PennState OutstandingTeaching Award. She iscurrently serving as vicechair of the IEEE DeviceResearch Conference,the Gordon ResearchConference on Nano-structure Fabrication,and the UEF MolecularElectronics Conference.

Mayer can be reachedby e-mail [email protected].

Abraham Nitzan hasbeen a professor ofchemistry at Tel AvivUniversity since 1982and also served as chair-man of the School ofChemistry and dean ofthe Faculty of Science.Nitzan’s research is inthe field of chemical dy-namics and transportphenomena in con-densed phases. His recentwork has focused onsolvation and transport

of ions in simple andcomplex solvents and onelectron dynamics andtransport at interfaces.Nitzan received his BSc degree in chemistryin 1964, his MSc degreein physical chemistry in 1966 (both from theHebrew University),and his PhD degree in1972 from TAU. He held a postdoctoral Ful-bright fellowship at MIT, was a research

associate at the Univer-sity of Chicago, andtaught at NorthwesternUniversity before joiningthe faculty at TAU.

He has received theKolthoff Prize, the Humboldt Award, andthe Israel Chemical Soci-ety Prize. He is a fellow of the American Physical Society and the Ameri-can Association for the Advancement of Science.

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

Ronald G. Reifenbergeris a professor of physics atPurdue University. He re-ceived his BSc degreefrom John Carroll Uni-versity and his PhD de-gree in physics from theUniversity of Chicago.

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



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