Single-Molecule Electronics: An Introduction to Synthesis, Measurement and Theory PDF
Preview Single-Molecule Electronics: An Introduction to Synthesis, Measurement and Theory
Manabu Kiguchi Editor Single- Molecule Electronics An Introduction to Synthesis, Measurement and Theory Single-Molecule Electronics Manabu Kiguchi Editor Single-Molecule Electronics An Introduction to Synthesis, Measurement and Theory 123 Editor ManabuKiguchi DepartmentofChemistry GraduateSchoolofScience andEngineering TokyoInstituteofTechnology Tokyo Japan ISBN978-981-10-0723-1 ISBN978-981-10-0724-8 (eBook) DOI10.1007/978-981-10-0724-8 LibraryofCongressControlNumber:2016939969 ©SpringerScience+BusinessMediaSingapore2016 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof thematerialisconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation, broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionorinformation storageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilarmethodology nowknownorhereafterdeveloped. Theuseofgeneraldescriptivenames,registerednames,trademarks,servicemarks,etc.inthispublication doesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevant protectivelawsandregulationsandthereforefreeforgeneraluse. Thepublisher,theauthorsandtheeditorsaresafetoassumethattheadviceandinformationinthisbook arebelievedtobetrueandaccurateatthedateofpublication.Neitherthepublishernortheauthorsor theeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinorforany errorsoromissionsthatmayhavebeenmade. Printedonacid-freepaper ThisSpringerimprintispublishedbySpringerNature TheregisteredcompanyisSpringerScience+BusinessMediaSingaporePteLtd. Preface Governingindividualmoleculesandtheirutilizationisoneofthescientificdreams of our age. The realization of this dream could open the door to a miniaturiza- tion revolution in electronics. Molecular electronics pursues the use of individ- ual molecules as fundamental electronic components. The inherent properties of molecules such as nano-size, low cost, scalability, and self-assembly are seen by many as a perfect complement to conventional silicon electronics. In addition, molecules can be designed with the desired functionality and prepared using common elements such as carbon, nitrogen and oxygen, without the need for rare earth metals. Understanding and governing the charge-transfer phenomena occurring at the molecular level could revolutionize a number of related fields, includingenergyharvesting,data storage,batteries,sensing devices,and displays. Forthesereasons,molecule-basedelectronicshascapturedtheattentionofabroad crosssectionofthescientificcommunity. Molecular electronics is an interdisciplinary science that requires researchers fromdifferentbackgroundstoworktogether.Thiscooperationincludesthedesign ofmoleculeswiththedesiredfunctionality,themeasurementoftheelectronicand structuralpropertiesofindividualmolecules,andtheintegrationofmoleculesinto operational devices. The feedback loop between molecular design, measurement, andultimatelydevicefabrication,iscrucialforthedevelopmentofthefield. The workhorse of molecular electronics is the molecular junction, where a single or few molecules are suspended across the gap between two metal elec- trodes (Fig. 1). The interaction between molecule and metal gives rise to novel functionality.A clear example of the importance of one metal–moleculeinterface is heterogeneous catalysis. Molecular junctions, featuring two metal–molecule interfacesareexceptionalsystemswherenovelphenomenacantakeplace.Hence, molecular junctions can be regarded as new materials that include the suspended molecule and both metal electrodes. The study of these systems can lead to the developmentofnewscientificfields. Thebroadnessofthefield,resultingfromthevastamountofworkdoneinrecent years, makes it impossible to include every point of view in a single book. Here, we focuson the basic science froma chemistrypointof view.Thisbookcontains v vi Preface Fig.1 Singlemolecular junction thecontributionofspecialistsintheareasofdesignandsynthesis,single-molecule measurements, and charge-transfer theory. In addition, Prof. Jan van Ruitenbeek, one of the molecular electronics pioneers, discusses the state of the art as well as the future development of functioning devices based on molecular electronics technology. We would like to thank Springer for the opportunity to prepare this book, especially Dr. Shinichi Koizumi and Ms. Risa Takizawa. We would also like to expressour deep gratitude to each of the authorswho have contributedwith their time and outstanding knowledge to make this book possible. Also, thanks to Dr. Santiago Marqués-González for the helpful discussions during the preparation of thebook.Finally,wehopethatthereadersofthisbookwillfinditbothusefuland delightful. Tokyo,Japan ManabuKiguchi January2016 Contents 1 MolecularElectronics:ABriefOverviewoftheStatusoftheField ... 1 JanM.vanRuitenbeek 2 Methods to Determine Electrical Conductance ofSingle-MoleculeJunctions ............................................... 25 RyoYamada 3 CharacterizationoftheSingleMolecularJunction...................... 61 ManabuKiguchiandShintaroFujii 4 MolecularWires:AnOverviewofthe Building Blocks ofMolecularElectronics .................................................... 87 PaulJ.LowandSantiagoMarqués-González 5 InsulatedOligothiophenes .................................................. 117 YutakaIe 6 SynthesisandPhysicalPropertiesofThree-Dimensionally InsulatedMolecularWires.................................................. 141 JunTerao 7 OrbitalRuleforElectronTransportofMolecularJunctions........... 165 TomofumiTada 8 Theoretical Aspects of Quantum Transport andComputationalModelingofMolecularElectronicDevice ......... 191 HisaoNakamura 9 Single-MoleculeSequencing ................................................ 217 MasateruTaniguchi vii Chapter 1 Molecular Electronics: A Brief Overview of the Status of the Field JanM.vanRuitenbeek Abstract The developmentsin the field of molecularelectronicshave seen many successes and many setbacks, but the field continues to inspire scientists around the world, now more than ever. The interest is, certainly, for a large part in the fundamental issues: molecules as conducting elements bring together questions from various fields of study and lead to profound new questions. However, this interest alone would not suffice to explain the large efforts in research. Indeed, the prospects of developing electronics with better performance, higher density, andnewfunctionalityarewhatmotivatesmostoftheresearch.Inthisintroductory chapter,Iwillattempttotakestockofthefield,toevaluatewhathasbeenachieved, andtoidentifytheinterestingchallengesthatlieahead. Keywords Molecularelectronics • Organicelectronics • Applicationsof molec- ularelectronics • Fundamentalquestionsofmolecularelectronics 1.1 DefinitionofMolecular Electronics Before we do so, we need to specify what we mean by the words molecular electronics.Polymers[1]andorganicmolecularcompounds[2]havebeenstudied widelyforapplicationsinelectronics.Polymerandprintableelectronicsarealready commercially available, and organic compounds are found in many commercial organic light-emitting diode (OLED) displays. Plastic photovoltaic cells are in productionandarecontinuouslyimprovinginperformance.Organiclayerscanbe spincoatedordropcasted,wheretheorganicmatterinthesestructuresisrandomly packed in the form of thin films, usually in contact with a metallic electrode at the top and bottom of the layers. The thickness of these films is many times the moleculardiameter,sothatonlyasmallfractionofthemoleculesisincontactwith theelectrodes. J.M.vanRuitenbeek((cid:2)) Huygens-KamerlinghOnnesLaboratory,LeidenUniversity,NielsBohrweg2,2333CALeiden, TheNetherlands e-mail:[email protected] ©SpringerScience+BusinessMediaSingapore2016 1 M.Kiguchi(ed.),Single-MoleculeElectronics,DOI10.1007/978-981-10-0724-8_1 2 J.M.vanRuitenbeek We willrefer to thiswide field ofstudy andtechnologyasorganicelectronics. The applications mentioned above illustrate the relevance of these developments, butthereisaprospectformoreadvancedexploitationofthepropertiesofmolecular building blocks when we connect just a single molecule, or a self-assembled single layer of molecules, between metal electrodes. This adds serious technical challenges,butprovidesaccesstothefullquantummechanicsofelectrontransport atthe molecularscale, evenat roomtemperature.Thisis expectedto providenew opportunities,e.g.,intermsoffunctionalityandminiaturizationofelectronics,and opensupnewareasofstudyofelectrontransportattheinterfacebetweenchemistry andphysics. In order to specify this latter field of study, we will call this molecular elec- tronics,orsingle-moleculeelectronics,whichwe considerasa subfieldof organic electronics.Molecularelectronicsisconcernedwithdeviceswhichhaveeachofthe moleculesconnectedtoelectrodesatboththeirends.Thiscanbeeitherinasingle- moleculeconfiguration(foracomprehensivereview,see[3])orinlargeassemblies of molecules, i.e., self-assembled monolayers (SAMs) [4]. In such SAMs, each moleculeisconnectedtoboththetopandbottomelectrodesplacedaboveandbelow the layer. In contrast to the many concrete applications already found in organic electronics, the subfield of molecular electronics is still in an earlier, exploratory phase. Although first niche applications are entering the market here, for its full potentialtobedeveloped,alotofresearchisstillneeded,asIwillarguebelow. 1.2 ABrief History 1.2.1 Molecular Monolayers:Langmuir-BlodgettTechnique As early as 1974, ideas were discussed of using organic molecules as electronic circuit elements. The theoretical ideas outlined in the seminal paper by Aviram and Ratner [5] could not be tested in experiments on individual molecules until muchlater,becausethetechnologyhadnotyetbeendeveloped.Ontheotherhand, many steps had already been taken for studying the electrical transport properties ofmonolayersofmolecules.BasedonearlierworkbyLordRayleighandbyAgnes Pockels, Langmuir [6] and Blodgett [7, 8] had shown in the 1920s and 1930s that it is possible to form ordered monolayers of amphiphilic molecules at the liquid-airinterfaceandthattheselayerscanbehomogeneouslytransferredtocover solidsurfaces.BythisLangmuir-Blodgett(LB)technique,MannandKuhn[9]first succeededin reproduciblymeasuringthe electricalresistance of a monolayerof a fattyacidontopofaluminumbottomcontacts.Thetopcontactwasapplied,either intheformofaliquidHgelectrodeoritwasformedbyevaporationanddeposition ofmetalssuchasAu,Pb,andAl. Aviram and Ratner had considered a (cid:2) bridged donor-acceptormolecule, with TTF (tetrathiafulvalene) as the donor and TCNQ (7,7,8,8-tetracyano-p-quino-
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