Introduction to Scanning Tunneling Microscopy

1 Introduction to ScanningTunneling MicroscopySecond EditionC. Julian ChenDepartment of Applied Physics and Applied MathematicsColumbia University, New YorkOXFORDUNIVERSITY PRESS istm: prelims 2007/7/19 17:54 page ii #2 MONOGRAPHS ON THE PHYSICS AND CHEMISTRY OF MATERIALST heory of dielectricsH. FrohlichStrong solids (Third edition)A. Kelly and N. H. MacmillanOptical spectroscopy of inorganic solidsB. Henderson and G. F. ImbuschQuantum theory of collective phenomenaG. L. SewellPrinciples of dielectricsB. K. P. ScaifeSurface analytical techniquesJ. C. Rivi`ereBasic theory of surface statesSydney G. Davison and Maria SteslickaAcoustic microscopyG. A. D. BriggsLight scattering: principles and developmentW. BrownQuasicrystals: a primer (Second edition)C. JanotInterfaces in crystalline materialsA.

2 P. Sutton and R. W. BalluffiAtom probe field ion microscopyM. K. Miller, A. Cerezo, M. G. Hetherington, andG. D. W. SmithRare-earth iron permanent magnetsJ. M. D. CoeyStatistical physics of fracture and breakdown in disordered systemsB. K. Chakrabartiand L. G. BenguiguiElectronic processes in organic crystals and polymers (Second edition)M. Pope andC. E. SwenbergNMR imaging of materialsB. Bl umichStatistical mechanics of solidsL. A. GirifalcoExperimental techniques in low-temperature physics (Fourth edition)G. K. White andP. J. MeesonHigh-resolution electron Microscopy (Third edition)J. C. H. SpenceHigh-energy electron diffraction and Peng, S. L. Dudarev, andM. J. WhelanThe physics of lyotropic liquid crystals: phase transitions and structural propertiesA. M. Figueiredo Neto and S.

3 SalinasInstabilities and self-organization in materials, Volume 1: Fundamentals of nanoscience,Volume 2: Applications in materials design and nanotechnologyN. Ghoniem andD. WalgraefIntroduction to Scanning Tunneling Microscopy (Second edition)C. J. ChenPreface to the Second EditionIn a 1959 speech entitledThere s Plenty of Room at the Bottom[1], RichardFeynman invited scientists to a new field of research: to see individual atomsdistinctly, and to arrange the atoms the way we want. Feynman envisionedthat, by achieving those goals, one could synthesize any chemical substancethat the chemist writes down, resolve many central and fundamental prob-lems in biology at the molecular level, and dramatically increase the densityof information storage. Some 20 years later, those goals began to be achievedthrough the invention and application of the Scanning Tunneling microscope(STM) [2, 3] and the atomic force microscope (AFM) [4].

4 The inventors ofSTM, two physicists at IBM Research Division, Gerd Binnig and HeinrichRohrer, shared the 1986 Nobel Prize in physics [5, 6].At that time, I was fortunate to be in the Department of Physical Sci-ences of IBM Research Division, and had the opportunity to design, build,and run those fascinating instruments. Partially based on my personal ex-perience and understanding, in 1993, the first edition of this book was pub-lished [7]. In the decade following, Feynman s foresight has grown into avast field of research, nanoscience and nanotechnology. As a result, tremen-dous advances have been achieved in the understanding of the basic physicsas well as instrument design and operation of STM and AFM. It is time topublish a second edition to include those recent advances, and to satisfy theurgent need for an updated, unified, accurate, and pedagogically assessabletextbook and reference book on STM and the years of 1994 to 2003, I was concentrating on the researchof human voice and languages, which were my favorite subjects ever sincemy college years.

5 And I received more corporate recognition than for mybasic research in physics [8]. However, the news about the advancements inSTM and AFM constantly called me to come back to nanoscience and nan-otechnology. In December 2003, I received a kind invitation from ProfessorRoland Wiesendanger, the Director of the Institute of Applied Physics atHamburg University, to become a guest scientist. This is one of the largestand most productive centers of STM and AFM research, especially in spin-polarized STM and non-contact AFM. And for the first time in my life,I could concentrate 100% of my time on nanoscience and nanotechnologyresearch. In the summer semester of 2005, in a graduate-level course innanostructure physics jointly given to the Department of Physics and theDepartment of Chemistry at Hamburg University, Professor Roland Wiesen-danger lectured the analyses of various nanostructures, and I lecturedtheprinciples and instrumentation of STM and AFM.

6 The lecture notes on STMand AFM then became the blueprint of the second edition of the STM are some examples of the additions to the second edition:Atomic force Microscopy , with a refined frequency-modulation mode,iiChen: Introduction to Scanning Tunneling Microscopyhas achieved true atomic resolution in theattractive atomic force regime,often referred to as thenon-contact AFM. In some cases, its resolutionhas even surpassed that of STM. The observed bias-dependence of atomicforces provides information about the details of electronic structure. Thisnew technique enables atomic-scale imaging and characterization not onlyfor conductors, but also for breakthrough in spin-polarized STM has enabled the observa-tion of local magnetic phenomena down to atomic scale. Such advancementwas to drive the development of nanomagnetism, which would have deepimpact on the technological applications of electron Tunneling spectroscopy (IETS), initially discovered inmetal-insulator-metal Tunneling junctions to observe vibrational frequen-cies of embedded molecules, was advanced to STM junctions, enablingtheobservation of vibrational states ofindividual molecules.

7 The successfuldemonstration of STM-IETS elevated the field of single-molecule chemistryto an unprecedented the time that the first edition was written, atom manipulation wasstill a highly specialized personal art. In the later years, the underlyingphysics has gradually been discovered, and the atom-manipulation process isbecoming a precise science. Besides single atoms, molecules are also subjectto manipulation. It was often said that STM is to nanotechnology whatthe telescope was to astronomy. Yet STM is capable ofmanipulatingtheobjects it observes, to build nanoscale structures never existedin telescope is capable of bringing Mars and Venus the process of further improving the resolution of STM and AFM,the understanding of its basic physics has been advanced. Numerouscon-vincing theoretical and experimental studies have shown that the imagingmechanism of both STM and AFM at atomic resolution can be understoodas a sequence of making and breaking of partial covalent bonds betweenthe anisotropic quasi-atomic orbitals on the tip and those on the nature of STM and AFM, including those with spin-polarized tips,canbe understood with a unified perspective based on Heisenberg s concept ofresonancein quantum of STM and AFM has been greatly advanced.

8 Owingto the rapidly expanding research in nanotechnology, especially in molecularbiology and in materials science, AFM with tapping mode operating in airor in liquid now constitutes the largest market share. Therefore, a briefpresentation of its basic principles is spite of the availability of commercial STMs and AFMs, researchgroups worldwide continue to design and build customized instruments toachieve advanced features and to serve special experimental ,those new designs are then adapted by instrument manufacturers to becomeproducts. Although the basic principles of the design and constructionof STM and AFM was laid down in the second part of the first edition,Copyright 2008 Oxford University PressChen: Introduction to Scanning Tunneling MicroscopyiiiInstrumentation, new trends and ideas have been basic organization of the second edition is essentially identicaltothe first edition.

9 All the materials in the first edition proven to beuseful arepreserved. Some of the less important materials are eliminated or convertedto Problems at the ends of various chapters. The first chapter,Overview,is preserved but updated. Several recent applications of STM and AFM,probably of interest to general readers, are added. The title of the first Partis changed toPrinciplesfromImaging Mechanismbecause of the inclusionof the physics ofatom and molecule manipulation. TheGallery of STMI magesis updated, with more historical photos and AFM images added,which is now entitled simplyGallery. To preserve the classical style of thefirst edition and to reduce the cost of printing, all photographs and imagesare in black-and-white. Similar to the first edition, only a few illustrativeapplications of STM and AFM are presented, because there are alreadymany excellent books on various applications.

10 For example, the monographScanning Probe Microscopy and Spectroscopy: Methods and ApplicationsbyR. Wiesendanger [9]; the book seriesScanning Tunneling MicroscopyI, II,and III edited by R. Wiesendanger and G untherodt [10];ScanningTunneling Microscopyedited by J. A. Stroscio and W. J. Kaiser [11]; thesecond edition of the monographScanning Tunneling Microscopy and itsApplicationsby C. Bai [12]; and the second edition ofScanning Probe Mi-croscopy and Spectroscopy: Theory, Techniques, and Applicationsedited byD. Bonnell [13]. Similar to the first edition, to ensure pedagogical soundness,the focus is on simple but useful theories, with every derivationpresented infull detail. Many new figures are added to illustrate the concepts in the second edition, care has been taken to use SI units as much as pos-sible.