SolidSurfaces, InterfacesandThinFilms Springer-Verlag Berlin Heidelberg GmbH ONLINE LIBRARY Physics and Astronomy http://www.springer.de/physl AdvancedTextsinPhysics Thisprogramofadvancedtextscoversabroadspectrumoftopicswhichareof currentandemerginginterestinphysics.Eachbookprovidesacomprehensiveand yetaccessibleintroductiontoafieldattheforefrontofmodernresearch.Assuch, thesetextsareintendedforseniorundergraduateandgraduatestudentsattheMS andPhDlevel;however,researchscientistsseekinganintroductiontoparticular areasofphysicswillalsobenefitfromthetitlesinthiscollection. Hans Lu¨th Solid Surfaces, Interfaces and Thin Films Fourth,RevisedandExtendedEdition With389Figuresand13Tables 1 3 ProfessorDr.HansLüth ForschungszentrumJu¨lichGmbH Institutfu¨rSchichtenundGrenzfla¨chen 52425Ju¨lich and Rheinisch-Westfa¨lischeTechnischeHochschule 52062Aachen Germany E-mail: [email protected] TheThirdEditionwaspublishedunderthetitle: SurfacesandInterfacesofSolidMaterials(SpringerStudyEdition) LibraryofCongressCataloging-in-PublicationDataappliedfor DiedeutscheBibliothek-CIP-Einheitsaufnahme Lu¨th,Hans:Solidsurfaces,interfacesandthinfilms/HansLu¨th.-4.,rev.andextendeded. (Advancedtextsinphysics) (Physicsandastronomyonlinelibrary) 3.Aufl.u.d.T.:Lu¨th,Hans:Surfacesandinterfacesofsolidmaterials ISBN 978-3-642-07609-1 ISBN 978-3-662-04352-3 (eBook) DOI 10.1007/978-3-662-04352-3 ISSN1439-2674 ISBN 978-3-642-07609-1 Thisworkissubjecttocopyright.Allrightsarereserved,whetherthewholeorpartofthematerial isconcerned,specificallytherightsoftranslation,reprinting,reuseofillustrations,recitation,broad- casting,reproductiononmicrofilmorinanyotherway,andstorageindatabanks.Duplicationof thispublicationorpartsthereofispermittedonlyundertheprovisionsoftheGermanCopyrightLaw ofSeptember9,1965,initscurrentversion,andpermissionforusemustalwaysbeobtainedfrom Springer-Verlag Berlin Heidelberg GmbH. ViolationsareliableforprosecutionundertheGermanCopyrightLaw. http://www.springer.de ©Springer-VerlagBerlinHeidelberg2001 Originally published by Springer-Verlag Berlin Heidelberg New York in 2001 Theuseofgeneraldescriptivenames,registerednames,trademarks,etc.inthispublicationdoesnot imply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevantpro- tectivelawsandregulationsandthereforefreeforgeneraluse. Typesetting:DataconversionbyVerlagsserviceAscheron,Mannheim Coverdesign:design&productionGmbH,Heidelberg Printedonacid-freepaper SPIN11006848 57/3111/di 54321 Preface Surface physics in the classical sense of ultrahigh vacuum (UHV) based ex- perimentalapproachestounderstandwell-definedsurfaceshasnowbecomea maturebranchofcondensedmatterresearch.Meanwhile,however,thetheo- reticalconceptsandexperimentaltechniquesdevelopedinthisfieldhavealso become the basis for modern interface, thin film and nanostructure science. Furthermore, these research fields are of fundamental importance for more appliedbranchesofscience,suchasmicro-andnanoelectronics,catalysisand corrosion research, surface protection, chemo- and biosensors, microsystems and nanostructured materials. Thephysicsofsolidsurfaces,interfacesandthinfilmsisthusanimportant field which needs to be taught to all students in physics, microelectronics, engineering and material science. It is thus no surprise that this topic has now entered the corresponding university curricula throughout the world. Inthepresent4theditionofthisbook(formerlyentitled“SurfacesandIn- terfacesofSolidMaterials”)moreemphasisisplacedontherelationbetween the surfaces, interfaces and thin films, and on newly discovered phenomena relatedtolowdimensions.Accordingly,afewtopicsoftheearliereditionsthat are now only of peripheral interest have been omitted. On the other hand, a newchapterdealingwithcollectivephenomenaatinterfaceshasbeenadded: Superconductor–semiconductor interfaces and thin ferromagnetic films have attractedconsiderableattentioninoflate.Thisismainlyduetoourimproved understandingofthesephenomena,butalsotoimportantapplicationaspects whichhaverecentlyemerged.Forexample,giantmagnetoresistance,atypical thin film phenomenon, is of considerable importance for read-out devices in magnetic information storage. Likewise, ferromagnetism in low dimensions may play an important role in future non-volatile memory device circuits. The corresponding topics have thus been added to the new edition and the titleofthebookhasbeenmodifiedslightlyto“SolidSurfaces,Interfacesand ThinFilms”.Thisnewtitlebetterdescribesthewiderrangeoftopicstreated in the new edition. Furthermore, in response to several suggestions from students and col- leagues, errors and inconsistencies in the text have been eliminated and im- provements made to clarity. On the topics superconductor–semiconductor interfaces and ferromagnetism in low dimensions, I have benefited from dis- VI Preface cussionswithThomasSch¨apersandStefanBlu¨gel,respectively.TheEnglish textwassignificantlyimprovedbyAngelaLahee,who,togetherwithKatha- rina Ascheron, also contributed much to the final production of the book. ParticularthanksareduetoClausAscheronofSpringer-Verlag,whoman- aged the whole publication process. Aachen and Ju¨lich Hans Lu¨th July 2001 Preface to the Second Edition Surface and interface physics has in recent decades become an ever more important subdiscipline within the physics of condensed matter. Many phe- nomena and experimental techniques, for example the quantum Hall effect and photoemission spectroscopy for investigating electronic band structures, which clearly belong to the general field of solid-state physics, cannot be treatedwithoutaprofoundknowledgeofsurfaceandinterfaceeffects.Thisis also true in view of the present general development in solid-state research, where the quantum physics of nanostructures is becoming increasingly rele- vant.Thisalsoholdsformoreappliedfieldssuchasmicroelectronics,catalysis and corrosion research. The more one strives to obtain an atomic-scale un- derstanding,andthegreatertheinterestinmicrostructures,themoresurface and interface physics becomes an essential prerequisite. In spite of this situation, there are only a very few books on the market which treat the subject in a comprehensive way, even though surface and interfacephysicshasnowbeentaughtforanumberofyearsatmanyuniver- sities around the world. In my own teaching and research activities I always have the same experience: when new students start their diploma or PhD work in my group I can recommend to them a number of good review ar- ticles or advanced monographs, but a real introductory and comprehensive textbook to usher them into this fascinating field of modern research has been lacking. I therefore wrote this book for my students to provide them with a text from which they can learn the basic models, together with fundamental ex- perimental techniques and the relationship to applied fields such as micro- analysis, catalysis and microelectronics. This textbook on the physics of surfaces and interfaces covers both ex- perimentalandtheoreticalaspectsofthesubject.Particularattentionispaid to practical considerations in a series of self-contained panels which describe UHVtechnology,electronoptics,surfacespectroscopyandelectricalandop- tical interface characterisation techniques. The main text provides a clear andcomprehensivedescriptionofsurfaceandinterfacepreparationmethods, structural, vibrational and electronic properties, and adsorption and layer growth. Because of their essential role in modern microelectronics, special emphasis is placed on the electronic properties of semiconductor interfaces VIII Preface and heterostructures. Emphasizing semiconductor microelectronics as one of themajorapplicationsofinterfacephysicsisfurthermorejustifiedbythefact thatherethegapbetweenapplicationandbasicresearchissmall,incontrast, for example, with catalysis or corrosion and surface-protection research. ThebookisbasedonlecturesgivenattheRheinisch-Westfa¨lischeTechni- scheHochschule(RWTH)Aachenandonstudentseminarsorganizedwithmy colleagues Pieter Balk, Hans Bonzel, Harald Ibach, Ju¨rgen Kirchner, Claus- Dieter Kohl and Bruno Lengeler. I am grateful to these colleagues and to a number of students participating in these seminars for their contributions andfortheniceatmosphereduringthesecourses.Othervaluablesuggestions were made by some of my former doctoral students, in particular by Arno F¨orster, Monika Mattern-Klosson, Richard Matz, Bernd Scha¨fer, Thomas Sch¨apers, Andreas Spitzer and Andreas Tulke. For her critical reading of the manuscript, as well as for many valuable contributions, I want to thank Angela Rizzi. The English text was significantly improved by Angela Lahee from Springer Verlag. For this help, and also for some scientific hints, I would like to thank her. For the pleasant collaboration during the final production of the book I thank Ilona Kaiser. The book would not have been finished without the permanent support of Helmut Lotsch; many thanks to him as well. Last,butnotleast,Iwanttothankmyfamilywhomissedmefrequently, butneverthelesssupportedmepatientlyandcontinuouslyduringthetimein which I wrote the book. Aachen and Ju¨lich Hans Lu¨th October 1992 Contents 1. Surface and Interface Physics: Its Definition and Importance ............................ 1 PanelI: Ultrahigh Vacuum (UHV) Technology............... 6 PanelII: Basics of Particle Optics and Spectroscopy........... 19 Problems .................................................. 31 2. Preparation of Well-Defined Surfaces, Interfaces and Thin Films ................................ 33 2.1 Why Is Ultrahigh Vacuum Used? ......................... 33 2.2 Cleavage in UHV....................................... 35 2.3 Ion Bombardment and Annealing......................... 38 2.4 Evaporation and Molecular Beam Epitaxy (MBE) .......... 40 2.5 Epitaxy by Means of Chemical Reactions.................. 53 PanelIII: Auger Electron Spectroscopy (AES) ................ 59 PanelIV: Secondary Ion Mass Spectroscopy (SIMS) ........... 66 Problems .................................................. 75 3. Morphology and Structure of Surfaces, Interfaces and Thin Films ................................ 77 3.1 Surface Energy and Macroscopic Shape ................... 77 3.2 Relaxation, Reconstruction, and Defects................... 83 3.3 Two-Dimensional Lattices, Superstructure, and Reciprocal Space ................................... 89 3.3.1 Surface Lattices and Superstructures................ 89 3.3.2 2D Reciprocal Lattice............................. 93 3.4 Structural Models of Solid–Solid Interfaces................. 94 3.5 Nucleation and Growth of Thin Films..................... 100 3.5.1 Modes of Film Growth............................ 100 3.5.2 “Capillary Model” of Nucleation ................... 103 3.6 Film-Growth Studies: Experimental Methods and Some Results.................. 107 PanelV: Scanning Electron Microscopy (SEM) and Microprobe Techniques........................ 121 PanelVI: Scanning Tunneling Microscopy (STM).............. 128 X Contents PanelVII: Surface Extended X-Ray Absorption Fine Structure (SEXAFS)....................................... 139 Problems .................................................. 145 4. Scattering from Surfaces and Thin Films ................. 147 4.1 Kinematic Theory of Surface Scattering ................... 148 4.2 The Kinematic Theory of Low-Energy Electron Diffraction .. 153 4.3 What Can We Learn from Inspection of a LEED Pattern? ... 156 4.4 Dynamic LEED Theory, and Structure Analysis............ 161 4.4.1 Matching Formalism.............................. 162 4.4.2 Multiple-Scattering Formalism ..................... 164 4.4.3 Structure Analysis................................ 166 4.5 Kinematics of an Inelastic Surface Scattering Experiment.... 167 4.6 Dielectric Theory of Inelastic Electron Scattering ........... 171 4.6.1 Bulk Scattering .................................. 172 4.6.2 Surface Scattering ................................ 175 4.7 Dielectric Scattering on a Thin Surface Layer .............. 181 4.8 Some Experimental Examples of Inelastic Scattering of Low-Energy Electrons at Surfaces ...................... 186 4.9 The Classical Limit of Particle Scattering.................. 192 4.10 Conservation Laws for Atomic Collisions: Chemical Surface Analysis............................... 195 4.11 Rutherford BackScattering (RBS): Channeling and Blocking ................................ 198 PanelVIII: Low-Energy Electron Diffraction (LEED) and Reflection High-Energy Electron Diffraction (RHEED) ....................................... 210 PanelIX: Electron Energy Loss Spectroscopy (EELS).......... 219 Problems .................................................. 227 5. Surface Phonons.......................................... 229 5.1 The Existence of “Surface” Lattice Vibrations on a Linear Chain ...................................... 230 5.2 Extension to a Three-Dimensional Solid with a Surface...... 234 5.3 Rayleigh Waves ........................................ 238 5.4 The Use of Rayleigh Waves as High-Frequency Filters....... 241 5.5 Surface-Phonon (Plasmon) Polaritons ..................... 242 5.6 Dispersion Curves from Experiment and from Realistic Calculations .......................... 253 PanelX: Atom and Molecular Beam Scattering............... 258 Problems .................................................. 264