Springer Series in Optical Sciences 176 Shigemasa Suga Akira Sekiyama Photoelectron Spectroscopy Bulk and Surface Electronic Structures Springer Series in Optical Sciences Volume 176 Founded by H. K. V. Lotsch Editor-in-Chief W. T. Rhodes Editorial Board Ali Adibi, Atlanta Toshimitsu Asakura, Sapporo Theodor W. Hänsch, Garching Takeshi Kamiya, Tokyo Ferenc Krausz, Garching Bo A. J. Monemar, Linköping Herbert Venghaus, Berlin Horst Weber, Berlin Harald Weinfurter, München For furthervolumes: http://www.springer.com/series/624 Springer Series in Optical Sciences TheSpringerSeriesinOpticalSciences,undertheleadershipofEditor-in-ChiefWilliamT.Rhodes, GeorgiaInstituteofTechnology,USA,providesanexpandingselectionofresearchmonographsinall majorareasofoptics:lasersandquantumoptics,ultrafastphenomena,opticalspectroscopytechniques, optoelectronics, quantum information, information optics, applied laser technology, industrial appli- cations,andothertopicsofcontemporaryinterest. 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Theeditorsencourageprospectiveauthorstocorrespondwiththeminadvanceofsubmittingaman- uscript.SubmissionofmanuscriptsshouldbemadetotheEditor-in-ChieforoneoftheEditors.Seealso www.springer.com/series/624 Editor-in-Chief WilliamT.Rhodes SchoolofElectricalandComputerEngineering GeorgiaInstituteofTechnology Atlanta,GA30332-0250 USA e-mail:[email protected] EditorialBoard AliAdibi BoA.J.Monemar SchoolofElectricalandComputerEngineering DepartmentofPhysicsandMeasurementTechnology GeorgiaInstituteofTechnology MaterialsScienceDivision Atlanta,GA30332-0250 LinköpingUniversity USA 58183Linköping,Sweden e-mail:[email protected] e-mail:[email protected] ToshimitsuAsakura HerbertVenghaus FacultyofEngineering FraunhoferInstitutfürNachrichtentechnik Hokkai-GakuenUniversity Heinrich-Hertz-Institut 1-1,Minami-26,Nishi11,Chuo-ku Einsteinufer37 Sapporo,Hokkaido064-0926,Japan 10587Berlin,Germany e-mail:[email protected] e-mail:[email protected] TheodorW.Hänsch HorstWeber Max-Planck-InstitutfürQuantenoptik OptischesInstitut Hans-Kopfermann-Straße1 TechnischeUniversitätBerlin 85748Garching,Germany Straßedes17.Juni135 e-mail:[email protected] 10623Berlin,Germany e-mail:[email protected] TakeshiKamiya MinistryofEducation,Culture,Sports HaraldWeinfurter ScienceandTechnology SektionPhysik NationalInstitutionforAcademicDegrees Ludwig-Maximilians-UniversitätMünchen 3-29-1OtsukaBunkyo-ku Schellingstraße4/III Tokyo112-0012,Japan 80799Munchen,Germany e-mail:[email protected] e-mail:[email protected] FerencKrausz Ludwig-Maximilians-UniversitätMünchen LehrstuhlfürExperimentellePhysik AmCoulombwall1 85748Garching,Germanyand Max-Planck-InstitutfürQuantenoptik Hans-Kopfermann-Straße1 85748Garching,Germany e-mail:[email protected] Shigemasa Suga Akira Sekiyama • Photoelectron Spectroscopy Bulk and Surface Electronic Structures 123 Shigemasa Suga Akira Sekiyama Institute of Scientific and Industrial Graduate School of Engineering Research Science Osaka University Osaka University Osaka Osaka Japan Japan ISSN 0342-4111 ISSN 1556-1534 (electronic) ISBN 978-3-642-37529-3 ISBN 978-3-642-37530-9 (eBook) DOI 10.1007/978-3-642-37530-9 SpringerHeidelbergNewYorkDordrechtLondon LibraryofCongressControlNumber:2013937610 (cid:2)Springer-VerlagBerlinHeidelberg2014 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodology now known or hereafter developed. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purposeofbeingenteredandexecutedonacomputersystem,forexclusiveusebythepurchaserofthe work. Duplication of this publication or parts thereof is permitted only under the provisions of theCopyright Law of the Publisher’s location, in its current version, and permission for use must always be obtained from Springer. Permissions for use may be obtained through RightsLink at the CopyrightClearanceCenter.ViolationsareliabletoprosecutionundertherespectiveCopyrightLaw. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexempt fromtherelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. While the advice and information in this book are believed to be true and accurate at the date of publication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityfor anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,with respecttothematerialcontainedherein. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) Preface The phenomenon of photoelectron emission was found more than a century ago andyieldedtheconceptofphotons.Therelationbetweenthephotonenergiesand the kinetic energies of photoelectrons was soon clarified. The usefulness of pho- toelectronspectroscopy(PES)formaterialsscienceswaswidelyrecognizedinthe last century. Electronic structures of gases and solids were mostly studied at low photon energies and chemical analyses were mainly performed in the X-ray region. Besides the development of high performance electron analyzers, light sourceshaveinparallelbeenintensivelyimprovedtilldate.Theuseofsynchrotron radiation has promoted the photoelectron spectroscopy since *1975 due to the tunabilityofphotonenergies.Thedevelopmentofundulatorlightsourcesenabled the high energy resolution photoelectron spectroscopy even in the regions of soft andhardX-rays.Now,synchrotronradiationcanprovidephotonswithenergy(hm) resolutions less than a few meV below 10 eV, 40 meV around 800 eV, and less than 300 leV at 14 keV by use of good monochromators. Meanwhile, the reso- lutionB1meVcanbeachievedinlaboratoriesbyuseofverylowenergy(*7eV) quasi-CW, high-repetition lasers as well as high resolution rare gas (Xe, Kr, Ar) lamps. Byutilizingtheangleresolvingpoweroftheelectronenergyanalyzer,theangle resolved photoelectron spectroscopy (ARPES) became very popular to probe the band dispersions of solids as well as the fermi surface topology in metals. In stronglycorrelatedelectronsystems,wherethesurfaceelectronicstructuresaswell as surface band dispersions are often noticeably different from those of the bulk electronic structures, the high energy photoelectron spectroscopy with high bulk sensitivity and enough energy and momentum resolutions is now extensively performed. Since the inelastic mean free path of photoelectrons becomes again increasedinsomematerialsbelowthekineticenergiesofafeweV,extremelyhigh resolution photoelectron spectroscopy is under development below hm *10 eV. For a complete understanding of electronic structures of strongly correlated elec- tronsystems,studiesinwidephotonenergiesintherangeof10keVdowntoafew eV will be highly desired. By utilizing the high brilliance of the synchrotron radiation, studies of micro- and nano-materials are progressing rapidly. The v vi Preface scanningphotoelectronmicroscopyandthephotoelectronemissionmicroscopyare suchexamples.Inaddition,spinpolarizedmeasurementsarewidelyusedtostudy the spin states. Complementary techniques to probe materials electronic structures are also under intensive development. For example, absorption and reflectivity spectros- copy as well as the resonance inelastic X-ray scattering are very powerful tech- niques with high bulk sensitivity. Inverse photoemission spectroscopy is a useful tool to probe the unoccupied electronic states. On the other hand, photoelectron diffraction can provide the structural information down to sub nm range. The scanningtunnelingspectroscopybyuseofscanningtunnelingmicroscopecanalso probe the occupied and unoccupied electronic states with extremely high spatial resolution down to the atomic resolution. By means of the Fourier transform, the information in the momentum space can also be obtained. Thus we intended to include up-to-date achievements in photoelectron spectroscopy and frontiers of some typical complementary techniques in this book. Osaka Shigemasa Suga Akira Sekiyama Acknowledgments The photoelectron spectroscopy with use of such a bright light source as syn- chrotron radiation has already a history of more than four decades. One of the authors S. S. has first experienced synchrotron radiation photoelectron spectros- copyin1975atDESYwithF.J.Himpsel.TheinitialinterestofS.S.inthisfield wasstimulatedbyM.CardonaofMax-Planck-InstitutefürFestkörperforschungin StuttgartinthelaststageofhisstayinGermanybetween1973and1976.S.S.was then engaged in the instrumentation, spectroscopy, and materials’ sciences in the synchrotronradiationlaboratoryoftheInstituteforSolidStatePhysics(ISSP),The UniversityofTokyo,withadedicated synchrotronlight source, SOR-RING (0.38 GeV), where he was responsible for the national use of this facility over 13 years togetherwithH.KanzakiandT.Ishii.TherehecooperatedwithM.Taniguchiand S. Shin in photoelectron spectroscopy. He also collaborated with A. Fujimori on XPSand S.-J. Oh on resonance photoelectronspectroscopy. He was alsoengaged inVUV-IPESandX-BISwithH.NamatameandS.Ogawa.Duringthisperiodhe also joined spin polarized electron experiments at BESSY-I and KFA, Jülich in collaboration with J. Kirschner. He also collaborated with A. Kakizaki, K. Soda, M. Fujisawa, and T. Kinoshita to construct two beam lines of the ISSP at Photon Factory (2.5 GeV) in Tsukuba. He then moved to Osaka University in 1989 to join the SPring-8 (8 GeV) project as an active outside user. He devoted the full potential of his old and new laboratories to the construction of the first soft X-ray beam line, BL25SU, of SPring-8withatwinhelicalundulator(designedbyH.Kitamura)togetherwithH. Daimon, S. Imada, and Y. Saitoh. Excellent performance of the soft X-ray monochromatorequippedwithvariedlinespacingplanegratingswasconfirmedat BL25SU in 2000 by the author’s group. Till the full commissioning of this new beam line with three different experimental stations (soft X-ray photoelectron spectroscopy, soft X-ray absorption magnetic circular dichroism, and photoelec- tron diffraction with two-dimensional electron analyzer) in 1998, he continued such experiments at Photon Factory. He met with the other author A. S. in 1995, who was a Ph.D. student under supervision of A. Fujimori in The University of Tokyo. A.S. partly collaborated with S. S.on the experimentsat Photon Factory, andthenmovedtoOsakaUniversityaftertakinghisPh.D.degreetojoinS.S.lab. Both authors did extensive PES studies on rare earth compounds. During this vii viii Acknowledgments period,theybecameacquaintedwithP.Baltzerwithwhomtheydiscussedquitea lot on electron analyzers and the future of bulk sensitive photoelectron spectros- copy. It must be mentioned here that four more soft X-ray beam lines were later constructed up to now in SPring-8, demonstrating that an 8 GeV storage ring is very useful for soft X-ray spectroscopy. Through various research collaborations making use of this high performance soft X-ray BL25SU, the authors profited immensely from discussions with J. W. Allen, D. Vollhardt, V. I. Anisimov, R. Claessen, M. Sing, G. Güntherodt, J. Osterwalder, J.-S. Kang, and W. Kuch. In our recent activity in the hard X-ray region,theauthorsaremuchobligedtoT.Ishikawa.S.S.isalsomuchobligedto C. M. Schneider and L. Plucinski for collaboration in the field of extremely low energy photoelectron spectroscopy. The authors would like to thank all of these peopleforfruitfulcollaborationsanddiscussions.Thisbookhasbenefittedquitea lot from continuous cooperation and discussions with many foreign and domestic friends as well as colleagues in the field of synchrotron radiation spectroscopy. Thecontentofthisbookisbasedonthelectures,whichS.S.gavefrom1980in the Graduate School of Applied Physics, The University of Tokyo and later from 1989 in the Graduate School of Engineering Science, Osaka University. It is also based on the lectures given by A. S. from 2010 in the latter graduate school. The very recent studiesperformedtogetherwith A.Yamasaki, H.Fujiwara, and many other students in the graduate school are included in this book and the authors acknowledge them all. Over a long period of his life, S. S. acknowledges his wife Sachiha for her patience and appreciation of his hard scientific job while taking care of their four children.A.S.acknowledgeshiswifeHarukoforsupportinghisresearchestilllate at night while taking care of two children. S. S. is much obliged to the Japan Society for Promotion of Science for twice supporting the Japan–Germany research collaborations and the Ministry of Education, Culture, Sports, Science and Technology, MEXT, Japan, for financial supports through COE, 21COE, and Grant-in-AidsforCreativeScientificResearch(15GS0213).A.S.thankstheJapan Society forpromotionofscience forfinancialsupportthroughGlobalCOE(G10) and scientific research on innovative areas ‘‘Heavy Electrons’’ (20102003). S. S. also thanks the Helmholtz Association and the Alexander von Humboldt Foun- dation for supporting the Japan–Germany research collaborations. The authors are much obliged to A. Yamasaki of Konan University, Japan, M. Sing of University of Würzburg, Germany, K. Sakamoto of Chiba University, and T Okuda of Hiroshima University Japan, for their careful reading of the first manuscript and many useful comments for further improvement. The stimulating discussion with A. Winkelmann of the Max-Planck Institute for Microstructure Physics, Germany, is highly acknowledged. This book would not have been completed withoutthe patience andcontinuous encouragementofC. Ascheron of Springer-Verlag. Contents 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 Theoretical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 Three-Step Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 Valence-Band Photoexcitation Process for Non-interacting Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.3 Valence-Band Photoexcitation Process for Strongly Correlated Electron Systems . . . . . . . . . . . . . . . . . . . . . . . . 16 2.4 Core-Level Photoemission Process for Strongly Correlated Electron Systems . . . . . . . . . . . . . . . . . . . . . . . . 18 2.5 Matrix Element Effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.6 Theoretical Models to Describe the Spectra of Strongly Correlated Electron Systems . . . . . . . . . . . . . . . . . . . . . . . . 21 2.6.1 Single Impurity Anderson Model . . . . . . . . . . . . . . . 24 2.6.2 Cluster Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.6.3 Hubbard Model . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.6.4 Dynamical Mean Field Theory. . . . . . . . . . . . . . . . . 28 2.6.5 New Directions and Some Remarks . . . . . . . . . . . . . 29 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3 Instrumentation and Methodology. . . . . . . . . . . . . . . . . . . . . . . . 33 3.1 Synchrotron Radiation and Undulator Radiation. . . . . . . . . . . 33 3.2 Principle of Grating and Crystal Monochromators . . . . . . . . . 37 3.2.1 Grating Monochromators. . . . . . . . . . . . . . . . . . . . . 38 3.2.2 Crystal Monochromators. . . . . . . . . . . . . . . . . . . . . 42 3.2.3 Focusing Mirrors . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.3 Examples of Light Sources . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.3.1 High Resolution Vacuum Ultraviolet Synchrotron Radiation Beam Lines. . . . . . . . . . . . . . . . . . . . . . . 45 3.3.2 High Resolution Soft X-ray Beam Lines. . . . . . . . . . 49 3.3.3 High Resolution Hard X-ray Beam Lines . . . . . . . . . 52 3.3.4 Laboratory Vacuum Ultraviolet Sources . . . . . . . . . . 54 ix