ELECTRON SPECTROSCOPIES APPLIED TO LOW-DIMENSIONAL STRUCTURES

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1 ELECTRON SPECTROSCOPIES APPLIED TO LOW-DIMENSIONAL STRUCTURES

2 Physics and Chemistry of Materials with Low-Dimensional Structures VOLUME 24 Editor-in-Chief F. LÉVY, Institut de Physique Appliquée, EPFL, Département de Physique, PHB-Ecublens, CH-1015 Lausanne, Switzerland Honorary Editor E. MOOSER, EPFL, Lausanne, Switzerland International Advisory Board J. V. ACRIVOS, San José State University, San José, Calif., U.S.A. R. GIRLANDA, Università di Messina, Messina, Italy H. KAMIMURA, Dept. of Physics, University of Tokyo, Japan W. Y LIANG, Cavendish Laboratory, Cambridge, U.K. P. MONCEAU, CNRS, Grenoble, France G. A. WIEGERS, University of Groningen, The Netherlands The titles published in this series are listed at the end of this volume.

3 ELECTRON SPECTROSCOPIES APPLIED TO LOW-DIMENSIONAL STRUCTURES Edited by H.P. Hughes University of Cambridge, Cambridge, United Kingdom and H.I. Starnberg Göteborg University and Chalmers University of Technology, Göteborg, Sweden KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW

4 ebook ISBN: Print ISBN: Kluwer Academic Publishers New York, Boston, Dordrecht, London, Moscow Print 2000 Kluwer Academic Publishers Dordrecht All rights reserved No part of this ebook may be reproduced or transmitted in any form or by any means, electronic, mechanical, recording, or otherwise, without written consent from the Publisher Created in the United States of America Visit Kluwer Online at: and Kluwer's ebookstore at:

5 TABLE OF CONTENTS PREFACE xi ASPECTS ON DIRECT AND INVERSE PHOTOEMISSION STUDIES OF LAYERED TRANSITION METAL DICHALCOGENIDES L. Kipp and M. Skibowski 2 Direct and Inverse Photoemission Theoretical Experimental Techniques... 3 Investigations on Selected Transition Metal Dichalcogenides 3.1 Metals: Semiconductors: Adsorbates vs. Intercalates: Epitaxial Layers of Charge Density Waves and Phase Transitions: PHOTOEMISSION FROM INTERCALATED TRANSITION METAL DICHALCOGENIDES H.I. Starnberg, H.E. Brauer and H.P. Hughes 2 Photoelectron Spectroscopy Pure TMDCs Structure and Polytypes Electronic Properties Intercalation of TMDCs... 5 Intercalation of TMDCs with Alkali Metals Crystallographic Structure Electronic Structure v

6 vi 6 Intercalation of TMDCs with Other Simple Metals... 7 Intercalation of TMDCs with 3d Transition Metals... 8 Some Other Intercalation Systems... 9 Concluding Remarks ELECTRONIC STRUCTURE FROM CORE LEVEL LINESHAPES IN CHARGE DENSITY WAVE AND INTERCALATE SYSTEMS H.P. Hughes and J.A. Scarfe 2 Modelling XPS Lineshapes in Metals Theoretical Background Analysis of XPS Data by Least-Squares Fitting Summary... 3 Transition Metal Dichalcogenides: Intercalates and Charge Density Wave Systems Polytypes of... 4 Experimental Details Experimental Data: and its Intercalates Data Analysis Discussion the JDOS in Summary... 6 Experimental Data: CDW Metals Summary... 7 Conclusion UNOCCUPIED BAND STRUCTURE OF LAYERED MATERIALS BY VERY-LOW-ENERGY ELECTRON DIFFRACTION: IMPLICATIONS IN PHOTOEMISSION V.N. Strocov 2 VLEED as a Band Structure Probe The Excited-State Nature of the Upper Bands The Connection of VLEED to E(k) Band Determination Methods

7 2.4 Experimental and Computational Techniques in VLEED Photoemission Implications of VLEED Inelastic Processes Comparison with Other Spectroscopies... 3 VLEED Studies on Layered Materials: Properties of the Upper Bands Case Studies Quantitative VLEED Band Determination Layer-Perpendicular E(k) Layer-Parallel E(k)... 4 Implications of VLEED for PE Bandmapping Final-State Effects in PE Principles of PE Determination of the Bulk E(k) Peculiarities of Bandmapping for Layered Materials 4.4 Absolute VLEED-PE Bandmapping of Layered Materials Conclusion... vii HIGH-RESOLUTION PHOTOEMISSION STUDIES OF LOW-DIMENSIONAL SYSTEMS M. Grioni and J. Voit 2 Generalities of ARPES Why Low-Dimensional Systems?. 3 2D Materials D Fermi Liquids Metal-Insulator Transitions Spectral Properties of the Fermi Liquid... 4 ARPES of 2D Systems A Fermi Liquid Reference Charge Density Waves in 2D An Anomalous 2D CDW System: Organic 2D Metals... 5 One-Dimensional Systems Materials What is a Luttinger Liquid Anyway? Spectral Properties of Luttinger Liquids ARPES on Quasi-lD Organic Systems: Where is the Luttinger Liquid?

8 viii 6 1D Mott Insulators: Theory Theory ARPES of Spin 1Ladders and Other 1D Mott Insulators 7 Charge Density Wave Materials Spin-Gapped Luttinger Liquids: 1D Peierls Systems andsuperconductors Fluctuating Peierls Insulators ARPES on Charge Density Wave Systems... 8 Conclusions PHOTOELECTRON SPECTROSCOPY OF LOW-DIMENSIONAL ORGANIC SYSTEMS N. Johansson and W.R. Salaneck 2 Conjugated Polymers... 3 Photoclectron Spectroscopy... 4 Chemical and Electronic Structure of Pristine PPV Comparison of the Electronic Structure of PPV, PPP, and LPPP... 6 PPVinAir... 7 Photo-Oxidation of PPV... 8 PPV and Secondary Low Energy Electrons Metal Atoms on PPV Sodium and Rubidium on PPV Calcium on PPV Aluminium on PPV Summary ELECTRONIC PROPERTIES OF VAN DER WAALS- EPITAXY FILMS AND INTERFACES Wolfram Jaegermann, Andreas Klein and Christian Pettenkofer 1 Introduction Scope of the Article Layered Chalcogenides The Concept of van der Waals-Epitaxy Electronic Properties of vdw-surfaces

9 ix 2 Growth Modes and Film Morphology in vdwe Growth Modes: Thermodynamic and Kinetic Parameters Structure and Morphology of vdwe Films Structure and Morphology of QvdWE Films... 3 Electronic Properties of vdwe Heterointerfaces Formation of Semiconductor Heterocontacts Theoretical Models of Band Lineup Photoemission Determination of Band Lineup Band Lineup of vdwe Heterojunctions Band Lineup of QvdWE Heterojunctions Summary of Heterojunction Properties... 4 Electronically Decoupled vdwe Quantum Films Electronic Coupling at Interfaces Electronically Decoupled vdwe-systems... 5 Summary, Conclusions, and Perspectives of vdwe SCANNING TUNNELLING SPECTROSCOPY OF LAYERED CUPRATES AND TRANSITION METAL CHALCOGENIDES T. Hasegawa, M.Z. Lin and O. Shiino 2 Scanning Tunnelling Microscopy/Spectroscopy... 3 Observations on High Temperature Superconductors Cross-Sectional Results for HTSCs Superconducting Properties of Cleaved B12212 Surfaces Pseudo-Gap Structure in Overdoped HTSCs... 4 Observations on Transition Metal Dichalcogenides Site-Specific Tunnelling Measurements of Transition Metal Dichalcogenides Compositional Dependence of the Tunnelling Spectrum Near the Mott Transition Subsurface Impurity Images in the Mott Localised States... 5 Conclusion

10 x ELECTRONIC BAND STRUCTURE OF LAYERED RUTHENATES A.V. Puchkov and Z.-X. Shen 2 Theoretical Band Structure Sr Sr de Haas-van Alphen Results on Sr Angle-Resolved Photoemission Results Fermi Surface of Sr Fermi Surface of Sr Ca Doping and the Mott Transition Ca214 and Ca Evidence for Correlation Effects... 5 Conclusions INDEX 497

11 xi PREFACE The effect of reduced dimensionality, inherent at the crystallographic level, on the electronic properties of low dimensional materials can be dramatic, leading to structural and electronic instabilities including superconductivity at high temperatures, charge density waves, and localisation which continue to attract widespread interest. The layered transition metal dichalcogenides have engaged attention for many years, partly arising from the charge density wave effects which some show and the controlled way in which their properties can be modified by intercalation, while the development of epitaxial growth techniques has opened up promising areas based on dichalcogenide heterostructures and quantum wells. The discovery of high-temperature superconducting oxides, and the realisation that polymeric materials too can be exploited in a controlled way for various opto-electronic applications, have further stimulated interest in the effects of structural dimensionality. It seems timely therefore to draw together some strands of recent research involving a range of disparate materials which share some common characteristics of low dimensionality. This resulting volume is aimed at researchers with specialist interests in the particular materials discussed but who may also wish to examine the related phenomena observed in different systems, and at a more general solid state audience with broad interests in electronic properties and low dimensional phenomena. Space limitations have required us to be selective as regards particular materials, though we have managed to include those as dissimilar as polymeric semiconductors, superconducting oxides, bronzes and layered chalcogenides. We have also had to be selective regarding the research techniques applied to them, and have concentrated on various electron spectroscopies, since these are capable of extracting directly many details of the materials electronic structure. In particular, high resolution and angle-resolved photoemission and inverse photoemission feature strongly, together with the spectroscopic aspects of scanning tunneling microscopy. We are grateful to the authors for their contributions, and for their forbearance towards the Editors requirements and delays. We also wish to thank warmly Francis Lévy, the Managing Editor of the Series Physics and Chemistry of Materials with Low Dimensional Structures, for his invitation to undertake the compilation of this volume and for his constant interest, patience and encouragement. Cambridge, May 2000 Göteborg, May 2000 HOWARD HUGHES HANS STARNBERG