Particle Induced Electron Emission II PDF
Preview Particle Induced Electron Emission II
Springer Tracts in Modern Physics Volume 321 Editor: G. H6hler Associate Editor: E. A. Niekisch Editorial Board: S. Fliigge H. Haken J. Hamilton W. Paul J o Treusch Springer Tracts in Modern Physics semuloV 111-09 are listed on the back inside cover 211 Tests of the Standard Theory of Electroweak Interactions By C. Kiesling 1988.86 figs. X, 212 pages 311 Radiative Transfer in Nontransparent Dispersed Media By H. Reiss 1988.72 figs. X, 502 pages I14 Electronic Transport in Hydrogenated Amorphous Semiconductors By H. Overhof and .P Thdmas 1989.65 ~sgif XIV, 471 pages t15 Scattering of Thermal Energy Atoms from Disordered Surfaces By B, Poelsema and G. Comsa 1989.74 figs. VIII, 801 pages 611 Optical Solitons in Fibers By A. Hasegawa 1989.22 figs. X, 75 pages !17 DeterminationofHydrogeninMateriais Nuclear Physics Methods By .P K. Khabibultaev and B. G. Skorodumov 1989.38 figs. X, 87 pages 811 Mechanical Relaxation of lnterstitials in Irradiated Metals By K.-H~ Robrock 1990.67 figs. VIII, 601 pages 911 Rigorous Methods in Particle Physics Edited by S. Ciulli, E Scheck, and .W Thirring 1990.21 figs. X, 220 pages 120" Nuclear Pion Photoproduction By A. Nagl, .V Devanathan, and H. l)berall 1991.53 figs. VIII, 471 pages 12t Current-Induced Nonequilibrium Phenomena in Quasi-One-Dimensional Superconductors By R. Tidecks 1990. 901 figs. IX, 143 pages 221 Particle Induced Electron Emission I With contributions by M. ROsier, .W Brauer and J. Devooght, J.-C. Dehaes, A. Dubus, M. Cailler, J.-P. Ganachaud 1991.64 figs. X, 931 pages 321 Particle Induced Electron Emission II With contributions by D. Hasselkamp and H. Rothard, K.-O. Groeneveld, J. Kemmler and .P Varga, H. Winter 1991.90 figs. X, 220pages 421 Ionization Measurements in High Energy Physics By B. Sitar, G. I. Merzon, .V A. Chechin, and Yu. A. Budagov .1991 591 figs. X, Approx. 350 pages 521 Inelastic Scallering of X-Rays with Very High Energy Resolution ByE. Burkel 1991.70figs. XV, 112pages 621 Critical Phenomena at Surfaces and Interfaces X-Ray and Neutron Scattering By H. Dosch 1992.56 figs. X, Approx. 451 pages * denotes a volume hcihw contains a deifissalC Index starting from emuloV 63 Particle Induced Electron Emission II With Contributions by .D Hasselkamp H. Rothard, K.-O. Groeneveld, .J Kemmler E Varga, H. Winter With 09 Figures galreV-regnirpS Berlin Heidelberg New York London Paris Tokyo Hong Kong Barcelona Budapest Dr. Dietmar Hasselkamp I. Physikalisches Institut der Universit~it Giessen, Heinrich-Buff-Ring 16, W-6300 Giessen, Fed. Rep. of Germany .rD Hermann Rothard Professor Dr. Karl-Ontjes Groeneveld .rD Jtirgen Kemmler Institut ftir Kernphysik der Johann-Wolfgang-Goethe-Universit~it, August-Euler-Strasse 6, W-6000 Frankfurt a. M. 90, Fed. Rep. of Germany Dr. Peter Varga Professor Dr. Hannspeter Winter Technische Universit~t Wien, Institut fiir Allgemeine Physik, Wiedner Hauptstrasse 8-10, A-1040 Wien, Austria Manuscripts for publication should be addressed to: Gerhard H6hler Institut ftir Theoretische Kernphysik der Universit~it Karlsruhe, Posffach 69 80, W-7500 Karlsruhe 1, Fed. Rep. of Germany Proofs and all correspondence concerning papers in the process of publication should be addressed to Ernst A. Niekisch Haubourdinstrasse 6, W-5170 Jiilich 1, Fed. Rep. of Germany ISBN 3-540-54147-0 Springer-Verlag Berlin Heidelberg New York ISBN 0-387-54147-0 Springer-Verlag New York Berlin Heidelberg This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9,1965, in its current version, and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1992 Printed in Germany The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Typesetting: Data Conversion by Springer-Verlag Production Editor: E Treiber 5-0413/75 4 3 2 1 0- Printed on acid-free paper Preface This book deals with experimental aspects of electron emission from solid surfaces under bombardment by heavy particles in a wide energy range from eV to GeV. In three articles the state of the art in this field of physics is reviewed with the main emphasis on the basic aspects of the phenomenon. This volume provides a thorough overview which will help both the special- ist on electron emission and physicists working in such fields as radiation effects in matter (e.g., radiation biology), particle induced emission phenom- ena, plasma-wall interactions, microteclmology, surface physics and surface analysis, atomic collision physics and others. Electron emission by impact of energetic ions and neutral particles on polycrystalline and amorphous massive solids is summarized in the article by D. Hasselkamp, which includes a fairly complete tabulation of exper- imental work from the last twenty years. Electron emission from forward and backward surfaces of thin foils is treated by Rothard et al., with special emphasis laid on non-equilibrium phenomena. Varga and Winter discuss re- cent developments with respect to slow projectiles (particularly also highly charged), electron emission statistics and the interplay between potential and kinetic electron emission. This book supplements Vol. 221 of this series, in which modern mi- croscopic theories of electron emission are presented. Both books together provide a comprehensive account of the physics of 'particle induced electron emission'. Giessen, D. Hasselkamp Frankfurt, and tI. Rothard, K.-O. Groeneveld, and J. Kemmler Wien, September 1991 P. Varga and H. Winter Contents Kinetic Electron Emission from Solid Surfaces Under Ion Bombardment By .D pmaklessaH (With 31 Figures) .......................... 1 1. Introduction ............................................ 1 2. Definitions and Basic Quantities .......................... 3 3. Experiment ............................................ 4 3.1 Experimental Conditions ............................ 4 3.1.1 Target Preparation ........................... 5 3.1.2 Target Characterization ....................... 6 3.2 Measurement of the Total Electron Yield .............. 8 3.2.1 The Quotient Method ......................... 8 3.2.2 The Ion-Electron-Converter .................... 12 3.3 Measurement of Energy Spectra of Emitted Electrons ... 14 3.4 Measurement of the Angular Distribution .............. 18 4. Theory ................................................ 19 4.1 General Considerations .............................. 19 4.1.1 Generation of Secondary Electrons ............. 19 4.1.2 The Diffusion Process ......................... 21 4.1.3 Penetration of the Surface Barrier .............. 22 4.2 Summary of Main Theoretical Results ................. 24 4.3 Special Effects in Electron Emission .................. 30 4.3.1 Recoil Ionization ............................. 30 4.3.2 One-Electron Plasmon Decay .................. 31 4.3.3 Electron Loss from the Projectile ............... 32 4.3.4 The Molecular Effect ......................... 33 4.3.5 Auger-Electron Emission ...................... 35 4.3.6 The Binary Encounter Peak ................... 35 5. Summary of Typical Results .............................. 36 5.1 Summary of Experimental Work in the Period from 1968 to 1990 ...................... 36 5.2 Energy Dependence of Total Yields from Metal Targets at Normal Incidence ................................ 36 5.2.1 Positive Ion Impact ........................... 42 5.2.2 Relation of Yields to the Inelastic Stopping Power 44 5.2.3 Impact by Neutral and Negative Particles ....... 48 5.2.4 Impact by Molecular Projectiles ................ 51 5.2.5 Cluster Impact ............................... 53 IIV 5.3 Dependence of the Total Yields on the Projectile-Target-Combination ................ 53 5.4 The Total Yield as a Function of the Angle of Incidence 56 5.5 The Angular Distribution of Emitted Electrons ......... 58 5.6 Energy Spectra of Emitted Electrons from Clean Metal Surfaces ........................... 58 5.7 Non-Metal Targets .................................. 65 5.7.1 Semi-Conducting Materials .................... 65 5.7.2 Insulating Targets ............................ 66 5.8 Influence of Surface Layers ........................... 69 5.9 Impact by Multiply-Charged Ions .................... 71 5.10 Temperature Dependence ............................ 74 5.tl Emission of Polarized Electrons ...................... 74 Applied Aspects of Ion-Induced Electron Emission .......... 75 . 7. Summary and Outlook ................................... 80 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Kinetic Electron Emission from Ion Penetration of Thin Foils in Relation to the Pre-Equillbrium of Charge Distributions By It. Ro~hard, K.O. Groeneveld and J. Kemmler (With 20 Figures) ........................................... 97 1. Introduction ............................................ 97 2. Forward and Backward Electron Yields in the Charge Equilibrium ................................ 99 2.1 Proportionality Between Secondary Electron Yields and Stopping Power ................................ 100 2.2 Forward to Backward Secondary Electron Yield Ratio ... 104 2.3 Projectile Dependence of Electron Yields and the Relation to the Effective Near-Surface Energy Loss for the Projectiles .................................. 106 3. Electron Energy and Angular Distributions in the Charge Equilibrium ................................ 109 3.1 Electron Spectra as a Function of the Emission Angle ... 109 3.2 Electron Angular Distributions: Refraction of Electrons 113 3.3 Dependence of Electron Spectra on the Surface Coverage with Adsorbates .............. 116 3.4 Molecular Effects ................................... 120 4. Pre-Equilibrium Electron Yields .......................... 122 4.1 Electron Yields as a Probe of Pre-Equilibrium Stopping Power ................... 122 4.2 Electron Emission from Molecular Ion Impact .......... 126 5. Pre-Equilibrium Electron Spectra: Convoy Electrons ......... 129 5.1 The Four-Step-Model for Electron Emission: Preparation-Production-Transport-Transmission ........ 130 5.2 Application to Convoy Electron Emission .............. 134 iiIV 6. Conclusion ............................................. 141 References .................................................. 142 Slow Particle-Induced Electron Emission from Solid Surfaces By P. Varga and .H Win~er (With 39 Figures) ................... 149 1. Introduction ............................................ 149 2. Experimental Techniques for Investigation of sPIE .......... 151 2.1 Preparation of Slow Particle Beams ................... 152 2.2 Target Preparation ................................. 154 2.3 Detection of Reaction Products ...................... 155 2.4 Measurement of Electron Emission Yields ............. 155 2.5 Measurement of Ejected Electron Energy Distributions .. 156 2.6 Measurement of Electron Emission Statistics ........... 157 3. Review on Potential Electron Emission Processes ............ 157 3.1 Models for Potential Electron Emission ................ 158 3.2 Experimental Results on PE - Total Electron Yields .... 166 3.2.1 Singly Charged Projectiles ..................... 167 3.2.2 Excited Neutral Projectiles (Metastable Atoms) .. 169 3.2.3 Doubly Charged Projectiles .................... 169 3.2.4 Multicharged Projectiles ...................... 171 3.3 Experimental Results on PE - Electron Energy Distribution ........................ 175 3.3.1 Impact of Metastable Atoms ................... 175 3.3.2 Impact of Ions ............................... 176 3.4 Experimental Results on PE - Electron Emission Statistics .......................... 187 4. Slow Particle-Induced Electron Emission at the Kinetic Threshold ................................. 196 4.1 The Precise Threshold of Kinetic Emission ............. 197 4.2 On the Interdependence of PE and KE ................ 198 4.3 Effects of Projectile Shielding in Slow Particle-Induced Kinetic Emission ............. 201 5. Conclusions and Outlook ................................. 208 References ................................................. 209 List of Abbreviations ........................................ 214 Subject Index .............................................. 215 XI Kinetic Electron Emission from Solid Surfaces Under Ion Bombardment .D pmaklessaH With 31 Figures 1. Introduction Electron emission from solid surfaces under bombardment by energetic par- ticles is a well-known emission phenomenon. Two different mechanisms must be distinguished. If the potential energy of the projectile is larger than twice the work function of the target material "potential electron emission" may proceed in front of the surface either by resonance neutralization followed by Auger deexcitation or by Auger neutralization (Hagstrum 1954, 1978). If electrons are excited within the solid by direct transfer of kinetic energy from the impinging projectiles the process is called "kinetic electron emission". It was first observed by Villard (1899) in experiments with canal rays and by Thomson (!904) and Rutherford (1905) for alpha particle bombardment of solid surfaces and was the subject of numerous review articles (Table 1.1). The present survey deals exclusively with kinetic electron emission from massive, polycrystalline or amorphous targets under heavy particle bombardment. Two aspects served as the motivation for the continuous interest in this effect. On one hand kinetic electron emission is a basic phenomenon which accompanies all interactions of energetic particles with solid surfaces. It is intimately connected to the energy deposition in the target by the projectiles and is further strongly related to such fields as atomic collision physics, solid state physics and surface physics. On the other hand it is of general impor- tance in applied physics as in plasma-surface interactions, in ion microscopies, in the development of heavy particle detectors and others. Renewed interest was motivated by the availability of UHV-techniques and surface analytical tools which allowed the performance of experiments on defined target surfaces under controlled conditions. It is the aim of the present survey to summarize experimental work on ki- netic electron emission in a comprehensive manner and to discuss the various aspects and facets of the phenomenon which emerged within the past twenty years. The review is intended to be a continuation of the work of Krebs (1968), i.e. experimental work before 1968 is only partly included. The point of view is that of an experimentahst, theoretical aspects are only covered briefly. The scope is restricted to heavy-particle induced kinetic electron emission from massive, polycrystalline or amorphous solids at impact energies of at least Table 1.1. Review articles on noi induced kinetic electron emission Author Year Topic Rtichardt 1927 impact by canal rays Geiger 1927 impact by a-rays Massey and Burhop 1952 extensive survey Little 1956 gas discharges Petrov 1960 general considerations Parilis 1962 theory MSllenstedt and Lenz 1963 ion microscopy Kaminsky 1965 extensive survey Medved and Strausser 1965 extensive survey Abroyan et al. 1967 short survey Krebs 1968 extensive survey Carter and Colligon 1968 extensive survey Dearnaley 1969 short survey Arifov 1969 extensive survey McDonald 1970 short survey Dettmann 1972 theory Petrov 1974 special problems Dorozhkin et al. 1974a special problems McCracken 1975 extensive survey Krebs 1976 semiconductors and insulators Krebs and Rogaschewski 1976 semiconductors and insulators Baragiola et al. 1979b short survey Krebs 1980 special problems Sigmund and Tougaard 1981 theory Benazeth 1982 short survey Krebs 1983b short survey Thomas 1984a data for fusion Ertl and Behrisch 1984 short survey Hasselkamp 1985 extensive survey Brusilovsky 1985 emission from single crystals Lai et al. 1986 short survey Benazeth 1987 Al-target Hasselkamp 1988 short survey Schou 1988 theory Hofer 1989 extensive survey Brusilovsky 1990 short survey 5 keV. Experiments dealing with emission from crystal targets or from thin foils are not considered, measurements of the statistics of electron emission are excluded from the discussion. Impact by multiply charged ions is only partly ineluded at very high projectile energies.
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