Table Of ContentSpringer 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
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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.
