Table Of ContentSTRUKTUR UNO EIGENSCHAFTEN DER MATERIE
IN EINZELDARSTELLUNGEN
BEGRONDET VON M. BORN UND J. FRANCK
HERAUSGEGEBEN VON S. FLOGGE
xxv
ATOMIC AND IONIC
IMPACT PHENOMENA ON
METAL SURFACES
BY
DR. MANFRED KAMINSKY
ARGON NE NATIONAL LABORATORY
ARGONNE, ILLINOIS
1965
NEW YORK
ACADEMIC PRESS INC., PUBLISHERS
BERLIN' HEIDELBERG' NEW YORK
SPRINGER-VERLAG
SPRINGER-VERLAG
BERLIN· HEIDELBERG· NEW YORK
Published in the U. S. A. and Canada by
ACADEMIC PRESS INC., PUBLISHERS
111 Fifth Avenue, New York, New York 10003
Library of Congress Catalog Card Number 64-24914
All rights reserved
No part of this book mt£Y be reproduced in a'!Y form, by microfilm or a'!Y other means,
without written permission from the publishers
ISBN-13: 978-3-642-46027-2 e-ISBN-13: 978-3-642-46025-8
001: 10.1007/978-3-642-46025-8
@ BY SPRINGER-VERLAG
Softcover reprint of the hardcover 1st edition 1965
BERLIN· HEIDELBERG
1965
Preface
The collisions of neutral or charged gaseous particles with solid
surfaces govern many physical and chemical phenomena, as has been
recognized for a long time. The gas/solid phenomena in turn depend on a
great variety of processes such as the charge transfer of the gas/solid
interface, adsorption and desorption, the energy transfer between an
incident particle and the surface, etc.
Our knowledge of these processes, however, is only fragmentary.
This is partly due to the difficulty in adequately controlling the ex
perimental conditions. Consequently, until recently the data were usually
so complex that reliable information about a particular elementary
process could not be deduced. Within the last five to ten years, however,
the techniques of ultra-high vacuum and surface preparation have
developed rapidly and there has been a booming and widespread interest
in the role of gas/solid interactions in such diverse fields as plasma
physics, thermonuclear reactions, thermionic energy conversion, ion
propulsion, sputtering corrosion of the surface of satellites and ion
engines, ion getter pumps, deposition of thin films, etc. This led to
extensive investigations of numerous gas/solid phenomena, such as
surface ionization, sputtering, emission of secondary electrons and ions
from surfaces under atom and/or ion impact, ion neutralization, and the
thermal accomodation of gaseous particles on surfaces. As a result, it has
become possible to gather a variety of valuable information. An un
fortunate result, however, has been that the studies of different impact
phenomena on surfaces have advanced so rapidly that often data have
been considered as isolated problems and contact between different fields
has tended to be lost.
The leading thought in the preparation of the manuscript has been to
give a compact s~opsis of certain atomic and ionic impact phenomena
on surfaces and thus to facilitate interdisciplinary communication bet
ween the different fields-as MASSEY and BURHOP [461] did so success
fully on a similar subject in chapterI X of their book published a decade ago.
The large amount of information available today on atomic and ionic
impact phenomena on solid surfaces obviously necessitates a selection of
topics. In the following, only impact phenomena on metal surfaces will
be considered; and even here only certain types of impact phenomena
IV Preface
have been selected. The author wishes to point out explicitly that his
selection by no means indicates the relative importance of the subjects
chosen but rather reflects his own interests and activities in the field.
The intention has been to give the reader a balanced view of the
subject, from both the experimental and theoretical standpoints, and to
emphasize the well established principles, which emerge and the many
peculiarities, obscurities, and uncertainties which still remain to be
resolved. In organizing the manuscript, consideration was given to the
sensitivity with which the atomic and ionic impact phenomena under
discussion depend on the nature of the metal surface and on the forces of
interaction between incident particles and the metal surface. These
topics have been treated in separate chapters at the beginning. In the
subsequent discussion of particular atomic and ionic impact phenomena,
each capter begins with a definition of the quantity investigated and
then presents a brief critical discussion of the experimental techniques
employed in the study of a particular collision phenomenon. This is
followed by a description of the experimental results.
The data have been considered against the available theoretical
background. However, in order to stay within the planned size of the
book, it often was not feasible to provide a detailed mathematical
theory. Instead, the emphasis has been laid on a presentation of the more
important concepts of the theories available and on a discussion of the
physical phenomena. Yet in most cases a physical account of different
theories has been given, and in some important cases even a more
detailed description of a particular theory has been provided.
An extensive bibliography enables the reader to go back to the
original literature for more detailed studies. Some pains have been taken
to formulate adequate definitions of the quantities discussed and, when
ever possible, to use the symbols consistently throughout the book. The
somewhat complicated designations of formulas, tables, and figures were
adopted to facilitate their identification with the appropriate section.
The original manuscript was prepared as an article in the "Ergebnisse
der Exakten Naturwissenschaften" on the invitation of one of the
editors, Professor S. Fr;UGGE. However, when it was completed in the
fall of 1962, Professor FLUGGE offered the alternative possibility of
publishing it as a monograph in the series "Struktur und Eigenschaften
der Materie". In pursuance of this suggestion, the author expanded the
very concise original manuscript in several places to clarify and strengthen
some of the points made and to include some of the more important new
contributions to the literature of the field. The references added in
bringing the survey up to the fall of 1963, when the type was actually
set, are the ones whose numbers are followed by a letter (to avoid
renumbering all the references).
Preface v
It is a pleasure to acknowledge the generous assistance received from
many people in preparing this monograph. I wish to express my sincere
gratitude to Dr. MORTON HAMMERMESH, Associate Director of the
Argonne National Laboratory and former Director of the Physics
Division, for his constant interest in the progress of the manuscript and
for giving me the opportunity and the facilities to undertake this task.
In addition, I am most heavily indebted to him for several stimulating
discussions concerning theoretical aspects of ionic impact phenomena
and especially for his kindness in translating a considerable portion of
the manuscript from German into English. I am also very grateful to
Dr. LOWELL M. BOLLINGER, Director of the Physics Division of the
Argonne National Laboratory, for his permission to carry this work to its
completion.
For communications concerning the original concept of the article,
the author is indebted to Professor W. WALCHER, University of Marburg,
Germany.
It is a pleasure to acknowledge the editorial assistance of Dr. FRANCIS
THROW, whose contributions to the article have been invaluable. His
great interest in the field reported here resulted in many helpful dis
cussions concerning the preparation of the article. In his careful reading
of the manuscript he directed the author's attention to numerous errors
and made many suggestions which helped to clarify the expression.
I am indebted to many colleagues for their permission to use their
drawings and figures. For assistance in the search for journals and
publications from the U.S.S.R., I acknowledge gratefully the help of
Mr. NORMAN P. ZAICHICK, from Argonne's library service.
I am very grateful to Mrs. CATHERINE YACK for the careful technical
preparation of the original German text. For their patience and careful
attention to detail in the accurate preparation of the final English text,
I wish to express special thanks to Mrs. JUDITH Z. MILLER, Mrs. KAy
PEMBLE, Miss JOANN METES, and in particular to Miss JOSEPHINE
MILLER, on whom fell the principal responsibility.
I also wish to acknowledge most gratefully the careful work of
Mr. RICHARD W. SNYDER and especially of Mr. BERNARD GREENBERG in
preparation of the figures. I sincerely appreciate the technical assistance
of Mr. GORDON GOODWIN in preparing some of the material used in the
manuscript. I should also like to thank my wife, Mrs. ELISABETH
KAMINSKY, for her invaluable help in correcting the proofs and for her
great understanding and encouragement in bringing the task to its
completion. The excellent cooperation of the Springer-Verlag in the
preparation of the book is gratefully acknowledged.
Argonne, Illinois, September, 1963 MANFRED KAMINSKY
Contents
Preface . . . . • . . . . . . III
1. The Nature of the Metal Surface 1
1.1. The Heterogeneous Surface 1
1.1.1. Physical Heterogeneity 1
1.1.1.1. Lattice Defects and Interstitial Positions 1
1.1.1.2. Occurrence of Different Crystal Planes on the Surface 3
1.1.2. Chemical Heterogeneity . . . . . . . . . . . . . . . 6
1.1.3. Induced Heterogeneity . . . . . . . . . . . . . . . 8
1.2. Theoretical Description of Metal Surfaces. The Work Function. 10
2. Determination of the Work Function of Metal Surfaces 17
2.1. Thermal Emission of Electrons . 17
2.2. Thermal Emission of Ions . . . . . . . . . . . 19
2.3. Photoelectric Method . . . . . . . . . . . . . 20
2.4. Method Based on the Field Emission of Electrons 24
2.5. Measurements of Contact Potential . 25
2.6. Electron Reflection Method . . . . . . . . . . 26
3. Preparation of Metal Surfaces . . . . . . . . . . . 28
3.1. Thermal Desorption; the Flash·F ilament Method. 28
3.2. Ion Bombardment of the Surface . 30
3.3. Evaporation of Thin Layers . . . . . . . . . . 31
3.4. Galvanotechnic Procedures. . . . . . . . . . . 33
4. Binding Forces Effective in the Collision of Atoms and Molecules with
Metal Surfaces • . . . . . . . . . . . . . . . 33
4.1. VAN DEB WAALS Forces-Physical Adsorption 33
4.1.1. Homogeneous Surfaces. . . . . . . . 33
4.1.2. Heterogeneous Surfaces . . . . . . . 36
4.2. Exchange Forces-Weak Chemisorption on Homogeneous and
Heterogeneous Surfaces . . . . . . . . . . . . . 36
4.3. Heteropolar Binding Forces-Strong Chemisorption 39
4.3.1. Atoms on Homogeneous Surfaces . . . . 39
4.3.2. Polar Molecules on Homogeneous Surfaces 40
4.3.3. Heterogeneous Surfaces . . 41
5. Energetics of Surface Reactions. . . . . . . . . 43
5.1. General Remarks and Definitions. . . . . . 43
5.2. Heats of Adsorption for Physical Adsorption . 45
5.3. Heats of Adsorption for Weak Chemisorption 48
5.4. Heats of Adsorption for Strong Chemisorption 52
6. Inelastic Collisions of Atoms and Molecules with Metal Surfaces: The
Accommodation Coefficient . . . . . . . . . . 56
6.1. Definition and General Remarks . . . . . . 56
6.2. Methods for Measuring Accommodation Coefficients 60
VIII Contents
6.2.1. Measurements in the Low·Pressure Range 60
6.2.1.1. Molecular-Beam Method . 60
6.2.1.2. Heat.Conductivity Method . . . 63
6.2.1.3. Recoil Methods ....... . 65
6.2.2. Measurements at High Pressures: the Temperature Jump 66
6.3. Experimental Results on Accommodation Coefficients . 68
6.3.1. Monatomic Gases. . . . . . . . 68
6.3.1.1. Experimental Data 68
6.3.1.2. Theoretical Considerations. 81
6.3.2. Diatomic Gases. . . . . . . . . 84
6.3.2.1. Experimental Data 84
6.3.2.2. Theoretical Considerations. 84
6.3.3. Polyatomic Gases. . . . . . . . 89
6.3.3.1. Experimental Data. . . . 89
6.3.3.2. Theoretical Considerations. 89
6.4. Determination of Relaxation Times for the Process of Energy Exchange
between the Normal Vibrational States of the System Comprising
Adsorbed Molecule and Metal Surface. . . . . . . . . 93
7. Elastic Collisions of Atoms and Molecules with Metal Surfaces . . . . . 95
8. Emission of Positive Ions Formed at Metal Surfaces (Surface Ionization) 98
8.1. Theoretical Considerations. . . . . . . . . . . . . . . . . . . 98
8.1.1. Equation for Emission from a Homogeneous Surface in the
Absence of External Electrical Fields . . . . . . . . 98
8.1.2. Equation for Emission from a Homogeneous Surface in an
External Electrical Field. . . . . . . . . . . . . .. 101
8.1.3. Equation for Emission from Heterogeneous Surfaces in the
Absence of External Electrical Fields . . . . . . . . 102
8.1.4. Equation for Emission from Heterogeneous Surfaces in an
External Electrical Field. . . . . . . . . . . . . . . . . 105
8.2. Relation of the SARA-LANGMUIR Equation to the FRENKEL Equation
and to Charge-Transfer Probabilities . . . . . . . . . . .. 107
8.3. Experimental Investigation of Positive Surface Ionization (PSI) . . 110
8.3.1. Experimental Methods ................. 110
8.3.1.1. "Bulb" Method without Mass Spectrometric Analysis 110
8.3.1.2. Single Filament Ion Source with Mass Spectrometer:
Plain Emitter-Porous Emitter . . . . . . .. 111
8.3.1.3. Multiple-Filament Source with Mass Spectrometer 114
8.3.1.4. Beam Methods 115
8.3.1.5. Pulsed-Beam Methods . . . . . . . . . . .. 115
8.3.2. Experimental Results . . . . . . . . . . . . . . .. 117
8.3.2.1. Positive Surface Ionization for Alkali Metal Atoms in
Weak Electric Fields .............. 117
8.3.2.2. Positive Surface Ionization of Some Alkali-Salt
Molecules on Metal Surfaces in Weak External Fields 124
8.3.2.3. Positive Surface Ionization of Alkaline Earth Elements
and Compounds in Weak External Fields. . .. 127
8.3.2.4. Positive Surface Ionization of Other Elements and
Compounds in Weak External Fields ........ 130
8.3.2.5. Positive Surface Ionization in Strong External Electric
Fields-Field Desorption ........•.... 133
Contents IX
9. Formation and Emission of Negative Ions at Metal Surfaces (NSI) 136
9.1. Theoretical Considerations. . . . . . . . . . . . . 136
9.1.1. Emission Equation for a Homogeneous Surface 136
9.1.2. Emission Equation for Heterogeneous Surfaces 137
9.2. Experimental Methods . . . . . . . . . . 137
9.3. Experimental Results . . . . . . . . . . 141
10. Sputtering of Metal Surfaces by Ion Bombardment 142
10.1. Introduction . . . . . . . . . . . . . . 142
10.2. Experimental Methods. . . . . . . . . . 142
10.2.1. Methods for Producing the Incident Ion 142
10.2.1.1. Glow Discharge . . . . . . 142
10.2.1.2. Low·Pressure Gas Discharge in a Magnetic Field 143
10.2.1.3. Supplemented Low-Pressure Arc 144
10.2.1.4. Ion Beams (Not Mass Analyzed) . . 145
10.2.1.5. Mass-Analyzed Ion Beams. . . . . 146
10.2.2. Methods of Determining the Sputtering Yield 147
10.2.2.1. Weight Change of Target and/or Collector 147
10.2.2.2. Optical Transmission through Sputtered Layers 149
10.2.2.3. Radioactive-Tracer Method . 149
10.2.2.4. Surface-Ionization . . . . . 150
10.2.2.5. Mass-Spectrometric Detection 150
10.2.2.6. Optical Spectroscopy . . . . 150
10.3. Experimental Results . . . . . . . . . . . 151
10.3.1. Sputtering of Neutral Target Atoms from Polycrystalline
Targets . . . . . . . . . . . . . . . . . . . . . . . 151
10.3.1.1. Threshold Values for Sputtering . . . . . . . . 151
10.3.1.2. Sputtering Yields in the Hard-Sphere Collision
Region . . . . . . . . . . . . . .. .. 153
10.3.1.2.1. Dependence on the Energy of the
Incident Ion . . . . . . . . 153
a) Energy Range 0.1-1.0 keV 153
b) Energy Range 1-60 keV . 156
10.3.1.2.2. Dependence on Angle of Incidence 159
10.3.1.2.3. Dependence on Target Temperature. 163
10.3.1.2.4. Self-Sputtering . . . . . . . . .. 164
10.3.1.2.5. Dependence on the Incident-Ion Current
Density . . . . . . . . . . . . . . 166
10.3.1.2.6. Dependence on Residual Gas Pressure . 167
10.3.1.2.7. Angular Distribution of Sputtered
Particles. . . . . . . • . . . .. 169
10.3.1.2.8. Mean Velocity of Sputtered Particles . 172
10.3.1.3. Sputtering Yields in the Weak-Screening Region . 175
10.3.1.3.1. Dependence on the Incident-Ion Energy 175
10.3.1.3.2. Angular Distribution of Sputtered
Particles. . . . . . . . . • • . . . 177
10.3.1.4. Sputtering Yields in the RUTHERFORD-Collision
Region ................... 178
10.3.2. Sputtering of Neutral Target Atoms from Monocrystalline
Targets . . . . . . . . . . . . . . . . • . . . . . . 179
10.3.2.1. Atom Ejection Pattern for Face-Centered Cubic
Metals . . . . . . • . . . 182
10.3.2.1.1. The (100) Surface. . . . . . . . . . 182
x Contents
10.3.2.1.2. The (110) Surface. . . . . . . .. 190
10.3.2.1.3. The (111) Surface. . . . . . . .. 192
10.3.2.2. Atom Ejection for Body-Centered Cubic Metals 197
10.3.2.2.1. The (100) Surface. 197
10.3.2.2.2. The (110) Surface. . . . . . . .. 198
10.3.2.2.3. The (111) Surface. . . . . . . .. 198
10.3.3. Sputtering of Target Particles in an Excited Neutral or
Ionized State from Polycrystalline and Mono-
crystalline Targets. ....... 199
10.3.3.1. Treshold Values for the Sputtering of Charged
Particles. . . . . . . . . . . . . . . . . . . 201
10.3.3.2. Species of Sputtered Positive and Negative Ions 201
10.3.3.3. Dependence on the Energy of the Primary Ion. 204
10.3.3.4. The Effect of Target Temperature . . . 206
10.3.3.5. Energy Distribution of Sputtered Ions. . 209
10.3.4. Etching of Surfaces by Sputtering . . . . . . . 211
10.3.4.1. Etching of Polycrystalline Metal Surfaces 211
10.3.4.2. Etching of Single-Crystal Surfaces . . . 214
10.3.5. Structural Changes in Pure Metals or Alloys as a Result ofIon
Bombardement. . . . . . . . . . . . . 217
10.4. Theoretical Treatments of the Sputtering Process . . . . . . . . 218
10.4.1. "Hot-Spot" Model-"Heated Spike" Model . . . . . . . 218
10.4.2. Collision Models. . . . . . . . . . . . . . . . . . . . 221
10.4.2.1. Collision Theories for the Energy Range E < EA
(Hard-Sphere-Region). . . . . . . . . . . . . 224
10.4.2.2. Collision Theories for the Energy Range
EA < E < EB (Weak-Screening Region) ..... 231
10.4.2.3. Collision Theories for the Energy Range E> EB
(RUTHERFORD-Collision Region) ... . . . . . 232
11. Ion Scattering from Metal Surfaces ................. 237
11.1 Definitions: Ion-Reflection Coefficient and Secondary-Emission
Coefficient . . . . . . . . . . . . . . . . . . . . . . . . . 237
11.2 Experimental Techniques ................... 239
11.3. Experimental Ion-Reflection and Secondary-Emission Coefficients 241
11.3.1. Dependence on the Incident Ion Energy. 241
11.3.1.1. Incident Noble-Gas Ions ........... 241
11.3.1.2. Incident Alkali Ions .•.. . . . . . . . . . 246
11.3.1.3. Incident Protons, Deuterons, and Various Other
Atomic and Molecular Ions. . . . . . . . . • . 248
11.3.2. Dependence on the Mass and Electronic Configuration of the
Incident Ion . . . . . . . . . . . . . . . . . . . . . 249
11.3.3. Dependence on the Mass and Work Function of the Target
Material. . . . . . . . . • . . . . . . . . . . 251
11.3.4. Dependence on the Angle of Incidence. . . . . . . . . . 251
11.3.5. Energy Distribution of Reflected and Secondary Ions . . . 253
11.3.6. Dependence on the Target Temperature and on Surface
Contamination . . . . . . . . . . . . . . . . . . . . 258
11.4. Theoretical Treatment of Ion Scattering from Metal Surfaces . . . 261
12. Neutralization of Ions on Metal Surfaces (Potential Emission of Secondary
Electrons) . . . . . . . . . . . . . . . . . . . . 263
12.1. Introductory Remarks and Definitions . . . . . 263
12.2. AUGER Neutralization; Resonance Neutralization 266
Contents XI
12.2.1. Experimental Methods 266
12.2.2. Experimental Results . 269
12.2.2.1. Singly-Charged Ions 269
12.2.2.1.1. Secondary-Electron Yield y and its De
pendence on the Energy E of the Incident
Ion ................ 269
12.2.2.1.2. Energy Distribution of Secondary Elec
trons and its Dependence on the
Incident-Ion Energy . . . . . . . . 274
12.2.2.1.3. Influence of Surface Contamination on
the Yield and Energy Distribution of the
Secondary Electrons . . . . 276
12.2.2.2. Multiply-Charged Ions ........... . 278
12.2.2.2.1. Secondary Electron Yield y and its
Dependence on the Energy E of the
Incident Ion . . . . . . . . . . . . 278
12.2.2.2.2. Energy Distribution of Secondary Elec-
trons ............... 280
12.2.2.2.3. Influence of Surface Contamination on
the Electron Yield and the Electron
Distribution . . . . . . . . . . . . 281
12.2.3. Theory of AUGER Neutralization . . . . . . . . . . . . 282
12.2.3.1. General Definitions of the Total Transition Rate and
Related Probability Functions . . . . . . . . . 282
12.2.3.2. Total Transition Rate and the Probability for
AUGER Neutralization. . . . . . . . . . . . . 285
12.2.3.3. The Probability of Emission of an Excited Electron
from the Metal Surface . . . . . . . . . . . . 286
12.2.3.4. Effects which Broaden the Electron Energy Distri-
bution ................... 289
12.2.3.5. Comparison of Experimental and Theoretical Values
for the Energy Distribution and Yield of Secondary
Electrons . . . . . . . . . . . . . . . .. 290
13. De-excitation of Metastable Atoms and Ions on Metal Surfaces. . . . . 292
13.1. Introductory Remarks and Description of Experimental Methods. . 292
13.2. Experimental Data for the Total Yield and Energy Distribution of
Secondary Electrons from De-excitation of Metastable Atoms and
Ions on Metal Surfaces. . . . . . . . . . . . . . . . . . . . 296
13.3. Theoretical Aspects of the AUGER De-excitation of Metastable Atoms
on Metal Surfaces . . . . . . . . . . . . . . . . . . . . . . 299
14. The Emission of Electrons from Metal Surfaces by Bombardment with
Charged and Uncharged Particles (Kinetic Emission) 300
14.1. Introduction . • . • . 300
14.2. Experimental Methods. . . . . . . . . . . 302
14.3. Experimental Results . . . . . . . . . . . 304
14.3.1. Dependence of Secondary-Electron Yield y on the Energy or
Velocity of an Incident Ion or Neutral Atom 304
14.3.1.1. Medium Energy Range . . . . . . . . . .. 305
14.3.1.1.1. Atoms and Ions of Noble Gases .. 305
14.3.1.1.2. Alkali or Alkaline Earth Metal Ions. 312
14.3.1.1.3. Ions of Various Kinds. . . . . .. 314
