Festkörperprobleme 23: Plenary Lectures of the Divisions “Semiconductor Physics” “Metal Physics” “Low Temperature Physics” “Thermodynamics and Statistical Physics” “Thin Films” “Surface Physics” “Surface Physics” “Magnetism” of the German Physical Society

327 Pages·1983·7.463 MB·German

by  Klaus Sattler (auth.), P. Grosse (eds.)

FESTKORPERPROBLEME XXIII
ADVANCES IN SOLID STATE PHYSICS
REPROKTSEF
EMELBORP IIlXX
SECHAVDA HI
DILOS ETATS
yranelP Lectures of the Divisions
SCISYHP "Semiconductor Physics"
"Metal Physics"
"Low Temperature Physics"
"Thermodynamics dna Statistical Physics"
"Thin Films"
"Surface Physics"
"Magnetism"
of the German Physical Society )GPD(
,tdatsneduerF March 12 .-25., 1983
Edited by
.P ,essorG nehcaA
With 212 figures
geweiV
ISSN 0430-3393
All rights reserved
(cid:14)9 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH, Braunschweig 1983
No part of this publication may be reproduced, stored in a retrieval system or transmitted,
mechanical, photocopying or otherwise, without prior permission of the copyright holder.
Set by Vieweg, Braunschweig
Printed by Lengericher Handelsdruckerei, Lengerich
Bookbinder: .W Langeliiddecke, Braunschweig
Cover design: Barbara Seebohm Braunschweig
ISBN 3-528-08029-9
Foreword
The spring meeting 1983 in Freudenstadt of the subgroup Solid State Physics -
Arbeitskreis Festk6rperphysik - of the Deutsche Physikalische GeseUschaft has
covered again a wide field of topics ranging from fundamental physics to technical
applications of semiconductors.
Volume XXIII of the ,,Festk6rperprobleme" contains a selection of the invited
talks presented at that conference.
The first contribution of K. Satfler deals with the connecting link between mole-
cules and crystals, the so-called microclusters. These fascinating experiments were
honored with the Walter-Schottky-prize 1983.
The next four papers concern more general aspects of condensed matter physics:
Nonlinear structures and solitons. - The transition from the B 1-type to the
Bl3-type lattice in IV-VI-compounds. That si an example for a ferroelectric phase
transition in a very simple crystallographic system. - Optical properties of small
particles, an inhomogeneous system which has to date a remarkable Renaissance. -
The x-ray synchrotron as a powerful, modem tool in solid state physics. This topic
si especially of interest considering the European facilities of the next future.
The further seven papers are addressed to physical problems in the field of prepara-
tion technique and modern ways to prepare "synthetic" semiconductors:
Ion implantation. - Laser annealing. - A nice atlas of defect patterns which arise
during the crystal growth from the melt. - The interaction of semiconductor
surface with hydrogen and oxygen as well as with metals. The first is a basic process
of interest during the oxidation of silicon. The second si of interest to understand
the properties of metal/semiconductor contacts. - The extension of the spectrum
of semiconducting systems due to the electronic properties of nipi-superlattices
and of the two dimensional electron gas, respectively.
Under these the paper of H. Kurz deals with the contradictory matter of explaining
the microscopic mechanisms of laser annealing. The paper contributes therefore in
an "up to date" way to a very excited discussion!
The last three papers concern the technical applications of semiconductors:
Semiconducting gas sensors. - Semiconductor devices in motor vehicles. - Optical
communication technique. In these contributions the state of the art and some
outlook are reviewed.
V
The editor thanks all the authors from research institutes, from industrial labora-
tories, and from universities for their collaboration at the conference and their
effort in preparing the manuscripts. I thank in addition the publisher, especially
Mr. A. Schubert and my coworker Mr. J. Brunn, who assisted me cautiously in
reading all the manuscripts and the proofs, and last not least I thank my colleagues
in Aachen and in some other places for their help in organizing the conference.
Aachen, Juni 1983
Peter Grosse
VI
Contents
Klaus Sattler
The Physics of Microclusters
Helmut Biittner, Heinz Bilz
Nonlinear Structures in Solid State Physics 13
Giinther Bauer, Wolfgang Jantseh, Eike Bangert
Band Edge Structure of Ferroelectric IV-VI Compounds 27
Donald R. Huffrnan
Optical Absorption Studies of Surface Plasmons and Surface
Phonons in Small Particles 49
Ulrich Bonse
Synchrotron X-Rays for Solid State Physics 77
Paul Ziemann
Ion Implantation - A Modem Tool of Solid State Physics 93
Heinrich Kurz
Fundamentals of Pulsed Laser Annealing 115
Elisabeth Bauser
Crystal Growth from the Melt 141
VII
Heribert ,rengaW Harald 1bach
Hydrogen and Oxygen Bonding on Silicon Surfaces 165
Gary .W Rubloff
Microscopic Properties and Behavior of Metal/Semiconductor Interfaces 179
Gottfried .H Dohler
n-i-p-i Doping Superlattices - Tailored Semiconductors with
Tunable Electronic Properties 207
Nuyen .T Linh
The Two-Dimensional Electron Gas and its Technical Applications 227
renreCl Hagen, Rainer .E Lambrich, Johannes Lagois
Semiconducting Gas Sensors 259
gnagfloW Heinke
The Use of Semiconductors in Motor Vehicles 275
A saerdn Schlachetzki
Optical Communication - Glass Fibres and Semiconductors 295
VIII
Festk6rperprobleme XXII I (1983)
The scisyhP of sretsulcorciM
Klaus Sattler
Fakult~t for Physik, Universitiit Konstanz, Konstanz, Federal Republic of Germany
Summary: A review on microcluster research in our laboratory is presented. Metallic-, tonic- and
van der Waals clusters between two and several thousand atoms or molecules per particle have
been generated and analysed by electronic time of flight mass spectrometry. Besides results con-
cerning the condensation mechanisms, the magic numbers of stability and the effect of Coulomb
explosion are discussed in detail.
1 Introduction
Growth of matter in the gas phase begins with the formation of clusters. Under certain
conditions atoms or molecules stick together forming agglomerates. Containing be-
tween two and about thousand atoms or molecules, these particles are called micro-
clusters 1-3. In this size range, most of the physical properties are different from
the corresponding bulk material. This is because the atomic arrangement and the
interatomic distances are different from the bulk and a high amount of atoms is
situated at surface positions. Furthermore, translational symmetry, transport prop-
erties, collective phenomena like ferromagnetism or superconductivity, characteristic
for the infinite bulk system, are not yet present.
Calculations on these finite systems can be done by molecular orbit treatments 4,
developed in molecular physics. On the other hand, the clusters can be approached
from the solid by extrapolating energy band structure results towards smaller dimen-
sions 5. Furthermore, computer simulation experiments (molecular dynamics or
Monte Carlo treatments) can be done 6, 7. The applicability of thermodynamic
treatments down to molecular dimensions 8, 9, is questionable.
A great deal of theoretical predictions has been made for microclusters, in many cases
contradicting each other I 0. "Crystallographic" and electronic structure calculation
results differ depending on the applied treatment, on the approximations, on inclu-
sion of refinements like electron-electron correlations and on the used parameters like
interatomic distances.
Experiments in the whole size range of microclusters have not yet been reported be-
cause no method was able to generate particles with high enough intensity. The
microcluster range, however, could be approached from both sides, going from the
atom to the dimer, trimer, tetramer etc. or going from the solid towards smaller di-
mensions 11 .
2 Microcluster Properties
What do we know about microclusters?
Most of the atoms in a microcluster are at surface positions. Even a 500 atom particle
consists of 250 surface atoms.
As the surface curvature increases with decreasing size, the surface tension increases
too. Therefore, going from the solid towards the atom, increasing pressure occurs and
cluster matter can be considered as ordinary solid state matter under high pressure.
The result si that the interatomic distances are reduced. This has been verified by
EXAFS-experiments - extended X-ray absorption fine structure - (10 % atomic
distance reduction for Cu- and Ni-particles) 12.
,3H the simplest microcluster si a equilateral triangle. This has been determined by
beam foil Coulomb explosion experiments 13. This result si important because it
shows that collective phenomena begin at very small sizes to occur. The addition of
one further atom effects that the covalent bond between the two protons in 2H
breaks off and the three 1 s-electrons in 3H occupy molecular orbits of the whole
trimer.
These results seem to contradict the conclusions from size distributions. In the mass
spectra of clusters from hydrogen, nitrogen, oxygen 14-16 or iodine 17 sequences
of maxima at X2, X,, 6X etc. are found. The conclusion could be that the dimers
retain their identity as covalently bound units with weak van der Waals forces in be-
tween. However, the observed sequences have also been expected from molecular
orbit considerations 18. From the combination possibilities for atomic orbitals for
different cluster sizes an odd-even effect in the potential energy of the highest oc-
cupied cluster valence state si expected which results in higher stability of even par-
ticles. These considerations would allow the dimers to loose their individual prop-
erties, the particles being considered as agglomerations of individual atoms.
There are several experimental results, however, which show the opposite. Spectra of
antimony or sodium chloride clusters (this work) show sequences of 4 n or 3 n, re-
spectively, according to multiples of the building units (Sb4, (NaCI)3), and we sup-
pose that the clusters contain these molecules as individual units. Therefore, con-
vergency to collective arrangements remains an open question and has to be inves-
tigated in the future.
To solve the question of convergency si one of the basic aims in microcluster research.
How many bound atoms are necessary to get bulk properties? Very likely this ques-
tion cannot be answered in common. The transition to bulk behaviour depends both
on the property being considered and on the kind of material being studied. The energy
position and width of the distribution of valence electron states may have reached
the bulk values at very small sizes {n = 6 19, n = 8 20 for transition metal clusters
(theory); n ~ 31 for carbon chains in organic molecules (theory and UPS-experiment
21 - ultraviolet photoemission spectroscopy -)}. If we consider, however, ionization
potentials, crystallography, conductivity, superconductivity or magnetism, the finite-
infinite transition si expected to occur at much bigger sizes. Atomic structure changes
from the bulk properties (found by electron diffraction experiments 22), or changes
in the plasma oscillations (measured by optical absorption 23), both are found at
particles containing about thousand atoms.
In this paper we mainly consider the stability of neutral and charged microclusters.
For nondirected short range forces (van der Waals coupling, inert gases), n <~ 1000,
particles with fivefold symmetry should have the highest binding energies. Computer
simulation experiments for a 13-atom Ar-cluster show a spontaneous rearrangement
from an initial fcc-structure to the icosahedron 24, 25. Furthermore, electron dif-
fraction pattern 26, 27 have been fitted with icosahedron structures assumed. Full
shell icosahedron numbers (one atom in the center, 12 nearest neighbours, 42 next
nearest neighbours etc.) are 13, 55, 147,309, 561 etc. 28.
Metal clusters, with directed (p-electrons) and long range forces influencing the next
nearest neighbours too, may have other magic numbers of stability. eW additionally
expect that the degree of delocalization of the valence electrons influences the atomic
arrangements. Ionic clusters, Coulomb interaction assumed alone, are predicted to have
multiring structure, composed of trimer units 29.
Ionized clusters could have different stability conditions compared to the neutral ones.
It is the subject of our investigations to decide, if the measured size distributions re-
flect the stability of the neutral clusters alone, of the ionized clusters alone or of both.
Multiply charged clusters are detected if the electron ionizing energies lie above the
corresponding thresholds. In the mass spectrum the peaks from X~-clusters appear
at positions half of the Xn-masses, X §3 and X4§ at 1/3 and 1/4 of their original
masses, respectively.
eW mainly review our studies on microclusters. More comprehensive reviews are given
elsewhere 30, 31.
3 Generation and Detection
eW apply two different methods for particle generation: (i) inert gas condensation
and (ii) adiabatic expansion.
Metallic and ionic clusters are grown by inert gas condensation. The vapours are co-
oled by He-gas in a diffusion chamber yielding the formation of microclusters. The
principle, the details of the cluster source and the condensation conditions are given
elsewhere 32, 33.
Van der Waals clusters are generated by adiabatic expansion of the gases through a
thin nozzle into vacuum. Within some nozzle diameters (diameter typically 0.2 mm)
apart from the exit the beam is cold and dense enough and condensation to clusters
occurs. Then, again some nozzle diameters more apart, there is a transition to a molecu-
lar beam, with the particle density being low enough, that no further clustering
occurs.