Table Of ContentN A N O S T R U C T U R E S
A N D M E S O S C O P I C
S Y S T E MS
Proceedings of the International Symposium
Santa Fe, New Mexico May 20-24,1991
Edited by
Wiley P. Kir k
Departmen t of Physics
Texas A&M University
College Station, Texas
Mark A. Reed
Departmen t of Electrical Engineering
Yale University
New Haven, Connecticut
ACADEMI C PRESS, INC.
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Copyright © 1992 by Academic Press, Inc.
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ACADEMIC PRESS, INC.
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United Kingdom edition published by
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Library of Congress Cataloging-in-Publication Data
Nanostructures and mesoscopci systems : proceedings of the
international symposium, Santa Fe, New Mexico, May 20-24, 1991
edited by Wiley Ñ Kirk, Mark A. Reed,
p. cm.
"Contains work presented at the 1991 International Symposium on
Nanostructures and Mesoscopci Systems, held in Santa Fe, New Mexico.
May 20 to 24" — Pref.
Includes bibliographical references.
ISBN 0-12-4096603-
1. Nanostructures — Congresse.s 2. Mesoscopci phenomena (Physics) —
Congresse.s 3. Superlattices as materials — Congresse.s
4. Microstructure — Congresse.s I. Kirk, Wiley Ñ II. Reed, Mark
A. III. International Symposium on Nanostructures and Mesoscopci
Systems (1991 : Santa Fe, New Mexico)
QC176.8.N35N36 1992
530.41 - dc20 91-44247
CIP
Printed in the United States of America
92 93 94 95 9 8 7 6 5 4 3 2 1
Preface
This book contains work presented at the 1991 International
Symposium on Nanostructures and Mesoscopci Systems, held in
Santa Fe, New Mexico, May 20 to 24. Roughly half of the work
presented at the symposium addressed general interest issues and,
consequently, was selected for appearance in this volume. The re-
mainder of the work presented at the symposium dealt with specia-l
ized topics which appear as articles in the Academic Press journal
Microstructures and Superlattices . The symposium focused on
advances in nanostructure studies and related mesoscopci behavior,
emphasizing physics, structure, quantum many-body properties,
transport behavior, advanced fabrication techniques, and unique
electronic effects found in materials and devices on the nanometer
scale. In attendance at the symposium were 167 researchers from
fourteen nations.
The symposium was organized into fifteen sessions of 42
oral presentations that spanned five days. In addition to the oral
session,s 85 posters were presented in a week long poster session.
All the posters were of exceptional quality and the following seven
were awarded cash prizes and a certificate for outstanding poster
presentations: Coulomb Blockade Oscillations in the Conductance
of a Si-MOSFET Point-Contact , C. de Graaf, J. Caro, S. Radelaar,
and K. Heyers; Numerical Evaluation of Resonan t States , W. R.
Frensley; Magnetic Edge States in a ID Channel with a Periodic
Array of Antidots, M. Leng and C. S. Lent; Commensurability in
Weak and Strong Periodic Potentials , D. Weiss, A. Menschig, M.
L. Roukes, and P. Grambow; Dephasing and Dissipation in
Resonan t Double-Barriers , S.-R. Eric Yang; Destruction of Elec-
tron Interference in Submicron Au Loops Doped with Fe Impurities,
H. Vloeberghs, C. Van Haesendonck, Y. Bruynseraede, A. H. Ver-
bruggen, P. A. M. Holweg, and S. Radelaar; Dissipative Scattering
and Transport in Mesoscopi cSystems ,F. Sols.
xi
We have organized this book into eleven chapters. In the
first chapter we unify and summarize briefly the various individual
contributions that appear in the following ten chapters. The
material in this book represents the products of a new field that is
very dynamic, with many interesting ideas and approaches being
pursued. Therefore, for the researcher who seeks a collection of up-
to-date information in the field, we believe this book should fulfill
that purpose well.
The book's origin and contents basically derives from the
symposium's succes,s which in turn was a result of the efforts and
fine suggestions put forward by the Organizing and Program Com-
mittee, as well as the Advisory Committee. In the background of
every successful conference is a coterie of students, research
associate,s and faculty colleagues who see that things get done. In
this regard, we want to especialyl express our gratitude to: Craig
Andrews, Digant Dave, Sally Kirk , Robert Klima, Pawel Kobiela,
Eric Lee, Feng Li, and Judy Weichold for all the help they provided
in running the symposium. We are very grateful to Professor Mark
Weichold for overseeing the Poster Sessions and to Dr. Brosl
Hasslacher for arranging the poster booths from Los Alamos
National Laboratory. We are especialyl indebted to Professor
Czeslaw Jedrzejek, and Drs. Wieslaw Szott and Gregory Spencer
for their assistance in handling nearly 125 manuscripts at the
manuscript desk. Each of the referees, who helped review the
contributions, deserve much praise from us. We want to thank
Sandra Campbell for her dedicated assistance with the book's
format. Finally, we express our appreciation for the financial
support provided by the sponsors listed on the next page, without
which none of this would have been possible.
Wiley P. Kirk Mark A. Reed
College Station, Texas New Haven, Connecticut
xii
Organizing and Program Committee
Wiley P. Kirk , Chairman, Texas A&M University
Mark A. Reed, Co-Chair, Yale University
Robert T. Bate, Texas Instruments
William R. Frensley, University of Texas , Dallas
Brosl Hasslacher, Los Alamos National Laboratory
Czeslaw Jedrzejek, Texas A&M University
Alex L. de Lozanne, University of Texas ,Austin
John N. Randall, Texas Instruments
Mark H. Weichold, Texas A&M University
Advisory Committee
Steven P. Beaumont, University of Glasgow
Alec N. Broers, Cambridge University
Federico Capasso, AT&T Bell Laboratories , Murray Hill
Leroy L. Chang, IBM, Thomas /. Watson Research Center
Larry R. Cooper, Office of Naval Research
Harold G. Craighead, Cornell University
Supriyo Datta, Purdue University
Laurence Eaves, University of Nottingham
Karl Hess, University of Illinois
Henk van Houten, Philips Research Laboratories , Eindhoven
Klaus v. Klitzing, Max Planck Institut, Stuttgart
Jorg P. Kotthaus, University of Munich
Rolf W. Landauer, IBM, Thomas J. Watson Research Center
Anthony J. Leggett, University of Illinois
Venkatesh Narayanamurti, Sandia National Laboratories
Daniel Prober, Yale University
Michael A. Stroscio, U. 5. Army Research Office
xiii
Organizing and Program Committee
Wiley P. Kirk , Chairman, Texas A&M University
Mark A. Reed, Co-Chair, Yale University
Robert T. Bate, Texas Instruments
William R. Frensley, University of Texas , Dallas
Brosl Hasslacher, Los Alamos National Laboratory
Czeslaw Jedrzejek, Texas A&M University
Alex L. de Lozanne, University of Texas ,Austin
John N. Randall, Texas Instruments
Mark H. Weichold, Texas A&M University
Advisory Committee
Steven P. Beaumont, University of Glasgow
Alec N. Broers, Cambridge University
Federico Capasso, AT&T Bell Laboratories , Murray Hill
Leroy L. Chang, IBM, Thomas /. Watson Research Center
Larry R. Cooper, Office of Naval Research
Harold G. Craighead, Cornell University
Supriyo Datta, Purdue University
Laurence Eaves, University of Nottingham
Karl Hess, University of Illinois
Henk van Houten, Philips Research Laboratories , Eindhoven
Klaus v. Klitzing, Max Planck Institut, Stuttgart
Jorg P. Kotthaus, University of Munich
Rolf W. Landauer, IBM, Thomas J. Watson Research Center
Anthony J. Leggett, University of Illinois
Venkatesh Narayanamurti, Sandia National Laboratories
Daniel Prober, Yale University
Michael A. Stroscio, U. 5. Army Research Office
xiii
Sponsors
Office of Naval Research
Air Force Office of Scientific Research
Defense Advanced Research Projects Agency
U. S. Army Research Office
Los Alamos National Laboratory
National Science Foundation
Texas Instruments, Inc.
Texas A&M University
Department of Physics
Texas Engineering Experiment Station
xiv
INTRODUCTIO N
Mark A. Reed
Departmen tof Electrical Engineering
Yale University
New Haven ,Connecticut
and
Wiley P. Kirk
Departmen tof Physics
Texas A&M University
College Station ,Texas
The last few years of condensde matter physics have seen a revolution that
only occurs rarely in a scientists' professionla caree.r Until recently, solid state
physics has been constrained to physical systems that were essentiayll provided
by nature. Then, in the early 1970s, when groups at Bell Laboratories and IBM
reported the first realizations of quantum wells, scientisst realized that they had
the ability to construct artificial systems for the study of basci transpotr and op-
tical properties. This exciting ability has now taken on new dimensions with the
ability to microfabricaet matter on an unprecedentde scale. Utilizing
nanofabrication technique,s such as atomically-precies crystal growth and elec-
tron beam lithography, the modern researchre can now literally creaet any type
of structure he is ingenious enough to conceive, with dominant quantum me-
chanical properties. This "designer capability" has opened up a fascinating
new realm of fundamentla physics to be explored, and in addition is motivated
by the eventual application of quantum effects in nanostructurse to electronci
devices. The ability to manipulaet matter on an atomic scale, to creaet unique
materials, and devices with self-designde properties, has a universal appea.l It
represenst the mastering of Natures' rules by which materiasl are formed, and
testing ones' ingenuity in creating new phenomen.a
In March of 1989, 160 scientisst met in College Station, Texas, for a mee-t
ing that sought to bring together the often disparaet interesst of nanofabrication
engineer,s transpotr and device experimentalist,s and mesoscopci theorists. The
Internationa lSymposium on Nanostructure Physics and Fabrication^ mostly by
lucky timing, did just that, and had much longer range implications than any of
Nanostructures and 3 Copyright © 1992 by Academic Press, Inc.
Mesoscopci All rights of reproduction in any form reserved.
Systems ISBN 0-12-4096603-
the participanst had anticipated. The meeting turned out to be the forum for a
number of fast-breaking researhc areas that are today the topic of intense inter-
est in many researhc laboratorie:s quantum point contacts, lateral surface supe-r
lattices, quantum dots, and edge states, to name a few.
In the following two years, the tools to fabricate these systems became more
widespread and better controlled. There appearde to be a need for a further
meeting, to pick up where the last had left off, and to introduce the new and
exciting results that seemed to be appearing weekly. Thus, the International
Symposium on Nanostructure sand Mesoscopi cSystem swas held in May 1991,
in Santa Fe, New Mexico, to see how far the field had advance.d The two pa-
pers of the next chapter (Chapter 2, "New Challenges",) the keynote address
by Yoseph Imry and the closing talk by Noel McDonald, illustrate just that. Yo-
seph Imry points out that the field of nanostructuer physics has passed the in-
itial, "fashionable" stage and has proceedde to get down to the serious busi-
ness of utilizing these systems for fundamentla exploration of mesoscopci
physics. Perhaps a gauge of this is the poising of difficult questions such as
how quantum mechanics and statistical mechanics reconciel themselves in
these system,s where perturbative approachse no longer are valid. The student
may find such questions uncomfortable, and conclude that not much is really
known about physics on this scale; the experiencde researchre instead takes this
as an encouraging sign that finally some progress is being made. The paper by
Noel McDonald (Jason Yao, Noel McDonald, and Susanne Arney), on the
other hand illustrates elegantyl the control we are gaining in the fabrication of
structures on the microscale. The enabler for nanoscael physics is fabrication;
not just the ability to form sub-lOnm structure,s but in the future to scael our
fabrication machineyr and analytical techniques to the microscale. Motors, sen-
sors, actuator,s and STMs can now be reduced to the tens-of-microns level, and
integrated with electronics. These techniques could heradl a new era in
nanostructuer engineering, and allow us to see how much room there really is at
the bottom.
As mentioned, the enabler for nanostructurse is fabrication, and Chapter 3
("Advances in Nanostructuer Fabrication") explores what the state of the art is
today. Fabian Peas,e a leader in the field of electron beam lithography, surveys
the field and the limitations conventional lithography will mee.t He suggesst
that conventional lithography may not inherentyl have sufficient dimensional
precision for the needs of nanostructuer engineer,s and that "business as
usua"l is not good enough; alternative technologie,s such as LB films ("wet
MBE"), STM lithography, and natural lithography all deserve attention. In-
deed, some imaginative techniques have been tried. Horst Stormer presenst
how one can creaet ID structure that are truly atomicalyl sharp, by in situ over-
growth of a cleaved superlattice. This imposes a true Kronig-Penny model po-
tential on an electron gas, and the transpotr of this system is detailed. A vari-
4
ation of in situ growth is also presentde by Eli Kapon, where ID quantum wires
are fabricated by growth on patterned substrate.s Next, a very novel fabrication
technique is presentde by Greg Timp, using a photon field to directionalyl de-
posit atoms on a substrat.e The ability to create, without any physical mask, an
arbitrary deposition pattern or 3D structure could be an exciting future tech-
nique. Following this is a paper by Walter Smith, demonstratign the use of a
STM for the fabrication of nanostructure. sThis is a frontier of researhc targeted
by Yoseph Imry, where we expect to see exciting new results that will enabel
many new nanoscael device structure.s Finally, Steven Berger presenst a tech-
nique known as projection electron-bema lithography, which may provide a
fabrication technique where the high resolution advantage of electron beam li-
thography can be utilized in a parallel (instead of the present seria)l exposuer
mode, making the large scael fabrication of nanoscael devices a real possibility.
The ability to nanofabricaet structures at these dimensional scales implies
that one can now easiyl reach the regime where the device size is smaller than
the ballistic length of electrons transiting the structure. Indeed, with recent im-
provemenst in material quality, this has begun to reach an almost absudr limit;
electron mobilities exceeding 10 million (cm /V-s) with correspondign electron
mean free paths of 100 microns are now possible. In this limit, electrons can be
steered, deflected, and focused in a manner very similar to optics, as illustrated
in Chapter 4 (*'Ballistic Transpotr and Coherence)" by Joe Specto.r One can
now construct a variety of optical analogue,s such as a Young's double slit ex-
periment as presentde by Uri Sivan, and measuer such quantities such as elec-
tron coherenec and phase-breakign lengths, to determine the amount of
electron-electrno scattering. These studies give a deeper insight to transpotr in
more conventional types of experiment,s such as that presentde by Seigo
Tarucha, or for complex multiple-bend and -reflection nanostructure, sas pre-
sented by Wipawan Yindeepo.l
The ability to combine heterojunction resonant tunneling structures with
modern nanofabrication techniques has opened up a whole area of exciting re-
search in low-dimensional tunneling. The first paper of the next chapter (Chap-
ter 5, "Low-Dimensional Tunneling"), by Seigo Tarucha, introduces the fasci-
nating transpotr seen in two- and three-dimensionalyit confined quantum wells.
This is followed by an analyssi of these and similar results by a pioneer in the
theoretical understandign of low dimensional resonant tunneling, Garnett Bry-
ant. These nanofabricatde structures can also enter a new regime, where the en-
ergy of discreet electronci charging ("Coulomb blockade") in appropriateyl
designed structures can compeet with the energy splittings of size-quantizde
states. Evidence for this is presentde in the paper by Vladimir Goldman, and a
clear theoretical discussion of the charging energies of confined electrons is
presented by Craig Lent The fascination with these structures is that, with
clever fabrication technique,s one can "tune" the dimensionaliyt of the tunne-l
5
