Table Of ContentM O L E C U L A R
E L E C T R O N I C S
Commercial Insights, Chemistry, Devices,
Architecture and Programming
James M Tour
Rice Universi3 USA
‘Q$
World Scientific
NewJersey London Singapore Hong Kong
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British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.
MOLECULAR ELECTRONICS: COMMERCIAL INSIGHTS, CHEMISTRY,
DEVICES, ARCHITECTURE AND PROGRAMMING
Copyright 0 2003 by World Scientific Publishing Co. Pte. Ltd.
All rights reserved. This book, or parts thereof; may not be reproduced in any form or by any means,
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ISBN 981-238-269-0
ISBN 981-238-341-7 (pbk)
Printed in Singapore by World Scientific Printers (S) Pte Ltd
Dedication
To Him Who demonstrated His love for me by giving
.
Himself for me. .
Preface
I was asked by the editors to write a book on molecular electronics that focuses
upon the work that has been conducted in my own research. A presentation of
one’s own work is far simpler to write than a compendium covering the work of
the many superb researchers in the field. Although I will make mention of
other’s work in the context of the research that we have done, no science, at
least not chemistry, is done in a perfect vacuum. I am deeply indebted to
numerous colleagues around the world for their inspiring discussions and
complements with work that far surpasses, in quantity and quality, that of my
own. To them I say, thank you 1000 times.
The editors permitted me the liberty to insert some learned experiences
regarding startup companies. Those experiences might prove insightful to the
prospective founder, corporate officer, or potential investor in the molecular
electronics business arena.
My entry into the field of molecular electronics occurred in 1988, at the
start of my independent research career in synthetic organic chemistry at the
University of South Carolina. I set out with my first graduate students, Jeffrey
Schumm and Ruilian Wu, to synthesize the orthogonal switch as proposed by
Ari Aviram, who was at IBM at the time. My students and I were blissfully
unaware of the steep slopes of challenge that awaited us and the colorful
comments that we would be obliged to entertain from concerned colleagues
around the world. Their disgruntlement was fundamentally with the basic
premise upon which molecular electronics is built, namely, molecules having to
perform switching in an addressable array. In 1992 we teamed with Professor
Mark Reed of Yale University. Mark’s device testing ability, his “can-do”
research spirit, his rich background in solid-state physics from his earlier
corporate days at Texas Instruments, and his ability to address the sharpest
attacks of the critics, became the sustaining grace of our molecular electronics
effort. Though unbelievers remained for a time, and some even remain until
today, the number of believers and true practitioners of molecular electronics
has risen sharply.
With generous federal support, primarily from the Defense Advanced
Research Projects Agency (DARPA), the Office of Naval Research (ONR), the
Army Research Office (ARO), the National Science Foundation (NSF), the US
Dept. of Commerce, National Institute of Standards and Testing (NIST), the
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viii Preface
National Aeronautics and Space Administration (NASA), and the early risk-
taking willingness by the program directors of those organizations (especially
Jane Alexander, Bill Warren, Bruce Gnade, Christie Marrion, and Kwan Kwok
of DARPA and John Pazik of ONR), the initial Reemour research team could
expand to add numerous complementary scientists who furthered the
accomplishments. The team now includes David Allara (surface science) and
Paul Weiss (probe microscopy) at Penn State University, Paul Franzon (device
engineering) at North Carolina State University, Jorge Seminario (chemical
theory) at the University of South Carolina, Patrick Lincoln (computer science)
at the Stanford Research Institute, Herb Goronkin, Ray Tsui, and Islamshah
Amlani (device physics and engineering) at Motorola Corp., A1 Bard at the
University of Texas (electronics measurements) and all of their respective
research groups. There are many other groups with which we collaborate, a
testament at the heart of molecular electronics, namely interdisciplinary
research. Most importantly, many portions of this book were derived from
collaboratively written works by and with my student and post doctoral
associates, primarily: Darren Pearson, LeRoy Jones, 11, Jeffrey Schumm, Ruilian
Wu, Timothy Burgin, Adam Rawlett, Masatoshi Kozaki, Yuxing Yao, Raymond
Jagessar, Shawn Dirk, David Price, Stephanie Chanteau, Dmitry Kosynkin, J. J.
Hwang, Michael Stewart, Summer Husband, Christopher Husband, William Van
Zandt, Lauren Wilson, Jonathan Daniels, Jay Henderson, and Dustin James.
Dustin also helped enormously with the organizing of this book. I also thank
Steve Currall, Professor of Business, for his insight and advice through the most
trying business situations; he’s never yet been incorrect in his counsel.
In summary, although the molecular electronics work I describe in this
book is not comprehensive, it will be broad in its scope of covered topics.
Specifically, the background, commercial landscape, synthetic chemistry, initial
device construction, architecture and programming are covered in a manner to
be of aid to the chemist, surface scientist, physicist, engineer, computer scientist,
mathematician. investor and the casual reader alike.
James M. Tour, Rice University
Contents
Preface vii
Chapter 1. Commercialization of Molecular Electronics 1
1.1. Introduction 1
1.2. Commercial Challenges of Molecular Electronics 2
1.2.1. Investments in Molecular Electronics 3
1.2.2. Molecular Electronics Market Insertion Strategy 8
1.3. Molecular Electronics-Focused Companies 11
1.4. Advice from the Trenches for the Wannabe Corporate Founder 16
1.5. From a Front Row Observer to the Aspiring CEO of an
Academically Founded Startup 22
Chapter 2. Molecular Electronics 25
2.1. Introduction 25
2.2. The DNA and Quantum Computing Distinctions 29
2.3. Present Microelectronics Technology 29
2.4. Monetary and Fundamental Physical Limitations of Present
Technology 30
Chapter 3. Chemical Synthesis 33
3.1. Iterative Approaches to oligo(2,5-thiophene ethyny1ene)s
Molecular Wires, Properties and Experimental Details 33
3.1.1. Introduction 33
3.1.2. Results and Discussion 34
3.1.2.1. Monomer Syntheses 34
3.1.2.2. Controlled Oligomer Syntheses 35
3.1.2.3. Oligomer Characterization 37
3.1.2.4. Attachment of Thiol End Groups 38
3.1.3. Summary 42
3.1.4. Experimental Procedures 42
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X Contents
3.2. Iterative Approaches to oligo( 1,4-phenylene ethyny1ene)s
Molecular Wires, Properties and Experimental Details 56
3.2.1.I ntroduction 56
3.2.2.R esults and Discussion 56
3.2.2.1. Monomer Syntheses for Solution-Based
Oligomerizations 56
3.2.2.2. Oligomer Syntheses in Solution 59
3.2.2.3. Monomer Syntheses for the Polymer Supported
Approach 60
3.2.2.4. Oligomer Syntheses on the Polymer Support 60
3.2.2.5. Spectroscopic Reaction Monitoring Techniques on
the Resin 62
3.2.2.6.A ssessing Solid Phase Reaction Yields 62
3.2.2.7. Characterization of the Oligomers 68
3.2.2.8.A ttachment of Thiol End Groups 71
3.2.3. Summary 73
3.2.4.E xperimental Procedures 74
3.3. Shorter Phenylene-Based Molecular Wires and Devices and
Experimental Details 110
3.3.1. Synthesis of Molecular Scale Wires 110
3.3.1.1. Synthesis of One-Terminal Oligo(pheny1ene
ethynylene) Molecular Wires 110
3.3.1.2.S ynthesis of Two-Terminal Oligo(pheny1ene
ethynylene) Molecular Wires 112
3.3.1.3. Syntheses of Three-Terminal Molecular Scale Wires 113
3.3.1.4.M olecular Wires with Internal Methylene and
Ethylene Transport Barriers 114
3.3.2.S ynthesis of Molecular Scale Devices with Heteroatomic
Functionalities 119
3.3.3. Porphyrin Containing Molecular Scale Wires 126
3.3.4.S ynthesis of Dipole-Possessing Molecular Wire SAMs to
Control Schottky Barriers in Organic Electronic Devices 128
3.3.5. Experimental 130
3.4. Highly Functional Molecular Wires and Devices with Diverse
Alligator Clips and Experimental Details 176
3.4.1. Introduction 176
3.4.2. Switches and Memory Components 177
3.4.3.A lligator Clips 180
Contents xi
3.4.4. Conclusions 184
3.4.5. Experimental 184
3.5. Combinatorial Routes to Molecular Wires and Devices and
Experimental Details 198
3.5.1. Introduction 198
3.5.2. Results and Discussion 198
3.5.2.1. Monomer Synthesis for the Combinatorial
Approach 198
3.5.2.2. Oligomer Syntheses in Solution 199
3.5.2.3, Oligomer Syntheses on a Solid Support 200
3.5.3. Summary 205
3.5.4. Experimental Section 206
Chapter 4. Molecular Self-Assembly, Device Construction, and
Testing 229
4.1. Self-Assembly and Molecular Ordering 229
4.2. Probe Addressing of Molecules 232
4.3. Switching and Memory in Molecular Bundles 238
4.4. Large Area Molecular Electronic Devices: The Large Area
Contact Problem 249
4.5. Summary 250
Chapter 5. Architectures in Molecular Electronics 251
5.1. Introduction 25 1
5.1.1. Quantum Cellular Automata (QCA) and Electrostatics
Architectures 252
5.1.2. Cross-Bar Arrays 256
5.1.3. The NanoCell Architecture 26 1
5.2. Summary 265
Chapter 6. Programming the Nanocell 266
6.1. NanoCell 266
6.1.1. Nanocell Design 267
6.1.2. Molecular Switches 268
6.1.3. Simulated Nanocell 272
6.1.4. The Nanocell as a Logic Gate 274
6.2. Training a NanoCell 279
6.2.1. NanoCell as an Optimization Problem 279
