Postdoctoral and Research Fellows
BSc (Hons) UNSW
PhD (Physics) UNSW
Senior Research Associate
(ARC Postdoctoral Fellow from May 2003)
Condensed Matter Physics
Quantum Electronic Devices Group

Organic/Molecular Electronics and Soft Condensed Matter Physics

AFM-based Fabrication of Nanoscale Electronic Devices

Novel Correlated States in Closely-spaced Bilayer Hole Systems

Quantum Chaos and Fractals in Semiconductor and Optical Billiards
Organic/Molecular Electronics and Soft Condensed Matter Physics
Organic polymers or plastics are generally accepted to be very poor conductors of electricity – in fact, they’re almost always considered insulators.
That’s why power-plugs are encased in poly-vinyl chloride (PVC) and electricians wear rubber-soled boots. However, in the late 1970s three scientists (Heeger, MacDiarmid and Shirakawa) demonstrated that polymers can be made to conduct electricity by manipulating their chemical structure 1 .
This groundbreaking work earned these researchers, one of them a physicist, the Nobel prize in Chemistry in 2000. The prospects for conducting polymer devices, or organic electronics, are very exciting from the point of view of both basic research and their tremendous commercial potential. Organic semiconductors have a number of significant advantages over conventional inorganic semiconductor materials such as silicon and gallium arsenide.
They are lighter, more flexible, more chemically versatile and far cheaper to produce. In addition, their potential for self-assembly and biocompatibility offer superior opportunities for their integration with future bio- and nanotechnologies.
In contrast to inorganic semiconductors such as Si and GaAs, conducting polymers are lighter, more rugged (they won’t shatter if dropped), chemically versatile, easier to process, and most importantly cheaper to produce! The

sum of these advantages is remarkably demonstrated in Fig. 1, where a complete integrated circuit (IC) of organic field-effect transistors (FETs) and other components is printed, using say an inkjet printer, onto a flexible plastic substrate (e.g., an overhead projector sheet). The circuit can be bent and twisted, treatment that would destroy a silicon IC, and continue working unaffected by the abuse. This technology is already on the market, its first major application being computer displays and LEDs. Other organic devices such as chips for smart cards, inventory control tags and photovoltaic solar cells are currently under development.
Organic electronics has experienced explosive growth in recent years.
Current research is strongly driven by the need for higher quality transistors with increased electron/hole mobilities, for faster operation. The main limitation on device quality is disorder, introduced by structural and compositional defects in the organic material. Advances in growth techniques for high-quality organic single-crystals 4 such as polyacenes and selfassembled organic thin-films 5 such as polythiophenes, allow devices with mobilities rivaling those found in amorphous Si and almost 10% of those found in the best single-crystal Si wafers, as shown in Fig. 2. UNSW is one of few institutes worldwide, and the only in Australia, presently developing this technology.
The sheer variety of organic materials means that it is possible to make organic devices from materials that display properties that simply cannot be achieved in inorganic semiconductors. The ability to tune electron-electron and electron-phonon interactions in these materials, as well as the band-gap, offers prospects for optically active and even superconducting transistors.
Indeed researchers at Bell laboratories in the USA caused a significant stir with a series of papers on the properties of organic transistors, including the observation of superconductivity at 117K in C
60
crystals 6 . Although these claims have since been discredited, there is a strong feeling in the community that organic devices, if made properly, should exhibit these phenomena because of the known properties of chemically doped organic crystals (e.g., doped-C
60
and other polymers such as TTF-TCNQ are well-known superconductors 7 ). In fact researchers at Los Alamos National Laboratory have observed field-effect induced metallic behavior 8 in C
60
and are confident that superconductivity will soon also be observed. Furthermore studies of field-effect transistors based on undoped pentacene single-crystals 9 and high-mobility polythiophene thin-films 4,10 by other researchers confirm that these devices do work. There is also much theoretical work 11 indicating that novel quantum effects should occur in high quality organic transistors. In collaboration with A/Prof. Alex Hamilton, I am attempting to reproduce the devices recently studied by the Bell labs group, with the hope that either the results that they reported can be reproduced, or that new physics and device

properties can be discovered in them, and working towards making organic devices a major research program within the School.
I also have a strong interest in soft condensed matter, in particular the potential for overlap between nanotechnology and biotechnology for future electronic and optoelectronic devices, or nanobioelectronics as it could be called. Nanoelectronics began as the end-game for miniaturization of inorganic semiconductor devices such as GaAs FETs, and in the late 1990s turned towards organic materials such as carbon nanotubes and dithiolated conjugated polymers. Only recently, scientists have started looking towards biology for the answers to nanotechnological problems, for example using the recognition properties of DNA to guide molecules and nanotubes into place, proteins as molecular motors, lipid bilayers as chemical sensors, and optically active proteins as light emitters/detectors.
AFM-based Fabrication of Nanoscale Electronic Devices
I am currently involved in a project with UNSW’s Electron Microscope Unit
(EMU) to develop Atomic Force Microscope (AFM) based lithography techniques on their AFM systems. The current focus is to develop a process known as local anodic oxidation (see Fig 3(a)), where current passed between a conductive tip and the sample, leads to dissociation of the surface water film and subsequent oxidation of the sample beneath the tip. The technique can be used to write insulating oxide lines < 100nm wide in semiconductors and metals, and hence fabricate nanoscale electronic devices such as that shown in Fig. 3(b). A major advantage of this technique is that the lithography can be imaged, and measured electrically in-situ , allowing corrections/additions to be made if necessary.
I am also interested in extensions to this technique involving AFM-based local electrochemistry, and other AFM-based techniques such as dip-pen nanolithography , where chemicals can be ‘written’ on the surface using the
AFM tip analogously to a feather quill, and direct manipulation of objects such as nanotubes, etc.
Novel Correlated States in Closely-spaced Bilayer Hole Systems
The quasi-two-dimensional electron and hole gases (2DEGS and 2DHGs) formed in Si-MOSFET inversion layers and at the interface of AlGaAs/GaAs heterojunctions, and devices such as quantum wires and dots formed in them, have been studied for over thirty years. In particular, the Integer and
Fractional quantum Hall effects, awarded the 1985 and 1998 Nobel Prizes in
Physics respectively, have highlighted the remarkable electronic properties of these systems. Developments in epitaxial growth of these systems now allow the fabrication of devices with two closely-spaced 2DHGs with independent

control of the interparticle spacing within each layer. In these devices, the interlayer particle spacing (and hence interaction strength) can be made comparable to the intralayer particle spacing (interaction strength) as shown in Fig. 4, leading to strongly coupled 2DHG bilayers. These systems exhibit remarkable properties including an interlayer coherent state in the absence of tunneling and interlayer frictional drag. In addition to the above, bilayer
2DEG/2DHG systems are predicted to exhibit a wealth of new physics including excitonic superfluids, Bose-Einstein condensation and Josephsonlike tunneling effects, these effects will be a focus for future studies in this area.
In collaboration with A/Prof. Alex Hamilton and students, I am currently involved in investigating the properties of the interlayer coherent state with low temperature, high magnetic field, electrical measurements, and developing new device structures and measurement capabilities to probe this remarkable state further. I am also interested in the electronic properties of devices such as semiconductor billiards in bilayer 2DEG samples, performing the first experiments on such samples in 1999 as part of my Ph.D. studies
(see below).
Quantum Chaos and Fractals in Semiconductor and Optical Billiards
In 1996-2000 I completed Ph.D. studies at UNSW, followed in 2000-2002 by a post-doc at the University of Oregon, working on quantum chaos and fractals in semiconductor billiards with A/Prof. Richard Taylor (now at UO) and A/Prof. Richard Newbury (UNSW) and collaborators at the Universities of
Cambridge (UK), Nottingham (UK), Arizona State University (USA) and
RIKEN Laboratories (Japan). The major focus of this work was the experimental study of fractal conductance fluctuations in semiconductor billiards as a function of geometry, soft-wall potential profile and other billiard and experimental parameters. I am also involved in a project in collaboration with the University of Oregon and the University of Nottingham to study quantum chaos in optical billiards based on GRIN optical fibers and microcavities.

Dependence of Fractal Conductance Fluctuations on Soft-wall
Profile in a Double-layer Semiconductor Billiard
A.P. Micolich, R.P. Taylor, A.G. Davies, T.M. Fromhold, H. Linke, L.D.
Macks, R. Newbury, A. Ehlert, W.R. Tribe, E.H. Linfield and D.A. Ritchie
Applied Physics Letters 80 , 4381 (2002) (pdf)


Evolution of Fractal Patterns during a Classical-Quantum
Transition
A.P. Micolich, R.P. Taylor, A.G. Davies, J.P. Bird, R. Newbury, T.M.
Fromhold, A. Ehlert, H. Linke, L.D. Macks, W.R. Tribe, E.H. Linfield,
D.A. Ritchie, J. Cooper, Y. Aoyagi and P.B. Wilkinson
Physical Review Letters 87 , 036802 (2001) (pdf)

Electromagnetic Wave Chaos in Gradient Refractive Index Optical
Cavities
P.B. Wilkinson, T.M. Fromhold, R.P. Taylor and A.P. Micolich
Physical Review Letters 86 , 5466 (2001) (pdf)

An Investigation of Weierstrass Self-similarity in a Semiconductor
Billiard
A.P. Micolich, R.P. Taylor, R. Newbury, T.M. Fromhold and C.R. Tench
Europhysics Letters 49 , 417 (2000) (pdf)
 Fractal Analysis of Pollock’s Drip Paintings
R.P. Taylor, A.P. Micolich and D. Jonas
Nature 399 , 422 (1999). (pdf)

Environmental Coupling and Phase Breaking in Open Quantum
Dots
J.P. Bird, A.P. Micolich, H. Linke, D.K. Ferry, R. Akis, Y. Ochiai, Y.
Aoyagi and T. Sugano
Journal of Physics: Condensed Matter 10 , L55 (1998). (pdf)
Office/Lab: OMB137B/OMB LG49/51
Mail Address
School of Physics
University of New South Wales
Sydney NSW 2052
Australia
E-mail Address mico@phys.unsw.edu.au
Phone Numbers

9385-6132
Facsimile Number
9385-6060
Figure Captions
Fig. 1: Conductive polymer (pentacene) circuit on a flexible polycarbonate substrate made by IBM Research Labs.
Fig. 2: Organic material quality increases tenfold every two years, and currently rivals that of amorphous silicon (graph from IBM Research Labs).
Fig. 3: (a) Schematic of the local anodic oxidation technique. (b) Image of a
GaAs nanostructured device from U.F. Keyser et al.
, Appl. Phys. Lett. 76 , 457
(2002).
Fig 4: When the interlayer spacing d becomes comparable to the intralayer spacing a, the interlayer and intralayer coulomb interactions become comparabl e leading to novel ‘interlayer coherent’ states similar to fractional quantum Hall states but spread across the two layers.
Fig 5: Wavefunction scarring along a periodic orbit of a semiconductor billiard, an important effect in quantum chaos.