HKUST
Physical Sciences 1 July 1993
* * * * * * * * * * *
Magnetotransport in spatially periodic fields The magnetotransport of a two-dimensional electron gas (2DEG) in a spatially periodic field is studied in the quantum Boltzmann equation formalism. The first case involves a 2DEG in a uniform magnetic field and a periodic electric field. A novel conductivity jump (of five orders of magnitude) occurs when the electric field changes slightly (i.e., changes of one order of magnitude). This is explained in terms of a field-induced transition in the electronic structure. The second case involves a 2DEG in a uniform magnetic field superposed with a spatially periodic magnetic field. Many new phenomena are predicted, including transitions similar to the first case but in situations more accessible to experimentalists.
Investigator(s)
Dr Kwok-Yip SZETO Physics, HKUST
Award
SponsorArea
Start datePersonal research HKUST
Physical Sciences 1 November 1993
* * * * * * * * * * *
Theory of pattern formation in two-dimensional soap froth
Study of the spatia-temporal evolution of soap froth is made in conjunction with experiments.
The methods of analysis involve topological classification of pattern, determination of shell distribution function, and mean field analysis of the critical temperature of froth breaking.
The qualitative explanation of the mean area evolution of soap froth under constant temperature ramping rate can be extended to
Research Report (1993 -94)
66
include few-neigbors effects in the theory of the critical temperature. Conductivity measurement is planned for the studies of the froth breaking as a stochastic process. Similar work on pattern formation in phyllotaxis is underway.
Investigator(s)
Dr Kwok-Yip SZETO Physics, HKUST
Award
Sponsor
Area
Start datePersonal research HKUST
Physical Sciences 1 January 1994
* * * * * * * * * * *
Light propagation in gain media
We study light propagation in a one-dimensional layered medium with gain by using the transfer-matrix method. Both transmission and reflection properties are studied as a function of gain coefficient and randomness for any given sample thickness.
The asymptotic behavior in a sample of infinite thickness is also studied. For a wide range of gain coefficient and randomness, interesting scaling behaviors with respect to localization length and saturation length are obtained.
Investigator(s)
Dr Zhao-Qing ZHANG Physics, HKUST
Award
SponsorArea
Start datePersonal research HKUST
Physical Sciences 1 May 1994
* * * * * * * * * * *
Photoluminescence diagnostic technique for nasopharyngeal carcinoma
This thesis research project will study native fluorescence from normal and malignant nasal tissues. Differences in fluorescence spectra of normal and the cancer nasal tissues will be studied in order to develop a new diagnostic technique. The effect of random scattering and of self-absorption in tissues on the fluorescence spectra will also be studied.
Investigator(s)
Dr Kwong-Mow YOO (Supervisor) Physics, HKUST
Mr John Kam Wai LEUNG
Award Thesis
Sponsor HKUST
Area Physical Sciences
Start date 1 September 1993
* * * * * * * * * * *
Theoretical study of Anderson localization effect on the electrical conductance of mesocopic amorphous thin film
Anderson localization is generic to wave propagation in random media. In one- and two-dimensonal systems, there exist only localized wave modes or states. In three dimensions, however, both extended and localized modes can exist. The crossover from localized to extended states is fundamental to the understanding of metal-insulator transition. In this project, the electrical conductances of mesoscopic amorphous thin films are studied by computer simulations on a 3D model of a random medium.
Calculation of dipole exciton binding energy An exciton is a bound pair of electrons and hole in a semiconductor, which is fundamental to the understanding of optical absorption properties of semiconductors. When a semiconductor is laid on a superconductor, it is anticipated that a dipole exciton (a bound pair of dipoles) will substitute for an exciton in the optical process. The comparison between theoretical calculation and experimental results will improve our understanding of this phenomenon.
Investigator(s)
Prof. Ping SHENG (Supervisor) Physics, HKUST MrTanLI
Award Sponsor Area Start date
Thesis HKUST
Physical Sciences 1 March 1994
* * * * * * * * * * *
Lateral transport and localization behaviors in layered media with isotropic scatterings The lateral transport and localization behaviors in layered media with isotropic scatterings are studied numerically. We consider a system of alternating propagating
67
and non-propagating layers. The propagating layers have different layer energies. The non-propagating layers, which serve as the barriers between two adjacent propagating layers, are assumed to have the same barrier height.
Scatterings introduce hopping and trapping behaviors among various propagation layers.
As a result, a dominating channel is formed and two lengths can be defined: an equilibration length and a localization length.
The equilibration length is the length the system takes to reach equilibri urn transmission ratios among various propagating channels. After equilibration all the channels aquire the same localization length. The dependence of the dominating channel, equilibration and localization lengths on the layer energies, barrier height, and the isotropic randomness will be discussed for various layer thicknesses.
Investigator(s)
Zhao-qing ZHANG (Supervisor) Physics, HKUST
Mr Alexander Kin Chit 0
Award Thesis
Sponsor HKUST
Area Physical Sciences
Start date 1 March 1994
* * * * * * * * * * *
Studies of optical nonlinearities in solid, liquid and thin film using novel femtosecond Z-scan techniques
Nonlinear materials with large optical nonlinearities and fast response speed are required for future photonic devices. In this research project, a novel femtosecond time-resolved Z-scan technique will be implemented to investigate the mechanism and the relaxation dynamics of optical nonlinearities in solid, liquid and thin film.
Investigator(s)
Dr Kam Sing WONG (Supervisor) Physics, HKUST
Mr Kei Yan TSENG
Award Thesis
Sponsor HKUST
Area Physical Sciences
Start date 1 September 1993
* * * * * * * *
* *
*Research Report (1993-94)
Spin-charge Separation and Recombination in t-JModel
Indirect experimental results show that spin-charge separation occurs in the normal state high-Tc superconductor with low hole doping concentration. Starting with the one-band t-J model and using the slave-boson method, the mean-field type solution can explain many of the essential features of these experimental results, and the entities of holons and spinors emerge. In contrast, it is believed that the over-doped normal state high-Tc superconductor shows no spin-charge separation and can be identified as usual fermi liquid. The purpose of this project is to examine the possibility of describing this state by the holon-spinor recombination in the slave-boson representation of the t-J model.
Investigator(s)
Dr Tai Kai NG (Supervisor) Physics, HKUST Mr Yu Fai TONG
Award Thesis
Sponsor HKUST
Area Physical Sciences
Start date 1 February 1994
* * * * * * * * * * *
ON-GOING RESEARCH PROJECTS
Quasicrystal growth simulation
The growth of two-dimensional quasicrystals is simulated in an energetic model using Penrose tiles. From the phason strain analysis of the numerical simulation, the data is better fitted by a power law than by the logarithmic prediction of the conventional random tiling model. This observation is explained using topological ideas and indicates that the assumption of entropy being the key factor in quasicrystal growth needs modification.
Investigator(s)
Dr Kwok-Yip SZETO Physics, HKUST Award
Sponsor Area Start date Project no.
Remarks
$50,000 RGC
Physical Sciences 1 February 1992 DAG91 /92.SC02 Project completed
Research Report (1993 -94)
68
Spin-polarized scanning tunnelling microscopy
In this project we develop a new spin-polarized scanning tunnelling microscope (SP-STM) and use it to study surface magnetism and magnetic domain structure. The novel experimental setup which we test incorporates into the STM for the first time elements of the spin- polarized electron production method used widely in the other surface magnetic techniques. Unlike previous approaches to SP-STM, our method should be routinely applicable and noninvasive since it utilizes an entirely nonmagnetic tunnelling tip. The important details which will become accessible through our research will permit a fuller understanding of surface magnetism.
Investigator(s)
Dr MichaelS. ALTMAN Physics, HKUST Award
Sponsor Area Start date Project no.
Remarks
$38,935 RGC
Physical Sciences 16 March 1992 DAG91 /92.SC16 Project completed
* * * * * * * * * * *
Measurement of third order optical susceptibilities in semiconductor thin films using Z-scan technique
To investigate
x<
3> processes in semiconductor thin films using Z-scan technique.Investigator(s)
Dr Kam-Sing WONG Physics, HKUST Award
Sponsor Area Start date Project no.
Remarks
$38,935 RGC
Physical Sciences 16 March 1992 DAG91 /92.SC28 Project completed
* * * * * * * * * * *
Theoretical study of S=l quantum spin chains
The problem of edge states in quantum spin chains is investigated in this project using the S=1 quantum spin chain as an example. In particular, the problem is studied using the
Schwinger Boson Mean Field Theory and the Large-N Quantum Field Theory techniques.
Investigator(s) Dr Tai-Kai NG Award
Sponsor Area
Physics, HKUST
$38,935 RGC Start date
Project no.
Remarks
Physical Sciences 16 March 1992 DAG91/92.SC29 Project completed
* * * * * * * * * * * Statistical mechanics of neural networks I introduce techniques to characterize the dynamics of neural networks, which can be generalized to the study of many other complex dynamical systems. Subsequently I propose new methods for pattern reconstruction which result in a great improvement in both retrieval precision and the basin of attraction when compared with conventional methods, even when the information is not optimally embedded in the network.
Investigator(s)
Dr Michael Kwok-Yee WONG Physics, HKUST Award
Sponsor Area Start date Project no.
Remarks
$38,935 RGC
Physical Sciences 16 March 1992 DAG91 /92.SC30 Project completed
* * * * * * * * * * *
Transmission electronmicroscopy study of epitaxial high temperature superconducting films on perovskite substrates
To study defects in thin layers of semiconductors (a few hundred
A
thick) grown by MBE by transmission electron microscopy. Specifically, we are interested in the elastic strain in the layers and the plastic strain (dislocations) at the interfaces of the layers. The layers studied are II-VI semiconductor epilayers and superlattices grown in the Zheng Ge Ru Thin Film Physics Laboratory at HKUST.69
Investigator(s)
Dr Kwok-Kwong FUNG Physics, HKUST Award
Sponsor Area Start date Project no.
Remarks
$38,935 RGC
Physical Sciences 16 March 1992 DAG91/92.SC31 Project completed
* * * * * * * * * * *
Scanning tunnelling microscopy and spectroscopy studies of carbon fullerene thin films and fullerene-based materials on metal and semiconductor substrates
Ultrathin films of carbon fullere:ne molecules, Cn, prepared on metallic and semiconductor substrates are studied by scanning tunnelling microscopy (STM) under ultrahigh vacuum conditions. The STM images provide direct real-space views of these fascinating molecules and their initial-stage growth patterns on metal and semiconductor surfaces. The topographic and spectroscopic (local tunnelling spectroscopy) information can be used to characterize the intermolecular interactions among Cn in the different growth stages, and to describe electronic density-of states effects due to the chemisorption of fullerene molecules on metal and semiconductor substrates with a wide range of electronic properties and morphological character.
Investigator(s) DrTingCHEN Award
Sponsor Area
Physics, HKUST
$56,490 RGC Start date
Project no.
Remarks
Physical Sciences 1 November 1992 DAG92/93.SC26 Project completed
* * * * * * * * * * *
Photon migration in multilayers of random media
The aim of this research is to investigate the fundamental physics of photon transport in multi-layers of rand,pm scattering media. The transport of photons will be investigated both numerically and experimentally using ultrafast laser pulses. The potential
Research Report ( 1993-94)
application of this system for blocking light will also be investigated.
Investigator(s)
Dr Kwong-Mow YOO Physics, HKUST Award
Sponsor Area Start date Project no.
$103,974 RGC
Physical Sciences 1 December 1992 DAG92/93.SC27
* * * * * * * * * * *
Green's Function Monte Carlo study of the quantum spin-1/2 antiferromagnet on a Kagome lattice
This project explores the possibility of applying Green's Function Monte Carlo (GFMC) to the spin-1 /2 quantum antiferromagnet on a Kagome lattice. GFMC is a powerful method for computing the ground state properties of quantum systems.
However, it is well-known that GFMC fails for frustrated fermion systems due to the "fermion sign problem". Therefore, GFMC calculations have been restricted to boson systems, or fermion systems without frustration. The spin-1/2 Kagome quantum antiferromagnet is a highly frustrated fermion system. To do this calculation, we have to overcome the "fermion sign problem". Although we do not expect to solve the sign problem completely, with the help of a good trial wavefunction and plenty of computer time, it should be at least possible to overcome the sign problem to a certain extent and extract useful information about the system using GFMC.
Investigator(s) Dr Pak-Wo LEUNG Award
Sponsor Area
Physics, HKUST
$59,950 RGC Start date
Project no.
Physical Sciences 30 November 1992 DAG92/93.SC28
* * * * * * * * * * *
Studies of the self-avoiding walk and the trail in finitely ramified fractal spaces
The transfer matrix method is used to study the self-avoiding walk and the trail in finitely ramified fractal spaces. The size exponents u
Research Report ( 1993-94)
70
on the Sierpinski gasket are calculated. The values will be compared with those from the conventional RG calculations.
Investigator(s)
Dr Xiang-Rong WANG, Physics, HKUST
Award $59,950
Sponsor RGC
Area Physical Sciences Start date 30 November 1992 Project no. DAG92/93.SC29 Remarks Project completed
* * * * * * * * * * *
Telecommunications networks: A neurocomputing approach to design, management and control
(Joint departmental project)
To meet the future challenges of the information age, telecommunication networks have to be designed and managed intelligently. Network design has been approached by heuristics, mathematical programming, simulated annealing, and expert systems, to name a few. Traditional methods of traffic control are mostly nonadaptive or deterministic in nature. This approach is not very satisfactory, since the actual network traffic at any instance may be very different from the expected traffic pattern. The recently developed technique of neurocomputing has proved to be very fruitful. This modem technique adopts an analogy with the human brain, performs an optimization task by simple processes taking place in parallel at the "neurons".
Investigator(s)
Dr Michael Kwok-Yee WONG (PM) Physics, HKUST
Prof. Donald A. GEORGE
Electrical & Electronic Engg, HKUST Dr Thomas R. JEFFERSON
Management of Organisations, HKUST
Dr Kwok-Yip SZETO Physics, HKUST Dr Kar Yan TAM
Info & Sys Management, HKUST Dr Dit-Yan YEUNG
Award Sponsor Area
Computer Science, HKUST
$1,500,000 HKTIIT /HKUST Computing Science &
Information Technology
Start date Project 1W.
Remarks
1 January 1993 HKTIIT92/93.002
Prof. George left HKUST in June 1993.
* * * * * * * * * * *
Lightwave technology research programme (Joint deparbnental project)
This multi-disciplinary programme aims at developing sophisticated laser sources as well as advanced nonlinear and quantum optics measurement capabilities that are not yet available in the Asia-Pacific region outside of Japan. A substantial portion of the research effort is devoted to studying the availability of reliable and precise nonlinear optical characterisation using advanced measurement techniques on thin-film materials for practical photonic devices. Organic and inorganic materials, in particular metal oxide thin films, are investigated for photonic applications.
Advanced techniques for measuring ultrafast (picosecond and shorter) third-order nonlinear optical nonlinearities needed for operation of all-optical switches and bistable devices are developed. Experimental demonstration of quantum-optics photonic devices and waveguide-optics devices are part of the research efforts involved in this project.
Investigator(s)
Prof. George K.L. WONG (PM) Physics, HKUST Prof. Hiroyuki HIRAOKA
Chemistry, HKUST Prof. Hoi Sing KWOK
Electrical & Electronic Engg, HKUST Dr Paul R. CARLIER
Chemistry, HKUST Dr Wa-Hung LEUNG
Chemistry, HKUST Dr Philip Iam-Keong SOU
Physics, HKUST Dr Kam-Sing WONG
Physics, HKUST Dr Kwong-Mow YOO
Physics, HKUST Award
Sponsor Area
Start date Project 1W.
$8,500,000 (Year 1) HKTIIT /HKUST
Electrical & Electronic Engg/
Physical Sciences/
Computing Science &
Information Technology 1 March 1993
HKTIIT92/93.003
71
Transmission electron diffraction andmicroscopy study of strains and misfit dislocations at interfaces of semiconductor epilayers and superlattices
See the DAG91/92.SC31 project abstract above.
Investigator(s)
Dr Kwok-Kwong FUNG Award
Sponsor Area
Physics, HKUST
$626,000 RGC Start date
Project 1W.
Physical Sciences 30 September 1992 HKUST118/92E
* * * * * * * * * * *
The influence of microstructure on phase transitions in non-metals
The influence of microstructure and microchemistry on phase transitions in selected non-metals, mainly perovskite-structured compounds, is becoming ever more · relevant to device applications. Structural phase transitions in such materials have many potentially valuable effects on physical properties but have not been widely explored.
New methods of preparing films of perovskite-structured compounds will allow their microstructures and chemical compositions to be controlled and modified.
The behaviour of these films at or dose to such phase transitions will be directly investigated by means of transmission electron microscopy and other relevant techniques. The resulting data should enable exploitable physical properties at temperatures dose to those of phase transitions to be "tailored" or optimized to match device requirements. En route new fundamental knowledge and expertise will be acquired about the formation and properties of thin-films of this important group of non-metallic materials, the chemical interactions between them and selected substrates, optimal thermal processing, and/ or methods of separating films from substrates, etc.
Investigator(s)
Prof. David J. BARBER
Award Sponsor Area
Materials Characterisation and Preparation Centre, HKUST Physics, HKUST
$627,000 RGC
Physical Sciences
Research Report ( 1993-94)
Start date Project no.
1 October 1992 HKUST119 /92E
* * * * * * * * * * *
Growth kinetics and structure at metal surfaces
The kinetic aspects of growth processes may offer a new route for exercising control of the structural character of thin films, multilayers and oxides at surfaces. In this project, dynamical scaling in ordering and growth processes at surfaces will be investigated.
These studies are intended to clarify the controversial existence of unique dynamical growth exponents characterizing distinct universality classes. Knowledge of these exponents can be used to distinguish between the numerous current theories. This work is expected to provide an experimental basis for control of morphological structures at surfaces.
Investigator(s)
Dr MichaelS. ALTMAN (PI) Physics, HKUST Prof. Nelson CUE Award
Sponsor Area
Physics, HKUST
$872,000
Start date Project no.
RGC
Physical Sciences 1 September 1992 HKUST120/92E
* * * * * * * * * * *
II-VI semiconductor quantum wells and superlattices: growth by molecular beam epitaxy (MBE), blue-green and uv laser, nonlinear optical properties, and magnetic phenomena
A highly interactive research program is proposed in which MBE will be used to grow ultra-thin II-VI semiconductor films with energy gap and light emission in the visible spectrum. The research will include the investigation of dopant incorporation, magnetic phenomena and nonlinear optical properties of such material systems.
Investigator(s)
Dr Philip Iam-Keong SOU (PI) Physics, HKUST Prof. George K.L. WONG
Physics, HKUST
Research Report ( 1993-94)
72
Dr Kam-Sing WONG Physics, HKUST Award
Sponsor Area Start date Project no.
$872,000 RGC
Physical Sciences 1 September 1992 HKUST121/92E
* * * * * * * * * * *
High Tc superconductors and submicron device physics
This project investigates two currently important areas in physics: (1) the problem of transports in submicron device structures, and (2) high Tc superconductors. In (1) we focus on building up the general theory of non-linear transports in mesoscopic systems and the problem of transports in submicron structures with artificial magnetic structures.
In (2) we focus on the magnetic properties of High Tc superconductors. In particular, the effect of non-magnetic impurities on magnetic and transport behaviours is being investigated in detail.
Investigator(s) Dr Tai-Kai NG (PI)
Physics, HKUST Dr Kwok-Yip SZETO Award
Sponsor Area
Physics, HKUST
$482,000
Start date Project no.
RGC
Physical Sciences 1 September 1992 HKUST123/92E
* * * * * * * * * * *
Training neural networks
The main aim of the project is to study and compare the training and operation of both fully connected and programmed diluted (or annealed diluted) neural networks, i.e. neural networks which store information with as simple a structure as possible. We shall consider their performance such as generalization ability, selectivity, and their metastability, i.e. their likelihood to be trapped in local minima during training. We shall then search for algorithms which attain the simplest structures, and ultimately apply them to solve practical optimization problems.
Investigator( s)
Dr Michael Kwok-Yee WONG (PM) Physics, HKUST
Dr Michael Kwok-Yee WONG (PM) Physics, HKUST