Seminars 2007

Title: Molecular Machines: Packers and Movers, Assemblers and Shredders
Speaker:Professor Debashish Chowdhury
Date:17 December 2007
Time:11.00am - 12.00pm 
Venue:PAP Meeting Room (SBSB3n-19)
Host: Professor Alfred Huan
Abstract: Biological functions in each living cell of higher organisms depend on coordinated operations of a wide variety of molecular machines. These natural nano-machines are either proteins or macromolecular complexes. Some of the motor proteins transport cargo to their respective destinations whereas some mobile workshops synthesize macromolecules while moving on their tracks. Some other machines are designed to function as packers of DNA whereas some machines shred nucleic acids and proteins into pieces for their eventual degradation. All these machines require input energy for performing their mechanical works and operate under conditions far from thermodynamic equilibrium. The typical size of these motors and the forces they generate are of the order of nano-meters and pico-Newtons, respectively. They are subjected to random bombardments by the molecules of the surrounding aqueous medium and, therefore, follow noisy trajectories. Because of their small inertia, their movements in the viscous intracellular space exhibits features that are characteristics of hydrodynamics at low Reynold's number.

In this talk, I'll begin by conducting a virtual guided tour of the intracellular micro-factory. This will be followed by an elementary introduction to the general principles underlying the mechanisms of linear and rotary motors. As practical illustrations of these mechanisms, I'll present our works from a broader perspective. The motors I'll discuss in detail are:(i) Kinesins and dyneins (``movers'');(ii) Genome packaging machines of viral capsids (``packers''); (iii) RNA polymerase and ribosomes (``assemblers''),(iv) Depolymerases (''shredders'').


Title: Metal Oxide Nanowire Arrays and Compound Oxide Nanotubes
Speaker:Dr Hongjin Fan
Date:30 November 2007
Time:11.00am - 12.00pm 
Venue:School of Biological Sciences Meeting Room 2, SBS-01n-35
Host: Professor Alfred Huan
Abstract: This talk presents the fabrication of 2-D ordered arrays of ZnO nanowires on surface of GaN layers via combining substrate nanopatterning and catalyst-directed epitaxial growth. First, gold nanodot arrays are obtained through various delicate-designed shadow masks, such as metal nanotube membrane, self-assembled PS monolayers, or templating via laser interference lithography. Subsequent CVD growth results in vertical-aligned and well-separated ZnO nanowires, in which the gold nanodots serve as both catalyst and site-specific-growth agent. Physical properties of individual nanowires are studied using high spatial resolution techniques: e.g., cathodoluminescence microscopy and micro-PL for optical properties, piezoresponse force microscopy (PFM) for determination of the piezoelectric coefficient, and SEM-manipulator system for in-situ manipulation and measurement of the Young’s modulus and fracture strength.

It’s known that ZnO and MgO can easily alloy with many other oxides to form more complex oxide which possess different functions. Therefore, fabrication of ternary compound oxide nanostructures would be straightforward starting with one binary metal oxide nanowires. I will show how ZnO and MgO nanowires are converted into spinel 1-D nanostructures via controlled nanoscale solid-state reactions. Their potential application will also be covered.

Finally, Kirkendall effect provides a new and intriguing method for nanotube fabrication (as well as hollow nanoparticles). At end of my talk, a brief literature review and discussion of the application of nanoscale Kirkendall effect in nanotube formation will be given.


Title: Electronic complexity on the Border of Magnetism
Speaker:Dr Christos Panagopoulos
Date:15 November 2007
Time:11.00am - 12.00pm 
Venue:PAP Meeting Room (SBSB3n-19)
Host: Professor Alfred Huan
Abstract: A variety of modern materials whose behaviour cannot be understood with traditional ideas have in common the dominant role played by electron-electron interaction effects. Examples of such systems are transition metal oxides, including high-temperature superconductors, heavy fermion metals, organic charge transfer compounds, and one-and two-dimensional electron gas systems.

In the transition metal oxides for example, the charge, spin, and orbital degrees of freedom, and their coupled dynamics, produce complex phases such as liquid-like, crystal-like, and liquid-crystallike states of electrons. Understanding and controlling the tendencies toward complexity will open the way to novel functionalities. In some cases, associated slow density fluctuations may even act in favour of superconductivity: New classes of materials may be discovered and even nanoscale room temperature superconducting electronics realised.

The talk will address the physics and implications of electronic complexity in low dimensional systems with rich phase diagrams including insulating, metallic and superconducting ground states.


Title: Magneto-Optic Kerr Effect
Speaker:Professor Z. Q. Qiu
Date:13 November 2007
Time:11.00am - 12.00pm 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Professor Alfred Huan
Abstract: Magneto-Optic Kerr Effect (MOKE) technique, was introduced in 1985 to measure the hysteresis loops magnetic thin films with atomic layer sensitivity. Since then MOKE has evolved into one of the most popular experimental techniques and made a significant impact on magnetic nanostructure research. In this talk, I will review the history of this topic, both successful and failed approaches, to outline the pathway from the discovery of the magneto-optic effect to today’s experimental MOKE setup. The talk will be given at the level of students who have not yet or just started to do research. The objective is to let students appreciate the real life research as opposed to the "clean physics" in classroom textbooks.


Title: DNA Quadruplexes & Applications to Telomeres
Speaker:Dr Jean-Louis Mergny
Date:12 November 2007
Time:11.00am - 12.00pm 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Dr Phan Anh Tuan
Abstract: DNA is prone to structural polymorphism: besides the famous double-helix, other structures, involving 3 or 4 strands may be formed. G-quadruplexes constitute an example of such unusual nucleic acids structures. They result from the hydrophobic stacking of several quartets; each quartet being a planar association of four guanines held together by 8 hydrogen bonds. Stable tetramolecular quadruplexes may be formed with short oligomers. The melting of these quadruplexes is kinetically irreversible, allowing us to study association and dissociation processes independently [1]. We analyzed the properties of parallel quadruplexes with a single thymine at the 5' and 3' extremities such as TG4T and TG5T, and sequence variants, in which each guanine of the central block was systematically substituted by a different base and promising base analogs have been identified [2].

Quadruplexes may find applications in areas ranging from nanotechnology (as nanodevices; [3]), biotechnology (as molecular beacons; [4]) to medicinal chemistry. Using a FRET assay [5], we have identified several series of G4 ligands [6]. Selectivity of these ligands towards G-quadruplexes was assessed by FRET competition experiments. Quadruplex ligands not only bind to preformed quadruplexes, but increase the association rate of these structures, acting as G4 chaperone agents [7] whereas some proteins can actively unwind quadruplexes [8]. We are currently trying to understand the rules that govern quadruplex stability [9].

Telomeres and telomerase represent, at least in theory, attractive targets for cancer therapy [10]. The 3’ G-rich telomeric overhang may adopt a G-quadruplex structure that blocks telomerase. We recently challenged the assumption that quadruplex ligands are telomerase inhibitors [11]. These molecules are actually more effective inhibitors of telomeric DNA amplification than extension by telomerase. We also demonstrate that the popular telomeric repeat amplification protocol (TRAP) is completely inappropriate for the determination of telomerase inhibition by quadruplex ligands [11]. Finally, these compounds may also target non-human telomeric overhangs, provided that a G-rich motif is present [12].

[1] a) Mergny et al. Nucleic Acids Res. 2005, 33: 81 and b) Nucleic Acids Res. 2006, 34: 2386
[2] a) Gros et al., Nucleic Acids Res., 2007, 35: 3064 and b) Gros et al. 2007, in preparation
[3] Alberti & Mergny. Org. Biomol. Chem. 2006, 4: 3383
[4] Bourdoncle et al. J. Am. Chem. Soc, 2006, 128: 11094
[5] De Cian et al. Methods, 2007, 42: 183
[6] a) Pennarun et al. Oncogene, 2005 24: 2917 b) Granotier et al. Nucleic Acids Res., 2005 33: 4182 c) Kaiser et al. Org. Biomol. Chem., 2006, 4: 1049 d) De Cian et al. J. Am. Chem. Soc., 2007, 129: 1856 e) Hounsou et al. ChemMedChem 2007, 2 : 655 f) Bertrand et al. Org. Biomol. Chem. 2007, 5: 2555. g) Brassart et al. Mol. Pharmacol.. 2007, 72: 641.
[7] De Cian et al. 2007, Nucleic Acids Res., 2007, 35: 2483
[8] Romero Salas et al. Nucleic Acids Res., 2006 34: 4857
[9] Guédin et al. 2007, in preparation
[10] De Cian et al. 2007, Biochimie, 2007, in press
[11] De Cian et al. Proc. Natl. Acad. Sci USA 2007, in press
[12] De Cian et al. 2007, in preparation


Title: Understanding the Thermodynamic Properties of InGaN Alloys Through a First-principles Approach
Speaker:Professor Alfred Huan
Date:7 November 2007
Time:11.00am - 12.00pm 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Professor Alfred Huan
Abstract: Group-III nitrides such as InGaN have attracted considerable theoretical and experimental attention due to its potential for highpower, high-frequency, and high-temperature opto-electronic applications. Theoretical calculations for the thermodynamics of the bulk materials require an accurate description of the interactions between the constituent atoms, a good representation of the random alloys, and a consideration of the effects of lattice vibrations and configurational entropy. We have used an accurate density-functional theory to calculate the heat of formation of the alloys (represented by special quasi-random structures). Phonon calculations are performed to obtain the lattice vibrational contribution to the free energy. Both wurtzite and zinc-blende structures are considered. The effect of lattice vibrations will be elucidated. The theoretical predictions have been checked with experiments. The thermodynamics of InN surfaces will also be presented. Finally I will outline a tight-binding method that will be used to simulate large systems.


Title: Growth and characterization of NLO materials: A Review on NLO Materials from the Amino Acid Family
Speaker:Dr S.Natarajan
Date:3 October 2007
Time:11.00am - 12.00pm 
Venue:PAP Meeting Room (SBS b3n-19)
Host: Associate Professor Shen Ze Xiang
Abstract: Nonlinear optics (NLO) is a frontier area of research and technology that is expected to play a major role in the emerging technology of photonics, the technology of the 21st century. Due to modern society's demand for improved telecommunications and data processing, photonics -- the use of light to acquire, store, process, and transmit data -- has become an active field of research. The design of devices that utilize photons instead of electrons in the transmission of information has created a need for new materials with unique optical properties. A number of organic, inorganic, semi-organic, thin film and polymer materials are being synthesized and investigated for the NLO property. Among these, organic NLO materials have several advantages. In this talk, a review of organic NLO materials form the amino acid family is presented. The parameters such as size of the crystal, transparency, SHG efficiency, stability, hardness and laser damage threshold, etc. are summarized for all the recently discovered NLO materials involving amino acids. The details presented will be useful in the investigation of those parameters which are not known till date, for these NLO compounds. It will indicate the advantages of some of these compounds over the other NLO compounds in this category of amino acid NLO materials, for useful NLO applications. The details will be presented.


Title: Ab initio Calculations as a Tool for Discovery: Origin of the Verwey Transition in Magnetite
Speaker:Professor Guang-Yu Guo
Date:10 September 2007 
Time:11.30am - 12.30pm 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Dr Kuo Jer Lai
Abstract: Today, ab initio calculations have become indispensable in materials research. In particular, they are essential to understand the intricate phenomena occurring in materials, to search for new materials and to design the materials with desired properties. In this talk, I will report how our recent ab initio calculations [1] lead to the discovery of a sophisticated t2g-orbital ordering in magnetite (Fe3O4) which helps to resolve a 60 year old fundamental problem in solid state physics. In the past ten years, there has been considerable interest in charge ordering in transition metal oxides because the electric transport and magnetic properties of transitionmetal oxides are intimately related to charge ordering. For example, dynamic fluctuations of charge ordered stripes have been proposed as a mechanism of high temperature superconductivity. The classic charge ordering problem is, however, that of magnetite (Fe3O4), which was first proposed by Verwey in early 1940’s in order to explain the observed metal-insulator (M-I) transition in the system. However, despite of intensive experimental and theoretical investigations in the past six decades, the origin and mechanism of the charge ordering and hence Verwey transition have remained a mystery and have fascinated generations of solid state physicists ever since. Our ab initio calculations reveal that magnetite forms an insulating charge-orbital ordered state below the Verwey transition temperature. More importantly, we find an associated t2g-orbital ordering on the octahedral Fe2+ sublattice. This finding resolves such fundamental issues about the Verwey transition as the mechanism for the charge ordering and for the formation of the insulating gap, as well as the nonobedience of the Anderson’s criterion for the charge ordering. Finally, the predicted t2gorbital ordering in magnetite has recently been observed in resonant x-ray scattering experiments [2].


Title: Phase-diagram Domains of a Colloidal Dispersion
Speaker:Dr S.K. Lai
Date:31 August 2007
Time:11.00am - 12.00pm 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Professor Alfred Huan
Abstract: We propose a novel means to construct the phase-diagram domains of a colloidal dispersion. It is based on the idea of treating the phases in coexistence as a composite system whose Helmholtz free energy density is written as the sum of the free energy densities of coexisting phases each of which is weighed by its volume occupation in the total volume. Differing from the conventional method in which boundaries of coexisting phases are the ultimate goal, the present work crosshatches the domains of homogeneous phases (gas, liquid and solid) and also phases in coexistence. The numerical procedure has the same spirit as that carried out in a laboratory experiment and has been applied to study the charged colloidal dispersion, thermally responsive microgel dispersion (Poly-N-isopropylacrylamide), colloid-polymer mixtures, etc. In this talk, we highlight some of these interesting results.


Title: Lowest Energy Structures of a Bimetallic Cluster
Speaker:Dr S.K. Lai
Date:30 August 2007
Time:11.00am - 12.00pm 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Professor Alfred Huan
Abstract: We report an optimization algorithm which is developed for probing the structures of bimetallic clusters. The algorithm has its origin in two state-ofthe-art techniques, the Monte Carlo based basin hopping and the genetic algorithm, both of which are used extensively in the literature for finding the lowest energy structures of pure metallic and nonmetallic clusters. To critically evaluate the present algorithm, we calculate the lowest energy structures of bimetallic clusters Cu_n-Ag_(38-n) and compare the results obtained with our recent studies of Cu_n-Au_(38-n) [J. Chem. Phys. 124, 044711 (2006)]. Through comparison, we examine the factors that determine the stability of clusters and study the structural consequences on Cu-Ag and Cu-Au. We show in this talk that the Au atoms, being larger in size than the Cu atoms, prefer to have Cu atoms as neighbors displaying the mixing behavior, whereas the Ag atoms although are also larger in size than the Cu atoms but are smaller in size than the Au atoms, prefer to have Ag atoms stayed close together displaying thus the segregating behavior.


Title: Anomalous Nernst effect in Novel Superconductors
Speaker:Dr Zhu’an Xu
Date:27 August 2007
Time:11.30am - 12.30pm 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Dr Tom Wu
Abstract: In this talk, I firstly introduce the large Nernst signals due to the vortex-like excitations exist in a certain temperature range above superconducting transition temperature TC in hole doped superconducting cuprates, which implys that the phase transition at TC is driven by the loss of long-range phase coherence. Then the large Nernst effect in normal state of electron doped cuprate superconductors is presented. Just similar to the case in NbSe2 and YNi2B2C superconductors, we propose that the ambipolar flow of different types of charge carriers can account for the anomalous Nernst signals in the normal state of these multi-band metals. Finally I present our recent results of anomalous Nernst signal just above Tc observed in p-wave superconductor Sr2RuO4. The different origins of the large Nernst signals above Tc in these novel superconductors are discussed.


Title: Division of Physics & Applied Physics
College of Technology, Vietnam National University
Joint Seminar
Date:13 August 2007
Time:8.30am - 12.30pm
Venue:Tutorial Room 85 (SS4-B1-26)

Title: Multifunctional Multiferroics for Spintronics
Speaker: Professor NGUYEN Huu Duc

Title: Magnetism and Devices with New “Spins”
Speaker: Dr WU Tao, Tom

Title: Magnetoelastic Properties of Nanostructured Ribbons FeCoSiB using for High-sensitive Stress Sensors
Speaker: Dr PHAM Duc Thang

Title: Metal Oxide Nanostructures: Synthesis, Characterization and Application
Speaker: Dr YU Ting

Title: MEMS Applications in Coltech
Speaker: Professor NGUYEN Thang Long

Title: Ultrafast Spectroscopy of Semiconducting Nanoparticles And Organic Polymers
Speaker: Dr Sum Tze Chien


Title: “Thermoelectric Properties of Low Bandgap Crystalline Polymers”
Speaker:Professor John S. Tse
Date:10 July 2007
Time:2.00pm - 3.30pm 
Venue:SBS Classroom 3 (SBS-01n-23)
Host: Dr Kuo Jer Lai
Abstract: In the quest for efficient thermoelectric polymeric materials, a numerical procedure has been developed for the predication of the Seebeck coefficient of crystalline materials based on its electronic band structure with the goal of testing this approach on simple crystalline polymers. Test calculations on dilute p-doped polythiophene polymer show surprisingly good agreement with experiment that might suggest that a band description may be appropriate. Further investigation on model systems reveal that the formation of polaron is suppressed in polymers with rigid backbones. Based on this finding, novel polycarbazole and polyindolocarbazole polymer with rigid frameworks were synthesized. Band structure calculations were used to predict the Seebeck coefficients. This family of polymers was found to possess good Seebeck coefficients but there is still a need to improve the electrical conductivity, in order to produce useful thermoelectric materials. The theoretical and experimental results suggest that bandstrcuture calculations can be used to guide the design of high-performance thermoelectric materials. Specially engineered doped lowband-gap polymers may be promising candidate materials for thermoelectric applications.


Title: The cooperative molecular field effect- Surprising magnetic and electronic properties at interfaces
Speaker:Dr Ron Naaman
Date:3 July 2007
Time:3.00pm - 4.30pm 
Venue:PAP Meeting Room (B3n-19)
Host: Dr Wang Lan
Abstract: New electronic and magnetic properties are induced by the adsorption of closed packed monolayers on solid substrates.[i] In layers made from chiral molecules, unexpectedly large electronic dichroism is observed, which manifests itself as spin specific electron transmission.[ii] For many thiolated molecules self-assembled on gold, a surprisingly large paramagnetism is observed.[iii] This type of magnetism is observed also for inorganicinorganic interfaces like silicon-silicon oxide.[iv]

All the observations can be rationalized by charge transfer occurring at the interfaces.[v] In the case of organic molecules, the charge transfer is induced by the organization as self-assembled monolayer.

Utilization of this cooperative molecular field effect will also be described.

[i]) Z. Vager, I. Carmeli, G. Leitus, S. Reich, R. Naaman, J. Phys. Chem. of Solids, 65, 13 (2004).
[ii]) I. Carmeli, V. Skakalova, R. Naaman, Z. Vager, Angewandte Chem. Int. Edition, 41,761 (2002). [iii]) I. Carmeli, G. Leitus, R. Naaman, S. Reich, Z. Vager, J. Chem. Phys. 118,10372 (2003).
[iv]) G. Kopnov, Z.Vager, R. Naaman, Adv. Mat. 19,925-928 (2007).
[v]) R. Naaman and Z. Vager, PCCP, 8, 2217–2224 (2006)


Title: Understanding Cellular Nanomachines: A minimalist approach to studying nuclear pore complex function by de novo design
Speaker:Dr Roderick Y.H. Lim
Date:26 March 2007
Time:2.00pm - 3.00pm 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Professor Alfred Huan
Abstract: The intrigue surrounding the nuclear pore complex (NPC) lies in its ability to restrict or promote cargo translocation between the cytoplasm and nucleus i.e. selective gating. To come to understand the modus operandi of the selective gating mechanism necessitates a detailed knowledge of both the biochemical ingredients and the corresponding biophysical responses of the NPC machinery. In particular, these are comprised of a group of nuclear pore proteins (i.e. nucleoporins or Nups) containing natively unfolded (unstructured) domains that are rich in phenylalanine-glycine (FG)-repeat motifs.

In our laboratory, we have developed a heuristic, interdisciplinary approach to elucidate how the FGdomains and the different transport factors (e.g. transport receptors, RanGTP/GDP) contribute to the selective gating mechanism. Specifically, FG-domains are tethered to gold nanostructures designed to mimic the dimensions of the NPC and topography. Atomic force microscope (AFM) force measurements reveal that the FG-domains are polymer brush–like and serve as an entropic barrier (i.e. steric repulsion) to would-be entrants to the NPC. Privileged access to the NPC is provided by transport receptors (e.g. importin-β), which negotiate the entropic barrier by causing a collapse of the FG-molecules via receptor-FG binding interactions. This striking effect is only reversed by RanGTP, which sequesters importin-β and inhibits FG-binding. Immunogold-labelling electron microscopy (EM) complement these findings by showing that the FG-domains of Nup153 are reversibly collapsed in vivo by importin-β and RanGTP. We anticipate that the receptor-driven collapse of the FG-domains defines the physical aspects of selective gating, and propose that the flux of collapsing and distending FG-domains serves to promote the translocation of receptor-cargo complexes while simultaneously maintaining the entropic barrier.

In closing, we will demonstrate how the aforementioned principles of selective gating can be applied to the construction of a de novo designed “minimalist” NPC. By being able to mimic the nucleocytoplasmic transport process, such an artificial NPC will have the potential to investigate, for example, the manner in which certain viruses hijack the nuclear trafficking machinery to infiltrate the nucleus via the NPC. On a separate note, the principle of selective gating may have potential applications in the development of future NPC-inspired nanopores for use in medical diagnostics and drug discovery technologies.


Title: Phynance: Science in the Financial World
Speaker:Dr Khoo Guan Seng
Date:9 March 2007
Time:3.30pm - 4.30pm 
Venue:School of Biological Sciences
60 Nanyang Drive Classroom 3, SBS-01n-23
Abstract: • Dr Khoo’s work
• The relevance of scientific concepts & applications in finance & the capital markets
• How Physics & Science have given me the kind of skills needed for it eg. analytical and quantitative skills, multitasking, synthesis of ideas, etc.
• Q & A


Title: Surface and Size Effects on Phase Transition Behaviors of Nanoscale Ferroelectric and Multiferroic Materials
Speaker:Professor Biao Wang
Date:27 February 2007
Time:10.30am - 11.30am 
Venue:PAP Meeting Room (SBS B3n-19)
Abstract: Nanoscale Ferroelectric and Multiferroic Materials have attracted many and many researchers in recent years. Related with these materials, basic understanding on the surface and size effects becomes a very hot topic. In this presentation, some recent works related with the Thermodynamics Analysis on the size effect of phase transition and the coupling effect between the electric field and magnetic field through the elastic interaction, etc., was discussed. By considering the elastic contribution, the Landau-Ginzburg theory was reformulated, and was applied to predict the phase transition characteristics, the phase diagrams, etc.. Finally some potential research topics in the related areas will be suggested.


Title: Multiferroic Heterostructures: 1 + 1 > 2
Speaker:Dr WU Tao
Date:7 February 2007
Time:11.30am - 12.30pm 
Venue:PAP Meeting Room (SBS B3n-19)
Abstract: Innovations bringing the synergy out of strategically important materials and functionalities have been an ever-lasting theme in materials research. Magnetism and ferroelectricity, arguably the two largest branches of condensed matter physics, however, are united only recently, which has been generating a tremendous amount of excitement. Multiferroics are materials or structures where different ferroic orders such as (anti)ferroelectrics and (anti)ferromagnetics coexist. Materials systems with a strong magnetoelectric (ME) effect have potential applications in sensing devices, data storage, transducers, etc. In this talk, I will discuss the origin of the scarcity of multiferroic materials and how we designed and characterized an epitaxial heterostructure showing a remarkable ME effect. The experimental results agree very well with the prediction of a phenomenological Landau-Ginzburg-Devonshire theory.


Title: Oscillating Exchange Bias in Fe/Cr Structure
Speaker:Dr. Wang Lan
Date:31 January 2007 
Time:11.30am - 12.30pm 
Venue:PAP Meeting Room (SBS B3n-19)
Abstract: We report clear multiple period oscillations in the temperature dependence of exchange bias in an Fe thin film exchange coupled to a neighboring Cr film. The oscillations arise due to an incommensurate spin density wave in the Cr, with wavevector perpendicular to the Fe/Cr (001) interface. The exchange bias and coercivity allow for a determination of the extent of the thermally-driven wavelength expansion, the (strain-suppressed) spin-flip transition temperature, and the Cr Néel temperature, which show a crossover from bulk-like to finite-size behavior at a Cr thickness of ~ 1100 Å. The data are consistent with a transition from a transverse to longitudinal on cooling.


Title: Composition Controlled Spin Polarization in Co1-xFexS2: Electronic, Magnetic, and Thermodynamic Properties
Speaker:Dr Wang Lan
Date:31 January 2007
Time:11.30am - 12.30pm 
Venue:PAP Meeting Room (SBS B3n-19)
Abstract: We demonstrated that alloy composition can be used to fine-tune the position of the Fermi level in Co1-xFexS2 alloys leading to composition controlled spin polarization and the ability to engineer high conduction electron spin polarizations of up to 85 %. We present here a comprehensive experimental investigation of the structure, stoichiometry, magnetic, magnetotransport, and thermodynamic properties of bulk polycrystalline solid solutions of Co1-xFexS2 and single crystalline CoS2. The experimentally determined spin polarization can be tuned by alloy composition between –57 % (x = 0) and +85 % (x = 0.15). The evolution of the magnetic, transport and thermodynamic properties with increasing Fe doping is discussed in terms of the composition dependence of the conduction electron spin polarization and the spin-dependent band structure.


Title: Transparent Electrode Modification For Enhancing OLED Performance
Speaker:Dr Zhu Fu Rong
Date:24 January 2007
Time:10.30am - 11.30am 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Professor Alfred Huan
Abstract: The electrode-organic interfacial properties play a critical role in determining the performance of OLEDs. A number of anode modification techniques and device architectures are developed for enhancing OLED performance. Accomplishments in developing techniques for engineering interfacial properties to ensure electron-hole current balance in OLEDs will be discussed. In practical applications, the visual contrast is more important than the brightness of image. As such, improving the visual contrast in OLEDs is another important issue to address with a significant technological implication. This talk will also discuss the progress in developing color tuning with graded anode thickness and gradient refractive index anode for enhancing the visual contrast of OLED displays.


Title: Monte Carlo Methods And Their Applications
Speaker:Dr Lee Hwee Kuan
Date:16 January 2007
Time:10.30am - 11.30am 
Venue:PAP Meeting Room (SBS B3n-19)
Host: Associate Professor Shen Ze Xiang
Abstract: Monte Carlo methods has been use extensively in very diverse fields such as Condensed Matter Physics, Bioinformatics, Finance and Image Processing.

Usefulness of Monte Carlo comes from its generic formulation and its ability to tackle problems with too many degrees-of-freedom to be handled by other methods. Being inherently stochastic, Monte Carlo methods provide additional advantage of giving a probabilistic interpretation to most problems.

Several recently developed Monte Carlo algorithms and their applications, including Time Quantification, Random Walk and Sequential Monte Carlo, will be discussed


Title: Magneto-Optical Imaging of Abrikosov Vortices and Flux Avalanches in Superconductors
Speaker:Dr Tom H. Johansen
Date:15 January 2007
Time:10.30am - 11.30am
Venue:PAP Meeting Room (SBS B3n-19)
Host: Dr Lars Egil Helseth
Abstract: Phenomena that create intriguing traces of activity that can be observed by direct visual methods are among the most fascinating events in nature. Penetration of magnetic flux in type-II superconductors seen by magneto-optical imaging (MOI) is one example, where especially the spectacular dendritic flux patterns occurring abruptly in superconducting films are currently attracting much attention.

In this talk I will first explain the basic principles for using MOI as a powerful experimental technique for superconductor research, and demonstrate its ability to resolve detailed magnetic flux behavior down to the smallest scales, i.e., the motion of individual Abrikosov vortices (flux quanta). Then, an overview of the recent work done on abrupt flux avalanches involving ~1 million vortices is presented. Focus is put on avalanches forming dendritic flux patterns in films of MgB2* and NbN, where this instability is most pronounced. The experimental findings are compared with a theoretical model based on a thermomagnetic underlying mechanism responsible for the instability, and it is shown that the model gives an excellent quantitative description of main features of the phenomenon.