Seminars 2010

Title:Topological defects on thin crystallized shell
Speaker:Yong Ee Hou
Date: 22 December 2010
Time: 11.00am - 12.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Professor Alfred Huan
Abstract: When a thin spherical shell membrane initially filled with fluid is dehydrated, it buckles and then starts to crumple, forming rich and interesting faceted structures. This formation of faceted structure is due to energy focusing where the elastic energy, which is initially smoothly distributed, becomes more and more non-uniform, with high energy concentrated in the bent regions. This energy focusing becomes more prominent in thinner rather than thicker shells. Such buckling in thin elastic shell membranes are ubiquitous, appearing in microscopic viruses, pollen grains, mesoscopic dried raisins and in the buckling of ping-pong and soccer balls in everyday life. In particular, David Nelson and collaborators have showed that the 5-fold disclinations are responsible for the faceting of an otherwise spherical triangulation into an icosahedral-like structure, which could explain the shapes of viruses. In this talk, I will explain the role of disclinations in the crumpling process and show that under the right combinations of 3,4,5-fold disclinations, highly symmetrical facetedstructures may arise.

 

Title:Exploring nanopatterns and microflows for cell regulation and monitoring
Speaker:Professor Yong Chen
Date: 22 December 2010
Time: 9.30am - 10.30am 
Venue: Hilbert Space (PAP‐02‐02)
Host: Assistant Professor Lew Wen Siang 
Abstract: Environmental adaptation is a characteristic of all living systems. At cell levels, the adaptation behaviour of the system is still poorly understood. Recent investigations have repeatedly shown the high potential of using nanoengineered substrates and microfluidic devices for the regulation and monitoring of cell adhesion, proliferation and differentiation activities. On one hand, a large variety of synthetic surfaces including chemical and topographic patterns could be easily produced, allowing systematic investigations on the cellular adaptation behaviors. By using both conventional and non conventional nanofabrication techniques, we were able to produce different types of patterns and demonstrated mechanical and chemical pattern influence on cell attachment, elongation and deformation as well as stem cell renewing and controlled differentiation. On the other hand, microfluidics provides unique tools for high resolution control of soluble cell factors. Our results, as well as many others, have shown that stem cells can be cultured and differentiated into different cell types under microfluidic conditions.

We also applied microfluidic devices for the study of shear stress dependent gene expression and drug effects on endothelial cells. Finally, nanofabrication and microfluidics allowed us to develop a number of new characterisation and manipulation techniques which should be relevant to the cellular engineering at single cell levels. Indeed, monitoring, understanding, and controlling the environmental adaptation of cells at single cell and tissue levels are extremely challenging but a lot of material processing technologies are now available. In this talk, we will present some examples of our recent achievements to illustrate the feasibility of performing such an investigation with a more clear research strategy.   

 

Title:Self-assembly of quasi-1D hierarchical nanostructures from the gas phase: a new tool in nano-manufacturing
Speaker:Dr Fabio Di Fonzo
Date: 16 December 2010
Time: 11.00am - 12.00pm 
Venue: MAS Executive Classroom 1 (MAS-03-06)
Host: Assistant Professor Cesare Soci
Abstract: The assembly of nanoscale building blocks in engineered mesostructures is one of the fundamental goals of nanotechnology. Among the various processes developed to date, self-assembly emerges as one of the most promising since it relays solely on basic physico-chemical forces. Our research is focused on a new type of self-assembly method from the gas-phase: Scattered Ballistic Growth (SBG). SBG arises from the interaction of a supersonic molecular beam with a static gas and enables the growth of quasi-1D hierarchical mesostructures. Overall, they resemble a forest composed of individual, high aspect-ratio, tree-like structures, assembled from crystalline nanoparticles. The hierarchical quasi-1D nature of each tree represents an innovative compromise between nanorods/nanotubes (better electron transport) and the conventional isotropic nanoparticle photoanode (high surface area). We demonstrate three examples of application of the novel structures in photocatalytic mineralization of organic compounds [1], protein research [2] and Dye Sensitized Solar Cells [3].

[1] F. Di Fonzo, C.S. Casari , V. Russo, M.F. Brunella, A. Li Bassi, and C.E. Bottani Nanotechnology 20, 015604 (2009)
[2] F. Torta , M. Fusi , C.S. Casari , C.E. Bottani and A. Bachi J. Proteome Res. 8, 1932-1942 (2009)
[3] F. Sauvage, F. Di Fonzo, A. Li Bassi, C. S. Casari, V. Russo, G. Divitini, C. Ducati, C. E. Bottani, P. Comte and M. Graetzel, on-line Nano Lett. (2010)

 

Title:Graphene-based Materials
Speaker:Professor Rod Ruoff
Date: 19 November 2010
Time: 2.00pm - 3.15pm 
Venue: SPMS-LT3 (SPMS-03-02)
Host: Assistant Professor Yu Ting
Abstract: Graphene-based materials hold promise for a variety of applications due to their exceptional electronic and thermal transport, mechanical properties, high specific surface area, and that they can act as an atom thick layer, barrier, or membrane. Our early top-down micromechanical exfoliation approaches [1,2] conceived of in 1998 yielded multilayer graphene. Two main thrust areas of my group are: (i) CVD growth of large area graphene on metal substrates and studies of such material, and (ii) the generation, study, and use of colloids containing graphene-based platelets dispersed in liquids. An update of our work on CVD growth of graphene on metal substrates and on the use of colloidal suspensions to make materials will be given. Support of our work by DARPA, ONR, SWAN NRI, NSF, ARO, AEC, and Graphene Energy, Inc., is appreciated.

1. Lu XK, Yu MF, Huang H, and Ruoff RS, Tailoring graphite with the goal of achieving single sheets, Nanotechnology, 10, 269-272 (1999).
2. Lu XK, Huang H, Nemchuk N, and Ruoff RS, Patterning of highly oriented pyrolytic graphite by oxygen plasma etching, Applied Physics Letters, 75, 193-195 (1999).

Ruoff group publications: http://bucky-central.me.utexas.edu/publications.htm 

 

Title:Spintronics: radiofrequency devices and their applications
Speaker:Dr Antonio Ruotolo
Date: 15 November 2010
Time: 11.00am - 12.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Assistant Professor Wang Lan
Abstract: Conventional electronic devices rely on the transport of electrical charge carriers in metals and semiconductors. The possibility to exploit the 'spin' of the electron rather than its charge has paved the way for the creation of a remarkable new generation of 'spintronic' devices. The discovery of the giant magnetoresistive (GMR) effect [1] in 1988 has had a huge impact on the data storage market. The use of GMR read-head sensors in hard disk drives has assured the possibility to double the data density at a rate that is twice that predicted by Moore’s law for transistors integration. More recently, the discovery of the spin transfer torque (STT) effect [2], i.e. the manipulation of the local magnetization by transferring spin-angular momentum from incoming electrons, has opened up the possibility of new nanoscale devices. This concept has been used to control the orientation of the free magnetic layer in non-volatile random access memories [3]. It can also drive the magnetic orientation of a layer into an oscillation at microwave frequencies, creating a spin transfer nano-oscillator (STNO) [4]. We have used the STT to excite a magnetic vortex into a precessional motion in nanocontact spin-valves. The power generated by this vortex-based STNO is much larger than that provided by standard uniform-mode STNOs. Moreover, the system is much more harmonic, resulting in a smaller output linewidth. To further increase these performances, we have proved [5] that vortex-based STNO can lock their phase through the mediation of antivortices. The phase locked state is characterized by a decreased linewidth and an increased power. Remarkably, the best working condition in our system is the absence of externally applied magnetic field, whereas large fields are required to sustain the output in standard STNO. This feature makes these devices more alluring for applications.

[1] M. N. Baibich et al., Phys. Rev. Lett. 61, 2472 (1988); G. Binasch et al., Phys. Rev. B 39, 4828 (1989);
[2]  J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1-L7 (1996); L. Berger, Phys. Rev. B 54, 9353 (1996);
[3]  J. A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000);
[4] S. I. Kiselev et al., Nature 425, 380 (2003); [5] A. Ruotolo et al. Nature Nanotech., 4, 528 (2009).

 

Title:A Tale of Twin Photons: Their Birth, Life and Future Prospects
Speaker:Dr Alexander Ling
Date: 12 November 2010
Time: 2.00pm - 3.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Professor Alfred Huan
Abstract: Photon pairs generated using nonlinear crystals were first observed by Burnham and Weinberg in 1970. In the last four decades, the quantum correlations between these twin photons have been used to perform a series of dramatic experiments that demonstrate the counter-intuitive predictions of quantum mechanics. Currently, research into twin photons covers both fundamental and applied areas: building better sources of photon pairs, conducting more tests of quantum theory, and exploring curious applications proposed by quantum information theory. In this talk, I will describe the standard technique for producing twin photons using a nonlinear optical process known as Spontaneous Parametric Down Conversion (SPDC) using both bulk and waveguide materials, and describe state-of-the art experimental configurations. I will also describe how quantum correlations can be generated from typical experimental configurations and discuss how the correlations have been applied to experiments, focusing on a novel test of quantum physics using an inequality derived by Anthony Leggett. I will also describe new developments in photon pair sources and exciting new technologies that will enable further experimentation with twin photons.

 

Title:Universal behavior in structural and ferroelectric properties for RE-substituted BiFeO3 thin films
Speaker:Dr Daisuke Kan
Date: 22 October 2010
Time: 2.00pm - 5.00pm 
Venue: MAS Executive Classroom 1 (MAS-03-06)
Host: Assistant Professor Tom Wu
Abstract: We have recently discovered substantial enhancement in dielectric/ferroelectric/piezoelectric properties at a rhombohedral to pseudo-orthorhombic structural boundary in (Bi,Sm)FeO3 .[1] In this talk, I would like to talk about systematic investigations on structural and ferroelectric properties of BiFeO3 thin films doped with rare-earth (RE) elements of Sm, Gd and Dy in a combinatorial manner[2]. Thin film composition spreads of (Bi,RE)FeO3 were fabricated by combinatorial pulsed laser deposition on SrTiO3 (100) substrates with SrRuO3 buffer layers. Scanning x-ray diffraction reveals that a rhombohedral to an orthorhombic structural transitions are universally observed for all RE elements studied here and that the structural properties can be described as a function of average ionic radius of A-site. This indicates that the primary cause of the transition is the chemical pressure effect due to the substitutions. We attribute the transition from a single ferroelectric hysteresis loop on the undoped BFO side to a double hysteresis loop on the orthorhombic side to an electric field induced structural transition at the boundary. In this presentation, we will also show from the orientation dependence of ferroelectric hysteresis loops that the polarization rotates from the [111] direction to the [001] direction with increasing dopant composition. This explains why we see the enhancement in piezoelectric coefficient along the [001] direction at the boundary [3].

This research was done in collaboration with V. Anbusathaiah, C. J. Cheng, V. Nagarajan and I. Takeuchi.

[1] S. Fujino, et al., Appl. Phys. Lett. 92, 202904 (2008).
[2] D. Kan et al., Advanced Functional Materials, 20, 1108 (2010).
[3] D. Kan et al., to be published.

 

Title:Excitons in Highly Uniform Supramolecular Dye Nanotubes
Speaker:Dr Dörthe M. Eisele
Date: 22 October 2010
Time: 11.00am - 12.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Assistant Professor Yu Ting 
Abstract: 

Molecules can self-assemble in solution to form supramolecular assemblies with unique collective properties, which arise from the coupling of the molecules in the assembly. Self-assembled molecular nanotubes, in particular those that strongly absorb visible light, are highly promising quasi one-dimensional (1D) systems for opto-electronic applications, such as energy transport nanowires, and for light harvesting applications. Recently discovered examples include tubular Jaggregates of amphiphilic molecules, porphyrin nanotubes, and chlorosomes in Green Sulfur Bacteria.

Here I report on an outstanding example of such systems, i.e. double-walled nanotubular aggregates of amphiphilic cyanine dyes, as displayed in the figure below. The use of such systems as fundamental model systems for light harvesting requires both, a welldefined and highly uniform structure as well as a basic understanding of the supramolecular origins of their exciton transitions.

Based on exciton fluorescence from individual nanotubes immobilized on a solid substrate it is reported here that the supramolecular structure of these aggregates is not only extremely uniform along the individual aggregate but also between all the aggregates in the system by means of polarization resolved near-field scanning optical microscopy [1]. Moreover, the supramolecular origin and coupling of the exciton transitions are elucdated. It is shown here that the nanotubular aggregate consists of two weakly coupled aggregate sub-systems with two distinct spectra. This could be accomplished by chemical oxidation of the chomophores in preferentially one of the nanotubes using an external oxidation agent [2,3]. It was found that there are only two spectral signatures, which can be clearly assigned such that the spectrum of the inner wall aggregate cylinder can be isolated [4], so that it is now possible to make advances in theoretical modeling of both, cylindrical aggregates and excitonic 1D nanoscale systems being in close proximity to better address how their supramolecular structure affects their electronic and optical properties as well their energy transfer properties.The fact that the nanotubes are electronically coupled even at a separation of about 4 nm offers the exciting possibility of coupling the systems to other systems such as inorganic nanostructures to form organic/inorganic hybrid structures.[4] Finally, I will give an application of the nanotubular aggregates beyond light harvesting, i.e. the use as a chemically active nanotubular template for the photo-induced formation of sub-7 nm silver nanowires providing access to quasi one-dimensional organic/inorganic hybrid structures with well defined metallic nanowires as a core. [3,4]

[1] D.M. Eisele, J. Knoester, S. Kirstein, J.P. Rabe and D.A. Vanden Bout, Nature Nanotechnology 4 (2009) 658;
[2] J.L. Lyon, D.M. Eisele, S. Kirstein, J.P. Rabe, D.A. Vanden Bout, and K.J. Stevenson, J. Phys. Chem. C 112 (2008), 1260; C.M. Weber, D.M. Eisele, J.P. Rabe, Y. Liang, X. Feng, L. Zhi, K. Müllen, J.L. Lyon, R. Williams, D.A. Vanden Bout, K.J. Stevenson, Small 6 (2010) 184,
[3] D.M. Eisele, H. v. Berlepsch, C. Böttcher, K.J. Stevenson, D.A. Vanden Bout, S. Kirstein, and J.P. Rabe, JACS 132 (2010) 2104; [4] D.M. Eisele; “Optical, Structural and Redox Properties of Nanotubular Jaggregates of Amphiphilic Cyanine Dyes.” (2010) Aachen. Shaker Verlag. ISBN 978-3-8322-9120-4 (PhD thesis, Humboldt-Universität of Berlin, Germany)

 

Title:Structural and electronic characterization of non-polar group-III-Nitride surfaces
Speaker:Dr Holger Eisele
Date: 19 October 2010
Time: 11.00am - 12.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Assistant Professor Sun Handong
Abstract: It will be shown how scanning tunneling microscopy (STM) and spectroscopy (STS) can be applied as extremely useful technique to study nitride semiconductor surfaces. Via STM the atomic structure of the surfaces can be imaged in real space and dislocations crossing the surface can be studied. STS provides detailed information about the electronic structure of the studied surface and therewith clarifies the energetic positions of surface states and the Fermi level. Applying cross-sectional STM to layered structures will lead to and comprehensive analysis of the spatial arrangement of the constituent materials From the first cross-sectional STM measurements (XSTM) on layer with different doping concentrations the imaging mechanisms could be unraveled: Similar to XSTM on zincblende semiconductor nano structures, a mechanical contrast contribution from strain relaxation as well as an electronic contribution originating from differently strong Fermi level pinning was found.

 

Title:Optical lattices, a quantum simulator for many-body physics
Speaker:Dr Andreas Hemmerich
Date: 12 October 2010
Time: 11.30am - 12.30pm 
Venue: Hilbert Space (PAP-02-02)
Host: Professor Alfred Huan
Abstract: Optical lattices are quantum gases arranged in synthetic lattices formed by light. They provide a new context to study many body physics with unprecedented control and precision. The successful emulation of the Hubbard model in optical lattices has stimulated world wide efforts to extend their scope to also capture more complex, incompletely understood scenarios of many-body physics, possibly relevant in condensed matter systems. I will discuss two possible paths in this direction. I will first present our recent experimental observations of superfluidity in higher bands of optical lattices, where orbital degrees of freedom play an essential role as in many condensed matter systems of interest, such as transition metal compounds. I will then discuss how periodic driving can be used to mimic the action of the Lorentz force upon electrons with neutral atoms in an optical lattices thus permitting the implementation of artificial magnetic fields. I will show that new scenarios become accessible in optical lattices such as the Bose-Hubbard model with complex tunneling, if bosons are used. For fermions a Dirac-like single particle dispersion as in Graphene or unconventional superfluidity with RVB-type BCS-pairing can be simulated.

 

Title:Sandwich Molecular Wires and Their Intriguing Properties
Speaker:Dr Shuo-Wang Yang
Date: 6 October 2010
Time: 3.00pm - 4.00pm 
Venue: Hilbert Space (PAP 02-02)
Host: Professor Shen Zexiang
Abstract: The well-designed low-dimensional molecules or molecular wires are the promising candidates for miniaturization of electronic devices’ components of future electronics and spintronics. Recently 1D sandwich molecular wires (SMWs) and related linear molecular clusters have been attracting increasing attentions due to their intriguing electrical and magnetic properties. In this talk, I will present our theoretical investigations on various SMWs, such as (V-Benzene)∞, (FeCp)∞, (EuCOT)∞, and even bimetallic (FeCpVCp)∞, and their fantastic properties, i.e. halfmetallic, profound spin filter efficiency, negative differential resistance (NDR) effects, and magnetic moment enhancement. More importantly, I will reveal the intrinsic mechanism behind aforementioned propertied by detailed analysis on electrical configurations. Some unusual electron spin flip phenomena will be uncovered. Finally, I will demonstrate some reversible multifunctional molecular switches between semiconducting and half metallic by application of external electrical field or oxidation ↔ reduction chemical reactions.

 

Title:Collective Phenomena in Semiconductor Microcavities
Speaker:Dr Ivan A. Shelykh 
Date: 29 September 2010

 

Title:Multiscale cell mechanics : from soft matter physics to medical applications
Speaker:Dr Pierre Nassoy
Date: 8 September 2010
Time: 11.00am - 12.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Professor Alfred Huan
Abstract: In the last 10 years, our research activity mostly focused on the role of the plasma membrane in various cellular functions or biological processes. Our methodology lies on a theoretical and experimental approach, which is inspired from soft matter physics concepts and techniques. We will exemplify this strategy by presenting an overview of our works aimed at understanding the physical mechanisms involved in cell adhesion and inter-cellular communication. Then, I will discuss my future biophysical and biomedical projects related to membrane tension homeostasis, confined 3D cell culture to mimic tumors and drug delivery design principles based on stimuli-responsive polymer vesicles

 

Title:Radiation Monitoring Systems in the Surrounding of Nuclear Power Stations
Speaker:Professor Wang Biao
Date: 6 September 2010
Time: 2.00pm - 3.00pm 
Venue: SPMS-PAP-02-02 (Hilbert Space)
Abstract: In this presentation, the requirement for radiation monitoring in the surrounding of nuclear power stations is reviewed, and the related key research topics are outlined. As a key element in the monitoring system, the radiation sensors are the most important devices. Therefore, they become our main research areas. The basic working principles of several kinds of the radiation sensors are briefly explored, and the fabrication electronic materials are discussed in detail. Finally, as examples, the radiation monitoring systems used in Dayabei and Taishan Nuclear Power Stations, China, were shown in details.

 

Title:Photonic crystal platforms: applications to silicon photonics
Speaker:Dr Dario Gerace
Date: 24 August 2010
Time: 11.00am - 12.00pm
Venue: Hilbert Space (PAP 02-02)
Host: Assistant Professor Cesare Soci
Abstract: Silicon photonics is emerging from the era of speculative research and slowly moving its first steps into market applications. The main motivations rely on the forthcoming need for fast optical interfaces between microelectronic circuitry and communication technology, which in perspective should be low-cost and CMOS-compatible. In order to siliconize photonics, there are three main areas of investigation: (i) generating the light, (ii) selectively guiding and transporting it within silicon, and (iii) enhancing nonlinear effects to perform logical operations. A promising platform to achieve these goals is given by silicon-based photonic crystal integrated circuits, i.e. nanostructured silicon-based wafers in which the periodicity of the refractive index is exploited to tailor the on-chip light confinement and propagation. In this talk we will give an overview of our past and ongoing research efforts in this field. Specific topics that will be discussed are: efficient light generation and extraction in 2D Erbium-doped silicon-based photonic crystals [1], all-optical switching in photonic wire nanocavities at ultra-low powers [2,3], and far-field optimized photonic crystal cavities for efficient out-coupling [4].

[1] M. Galli et al., Applied Physics Letters 88, 251114 (2006).
[2] M. Belotti et al., Optics Express 16, 11624-11636 (2008).
[3] M. Belotti et al., Optics Express 18, 1450-1461 (2010).
[4] S. L. Portalupi et al., Optics Express 18, 16064-16073 (2010).

 

Title:Toward Self-Powered Nanosystems: Nanogenerators, Piezotronics and Piezo-Phototronics
Speaker:Dr Zhong Lin Wang
Date: 16 August 2010
Time: 2.00pm - 3.00pm 
Venue: LT23
Host: Assistant Professor Fan Hongjin
Abstract: Developing wireless nanodevices and nanosystems is of critical importance for sensing, medical science, environmental/infrastructure monitoring, defense technology and even personal electronics. It is highly desirable for wireless devices to be self-powered without using battery. This is a new initiative in today’s energy research for mico/nano-systems in searching for sustainable self-sufficient power sources [1]. It is essential to explore innovative nanotechnologies for converting mechanical energy, vibration energy, and hydraulic energy into electric energy that will be used to power nanodevices. We have invented an innovative approach for converting nano-scale mechanical energy into electric energy by piezoelectric zinc oxide nanowire arrays [2]. The operation mechanism of the nanogenerator relies on the piezoelectric potential created by an external strain; a dynamic straining of the nanowire results in a transient flow of the electrons in the external load due to the driving force of the piezopotential. We have developed the nanogenerator from fundamental science, to engineering integration and to technological scale-up [3-6]. As today, a gentle straining can output 1.2 V from an integrated nanogenerator [6], using which a self-powered nanosensor has been demonstrated [1]. This is a key step for developing a totally nanowire-based nanosystem [6]. Alternatively, by substituting the gate voltage in a field effect transistor (FET) with the piezopotential creating by an external strain, we have fabricated a series of devices that rely on a coupling between semiconductor and piezoelectric properties and are controlled/tuned by externally applied force/pressure, such as diode, strain sensor and strain-gated logic unites, which are a new field called piezotronics [7]. A three way coupling among piezoelectricity, semiconductor and photonic excitation has demonstrated the piezo-phototronic effect [8].

[1] Z.L. Wang “Self-powering nanotech”, Scientific American, 298 (2008) 82-87; Z.L. Wang “Towards self-powered nanosystems: from nanogenerators to nanopiezotronics” (feature article), Advanced Functional Materials, 18 (2008) 3553-3567.
[2] Z.L. Wang and J.H. Song “Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays”, Science, 312 (2006) 242-246.
[3] X.D. Wang, J.H. Song J. Liu, and Z.L. Wang “Direct current nanogenerator driven by ultrasonic wave”, Science, 316 (2007) 102-105.
[4] Y. Qin, X.D. Wang and Z.L. Wang ”Microfiber-Nanowire Hybrid Structure for Energy Scavenging”, Nature, 451 (2008) 809-813.
[5] R.S. Yang, Y. Qin, L.M. Dai and Z.L. Wang “Flexible charge-pump for power generation using laterally packaged piezoelectric-wires”, Nature Nanotechnology, 4 (2009) 34-39.
[6] S. Xu, Y. Qin, C. Xu, Y.G. Wei, R.S. Yang, Z.L. Wang* “Self-powered Nanowire Devices”, Nature Nanotechnology, in press.
[7] Z.L. Wang “Nano-piezotronics”, Adv. Mater., 19 (2007) 889-992.
[8] Y.F. Hu, Y.L. Chang, P. Fei, R.L. Snyder and Z.L. Wang “Designing the electric transport characteristics of ZnO micro/nanowire devices by coupling piezoelectric and photoexcitation effects”, ACS Nano, 4 (2010) 1234–1240.

 

Title:Photoexcitation dynamics and lasing in nanocrystals
Speaker:Dr Guglielmo Lanzani
Date: 12 August 2010
Time: 11.00am - 12.00pm 
Venue: Hilbert Space (PAP 02-02)
Host: Assistant Professor Cesare Soci
Abstract: The target of this research is to establish a link between shape-volume-composition of a nanocrystal and its properties, in order to develop new devices or design new materials. First electron delocalization in several dot/rod nanocrystals based on CdSe/CdS will be discussed according to the information obtained by transient spectroscopy. Then recent applications of these nanocrystals in photonics will be presented. In particular, the realization of super-crystals by self-assembly which behave as micro-resonators and show lasing will be demonstrated.*

* M. Zavelani-Rossi, M. G. Lupo, R. Krahne, L. Manna, and G. Lanzani, Nanoscale 2, 931 (2010).

 

Title:Molecular Photonics
Speaker:Dr Guglielmo Lanzani
Date: 11 August 2010
Time: 11am - 12pm 
Venue: Hilbert Space (PAP 02-02)
Host: Assistant Professor Cesare Soci
Abstract: Photonics regards all practical applications of light. As such it is a very broad area of science and technology, which involves many disciplines, materials and products. Here we will focus on the contribution of molecular semiconductors,* based on carbon, and onto applications as light sources, amplification, lasing and optical switching. Photophysical phenomena behind those applications will be introduced, as a necessary knowledge for driving innovation in a growing field of research. Recent results in the area of bio-organic interfaces will conclude this presentation. * Jenny Clark and Guglielmo Lanzani, Nature Photonics 4, 438 (2010).

 

Title:Spontaneous Quantum Hall Effect in Frustrated Magnets
Speaker:Dr Cristian D. Batista
Date: 6 August 2010
Time: 11.00am - 12.00pm 
Venue: Hilbert Space (PAP 02-02)
Host: Assistant Professor Pinaki Sengupta
Abstract: I will present results on the Kondo Lattice models on a triangular lattice for band filling factors n=3/4 and n=1/4. We will see that a simple non-coplanar chiral spin ordering with uniform scalar spin chirality is naturally realized for different coupling regimes of each of the two filling factors under consideration. The n=3/4 case corresponds to a weak-coupling instability driven by perfect nesting of the Fermi surface. The n=1/4 instability takes place in the intermediate coupling regime. The resulting triple-Q magnetic ordering is a natural counterpart of the collinear Neel ordering of the half-filled square lattice Hubbard model. We will also see that the obtained chiral phase exhibits a spontaneous quantum Hall-effect with xy = e 2 /h.

*Work done in collaboration with Ivar Martin.

 

Title:1D goes 2D: Berezinskii-Kosterlitz-Thouless transitions in Quasi 1D Superconductors
Speaker:Dr Rolf Lortz
Date: 4 August 2010
Time: 2.30pm - 4.00pm 
Venue: Hilbert Space (PAP 02-02)
Host: Associate Professor Christos Panagopoulos and Dr. Alexander Petrovic
Abstract: I will review recent work done in our research team in the Department of Physics at HKUST on arrays of 4 Ångstrom single-walled carbon nanotubes. We grow these world-thinnest carbon nanotubes in the linear pores of AlPO4 -5 zeolite single crystals in which they form a network of parallel nanotubes embedded in an insulating host. This novel composite material shows a highly complex superconducting transition with superconductivity appearing in 2 stages: Quasi 1D superconducting fluctuations start to form below 15 K. Upon further cooling neighbouring nanotubes undergo a Berezinskii-Kosterlitz-Thouless type of phase ordering transition in the lateral plane which establishes the global 3D phase coherence via the Josephson Effect. The system shows intrinsically Physics known from artificial arrays of superconductors and metals (proximity junctions) as well as arrays of superconductors and insulators (Josephson junctions). I will furthermore show on the example of the superconductor Tl2Mo6 Se6 that this behaviour is not limited to carbon nanotubes but a rather universal property of quasi 1D superconductors. These superconductors turn out to be a model system to study the influence of intrinsic Josephson junctions in the crystalline structure of anisotropic superconductors and may provide a clue about the nature of high-temperature superconductivity in the cuprates or pnictides.

 

Title:Workshop on Physics with Ultra Cold Atoms
Date: 21 July 2010
Host: Institute of Advanced Studies

 

Title:Spintronics nanomaterials for future computer - investigation of ferromagnetic semiconductor and giant positive magnetoresistance
Speaker:Professor You Qiang
Date: 20 July 2010
Time: 2.00pm - 3.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Assistant Professor Tom Wu
Abstract: Much interest has been sparked by the discovery of ferromagnetism in a range of oxide semiconductors doped with a few percent of transition metal (TM) cations. The development of ferromagnetic oxide semiconductor materials with giant magnetoresistance (GMR) offers many advantages in spintronics devices for future miniaturization of computers. Among them, TMdoped ZnO is an extensively studied n-type wide-band-gap (3.36 eV) semiconductor with a tremendous interest as future mini-computer, blue light emitting, and solar cells. In this talk, Codoped ZnO and Co-doped Cu2O semiconductor nanoclusters are successfully synthesized by a third generation sputtering-gas-aggregation cluster technique. The Co-doped nanoclusters are ferromagnetic with Curie temperature above room temperature. Both of Co-doped nanoclusters show positive magnetoresistance (PMR) at low temperature, but the amplitude of the PMRs shows an anomalous difference. For similar Co doping concentration at 5 K, PMR is greater than 800% for Co-doped ZnO but only 5% for Co-doped Cu2O nanoclusters. Giant PMR in Co-doped ZnO which is attributed to large Zeeman splitting effect has a linear dependence on applied magnetic field with very high sensitivity, which makes it convenient for the future spintronics applications. The small PMR in Co-doped Cu2O is related to its vanishing density of states at Fermi level. Research work is supported by DOE-BES and DOE-EPSCoR in USA.

 

Title:How a Ti:Sapphire Laser Amplifier Works
Speaker:Dr Stephen Fels
Date: 19 July 2010
Time: 9.00am - 12.00pm 
Venue: MAS Executive Classroom 1 (MAS-03-06)
Host: Assistant Professor Elbert Chia
Abstract: In this lecture I will present the principles of operation of the Ti:Sapphire amplifier. Topic covered are:
(1) Ultrafast Laser Presentation: Kerr-Lens mode locking, dispersion compensation.
(2) Amplifier presentation: chirped-pulse amplification, regenerative amplification, switching, timing
(3) Coherent Legend presentation: cavity layout, parts and functions.

 

Title:Precision Atomic Quantum Sensors
Speaker:Dr Tobias Muller
Date: 1 June 2010
Time: 2.00pm - 3.00pm 
Venue: Hilbert Space (PAP 02‐02)
Host: Professor Alfred Huan
Abstract: Atomic quantum sensors have become a successful and fast-growing research area over the past years providing the basis for precision measurements in various fields. They are employed for ultra-stable clocks [1], precision force measurements [2], inertial navigation sensors [3] or accurate determination of fundamental physical constants [4]. Atomic quantum sensors rely on the wave character of matter as implied by quantum mechanical principles and utilize these wave properties for precision interferometry. Compared to nowadays employed laser light, atomic matter waves offer to enhance the precision of interferometric measurements drastically due to their high intrinsic sensitivity. In this talk, I will introduce the basic concepts of atomic quantum sensors for precision measurements and present results formerly obtained with an atomic inertial sensor based on laser cooled rubidium atoms. I will outline the concept of a novel sensor based on a two atomic species interferometer, which is currently under construction at PAP, NTU. This project is a collaboration between NTU and the Defence Science Organization (DSO) and is funded by the Ministry of Defence, Singapore. Additionally, I will introduce closely related work on ultra-cold atoms performed at NTU. This includes novel concepts for controlled magnetic manipulation directed towards the implementation of interferometers based on ultra-cold atoms in magnetic waveguides.

[1] A.D. Ludlow et al., Science 319, 1805, (2008)
[2] H. Mueller, S-w. Chiow, S. Hermann, S. Chu, K.-Y. Chung, Phys. Rev. Lett. 100, 031101, (2008)
[3] B. Canuel, F. Leduc, A. Gauguet, J. Fils, A. Virdis, A. Clairon, N.Dimarcq, Ch.J. Borde, A. Landragin, P. Bouyer, Phys. Rev. Lett., 97, 010402, (2006)
[4] P. Clade, E. de Mirandes, M. Cadoret, S. Guellati-Khelifa, C. Schwob, F. Nez, L. Julien, F. Biraben, Phys. Rev. Lett. 96, 033001, (2006)

 

Title:First Principle guided Design of Surfaces and Interfaces: Catalysts and Tunneling Junctions
Speaker:Dr Mark Saeys
Date: 14 May 2010
Time: 3.30pm - 4.30pm 
Venue: Hilbert Space (PAP-02‐02)
Host: Professor Alfred Huan
Abstract: Material design has long been based on chemical intuition, i.e., the combination of a large empirical database and qualitative concepts relating structure and composition to function and activity. In recent years, first principle based quantum mechanical modeling has become an important tool to guide the design of materials with desired functionality. In combination with experimental validation, such a first principle guided approach has enabled dramatic progress in our understanding of technologically important surfaces and interfaces. In this presentation, I will discuss our recent progress in three areas: (i) the design of Co and Ni catalysts with improved stability for the production of clean fuels1; (ii) the design of core‐shell oxygen reduction catalysts with optimal activity for fuel cell applications2; and (iii) the design of atom‐scale logic devices on a Si(100) platform3. For each of the examples, the atom‐level understanding of the surface electronic structure provided by the first principle calculations guided the design of improved materials.

Selected References.
1Xu, Chen, Tan, Borgna, Saeys*, J. Catal. 261 (2009) 158; Tan, Xu, Jie, Borgna*, Saeys*, J. Catal. (under review)
2Xu, Yang, Lee, Saeys*, Ind. Eng. Chem. Res. (accepted)
3Yong, Otalvaro, Duchemin, Saeys*, Joachim*, Phys. Rev. B 77, 205429 (2008); Kawai, Yeo, Saeys*, Joachim*, Phys. Rev. B (accepted)

 

Title:Application of gauge theory to acoustics
Speaker:Dr  Woon Siong GAN
Date: 20 April 2010
Time: 11.00am - 12.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Assistant Professor Cheong Siew Ann
Abstract: Gauge theory can be applied to both quantum regime and classical regime. The world’s oldest gauge theory is the Maxwell’s equations. In the quantum regime, gauge theory has been successfully applied to the standard model of particle physics, YangMills theory and the theory of superconductivity. In my talk I will focus on the application of gauge theory to the classical regime. Sound waves propagation in fluids and in solids obey Galilean transformation which is a form of gauge transformation and involves translational symmetry and rotational symmetry. For gauge formulation the time derivative has to be replaced by the covariant derivative for Galilean transformation. The sound velocity has to be expressed in terms of the scalar potential and the vector potential which is a gauge field. We discovered symmetries in the stress field and the velocity field in the acoustic field equations and also derived the new stress field equation. We derived the Lagrangian for sound propagation in solids for both cases of global gauge invariance and local gauge invariance. Their difference will give rise to the Lagrangian for interaction. The applications of gauge theory are in broken symmetry. For instance the origin of phonons is due to the broken translational symmetry during phase change from the fluid phase to the solid phase. Another application is the application of spontaneous broken symmetry to turbulence. We interpret the transition from laminar flow to turbulence flow as a second order phase transition according to Landau’s phenomenology of second order phase transition using the order parameter but I extended to a more rigorous theory by incorporating Nambu’s theory of spontaneous broken symmetry to explain the degeneracy of the ground state of the Landau free energy level during phase transition.

 

Title:"Strange Bedfellows: Quantum Mechanics and Data Mining“
Speaker:Professor Weinstein, Marvin
Date: 16 April 2010
Time: 2.00pm - 3.00pm 
Venue: MAS Executive Classroom 1 (MAS-03-06)
Host: Assistant Professor Chew Lock Yue
Abstract: Dynamic Quantum Clustering (DQC) is a highly visual and completely novel approach to finding clusters in arbitrary high-dimensional sets of data. As such it falls into the quickly evolving area referred to as visual-analytics. One reason it is interesting is that the basic algorithm is completely different from other algorithms used to cluster unstructured data, and so it can be expected to not share the failure modes of these other approaches. Another is that DQC works well with high-dimensional data and the visual interface makes it possible to develop an intuitive feeling for the structure of the data in a large number of dimensions.

What makes DQC unusual is that it maps the problem of clustering into a problem in quantum mechanics and then uses properties of quantum systems to cluster the data. In this talk I will review the basic problem of data clustering, review the basics of clustering approaches and then explain how DQC works. I will show a demonstration of the computation for a simple, small data set

 

Title:The understanding of the primary photochemistry of bacteriophytochromes opens ways to engineer the light sensing protein into an efficient fluorescent marker
Speaker:Dr KC Toh
Date: 15 April 2010
Time: 4.00pm - 5.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Professor Michel-Beyerle
Abstract: Bacteriophytochromes (Bph) are a kind of photoreceptor proteins that is interconvertible between two states, i.e. the red absorbing and far‐red absorbing states. Light detection of the protein is possible through a linear tetrapyrrole chromophore, the biliverdin (BV) that is embedded in the proteins. The chromophore isomerizes at the ring D methine bridge of BV upon light activation. The photochemistry of Bph is influenced by interactions between the BV and the chromophore‐binding pocket. These interactions happen on a picoto nanoseconds timescale. To study the primary photochemistry of Bph, time-resolved UV‐visible spectroscopy that using femtoseconds laser pulses was employed. Two types of Bph, a classical red‐ and far‐red absorbing Bph (RpBphP2), and a red‐ and near‐red absorbing Bph (RpBphP3) were studied. The study reveals a de‐protonation pathway in the primary photochemistry of the Bph. Bph mutants by replacing the two amino acids at the vicinity of the ring D of BV were also investigated. These studies show that the photochemical efficiency of the Bph is determined by the hydrogen bond interactions between the BV and the protein environment, and in competition with the proton transfer in the deactivation channel. This work has provided us a rational way to engineer the protein into an efficient fluorescent marker.

 

Title:A Computational Perspective on Transition Metal Clusters: From Molecular Species to Nanoparticles
Speaker:Professor Notker Rösch
Date: 5 April 2010
Time: 2.00pm - 3.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Professor Alfred Huan
Abstract: Metal clusters and their compounds form a state of matter with properties intermediate between molecules and solids. For the example of transition metal clusters the size dependence of various properties is discussed. For small clusters, properties do not scale with size; rather, every atom counts and the properties of the clusters change in an individual manner. In contrast, properties of nanoparticles of high nuclearity, n > 100, are scalable. Starting with small clusters the effects of ligand decoration are probed for different metals, where the effects not only on the clusters are reported but also the competition to adsorb further ligands. The scaling of metal-metal bond lengths with the cluster size can be exploited to construct model species which mimic the physical and chemical properties of much larger clusters. In this way the regime of nanoparticles comprising thousands of atoms has been made accessible to accurate quantum chemical methods. The variation of the reactivity of clusters with size is exemplified for the interaction with CO probe molecules and applications of symmetric transition metal clusters as models of nanometer sized catalytic materials are discussed.

I. V. Yudanov, R. Sahnoun, K. M. Neyman, N. Rösch, J. Chem. Phys. 117, 9887-9896 (2002).
I. V. Yudanov, M. Metzner, A. Genest, N. Rösch, J. Phys. Chem. C 112, 20269–20275 (2008).
I. V. Yudanov, A. V. Matveev, K. M. Neyman, N. Rösch, J. Am. Chem. Soc. 130, 9342-9352, (2008).
P. S. Petkov, G. N. Vayssilov, S. Krüger, N. Rösch, Chem. Phys. 348, 61-68 (2008).
A. Genest, S. Krüger, N. Rösch, Z. Naturforsch. B 64, 1246-1258 (2009).

 

Title:What is quantum entanglement and why are we so fascinated by it?
Speaker:Professor Kwek Leong Chuan
Date: 26 March 2010
Time: 4.30pm - 5.30pm 
Venue: SPMS‐LT3
Host: Assistant Professor Chew Lock Yue
Abstract: Although quantum entanglement was first studied by Einstein, Podolsky and Rosen as well as Erwin Schrodinger in the early years of quantum theory, useful applications of quantum entanglement as a resource was never highlighted till the seminal paper on quantum teleportation by Bennett et al. Nowadays in quantum information science, the words “quantum entanglement” have become a buzz word. But what is quantum entanglement? In this talk we look at quantum entanglement and some recent developments on the topic.

 

Title:Microbubbles Under an Acoustic Field within a Lab‐on‐a‐chip: Manipulation and Self‐organised “Ballet”
Speaker:Dr Philippe Marmottant
Date: 17 March 2010
Time: 4.15pm - 5.15pm 
Venue: SPMS‐PAP‐02‐02 (Hilbert Space)
Host: Assistant Professor Claus Dieter‐Ohl
Abstract: A Lab‐on‐a‐chip handles minute fluid quantities that take the form of microbubbles (gas) or microdroplets (liquid). In this presentation we introduce a new tool to manipulate bubbles at small scale, based on the application acoustic standing waves. Because of their compressibility, bubbles exhibit strong resonances to acoustic waves, and happen to be very sensitive to acoustic forces.

Manipulation is achieved by harnessing primary acoustic radiation forces. These forces, also called Bjerknes forces, cause the bubbles entering an acoustic standing wave region to be attracted either towards the nodes or the anti‐nodes. We measure large acoustic forces of a few hundreds of nanoNewtons in amplitude (thousand times larger than forces generated by optical tweezers!), while using moderate sound amplitudes of order of 10kPa.

Bubbles interact with neighbor bubbles through secondary acoustic forces. These secondary forces between two bubbles are caused by the pressure field radiated from one pulsating bubble, that act on its neighbor bubble. It usually makes bubbles either to agglomerate, or to repulse.

We have evidenced a new phenomenon that manifests by a self‐organization of bubbles into a periodic arrangement of positions, with temporary "ballet" like motions. In order to explain the existence of this "bubble crystal" that moves independently of the acoustic standing wave, existence parameters (size of the bubbles, acoustic amplitude, frequency) have been systematically investigated, leading to a new phenomenological and theoretical description based on bubble‐ bubble interactions mediated by acoustic waves

 

Title:New materials for organic electronics
Speaker:Dr Andrew Grimsdale
Date: 17 March 2010
Time: 3.00pm - 4.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Assistant Professor Sum Tze Chien
Abstract: Organic polymers and molecules are of great interest for use in semiconducting devices such as transistors, LEDs and solar cells, in energy storage devices, and in medicine. A brief overview is given of work currently being done in my group on synthesis of organic functional materials for use in applications such as solar cells, batteries and drug delivery.

 

Title:Complex Systems Single Molecule Studies of Charge Transfers
Speaker:Professor Rudolph A. Marcus
Date: 16 March 2010
Time: 11.00am - 12.00pm 
Venue: SPMS‐PAP‐02‐02 (Hilbert Space)
Abstract: There is an increasing body of single molecule studies of electron transfers between various dyes and nanoparticles or crystal surfaces. Much of this work is stimulated by the inherent interest in the fundamentals of these charge transfer processes as well as by their potential application to solar energy conversion and sensoric devices. Although the usual power law for quantum dot fluorescence is frequently around -1.5, there are preliminary indications that for some of the dye--nanoparticle/dye-surface interactions the power law may be around -1.0 and result from a charge injection from the dye into the nanoparticle or surface, followed by a surface-trap diffusion. We discuss both systems. The field is in its infant stage, the importance of such charge transfers notwithstanding. We also discuss single molecule studies of enzyme catalysis and other properties. Some of the experiments in this evolving single molecule field supplement the respective bulk ensemble studies, thus providing new information.

 

Title:Experiments, Theory, Predictions, Tests, and Unknowns
Speaker:Professor R. A. Marcus
Date: 11 March 2010
Time: 3.00pm - 4.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Professor Alfred Huan
Abstract: One of the newer types of experiments on nanopartices (quantum dots QDs) is that of single molecule studies. They range from those on small inorganic and organic nanoparticles to large biological units. We illustrate some of the issues that arise, using the topic of QDs and choosing a particular inorganic nanoparticle, CdSe, the most studied of these systems. Its study reflects the problems that arise in experiments and theories in this field. Prominent is the power law for the intermitted fluorescence for ‘light’ and ‘dark’ states, and the dependence on experimental conditions, such as time scale, effect of light intensity, temperature, and other external parameters. The complementary nature of ensemble and single molecule experiments is described and is illustrated by trajectories for the two types of experiments. The research in the QD field is both experimentally and theoretically a currently ongoing process, for which the answers are not fully known in spite of the large body of research. The detailed role of surface states and Auger processes is part of the problem. As this field continues to yield new and unexpected results this lecture is a sense an interim report that illustrates one analytic approach to the topic and where computer calculations and simulations can be expected to provide additional insight.

 

Title:First-principles Study of Redox Reactions: From Electron Transfer between Metal Ions to the Enzymatic Reaction of Superoxide Reductase
Speaker:Dr Patrick Sit
Date: 24 February 2010

 

Title:Topologically-protected one-way modes in photonic crystals
Speaker:Dr Chong Yidong  
Date: 12 February 2010

 

Title:Applications in Terahertz Imaging and Spectroscopy
Speaker:Dr Jesse Alton
Date: 10 February 2010
Time: 1.00pm - 2.00pm 
Venue: Hilbert Space (PAP-02-02)
Host: Assistant Professor Elbert Chia
Abstract: The terahertz (THz) region of the electromagnetic (EM) spectrum is commonly defined as spanning 0.1 THz to 10 THz. This region is of particular interest as many solids, liquids and gases have resonances in this area, the radiation is low energy (non-ionising) and can penetrate many common materials such as plastics, papers and ceramics. In the last decade the advent of commercially available turn key terahertz spectroscopy and imaging systems has unlocked this rich area of the EM spectrum. Terahertz imaging and spectroscopy techniques are now commonly used in a wide variety of fields ranging from medical, security and pharmaceutics to art restoration and non-destructive testing of space shuttle foam. Here I will present an overview of the technology and applications that TeraView are currently involved in.

 

Title:Template Directed Self-Assembly
Speaker:Professor Lifeng Chi
Date: 10 February 2010

 

Title:Physics based simulation of clothes, hair and soft tissues
Speaker:Professor Nadia M. Thalmann
Date: 19 January 2010

 

Title:Nanowires: A Platform for Nanoscienceand Nanotechnology
Speaker:Professor Charles Lieber
Date: 7 January 2010