|
Abstracts
___________________________________________________________________
Exploring new applications of ZnO
Xiaowei Sun
School of Electrical and Electronic Engineering
Nanyang Technological University
Email: exwsun@ntu.edu.sg
Abstract:
In this talk, the research activities on ZnO in our group will be introduced:
(1)Applying ZnO nanostructures for field emission using diode and triode configurations
(2)p-n and isotype ZnO-Si heterostructure diodes by MOCVD
(3)UV LED made of ZnO-NPB organic-inorganic heterostructures
(4)Applying ZnO in gas and biochemical sensing
(5)ZnO application in dye-sensitized solar cells
(6)Electrochromic type electronic paper making use of ZnO nanorod electrode
Research Interests:
(1)MOCVD growth of ZnO.
(2)Display technologies: organic light-emitting devices (OLED) and liquid-crystal-on-silicon (LCoS) microdisplay.
(3)Nanotechnology: one-dimensional oxide semiconductors and their applications.
_____________________________________________________________________
The syntheses, properties and applications on nanowires
Jing Zhu
Department of Materials Science and Engineering,
Tsinghua University
Email: jzhu@mail.tsinghua.edu.cn
Abstract:
One-dimensional nanostructures are promising components in a wide range of nanoscale device applications. In this talk, we will talk about some progress in our group in the field of one-dimensional nanowires, including the syntheses, structures, properties and applications of nanowires (arrays), especially Si, heterojunctions, ZnO, and metal nanowires.
Research interests:
Her team research interests include nanomaterials and nanostructures, electron microscopy in materials science, interfaces and surfaces in materials, research and development of in-situ specimen holders in electron microscopes. More details can be found on our website: http://www.mse.tsinghua.edu.cn/faculty/zhuj/index.htm
_____________________________________________________________________
The electrical nanodevices based on metal oxide nanowires: high performance field effect transistor, gas sensor and waveguide
Ting Yu
Division of Physics and Applied Physics
School of Physical and Mathematical Sciences
Nanyang Technological University
Email: yuting@ntu.edu.sg
Abstract:
This presentation will talk about the nanodevices of transition metal oxide nanowires, such as field effect transistors, gas sensors and waveguide.
We will first report on a simple and efficient method developed in our group for fabrication of metal oxide nanostructures. To demonstrate our attempts on developing nanoelectronics, ZnO nanowire will be selected as an example. This project covers (i) tuning the electrical transport properties of n-type transistor based on ZnO nanowires (NWs) from semiconducting to metallic by appropriate Ti plasma ion immersion; (ii) extending the applications of ZnO nanodevices and developing ZnO NW ferroelectrical field effect transistor (FeFET). The former approach may offer a facile method to produce an inexpensive alternative to ITO as transparent conducting oxide materials. The latter substantially enhances performance of ZnO FET due to the high dielectric constant of ferroelectric gate. Meanwhile, such ZnO FeFET could function as memory unit because of the switchable remnant polarization of ferroelectrics.
It is well known that ZnO is initially n-type due to defects effect. The efforts on seeking p-type nanowires are never stopped. In our group, nanodevices based on CuO, an in-direct p-type semiconductor nanowire such as field effect transistor has been studied. Single nanowire-based field effect transistor exhibits uniform p-type electrical properties. It is a very important result because most of transition metal oxide nanowires are researched as natural n-type semicondcutors.
Cu2O is a p-type semiconductor of cubic structure with a direct band gap of 2.17 eV. Its outstanding excitonic properties including a large exciton binding energy (~ 140 meV) have been the target of much fundamental research during the past decades. To continue improving the progress of metal oxide nanowire, the Cu2O nanowires have been synthesized in our lab. The strong photoluminescence (2.10 eV) of Cu2O is observed and the FET shows typical p-channel and high on-off ratio.
Finally, we will report on the synthesis of single crystalline vanadium pentoxide nanofiber by a simple thermal vapor deposition technique. The first demonstration of the efficient light propagation of V2O5 will be presented. These results provide useful information for the construction of future nanoscaled waveguide structures. Moreover, regular V2O5 waveguides are found to successfully exhibit Raman signal with near-resonance excitation apparent in spectra of PL emission out-coupled at the nanofiber tips. The initial results provide experimental support for the development of novel nanophotonic elements.
Research Interests:
Synthesis of nanostructures, assembly and manipulation of 1D nanostructure, and development of nanodevices.
(1)Substrate-friendly synthesizes of metal oxide nanostructures with controlled morphologies and patterns.
(2)Wet-chemical method is one of our current approaches for fabrication of metal hydroxides and metal oxides nanostructures.
(3) Field induced electron emission of individual nanowires or nanowire array
(4) Assembly and manipulation of nanostructures by dielectrophoresis (DEP) effect, line optical tweezers and nanomanipulator
(5) Electronic transport and mechanical properties of individual nanostructures
(6) Wettability and antiwettability of nanostructures
(7) Graphene
_____________________________________________________________________
Carbon nanotube based electronic devices and their applications
Qing Zhang
School of Electrical and Electronic Engineering,
Nanyang Technologicial University
Email: eqzhang@ntu.edu.sg
Abstract:
In this talk, I shall outline our research activities relevant to carbon nanotubes (CNTs). I will begin with discussion on the assembly of CNTs using AC dielectrophoresis and sub-micron channel fluidic alignment techniques. The unique electron transport properties and optical properties for single walled CNTs and double walled CNTs will be reported and compared Several applications of CNTFETs have been attempted and the detailed discussions will also be focused on CNTFET sensoring, including NH3 gas, real-time organophosphate detection and nitrophenol detection, etc.
Research interests:
His team has developed the first batch of CNT-FETs, CNT-glucose sensors, NH3-gas sensors in Singapore. Currently, he is focusing his attention on.
_____________________________________________________________________
Super-aligned Carbon nanotube Arrays: Controlled Synthesis, Physical Properties and Applications
Kaili Jiang
Department of Physics & Tsinghua-Foxconn Nanotechnology Research Center,
Tsinghua University
Email: JiangKL@tsinghua.edu.cn
Abstract:
Super-aligned carbon nanotube (CNT) arrays are distinguished from normal vertically-aligned CNT arrays by their “super-aligned” nature, i.e., the CNTs in super-aligned arrays have a much better alignment than those in normal arrays.1,2 The key feature of a super-aligned CNT array is that continuous yarns or sheets, which are composed of a thin layer of parallelly-aligned pure CNTs, can be directly drawn from it in solid state.1-4 The as-produced yarns or sheets are transparent and highly conductive, with aligned CNTs parallel to the draw direction. Many potential applications for these have been demonstrated, for example as polarizers, transparent conducting films, and polarized light sources etc.1 After passing through volatile solutions2 or being twisted, the yarns or sheets can be further condensed into shrunk yarns. These shrunk yarns have high tensile strengths and Young’s moduli,2 and are good candidates for thermionic3 and field emission4 electron sources. In this talk, I will present our progress in controlled synthesis5, physical properties6 of super-aligned CNT arrays, and more applications such as high reduced brightness field emission electron source7 low work function thermionic emission electron source8, CNT-based Nanogrid for HRTEM9, CNT loudspeaker10 etc. will be demonstrated.
1. K. L. Jiang, Q. Q. Li, S. S. Fan, Nature 419 (2002) 801.
2. X. B. Zhang, K. L. Jiang, et al. Adv. Mater. 18 (2006) 1505.
3. P. Liu, Y. Wei, K. L. Jiang et al. Phys. Rev. B. 73 (2006) 235412.
4. Y. Wei, et al. Appl. Phys. Lett. 89 (2006) 063101.
5. K. Liu, et al. Nano Lett. 8 (2008) 700.
6. Y. Wei, K. L. Jiang, X. F. Feng, P. Liu, L. Liang, S. S. Fan, Phys. Rev. B. 76 (2007) 045423.
7. Y. Wei, K. L. Jiang, L. Liang, Z. Chen, S. S. Fan, Nano Lett. 7 (2007) 3792.
8. L. Xiao, et al. Appl. Phys. Lett. 92 (2008) 153108.
9. L. N. Zhang, et al. Nano Lett. (2008) 8,2564.
10. L. Xiao et al., Nano Lett. (2008) 8, 4539.
Research interests:
Current research interest includes:
(1) Controlled synthesis of carbon nanotube.
(2) Growth mechanisms of carbon nanotube.
(3) Physical properties and applications of carbon nanotube.
_____________________________________________________________________
Template-based nanofabrication: nanowires, nanotubes, and more…
Hongjin Fan
Division of Physics and Applied Physics,
School of Physical and Mathematic Sciences,
Nanyang Technologicial University
Email: fanhj@ntu.edu.sg
Abstract:
Fabrication of simple and complex nanostructures (e.g., wires, tubes, hollow particles, core/shell…) relies largely on templates. Template-based fabrication allows for more precise control of the growth kinetics and insights to the mechanism. In this talk, I will first give a general overview of the various fabrication routes to nanowires and nanotubes. Then I will give selective examples on fabrication of metal-oxides nanowires using various template techniques including AAO, laser interference lithography, PS spheres. As a result, 2-D ordered arrays of nanowires vertically standing on GaN surfaces are obtained via combining substrate nanopatterning and catalyst-directed epitaxial growth will be presented.
In the 3rd part, I will demonstrate that the template application of nanowires for formation of more complex nanomaterials. As a physical template, the nanowries are used for the fabrication of 3-D ferroelectric nanocapacitors such as Pb(Zr,Ti)O3 and BaTiO3. The ferroelectric materials are deposited either by pulsed laser deposition or chemical solution deposition. As a chemical template, ZnO is also a reactive material and therefore a wide range of ternary compound nanotubes/wires can be formed via reaction with ZnO nanowires. Examples of spinel-type ZnAl2O4 nanotubes and Zn2TiO4 nanowires will be shown. The former involves the nanoscale Kirkendall effect, which is nowadays becoming a generic fabrication method towards hollow metal oxide nanostructures. The latter, Zn2TiO4, has a quasi-periodic twinned structure, which is a common morphology among many cubic-structure nanowires.
Research interests:
(1)Oxide semiconductor nanowire arrays and their individual physical properties
(2)ZnO-based ternary oxide nanowires and nanotubes
(3)Atomic layer deposition for nanofabrication, and tuning the surface properties of oxide nanostructures
(4)Hollowing method and mechanism on the nanoscale
_____________________________________________________________________
Structure Control and Mass Production of Carbon Nanotube
Fei Wei
Beijing Key laboratory of Green Chemical Reaction Engineering and Technology
Department of Chemical Engineering, Tsinghua University, Beijing, 100084, China
Email: wf-dce@tsinghua.edu.cn
Abstract:
In this talk, I shall outline our research activities relevant to carbon nanotubes structure control and mass production. To produce more aligned CNT forest, various ways were developed to solve this problem. The first one approach is to increase CNTs length. It is relatively difficult because, in most of the cases, the CNT arrays stop the growth within several millimeters. Since CNT array yield is proportional to size of the growth region, another way, which is more controllable and promising, is to grow in larger area. Moreover, continuous operation is much more preferred than the batchwise one because of its higher efficiency and lower cost. Nevertheless, it is much difficult to achieve large-area growth on conventional flat wafers and also to transport the as-grown wafers out in situ. We used spheres as the substrate, and successfully obtained large amount CNT forests. 100g of product are obtained along all the directions of the spherical substrate in 30mins. The phoenix tree ball structure and good fluidness of the spheres after the reaction makes it possible to remove array out of the high temperature reactor in situ. Further applications MWNT forest were developed, including CNT areogel, CNT paper, CNT foams, transparent conductive film, CNT yarn, which show excellent performance of large aspect ratio of CNT in forest form.
Research interests:
His team has developed the nano-agglomerated fluidized bed mass production of CNT, aligned CNT growth on spherical ball. Currently, he is focusing his attention on mass production of aligned SWNT.
_____________________________________________________________________
Dual metal gate technologies for 45nm and beyond CMOS devices
HongYu Yu
School of Electrical and Electronic Engineering
Nanyang Technological University
Email: hyyu@ntu.edu.sg
Abstract:
Advanced gate stack (metal gate and high-K dielectrics) is one of the important technology enablers for 45nm and beyond CMOS technologies. In this talk, the challenges and opportunities for the advanced gate stack development would be reviewed. Several promising dual metal gate technologies (such as MIPS, FUSI and RPG) would be discussed.
Research interests:
Emerging Si-based Nano Electronic Device in the areas of both “More Moore” and “More than Moore”
(1) Novel Non-Volatile Memory Research
(2) Sub-22nm CMOS devices
(3) SiGe based Nano-wire devices
(4) Si based Photovoltaic devices
(5) Si photonics
_____________________________________________________________________
Nanoelectronics research in the Institute of Microelectronics
Wei Chen
Institute of Microelectronics
Tsinghua University
Email: weichen@tsinghua.edu.cn
Abstract:
In this talk, I will give an overview of our research activities in the area of nanoelectronics in the Institute of Microelectronics at Tsinghua University. Research projects include the study of superconducting devices for application in quantum information process, molecular electronics, materials and devices for 32nm and beyond CMOS and NVM, spin based devices and MEMS/NEMS.
Research interests:
Quantum information process based on Superconducting devices, Molecular electronics, spintronics, nanofabrication, nanostructure physics.
_____________________________________________________________________
Nanophase magnetic material using pulsed laser deposition and energetic pulsed plasma driver
Rajdeep Singh Rawat
Natural Sciences and Science Education
National Institute of Education
Nanyang Technological University
Email: rajdeep.rawat@nie.edu.sg
Abstract:
The nanophase magnetic materials, in the form of nanoparticles, nanoclusters and nanocomposites, have been successfully synthesized using pulsed laser deposition and energetic pulsed plasma driver called plasma focus device. The dense plasma focus (DPF) device is a coaxial plasma gun that uses a large electric current to heat and compress a gas to high temperatures (1-2 keV), densities (1025-26 m-3). Under such extreme conditions, the gas radiates copious ultraviolet, X-rays and particle beams such as relativistic electrons and ion beams. We have successfully used the single shot and “repetitive” PF device for synthesis of nanophase magnetic material of Fe/FeCo. The plasma focus device is operated at 1 Hz repetition rate at various combinations of charging voltage and filling pressure of hydrogen gas for different number of focus deposition shots to tune the morphology, structure and magnetic properties of the nanophase magnetic material.
We have also employed different pulsed laser deposition (PLD) based techniques, such as conventional PLD, backward plume deposition (BPD) and magnetic trapping assisted PLD for synthesis of nanophase materials. It was found that morphological features of deposited nanostructures, such as thin films, nanoclusters, and floccule-like nanoparticle networks, are governed by the surface mobility of ablated species and can be tailored using deposition conditions, such as ambient gas pressure and deposition shots. It was reported that BPD, as special target-substrate geometry, can synthesize nanostructures at much higher deposition rate and reduce the number of laser droplets. The fct phase FePt nanoparticles have high anisotropy constant (Ku>3´107 ergs/cm3) and can remain ferromagneic when the particle size is reduced to nano range and hence are very useful for high density magnetic data storage. However, as-deposited FePt normally exhibits magnetically soft fcc phase, which requires annealing at about 600 °C for phase transition to fct. FePt nanoparticles synthesized by ion irradiation induced nanostructuring of its thin films deposited by PLD, are found to have lower phase transition temperature of about 400 °C. To reduce the exchange coupling effects (source of media noise) and thermal annealing effects (such as grain growth and agglomeration), FePt nanoparticles embedded in Al2O3 nonmagnetic matrix materials are synthesized by PLD and magnetic trapping assisted PLD. Experimental results show that magnetic properties of FePt nanoparticles are improved by introducing this nonmagnetic Al2O3 matrix in both cases. The magnetic trapping assisted PLD based FePt:Al2O3 nanocomposite thin films found to have lower phase transition temperature of 300 °C. The lower phase transition temperature together with nonmagnetic materials can prevent grain growth and agglomeration during annealing and in turn reduce the exchange coupling effects in the FePt:Al2O3 nanocomposite thin films.
Research interes:
Pulsed plasma devices such as Plasma focus device and pulsed laser deposition, basic plasma diagnostic techniques like laser shadowgraphy, x-ray spectrometry, x-ray imaging, optical emission spectroscopy, ion beam analysis, optical streak photography, neutrons and charged particles measurement techniques etc. Others: magnetic thin films, magnetic nanoparticles, magnetic nano-composites and diluted magnetic semiconductor thin films. Well versed with various thin film characterization and analysis techniques.
_____________________________________________________________________
Characterization of InAs/InxGa1-xAs dots-in-a-well (DWELL) structures
Handong Sun
Division of Physics and Applied Physics,
School of Physical & Mathematic Sciences,
Nanyang Technologicial University
Email: hdsun@ntu.edu.sg
Abstract:
InAs/InxGa1-xAs dots-in-a-well (DWELL) material systems are of great interest due to their unique physical properties and promising device application. In this talk, we focus on the carriers capture process from QW to QD of this novel structure through photoluminescence (PL) and photoluminescence excitation (PLE) studies. Numerical simulation regarding the electronic structures is also carried out in the framework of effective-mass envelope function theory by finite element method (FEM), and compared with experiment. Novel application of QD materials in vertical cavity devices will be discussed.
Research Interests:
(1) Optical spectroscopic characterization.
(2) GaAs-based QD optical-pumped vertical external cavity surface emitting laser.
(3) Microcavity physics and devices based on wide bandgap materials.
(4) Plasmonics optics.
(5) Förster resonance energy transfer (FRET) and applications.
___________________________________________________________________
Jahn-Teller Distortion, Electron Correlation, and Orientational Ordering in KxC60 Fullerides
Yayu Wang
Department of Physics
Tsinghua University
Email: yayuwang@tsinghua.edu.cn
Abstract:
Alkali metal doped C60 fullerides are uniquely flexible molecular systems that exhibit a rich variety of behaviors exemplified by organic superconductivity, metal insulator transition, and novel orientational orderings. The various competing interactions in fullerides, such as strong electron correlation and Jahn-Teller distortion, create controversies in how their physical properties evolve with dimensionality and carrier density. In this talk I will present high-resolution STM studies of potassium doped C60 (KxC60) ultra-thin films on Au(111) surface. By systematically tuning the layer structure and doping content, we are able to map out the structural and electronic phase diagram of the fullerides. In KxC60 monolayers, we directly visualized a metal-insulator phase transition from K3C60 to K4C60 induced by molecular Jahn-Teller distortion. The electronic phase transition is accompanied by novel cross-like and pinwheel-like orientational orderings that has never been observed before. We also found a series of electronic phase transitions as the fullerides change from a two-dimensional monolayer to a quasi-three-dimensional multilayer, which can be understood quantitatively by considering the change of electron correlation strength with dimensionality and proximity to a metal surface.
Research interests:
My main research interests lie in experimental investigations of the behavior of electrons in novel low dimensional materials with strong electron correlations, exemplified by quasi-2D transition metal oxides and organic metals/magnets. We employ a number of experimental probes, such as electro-thermal transport, high resolution magnetometer, and low temperature scanning tunneling spectroscopy to provide complimentary information regarding the exotic properties in these quantum materials.
_____________________________________________________________________
Raman Microscipy study of graphene: From foundamental studies to application
Zexiang Shen
Division of Physics and Applied Physics
School of Physical and Mathematical Sciences
Nanyang Technological University
Email: zexiang@ntu.edu.sg
Abstract:
This presentation will talk about the Raman spectroscopy and imaging of graphene. Graphene comprises one monolayer of carbon atoms packed into a two-dimensional (2D) honeycomb lattice. It has exhibited a series of new electronic properties such as anomalously quantized Hall effects, massless Dirac-Fermions like charge carrier, absence of weak localization and the existence of a minimum conductivity. All these properties make graphene a promising candidate for potential device applications as well as for fundamental studies.
In the device application, several factors will affect the properties of graphene, including: (1) the substrate (2) the top insulator deposition (3) the annealing process. Here, we carry out systematical Raman study of monolayer graphene on different substrates. Our results suggest that the weak interaction (Van de Waals force) between graphene and substrates play a negligible role in affecting the properties of graphene made by micromechanical cleavage. Only epitaxial graphene grown on SiC substrate shows significant blueshift of G-band which can be understood by the strong compressive strain on graphene induced by the interaction with SiC substrate.
Top local gates have been employed to develop more complex graphene devices. The gate oxides (such as HfO2, Al2O3 and SiO2) should influence the graphene sheets in at least three ways: doping, defects, and various mechanical deformations. While defects lead to the observation of defect-related Raman bands, stress causes shift in phonon frequency. A compressive stress (as high as 2.1 GPa) is induced in graphene by depositing a 5 nm SiO2 followed by annealing. The results presented here are closely related to the application of graphene on nano-electronic device.
Research interests:
(1)Near-field scanning Raman microscopy
(2)Characterization of nano materials and devices
(3)Strain/stress study of Si based devices
(4)Nano plasmonics
(5)Nano photonics
_____________________________________________________________________
Intrinsic Transport Properties of Graphene Nanoribbons
Wenhui Duan
Department of Physics
Tsinghua University
Email: dwh@tsinghua.edu.cn
Abstract:
Graphene nanoribbons (GNRs) have recently attracted intensive interests, because they are recognized as a new class of materials in the carbon family as promising building blocks for molecular electronic, optoelectronic, and spintronic devices. In this talk, I will discuss our theoretical research on the electronic and transport properties of Graphene nanoribbons and its implication to device applications. Using extensive first-principles transport calculations, we determine the intrinsic current-voltage characteristics of GNR-based field effect transistor and demonstrate its high levels of performance. Especially the intrinsic transport properties of zigzag graphene nanoribbons (ZGNRs) are investigated using first principles calculations. It is found that although all ZGNRs have similar metallic band structure, they show distinctly different transport behaviors under bias voltages, depending on whether they are mirror symmetric with respect to the midplane between two edges. Asymmetric ZGNRs behave as conventional conductors with linear current-voltage dependence, while symmetric ZGNRs exhibit unexpected very small currents with the presence of a conductance gap around the Fermi level. This difference is revealed to arise from different coupling between the conducting subbands around the Fermi level, which is dependent on the symmetry of the systems.
Research interests:
(1) Electronic properties of nano-structures, clusters, surfaces, and solids;
(2) Electronic and transport properties of low-dimensional systems
(3) Carbon and BN nanotubes, graphene, and their device applications
(4) Monte Carlo simulation of perovskite ferroelectrics
____________________________________________________________________
Plasma-aided nanofabrication: bridging the gap of nine orders of magnitude
Shuyan Xu
Plasma Sources and Applications Center
NIE and Institute of Advanced Studies
Nanyang Technological University
Email: Shuyan.Xu@nie.edu.sg; Shuyan@ntu.edu.sg
Abstract:
Plasma-aided nanofabrication is an emerging research area at the cutting edge of the physics of plasmas and gas discharges, nanoscience and nanotechnology, materials science and engineering, and structural chemistry.The existing approaches to fabricating functional nanostructures are mostly process-specific and suffer from cost-inefficient ``trial and error” practices. One of the reasons is that the ability to control the generation, transport, deposition, and structural incorporation of the building units of such films and structures, still remains elusive. On the other hand, the pioneering concept of deterministic plasma-aided nanofabrication is treated with extreme caution due to inherent chaotic nature of the plasma at the microscopic level.
This contribution shows how to challenge one of the previously intractable problems of bridging nine orders of magnitude between the sizes of plasma nanofabrication facilities (~ m) and self-organization of adsorbed building units on solid surfaces (~ nm). One effective approach is to manipulate the ionic building blocks in the non-neutral layer of space charge that separates the plasma and solid surfaces and control self-organization of nanostructure building blocks on plasma-exposed surfaces and their insertion into the nanoassemblies. As an example, the hybrid reactive plasmas assisted nanofabrication processes are investigated within the framework of the "cause and effect" approach. The approach builds up on extensive experimental data on plasma diagnostics, nanostructure characterization, numerical simulation of the species composition in the ionized gas phase and atomistic modeling based on Density Functional Theory. In addition, the generation and applications of hybrid reactive plasmas for fabrication of ordered nanostructures and uniform semiconducting quantum dots, superlattices and microstructures for photovoltaic materials are discussed. Finally, the issues of tailoring the reactive plasma environments and development of integrated plasma nanofabrication facilities for potential industrial applications are also addressed.
Research Interests:
(1) high density inductively coupled plasma sources, integrated plasma facilities for industrial applications
(2) thin film Si/SiC photovoltaic materials and solar cells
(3) plasma nanoscience, assembly of nanomaterials, quantum dots, wires, superlattices and biomedical materials materials synthesis and surface processing, modification and implantation
(4) modelling, simulation and diagnostics of reactive plasma and self-organization processes
_____________________________________________________________________
A Strategy for Constructing Self-reporting Chemical Sensors with High Sensitivity and Specificity
Guangtao Li
Key Lab of Optoelectronic & Molecular Engineering, Department of Chemistry, Tsinghua University, 100084 Beijing, China
Email: LGT@mail.tsinghua.edu.cn
Abstract:
It is highly desirable in analytes detection, medical diagnostics and stimulant control to develop ideal molecular sensors that should not only exhibit high specificity, sensitivity and quick response, but also be easily regenerable and simply operational for assays. Although some progress has been made to improve the performances of sensors by utilizing mimic antibodies, label-free affinity assays and immunoassays, it is still a challenge to find an efficient and general way to construct an extensively practicable sensor that simultaneously possesses above mentioned desirable features, rather than improve one feature but lose another. Based on the combination of photonic crystals and molecular imprinting techniques, we report a general strategy to construct such high-performance sensors. These sensors consist of a three-dimensional highly ordered and interconnected macrospores array with a thin hydrogel wall, in which nanocavites complementary to analytes in shape and binding sites are distributed. This special hierarchical structure endows these sensors enable quickly, easily, sensitively and directly to report recognition event by a change of absorption color without any transducers and treatments for analytes. The inherently affinity of nanocavites, deriving from molecular imprinting, makes these sensors highly specific to analytes, even if in a competitive environment. Furthermore, these sensors can swell or deswell upon external stimuli, exhibiting well regenerability. As a demonstration, a biosensor affinitive to protein was constructed by using this strategy. This convenient and simple approach could be extended to detect a wide range of analytes, such as chiral drugs, viruses, amino acids and other macromolecules. We also anticipate that this technology may provide an appealing application in drug delivery, catalysts and film separations.
References:
1. Xiaobin Hu, Guangtao Li, Mohan Li, Jing Huang, Yan Li, Yongbin Gao, Yihe Zhang Advanced Functional Materials 18, 575-583 (2008)
2. Xiaobin Hu, Guangtao Li, Jing Huang, Di Zhang, Yong Qiu Advanced Materials 19, 4327-4332 (2007)
3. Xiaobin Hu, Qi An, Guangtao Li, Shengyang Tao, Jian Liu Angewandte Chemie. Int. Ed., 45, 8145-8148 (2006)
4. Xiaobin Hu, Jing Huang, Weixia Zhang, Mohan Li, Chengan Tao, Guangtao Li Advanced Materials, in press (2008)
Research interests:
Chemical sensors, Nanostructured materials, Photonics, Supramolular chemistry.
_____________________________________________________________________
Optical Induced acoustic vibrations in nanosized spherical and elliptical
gold-shell particles
Xinyan Shan
Department of Physics
Tsinghua University
Email: shanxinyan@mail.tsinghua.edu.cne
Abstract:
We examine linear and ultrafast nonlinear optical properties of 3D photonic crystals, for example, crystals composed of silica-core-gold-shell spheres capped with a silica outer layer. A highly directional diffraction pattern was observed with hexagonal or cubic symmetry. We demonstrated for the first time a time-resolved coherent oscillation of the gold-shell photonic crystals and detected the acoustic vibrations which were excited by employing ultrashort optical pulses (100 fs). The frequencies of these oscillations are in the GHz range and demonstrated to be in agreement with Lamb theory. Further more, using ultrafast pump-probe spectroscopy with asynchronous optical sampling (ASOPS) technique, we excite the acoustic vibrations of the shells and detect the oscillations via modulations of the optical reflectivity. Fast oscillations were observed, corresponding to longitudinal acoustic vibrations traveling back and forth through the gold layer. In addition, slow oscillations appear at later times following the fast oscillations, corresponding to free oscillations of the gold shell and accounted for by Lamb’s theory.
Research interests:
Our group focuses on surface and interface properties using STM, SPM and AFM techniques. Currently, we extend our attention to optical techniques, including Raman spectroscopy, ultrafast dynamic experiment of surface and interface properties.
_____________________________________________________________________
Morphology and structure controlled synthesis of oxide and silicid nanomaterials
Tom Wu
School of Physical and Mathematical Sciences
Nanyang Technological University
Email: tomwu@ntu.edu.sg
Abstract:
For oxides, we prepared Cu-doped ZnO nanowires using different bottom-up approaches and carried out a comparative study of their magnetic properties. Compared with the conventional vapor transport method, annealing a ZnO core/Cu shell structure leads to significantly enhanced room-temperature ferromagnetism. We suggest that the structural inhomogeneity boosts the ferromagnetism by promoting the formation of bound magnetic polarons. A similar mechanism can also be applied to Cr-doped In2O3 nanomaterials, where we observed a strong correlation between the magnetism and the level of oxygen deficiency.
Controlling morphology and structure is important for nanomaterials due to its strong correlation with functionalities. As a key ingredient for high-density device integration, nanoscale geometrical confinement often brings about novel phenomena and functionalities. In this talk, I will focus on two particular materials families: transition-metal-doped wide-band gap oxides and metal silicides.
For silicides, controlling shape and orientation is equally important. In this work, nanoscale Cu3Si triangles, squares, and wires have been grown on Si(111), (100), and (110) substrates, respectively, through a template-free Au-nanoparticle-assisted vapor transport method. The sides of triangles and squares and the growth direction of the nanowires are all along Si <110>, giving rise to long-range ordering of the nanostructures. Au nanoparticles absorb Cu vapor and facilitate the rate-limited diffusion of Si, which is critical for the shape-controlled growth of Cu3Si.
Using the above examples, we demonstrate that it is important to develop synthesis strategies to control the morphology and structure of nanomaterials. These advanced synthesis routes help us to study the emergent materials physics, and to create novel physical functionalities in many versatile materials, which is strategically important for both basic sciences and potential applications.
References:
(1) G. Z. Xing, J. B. Yi, J. G. Tao, T. Liu, L. M. Wong, Z. Zhang, G. P. Li, S. J. Wang, J. Ding, T.. C. Sum, C. H. A. Huan, and T. Wu, Adv. Mater. (published on line).
(2) Z. Zhang, L. M. Wong, H. G. Ong, X. J. Wang, J. L. Wang, S. J. Wang, H. Y. Chen, and T. Wu, Nano Lett. (accepted).
_____________________________________________________________________
Impurity induced bound states in superconducting gap and their applications in chemistry
Xi Chen
Department of Physics
Tsinghua University
Email: xc@mail.tsinghua.edu.cn
Abstract:
Tunneling spectra for individual atoms and dimers of Mn and Cr adsorbed on superconducting Pb thin films were measured by a low temperature scanning tunneling microscope. Multiple-resonance structures within the superconducting gap on the adsorbates were resolved and interpreted as the magnetic impurity induced bound states associated with different scattering channels. The experiment demonstrates a spectroscopic approach to characterizing the spin states of magnetic structures and exploring the competition between superconductivity and magnetism at the nanometer scale.
Research interests:
Scanning tunneling microscopy, molecular spintronics, single molecule chemistry.
|