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KINC/CNSI Cooperative Symposium on Nanoscience
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August 19, 2008
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UCLA Speakers
Ya-Hong Xie, Materials Science & Engineering
Aydogan Ozcan, Electrical Engineering
Diana L. Huffaker, Electrical Engineering
Suneel Kodambaka, Materials Science and Engineering
Kang Wang, Electrical Engineering
KAIST Speakers
Jeung Ku Kang, Materials Science & Engineering
Yong-Hee Lee, Physics
Soon Hyung Hong, Materials Science and Engineering
Jung H. Shin, Nanoscience and Technology
Sang Ouk Kim, Materials Science & Engineering
UCLA Speakers |
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Ya-Hong Xie
Professor and Vice Chair, Department of Materials Science & Engineering
CNSI Member
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TITLE: Understanding the Scaling Limit of PcRAM of Chalcogenide Material
ABSTRACT: I will present the work in progress of our study of the phase change dynamics in chalcogenide materials (GeSbTe) when the volume is scaled to nanometer and below. The experimental plan for studying the nucleation versus growth mode of crystallization process will be presented. An experimental platform for fabricating large uniform arrays of nanometer volume samples suitable for in-situ TEM analysis will be described. Finally, some results of numerical calculation using FEM will be reported that look at the thermal response of a new device structure for use in phase-change random access memory (PcRAM) applications. If time allows, I will also give an overview of the other research activities in the Semiconductor Materials Research Laboratory (SMRL) at UCLA. These activities include the fabrication of high mobility 2dimensional electron systems for transport physics studies, the understanding of epitaxial growth of self-assembled quantum dots of semiconductor materials, and a novel approach for epitaxial lateral overgrowth of GaN on sapphire. |
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Aydogan Ozcan
Assistant Professor, Department of Electrical Engineering
CNSI Member
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TITLE: High-throughput On-Chip Imaging and Characterization of a Heterogeneous Cell Solution
ABSTRACT: A high-throughput on-chip imaging platform that can rapidly monitor and characterize various cell types within a heterogeneous solution over a depth-of-field of >4 mm and a field-of-view of ~10 cm2 is introduced. This powerful system can image/monitor multiple layers of micro-particles, including cells, within a volume of >4 ml all in parallel without the need for any lens, microscope-objective or any mechanical scanning. In this high-throughput particle imaging scheme, the diffraction pattern (i.e., the shadow) of each micro-particle within the entire sample volume is detected in less than a second using an opto-electronic sensor array. The acquired shadow image is then digitally processed using a custom developed “decision algorithm” to enable both the identification of the particle location in 3D and the characterization of each micro-particle type within the sample volume. Through experimental results, we show that different cell types (e.g., red blood cells, fibroblasts, etc) or other micro-particles all exhibit uniquely different shadow patterns and therefore can be rapidly identified without any ambiguity using the developed decision algorithm, enabling high-throughput characterization of a heterogeneous solution. This lensfree on chip cell imaging platform shows a significant promise especially for medical diagnostic applications relevant to global health problems, where compact and cost-effective diagnostic tools are urgently needed in resource limited settings. |
Diana L. Huffaker
Associate Professor, Department of Electrical Engineering
Director, CNSI Integrated NanoMaterials Core Lab
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TITLE: Patterned InAs Quantum Dot and Nanopillars Formation and Characterization
ABSTRACT: We overview our work in controlled patterned nanostructure formation and dependence on MOCVD growth parameters. The catalyst-free growth of the GaAs/InGaAs/AlGaAs nanopillars is carried out using MOCVD. The two-dimensional circular pattern array is formed on the GaAs (111)B substrate via interferometric lithography and wet etching on the SiO2 mask of 25 nm thick. The pitch and diameter of the patterns can be controlled through the experiment setups and the exposure parameters. We choose the pattern pitch and diameter to be ~ 300 nm and <100 nm, respectively, for the controllability of the nanopillar growth rate and the open spacing among nanopillars. Nanopillars grown on such patterned substrate are vertically aligned, highly faceted with hexagonal cross-sections bound by (110) planes, as shown in Figure 1.
The vertical and lateral dimensions of the nanopillars can be controlled by growth parameters such as the growth temperature and group V overpressure. Dimensions of homo- and hetero-structures can then be controlled in the lateral and axial direction. We have already demonstrated RTPL from InGaAs/GaAs nanopillars emitting at 1.3 µm along with IV curves from a single nanopillar.
Chemical wet etch can be used to remove unwanted core-shell heterostructures, and the subsequent lateral overgrowth can serve three purposes: 1) to passivate the processed surfaces and 2) to bury the axial heterostructures, and 3) to provide optical and electrical confinements. To properly planarize the lateral overgrowth from nanopillars with hexagonal cross-sections, hexagonal closely packed (HCP) patterns are desirable. |
Suneel Kodambaka
Assistant Professor, Materials Science and Engineering
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TITLE: Vapor-Liquid-Solid and Vapor-Solid-Solid Growth of Si and Ge Nanowire
ABSTRACT: Si and Ge nanowires have promising applications in nanoelectronics, optoelectronics, piezotronics, thermoelectrics, and sensors. Nanowires are most commonly grown via the vapor-liquidsolid (VLS) process, first discovered over 40 years ago. During the growth of Si nanowires, for example, a vapor phase containing Si preferentially dissociates at a liquid catalyst (typically AuSi eutectic) and is incorporated as a one-dimensional solid at the solid-liquid interface. Despite several decades of research in this area, several aspects of nanowire nucleation and growth are not well understood.
Here, we present in situ transmission electron microscopy (TEM) investigations of the nanowire nucleation and growth kinetics. Using Au as the catalyst, Si and Ge nanowires are grown inside an ultrahigh vacuum TEM (UHV-TEM) equipped with facilities for in situ deposition. Nanowires of Si and Ge are grown with Au as the catalyst using disilane and digermane, respectively. TEM images are acquired at video rate during deposition. We find that the pressure- and temperature-dependent growth behavior of Si and Ge nanowires to be surprisingly different [1-3]. From the in situ TEM experiments, carried out as a function of deposition parameters, we identify the factors controlling the nanowire morphology and structure. The new insights gained from our results may help develop methods for large-scale fabrication of wires with controlled morphologies. |
Kang Wang
Professor, Electrical Engineering
Director, MARCO Focus Center
Functional Engineered Nano Architectonics Focus Center (FENA)
Associate Director, CNSI
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TITLE: TBD
ABSTRACT: TBD |
KAIST Speakers |
Dr. Jeung Ku Kang
Professor, Department of Materials Science & Engineering
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TITLE: First-Principles Design and Generic Synthesis of Nanomaterials for Green Energy Technology
ABSTRACT: Hydrogen is an attractive fuel alternative to conventional hydrocarbon fuels because water is the only product when hydrogen burns with oxygen in a fuel cell. On the other hand, one of the main issues for hydrogen economy is the development of a suitable hydrogen storage material that is small, light, and safe. In addition achieving at least the weight percent of 6.5 wt % is the goal of the US Department of Energy (DOE). Because of these requirements, early in the development of hydrogen storage materials various carbon materials were investigated. This is because carbon materials can give many different types of structures, which provide a variety of hydrogen storage sites. For example, the carbon nanotubes (CNTs) having high surface-to-volume ratios were suggested as ideal structures for fast kinetics because of their reversible characteristics during hydrogenation and dehydrogenation. Despite these advantages, recent studies have shown that the hydrogen stored on a pristine carbon nanotube (CNT) is less than 0.01 wt% at 1 bar condition and room temperature.
On the other hand, here our first-principles and experimental works demonstrate that nanopores with ~6 Å diameters on the stems of the nanotubes are capable of giving great potentials to reversible hydrogen storage sites. However, if carbon atoms bonded in the perimeter of carbon-based nanopores could be replaced with other elements such as nitrogen atoms (or hereafter called as the carbon nitride nanotube, the physical interaction diameters of N-doped nanopores for possible penetration of H2 could be reduced such that hydrogen could desorb at the temperatures ranging from room temperature to 80oC, which is the ideal condition for various applications. Here, we report that the carbon nitride nanotube having 6 Å pores is an ideal structure being capable of satisfying the required temperature condition. Our experiments also demonstrate that versatile 6 Å pores could be created on the stems of the multi-walled carbon nitride nanotubes with the uniform distribution. |
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Yong-Hee Lee
Professor, Department of Physics
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TITLE: Spatial and spectral nano-control of micro-resonators
ABSTRACT: Spatially reconfigurable Gaussian-shaped photonic well is generated by contacting a curved tapered micro-fiber onto a photonic crystal waveguide. We confirm the photon trapping in this relocatable well by observing lasing action slightly below the corresponding band edge. In addition, the feasibility of sub-nanometer resonant tuning is demonstrated by growing electron-beam-induced nanodots inside high-Q photonic crystal resonators. |
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Soon Hyung Hong
Professor and Director, Department of Materials Science and Engineering
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TITLE: Fabrication Processes and Properties of Carbon Nanotube Nanocomposites
ABSTRACT: Carbon nanotube(CNT) is promising nanomaterial for reinforcement or functional filler of nanocomposites to overcome the performance limits of conventional materials. Critical issue to fabricate CNT nanocomposites is to distribute CNTs homogeneously in matrices because the dispersion of CNTs is difficult due to strong Van der Waals interactions between CNTs. In this study, a novel fabrication process, i.e. molecular level mixing process, is suggested to fabricate CNT nanocomposites with homogeneously distributed CNTs with strong interface in matrices. For structural applications, CNT/Cu, CNT/Co nanocomposites could be fabricated with excellent strength and high elastic modulus. For functional applications, thin film CNT/Co nanocomposite could be fabricated for high-efficiency field emitter. CNT/Metal/Polymer nanocomposite could be fabricated by mixing CNT/Metal nanocomposite powders with polymer matrices for possible applications of EMI shielding materials, supercapacitor electrodes, etc. |
Jung H. Shin
Professor, Department of Physics and Department of Nanoscience and Technology
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TITLE: Rare earth doped silicon-rich silicon nitride microdisks for on-chip microphotonic applications
ABSTRACT: A micro-disk or similar micro-resonators have attracted much attention recently as they can be the basic functional building block for a sophisticated on-chip microphotonic circuits. By now, micro-disk filters, modulators, and when doped with rare earth ions, lasers have been demonstrated. In most of the cases, however, obtaining photonic functionality from such a micro-disk required evanescent coupling of a laser beam that is tuned exquisitely to one of the whispering gallery modes of the microdisk that can change upon changes in the environment. In this presentation, I will present recent results of using rare-earth doped silicon-rich silicon nitride (SRSN) microdisks for on-chip microphotonic applications. Silicon-rich silicon nitride, which consist of silicon nanoclusters inside a SiN matrix, was used for several reasons. First, it has a high and controllable refractive index. Second, it has a good mechanical robustness and selectivity against SiO2. Finally, when doped with rare earth, it can sensitize the rare earth ions such that the entire device can be excited efficiently from the top using a broadband light source. This de-couples excitation and emission processes, enabling low-cost, environment-state excitation as well as simultaneous achievement of strong pump absorption and low signal absorption. In one case, Er-doped SRSN microdisk of 25 μm diameter was fabricated. High intrinsic Q-factors of about 19,000 have been obtained at 1.54 μm, and coupling of the Er3+ luminescence to the whispering gallery modes under top-pumping is observed. Second, Tb-doped SRSN microdisks of <10 μm diameter was fabricated. Coupling of Tb3+ luminescence at 550 nm to the whispering gallery mode under top-pumping is observed. Preliminary calculation suggest that such a self-luminescent, ultra-thin micro-resonators may offer comparative advantage in biosensing applications. |
Sang Ouk Kim
Professor, Materials Science & Engineering
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TITLE: Directed Molecular Assembly of Soft Nanomaterials for Nanofabrication
ABSTRACT: TBD |
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