Agenda
09:45–11:30 Session 6: Nanostructured Sensors
Professor Huey Liang Hwang (National Tsing Hua University), Chair
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09:45–10:10
Generating and manipulating spins in semiconductors
David D. Awschalom
Department of Physics, University of California, Santa Barbara, CA 93106 USA
Spin-orbit coupling in semiconductors relates the spin of an electron to its momentum, and provides a pathway for electrically initializing and manipulating electron spins for applications in spintronics and spin-based quantum information processing. This coupling can be regulated with strain in bulk semiconductors and quantum confinement in semiconductor heterostructures. We provide an overview of optical studies exploring spin dynamics in conventional semiconductors, followed by recent experiments probing the all-electrical generation and manipulation of spins. Using magneto-optical spectroscopies with temporal and spatial resolution, new phenomena including current-induced spin polarization and the spin Hall effect have been observed in bulk semiconductors and heterostructures. These effects have recently been exploited to electrically generate on-chip spin currents that exceed the spin diffusion length and propagate macroscopic distances in the solid state. Surprisingly, both of these phenomena are observed over a broad range of temperatures and persist to room temperature in some materials despite no evidence for electrically-induced internal magnetic fields and notably weak spin-orbit coupling. Finally, we present experiments in diamond – a wide bandgap semiconductor – using angle-resolved magneto-photoluminescence microscopy to image and manipulate single electron and nearby nitrogen spins at room temperature. These experiments enable the polarization and readout of single and coupled spins for information processing. The remarkable ability for all-electrical spin control at room temperature suggests that low power spin-based logic is technologically feasible in semiconductor devices.
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10:10–10:30
Thiophenol-modified CdS nanoparticles enhance the luminescence of benzoxyl dendron-substituted polyfluorene copolymers
Chia-Hung Chou1, Hsu-Shen Wang1, Kung-Hwa Wei1*, and Jung Y. Huang2
1Department of Materials Science and Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 30050, Taiwan
2Department of Electro-Optical Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 30050, Taiwan
Highly luminescent dendron-substituted copolyfluorenes that incorporate surface-modified cadmium sulfide nanoparticles have been prepared. A small percentage of these nanoparticles can be incorporated into the dendritic structures upon tailoring the interfaces between the ligands on the nanoparticles and the dendritic structures in the copolyfluorene. Both the photoluminescence and electroluminescence efficiencies of the polymer nanocomposites are dramatically enhanced-sometimes more than doubled-relative to the values of the pure polymer.
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10:30–10:50
Shape-Controlled Synthesis of Metallic Copper Pyramids for Electrocatalytic Reduction of Nitrite Ions
Wen-Yin Ko,1 Wei-Hung Chen,1 Shien-Der Tzeng,2 Shangjr Gwo3 and Kuan-Jiuh Lin1*
1Department of Chemistry, Center of Nanoscience and Nanotechnology, National Chung Hsing University, Taichung 402, Taiwan. 2Department of Electric Engineering, Center of Nanoscience and Nanotechnology, National Chung Hsing University, Taichung 402, Taiwan. 3Department of Physics, National Tsing Hua University, Taiwan
Free-standing pyramidal Cu nanoparticles have been synthesized in large quantities (over 90 %) on Au surface by using electrodeposition process. It has been found that the concentration rations of dodecylbenzenesulfonic acid sodium salt (DBSA) to Cu ion played an important role for the formation of Cu pyramidal islands. FESEM images reveal that the edge lengths of Cu pyramids range from 100 to 800 nm. Electron diffraction pattern shows that they crystallized in face-center-cubic (fcc). As an efficient electrocatalytic sensor, Cu nanoparticles were electrochemically grown on top of self-assembled 1-decanethiol (thio) layers on Au surface. The Cu NPs/thio/Au modified electrode shows high electrocatalytic activity for the reduction of NO2- and exhibits a good reproducibility and stability. The catalytic peak current is found to show linear relationship with the nitrite concentration in the range of 0.001 – 0.3 mM with a correlation coefficient of 0.994. The detection limit approaches ~ 10-5 mM and the response time is less than 2 seconds.
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10:50–11:10
Multifunction Nanoparticle-Nanotube/Nanotip Composites and Micro-devices for Energy and Sensing Applications
Li-Chyong Chen* and Kuei-Hsien Chen
National Taiwan University, Center for Condensed Matter Sciences, 1 Roosevelt Road, Section 4, Taipei 107, Taiwan
Interactions between the electromagnetic wave, molecules and the noble-metal nanoparticles (NPs) having different shape, size and geometric arrangement result in many interesting physical and chemical properties, including surface enhanced Raman scattering (SERS), surface plamon resonance and enhanced catalytic reaction. Nanoscale engineering and strategies that exemplify these novel properties will be presented in two cases: (1) dispersing metal NPs on the arrayed carbon nanotubes (CNTs) for electrochemical energy applications; (2) dispersing metal NPs on the arrayed Si nanotips for molecular sensing applications. For the first case, direct growth approaches of both NPs and CNTs were employed. Nitrogen incorporation in CNTs, whose structural behavior was understood in atomic level [JACS 2006], has played a key role in controlling the distribution and size of Pt/Ru NPs to enhance their catalytic activity and electron kinetics in the electrochemical environments. Such micro-device platform established in our lab has shown superior current collection efficiency and is amenable for energy applications [J. Power Sources 2006]. For the second case, well-aligned Si nanotip arrays with ultrahigh tip density were prepared by single-step electron cyclotron resonance plasma process at first [US Patent 2005]. These sub-wavelength nanostructures exhibit extraordinary broadband (from UV to FIR) antireflection properties, which are only partly explainable by gradient index model, however. Moreover, when dispersed (via simple sputtering technique) with Ag NPs, they show excellent SERS properties. By optimizing the size of Ag NPs and their inter-particle distance, SERS of 8-order has been achieved, suggesting potential application of Ag NPs-dispersed nanotip arrays as molecular sensors.
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11:10–11:30
Flow Loop Experiments using Nanofluid Coolants
Debjyoti Banerjee, Ph.D.1, Rengasamy Ponnappan, Ph.D.2
1Texas A&M University, College Station, TX 77843-3123, USA; 2AOARD, 7-23-17 Roppongi, Minato-ku, Tokyo 106-0032, JAPAN
Experiments were performed using a flow loop apparatus to explore the performance of nano-fluids in cooling applications for aircraft thermal management. The experiments were performed using exfoliated graphite nano-particle fibers suspended in Poly-Alpha-Olefin oil at mass concentrations of 0.6% and 0.3%. The experimental set-up consisted of a test section containing plain offset-fin cooler apparatus (gap fin or non-gap fin) which was connected to a flow loop consisting of a gear pump, a shell and tube heat exchanger (which was cooled or heated by constant temperature bath chiller/heater), and a reservoir. Experiments were conducted using nanofluid for two different fin strip layouts. Heat transfer data were obtained by parametrically varying the operating conditions (heat flux and flow rates). The heat transfer data for nanofluids were compared with heat transfer data for pure fluid under similar conditions. The change in surface morphology of the fins was investigated using Scanning Electron Micrography. The nanofluid properties were measured. It was observed that the viscosity is ~10 times higher for nanofluids and was found to increase with temperature. Specific heat of nanofluid was found to be 50% higher and was found to increase with temperature. The thermal diffusivity for nanofluids was found to increase with temperature and was measured to be 4 times higher. It was found that the convective heat transfer was enhanced by ~10% using nanofluids. Microscopy measurements show that the nanofluids deposit nano-particles on the surface which act as enhanced heat transfer surfaces (“nano-fins”).
Cleared as AFRL-WS 07-0132.
