Papers

ICMCTF2009 Session H1-2: Nanotube, Nanowire and Nanoparticle Thin-Films and Coatings

Tuesday, April 28, 2009 1:30 PM in Room Tiki Pavilion

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		H1-2-1 Temperature Dependent Conduction in ZnO Nanowires J. Lu (University of Southern California) ZnO nanowire has been intensively studied due to its excellent optical property, relative high conductivity, and versatile applications as electro-optic and electro-mechanical devices. Thin nanowires with diameters ranging from 20 to 50 nanometers were synthesized via chemical vapor deposition. The as-grown ZnO nanowires were then configured into field effect transistor (FET) devices through a series of fabrication processes and measured in a 4 K helium cryostat with quartz optical view port. From the transport measurement of ZnO FET, the Arrhenius behavior of the DC conductivity curve exhibits two regions. For T > 50 K, the conductivity show thermionic emission conduction in non-degenerate semiconductor and can be expressed as σ = σ₀exp(-E_a/kT), where E_a is the activation energy, and k is the Boltzman constant. Without gate voltage, the activation energy value extracted from multiple samples falls in the range between 30-60 meV, correspond ing to shallow donor levels below the conduction band edge that are mainly contributed by oxygen vacancies. Under applied gate voltages, band bending occurs and lowers the activation energy, and the reduction in Ea is extracted experimentally. On the other hand, the activation energy at T < 50K is all below 1 meV. It was found that in this regime, 3D Mott’s variable range hopping model governs the transport, with conductivity σ = σ₀exp (-AT^-1/4), where A and σ0 are material parameters. Furthermore, it is observed that the ZnO nanowires under continuous UV irradiation shows a metallic behavior for temperature above 210 K. This phenomenon is attributed to the reduction in mobility as a result of significantly increased charge carriers.
2:10 PM		H1-2-3 Growth and Characterizations of ZnO Nanorod/Film Structures W.Y. Wu, M.D. Chen, J.M. Ting (National Cheng Kung University, Taiwan) 1D nanostructure materials such as nanowires, nanotubes, and nanorods attract much attention due to their unique properties to bulk materials. Among them, ZnO nanorods, representing one of the most important low-dimensional materials, find its applications in many different fields. There are a number of methods that are used for the growth of ZnO nanorods and a common mechanism of the so-called vapor-liquid-solid (VLS) mechanism has been used widely to explain the growth of ZnO nanorods. However, we have recently reported a new mechanism for the growth of ZnO nanorods using a sputter deposition process¹. In this paper, we further examine the characteristics of the sputter deposited ZnO. The deposits were characterized using x-ray diffractometry, scanning electron microscopy, and atomic force microscopy. The deposited ZnO was found to consist of ZnO nanorods and the roots of the nanorods were embedded in a ZnO layer that was co-deposited with the nanorods at the beginning of the process. Effects of processing conditions are presented and discussed. ¹Ming-Ta Chen, Jyh-Ming Ting, Thin Solid Films v.494 (2006) p.250 – 254.
2:30 PM		H1-2-4 Sputter Deposited ZnO Nanowire/Thin Film Structures T.L. Chou, W.Y. Wu, J.M. Ting (National Cheng Kung University, Taiwan) Integrated ZnO nanowires/thin film structures were obtained on amorphous glass substrates having an electroless plated copper surface layer using an rf magnetron sputter deposition technique. The growth took place under different O₂/Ar ratios. For ZnO nanowires, a higher O₂ partial pressure makes their averaged diameters decrease slightly but the area densities increase. The growth and the characteristics of the integrated ZnO nanowires/thin film structures are presented. X-ray diffraction and transmission electron microscopy characterizations show that the as-grown nanowires and the thin films are both polycrystalline with a (002) preferred orientation. No catalyst was found at the ends of the nanowires, indicating the vapor-liquid-solid mechanism is not applicable in the sputter deposition process. It was also found that the growth of nanowires competes with that of thin film. The length of the ZnO nanowires is nearly proportional to time^0.5, indicating a diffusion controlled growth; however, the thickness of the ZnO thin films increases linearly with the growth time. Furthermore, a higher oxygen partial pressure leads to a lower deposition rate for the ZnO thin films; while a higher oxygen partial pressure gives a smaller average diameter and lower area density for the ZnO nanowires.
2:50 PM		H1-2-5 Formation of Titanium Germanosilicide Nanocrystals for Nonvolatile Memory Application L.-W. Feng (National Chiao Tung University, Taiwan); T.-C. Chang (National Sun Yat-Sen University, Taiwan); C.-H. Tu, P.-S. Wang (National Chiao Tung University, Taiwan); D.-S. Gan, N.-J. Ho, H.-J. Huang, M.-C. Chen (National Sun Yat-Sen University, Taiwan); C.-Y. Chang (National Chiao Tung University, Taiwan) Titanium Germanosilicide nanocrystals fabricated by co-sputtering titanium silicide and germanium were investigated in this paper. The characteristics of Titanium Germanosilicide composition were analyzed by X-ray photon-emission spectra and the formations of nanocrystals were observed by high resolution transmission electron microscopy under the various post-annealing temperatures. It was found that the post-annealing temperature of Titanium Germanosilicide nanocrystals for memory application can be lowered which was compared to those proposed in TiSi₂-based papers. However, the pre-capped silicon dioxide before thermal annealing was needed due to the out-diffusion of the germanium at relatively higher annealing temperature. Electrical measurements of the flat band voltage shift and retention characteristics are exhibited for nonvolatile memory application.
3:10 PM		H1-2-6 Fabrication of Molybdenum Oxide Nanowires Grown by Thermal CVD H.C. Hsih (Chinese Culture University, & National Tsing Hua University, Taiwan); C.C. Chang (National Tsing Hua University, Taiwan); M.W. Huang (National Chung Hsing University, Taiwan); Y.T. Hsieh (National Tsing Hua University, Taiwan); B.J. Wei (National Chung Hsing University, Taiwan) Molybdenum oxide (Mo_xO_y ) nanowires were prepared successfully by thermal chemical vapor deposition through a two-step evaporation process and distributed on a p-type Si (100) substrate from Molybdenum powders (purity: 99.99%). The growth of the Mo_xO_y nanowires was made in a vacuumed quartz tube at a pressure of 6 x 10-5 torr and with heating rate of 15 degree centigrade per minute using a mixture gases of Ar and oxide at the first stage to preheat the substrate at 450 degree centigrade, the reheating sample to synthesis temperature at 850 degree centigrade. The as-synthesized Mo_xO_y nanowires were characterized by high-resolution transmission electron microscopy, field emission scanning electron microscopy, x-ray diffraction, and Raman scattered. The morphologies of Molybdenum oxide nanowires were rod-like shape and the diameter were range from 10 to 500 nanometer and length up to several hundreds nanometers. The optical properties of the Mo_xO_y nanowires were also inves ted by photoluminescence and cathodluminescence spectra. The effects of the Mo_xO_y nanowires on the fluorescence properties were also investigated in detail.
3:30 PM		H1-2-7 Thermally Evaporated Sb-Doped SnO₂ Nanobelts for Ethanol Gas Sensors P.-S. Lee, Y.-H. Lin, C.-C. Kuo (National Tsing Hua University, Taiwan); J.-M. Wu (Feng-Cha University, Taiwan); Y.-S. Chang, H.C. Shih (National Tsing Hua University, Taiwan) One-dimensional (1-D) tin oxide nanostructures including nanowires, nanorods and nanobelts have attracted much attention owing to their extraordinary application in nanoscale devices@super 1-3@. In order to enhance and modulate the various properties, SnO₂ thin films and nanostructures are frequently doped with an amount of appreciate elements, such as indium (In) and antimony (Sb)@super 4-5@. In this study, single crystalline tetragonal rutile Sb-doped SnO₂ nanobelts were synthesized on the Al₂O₃substrate using a thermal evaporation method. The morphology and microstructure of Sb-doped SnO₂nanobelts were characterized by a field emission scanning electron microscope (FESEM) and a transmission electron microscope (TEM). The composition and chemical bonding nature were investigated by x-ray photoelectron spectroscopy (XPS) and nano-Auger analysis (nano-AES). At room temperature, the Sb-doped SnO₂ nanobelts exhibit a high sensitivity towards eth anol gas of concentrations ranging from 50 to 500 ppm. Comparative gas sensing results reveal that the prepared Sb-doped SnO₂ nanobelts sensors exhibit a much higher sensing sensitivity and recovery property in detecting ethanol gas at room temperature than the pure SnO₂ nanowires sensor. This study shows that doping with Sb can improve the sensitivity of SnO₂ nanostructures significantly. ¹Z. L. Wang: Adv. Mater. 15 (2003) 432. super 2@C. Y. Wang, T. W. Chen, C. C. Lin, W. J. Hsieh, K. L. Chang, and H. C. Shih: J. Phys. D 40 (2007) 2787. ³Y. Zhang, A. Kolmakov, S. Chretien, H. Metiu, and M. Moskovits: Nano Lett. 4 (2004) 403. ⁴ H. Kim, A. Pique´, Appl. Phys. Lett.84 (2004) 218. ⁵Q. Wan, E.N. Dattoli and W. Lu, Appl. Phys. Lett., 90 (2007) 222107.
3:50 PM		H1-2-9 Hybrid Manganese Oxide Films for Supercapacitor Application Prepared by Sol-Gel Technique C.-K. Lin, C.-H. Cheng, Y.-H. Tien, C.-Y. Chen (Feng Chia University, Taiwan); S.-C. Wang (Southern Taiwan University, Taiwan); W.T. Tsai (National Cheng Kung University, Taiwan) Hybrid films were prepared by adding various concentrations of Meso-Carbon Microbeads (MCMB) during sol-gel processing of manganese oxide films. The as-prepared and heat-treated films were characterized by scanning electron microscopy, X-ray diffraction, and synchrotron X-ray absorption spectroscopy. In addition, electrochemical performance of the hybrid manganese oxide films was evaluated by cyclic voltammetry (CV) and compared with its pure counterpart. Experimental results showed that manganese oxide films exhibited a mixture of Mn₂O₃ and Mn₃O₄ phases. The higher is the heat-treating temperature, the more the Mn₂O₃ can be observed. The specific capacitance of the pure manganese oxide electrodes is 209.2 F/g. A significant improvement, however, can be noticed by adding MCMB. The 350 °C heat-treated hybrid manganese oxide films (MnOx:MCMB = 5:1) exhibit the highest specific capacitance of 456.7 F/g (~120% increase). After 1200 repetitive charging-discharging cycles, the specific capacitance of pure MnO_x film decreases to ~50 % of its maximum value. While that of the hybrid MnOx/MCMB film can still have 407.4 F/g, ~90% of its maximum value. Not only specific capacitance increases but chemical stability enhances with the addition of MCMB.