Papers

ICMCTF2007 Session TS4-2: Nanostructured Thin Film Assemblies and Composites

Tuesday, April 24, 2007 1:30 PM in Room Royal Palm 1-3

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		TS4-2-1 Correlation Between Properties and Microstructure in Si-O-N Nanostructured Coatings Obtained by Magnetron Sputtering V. Godinho, C. Fernandez-Ramos, T.C. Rojas (Instituto de Ciencia de Materiales de Sevilla, Spain); M.P. DelplanckeOgletree (Universitat Libre de Bruxelles, Belgium); A. Fernandez (Instituto de Ciencia de Materiales de Sevilla, Spain) The microstructure, chemical composition and bonding type of thin Si-O-N films synthesised by magnetron sputtering have been studied by SEM, TEM, EELS and XPS. The samples were deposited onto steel or silicon substrates and showed either nanocrystalline grains embedded in an amorphous matrix or a totally amorphous structure depending on the preparation conditions. Differences in bonding type and stoichiometry were also found and correlated with experimental parameters such as power source, or pressure of the sputtering gases. Nanoindentation measurements were carried out in order to evaluate the mechanical properties of the films. The thermal stability and resistance of the coatings to oxidation have been also evaluated by annealing under different atmospheres.
1:50 PM		TS4-2-2 Nanocrystalline Manganese Oxide Films Prepared by Sol-Gel Process for Supercapacitor Application C.-K. Lin, K.-H. Chuang, C.-Y. Lin, C.-Y. Tsay, C.-Y. Chen (Feng Chia University, Taiwan) The usual oxides to be used as the electrodes of supercapacitors are relatively expensive material, such as RuO₂ or IrO₂. Under the cost consideration, transition metal oxide that possesses multi-valence characteristics, easy to be obtained, and relative low cost is potential to be used as replacement. In the present study, manganese oxide electrodes with promising pseudo-capacitive behavior were prepared successfully by sol-gel process using manganese acetate as the precursor. Effects of post heat treatment on material characteristics and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis, synchrotron X-ray absorption spectroscopy (XAS), and cycling voltammetry (CV). Experimental results showed that manganese oxide films prepared by sol-gel technique exhibited Mn₂O₃ and Mn₃O₄ phases after heat treating at a temperature higher than 300°C. Meanwhile, a porous manganese oxide film was observed due to the burnout of organics. The specific capacitance of the manganese oxide electrodes was 53.2, 230.5, 185.6, and 189.9 F/g after heat treating at 250, 300, 350, and 400°C, respectively. In the present study, the manganese oxide electrodes heat treated at 300°C exhibited the best electrochemical performance and, thus, its stability and reaction mechanism were further examined by cycling test and novel synchrotron X-ray absorption technique. It is found that the manganese oxide electrodes exhibited good stability where only a slight decrease in specific capacitance can be noted after hundreds of charging-discharging cycles. Synchrotron XAS examination revealed that manganese oxide electrodes exhibited the same trend where the trivalent manganese was transited into tetravalent manganese after cyclic voltammetry tests.
2:10 PM		TS4-2-3 Characterization of Spray Pyrolyzed Manganese Oxide Powders Deposited by Electrophoretic Deposition Technique C.-Y. Chen, Y.-R. Lyu (Feng Chia University, Taiwan); C.Y. Su (National Taipei University of Technology, Taiwan); H.-M. Lin (Tatung University, Taiwan); C.-K. Lin (Feng Chia University, Taiwan) Nanocrystalline manganese oxide powders were prepared by spray pyrolysis (SP) from manganese acetate solution at 400, 500, and 650°C, respectively. The as-obtained powders were subsequently coated onto graphite substrates via an electrophorectic deposition technique (EPD). The as-prepared powders and/or coatings were examined by transmission electron microscopy (TEM), X-ray diffractometry (XRD), synchrotron X-ray absorption spectroscopy (XAS), cycling voltammetry (CV), etc. Experimental results showed that manganese oxide powders prepared at 400°C were hollow spherical particles with fractured shells and possessed the highest surface area. CV examination showed that the as-deposited coatings also exhibited the highest specific capacitance of ~270 F/g. After hundreds CV cycles, the specific capacitance decreased to ~230 F/g which was still comparable to those reported in the literature. Structural investigation by TEM and XRD revealed that the as-deposited coatings exhibited Mn₃O₄ phase with amorphous-like structure. While synchrotron XAS results showed that the manganese with a valence of +2.67 was transited into tetravalent manganese after cyclic voltammetry.
2:30 PM		TS4-2-4 Assembly and Optoelectronic Properties of Carbon Nanotube Films R. Martel (Université de Montréal, Canada) Single Wall Carbon Nanotubes (SWNT) form a new class of electronic materials with outstanding conductive and optical properties. This lightweight molecular conductor is robust chemically, resistant to high temperature or deformation and compatible with semiconductor processing techniques. The last 10 years of research provided several demonstrations of electronic devices including transistors, field-emitters, super-capacitor and more recently conductive transparent electrodes for charge injection, collection and emission. Most of these prototype devices are currently made at low yield and without much control on the assembly process. The main issue appears to be related to the absence of a reliable chemical technique for nanotubes separation, control placement or assembly. For basic science, the lack of chemical control prevents more elaborated SWNT junctions to be explored. I will first review our work on the electro-optical properties of SWNT devices and then discuss on nanotubes films being used as transparent conductive electrodes for Organic Light Emitting Diode (OLED) devices. These works and related issues stimulate our current efforts to acquire a better understanding of the surface chemistry and the electro-optical properties of SWNT.
3:10 PM		TS4-2-6 Alignment and Organization of Single-Walled Carbon Nanotubes A.R. Hopkins, R.A. Lipeles (The Aerospace Corporation) We report the progress of alignment and organization single-walled carbon nanotubes (SWNTs). Using single strands of DNA, as received bundled SWNTs are effectively dispersed in a water-based medium. This high level of dispersity was evident from the resulting stable, homogeneous solutions provided by the helical wrapping of the DNA to the SWNT. We have also demonstrated that these DNA-coated carbon nanotubes can be orientated with non-contact methods. Specifically, we utilize a modified inkjet printer as a tool for direct printing and alignment of DNA-wrapped carbon nanotubes on mica and silicone substrates. In addition, we see evidence of orientation due to centrifugal forces in the radial direction of the spin coater. These layers of oriented tubes are characterized by both scanning electron microscopy (SEM) and atomic force microscopy (AFM). This inkjet fabrication process is a promising method for increasing the directional strength of high strength, carbon nanotube materials.
3:30 PM		TS4-2-7 Characteristics of Nonvolatile SONOS-TFT Memory with Nanowire Channels Strucutre S.C. Chen (National Tsing Hua University, Taiwan); T.-C. Chang (National Sun Yat-Sen University, Taiwan); P.-T. Liu, Y.C. Wu, S.M. Sze, Y.C. Chang (National Chiao Tung University, Taiwan); C.H. Lien (National Tsing Hua University, Taiwan) In this work we study a novel polycrystalline silicon thin-film transistor (poly-Si TFT) combined with nonvolatile SONOS memory and nanowire channels for transistor and nonvolatile memory application for the first time. The proposed device named with NW SONOS-TFT has superior electrical characteristics of transistor, such as a higher ON/OFF current ratio, a smaller threshold voltage (V_th), and a steeper subthreshold slope (SS) due to the good gate control ability induced by fringing electrical field effect and corner effects. Moreover, the proposed device under adequate operation scheme can exhibit high program/erase (P/E) efficiency and large memory window with 10-year retention time tested at 85⁰C.
3:50 PM		TS4-2-8 Formation of the Stacking Ni-Silicide Nanocrystals by Using a Co-Mixed Target for Nonvolatile Memory Application W.-R. Chen (National Chiao Tung University, Taiwan); T.-C. Chang (National Sun Yat-Sen University, Taiwan); P.-T. Liu, C.-H. Tu, C.-Y. Chang (National Chiao Tung University, Taiwan); F.-W. Chi, S.-W. Tsao (National Sun Yat-Sen University, Taiwan) In the present research, the Nickel-Silicon (Ni_xSi_1-x) film was deposited by co-sputtering for two targets. The deposition conditions of Nickel-Silicon film, such as the depth and component, were critical to determine the results of the size of the nanocrystals and the memory effect. In order to control the thickness and the composition of the Ni_xSi_1-x film precisely, a particular method was proposed in this study. The uniform component and thickness of NixSi1-x film can be realized by using a co-mixed target which is composed by the powder of Nickel (30%)-Silicon (70%). The stacking Ni-Silicide Nanocrystals that are about 5~7 nm were synthesized by rapid thermal oxidation of the co-sputtered Ni_xSi_1-x films, and the memory effect was observed by the hysteresis in the C-V curve. The electronic characteristic of program/erase of electrons was obtained by the threshold voltage shift versus program/erase time. At the programming condition for programming voltage and duration are 3.0 V and 500 µs, the 0.5 V memory window can be achieved. It is enough memory window to be defined as "1" or "0" for the application of memory design and high speed devices. Furthermore, a physical model is proposed to explain the saturation phenomenon of threshold voltage at different programming voltage with time. Finally, data retention time and endurance cycles of the stacking Ni-Silicide nanocrystals were obtained under electrical measurement. In addition, the process is compatible with the current fabrication technology.