Jyh-Ming Ting

Growth of single crystal ZnO nanowires using sputter deposition

Abstract Single crystal zinc oxide is a very promising material for light-emitting devices in blue, violet, and ultraviolet regions due to its wide direct band gap of 3.37 eV. Single crystal ZnO has been in a form of thin film or tetrapod-like whisker. Recently, the growth of highly oriented ZnO whiskers was also reported. Irrespective of the form and growth technique, successful growth of single crystal films or whiskers inevitably requires the use of a single-crystal substrate such as sapphire and diamond. In this paper, we report the growth of single crystal ZnO nanowires on a non-single-crystal substrate using a conventional sputter deposition technique. An r.f. magnetron sputter deposition system was used for the growth of ZnO nanowires in O2/Ar mixtures. The substrate used was silicon wafers with copper metallization. After the ZnO deposition, specimens were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and selected area diffraction (SAD).

Production and Assessment of Polycarbonate Composites Reinforced with Vapour-Grown Carbon Fibres

Abstract Vapour-grown carbon fibres were produced from methane in a flow reactor. The fibres were compounded with poly-carbonate in a co-rotating twin-screw extruder and the composites were subsequently injection moulded. The rheological characteristics of the polycarbonate composites reinforced with these vapour-grown carbon fibres were determined by using capillary and rotational rheometry. The tensile properties of the injection-moulded specimens were marginally better than those of the un-reinforced polycarbonate, but the impact resistance was severely diminished by the addition of the carbon fibres. This was attributed to the presence of polycyclic aromatic hydrocarbons on the surface of the fibres, that may impair the impact resistance of polycarbonate by chemical stress cracking.

Growth of ZnO Thin Films and Whiskers

Copper-metallized silicon wafers were used as substrates for the deposition of zinc oxide thin films using a radio frequency sputter deposition technique. Copper metallization on silicon wafer was performed using two different methods, a plating technique and a sputter deposition technique. Copper-metallized silicon substrates were then deposited with zinc oxide thin films under various sputter deposition conditions. The characteristics of zinc oxide thin films were found to not only depend on the deposition conditions, but also be strongly influenced by the type and characteristics of the copper layers. In addition to polycrystalline thin-film zinc oxide, single-crystal zinc oxide whiskers were also found on silicon substrates with plated copper.

Growth and characteristics of carbon films with nano-sized metal particles

Metal containing carbon thin films were prepared using a reactive sputter deposition technique. A number of growth parameters, including argon to methane ratio, working pressure, electrode distance, and d.c. power were examined. Metallic elements in the resulting films are uniformly-distributed nanoparticles with various sizes, depending on the metal type and growth parameters. Correlation was made among the argon/methane ratio, the deposition rate and the composition. Crystallinity and microstructure of the resulting films were analyzed using transmission electron microscopy and Raman microscopy.

DLC composite thin films by sputter deposition

Abstract This paper reports a new composite thin film of Pt–DLC for used as a microelectrode for electrochemical analysis. An RF sputter deposition technique was used for the preparation of these thin films under various ratios of Ar/CH4. The microstructure of as-deposited thin films was characterized using transmission electron microscopy and Raman spectroscopy, the composition using electron probe microanalysis, the surface morphology using scanning electron microscopy, and the sheet resistance using a four-point probe. Correlation among the growth parameters, film composition, and structure are presented. Both the composition and Raman characteristics were found to be strong functions of the deposition rate. Improved electrical conductivity and reduced film stress were also found due to the addition of platinum into DLC.

A binder-free process for making all-plastic substrate flexible dye-sensitized solar cells having a gel electrolyte

Binder-free electrophoretic deposition (EPD) and mechanical compression were employed to fabricate TiO2 photoanodes for use in all-plastic substrate flexible dye-sensitized solar cells having a gel electrolyte. The photoanodes were composed of commercial 20 nm TiO2 powders with and without the addition of 160 nm TiO2 powders. The EPD was performed under different DC powers and deposition times to obtain photoanodes having different thicknesses. Depending on the thickness, various electron diffusion times, ranging from 8.08 to 12.40 ms, and electron lifetimes, ranging from 16.79 to 32.05 ms, were obtained for the photoanodes consisting of only commercial 20 nm TiO2. The electron diffusion time was reduced and the electron lifetime remained the same as a result of the addition of another commercial 160 nm TiO2 powder. The added 160 nm TiO2 powders enhanced the light absorptance by serving as light scattering centers. All-plastic flexible dye-sensitized solar cells were made and evaluated. Compared to the 20 nm TiO2 only cells, the cells containing mixed powders exhibit enhanced efficiencies and the enhancement can be as much as 22%.

Growth of carbon nanotubes and nanowires using selected catalysts

A number of catalysts with different characteristics were prepared using various techniques and used as the catalysts for the growth of carbon nanotubes (CNTs). They include dc sputter deposited Ni thin films, rf sputter deposited Ni-containing diamond-like carbon (Ni-DLC), and Co thin films deposited using a molecular beam epitaxy (MBE) technique. The growth of CNT from MBE-Co thin films was favored under a higher pressure, MW power, and/or methane concentration. For the Ni thin films, exhibiting different crystallinity, it appears that an optimal or largest diameter can be obtained under a lower pressure when an amorphous catalyst is used. Various amounts of carbon nanowires (CNWs) were observed, depending on the thickness or the crystallinity of the catalyst. The formation of CNW also depends on the pressure. Finally, the CNT diameter seems to increase with the nanoparticle size in the Ni-DLC. Furthermore, the yield tends to increase with the concentration of Ni nano-particles in the DLC.

Systematic studies of the nucleation and growth of ultrananocrystalline diamond films on silicon substrates coated with a tungsten layer

We report on effects of a tungsten layer deposited on silicon surface on the effectiveness for diamond nanoparticles to be seeded for the deposition of ultrananocrystalline diamond (UNCD). Rough tungsten surface and electrostatic forces between nanodiamond seeds and the tungsten surface layer help to improve the adhesion of nanodiamond seeds on the tungsten surface. The seeding density on tungsten coated silicon thus increases. Tungsten carbide is formed by reactions of the tungsten layer with carbon containing plasma species. It provides favorable (001) crystal planes for the nucleation of (111) crystal planes by Microwave Plasma Enhanced Chemical Vapor Deposition (MPECVD) in argon diluted methane plasma and further improves the density of diamond seeds/nuclei. UNCD films grown at different gas pressures on tungsten coated silicon which is pre-seeded by nanodiamond along with heteroepitaxially nucleated diamond nuclei were characterized by Raman scattering, field emission-scanning electron microscopy, an...

Characteristics of TiNi alloy thin films

Deposition and characterization of TiNi shape memory alloy thin films were performed using a DC magnetron sputter deposition technique. As-deposited TiNi thin films were found to exhibit an amorphous structure, which crystallized upon heat treatment at 550 or 600°C. An uncommon dependence of the deposition rate on the deposition pressure was observed. Dependence of composition on the deposition pressure was also determined. The crystallization behavior of amorphous TiNi thin films was found to be different from that of bulk TiNi. The activation energies for the crystallization of the resulting TiNi thin films were calculated and found to be higher than that of bulk TiNi.

Direct Growth of MoS2 Nanowalls on Carbon Nanofibers for Use in Supercapacitor

Direct growth of MoS2 nanowalls on vapor grown carbon nanofibers (VGCNFs) has been achieved using a microwave-assisted hydrothermal (MAH) method under an acidic condition. The acidic condition was obtained through the addition of an HCl aqueous solution. We demonstrate that the HCl not only modifies the pH value for limiting the growth rate but also leads to the formation of NaCl, which is the key for the direct and unique growth of MoS2 on the VGCNF surface. A growth mechanism is therefore proposed. The growth of MoS2 onto the high electrically conducting VGCNF creates a unique structure that not only reduces the aggregation of MoS2 but also improves the electrical conductivity of the resulting composite electrode. The MoS2 nanowall/VGCNF composite shows Csp as high as 248 F g−1 at 5 mV s−1 and excellent electrochemical stability with a retention of 96% after 1,000 cycles at a high charge rate of 200 mV s−1. The ease of composite fabrication and electrochemical stability suggest that the MoS2 nanowall/VGCNF composite is a promising candidate electrode material for supercapacitor.