Han C. Shih

Formation and photoluminescence of single-crystalline rutile TiO2 nanowires synthesized by thermal evaporation

Uniform nanowires were grown over a selected area of a TiO2/sapphire substrate using a horizontal furnace system with a radio frequency (RF) heater. The growth of the nanowire was governed by a catalyst-free vapour?solid (VS) mechanism. The x-ray diffraction pattern showed that the nanowires comprised TiO2 in the pure rutile phase. The size of the TiO2 nanowires was verified using field emission scanning electron microscopy (FESEM), which showed that the diameters were in the range 50?100?nm and the lengths were in the range 1?2??m. The nanowire growth direction and its crystalline structure were examined using high-resolution transmission electron microscopy (HRTEM), indicating that these nanowires had a single-crystalline structure and grew along the [110] axis. A?blue emission peak at ~380?nm was obtained under examination by photoluminescence (PL), which revealed only single-crystalline rutile TiO2 nanowires, and thus indicated that the single-crystalline TiO2 nanowire could be a candidate for use in optoelectronic devices.

Characterizing well-ordered CuO nanofibrils synthesized through gas-solid reactions

Films of well-ordered crystalline copper oxide (CuO) nanofibril arrays were synthesized using a procedure involving electrodeposition followed by a gas-solid reaction. Analyses showed that the nanocrystalline CuO nanofibrils with a mean length of 8 μm have an average density of 107–108/cm2. Photoluminescence measurements showed a main peak in the visible light band at 410 nm, and the band gap energy was estimated to be 1.67 eV. It was found that the film of aligned CuO nanofibrils has typical Fowler–Nordheim plots in the follow-up electron field emission test. Typical turn-on voltage was detected at ∼6 V/μm with an emission area of 1 mm2. The Fowler–Nordheim model was employed to analyze the I–V data obtained. The work function of the nanofibrils was estimated to be in the range of 4.1–4.3 eV.

EIS behavior of anodized zinc in chloride environments

Abstract Electrochemical impedance spectroscopy (EIS) technique was applied to the corrosion study of the anodic coatings (ANC) on zinc. The ANC consists of a porous out-layer over a barrier layer and a modified one (CoANC) by adding cobalt ions to the electrolyte in the anodic treatment would refine the pores of the outer layer. The limited layer diffusion effect was found in the impedance plot of CoANC-coated zinc (CoANC-ZN) due to its finer pores. By comparing the EIS, the corrosion of both ANC-coated zinc (ANC-ZN) and CoANC-ZN was found changing from charge transfer control process to diffusion control process during the prolonged immersion in chloride environments. Two modes of corrosion process based on the immersion time and their equivalent circuits were proposed in considering the chemical products and physical structures resulting from the corrosion reactions. All parameters in equivalent circuits were adjusted simultaneously to obtain an optimum fit to the measured data. The simulated diagrams for the proposed equivalent circuits are in good agreement with the measured data.

Mechanism of solid-liquid-solid on the silicon oxide nanowire growth

The solid-liquid-solid growth mechanism of synthesizing SiOx nanowires is expressed in detail through analyzing the structure and composition of the catalysts and the nanowires. The silicon source for growing nanowires was directly provided from the silicon wafer. A thin catalyst layer of platinum (∼5nm) was first deposited on the silicon wafer by sputtering. The platinum film collapsed into dots with diameter about hundreds of nanometers during the thermal process. These dots transformed into crystalline platinum silicide (Pt3Si) and served as nucleation seeds for the silicon oxide nanowire growth. Due to the high process temperature (∼1100°C) and long duration time (∼5h), the silicon wafer transformed into amorphous silicon oxides and melted into the Pt3Si catalyst dots until supersaturated to form SiOx nanowires. Such nanowires are amorphous and have an average diameter of about 40–60 nm and length of several hundreds of micrometers.

The Preparation and High Photon-Sensing Properties of Fluorinated Tin Dioxide Nanowires

The photon-sensing abilities of SnO 2 nanowires have been investigated before and after surface fluorination by microwave plasma-enhanced chemical vapor deposition. The electrical conductance and photon-sensing abilities of SnO 2 nanowires were remarkably improved by an effective doping of fluorine into the surface of the nanowires. These results demonstrated that the fluorinated SnO 2 nanowires have potential applications as UV photodetectors with high photon-sensing properties.

Characterization of Single-Crystalline TiO2 Nanowires Grown by Thermal Evaporation

Single-crystalline TiO 2 nanowires (NWs) were grown all over a TiO 2 /silicon (Si) substrate by thermal evaporation using a radio frequency heater. The TiO 2 layer is experimentally determined to have better growing sites than the Si substrate. NWs were investigated by field-emission scanning electron microscopy (FESEM). The images showed NWs with uniform diameters of 60-90 nm and lengths of up to 3 μm. The X-ray diffraction pattern indicates that the NWs are composed of the TiO 2 rutile phase. TiO 2 NWs were also examined using high-resolution transmission electron microscopy, which demonstrated that the NWs grew along the [110] axis as single crystalline. Adding nitrogen (N) during the growth process enabled n-doped TiO 2 NWs to be synthesized. The luminescence characteristics and the doping effect of TiO 2 NWs were studied by cathodoluminescence (CL) in FESEM at room temperature. The CL spectra revealed a broad blue band of ∼402 nm (3.08 eV) for undoped NWs and one of 439 nm (2.82 eV) for n-doped NWs, respectively.

Fabrication of tin dioxide nanowires with ultrahigh gas sensitivity by atomic layer deposition of platinum

Gas-sensing properties of SnO2 nanowires were investigated before and after their surface functionalization by the atomic layer deposition (ALD) of Pt nanoparticles. The morphology, size, and concentration of Pt particles on SnO2 nanowires can be controlled by varying the number of ALD reaction cycles, and therefore, the gas-sensing properties of the nanowires can be altered via the Pt catalyst effect and the modification of Schottky barrier junctions on the nanowire surface in the vicinity of Pt nanoparticles. The Pt-decorated SnO2 nanowires obtained after 200 ALD reaction cycles exhibited an ultrahigh gas sensitivity (S = Ig/Ia) of ∼8400 to 500 ppm ethanol vapor at 200 °C. This provides an efficient route for strongly enhancing the gas sensitivity of semiconducting nanostructures and fabricating gas sensors that are highly sensitive and responsive.

Corrosion and tribological studies of chromium nitride coated on steel with an interlayer of electroplated chromium

Abstract The electrochemical and tribological behavior of CrN coatings on steel are investigated. A single layer of chromium nitride coating is compared with a double layer of the coating (CrN/Cr/steel) in which the interlayer chromium was produced by electroplating with the aim of improving the corrosion and tribological performance of the steel. The CrN coatings are deposited by using a reactive cathodic arc plasma deposition technology in an industrial scale, while the interlayer of chromium produced by electroplating. The coating assemblies have been compared in terms of hardness, wear and corrosion resistance. The composition and structure of the chromium nitride have been studied by X-ray diffraction (XRD), using both θ/2θ diffraction mode and the glancing-incidence X-ray diffraction mode. The surface morphology was examined by using SEM. The improvement in wear and corrosion resistance after cathodic arc plasma deposition with and without a hard chrome as an interlayer are discussed in considering the microstructure changes.

Application of diamond coating to tool steels

Abstract Various attempts were made to grow diamond film on SKD 61 for tribological applications in the laboratory. One of the promising ways in which to achieve this end is to interpose an intermediate layer which is compatible with both diamond film and the substrate of SKD 61. Some refractory metals were found to be satisfactory for this particular purpose. Molybdenum, for instance, was first deposited on SKD 61 by an electron beam evaporator at ambient temperature. Such molybdenum-deposited SKD 61 was first dry etched in hydrogen plasma to remove possible oxides and contaminations. Then diamond film was allowed to grow at a temperature of ∼ 500°C without much disturbance of the mechanical strength of the tool. This combination of diamond/molybednum/SKD 61 provided two interfaces leading to satisfactory adhesion strengths and an overall mechanical integrity. Carbides were often observed at the interface, but no oxide was detected. Multilayers of Mo and Ni as well as a single layer of TiN on SKD 61 were also explored in this research and they were proved to be effective in retarding the mutual alloying effect between carbonaceous materials and ferrous alloys.

The effect of Cr interlayer on the microstructure of CrN coatings on steel

The effect of electroplated Cr interlayer on the microstructure of CrN coatings on AISI 4140 steel were investigated. Two types of CrN-coated specimens by cathodic arc plasmas were prepared with and without an intermediate layer deposited by electroplated hard chrome (CrN/steel and CrN/Cr/steel). The microstructure and crystallinity of chromium nitride have been investigated using X-ray diffraction (XRD), cross-sectional transmission electron microscopy (XTEM) and selected area diffraction (SAD). Both CrN/steel and CrN/Cr/steel coating assemblies exhibit microcolumnar morphologies. However, it is noted that the columnar structure of CrN coating directly on steel is less evident, strong, and upward in comparison with that deposited on electroplated chromium layer. For CrN/Cr/steel assembly, the preferred orientations of CrN(220) and Cr(200) are observed.