Chih-Chieh Wang

Electron field emission from Fe-doped TiO2 nanotubes

Titanium dioxide nanotubes were prepared by refluxing TiO2 in 10 M NaOH at 200 °C for 12 h. The light absorption edge was slightly shifted to a longer wavelength when 0.025 mol % of iron was incorporated to TiO2 nanotubes. A turn-on field at 12 V/μm and a maximum current density of 12 mA/cm2 at 19 V/μm was observed for the Fe-doped but not for pure TiO2. The field emission behavior can be correlated with the geometry and electronic states of the nanotubes.

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.

Deposition of platinum on oxygen plasma treated carbon nanotubes by atomic layer deposition

Platinum nanoparticles were deposited on oxygen plasma treated carbon nanotubes (CNTs) by atomic layer deposition (ALD). The treatment time with oxygen plasma generated by microwaves under a power of 600 W varied from 5 to 20 s. The number of ALD cycles was controlled at 5-125. X-ray photoelectron spectroscopic analysis indicated that oxygen plasma can graft oxygen-containing functional groups to the CNT surface to act as nucleation sites for growth of Pt nanoparticles. Formation of very uniform and well distributed Pt nanoparticles of a size of 1.60-4.80 nm was achieved. The growth rate of Pt nanoparticles could be controlled by the number of ALD cycles and oxygen plasma treatment time. This offers a dry process to deposit well-dispersed metallic nanoparticles on selected support materials.

Fabrication of TiO2 nanotubes by atomic layer deposition and their photocatalytic and photoelectrochemical applications.

The formation of TiO(2) nanotubes was conducted by atomic layer deposition (ALD) with tris-(8-hydroxyquinoline) gallium (GaQ(3)) nanowires as a template at different substrate temperatures, 50, 100, and 200 °C. TiO(2) nanotubes were formed only at 50 and 100 °C. Although a higher growth rate at 50 °C was observed, nanotubes with better uniformity, conformality, and less residual chloride were obtained at 100 °C because of a different formation mechanism. A photocatalysis test of TiO(2) nanotubes prepared by different cycle numbers at 100 °C was conducted. It showed that TiO(2) nanotubes prepared by 400 cycles of ALD and treated at 700 °C for 1 h to form anatase phase had the best photocatalytic performance. Compared with P-25, the nanotubes showed higher photocatalytic degradation of rhodamine B and water splitting efficiency.

Enhancing the Photon-Sensing Properties of ZnO Nanowires by Atomic Layer Deposition of Platinum

Platinum nanoparticles were uniformily deposited on ZnO nanowires for photon-sensing applications. The morphology, size, and concentration of Pt particles on the ZnO nanowires can be controlled by varying the number of atomic layer deposition reaction cycles. The Pt-decorated ZnO nanowires exhibit much faster photon response and recovery speeds than the pristine ZnO nanowires. This provides an efficient route for strongly enhancing the photon-sensing properties of nanostructured metal oxides and fabricating photodetectors with fast response and recovery speeds.

The formation of TiO2 nanowires directly from nanoparticles

TiO(2) nanowires were fabricated by annealing TiO(2) nanoparticles on silicon substrate at 1000 degrees C in air. When a polystyrene nanosphere monolayer was used as a template to separate the TiO(2) nanoparticles, they could more easily react with the silicon substrate to form Ti(5)Si(3). The TiO(2) nanowires were formed upon further oxidation of Ti(5)Si(3). The diameters and lengths of TiO(2) nanowires were 30-80 nm and 1-3 microm, respectively. The nanowires had a rutile structure with the growth direction [112]. It is believed that the formation of TiO(2) nanowires involved a precipitation process in the mixture of SiO(2) and TiO(2). The nanowires show different photoluminescence behavior from that of the powder.

Preparation of Pt / SnO2 Core–Shell Nanowires with Enhanced Ethanol Gas- and Photon-Sensing Properties

Pt/SnO 2 core-shell nanowires were prepared by a process that involves thermal evaporation of SnO 2 nanowires and subsequent atomic layer deposition of Pt, and their gas- and photon-sensing properties were investigated systematically. Transmission electron microscopy analysis showed that the Pt shell with a thickness of 8.8 nm is composed of numerous Pt nanoparticles with average diameters of ∼5.3 nm. The Pt/SnO 2 core-shell nanowires with high electrical conductance exhibit remarkably enhanced ethanol gas- and photon-sensing properties due to the surface functionalization resulting from the effective Pt catalyst and the formation of hetero-nanostructures fabricated by the SnO 2 core and Pt shell.

Photoluminescence of GaQ3 – Al2O3 Core-Shell Nanowires

Tris(8-hydroxyquinoline) gallium(III) (GaQ 3 )―Al 2 O 3 core-shell nanowires with different shell thicknesses of Al 2 O 3 coated on GaQ 3 nanowires were prepared by atomic layer deposition (ALD). The uncoated and coated nanowires exhibited similar photoluminescence (PL) spectra in the atmospheres of air, oxygen, argon, and water vapor at room temperature. The PL stability of the nanowires in these atmospheres was then examined for up to 4 h. Degradation of uncoated GaQ 3 nanowires in PL intensity with time was observed in air, oxygen, and water vapor. GaQ 3 ―Al 2 O 3 core-shell nanowires were only degraded in oxygen, but to a lesser degree than uncoated nanowires. Therefore, ALD of Al 2 O 3 is effective in protecting the nanowires.

Preparation and Optical Property of TiO2 Nanohoneycomb

TiO2 nanohoneycomb was fabricated by solution-based nanosphere lithography. TiCl4 solution was used as a precursor to fill in the interspace of the self-assembled polystyrene nanosphere mask. After removing the polystyrene (PS) nanosphere monolayer by heating, an anatase nanohoneycomb was formed. A more uniform nanohoneycomb was obtained by using t-butanol as the solvent for TiCl4 because of its better wetting with the nanospheres. UV–visible spectra of the nanohoneycombs showed that there were two absorption edges at 320 and 470 nm. The photocatalytic activity measurement showed that the nanohoneycomb had a better photodecomposition efficiency than the film.

Anti-Corroded Molybdenum Back Electrodes by Al Doping for CuIn1-xAlxSe2 Solar Cells

The effects of Al doping into Mo films, used as back electrodes of CuIn1-xAlxSe2 solar cells, were systematically investigated. The Mo1-XAlX films fabricated by co-sputtering were exposed in a damp-heat (DH) chamber with 85 C and 85% relativity humidity for 168 h to verify the reliability. The resistivity of the Mo79Al21 films after DH exposure was only slightly increased from 2 10 6 X m to 2.3 10 6 X m; however, the pure Mo films after DH exposure became insulating due to the formation of the MoOx layer. Based on the analyses of the x-ray diffraction and x-ray photoelectron spectrum, we suggest that the Al atoms are dissolved into the Mo films in the as-deposited state and segregate to the surface of Mo1-XAlX films during DH exposure. A thin Al-oxide layer is formed on the surface and behaves as an anti-corrosion layer, which enhances reliability. On the other hand, with increasing the Al content, increased amount of the Al2O3 layer may suppress the formation of the MoSe2 layer at the interface between Mo and CIS-based films. Consequently, the Mo film with the optimized Al doping, for example, the Mo79Al21 film may become a good candidate of the back electrode for CuIn1-xAlxSe2 solar cells to maintain good reliability as well as to achieve good adhesion and low series resistance. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3582824] All rights reserved.