Napat Triroj

Tuning Optical Properties of Electrospun Titanium Dioxide Nanofibers by Controlling Particle Sizes

Titanium dioxide (TiO2) nanofibers with different particle sizes were fabricated using an electrospinning technique. The nanofibers were prepared from a mixture of titanium tetraisopropoxide and polyvinyl pyrrolidone (PVP). The scanning electron microscope (SEM) and the transmission electron microscope (TEM) were used to analyze the morphology and sizes of TiO2 nanoparticles within the nanofibers. The particle sizes of TiO2 were measured to be 17 nm, 28 nm and 35 nm for nanofibers calcined at 500 °C, 600 °C and 700 °C, respectively. Ultraviolet-visible absorption spectroscopy analysis and the application of the KubelkaMunk function reveal the size-dependent band gap energy of TiO2 nanofibers. The band gap energies are measured to be 2.9 eV, 2.6 eV and 2.5 eV for TiO2 nanofibers with average particle sizes of 17 nm, 28 nm and 35 nm, respectively.

Particle size-dependent electrical resistances of WO 3 nanofibers

This work reports the fabrication steps and the particle size-dependent electrical resistances of WO3 nanofibers produced by an electrospinning technique. The nanofibers are prepared by mixing ammonium metatungstate hydrate (AMH) in deionized water at various concentrations with polyvinyl alcohol (PVA). Such mixture is then electrospun onto platinum interdigitated electrodes, following by a hot pressing and calcination processes. It is found that lower precursor concentrations and lower calcination temperatures resulted in smaller WO3 particles consisting in the nanofibers. Particle size-dependent electrical resistances are found in these nanofibers, and are believed to be related to the size of the space-charge layer in individual WO3 particle. This study provides information about synthesis parameters used to control physical dimensions of the WO3 particles and the magnitudes of the electrical resistances associated with the structures.

Impedance Spectroscopic Inspection Toward Sensitivity Enhancement of Ag-Doped WO3 Nanofiber-Based Carbon Monoxide Gas Sensor

This work reports the impedance analysis and carbon monoxide gas sensing response of tungsten oxide (WO3) nanofibers with silver (Ag) nanoparticle doping. The Ag-doped WO3 nanofibers were prepared by an electrospinning technique. The impedance spectroscopic measurements of undoped and Ag-doped WO3 nanofibers were performed to study the contribution of electrical parameters involved in the electron transport. The impedance modeling obtained from the fitted Nyquist plot shows that the RC components attributed to Ag-WO3 interface are introduced to the system upon Ag addition. Carbon monoxide (CO) gas detection was carried out by resistance measurement using a DC method. The sensitivity of Ag-doped WO3 nanofibers is found to be greater than that of the undoped sample. The improved sensitivity is derived from the high interface resistance between Ag and WO3 grains. The contribution of Ag dopants is conceived to induce electronic structure alteration of the sensor material.

Influence of Substrate Temperature on Deposition Rate and Optical Properties of Aluminum Oxide Thin Films Prepared by Reactive DC Sputtering Technique

Aluminum oxide films were grown on (100) silicon wafers and glass substrates by pulsed dc reactive magnetron sputtering deposition. In this experiment, substrate temperatures were varied from room temperature to 500°C. Grazing-incidence X-ray diffraction (GIXRD) analysis revealed that the resulting films have amorphous structures. Field-emission scanning electron microscope (FESEM) was used to characterize the morphology of the films. The films’ optical properties were determined by UV-Vis spectroscopy. The results demonstrated that the deposition rate, the surface roughness and the transmittance spectra of the aluminum oxide films were strongly influenced by the substrate temperature. The deposition rate and the surface roughness of the films were higher at higher substrate temperatures. In the range between 100°C and 200°C, the transmittance spectra were found to be lower than those of the films deposited at other substrate temperatures. This was due to the sub-aluminum oxide condition in the films. The dependence of films’ optical properties on the substrate temperature might result from the change in chemical compositions during the sputtering process.

Investigation of Photoelectrochemical Parameters of Electrospun TiO2 Nanofiber Electrode

This work reports the fabrication and photoelectrochemical response of titanium dioxide (TiO2) nanofiber photoelectrode prepared by an electrospinning technique. Transmission electron microscopy (TEM) images reveal that the electropun nanofibers are composed of TiO2 nanoparticles with the average diameter size of 25 nm. The scanning electron microscopy (SEM) image of the photoelectrode confirms the existence of TiO2 nanofiber networks on Ti/Si substrate after the electrode preparation using a doctor-blade technique. The photoelectrochemical performance of TiO2 nanofiber electrode is investigated in comparison with that of TiO2 (Aeroxide P25) nanoparticle electrode. When the TiO2 electrodes are subjected to light illumination at 100 mW/cm2, the maximum photoconversion efficiency (PCE) of 0.95% is obtained at the TiO2 nanofiber electrode while reduced PCE of 0.75% is obtained at the TiO2 nanoparticle electrode.

Investigation of Trapped Charges-Induced Stain Formation on RF-PECVD Diamond-Like Carbon Films

This paper reports the investigation of a root cause of stain formation on the surfaces of diamond-like carbon (DLC) films. The DLC thin films are prepared using a radio-frequency plasma enhance chemical vapor deposition (RF-PECVD) technique with C2H4 as a carbon precursor gas. We have observed water spot-like stains on the DLC surfaces after treating the films with a dilute solution of dipropylene glycol monomethyl ether (DPGME). Low voltage-scanning electron microscopy (SEM) is employed to examine the thin layer of agglomerated stains on the surfaces. The results from capacitance-voltage (C-V) measurements show that as-deposited films inherit some trapped charge accumulations within the structure, thereby resulting in the pronounced shift in the flat-band voltage. These trapped charges make the films prone to surface stain formation. Post-annealing of the DLC films at 200 °C in N2 for 1 h has proven to reduce the trapped charge density, and therefore prevent stain formation on the DLC films.

1.2.4 Gas-Assisted Focused Ion Beam Fabrication of Gold Nanoelectrode Arrays in Electron-Beam Evaporated Alumina Films for Biosensing Applications

This work reports the fabrication details used to prepare gold nanoelectrode arrays in alumina substrates. The fabrication steps include electron-beam evaporation of 20-nm Ti and 300-nm thick Au for the electrode platform on a glass substrate, followed by electron-beam evaporation of 800-nm thick Al2O3 as a passivation layer. I2-assisted focused ion beam (FIB) milling is employed to create highaspect-ratio pores in the alumina films. The final pore size of 60-120 nm is achieved by ion beam sculpting after the initial milling process. The nanopores are then filled with Au via electrodeposition to obtain a nanoelectrode structure. Cyclic voltammetry (CV) responses of a standard redox species exhibit a nonclassical behavior of which a well-defined steady-state limiting current plateau is not observed.