Papers by Author: Napat Triroj

Abstract: This work describes the fabrication steps and surface-enhanced Raman scattering (SERS) activities of the cross-linked polyvinyl alcohol (PVA)/Ag nanofibers. The water-insoluble electrospun PVA/Ag nanofibers were achieved by post-electrospinning treatment processes. Physical crosslinking was induced by heat treatments, while chemical crosslinking took place through the reactions with glutaraldehyde (GA). Scanning electron microscopy (SEM) images have shown that cross-linked PVA/Ag nanofibers remained mostly intact after immerging in water for 30 min. The testing of SERS activities was performed on these substrates using the methylene blue (MB) molecules as tested substances. The results have shown that the PVA/Ag nanofibers can be used as SERS substrates for rapid screening of biochemical substances. The Raman enhancement factor (EF) of approximately 10⁴ corresponding to the detection limit of 10^-4 M of MB molecules was achieved.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.