Papot Jaroenapibal

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.

Many-Objective Optimisation of Trusses Through Meta-Heuristics

A truss is one of the most used engineering structures in daily life due to several advantages. A process for truss optimisation is usually set to minimise its mass while structural safety constraints are imposed. This design problem always leads to structures with less reliability since the solution is generally on the borderline of structural failure. Such a phenomenon can be alleviated by adding effects of all possible load cases with safety factors to design constraints. Alternatively, the design problem should be many-objective optimisation assigned to optimise mass and reliability indicators for all load cases. This paper is the first attempt to study such a design process. A number of many-objective meta-heuristics are employed to solve the test problems for many-objective truss optimization where their performances are compared.

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.

Effects of TEOS Precursor and Reaction Time on the Synthesis of Silica Coated Single-Walled Carbon Nanotubes

This paper demonstrates a technique to synthesize silica-coated single-walled carbon nanotubes (SWNTs@SiO2) based on sodium dodecyl sulfate (SDS), 3-aminopropyltriethoxysilane (APTES), ammonium hydroxide (NH4OH) and tetraethyl orthosilicate (TEOS). The coating of silica is done to promote bond strength between SWNTs@SiO2 and other materials. The anionic surfactant used in the coating process helps create linkages between the silica coupling agent and the SWNTs’ walls without compromising the excellent properties of SWNTs. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX) were employed to characterize the sizes of SiO2 particles, the structure of SWNTs@SiO2, and the elements existed in the materials. The size of SiO2 particles has shown to be dependent on the amount of TEOS concentration and reaction time. Higher TEOS concentration and longer reaction time led to larger SiO2 particles. Successful coatings of SiO2 on SWNTs have been demonstrated. Silica appeared to be uniformly coated on the SWNTs surfaces. The thickness of the coating layer was found to be approximately 3-7 nm.

Improvement of Early Compressive Strength in Belite Cement by Incorporating Silica Coated Single-Walled Carbon Nanotubes

This work demonstrated the improvement of belite cement compressive strength by incorporating nanosilica coated single-walled carbon nanotubes (SWNTs@SiO2) into the cement paste. The structure and chemical compositions of SWNTs@SiO2 materials were characterized by transmission electron microscopy and energy dispersive X-ray spectroscopy techniques, respectively. Belite cement composites were prepared by mixing belite cement paste with different loadings of SWNTs@SiO2 ranging from 0.02 – 0.1 wt%. In order to measure the early strength of cement composites, the samples were aged for 7 days, and then subjected to compression tests. Effects of uncoated SWNTs and silica coated SWNTs loadings on the compressive strength of belite cement composites were studied. Without pre-coating SWNTs with nanosilica, the SWNTs additives led to large decrease in compressive strength of belite cement composite. Improvements in compressive strength of belite cement are shown in samples that incorporated SWNTs@SiO2 loadings. The coating layer helps enhance bonding strength between reinforced SWNTs and the matrix, as well as promote hydration reactions in the cement paste. The highest increase in the compressive strength of 18.8 % is found in the sample with the minimal SWNTs@SiO2 loading of 0.02%.

Spectroscopic Ellipsometry Analyses on Plasma Treatment of Aluminium Oxide Thin Film

Spectroscopic Ellipsometry (SE) was used to analyse the effect of plasma treatment on aluminium oxide thin films. The aluminium oxide thin films were fabricated by reactive DC magnetron sputtering at different operating pressures. The as-deposited thin films were plasma treated at different ambient Ar and O2 conditions. The prepared samples were investigated for physical microstructures with scanning electron microscopy (SEM) and optical characteristics with ellipsometry. The ellipsometric spectra of the prepared samples were measured in the range of 250 to 1650 nm with the incidence angle of 70 degree. Based on the optical model with the Tauc-Lorentz function, the thickness and the refractive index of the films were determined and discussed. The results showed that the thickness and the refractive index of the aluminium oxide thin films were greatly affected after the plasma treatments. In comparison, the results of those prepared at different operating pressures were also discussed. The SE results were confirmed with those from SEM.

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.