M. Horprathum

Functionalization of Au Nanoparticles on ZnO Nanorods through Low-Temperature Synthesis

Hybrid nanomaterials exhibit multi-functionalities, which is synergy or enhanced physical and optical properties over their single components with promising potentials for various applications in dye-sensitized solar cell and photocatalytic materials. In this present research, the Au nanoparticles were prepared at HAuCl4 concentration of 0.5 mM on ZnO nanorod templates and silicon wafer substrate by hydrothermal reaction process. The prepared samples were investigated the crystal structure, chemical composition and morphologies by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and field-emission scanning electron microscopy (FESEM), respectively. The XRD results shown that ZnO was preferred orientation along the c-axis (002). The FE-SEM images indicated to the difference of size-Au NPs decorated on ZnO nanorods and silicon wafer. The relationship between the surface area and the size of Au NPs of the prepared samples was investigated and possible growing mechanism of Au NPs on ZnO nanorods templates will be discussed.

[Bi]:[Te] Control, Structural and Thermoelectric Properties of Flexible Bi x Te y Thin Films Prepared by RF Magnetron Sputtering at Different Sputtering Pressures

In this work, flexible BixTey thin films were prepared by radio frequency (RF) magnetron sputtering using a Bi2Te3 target on polyimide substrate. The effects of sputtering pressures, which ranged between 0.6xa0Pa and 1.6xa0Pa on the [Bi]:[Te] ratio, and structural and thermoelectric properties were investigated. The [Bi]:[Te] ratio of thin film was determined by energy-dispersive spectrometry (EDS). The EDS spectra show the variation of the [Bi]:[Te] ratio as the sputtering pressure is varied. The film deposited at 1.4xa0Pa almost has a stoichiometric composition. The selective films with different [Bi]:[Te] ratios and sputtering pressures were characterized by their surface morphologies, crystal and chemical structures by field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD) and Raman spectroscopy, respectively. Electrical transport properties, including carrier concentration and mobility, were measured by Hall effect measurements. Seebeck coefficients and electrical conductivities were simultaneously measured by a direct current four-terminal method (ZEM-3). The XRD and Raman spectroscopy results show a difference in microstructure between BiTe and Bi2Te3 depending on the [Bi]:[Te] ratio. Electrical conductivity and Seebeck coefficient are related to the crystal and chemical structures. The maximum power factor of the Bi2Te3 thin film is 9.5xa0×xa010−4xa0W/K2xa0m at room temperature, and it increases to 12.0xa0×xa010−4xa0W/K2xa0m at 195°C.

Effect of Annealing Temperature on Structure and Optical Properties of Ta2O5 Thin Films Prepared by DC Magnetron Sputtering

Tantalum oxide (Ta2O5) films at 400 nm thickness were prepared at room temperature by DC reactive magnetron sputtering. The effect of annealing temperature on film crystallinity, microstructure and optical properties were investigated. In order to indentify the crystalline structure and film morphology, X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM) measurements were performance. The optical properties were determined by UV-Vis spectrophotometer and spectroscopic ellipsometry (SE). The result showed that, with the annealing treatment at high temperature (700-900°C), the as-deposited films were crystallized to orthorhombic phase of tantalum pentaoxide (β-Ta2O5). In addition, the transmittance spectrum percentage indicated 87%, which corresponded to the obtained optical characteristic. The refractive index varied at 550 nm from 2.17 to 2.21 with increased of the annealing temperature.

Effects of Precursor Concentration on Hexagonal Structures of ZnO Nanorods Grown by Aqueous Solution Method

The ZnO nanorods were fabricated on top of the seeded gold layer by the aqueous solution method with the solution of zinc nitrate and hexamethylenetetramine (HTMA) at 90°C for 24 hours. The variety of the ZnO nanorods were prepared and investigated based on the precursor concentrations, in a range of 1 to 40 mM. The physical morphologies and crystal structures were characterized by field-emission scanning electron microscopy (FE-SEM) and X-ray diffractometry (XRD), respectively. The results showed that, with the small precursor concentrations, the lateral growth of the nanorods was highly significant when compared to their axial growth. The precursor concentration of 20 mM was best optimized for the preparation of the ZnO nanorod arrays with the hexagonal structures at the highest rod diameter and length. At the higher concentrations, although the nanorod size remained nearly constant, the length was however rapidly decreased. Further analyses also proved that, with the increased precursor concentrations, the number density of the ZnO nanorods was progressively increased along with the more complete hexagonal wurtzite structures.

Optimizations of Sealing Conditions for Blank Silver Nanorod Used as SERS Substrates

Silver nanorods, prepared on Si substrates by sputtering deposition with the technique glancing-angle deposition (GLAD), were used as surface-enhanced Raman scattering (SERS) substrates. The prepared samples were categorized into two groups based on sealing conditions after the nanorod fabrications. The non-sealed SERS substrates were prepared by purging in the vacuum chamber with argon, oxygen, and ambient air. The sealed SERS substrates were enveloped with several types of packages, i.e., petri dishes, plastic bags, and foils, where they were all handled in a controlled glove box. The samples were characterized by field-emission scanning electron microscopy (FESEM) for the physical morphologies. The samples were further investigated by Raman spectroscopy for Raman spectra of blank substrates of each condition. The results showed that, in case of the non-sealed category, the SERS substrates purged under the argon gas was best optimized to prevent ambient contamination during prolonged period of time. In the case of the sealed category by different packages, the SERS substrates demonstrated the enhancement of the Raman-shift spectra with very small unwanted peaks, and in addition the extended lifetime.

Investigation of Electrochromic WO3 Nanorods Prepared by DС Reactive Magnetron Sputtering with GLAD Technique

Tungsten oxide (WO3) nanorods were prepared by a DC reactive magnetron sputtering with a glancing-angle deposition (GLAD) technique, which promoted high surface area, for electrochromic applications. During the deposition, a high-quality tungsten target was sputtered under oxygen ambience on to Si (100) and glass/ITO substrates. The variation of the deposition time, which affected the length, size and patterns of the nanorods, was investigated based on their electrochromic properties. For physical studies, the prepared nanorods were examined by X-ray diffraction and field-emission scanning electron microscopy, which demonstrated moderately ordered nanorods with amorphous phase. The results showed that the length and size of nanorod were increased, in nearly linear order, with increasing the deposition time. For optical characteristics of the prepared films, the UV-Vis spectrophotometry was use to determined their transmission spectra and optical contrasts from the colored and bleached state. The electrochromic properties were also determined from cyclic voltammetry. The results indicated that, because of the optimal relations between the nanostructural length and size, the WO3 nanorods prepared at 75 minutes (approximately 422 nm) yielded the highest optical contrast and electrochromic functions.

Effect of Sputtering Power on Physical Properties and Electrochromic Performance of Sputtered-WO3 Thin Films

Tungsten oxide (WO3) electrochromic thin films were deposited onto F-doped tin oxide (FTO) substrates using DC sputtering of tungsten target in presence of oxygen and argon gas. As-deposited films were prepared with different sputtering power at 50 W, 100W and 200W. The effect of power on structural, surface morphology optical and electrochromic properties of the WO3 thin films were characterized by X-ray diffractometer, scanning electron microscope, UV-VIS spectrophotometer and Cyclic voltammetry, respectively. The XRD results show that the crystalline of WO3 can be identified an orientation growth along (222) plane. The average grain size evaluated from SEM image is approximately 200 nm. The films deposited at power of 200 W exhibited better electrochromic properties with greatest optical modulation (∆T) value of ∆T = 31.2 % at l= 550 nm. The cyclic voltammograms (CV) of WO3 thin films evidently exhibited that the WO3 films prepared at power of 200 W displayed the superior electrochromic performance, compared to the others.

Annealing Temperature Dependent on Microstructure and Ethanol Gas Sensing Properties of TiO2Thin Films

The TiO2 thin films were prepared by a dc reactive magnetron sputtering technique from high purity Ti target on silicon (100) wafers and alumina substrates inter-digital with gold electrodes. The as-deposited films were annealed from 400°C up to 800°C with 100 °C steps for 1 hour in air ambience in order to promote microstructure, morphology and gas-sensing properties. The change in microstructure and morphology of the films were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The enhancement in the gas-sensing properties was test by ethanol gas. The prepared thin films were exposed to ethanol gas at concentration 1,000 ppm in purify dry air carrier. The resistance was measured as a function of the ethanol concentration of the films at operated temperatures in the range of 250 - 350°C. The influence of annealing temperature at 500 °C of TiO2 thin film has a highest sensitivity at 350 °C operated temperature.

Effect of Operated Pressure on Anticorrosive Behavior of Ta2O5 Thin Film Grown by D.C. Reactive Magnetron Sputtering System

Tantalum oxide (Ta2O5) thin films, 100 nm thick were deposited by D.C. reactive magnetron sputtering system at different operated pressure on unheated p-type silicon (100) wafer and 304 stainless substrates. Their crystalline structure, film surface morphology and optical properties, as well as anticorrosive behavior, were investigated. The structure and morphology of films were characterized by grazing-incidence X-ray diffraction (GIXRD) and atomic force microscopy (AFM). The optical properties were determined by spectroscopic ellipsometry (SE). The corrosion performances of the films were investigated through potentiostat and immersion tests in 1 M NaCl solutions. The results showed that as-deposited Ta2O5 thin films were amorphous. The refractive index varied from 2.06 to 2.17 (at 550 nm) with increasing operated pressure. The corrosion rate of Ta2O5 thin film improves as the operated pressure decreases. The Ta2O5 thin films deposited at 3 mTorr operated pressure could be exhibited high performance anticorrosive behavior.

Preparation of WO3 Nanorods by Glancing Angle DC Reactive Magnetron Sputtering Deposition for NO2 Gas Sensing Application

In this study, we present a tungsten trioxide (WO3) nanorods based gas sensor for NO2 sensing at operating temperature range 150-350 °C in purify dry air carrier. WO3 nanorods were fabricated by dc reactive magnetron sputtering with glancing angle deposition (GLAD) technique on silicon (100) wafer and alumina substrates interdigitated with gold electrode. The length of WO3 nanorods was varied from 370 nm to 620 nm. As-deposited nanorods were annealed at a temperature of 400 °C in air for 1 h. The microstructure and phase structure of WO3 nanorod were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM), respectively. XRD of annealed WO3 nanorod showed polycrystalline phase. The WO3 nanorods length 420 nm exhibit excellent NO2 sensing properties with a maximum sensitivity of 360 at 250 °C operating temperature with fast response and recovery time.