Puenisara Limnonthakul

Dynamic in situ spectroscopic ellipsometric study in inhomogeneous TiO2 thin-film growth

We investigate the film-growth process of the inhomogeneous sputtered TiO2 thin films by the in situ real-time spectroscopic ellipsometer. The growth process of the film is analyzed by both the uniform and the island film growth models. Based on the analyses from the Ψ-Δ trajectories, the initial thin-film growth corresponds to the island film growth model for a single-layer film. As the film grows, the microstructural phase changes cause the transition from the single-to the double-layer physical model, because of the development of the inhomogeneity in the TiO2 thin film. The dynamic fits with the double-layer physical model and the Cody–Lorentz optical model indicate three different stages of the film growth: the nucleation stage, the coalescence stage, and the continuous-layer stage. Although our presented model works well for most of the experimental data, the determination of the refractive index at the ultrathin thickness may be problematic.

Portable surface-enhanced Raman spectroscopy for insecticide detection using silver nanorod film fabricated by magnetron sputtering

In order to increase agricultural productivity, several countries heavily rely on deadly insecticides, known to be toxic to most living organisms and thus significantly affect the food chain. The most obvious impact is to human beings who come into contact, or even consume, pesticide-exposed crops. This work hence focused on an alternative method for insecticide detection at trace concentration under field tests. We proposed a compact Raman spectroscopy system, which consisted of a portable Raman spectroscope, and a surface-enhanced Raman scattering (SERS) substrate, developed for the purpose of such application, on a chip. For the selected portable Raman spectroscope, a laser diode of 785 nm for excitation and a thermoelectric-cooled CCD spectrometer for detection were used. The affordable SERS substrates, with a structure of distributed silver nanorods, were however fabricated by a low-energy magnetron sputtering system. Based on an oblique-angle deposition technique, several deposition parameters, which include a deposition angle, an operating pressure and a substrate rotation, were investigated for their immediate effects on the formation of the nanorods. Trace concentration of organophosphorous chemical agents, including methyl parathion, chlorpyrifos, and malathion, adsorbed on the fabricated SERS substrates were analyzed. The obtained results indicated a sensitive detection for the trace organic analyses of the toxic chemical agents from the purposed portable SERS system.

Surface-enhanced Raman scattering using silver nanocluster on anodic aluminum oxide template sensor toward protein detection.

Abstract The affordable surface-enhanced Raman scattering (SERS) substrates, with a structure consisting of densely distributed round-shape silver nanoclusters on anodic aluminum oxide (AAO) template, is fabricated by magnetron sputtering and anodization processes. The physical investigations show that the silver nanoclusters with size distribution ranging from 10 to 30 nm uniformly distributed on the top and in the bottom of the AAO nanochannels. The SERS activities from adsorbed probe molecules, i.e., methylene blue, on the SERS substrate surface indicate a high Raman enhancement factor for trace organic analysis. The SERS substrate is successfully utilized in the detection of a trace amount of three different proteins, bovin serum albumin, immunoglobulin G, and cardiac troponin T, also adsorbed on the substrate surface. Several spectral bands containing important molecular structures of these proteins are clearly observed and identified. The obtained results indicated a step forward to label-free biomolecular detections in chip-based biosensors.

Fabrication and characterization of hydrophilic TiO 2 thin films on unheated substrates prepared by pulsed DC reactive magnetron sputtering

TiO2 thin films were deposited on unheated silicon wafers (100) and glass slides by a pulsed DC reactive magnetron sputtering in an ultrahigh vacuum (UHV) system. The effects of both an operating pressure and deposition time on film structure, surface morphology, and optical property were studied. The film structure and microstructure were characterized by grazing-incidence X-ray diffraction (GIXRD) technique and transmission electron microscopy (TEM). The surface morphology was investigated by field emission scanning electron microscopy (FE-SEM). The optical property of the TiO2 thin films was determined by spectroscopic ellipsometry (SE). The water contact angle measurement was also used to determine hydrophilicity of the films after exposed to UV light. The results suggested that the TiO2 thin film at less than 40 nm was amorphous. As the thickness was increased, the mixture of anatase and rutile phases of TiO2 began to form. By reducing the operating pressure during the film deposition, the rutile phase component can also be enhanced. Both the increased film thickness and decrease operating pressure were the critical factors to improve the hydrophilicity of the TiO2 thin films.

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.

Facile Preparation of Gold Nanoparticle Modified Pencil Graphite Electrode

The purpose of this research was to prepare gold nanoparticle (AuNP) modified disposable pencil graphite electrode (PGE). The AuNP was prepared using trisodium citrate reduced gold ion solution. The PGE surface modification was carried out by immersing a bare PGE in poly (diallyldimethylammonium chloride) (PDDA) and then in AuNP solution at room temperature. The characterization of the bare and modified PGE surfaces was carried out using field emission scanning electron microscopy (FESEM) and cyclic voltammetry in the presence of 0.1 M NaOH. The electrochemical behavior of the modified PGE electrode was investigated using cyclic voltammetry, and impedance spectroscopy in the presence of 5 mM [Fe (CN)6]3-/4- redox probe solution. The obtained result indicated that the modification of AuNP on the PGE surface provided a good electrochemical signal. In order to obtain more sensitive electrochemical signals, the effect of adsorbed AuNP on the PGE surface was also studied.

Influence of Growth Conditions on Morphology of ZnO Nanorods by Low-Temperature Hydrothermal Method

Zinc oxide (ZnO) nanorods (NRs) promise high potentials in several applications, such as photovoltaic device, thermoelectric device, sensor and solar cell. In this research, the vertical alignment of ZnO NRs was fabricated by hydrothermal method with various precursor concentrations and growth time on different seed layers (ZnO and Au), which deposited on silicon wafer substrate (100). The crystalline structure and morphology of ZnO NRs have been characterized by x-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) techniques, respectively. The x-ray diffraction pattern shows that the prepared samples have a strong preferred orientation (002) plane. FE-SEM images of the ZnO NRs, it found that the density and aspect ratio were strongly influenced by the seed layer and precursor concentration. In addition, the aspect ratio of ZnO NRs was increased with increasing growth time. This study provides a cost effective method for the fabrication of well aligned ZnO NRs for nano-electronic devices.

Growth of Nanostructure Silver Films by DC Magnetron Sputtering for Surface Enhanced Raman Scattering Substrate

Nanostructure silver films were obtained by dc magnetron sputtering at room temperature. The influences of deposition time on the morphology and optical properties were studied by field-emission scanning electron microscope and UV-vis NIR spectrophotometer. It was found that the optical properties of the nanostructure silver film can be effect by surface morphology. The surface enhanced Raman scattering activities of nanostructure Ag films were demonstrated by methylene blue (MB) as probing molecules while the detection limit of MB was found to be as low as 10-5 M from this SERS substrate.

Ultra-Thin Al2O3 Formation at Room Temperature

Ultra-thin Al films were deposited with different deposition times on silicon wafer and copper grid by dc magnetron sputtering. The sputtering power of 200 watt and Ar flow rate of 20 sccm were used to prepare the films. The deposition times were 40, 120 and 240 second, respectively. The deposited Al films were, then, left in the air under the humidity of 60% for 20 days. The crystal structure of ultra-thin Al films deposited on silicon wafer and copper grid were investigated by glazing x-ray diffraction (GXRD) and transmission electron microscopy (TEM), respectively. The XRD results show that after the ultra thin Al films were exposed to the air, the Al was oxidized and the Al2O3 was formed at room temperature. In addition, Al deposited for 120 and 240 second can form polycrystalline of -Al2O3 with preferred orientations of (110) and (311) planes. The TEM images show that the particle size of -Al2O3 was about 8.5 nm for deposited time of 120 second. Moreover, the spectroscopic ellipsometry (SE) data and simulation model of Bruggemann effective medium approximation (BEMA) was used to determine the volume fraction of Al2O3.