Papers by Author: P. Chindaudom

Abstract: 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.

Abstract: This work is to study the diffusion of Al into amorphous silicon (a-Si) thin film at the elevated temperature by in-situ Spectroscopic Ellipsometry (SE). The sputtered a-Si film 60 nm thick on an optically opaque Al (100 nm) layer on silicon wafer was heated in a temperature controlled heating sample stage from room temperature to 300°C and slowly cooled down to room temperature while the dynamic SE data were measured. It was found that the ∆ and Ψ spectra began to change quickly at 200°C until the temperature reached 250°C, then continue to changed very slowly until 300°C. No significant change could be observed while the sample was cooling down to room temperature. The full spectral SE measurements were also taken at every 50°C steps and used to model the diffusion of Al into the top a-Si film. The interface layer due to diffusion was modeled by Bruggeman Effective Medium Approximation (EMA) theory as the mixture of Al and Si.

Abstract: A silver film was deposited on silicon wafer by DC unbalance magnetron sputtering system. The temperature dependence of the silver film was investigated. The spectroscopic ellipsometry (SE) with the heating of sample stage (HTC100) was employed for the in situ SE measurement under annealing cycles of the sample from room temperature to 300°C in dry nitrogen gas. The results show that the pseudo dielectric constants (<ε1>, < ε2>) of the sample varied with an annealing temperature. The real part of pseudo dielectric constant (<ε1>) of annealed Ag film was slightly changed and the imaginary part (< ε2>) was strongly increased at a photon energy below the optical band gap (3.5-4.5 eV). Furthermore, the pseudo dielectric constant of imaginary part at low energy region was changed due to the enhancement of crystallinity of Ag film at 300°C. All measured SE spectra were fitted by Drude-Lorentz optical model, the scattering time and resistivity were obtained.

Abstract: Titanium dioxide (TiO2) thin films, 80-170 nm thick were deposited on unheated silicon wafers (100) and glass slides with controlled operating pressure in UHV dc sputtering system with a pressure control gate valve. The dependence of hydrophilic property of the films on the total sputtering pressure of mixed Ar and O2 gases (1-10 mTorr) was investigated. We found that hydrophilic activity as well as the structural and optical properties of the films were strongly related to the pressure maintained during the deposition. The TiO2 film structure and surface morphology were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and spectroscopic ellipsometry (SE). The optical constants of the TiO2 films was determined by SE. XRD showed that the films deposited between 1 – 5 mTorr had both anatase and rutile phase, but the rutile component reduced as the pressure increased. Only anatase peaks were obtained for the films deposited at pressure >5 mTorr. The AFM surface roughness decreased from 4.0 to 1.8 nm as the pressure increased from 1 – 10 mTorr. The contact angle measurement was used to determine the hydrophilicity of the films after exposed to UV light. I