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Abstract In this work, the low-temperature H2-sensing properties of palladium (Pd) and palladium oxide (PdO) nanoparticles decorated titanium dioxide (TiO2) thin film were studied. The TiO2 thin films were prepared by the dc reactive magnetron sputtering. The Pd and PdO nanoparticles were sputtered on the top surface of TiO2 surface in order to enhance the sensitivity to the H2 gas. Morphologies, crystal structures, and chemical element of the examiner samples were investigated by the field-emission scanning electron microscopy (FE-SEM), grazing-incident X-ray diffraction (GIXRD), and X-ray photoelectron spectroscopy (XPS), respectively. The effects of the Pd and PdO nanoparticles on H2-sensing performance of TiO2 were investigated over a low concentration range of 150-3,000 ppm H2 at 50-250°C-operating temperatures. This result exhibited that the PdO decorated on TiO2 surface showed very high response to H2 at a low operating temperature of 150°C.

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.

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.

Periodic nanohole pattern was created in spin-coated photoresist S1805 on Si substrates by Laser Interference Lithography (LIL). Wavelength of a laser source used in the optical system is 442 nm with the photon energy 2.80 eV. The system was set up to employ two laser beams from a beam splitter to generate interference pattern and expose to the photoresist. There are two parameters (incident angle and exposure time) which are determined due to affecting the ordering and feature of nanohole array. Therefore, the relation of these two parameters and actual dose were investigated and theoretically analyzed to optimize the resolution of LIL technique for nanoholes. The prepared samples after developing in the M26A for 5 sec were analyzed by field-emission scanning electron microscopy (FE-SEM). The results show that the pitch of the pattern is 440 nm and the smallest hole size is 190 nm The best feature is found for a laser fluence of 140 mJ/cm2. This nanohole array patterned by LIL consists of periodic nanostructures for high density storage to fabricate various nanodevices.

In this work, we report an ultrasensitive hydrogen (H2) sensor based on tungsten trioxide (WO3) nanorods decorated with platinum (Pt) nanoparticles. WO3nanorods were fabricated by dc magnetron sputtering with a glancing angle deposition (GLAD) technique, and decorations of Pt nanoparticles were performed by normal dc sputtering on WO3nanorods with varying deposition time from 2.5 to 15 s. Crystal structures, morphologies, and chemical information on Pt-decorated WO3nanorods were characterized by grazing-incident X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and photoelectron spectroscopy, respectively. The effect of the Pt nanoparticles on the H2-sensing performance of WO3nanorods was investigated over a low concentration range of 150–3000 ppm of H2at 150–350 °C working temperatures. The results showed that the H2response greatly increased with increasing Pt-deposition time up to 10 s but then substantially deteriorated as the deposition time increased further. The optimally decorated Pt–WO3nanorod sensor exhibited an ultrahigh H2response from 1530 and 214 000 to 150 and 3000 ppm of H2, respectively, at 200 °C. The outstanding gas-sensing properties may be attributed to the excellent dispersion of fine Pt nanoparticles on WO3nanorods having a very large effective surface area, leading to highly effective spillover of molecular hydrogen through Pt nanoparticles onto the WO3nanorod surface.

Three-dimensional (3D)-hybrid surface-enhanced Raman scattering (SERS) substrates have been achieved via simultaneous assembled silver nanoparticles (AgNPs) onto the anodic aluminum oxide (AAO) templates. The AAO templates were prepared from the UHV aluminum foil in 0.3 M oxalic acid using the two-step anodization process at 0°C. The effect of applied voltage ranging from 30 to 50 V on the porous diameter and the inter-porous distance of the AAO templates was investigated and observed with filed-emission scanning electron microscope (FE-SEM). The results showed that the porous distance and the inter-porous distance were linearly increased with the increase in the voltage potentials. To investigate the pore-size effect on the SERS activities, the AgNPs were deposited on the AAO nanoporous templates. The SERS activities of these nanostructures were demonstrated with the methylene blue (MB) as the probing molecules.

Transparent conductive oxides (TCOs) with indium tin oxide (ITO) thin films were deposited without substrate heating and post-deposition anneal using ion-beam assisted evaporation technique on glass and silicon substrates. The oxygen ion with emitting current produced using End-Hall ion source for bombardment of growing surface to improve ITO films structure. In this study, we investigate the effect of an ion flux to ITO films in terms of structural, optical and electrical properties. The emitting current can be varied from 0.5 to 2.0 A with the oxygen flow rate 7 sccm. The total film thickness and deposition rate are 200 nm and 0.2 nm/s, respectively. The structural properties of thin films were characterized by X-ray diffraction (XRD) to discover the preferred orientation with phase of crystalline and scanning electron microscopy (SEM) to examine the surface morphology in cross-section view. To determine the transmission spectra of the films, UV-visible spectrometer is introduced. Moreover, the films were also measured to investigate resistivity, carrier concentration, mobility and sheet resistance by Hall-effect measurements and four-point probe. It has been found that the ITO films with lowest electrical resistivity for the emitting current of 1 A about 5.57x10-4 Ω.cm and slightly increases with increase of the emitting current. The mobility and carrier concentration rapidly decreases with increase the emitting current from 1.0 A to 2.0 A.

According to the growing interest in development of high-sensitivity surface-enhanced Raman scattering (SERS) substrates, this study focused on the fabrication of silver nanorods (AgNRs) based on the DC magnetron sputtering, with the glancing-angle deposition (GLAD) technique. The influence of incident angles on the film morphologies and SERS activities of the deposited films were investigated by field-emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. With methylene blue as the test agent, the vertical aligned silver nanorods proved highly potential in highly sensitive SERS detections. The pesticidal cypermethrin were also used as the probe molecules to investigate for future practical applications. This work showed that the increase in the incident angle during the deposition helped promote the porosity of the AgNRs. The SERS signals were significantly enhanced from the vertically aligned silver nanorods grown at 85o incident deposition angle and 20 rpm substrate rotational speed.

This work investigated the decoration of the gold (Au) nanoparticles (NPs) on the TiO2 thin films for the applications in ethanol gas sensors. The Au-decorated TiO2 thin films (Au-TiO2) were prepared by the DC magnetron sputtering on the silicon (100) wafers and alumina substrates, interdigitated with Au electrodes. The distribution and size of Au nanoparticles were controlled by varying the sputtering time. Morphologies and element composition of the Au-TiO2 films were examined by field-emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX) respectively. The FE-SEM micrographs when the sputtering time was increased, the average size of the Au NPs was also increased. On the other hand, the distribution of the Au NPs was decreased. The change in size and distribution of the Au NPs consequently improved the response of ethanol gas sensors. The prepared Au-TiO2 was tested, in comparison with TiO2 reference films, as the ethanol sensors at 250-350oC in 50-1,000 ppm gas concentration. The results showed that the TiO2 thin film with Au-decorated at 6 sec sputtering time yielded the highest response of 514 at 350oC operating temperature and 1,000 ppm gas concentration.

Tantalum oxide (Ta2O5) thin films were prepared, at different deposition time, by a DC reactive magnetron sputtering. During the deposition, a high-quality tantalum target was sputtered under argon and oxygen ambience on to silicon (100) and glass substrates. The prepared thin films were systematically characterized for both physical and optical properties based on spectroscopic ellipsometry (SE), and consequently confirmed by several methods. With the SE physical models, we could determine the thin film thickness as well as their inhomogeneity. The films thickness results were directly confirmed by field-emission scanning electron microscopy (FE-SEM) used to observe cross-sections, and surface profiler used to measure the physical thickness of the films. With the SE optical models, we applied both the Cauchy and Tauc-Lorentz dispersions in order to obtain the optical constants, to be directly compared with those from the Swanepoel method (SM). Our result showed that from the SE analyses, the SE physical model was obtained as the multi-layer configurations. The obtained Ta2O5 thin film thickness was closely related with the measured result from the FE-SEM cross-sectional micrographs and the surface profiler. For the optical characteristic, the double layer physical model was best optimized with the Tauc Lorentz dispersion model for the most accurate results. In comparison, the SM technique also demonstrated a capability to determine both the film thickness and its refractive index only from some samples. Therefore, this study proved that the SE technique successfully and accurately determine both the physical and optical properties of the Ta2O5 thin films.

Tantalum oxide (Ta2O5) thin films were deposited as the protective layers for the metal surface finishing by the DC reactive magnetron sputtering system. The effect of the Ta2O5 film thickness, ranging from 25 nm to 200 nm, on the physical properties and the anti-corrosive performance were investigated. The grazing-incidence X-ray diffraction (GIXRD) and the atomic force microscopy (AFM) were used to examine the crystal structures and the surface topologies of the prepared films, respectively. The XRD results showed that the Ta2O5 thin films were all amorphous. The AFM micrographs demonstrated the film morphology with quite smooth surface features. The surface roughness tended to be rough when the film thickness was increased. To examine the protective performance of the films, the poteniostat and galvanometer was utilized to examine the electrochemical activities with the 1M NaCl as the corrosive electrolyte. The results from the I-V polarization curves (Tafel slope) indicated that, with the Ta2O5 thin film, the current density was significantly reduced by 3 orders of magnitude when compared with the blank sample. Such results were observed because of fully encapsulated surface of the samples were covered with the sputtered Ta2O5 thin films. The study also showed that the Ta2O5 thin film deposited at 50 nm yielded the most extreme protective performance. The Ta2O5 thin films therefore could be optimized for the smallest film thickness for highly potential role in the protective performance of the metal surface finishing products.

Based on recent discovery of high-rate reactive magnetron sputtering, which was a key requirement for production of coating industry, this study focused on enhanced deposition rate of TiO2 films for photo-induce hydrophilic applications. The TiO2 thin films were reactively sputtered, which a pulsed DC source, from high-purity (99.995%) titanium (Ti) target on glass and silicon (100) and wafer substrates. During the deposition, a mesh grid cover was installed on the sputtering source with varying argon gas flow rates. Properties of the TiO2 films were compared between deposition with and without a mesh grid cover. The microstructure of the TiO2 films was studies by grazing-incidence X-ray diffraction (GIXRD) and field-emission scanning electron microscope (FE-SEM). The optical properties were determined by UV-Vis spectrophotometer. The contact angle measurement was used to determine the hydrophilicity of the films after exposing to UV light. For using the mesh grid during film deposition, it was found that the deposition rate of the TiO2 films was increased in oxide mode with a small grain size. In this case, the TiO2 films showed high transparent and good photo-induced hydrophilic properties.

n 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.

Titanium dioxide (TiO2) films were prepared by thermal oxidation from Ti films. The Ti films were deposited on glass and silicon (100) wafer substrate by dc magnetron sputtering and subsequent with thermal oxidation process. The crystal structure and morphology of TiO2 films were estimated by using X-ray diffractometry (XRD) and field-emission scanning electron microscopy (FE-SEM), respectively. The optical property of TiO2 films was determined by UV-Visible spectrophotometer. The influences of annealing temperature between 200 to 500°C in air for 1 hour on the structure and optical properties of TiO2 films were investigated. The increasing of annealing temperature was directly affected the phase transition from Ti to TiO2. The optical and structural properties of TiO2 films are the best exhibited with increasing the annealing temperature at 500 °C.

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 400oC up to 800oC with 100 oC 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 oC of TiO2 thin film has a highest sensitivity at 350 oC operated temperature.

Zirconium Nitride (ZrN) thin films were prepared by dc reactive magnetron sputtering without an external substrate heating on silicon (100) wafer and glass slide. The as-deposited films obtained from different conditions and various films thickness was investigated for physical, optical and electrical properties. First, the microstructure and film morphology were examined by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM). The optical transparency was measured by UV-vis spectrophotometer. Finally, the electrical properties, based on measured resistivity, were studied by four-point probe. The result showed that the ZrN films were all well orientated in the (111) plane. When the film thickness was increased, the grain size was also increased. The effect of the film thickness was observed in the charge in colors and optical transmission of the films.

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.

Y-doped BaZrO3 (BYZ) pellets and thin films were fabricated by solid state reaction and co-sputtering technique, respectively. The conductivity of BYZ samples was measured using electrochemical impedance spectroscopy technique in the atmospheres of air, dry H2, and wet H2. As Y content increases from 6 at.% to 20 at.%, the increase of bulk and grain boundary conductivity is observed, while at 30 at.%, the conductivity starts to degrade. The activation energies in bulk and grain boundary are in the range of 0.28-0.40 eV and 0.91-0.96 eV, respectively. BYZ pellets have the highest proton conductivity at the Y doping concentration of 20 at.%. Furthermore, the dense and uniform BYZ thin films of 130-140 nm in thickness were obtained by co-sputtering technique. The conductivities of the BYZ thin films are about 10^3 - 10^4 times those of the pellet samples. The reason of the observed high conductivity is still under further investigation.

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.

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

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.

By incorporation of an achromatic three-reflection quarterwave retarder to a spectroscopic ellipsometer and application of appropriate calibration and error correction procedures, it has been possible to characterize real thin-film fluoride optical coatings that are inhomogeneous. The refractive index and its dispersion with wavelengths greater than 300–700 nm as well as the depth profile of voids in the film have been determined for AlF_3, CeF_3, HfF_4, LaF_3, ScF_3, and YF_3 films on vitreous silica substrates.

By incorporating an achromatic three-reflection quarter-wave retarder in a spectroscopic ellipsometer and applying appropriate calibration and error correction procedures it has been possible to characterize fully real fluoride and oxide optical coatings which are truly inhomogeneous. The refractive index and its dispersion with wavelength as well as the depth profile of voids in the films have been determined for AlF3, CeF3, HfF4, LaF3, ScF3, YF3, Al2O3, HfO2, Sc2O3, ThO2, Y2O3, and ZrO2films on vitreous silica substrates.