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Spectroscopic ellipsometry (SE) was used to characterize the effect of the CO2/SiH4 ratios on the p-type hydrogenated microcrystalline silicon oxide (p-μc-SiOx:H) thin films. The p-μc-SiOx:H thin films were fabricated by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) method on the soda-lime glass substrates. The CO2/SiH4 ratios were varied from 0.0 to 0.5 with constant H2-dilution during the deposition. The p-μc-SiOx:H samples were analyzed for thickness, microstructure, and optical characteristics by SE. The ellipsometric measurements were performed in the range of 0.75–5.5 eV with the incident angle of 50, 60 and 70 degrees. The physical structures were proposed as either the double- and triple-layer models. The optical dispersion was proposed based on Tauc-Lorentz (TL) model in order to extract the information of interest including dielectric dispersion and crystalline fraction. The results from the SE analyses showed that the thin films prepared with pure SiH4 could only be fitted by the triple-layer model, whose effect refractive index was gradually decreased from 3.92 to 2.53 with the increased CO2/SiH4 ratio. With the introduction of the CO2, the obtained films were instead best represented by the double-layer model. The calculated crystalline fractions could be determined from the SE results, which accurately corresponded to those from the Raman spectroscopy and high-resolution transmission electron microscope (HRTEM). In addition, the dielectric dispersion of the thin films was related directly with CO2/SiH4 ratios, but inversely with crystalline fraction with the values of 53 down to 18% with the increased gas mixture ratio.

Iron nitride (FeN) thin films were deposited on silicon wafer substrates by dc reactive magnetron sputtering techniques. The FeN thin films were prepared at the fixed substrate temperature 200°C under different nitrogen flow rates. The crystal structures, physical morphologies, and surface roughness of the prepared FeN thin films were characterized by the grazing-incident X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM), respectively. From the results, the GIXRD patterns indicated the change in the film orientations from ξ-Fe2N to γ”-FeN along with the increased nitrogen flow rates. In addition, the FE-SEM micrographs demonstrated the decrease of the FeN film thickness. The effects of the nitrogen flow rates towards the crystallinity, the physical morphology, and surface roughness of the thin films were investigated and discussed.

Highly responsive NO2 gas sensors at low operating temperature based on tin dioxide (SnO2) nanorods were successfully developed by DC reactive magnetron sputtering with the glancing angle deposition technique. Characterization results by grazing incident X-ray diffraction (GIXRD) and field-emission scanning electron microscopy (FE-SEM) showed that the as-deposited and annealed SnO2 nanorod structures exhibited rutile phase and crystallinity was improved after annealing at 300 and 400 °C. The gas-sensing results indicated that nanorod structure and annealing treatment provide significant improvement on NO2 response and selectivity against H2, H2S, ethanol and CO. As a result, 400 °C-annealed SnO2 nanorods exhibited a very high NO2 response of 5310 to 5 ppm NO2 at the optimal operating temperature of 150 °C. Thus, SnO2 nanorod prepared by sputtering with GLAD is a promising candidate for ultra sensitive and selective NO2 detection.

In this work, we report an ultrasensitive hydrogen (H2) sensor based on tungsten trioxide (WO3) nanorods decorated with platinum (Pt) nanoparticles. WO3 nanorods 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 WO3 nanorods with varying deposition time from 2.5 to 15 s. Crystal structures, morphologies, and chemical information on Pt-decorated WO3 nanorods 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 WO3 nanorods was investigated over a low concentration range of 150–3000 ppm of H2 at 150–350 °C working temperatures. The results showed that the H2 response greatly increased with increasing Pt-deposition time up to 10 s but then substantially deteriorated as the deposition time i...

With increasing air pollution problems, gas sensors for toxic gas detection have recently gained much attention. Among different types of gas sensors, thin film devices have been much of interest because of microelectronic batch-fabricated compatibility, reproducibility, and the ability to form multilayer device structures. In this work, thin film based gas sensors fabricated by electron beam evaporation with ion-assisted deposition (IAD) are developed for immediate applications of CO detection for environmental monitoring and Alcohol testing for drivers. The IAD process offers several advantages for gas sensor fabrication, including reactive deposition for gas-sensitive metal-oxide material optimization and improved thin film adhesion for better device reliability. Gas-sensing performance of ion-assisted electron beam evaporated metal oxide thin film materials, including SnO2 and WO3, has been characterized as a function of IAD deposition parameters. The metal oxide layer was deposited on Au/Al interdigitated electrodes on alumina or glass substrates with an unpatterned NiCr thin film heater on the backside. The sensors were tested with reducing gases, including alcohol vapour and CO, in the temperature range between 200 and 350 °C. Experimental results indicate that the SnO2 thin film has higher sensitivity to both alcohol and CO than the WO3 thin film under the same IAD deposition parameters. In addition, alcohol and CO sensitivity tends to improve with increased oxygen-ion addition during e-beam evaporation. Our results indicate that ion-assisted e-beam evaporation is a useful and well-controlled process suitable for gas sensor fabrication.

A nanostructural thin film is one of the highly exploiting research areas particularly in applications in sensor, photocatalytic, and solar-cell technologies. In the past two decades, the integration of glancing-angle deposition (GLAD) technique to physical vapor deposition (PVD) process has gained significant attention for well-controlled multidimensional nanomorphologies because of fast, simple, cost-effective, and mass-production capability. The performance and functional properties of the coated thin films generally depend upon their nanostructural compositions, i.e., large aspect ratio, controllable porosity, and shape. Such structural platforms make the fabricated thin films very practical for several realistic applications. We therefore present morphological and nanostructural properties of various deposited materials, which included metals, i.e., silver (Ag), and oxide compounds, i.e., tungsten oxide (WO3), titanium dioxide (TiO2), and indium tin oxide (ITO). Different PVD techniques based on DC m...

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 AlF 3 , CeF 3 , HfF 4 , LaF 3 , ScF 3 , YF 3 , Al 2 O 3 , HfO 2 , Sc 2 O 3 , ThO 2 , Y 2 O 3 , and ZrO 2 films on vitreous silica substrates

Spectroscopic ellipsometry has been utilized to non-destructively depth profile multi-ion beam reactively sputtered lead zirconate titanate films. Some degree of inhomogeneity (in the form of low density layers or surface roughness) was found in all of the films examined. The evolution in the structure and microstructure of such films during post-deposition annealing was investigated with in situ spectroscopic ellipsometry. It was found that the onset of microstructural inhomogeneities was associated with the crystallization of the perovskite phase, and that the final film microstructure was dependent on the details of the annealing process. A model was developed to approximate the effect that local density variations play in determining the net electrical properties of ferroelectric films. Depending on the configuration of the embedded porosity, it was demonstrated that microstructural inhomogeneities can significantly change the net dielectric constant, coercive field, and remanent polarization of ferroelectric films. It has also been shown that low density regions near the film/substrate interface can result in apparent size effects in ferroelectric films.

Electrochromic tungsten oxide thin films have been prepared by reactive dc‐magnetron sputtering under different deposition conditions. Through the use of electrochromic coloration and spectroscopic ellipsometry experiments, the effect of preparation conditions on film morphology and electrochromic properties has been studied. The results of this study are consistent with previous reports finding that amorphous tungsten oxide thin films are dominated by a columnar morphology and an intercolumnar void network that strongly influence the electrochromic properties. In addition real‐time spectroscopic ellipsometry (SE) experiments on the tungsten oxide electrochromic coloration process have been performed for the first time. In studies of very thin (∼15 nm) films by real‐time SE, the formation of tungsten bronze exhibits reaction‐limited kinetic behavior, and thus we are able to extract accurate dielectric function spectra for the film in different stages of the coloration process. These spectra can be understood in terms of a two‐phase physical mixture of tungsten oxide and tungsten bronze components with relative volume fractions determined in a regression analysis of the spectra.

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.

Studies of dielectric materials by rotating-element spectroscopic ellipsometry (SE) are beset with a number of problems such as (1) low reflectance and hence low signal-to-noise ratio and (2) an almost zero (or 1800) change in the ellipsometric parameter A on reflection from the sample, which leads to significant errors in the measured parameters. These difficulties were overcome (1) by developing suitable procedures for correcting nonlinearity in the detection system and the deleterious effects of ambient light and (2) by incorporating an achromatic quarter-wave compensator in the SE system, respectively. A new rapid method of aligning and calibrating the compensator has also been developed. Test measurements with such an SE system on a vitreous silica sample revealed that the accuracy of measurements of Δ and Ψ are 0.03° and 0.015°, respectively, over the spectral range of 300-700 nm. The SE data were then analyzed by standard procedures with linear regression analysis to determine the optical function n(λ) (i.e., refractive index and its dispersion with wavelength) of vitreous silica and at the same time to characterize the microroughness of the surface layer of the sample. The refractive index of vitreous silica determined by this technique is within ±0.0004 of the best reported values in the literature over the spectral range of 300-700 nm. The SE data obtained on the vitreous silica sample revealed the presence of a 1.0-nm-thick microrough layer on the surface of the sample.