Diamond is a prospective electrode material for a number of applications providing efficient electron transport, high stability of electrolytic performance with time, a possibility for dye-sensitizing with photosensitive molecules, etc. It can be functionalized with electron-donor molecules, like phthalocyanines or porphyrins, for the development of light energy conversion systems. For effective attachment of such molecules, the diamond surface has to be modified by plasma- or photo-chemical processes in order to achieve the desired surface termination. In the present work we have investigated the immobilization of diverse phthalocyanines (Pc) on nanocrystalline diamond (NCD) surfaces with different terminations. The NCD films have been prepared by hot filament chemical vapor deposition (HFCVD) on silicon substrates and thereafter subjected to modification with O₂ plasma for exchange of the H-termination of the as-grown surface. The effectiveness of the modification was studied by contact angle measurements and X-ray photoelectron spectroscopy (XPS). The as-grown and the modified NCD surfaces were exposed to phthalocyanines with different metal centers (Ti, Cu, Mn) or with different side chains. The results of the Pc grafting were characterized by XPS and Raman spectroscopy. XPS revealed the presence of the nitrogen stemming from Pc molecules and traces of the respective metal with ratios close to those in the applied Pc. As a next step the Raman spectra of Ti-Pc, Cu-Pc and Mn-Pc were obtained with two different excitation wavelengths (488 and 785 nm) from droplet samples on Si after evaporation of the solvent in order to establish their Raman fingerprints. The major differences in the spectra can be assigned to the effect of the size of the metal ion on the structure of the phthalocyanine ring. The obtained spectra were used as references for the Raman spectra of NCD surfaces grafted with Pc.

We report on a systematic study of hydroxyl-containing polyimide (PI)-TiO₂ nanoparticles (NPs) hybrid dielectric materials, to determine the effects of TIO₂ NPs loadings (X) for X = 0, 2, 5, 8, 10, 13 and 15 wt%, on p-type pentacene organic thin film transistors (OTFTs). A condensation reaction to produce well-dispersed TIO₂ NPs within the PI matrix was followed by spin coating to form a dielectric thin film directly on a silicon substrate. The thermal, optical, surface, dielectric, and electrical properties of the PI-TiO₂ hybrid dielectric composite correlated to TiO₂ content for each sample. The hybrid dielectric composites exhibit tunable insulating properties, including high dielectric constant, high capacitances, and low leakage current densities. Bottom-gate top-contact OTFTs fabricated using various PI-TiO₂ hybrid dielectrics, exhibit low threshold voltages, moderately high field-effect mobility rates, and high ON/OFF ratios. This study opens a route towards transparent and highly stable hybrid dielectric materials with tunable dielectric properties, by careful selection of NPs and polymer matrix combinations.

Optical thin films are a valuable component in optical systems and can determine the spectral band-pass of the system. Metal fluorides are known for their high transmittance from the ultraviolet (UV) to the infrared (IR). Magnesium Fluoride (MgF₂) is one of the most commonly used metal fluorides, primarily as an anti-reflection coating for glass lenses for visible wavelengths and additionally as a protective overcoat to prevent oxidation of metallic mirrors. The latter use is important to the astronomical community, where metallic mirrors are commonly used to enable high efficiency optical systems for remote sensing of astronomical objects. Very thin layers of transmissive MgF₂ may serve as an overcoat for aluminum to potentially provide high reflectivity from 90 – 2,000 nm. We are developing thin layers of MgF₂ by Atomic Layer Deposition (ALD) to assess their potential use for future astronomical satellite missions. We present characterization of optical, mechanical and chemical properties of ALD MgF₂ on silicon wafers. Results include measurements of reflectance from 90 – 800 nm, surface roughness, adhesion tests and etch rate tests.

In this study, we investigated the electrical, optical and structural properties of aluminum-doped ZnO (30 nm)/Copper (5-20 nm)/ aluminum-doped ZnO (30 nm) multilayer thin films on glass substrate deposited by rf and dc magnetron sputtering. The prepared AZO/Cu/AZO films were having the optimization of low resistivity of 6.72 × 10^-6 Ω-cm, mobility of 10.45 cm²/V-s and carrier concentration of 6.152 × 10²² cm^-3 at the Cu layer thickness of 20 nm. Maximum transmittance of 73.52 % at 610 nm wavelengths and Haacke figure of merit (FOM) are 1.16 × 10^-3 Ω^-1 (380-780 nm) of AZO/Cu/AZO films with the Cu layer thickness of 8 nm have been well demonstrated. These results indicate that the AZO/Cu/AZO films are a promising transparent conductive electrode scheme for various display applications.

For transparent electrode applications in thin-film solar cells, the textured surface structure formed on impurity-doped ZnO thin films must induce a significant scattering of incident visible and near-infrared light. This paper describes a comparative study of optical and electrical properties in surface-textured Al-doped ZnO (AZO) films formed by using various techniques. The transparent conductive AZO films were prepared on glass (OA-10) substrates by direct current magnetron sputtering (dc-MS) and radio frequency power superimposed dc-MS (rf+dc-MS). We used four surface texture formation techniques as follows: (a) formation by post-etching c-axis oriented AZO films deposited by MS, (b) formation during the crystal growth of AZO films deposited by MS under conditions suppressing c-axis orientation, (c) formation by post-etching the surface-textured AZO films grown in case (b), and (d) formation by post-etching the surface-textured AZO films resulting from the deposition of the case (b) AZO films onto the case (a) AZO films. In case (a), AZO films were prepared at a sputter Ar gas pressure of 0.6 Pa and a substrate temperature of 200^oC. In case (b), surface-textured AZO films were first prepared at a sputter Ar gas pressure of 12 Pa and a substrate temperature of 350^oC, and then the films were heat treated in a H₂ gas atmosphere for 30 min. In case (d), low resistivity AZO films with a thickness of 1μm were first deposited under the same conditions used in case (a), and then surface-textured AZO films were deposited onto the case (a) AZO films. The textured surface structure formed by case (a) features relatively large etch pits (crater-like) with diameters in the range of 1-2μm, resulting from a wet-chemical etching (in a 0.1% HCl solution at 25^oC). In case (b), the rough textured surface structure resulting on AZO films features wedge-shapes (pyramidal) with an average size below 1μm, which increased as the film thickness was increased up to 3.5μm. In case (c), the resulting structure features a double texture that combines the crater-like and pyramidal surfaces. However, it should be noted that both the surface-textured AZO films formed in cases (b) and (c) were found to exhibit low optical transmittance (or high absorption) near the band edge. Although the transmittance of the surface-textured AZO films was improved by decreasing the thickness, the resulting sheet resistance increased. The results of case (d) show that a double textured surface as well as a low sheet resistance could be achieved in surface-textured AZO films.

Silicon nitride has been widely studied due to their physicochemical properties, which have allowed it to be used in applications such as mechanical components of motors, bearings and cutting tools; electronic: microelectronic devices and charge storage memories; and electro-optics: antireflective coatings of solar cells. The work reported in the literature shows that silicon nitride films are mainly deposited using the sputtering technique in reactive phase. In this work we have grown films of Si_xN_y from a target with Si₃N₄ stoichiometry by RF magnetron sputtering technique on common glass substrates, with two mainly objectives: 1. to characterize the chemical composition based on the deposit parameters (electric power applied to the target, argon flow and substrate temperature), and 2. Relate the chemical composition with the optical response of the films.

In this study, hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared using ICP-CVD system attached with four internal U-shaped low inductance antennas. Ar, He, and Ne gases were introduced into SiH₄/H₂ plasma during deposition, with the variation of gas flow rate and SiH₄/H₂ ratios. During deposition, an OES (optical emission spectrometer) and a plasma probe were used to characterize the conditions of plasma. The crystalllinity, structure, and Si-H bonding of these Si:H films were investigated using Raman scattering spectroscopy, XRD, and FTIR. The correlations of plasma characteristics and thin film properties were studied. It is found that the crystallinity of nc-Si:H film increases with the introduction of Ar, He, and Ne gases, especially when Ar is added. The plasma density and I_H* increase with the increase of the inert gases, most likely due to penning ionization effect. The deposition rate decreases with the inert gases. This might be caused by the enhancement of hydrogen etching.

Noble metals such as gold and silver have been used traditionally as metallic components in plasmonic and metamaterial devices. However, conventional metals with high carrier concentrations are not suitable for near infrared (IR) plasmonic applications due to their relatively large optical losses, which are detrimental to the performance of plasmonic devices. Thus, it is necessary to develop less metallic materials (i.e., lower carrier concentrations) as an alternative for traditional metals in the near IR. Transparent conducting oxides (TCOs) have been recognized as low loss metallic components for plasmonic and metamaterials applications in the near IR. Through doping, the optical loses of these TCOs can be reduced over four times below what is achievable with conventional metals in the near IR. We have investigated various types of TCOs, such as Al-doped ZnO, Ga-doped ZnO, Sn-doped In₂O₃, and F-doped SnO₂ using pulsed laser deposition. We will present details on the synthesis and optimization of these TCOs along with TCO-based plasmonic devices.

This work was funded by the Office of Naval Research (ONR) through the Naval Research Laboratory Basic Research Program.

Chalcopyrite Cu(InGa)Se₂ (CIGS) solar cells have been considered as the most promising thin film solar cell, recently reporting the highest cell efficiency of 20.8% (ZSW, 2013) using 3-stage co-evaporation process and 20.9% (Solar Frontier, 2014) using two-step metal sputtering followed by selenization while efficiency of multi-crystalline Si solar cells remained 20.4%. However, process time of both processes, i.e., 3-stage co-evaporation process and two-step metal sputtering followed by selenization, is known to be still too long.

Recently, the various transparent electrode (TE) materials, such as carbon nanotube (CNT), graphene, conductive polymer, and metal mesh, have been researched in order to replace the conventional indium-tin-oxide (ITO). Generally, in the case of electrode made of single material, there is a limited for replacement of ITO because of insufficiency properties of each material. For instance, CNTs have excellent visibility, chemical and mechanical stability, but they have a high sheet resistance because of a high contact resistance of the tube-tube junction. Metal meshes have some advantages such as lower sheet resistance and high transmittance, but they have the problem of low visibility due to high reflectance and oxidation. Conductive polymer materials reveal color problem and are sensitive to humidity. To overcome these problems that those materials have, hybrid-type TEs have attracted much interest. For instance, hybrid electrodes composed of aluminum-zinc-oxide (AZO) and multi-walled CNTs (MWNTs) were fabricated, which led to the reduction in sheet resistance. Graphene-silver nanowire hybrid electrodes were prepared via self-assembly method, which provided highly controllable transmittance and surface electrical resistance. Also, our group fabricated hybrid-type TEs using PEDOT:PSS-coated CNTs and characterized their electrical, optical, and color properties for touch screen panels.

In this study, the hybrid-type electrodes have been fabricated by coating the CNTs on the metal meshes and their characteristics for the use of flexible TEs have been examined. The surface and cross-sectional morphologies were inspected using a field-emission scanning electron microscope (FE-SEM, SIGMA, Carl Zeiss). The electric sheet resistance was measured using a four-point probe (Chang Min Tech, CRT-SR-100), and the optical properties, such as transmittance, reflectance, and haze, were measured using a spectrum colorimeter (Konica Minolta, CM-5). Also, flexibility inspection (bending tester, JUNIL TECH, JIBT-200) was performed for a total of 30,000 times with a 12 mm bending radius and a 40 mm/s bending speed at normal temperature and pressure. Stability test was also conducted by measuring the sheet resistance variations of the manufactured hybrid TEs for a long period of 250 h under the conditions of the temperature of 85 °C and the humidity of 85 %. All the measured results were analyzed as functions of the fabrication conditions. The results obtained in this study confirmed that the fabricated CNTs/metal mesh hybrid electrodes possessed desirable properties as flexible TEs for touch screen panels.

Tungsten Oxide (WO₃) films and low-dimensional structures have proven to be promising candidates in the fields of optics and electronics. WO₃ is a well-established n-type semiconductor characterized by unique electrochromic behavior, an ideal optical band gap that permits transparency over a wide spectral range, and high chemical integrity. The plethora of diverse properties endow WO₃ to be highly effective in applications related to electrochromism, gas sensing, and deriving economical energy. Compared to the bulk films, a materials system involving WO₃ and a related species (elements or metal oxides) offer the opportunity to tailor the electrochromic response, and an overall enhancement of the physio-chemical and optical properties. In the present case, W-Ti- composite oxide films have been fabricated by co-sputtering titanium and tungsten metal targets employing DC sputtering. The films were grown at room temperature and based on the growth kinetics and sputtering behavior of the metals the sputtering power for Ti was kept constant at 50 W, and the W power was varied from 50 W to 150 W in order to obtain films with variable W-content. The behavior of the refractive index ‘n’ demonstrates an increase at λ<400 nm typical of the energy absorption across the bandgap. In the visible spectrum ‘n’ decreases with increasing W-power, however higher than 120 W the ‘n’ behavior increases. At λ>800 nm the ‘n’ behavior increases with increasing W-power. The extinction coefficient shows a similar trend, this optical behavior is attributed to additional photon absorption resulting from the increase in W-power which demonstrates a more metallic behavior in the optical data as well as in the physical appearance of the films. Correlating with band gap measurements, the band gap values for W-power less than 110 W are all above 3.0 eV as the power is increased to 150 W the band gap values decreased confirming a stronger metallic behavior of the films with increasing W-power.

Silicon zinc oxide (SZO) thin films have been deposited by co-sputtering and the thin film

transistors (TFTs) using the SZO film as the active layer have been fabricated with the bottom-gate configuration. Two kinds of post-treatment, such as furnace-annealing and hot-pressing, have been carried out on the deposited SZO films. The effects of post-treatment on the crystalline structure, chemical bond, surface roughness, and optical transmittance of the deposited SZO films have been analyzed as functions of the post-treatment conditions used. The electrical characteristics of the fabricated SZO-TFTs have also been measured and compared before and after the post-treatment being conducted. The on-off current ratio of the SZO-TFT has been improved by low-temperature (200 oC) furnace-annealing. The hot-pressing method would also be favorable in that the electrical characteristic of the SZO-TFT can be improved nearly similar to the case of carrying out the furnace annealing with the process time of about 60 min in spite of its short process time for about 30 s.

Carbon nanotubes (CNTs) are considered as an ideal candidate for use in flexible electrodes due to their unique properties such as chemical stability, thermal conductivity, mechanical strength, and flexibility. For the application of CNTs to flexible electrodes, however, they still have problems which should be overcome been limited of application for flexible transparent electrode. One of them is the relatively high contact resistance caused by tube-tube junctions in CNTs. To improve the electric characteristics of CNTs, various types of hybrid electrodes have been studied. It has been reported that the electric characteristics of CNTs, with which the conductive polymer is mixed, can be improved as the conductive polymer plays a role in decreasing the contact resistance of tube-tube junction. However, the conductive polymer material is generally known to be tinged with blue. Also, the properties of polymer-CNTs electrodes may be sensitive to the methods and conditions used for the preparation of the polymer materials. Furthermore, the coating of polymer films on CNTs may decrease the transmittance and visibility of the electrodes.

Recently, many zinc-oxide based thin-film transistors (ZnO-TFTs) have shown specific characteristics for transparent displays. M ost of the successful ZnO-based TFTs incorporate indium (In) such as indium zinc oxide (IZO), indium hafnium zinc oxide (IHZO), and indium gallium zinc oxide (IGZO). However, In is expensive and relatively rare on Earth. So recently, some researchers have reported experimental results which demonstrate new In-free or Ga-free oxide semiconductors, such as silicon-zinc-oxide (SZO), aluminum-zinc-oxide (AZO), and gallium-zinc-oxide (GZO). It is believed that aluminum (Al, group III) element acts as effective donors in the ZnO lattice. Because they may be substitutionally placed on Zn sites and will then enhance the carrier concentration and conductivity. Also, hafnium (Hf, group IV) is stable at high temperature stress and bias stress in ZnO lattice. Until now, however, there has been a scarcity of comprehensive studies on the hafnium-aluminum-zinc-oxide (HAZO) films and their applications for TFTs.

BaTiO3 is one of the most studied ferroelectric materials for its potential applications in electro-optical switching as well as piezoelectric actuation, among variety of other applications. However, few challenges, such as temperature stability and film growth rate should be overcome for widespread applications. BaTiO₃ thin film grown by RF-magnetron sputtering often encountered re-sputtering due to the accelerated negative oxygen ions (O^-), which could significantly alter the stoichiometry (micro-effect) of the deposit, and at higher power densities result in complete suppression of film growth (deposition rate = re-sputtering rate) and even substrate etching (deposition rate < re-sputtering rate). Using optical emission spectroscopy of depositing plasma, we have established an operation parameter range for the power density on the target, where the detrimental effects of negative ions (O-) could be minimized. For optimal power density range, we have also studied the role of oxygen- argon mixing ratio (0 to 100%) and operation pressure on structure of the deposited film using XRD and XPS characterization techniques. Study of the effects of deposition temperature on structure of thin film deposited on SrTiO₃ (001) and platinized silicon substrates are in progress. Additionally, surface morphology, ferroelectric and dielectric properties of these films will also be studied and results will be presented.

The carbon films have been synthesized by chemical vapor deposition (CVD) on AISI304 stainless steel (304SS) sheets with various C₂H₂/H₂ flow ratios at 810^oC. The films exhibit three different morphologies: filament (C25), sphere (C150) and transition types (C70) at different C₂H₂/H₂ flow ratios, as characterized by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. It was found that the degree of graphitization increases with decreasing C₂H₂/H₂ flow ratios. Activated carbon and conductive carbon were plated on different types of carbon coated 304SS sheets and 304SS as the electrodes for electric double layer capacitor (EDLC). The electrochemical properties of these electrodes were investigated. The capacitance of the C70 electrode with the transition type carbon film current collector is 37.5 % higher than that of the electrode without carbon film in high current density (12 A/g). The results also indicate that the transition type carbon film efficiently improves the performances of high current density charge-discharge, which can be attributed to the reduction of contact resistance measured by electrochemical impedance spectroscopy.

Recently, the climate change issue stimulates people to consider the environmental impacts of materials fabrication processes. There are only very few studies that have noticed the impacts of materials fabricated by different process and applied to various systems.

In this work, two photocatalytic TiO₂ thin films on pure Ti substrates fabricated by anodic oxidation (AO) and plasma electrolytic oxidation (PEO), respectively, were studied. Microstructures and crystalline phases of TiO₂ nanotube (TNT) thin films by AO process and porous TiO₂ thin films by PEO treatment were investigated. The water treatment ability of two different TiO₂ thin films was evaluated by methylene blue (MB) degradation test. The MB photocatalytic degradation rate was measured and the photocatalytic reaction rate was calculated. Effects of processing parameters on the photocatalytic ability were further discussed. In addition, the environmental impact assessments of two TiO₂ thin films were conducted by the life cycle assessment (LCA) method. Environmental impacts yielded from fabrication and application stages were integrated to assess the total impact under different assume conditions, or scenario. For the LCA method, the time and reaction surface area required for two different TiO₂ thin films to degrade the MB concentration from 2×10^-5 M to 2×10^-6 M in 6 m³ water were estimated. Two scenarios, 90 and 9000 cm² of TiO₂ thin film area were set to treat MB in water. It was showed that the environmental impact of the TiO₂ fabricated by AO were 300 times more than that fabricated by PEO during the fabrication stage; however, the relationship was opposed during the application stage. When the scenario of surface area changed from 90 to 9000 cm², increases of environmental impact by 38% and 95% were found for PEO and AO fabrication processes, respectively. It can be concluded that the systematic LCA developed in this study provided a good alternative selection for an environmentally friendly water treat method.

The perylene dyes are excellent electron acceptors and the properties mainly depend on the substitution at multiple positions of the perylene chromophore². The bay/core positions are much more effective in manipulating the electronic properties of these dyes. The possibility of substitution leading to bay-substituted perylene diimides and polyimides is another advantage to manipulate the thin-film properties of various perylene derivative materials.

In this study, novel bay-substituted perylene diimides and perylene polyimides have been synthesized in high yields and characterized by UV-Vis, IR, Fluorescence Spectroscopy, NMR, DSC, TGA and CV measurements. The prevention of face-to-face π-π stacking in the designed bay-substituted perylene dyes gave enhanced solubility when compared to the imide-substituted perylene dyes^2,3. This makes the thin-film studies easier to explore the potential of the synthesized perylene dyes in OFETs. Accordingly, we reported the thin-film studies in detail along with the electronic properties which were studied through CV and square wave measurements. Importantly, we also reported the optical properties in detail as they are potential candidates for constructing organic light-emitting field effect transistors.

References:

1. J.B. Bodapati, H. Icil, Dyes Pigm. 2008, 79, 224.

2. E. Fron, G. Schweitzer, P. Osswald, F. Würthner, P. Marsal, D. Beljonne, K. Müllen, F.C.D. Schryver, M.V.D. Auweraer, Photochem. Photobiol. Sci., 2008, 7, 1509.

3. A.C. Grimsdale, K.L. Chan, R.E. Martin, P.G. Jokisz, A.B. Holmes, Chem Rev., 2009, 109, 897.

In the present work, Titanium (Ti) thin films of thickness (~11-1650 nm) have been successfully deposited onto glass substrates at room temperature by direct current (DC) magnetron sputtering technique. Thickness was varied by regularly increasing the deposition time, keeping all the other deposition parameters constant. The effect of thickness on the films have been studied for their structural, morphological and optical properties using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Atomic force microscopy ( AFM) techniques and Variable angle spectroscopic ellipsometry (VASE). The most universal and reliable method of determining the optical constants of metal thin films is Ellipsometry. The XRD analysis exhibited hexagonal closed packed (hcp) crystalline structure with predominant (100) crystallite orientation and an additional (002) orientation particularly. The experimental results revealed a systematic grain growth with increasing film thickness, along with enhanced film crystallinity . The average particle size and surface roughness in the films varied with the film thickness. It has been observed that maximum near infrared absorption coefficient occurs in the film exhibiting large thickness (~1650 nm), which may be associated with more light interaction path. All the films exhibit optical properties with the laser wavelength depending strongly on the thickness of the film. Enhancement and manipulation of near infrared light absorption in titanium film is a significant issue for applications of titanium-based optoelectronic and advanced photonic devices. The results are far-reaching with particularly promising opportunities for Nd-YAG laser based applications also.

A vanadium dioxide (VO₂) thin film shows a reversible phase transition (PT) between an insulating state and a metallic state, which is induced by temperature, pressure, light, and so forth. Electric field can also trigger the PT in a two-terminal device based on a VO₂ thin film, showing the highly nonlinear current-voltage behavior. An optical stimulus facilitates the electric-field-induced PT and even triggers the PT. Here, by utilizing a 10.6mm CO₂ laser as an optical stimulus, we demonstrated bidirectional current switching in a two-terminal planar device based on a highly resistive VO₂ thin film. The bidirectional current switching implies that the device resistance is changed according to the switched state of the laser, that is, high or low device current flows with the laser switched on or off. Two-terminal devices based on VO₂ films grown by pulsed laser deposition were fabricated through etching and metallization processes. To optically stimulate the VO₂ film, the CO₂ laser beam was focused with an aspheric lens, and the focused beam illuminated the film of the device. The bidirectional current switching of up to 20 mA was realized by switching on or off the CO₂ laser illuminating the film. The transient responses of laser-triggered currents, which were obtained in a circuit composed of a standard resistor, a DC voltage source, and the VO₂ device, were analyzed when periodical laser pulses activated the device at various pulse widths and repetition rates. A switching contrast between off-state and on-state currents was measured as ~7067 with an off-state current of ~2.83 mA, and rising and falling times were measured as ~30 and ~16 ms, respectively, for 100 ms laser pulses.

[Acknowledgments] This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT and future Planning(2013R1A2A2A01068390).

ABO₃-type perovskite oxides, where A and B denote two different cations, have recently attracted a great interest for their potentials in oxide-based electronics, because of their multifunctional opto-electronic properties including their high optical band gap and dielectric constants. Among several perovskite thin films BaSrTiO₃ (BST) thin films are key elements for the development of high performance electronic devices, and their reliability and efficiency depend strongly on the precise knowledge of microstructure, as well as optical and electrical constants. Furthermore, the possibility of controlling the dielectric properties of BST thin films by optimization of the deposition conditions also brought new opportunities in emerging device applications. BST films have been deposited by chemical vapor deposition, sol-gel and sputtering techniques. Although numerous studies on BST thin films were reported in the recent years, the efforts mainly concentrated on the determination of a single physical property (i.e. either structural, optical, or electrical properties), and the correlation between multifunctional properties therefore remained unexplored. In the present work, we have deposited BaSrTiO_x films with rf magnetron sputtering technique at room temperature on UV fused silica and Si substrates. The dependences of film microstructure, surface morphology, absorption edge, refractive index, and dielectric constants on deposition pressure, partial oxygen flow and the post-deposition annealing were examined by grazing-incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), spectrophotometry, ellipsometry, as well as photoluminescence, capacitance-voltage and current-voltage measurements. Well-adhered, uniform and amorphous films were prepared at low deposition temperatures. For all as-deposited films, the average optical transmission was ~85% in the visible and near infrared spectrum. The refractive indices of BST films were in the range of 1.90-1.98 (λ = 550 nm) as a function of deposition conditions. Post-deposition annealing at 800 ^oC for 1 h considerably lowered the optical transmission, and the absorption edge shifted to VIS spectrum indicating lower optical band gap. Metal-insulator-semiconductor (Ag/BST/p-Si) diodes were fabricated and characterized by capacitance-voltage and current-voltage measurements. Initial results revealed that low-temperature-grown BST thin films have promising properties for device applications.