Heteroepitaxial InP films have been grown on GaAs substrates to study the effects of the nucleation layer`s surface roughness on the epitaxial layer`s quality. For this, InP nucleation layers were grown at 400℃ with various ethyldimethylindium (EDMIn) flow rates and durations of growth, annealed at 620℃ for 10 minutes and then InP epitaxial layers were grown at 550℃. It has been found that the nucleation layer`s surface roughness is a critical factor on the epitaxial layer`s quality. When a nucleation layer is grown with an EDMIn flow rate of 2.3 μmole/min for 12 minutes, the surface roughness of the nucleation layer is minimum and the successively grown epitaxial layer`s qualities are comparable to those of the homoepitaxial InP layers reported. The minimum full width at half maximum of InP (200) x-ray diffraction peak and that of near-band-edge peak from a 4.4 K photoluminescence are 60 arcmin and 6.33 meV, respectively.

The dependency of processing pressure on the electrical performances in amorphous silicon -zinc-tin-oxide thin film transistors (SZTO-TFT) has been investigated. The SZTO channel layers were deposited by using radio frequency (RF) magnetron sputtering method with different partial pressure. The field effect mobility (μFE) increased and threshold voltage (Vth) shifted to negative direction with increasing pressure during deposition processing. As a result, oxygen vacancies generated in SZTO channel layer with increasing partial pressure resulted in negative shift in Vth and increase in on-current.

Room temperature powder spray in vacuum process, so called Aerosol deposition (AD) is a room temperature (RT) process to fabricate thick and dense ceramic films, based on collision of solid ceramic particles. This technique can provide crack-free dense thin and thick films with thicknesses ranging from sub micrometer to several hundred micrometers with very fast deposition rates at RT. In addition, this technique is using solid particles to form the ceramic films at RT, thus there is few limitation of the substrate and easy to control the compositions of the films. In this article, we review the progress made in synthesis of piezoelectric thin/thick films, multi-layer structures, NTC thermistor thin/thick films, oxide electrode thin films for actuators or sensor applications by AD at Korea Institute of Materials Science (KIMS) during the last 4 years.

Ordered mesoporous oxide films have been focused because of their low density, high interior specific surface area, and high thermal insulation. Specially, the ordered mesoporous oxide films prepared by self-assembly has many advantages due to easy process and high reproducibility. In this work, ordered mesoporous SiO2, Al2O3, and TiO2 films were synthesized by control of composition and processing parameter. Also, their structural, thermal, and mechanical properties were characterized variously. In conclusion, ordered mesoporous oxides will be one of core materials in new technology due to their excellent and unique properties.

The powders for the NaxWO3 (x= 1 and 0.75) sputtering targets were synthesized by the calcination in reductive atmosphere. Near single-phase NaWO3 and single-phase Na0.75WO3 powder targets were prepared. By using the targets, thin films of each composition were deposited by rf magnetron sputtering on the SiO2 (100 nm)/Si substrates and annealed by RTP (rapid thermal processing) for crystallization. In the case of the NaWO3 composition, single-phase NaxWO3 thin films, where x was believed to be slightly less than 1, were fabricated accompanying the Na-diffusion into the substrates during RTP. However, in the case of the Na0.75WO3 thin film preparation, it was unable to make single-phase thin films. From the phase formation behaviors of both powders and thin films, it was revealed that NaxWO3 with nonstoichiometric composition of x, which was slightly less than 1, was favorable. The good electrical conduction properties were obtained from the single-phase NaxWO3 thin films. Their electrical resistivities were as low as 7.5 × 10-4 Ω·cm.

In this study non-stoichiometric (K0.5Na0.5)0.97(Nb0.96-xTaxSb0.04)O3 ceramics were prepared by the conventional soild-state teaction method. The effect of Ta-substitution on the dielectric and piezoelectric properties were investigated. X-ray diffraction analysis of all the specimens less than x= 15 mol% indicated orthorhombic phase. Thereafter, the specimens showed orthorhombic phase near to pseudo-cubic. Sinterablity of all the specimens was improved due to secondary products such as KCT and KCN. The ceramics with x= 5 mol% showed the optimum velues of pizoelectric constant(d33)= 150 pC/N, electromechanical coupling factor (kp)= 0.45, electromechanical quality factor (Qm)= 418.9 and dielectric constant(εr)= 567. Accordingly, These results indicate that the composition ceramics is a promising candidate for lead-free material.

Oxides possess several interesting properties, such as ferroelectricity, magnetism, superconductivity, and multiferroic behavior, which can effectively be used oxide electronics based on epitaxially grown heterostructures. The microscopic properties of oxide interfaces may have a strong impact on the electrical transport properties of these heterostructures. It was recently demonstrated that high electrical conductivity and mobility can be achieved in the system of an ultrathin LaAlO3 film deposited on a TiO2-terminated SrTiO3 substrate, which was a remarkable result because the conducting layer was at the interface between two insulators. In this study, we observe that the current-voltage characteristics exhibit LaAlO3 thickness dependence of electrical conductivity in TiO2-terminated SrTiO3. We find that the LaAlO3 layers with a thickness of up 3 unit cells, result in highly insulating interfaces, whereas those with thickness of 4 unit cells and above result in conducting interfaces.

The sol-gel method has been widely used to synthesize the TiO2 for dye sensitized solar cells and has advantages of easily fabrication process, controlling the TiO2 phase and getting transparent thin-film composed of the TiO2. In this paper, we synthesized the crystalline TiO2 by sol-gel method controlled by the quantity ratio of Nitric acid and Ammonium hydroxide additives. The best efficiency result was obtained by 0.05 M Ammonium hydroxide and that results of Voc, Jsc, FF, and efficiency were 0.68 V, 3.28 mA/cm2, 58.14 and 5.21%, respectively.

SnO2 nanoparticles were synthesized by flame spray pyrolysis, which were directly deposited on Pt interdigitated substrates. Gas sensing performance was evaluated for various gases such as H2, CO, H2S, and NH3, and it was compared with that of commercial SnO2 nanopowder. The synthesis of SnO2 nanoparticles was also conducted in various solvents. As a result, the primary particle size was changed with the solvent of precursor solution, and their H2 sensing properties were significantly affected.

The prepartion of various metal oxide nanostructures via hydrothermal method, hydrolysis, thermal evaporation and electrospinning and their applications to chemoresistive sensors have been investigated. Hierarchical and hollow nanostructures prepared by hydrothermal method and hydrolysis showed the high response and fast responding kinetics on account of their high gas accessibility. Thermal evaporation and electrospinning provide the facile routes to prepare catalyst-loaded oxide nanowires and nanofibers, respectively. The loading of noble metal and metal oxide catalyst were effective to achieve rapid response/recovery and selective gas detection.

Embossed TiO2 thin films with high surface areas are achieved using soft-templates composed of monolayer polystyrene beads. The form of links between the beads in the templates is controlled by varying the O2 plasma etching time on the templates, resulting in various templates with close-linked, nano-linked, and isolated beads. Room-temperature deposition of TiO2 on the plasma-treated templates and calcination at 550℃ result in embossed films with tailored links between anatase TiO2 hollow hemispheres. Although all the embossed films have similar surface areas, the sensitivity of films with nano-linked TiO2 hollow hemispheres to 500 ppm CO and ethanol gases are much higher than that of films with close-linked and isolated hollow hemispheres, and the detection limits of them are as low as 0.6 ppm for CO and 0.1 ppm for ethanol. The strong correlation of sensitivity with the form of links between hollow hemispheres reveals the critical role of potential barriers formed at the links. The facile, large-scale, and on-chip fabrication of embossed TiO2 films with nano-linked hollow hemispheres on Si substrate and the high sensitivity without the aid of additives give us a sustainable competitive advantage over various methods for the fabrication of highly sensitive TiO2-based sensors.

Multifunctional structures with two kinds of materials have been intensively investigated in order to improve their electrical characteristic with two functions simultaneously. However, the research regarding of multifunctional ceramic sensor is still in a preliminary stage and how to integrate them with low-cost and high-yield mass production process remains a challenge issue. In this study, we fabricated the multifunctional ceramic sensor composed of temperature and gas sensors. Moreover, we investigated the CO sensing properties of three dimensional nanostuctured Nb2O5 thin film gas sensors fabricated with silica (SiO2) nanosphere (Ø= 750 nm). Compared to plain films, the nanostructured films show enhanced gas sensing of greater sensitivity and a faster response. This result reveals that significantly increased sensitivity is an increase in the effective surface area for the adsorption of gas molecules.

A study on capacitive characteristics of stylus pen for touch panel are progressed in this paper. Also the main factors for capacitive sensitivity are studied. Namely, highly sensitive stylus pen which can be applied to capacitive touch panel are studied based on the analysis of materials and process conditions regardless of pattern shapes. Stylus pen was made of PDMS(Poly-Di-Methyl-Siloxane) and conductive metal powders which does not damage the touch panel surface. We tried to get the advantages of both the properties of soft PDMS and conductive metal powders. We found that potential difference of capacitance change with conductivity of the composite materials(PDMS + metal powders) it implies that during touch process, large voltage difference can be caused by the high conductive materials of stylus pen. Stylus pen made by PDMS with mixed with Ag powders which has large conductivity shows more capacitance change of 1 pF than PDMS with other materials of Ni or C powders.

The spherical mesoporous silica is synthesized and incorporated with CdSe/ZnS quantum dots(QDs) for preparing micro beads to detect toxic and bio-materials with high sensitivity. The spherical silica beads with the brunauer-emmett-telle(BET) average pore size of 15 nm were prepared with a ratio 1, 3, 5-trimethylbenzen, as a swelling agent, to the block-copolymer template surfactant of over 1 and under vigorous mixing condition. The surface of spherical mesoporous silica is modified using octadecylsilane for incorporating QDs. Based on photoluminescence(PL) spectra, the relative brightness of mesoporous silica beads incorporated with 10 nM of QDs is 79,000 times brighter than that of Rodamine 6 G.

Nano-structured one-dimensional Na2Ti6O13 particles were synthesized by a molten salt process. Effects of processing parameters on the microstructure and band gap energy of the Na2Ti6O13 powder were studied in this paper. For the synthesis of the Na2Ti6O13 particles, two different raw materials of tubular shaped Na-titanate (Na-TiNT) and spherical shaped TiO2 were utilized. Synthesizing with the raw material of Na-TiNT, around 70nm thick 1D-Na2Ti6O13 with the bandgap energy of 3.5 eV was obtained at 810℃. Below 810℃ or without the presence of NaCl, 1D-Na2Ti6O13 was in a relatively short in length and agglomerated state. With the processing temperature increased, the thickness of the 1D-Na2Ti6O13 was also observed to be increased. On the other hand, when TiO2 was employed as a raw material, the mixed amount of Na2CO3 played an important role in transforming the morphology and phase of the raw material, affecting the bandgap energy of the synthesized product. Specific surface area of the synthesized 1D-Na2Ti6O13 was significantly affected by the raw and mixed materials as well as processing temperature. When Na-TiNT was processed at 810℃ with NaCl, the specific surface area of the 1D-Na2Ti6O13 showed the best value of 30.63 m2/g.