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We report on the electrical characteristics of AlGaN/GaN high-electron mobility transistors (HEMTs) with hexagonal boron nitride (h-BN) as a passivation capping layer. The HEMTs with h-BN layers showed an increase in current drainage and 103-times reduction in the gate-leakage current compared with those of conventional unpassivated HEMTs. Moreover, the extrinsic transconductance and the pulse responses were improved due to the reduced charge-trapping effect at the surface of HEMTs. From our observations, the h-BN can be used as a passivation capping layer for high-power electronic devices.

Vanadium oxide (VOx) thin films were deposited by an unbalanced magnetron (UBM) sputtering system with a vanadium metal target and O₂ reaction gas, and thermally treated at various annealing temperatures. In this work, the structural, electrical, and optical properties of the fabricated VOx films with various annealing temperatures were experimentally investigated. The UBM sputter grown VOx thin films exhibited amorphous structure, and had a very weak peak of V₂O 5 (002) owing to very thin films. However, the crystallite size of VOx films increased with increasing annealing temperature. The surface roughness of VOx films and average transmittance decreased with increasing annealing temperature. The resistivity of VOx films also decreased with increasing annealing temperature, while the electrical properties of films improved.

Cr metal electrode was suggested as the working electrode material to fabricate DSSCs without the TCO, and thin films were fabricated by an unbalanced magnetron sputtering system. The surface morphologies show uniform and smooth surfaces regardless of various film thicknesses, and the small crystallites of various sizes were showed with the vertical direction on the surface of Cr thin films with the increase of film thickness. And also, the root mean square (RMS) surface roughness value of Cr thin films increased, and the sheet resistance is decreased with the increase of film thickness. The maximum cell efficiency of the TCO-less DSSC was observed when a Cr working electrode with a thickness of 80 nm was applied to the TCO-less DSSC. Consequently, these results are related to the result of the optimization of conduction characteristics, transmission properties and surface properties of Cr thin films.

Macro-porous tin oxide was prepared as an enhanced sensing material for sulfur compounds, such as hydrogen sulfide. Poly-methyl-methacrylate (PMMA) was used as a template for the formation of macro-pores. Tin chloride was used as a precursor for the synthesis of tin oxide, and was impregnated over PMMA beads using a rotary vacuum evaporator. The solid Sn/PMMA material was treated thermally for 4 h at 600 degrees C. The porous morphology of tin oxide prepared in this study was observed by scanning electron microscopy. The surface area of this material measured by the nitrogen adsorption method was approximately 56 m2/g. The crystal structure of the porous material analyzed by XRD was a typical structure of tin oxide. The response of macro-porous tin oxide as a chemical gas sensor was measured using an I-V source meter and the change in signal was observed with the repeated injection of hydrogen sulfide and air. The sensing tests for macro-porous tin oxide were carried out at 200 degrees C and the fast response of macro-porous sensing material was also confirmed.

Macro-porous Al2O3 as the catalytic support material was synthesized using colloidal polystyrene spheres over a micro-channel plate. The colloidal polystyrene spheres were used as a template for the production of an ordered macro porous material using an alumina nitrate solution as the precursor for Al2O3. The close-packed colloidal crystal array template method was applied to the formulation of ordered macro-porous Al2O3 used as a catalytic support material over a micro-channel plate. The solvent in the mixture solution, which also contained the colloidal polystyrene solution, aluminum nitrate solution and the precursor of the catalytic active materials (Rh), was evaporated in a vacuum oven at 50 degrees C. The ordered polystyrene spheres and aluminum salt of the solid state were deposited over a micro channel plate, and macro-porous Al2O3 was formed after calcination at 600 degrees C to remove the polystyrene spheres. The catalytic activity of the Rh/macro-porous alumina supported over the micro-channel plate was tested for diesel reforming.

Thin film transparent oxides have attracted considerable attention over the last few decades for transparent electronic applications, such as flat panel displays, solar cells, touch-pads, and mobile devices. Metallic doped InZnO (IZO) films have been suggested for the transparent layer exhibiting semiconducting or metallic properties because of its controllable mobility and excellent electrical properties, but they show a degradation of the electrical performance under bending conditions. This study assessed Ni doped IZO (NIZO) films as a flexible transparent electrode on different flexible transparent substrates for flexible electronic applications. Thin NIZO films were deposited on cellulose, PES and glass substrates using a sputtering system with a single NIZO target (In2O3 73.8/ZnO 15.7/NiO 10.5 mol.%) at room temperature. During deposition of the NIZO films, the total flow rate of the carrier gas was maintained using a regulating system. The effects of the oxygen content in the carrier gas on the structural, electrical and optical properties of the thin films deposited on flexible substrates was characterized. The results highlight the feasibility of the transparent NIZO oxide layer on flexible substrates as a flexible electrode with a relatively high sheet resistance, which is strongly related to the crystallographic structure and oxygen content during the film deposition process.

Optical properties of photonic crystal film were investigated by tuning photonic band gap (PBG). The lamellar-forming photonic films were prepared by nearly symmetric poly(styrene-b-2-vinyl pyridine) (PS-b-P2VP) block copolymers. Molecular weight of PS block and P2VP block is 52 kg/mol, and 57 kg/mol, respectively. When submerged in water, the lamellar films were swollen and show Bragg reflection in visible light region. We observed that the reflection color can be tuned by ion concentration (e.g., hydrogen or metal ion) in water. The higher concentration of hydrogen ion in solution, the longer reflectance wavelength shifted (from 537 nm to 743 nm). In addition, max-reflectance wavelength is dependent on both metal ion and the concentration. The max-reflectance wavelength is shifted from 653 nm (i.e., in water without ion) to 430 nm, 465 nm, and 505 nm for 120 mM of Ca2+, Fe2+, and Cu2+, respectively. Therefore, we can control the photonic band gap of photonic devices by changing the condition of swelling solution.

Optical and electrical characteristics of the devices using photonic gel film and hydrogel electrolyte were studied. Poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) lamellar film with alternating hydrophobic block and hydrophilic polyelectrolyte block polymers (52 kg/mol-b-57 kg/mol) were prepared for the photonic gel. Poly(isobutylene-co-maleic acid) sodium salts were prepared for the hydrogel. This hydrogel fiber is common water swelling material and it owned ions for a device has conductivity. Photonic gel and hydrogel was spin coating onto Indium-tin-oxide (ITO) glass for make electric fields. The reflectance maximum wavelength of photonic crystal device shifted from 538 nm and reached to 557 nm, 585 nm and 604 nm during 30 min voltage applying time. The bandwidth variation was very limited. Loss of electrolyte was much less with hydrogel compared to the pure water. We can control color of hydrogel used photonic device by electric field with reasonable time range under moderate electric field by applying 2 V between two facing electrodes.

In this study, pentacene organic thin film was prepared using newly developed organic material auto-feeding system integrated with linear cell and characterized. The newly developed organic material auto-feeding system consists of 4 major parts: reservoir, micro auto-feeder, vaporizer, and linear cell. The deposition of organic thin film could be precisely controlled by adjusting feeding rate, main tube size, position and size of nozzle. 10 nm thick pentacene thin film prepared on glass substrate exhibited high uniformity of 3.46% which is higher than that of conventional evaporation method using point cell. The continuous deposition without replenishment of organic material can be performed over 144 hours with regulated deposition control. The grain size of pentacene film which affect to mobility of OTFT, was controlled as a function of the temperature.

We synthesized bimetallic nanoparticles and used them to grow CNTs with an atmospheric-pressure plasma-enhanced chemical vapor deposition system. FePt and FeCo bimetallic nanoparticles were synthesized by the bottom-up high-temperature polyol process using a simple centrifugal method. The diameter of synthesized nanoparticles ranged from 2 to 5 nm with high uniformity, as measured with a transmission electron microscope. The CNTs synthesis was carried out on bimetallic nanoparticles as a catalyst using acetylene as a carbon source gas. The CNT forests grown exhibited a maximum height of 96 microm, which is relatively high compared with other growth technologies. A forest of highly pure multiwalled CNTs with diameters of 10-20 nm was successfully synthesized on a bimetallic nanoparticle catalyzed substrate. As the growth temperature increased, the quality of CNTs improved remarkably, indicating that the graphitization could be controlled by varying the growth temperature. Furthermore, the oxygen plasma pre-treatment of dispersed bimetallic nanoparticles before CNTs growth could contribute to the production of highly pure CNTs. By TEM measurements, we observed that pure multiwall CNTs without defects or amorphous carbon could be synthesized.

We have studied growth behavior of carbon nanotubes (CNTs) on iron (Fe) catalyzed substrate using newly developed atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) system. To investigate the improved growth performance with simple equipment and process on large scale, a new AP-PECVD system containing different concept on downstream gas was designed and manufactured. As a catalyst, either sputtered or evaporated Fe thin film on SiO2/Si substrate was used and acetylene gas was used as a carbon source. We observed growth behavior of CNTs such as height, rate and density were strongly affected by plasma power. The maximum height of 427 microm and 267 microm was synthesized under RF plasma power of 30 W for 30 min and 40 W for 3 min, respectively. The growth rate dramatically increased to 6.27 times as plasma power increased from 30 to 40 W which opens the possibility the mass production of CNTs. By SEM and TEM observation, it was verified the grown CNTs was consists of mixture of single-wall and multi-wall CNTs. The graphitization ratio was measured to be 0.93, indicating that the graphitized CNTs forest was formed and relatively high purity of CNTs was synthesized, being useful for nano-composite materials to reinforce the strength. From our experiments, we can observe that the height and growth rate of CNTs is strong function of plasma power.