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Lithium-ion batteries have been considered the most important devices to power mobile or small-sized devices due to their high energy density. LixCoO2 has been studied as a cathode material for the Li-ion battery. However, the limitation of its capacity impedes the development of high capacity cathode materials with Ni, Mn, etc. in them. The substitution of Mn and Ni for Co leads to the formation of solid solution phase LiNixMnyCo1-x-yO2 (NMC, both x and y 0.8 in the metal site), poor cycle retention capability still remains to be overcome. In this study, aiming to improve the stability of the physical and chemical bonding, we investigate the stabilization effect of Ca in the Ni-rich layered compound Li(Ni0.83Co0.12Mn0.05)O2, and then Ca is added to the modified secondary particles to lower the degree of cationic mixing of the final particles. For the optimization of the final grains added with Ca, the Ca content (x = 0, 2.5, 5.0, 10.0 at.%) versus Li is analyzed.

We report on the fabrication and photoelectrochemical(PEC) properties of a Cu2O thin film/ZnO nanorod array oxide p-n heterojunction structure with ZnO nanorods embedded in Cu2O thin film as an efficient photoelectrode for solardriven water splitting. A vertically oriented n-type ZnO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type Cu2O thin film was directly electrodeposited onto the vertically oriented ZnO nanorods array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were characterized using X-ray diffraction and scanning electron microscopy as well as Raman scattering. The PEC properties of the fabricated Cu2O/ZnO p-n heterojunction photoelectrode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the Cu2O/ZnO photoelectrode was found to exhibit a negligible dark current and high photocurrent density, e.g., 0.77 mA/cm2 at 0.5 V vs Hg/HgCl2 in a 1 mM Na2SO4 electrolyte, revealing an effective operation of the oxide heterostructure. In particular, a significant PEC performance was observed even at an applied bias of 0 V vs Hg/ HgCl2, which made the device self-powered. The observed PEC performance was attributed to some synergistic effect of the p-n bilayer heterostructure on the formation of a built-in potential, including the light absorption and separation processes of photoinduced charge carriers.

We report on the fabrication and characterization of a novel Cu2O/CuO heterojunction structure with CuO nanorods embedded in Cu2O thin film as an efficient photocathode for photoelectrochemical (PEC) solar water splitting. A CuO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method; then, a Cu2O thin film was electrodeposited onto the CuO nanorod array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were examined using X-ray diffraction and scanning electron microscopy, as well as Raman scattering. The PEC properties of the fabricated Cu2O/CuO heterojunction photocathode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the Cu2O/CuO photocathode was found to exhibit negligible dark current and high photocurrent density, e.g. −1.05 mA/cm2 at −0.6 V vs. Hg/HgCl2 in 1 mM Na2SO4 electrolyte, revealing the effective operation of the oxide heterostructure. The photocurrent conversion efficiency of the Cu2O/CuO photocathode was estimated to be 1.27% at −0.6 V vs. Hg/HgCl2. Moreover, the PEC current density versus time (J-T) profile measured at −0.5 V vs. Hg/HgCl2 on the Cu2O/CuO photocathode indicated a 3-fold increase in the photocurrent density compared to that of a simple Cu2O thin film photocathode. The improved PEC performance was attributed to a certain synergistic effect of the bilayer heterostructure on the light absorption and electron-hole recombination processes.

Fabrication of iron oxide/carbon nanotube composite structures for detection of ammonia gas at room temperature is reported. The iron oxide/carbon nanotube composite structures are fabricated by in situ co-arc-discharge method using a graphite source with varying numbers of iron wires inserted. The composite structures reveal higher response signals at room temperature than at high temperatures. As the number of iron wires inserted increased, the volume of carbon nanotubes and iron nanoparticles produced increased. The oxidation condition of the composite structures varied the carbon nanotube/iron oxide ratio in the structure and, consequently, the resistance of the structures and, finally, the ammonia gas sensing performance. The highest sensor performance was realized with oxidation heat-treatment condition, in which most of the carbon nanotubes were removed from the composite and iron oxide played the main role of ammonia sensing. The response signal level was 62% at room temperature. We also found that UV irradiation enhances the sensing response with reduced recovery time.

We report the nitrogen monoxide (NO) gas sensing properties of p-type CuO-nanorod-based gas sensors. Wesynthesized the p-type CuO nanorods with breadth of about 30 nm and length of about 330 nm by a hydrothermal method usingan as-deposited CuO seed layer prepared on a Si/SiO 2 substrate by the sputtering method. We fabricated polycrystalline CuOnanorod arrays at 80 o C under the hydrothermal condition of 1:1 morality ratio between copper nitrate trihydrate[Cu(NO 2 ) 2 ·3H 2 O] and hexamethylenetetramine (C 6 H 12 N 4 ). Structural characterizations revealed that we prepared the pure CuOnanorod array of a monoclinic crystalline structure without any obvious formation of secondary phase. It was found from thegas sensing measurements that the p-type CuO nanorod gas sensors exhibited a maximum sensitivity to NO gas in dry air atan operating temperature as low as 200 o C. We also found that these CuO nanorod gas sensors showed reversible and reliableelectrical response to NO gas at a range of operating temperatures. These results would indicate some potential applicationsof the p-type semiconductor CuO nanorods as promising sensing materials for gas sensors, including various types of p-njunction gas sensors.Key wordsOxide gas sensor, CuO, nanorod, NO gas, hydrothermal method.

We present an excellent detection for nitrogen monoxide (NO) gas using polycrystalline ZnO wire-like films synthesized via a simple method combined with sputtering of Zn metallic films and subsequent thermal oxidation of the sputtered Zn nanowire films in dry air. Structural and morphological characterization revealed that it would be possible to synthesize polycrystalline hexagonal wurtzite ZnO films of a wire-like nanostructure with widths of 100-150 nm and lengths of several microns by controlling the sputtering conditions. It was found from the gas sensing measurements that the ZnO wire-like thin film gas sensor showed a significantly high response, with a maximum value of 29.2 for 2 ppm NO at , as well as a reversible fast response to NO with a very low detection limit of 50 ppb. In addition, the ZnO wire-like thin film gas sensor also displayed an NO-selective sensing response for NO, , , , and CO gases. Our results illustrate that polycrystalline ZnO wire-like thin films are potential sensing materials for the fabrication of NO-sensitive high-performance gas sensors.

Light scattering enhancement is widely used to enhance the optical absorption efficiency of dye-sensitized solar cells. In this work, we systematically analyzed the effects of spherical voids distributed as light-scattering centers in photoanode films made of an assembly of zinc oxide nanoparticles. Spherical voids in electrode films were formed using a sacrificial template of polystyrene (PS) spheres. The diameter and volume concentration of these spheres was varied to optimize the efficiency of dye-sensitized solar cells. The effects of film thickness on this efficiency was also examined. Electrochemical impedance spectroscopy was performed to study electron transport in the electrodes. The highest power conversion efficiency of 4.07 % was observed with film thickness. This relatively low optimum thickness of the electrode film is due to the enhanced light absorption caused by the light scattering centers of voids distributed in the film.

We present an easy method of preparing two-dimensional (2D) periodic hollow tin oxide (SnO2) hemisphere array gas sensors using polystyrene (PS) spheres as a template. The structures were fabricated by the sputter deposition of thin tin (Sn) metal over an array of PS spheres on a planar substrate followed by calcination at an elevated temperature to oxidize Sn to SnO2 while removing the PS template cores. The SnO2 hemisphere array structures were examined by scanning electron microscopy and X-ray diffraction. The structures were calcined at various temperatures and their sensing properties were examined with varying operation temperatures and concentrations of nitric oxide (NO) gas. Their gas-sensing properties were investigated by measuring the electrical resistances in air and the target gases. The measurements were conducted at different NO concentrations and substrate temperatures. A minimum detection limit of 30 ppb, showing a sensitivity of S = 1.6, was observed for NO gas at an operation temperature of 150 oC for a sample having an Sn metal layer thickness corresponding to 30 sec sputtering time and calcined at 600 oC for 2 hr in air. We proved that high porosity in a hollow SnO2 hemisphere structure allows easy diffusion of the target gas molecules. The results confirm that a 2D hollow SnO2 hemisphere array structure of micronmeter sizes can be a good structural morphology for high sensitivity gas sensors.

Photoelectrochemical cells have been used in photolysis of water to generate hydrogen as a clean energy source. A high efficiency electrode for photoelectrochemical cell systems was realized using a ZnO hierarchical nanostructure. A ZnO nanofiber mat structure was fabricated by electrospinning of Zn solution on the substrate, followed by oxidation; on this substrate, hydrothermal synthesis of ZnO nanorods on the ZnO nanofibers was carried out to form a ZnO hierarchical structure. The thickness of the nanofiber mat and the thermal annealing temperature were determined as the parameters for optimization. The morphology of the structures was examined by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The performance of the ZnO nanofiber mat and the potential of the ZnO hierarchical structures as photoelectrochemical cell electrodes were evaluated by measurement of the photoelectron conversion efficiencies under UV light. The highest photoconversion efficiency observed was 63 % with a ZnO hierarchical structure annealed at in air. The morphology and the crystalline quality of the electrode materials greatly influenced the electrode performance. Therefore, the combination of the two fabrication methods, electrospinning and hydrothermal synthesis, was successfully applied to fabricate a high performance photoelectrochemical cell electrode.

We investigated the detection properties of nitrogen monoxide (NO) gas using transparent p-type thin film gas sensors. The film was fabricated on an indium tin oxide (ITO)/glass substrate by pulsed laser deposition (PLD), and then the transparent p-type active layer was formed by annealing. Structural and optical characterizations revealed that the transparent p-type layer with a thickness of around 200 nm had a non-crystalline structure, showing a quite flat surface and a high transparency above 65 % in the range of visible light. From the NO gas sensing measurements, it was found that the transparent p-type thin film gas sensors exhibited the maximum sensitivity to NO gas in dry air at an operating temperature of . We also found that these thin film gas sensors showed reversible and reliable electrical resistance-response to NO gas in the operating temperature range. These results indicate that the transparent p-type semiconductor thin films are very promising for application as sensing materials for gas sensors, in particular, various types of transparent p-n junction gas sensors. Also, these transparent p-type semiconductor thin films could be combined with an n-type oxide semiconductor to fabricate p-n heterojunction oxide semiconductor gas sensors.

A simple thermal oxidation of Cu thin films deposited on planar substrates established a growth of vertically aligned copper oxide (CuO) nanorods. DC sputter-deposited Cu thin films with various thicknesses were oxidized in environments of various oxygen partial pressures to control the kinetics of oxidation. This is a method to synthesize vertically aligned CuO nanorods in a relatively shorter time and at a lower cost than those of other methods such as the popular hydrothermal synthesis. Also, this is a method that does not require a catalyst to synthesize CuO nanorods. The grown CuO nanorods had diameters of ~100 nm and lengths of 1~25μm. We examined the morphology of the synthesized CuO nanorods as a function of the thickness of the Cu films, the gas environment, the oxidation time, the oxidation temperature, the oxygen gas flow rate, etc. The parameters all influence the kinetics of the oxidation, and consequently, the volume expansion in the films. Patterned growth was also carried out to confirm the hypothesis of the CuO nanorod protrusion and growth mechanism. It was found that the compressive stress built up in the Cu film while oxygen molecules incorporated into the film drove CuO nanorods out of the film.

We report on the NO gas sensing properties of non-directional ZnO nanofibers synthesized using a typical electrospinning technique. These non-directional ZnO nanofibers were electrospun on an /Si substrate from a solution containing poly vinyl alcohol (PVA) and zinc nitrate hexahydrate dissolved in distilled water. Calcination processing of the ZnO/PVA composite nanofibers resulted in a random network of polycrystalline ZnO nanofibers of 50 nm to 100 nm in diameter. The diameter of the nanofibers was found to depend primarily on the solution viscosity; a proper viscosity was maintained by adding PVA to fabricate uniform ZnO nanofibers. Microstructural measurements using scanning electron microscopy revealed that our synthesized ZnO nanofibers after calcination had coarser surface morphology than those before calcination, indicating that the calcination processing was sufficient to remove organic contents. From the gas sensing response measurements for various NO gas concentrations in dry air at several working temperatures, it was found that gas sensors based on electrospun ZnO nanofibers showed quite good responses, exhibiting a maximum sensitivity to NO gas in dry air at an operating temperature of . In particular, the non-directional electrospun ZnO nanofiber gas sensors were found to have a good NO gas detection limit of sub-ppm levels in dry air. These results illustrate that non-directional electrospun ZnO nanofibers are promising for use in low-cost, high-performance practical NO gas sensors.

We report on the NO gas sensing properties of Al-doped zinc oxide-carbon nanotube (ZnO-CNT) wire-like layeredcomposites fabricated by coaxially coating Al-doped ZnO thin films on randomly oriented single-walled carbon nanotubes. Wewere able to wrap thin ZnO layers around the CNTs using the pulsed laser deposition method, forming wire-like nanostructuresof ZnO-CNT. Microstructural observations revealed an ultrathin wire-like structure with a diameter of several tens of nm. Gassensors based on ZnO-CNT wire-like layered composites were found to exhibit a novel sensing capability that originated fromthe genuine characteristics of the composites. Specifically, it was observed by measured gas sensing characteristics that the gassensors based on ZnO-CNT layered composites showed a very high sensitivity of above 1,500% for NO gas in dry air at anoptimal operating temperature of 200 o C; the sensors also showed a low NO gas detection limit at a sub-ppm level in dry air.The enhanced gas sensing properties of the ZnO-CNT wire-like layered composites are ascribed to a catalytic effect of Alelements on the surface reaction and an increase in the effective surface reaction area of the active ZnO layer due to the coatingof CNT templates with a higher surface-to-volume ratio structure. These results suggest that ZnO-CNT composites made ofultrathin Al-doped ZnO layers uniformly coated around carbon nanotubes can be promising materials for use in practical high-performance NO gas sensors.Key wordsoxide gas sensor, zinc oxide, carbon nanotube, ZnO-CNT composite.

Due to their novel properties, GaN based semiconductors and their nanostructures are promising components in a wide range of nanoscale device applications. In this work, the gallium nitride is deposited on c-axis oriented sapphire and porous SWCNT substrates by molecular beam epitaxy using a novel single source precursor of with ammonia as an additional source of nitrogen. The advantage of using a single molecular precursor is possible deposition at low substrate temperature with good crystal quality. The deposition is carried out in a substrate temperature range of 600-750. The microstructural, structural, and optical properties of the samples were analyzed by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and photoluminescence. The results show that substrate oriented columnar-like morphology is obtained on the sapphire substrate while sword-like GaN nanorods are obtained on porous SWCNT substrates with rough facets. The crystallinity and surface morphology of the deposited GaN were influenced significantly by deposition temperature and the nature of the substrate used. The growth mechanism of GaN on sapphire as well as porous SWCNT substrates is discussed briefly.

Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized substrates followed by sputter deposition of Zn and thermal oxidation at in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of . The highest sensor responses were observed at in ZnO film and in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of .

A cobalt oxide - tin oxide nanocomposite based gas sensor on an substrate was fabricated. Granular thin film of tin oxide was formed by a rheotaxial growth and thermal oxidation method using dc magnetron sputtering of Sn. Nano particles of cobalt oxide were spin-coated on the tin oxide. The cobalt oxide nanoparticles were synthesized by polymer-assisted deposition method, which is a simple cost-effective versatile synthesis method for various metal oxides. The thickness of the film can be controlled over a wide range of thicknesses. The composite structures thus formed were characterized in terms of morphology and gas sensing properties for reduction gas of . The composites showed a highest response of 240% at upon exposure to 4% . This response is higher than those observed in pure (90%) and (70%) thin films. The improved response with the composite structure may be related to the additional formation of electrically active defects at the interfaces. The composite sensor shows a very fast response and good reproducibility.

We investigated the carbon monoxide (CO) gas-sensing properties of nanostructured Al-doped zinc oxide thin films deposited on self-assembled Au nanodots (ZnO/Au thin films). The Al-doped ZnO thin film was deposited onto the structure by rf sputtering, resulting in a gas-sensing element comprising a ZnO-based active layer with an embedded Pt/Ti electrode covered by the self-assembled Au nanodots. Prior to the growth of the active ZnO layer, the Au nanodots were formed via annealing a thin Au layer with a thickness of 2 nm at a moderate temperature of . It was found that the ZnO/Au nanostructured thin film gas sensors showed a high maximum sensitivity to CO gas at and a low CO detection limit of 5 ppm in dry air. Furthermore, the ZnO/Au thin film CO gas sensors exhibited fast response and recovery behaviors. The observed excellent CO gas-sensing properties of the nanostructured ZnO/Au thin films can be ascribed to the Au nanodots, acting as both a nucleation layer for the formation of the ZnO nanostructure and a catalyst in the CO surface reaction. These results suggest that the ZnO thin films deposited on self-assembled Au nanodots are promising for practical high-performance CO gas sensors.

Hybridization of semiconductor materials with carbon nanotubes (CNTs) is a recent field of interest in which new nanodevice fabrication and applications are expected. In this work, nanowire type GaAs structures are synthesized on porous single-wall carbon nanotubes (SWCNTs) as templates using the molecular beam epitaxy (MBE) technique. The field emission properties of the as-synthesized products were investigated to suggest their potential applications as cold electron sources, as well. The SWCNT template was synthesized by the arc-discharge method. SWCNT samples were heat-treated at under an atmosphere to remove amorphous carbon. After heat treatment, GaAs was grown on the SWCNT template. The growth conditions of the GaAs in the MBE system were set by changing the growth temperatures from to . The morphology of the GaAs synthesized on the SWCNTs strongly depends on the substrate temperature. Namely, nano-crystalline beads of GaAs are formed on the CNTs under , while nanowire structures begin to form on the beads above . The crystal qualities of GaAs and SWCNT were examined by X-ray diffraction and Raman spectra. The field emission properties of the synthesized GaAs nanowires were also investigated and a low turn-on field of was achieved. But, the turn-on field was increased in the second and third measurements. It is thought that arsenic atoms were evaporated during the measurement of the field emission.

We investigated the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with a thin layer of 1 wt% Al-doped ZnO using rf magnetron sputtering deposition. Morphological studies clearly revealed that the ZnO appeared to form beadshaped crystalline nanoparticles with an average diameter as small as 30 nm, attaching to the surface of the nanotubes. It was found that the NO gas sensing properties of the ZnO-CNT layered composites were dramatically improved over Al-doped ZnO thin films. It is reasoned from these observations that an increase in the surface-to-volume ratio associated with the numerous ZnO “nanobeads” on the surface of the CNTs results in the enhancement of the NO gas sensing properties. The ZnO-CNT layered composite sensors exhibited a maximum sensitivity of 13.7 to 2 ppm NO gas at a temperature of 200 and a low NO gas detection limit of 0.2 ppm in dry air.

)Abstract We investigated the effects of Co doping on the NO gas sensing characteristics of ZnO-carbonnanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with ZnO usingpulsed laser deposition. Structural examinations clearly confirmed a distinct nanostructure of the CNTs coatedwith ZnO nanoparticles of an average diameter as small as 10 nm and showed little influence of doping 1 at.%Co into ZnO on the morphology of the ZnO-CNT composites. It was found from the gas sensing measurementsthat 1 at.% Co doping into ZnO gave rise to a significant improvement in the response of the ZnO-CNTcomposite sensor to NO gas exposure. In particular, the Co-doped ZnO-CNT composite sensor shows a highlysensitive and fast response to NO gas at relatively low temperatures and even at low NO concentrations. Theobserved significant improvement of the NO gas sensing properties is attributed to an increase in the specificsurface area and the role as a catalyst of the doped Co elements. These results suggest that Co-doped ZnO-CNT composites are suitable for use as practical high-performance NO gas sensors.Key wordsZnO gas sensor, ZnO-carbon nanotube composite, Co doping effect.

Thin films of single-wall carbon nanotubes (SWNT) with various thicknesses were fabricated, and their optical andelectrical properties were investigated. The SWNTs of various thicknesses were directly coated in the arc-discharge chamberduring the synthesis and then thermally and chemically purified. The crystalline quality of the SWNTs was improved by thepurification processes as determined by Raman spectroscopy measurements. The resistance of the film is the lowest for thechemically purified SWNTs. The resistance vs. thickness measurements reveal the percolation thickness of the SWNT film tobe ~50nm. Optical absorption coefficient due to Beer-Lambert is estimated to be 7.1×10-2nm-1. The film thickness for 80%transparency is about 32nm, and the sheet resistance is 242Ω/sq. The authors also confirmed the relation between electricalconductance and optical conductance with very good reliability by measuring the resistance and transparency measurements.

ZnO wire-like thin films were synthesized through thermal oxidation of sputtered Zn metal films in dry air. Their nanostructure was confirmed by SEM, revealing a wire-like structure with a width of less than 100 nm and a length of several microns. The gas sensors using ZnO wire-like films were found to exhibit excellent H gas sensing properties. In particular, the observed high sensitivity and fast response to H gas at a comparatively low temperature of 200 C would lead to a reduction in the optimal operating temperature of ZnO-based H gas sensors. These features, together with the simple synthesis process, demonstrate that ZnO wire-like films are promising for fabrication of low-cost and high-performance H gas sensors operable at low temperatures. The relationship between the sensor sensitivity and H gas concentration suggests that the adsorbed oxygen species at the surface is O.

Titanium dioxide thin films were fabricated as hydrogen sensors and its sensing properties were tested. The titanium was deposited on a SiO /Si substrate by the DC magnetron sputtering method and was oxidized at an optimized temperature of 850 C in air. The titanium film originally had smooth surface morphology, but the film agglomerated to nano-size grains when the temperature reached oxidation temperature where it formed titanium oxide with a rutile structure. The oxide thin film formed by grains of tens of nanometers size also showed many short cracks and voids between the grains. The response to 1% hydrogen gas was ~2 × 10 at the optimum sensing temperature of 200 C, and ~10 at room temperature. This extremely high sensitivity of the thin film to hydrogen was due partly to the porous structure of the nano- sized sensing particles. Other sensor properties were also examined.

The NO gas sensing properties of ZnO-carbon nanotube (ZnO-CNT) composites fabricated by thecoaxial coating of single-walled CNTs with ZnO were investigated using pulsed laser deposition. Uponexamination, the morphology and crystallinity of the ZnO-CNT composites showed that CNTs were uniformlycoated with polycrystalline ZnO with a grain size as small as 5-10 nm. Gas sensing measurements clearlyindicated a remarkable enhancement of the sensitivity of ZnO-CNT composites for NO gas compared to thatof ZnO films while maintaining the strong sensing stability of the composites, properties that CNT-basedsensing materials do not have. The enhanced gas sensing properties of the ZnO-CNT composites are attributedto an increase in the surface adsorption area of the ZnO layer via the coating by CNTs of a high surface-to-volume ratio structure. These results suggest that the ZnO-CNT composite is a promising template for novelsolid-state semiconducting gas sensors.Key words ZnO gas sensor, carbon nanotube, ZnO-CNT composite

The hydrogen gas sensing properties of a zinc oxide nanowire structure were studied. Porous zinc oxide nanowire structures were fabricated by oxidizing zinc deposited on a single-wall carbon nanotube (SWNT) template. This revealed a porous ZnO-SWNT composite due to the porosity in the SWNT film. The gas sensing properties were compared with those of zinc oxide thin films deposited on SiO2/Si substrates in sensitivity and operating temperature. The composite structure showed higher sensitivity and lower operating temperature than the zinc oxide film. It showed a response even at room temperature while the film structure did not.

)Abstract Samples of GaMnAs, GaMnAs codoped with Be, and GaMnAs simultaneously codoped with Be andMg were grown via low-temperature molecular beam epitaxy (LT-MBE). Be codoping is shown to take the Gasites into the lattice efficiently and to increase the conductivity of GaMnAs. Additionally, it shifts thesemiconducting behavior of GaMnAs to metallic while the Mn concentration in the GaMnAs solid solution isreduced. However, with simultaneous codoping of GaMnAs with Be and Mg, the Mn concentration increasesdramatically several times over that in a GaMnAs sample alone. Mg and Be are shown to eject Mn from theGa sites to form MnAs and MnGa precipitates.Key wordsGaMnAs, Be codoping, Mg codoping, MBE, Magnetic semiconductor PACS: 75.50Pp, 75.70Ak, 81.15.Hi

The effects of the field emission property in relation to the surface morphology and adhesion force were investigated. The single-wall-nanotube-based cathode was obtained by use of an in-situ arc discharge synthesis method, a screen-printing method and a spray method. The morphologies of the formed emitter layers were very different. The emission stability and uniformity were dramatically improved by employing an in-situ arc discharge synthesis method. In this study, it was confirmed that the current stability and uniformity of the field emission of the cathode depend on the surface morphology and adhesion force of the emitters. The current stability of the field emission device was also studied through an electrical aging process by varying the current and electric field.

We report the synthesis of cubic spinel thin films and the tunability of the conduction type by control of the oxygen partial pressure ratio. Zinc cobalt oxide films were grown on(200 nm)/Si substrates by reactive magnetron sputtering method using Zn and Co metal targets in a mixed Ar/atmosphere. We found from X-ray diffraction measurements that the crystal structure of the zinc cobalt oxide films grown under an oxygen-rich condition (the /Ar partial pressure ratio of 9/1) changes from wurtzite-type O to spinel-type with the increase of the Co/Zn sputtering ratio, . We noted that the above structural change accompanied by the variation of the majority electrical conduction type from n-type (electrons) to p-type (holes). For a fixed / of 2.0 yielding homogeneous spinel-type Ofilms, the type of the majority carriers also varied, depending on the/Ar partial pressure ratio: p-type for an -rich and n-type for an Ar-rich atmosphere. The maximum electron and hole concentrations for the Zn films were found to be 1.3710 c and 2.4110 c , respectively, with a mobility of about 0.2 /Vs and a high conductivity of about 1.8 Ω/ /.