Tomoaki Ikegami

Investigation of Transparent Conductive Oxide Al-Doped ZnO Films Produced by Pulsed Laser Deposition

High-quality transparent conductive aluminum-doped ZnO (AZO) thin films were deposited on quartz glass substrates using pulsed laser deposition (PLD). We varied the growth conditions in terms of substrate temperature and oxygen pressure. The crystallographic structure and electrical and optical properties of the as-grown AZO films were mainly investigated. In X-ray diffraction (XRD), (002) and (004) peaks were detected, indicating that Al doping did not cause structural degradation of wurtzite ZnO. The AZO films formed at a substrate temperature of 300°C showed a low electrical resistivity of 1.33×10-4 Ω cm, a carrier concentration of 1.25×1021 cm-3 and a carrier mobility of 37.6 cm2/(V s) at an oxygen pressure of 5 mTorr. A visible transmittance of above 88% was obtained. The AZO films show comparable electrical and optical properties to those of indium tin oxide (ITO) films and are emerging as a potential good challenger to ITO films.

Synthesis of p-type ZnO thin films using co-doping techniques based on KrF excimer laser deposition

Preparation of N-doped ZnO thin films was attempted using various co-doping methods. A ZnO:Ga (Ga 2 O 3 of 5 wt.%) target was ablated in NO gas by pulsed laser deposition (PLD). In addition, a nitrogen ion gun and an ECR nitrogen plasma source were used as post-N-doping treatment of undoped ZnO films. Optical emission from elemental Zn I, Ga I and O I, as well as from N 2 molecules, was identified in the plasma plume. The structural, optical and electrical properties of these synthesized films were investigated. All films show n-type conduction, with resistivity in the range 10 -3 -10 -2 Ω cm and carrier density from 10 17 to 10 20 cm -3 .

Growth of Transparent Conductive Al-Doped ZnO Thin Films and Device Applications

High-purity transparent conductive Al-doped ZnO (AZO) films were grown by KrF excimer pulsed laser deposition. We used ultraviolet and X-ray photoelectron spectroscopes to directly measure the absolute values of the vacuum work function of AZO films. The structure and electrical and optical properties of the as-grown AZO films were studied using X-ray diffraction, room temperature Hall effect measurement and spectro photometer, respectively. Finally, organic light emitting diodes (OLED) were fabricated on these AZO films. OLED device measurement showed that the current of the OLED with AZO was clearly increased. Our AZO thin films showed a higher conductivity (ρ=1.33×10-4 Ω cm, Rs=10.1 Ω/sq) than conventional indium tin oxide films.

Preparation of boron carbide thin film by pulsed KrF excimer laser deposition process

Pulsed laser deposition (PLD) technique has been widely used in thin film preparation because of its wonderful and excellent properties. Boron carbide (B 4 C) thin films are recognized to have potential for applications like hard coating and electron field emission devices. B 4 C is the third hardest material after diamond and cBN, with a highest hardness of HV ∼5000. Furthermore, B 4 C is interesting from the point of view of wear resistance and stability at high temperature. We have deposited B 4 C thin films by KrF excimer laser (λ = 248 nm) ablation of a stoichiometric B 4 C target in high vacuum. In this paper, we have prepared the B 4 C thin films on Si(100) substrates under various conditions, such as substrate negative DC bias voltage from between 0 to -800 V, substrate temperatures from room temperature up to 550 °C, and laser fluence between 2 and 8 J/cm 2 on the target. The typical absorption of B-C stretching bonds was detected from the infrared absorption measurement by FTIR of the deposited B 4 C thin films. We concluded that the hardness of the B 4 C thin films increases as the boron/carbon (B/C) ratio increases. The B/C ratio depends on the laser fluence. We obtained the maximum B/C ratio of 3.42 at 5 J/cm 2 . The hardness of that sample reached 5.84 times of that of the Si(100) substrate.

Modeling and operation of a 10 kW photovoltaic power generator using equivalent electric circuit method

The output power of a photovoltaic power generator system (PV system) changes continuously as it strongly depends on the weather condition (solar radiation and temperature). Large fluctuations of output of PV system result in fluctuation and hence of harmonics in the inverter output. The PV systems are usually connected to the power grid lines, therefore, it is necessary to simulate the effects of the PV power systems on the commercial distribution line. In this paper, the authors have modeled a 10 kW PV module using current-voltage characteristic of a PV module by estimating its equivalent electrical circuit parameters.

NO sensing property of carbon nanotube based thin film gas sensors prepared by chemical vapor deposition techniques

To prepare a gas sensor that can operate at room temperature, carbon nanotubes (CNTs) were grown on Al2O3 substrates with interdigital Pt electrodes (Al2O3 substrate) by both pulsed laser deposition (PLD) and chemical vapor deposition (CVD). In this combined method, Fe catalytic thin film was prepared by PLD and then CNTs were grown on the Fe thin film by thermal CVD using an ethylene gas. The surface images of the prepared CNTs on the substrates were observed by scanning electron microscopy (SEM), and the sensitivity to NO gas was measured. The resistance of the prepared CNT-based gas sensor was found to decrease with increasing sensor temperature, and it decreased with increasing NO gas concentration at room temperature. In this paper, it is suggested that CNT gas sensors have a great possibility to be applied as innovative NO gas sensors on the basis of the experimental results.

Optical emission study of the laser plasma plume produced during diamondlike carbon thin film preparation

Abstract We have studied the application of the diamondlike carbon (DLC) film as a protective coating layer for high temperature superconducting thin films. Recently, the DLC film was proposed as an attractive material for field electron emitter device. We report on spectroscopic properties of the KrF laser plasma plume produced during the DLC thin film deposition. Optical emission measurements showed appearance of such neutral and ionic species as H, C, C + , CH, CH + , C 2 H + . Strong emission from neutral and ionic molecules CH, C 2 , C 2 H + produced by the reaction in the gaseous phase has been observed with the ambient hydrogen gas pressure increase. The calculated velocities of CH and C 2 H + molecules at the distances of 10–20 mm from the target are found to be 5.0×10 3 m/s and 9.1×10 3 m/s, correspondingly. The properties of the DLC thin films are strongly affected by the laser plasma plume dynamics. The DLC film deposited on MgO (100) at room temperature and 200 mTorr hydrogen pressure was almost transparent in the visible light range and had an optical band energy gap of 2.0 eV, which is about half of that of a diamond.

Pulsed laser deposited WO3 thin films for gas sensor

Abstract WO 3 has attracted attention because of its potential for NO x gas sensing. Thin films of WO 3− x were prepared by KrF excimer pulsed laser deposition technique on quartz and Al 2 O 3 with Pt electrode. The films were deposited at various substrate temperature, oxygen pressure and conditions of the post-annealing. The substrate temperature over 400 °C was needed for the crystallization of the WO 3− x thin film. The crystal structure of the WO 3− x thin film deposited at oxygen pressure of 100 mTorr and the substrate temperature of 400 °C was tetragonal phase, however, the films deposited at the oxygen pressure over 200 mTorr showed triclinic phase. The atomic force microscopy image of the WO 3− x thin film post-annealed in oxygen atmosphere for 30 min showed an average grain size of 268 nm. It was approximately two times larger than that of the as-deposited film. The maximum sensitivity ( R NO / R N 2 ) of the as-deposited triclinic WO 3− x thin film gas sensor in the NO gas (60 ppm in N 2 ) was 4.2 at an operating temperature of 200 °C.

Application of the dielectric barrier discharge to detect defects in a teflon coated metal surface

In the semiconductor industry, flexible stainless steel tubes, the inside of which are coated with thick Teflon films, by the splay coating method, have been used to prevent their degradation and erosion by organic solvents. We have developed an inspection system to detect pinholes and cracks in the deposited Teflon films, and the dielectric barrier discharge (DBD) was employed to reduce residual substances and damages to the coated film in the tube. Conducting water contained in the cylinder-like glass pipe was used as a liquid electrode to apply a high voltage at any portion of the tube tested. A defective part with a pinhole was modelled by a point electrode in this experiment, because the uncoated defective part has a lower electric breakdown voltage. High frequency voltage (10 kHz) was applied between the point electrode and the liquid electrode. The level of the liquid electrode was varied to detect the occurrence of a microdischarge. It is found that the number of current pulses due to the microdischarge can be used to estimate the size and location of the defective uncoated point of the sample tube.

Development of agricultural soil sterilization using ozone generated by high frequency dielectric barrier discharge

Abstract We have developed the ozone generation system suitable for soil sterilization and ozone supplying system into the soil. The coaxial dielectric barrier discharge produced the ozone with high concentration at high efficiency. Injection of the on- site generated ozone gas into the soil resulted in decreasing soil pathogen and changing chemical properties of the soil. We studied ozone sterilization of agricultural soil when it was treated by varying ozone dosages and process duration. The temporal and spatial properties of the soil were monitored using the pH and electrical conductivity. The bacteria populations, pathogen and soil-borne fungi were measured after various ozone treatment procedures. 100g/m3 of ozone was injected into the soil at a flow rate of 2 liter/min during 60 min. The pH shows drastic change in 40 min that will be one of indexes indicating the sterilization level. In this treatment 100% of the bacteria in the agricultural soil was killed.