Kenji Ebihara

Estimation of equivalent circuit parameters of PV module and its application to optimal operation of PV system

A method to estimate the equivalent circuit parameters of a PV (photovoltaic) module is presented. The parameters are calculated using a least-squares tting of the equivalent model current}voltage characteristic with the measured one. For applications of the equivalent circuit model parameters, a quantitative diagnostic method of the PV modules by evaluating the parameters is introduced and examined by simulation. A new maximum peak power tracking (MPPT) method using the model parameters, a solar insolation, and a cell temperature is also shown. Its performance is compared with other MPPT control algorithms by simulations. The performance of the proposed method was better than other MPPT methods. ( 2001 Elsevier Science B.V. All rights reserved.

Optical emission study of ablation plasma plume in the preparation of diamond-like carbon films by KrF excimer laser

Optical emission study of the laser ablation plasma plume during the preparation of diamond-like carbon (DLC) films using KrF excimer (248 nm) pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum (1×10−7u200aTorr), the emission lines from carbon ions of C+,u200aC2+, and C3+ are observed in addition to atomic carbon emission lines, while no emission from the diatomic carbon molecule (C2) is observed. With increasing background nitrogen pressure up to 500 mTorr, the emission intensities of the C2 Swan band and the carbon nitride (CN) violet band increase. The diamond-like character of deposited DLC film degrades with background nitrogen pressure. The vibrational temperature of C2 and CN molecules decreases with the increasing of nitrogen pressure. The CN vibrational temperature for the first 2 μs after the laser pulse is very high and in agreement with the kinetic energy of monatomic carbon ions. The C2 vibrational ...

Interaction of ambient nitrogen gas and laser ablated carbon plume: Formation of CN

Abstract Pulsed laser ablated carbon plasma in a nitrogen background gas in the pressure range from 10 mTorr to 100 Torr is investigated by optical emission spectroscopy using 1.064 and 0.355 μm laser wavelengths. C 2 and CN emission bands dominated the emitted spectrum at all ambient gas pressures at low incident laser intensity commonly used for pulsed laser deposition of thin films. The light intensity of C 2 and CN band heads is highly dependent on laser wavelength, laser energy, and ambient gas pressures. Emission from N 2 + was detected at all nitrogen pressures. N I and N II are also observed in the emitted spectrum at the background gas pressure greater than 1 Torr. The vibrational temperature of CN species is found to be greater than that of C 2 species. The mechanism of formation of C 2 and CN molecules is discussed.

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.

Excimer laser ablation process characteristics for carbon nitride and diamond-like films preparation

Abstract We deposited diamond-like carbon (DLC) thin films and carbon nitride (CN) thin films by KrF excimer laser ablation of graphite carbon target in helium, hydrogen, nitrogen and mixed nitrogen and hydrogen gas ambient conditions. We report spectroscopic properties of the laser plasma plume produced during DLC and CN thin film deposition. Optical emission measurements at non-reactive helium ambient gas showed the appearance of neutral and ionic species such as C and C+. Strong emission from molecules, CH, C2 and CN produced by the reaction in gaseous phase was observed with the ambient hydrogen and nitrogen gases. The properties of DLC and CN thin films are strongly affected by the laser plume dynamics. DLC and CN films were deposited on a quartz substrate and a single-crystalline Si(100) wafer at room temperature. Typical deposited DLC and CN thin films had an optical band gap of ∼2.0xa0eV.

Experimental and numerical study on pulsed-laser annealing process of diamond-like carbon thin films

Abstract The diamond-like carbon (DLC) films were deposited by KrF excimer laser (λ=248 nm) ablation under H 2 atmosphere of 200 mtorr with 6 J/cm 2 . The prepared DLC thin film was mounted on the holder and the film surface was irradiated with the third harmonic of a single pulsed of Nd:YAG laser (λ=355 nm) or a pulsed KrF excimer laser. The experiments were performed in air and the substrate was held at room temperature. The threshold energy density for surface damage is measured by inspecting the surface after a single laser shot of increasing fluence to observe the onset of surface damage. The damage threshold energy density for DLC film flashed by a pulsed Nd:YAG laser is in the range 60–80 mJ/cm 2 . The dynamics of pulsed nanosecond laser heating process is simulated by the solution of the one-dimensional heat conduction equation. The finite element method (FEM) is applied to solve the equation. At the laser fluence of 80 mJ/cm 2 with the Nd:YAG laser, the surface reaches the maximum temperature of 785°C at 48 ns. The experimental and calculated results show that the damage temperature of DLC film is smaller than the vaporization temperature of solid carbon. Moreover, the transmission spectra of DLC films before and after irradiation were measured. The graphitization occurred on the sample after irradiation over threshold energy for surface damage.

Pulsed laser deposition of carbon nitride thin films from graphite targets

Abstract Carbon nitride thin films were synthesized on Si(100) substrates by a pulsed Nd:YAG laser deposition. The laser beam is incident on the high-purity graphite targets. The films are grown using an energy density 3.8 J cm−2 at a laser repetition rate of 10 Hz. The nitrogen gas pressure in the chamber is 10.0 Pa. Morphology features of the films have been obtained by employing the technique of scanning electron microscopy. Auger electron spectroscopy has been used to obtain compositional information about the films. The N C composition ratio was found to vary from zero to 0.32 depending on deposition conditions. IR absorption spectra show two characteristic bands: a broad band composed of the graphite G-band and disordered D-band of carbon, and another associated with Cue5fcN triple bonds. Raman spectra have also been used to characterize the films.

Pulsed laser deposition of tungsten carbide thin films on silicon (100) substrate

Abstract A method of synthesizing tungsten carbide (WC) thin films by a pulsed YAG laser deposition is investigated. WC thin films are deposited on silicon (100) substrates by using WCue5f85%Co alloy targets. Glancing angle X-ray diffraction shows that the strong peaks of W 2 C appear at the substrate temperature of 500°C. Beside the strong peaks of W 2 C, weak peaks of WC and W 3 Co 3 C appear at the substrate temperature of 650°C. Auger electron spectroscopy shows that the almost stoichiometric WC films are deposited at the methane gas pressure of 1.0 Pa. Morphological features of the samples have been obtained by employing the technique of scanning electron microscopy. X-ray photoelectron spectroscopy has been used to obtain structural and compositional information about the samples.

Laser-ablated plasma for deposition of ZnO thin films on various substrates

Abstract We report optical and structural properties of ZnO films deposited by pulsed laser deposition technique on 1100) n-typesilicon and quartz substrates at various pressures of back ground gas. ZnO plasma was created using KrF laser 1248 nm) atvarious pressures of the ambient gas, oxygen. Laser induced plasma at varying fluence on the target was investigated using optical emission spectroscopy and 2-D images of the expanding plumes. X-ray diffraction, atomic force microscopy, and spectro-photometry were used to characterize as grown films.

Spatial distribution of carbon species in laser ablation of graphite target

We report on the temporal evolution and spatial distribution of C2 and C3 molecules produced by KrF laser ablation of a graphite target using laser induced fluorescence imaging and optical emission spectroscopy. Spatial density profiles of C2 were measured using two-dimensional fluorescence in various pressures of different ambient (vacuum, nitrogen, oxygen, hydrogen, helium, and argon) gases at various ablation laser fluences and ablation area. A large yield of C2 is observed in the central part of the plume and near the target surface and its density and distribution was affected by the laser fluence and ambient gas. Fluorescent C3 was studied in Ar gas and the yield of C3 is enhanced at higher gas pressure and longer delay times after ablation.