Akimori Tabata

Evaluation of LFC capacity for output fluctuation of photovoltaic power generation systems based on multi-point observation of insolation

The output of a photovoltaic power generation system (PV system) fluctuates depending on weather conditions. Large-scale introduction of PV systems may cause some difficulties in the operation of an electric power system. The evaluation of the influence of PV systems on the power system operation should consider the smoothing effect of the outputs by the dispersed introduction of PV systems. This paper discusses the LFC (load frequency control) capacity for output fluctuation of PV systems based on the insolation data simultaneously observed at 5 points around Nagoya, Japan. As a result, when the weather was clear but clouds moved frequently, the capacity. for LFC based on the regional averaged insolation was evaluated less than a half of that evaluated by the insolation at one point. Furthermore, LFC capacity might be dominated by the speed factor rather than the magnitude factor of load fluctuation including PV systems output when a large capacity of PV systems is installed.

X-ray photoelectron spectroscopy (XPS) of hydrogenated amorphous silicon carbide (a-SixC1-x:H) prepared by the plasma CVD method

The XPS of a-SixC1-x:H films prepared by the plasma CVD method from a mixture of silane and methane gases were measured. The separation of the XPS spectra into several peaks revealed the nature of the chemical bonds of silicon and carbon atoms. The coordination of the carbon atom was diamond-like and fourfold in silicon-rich films, while the graphitic threefold coordination was dominant in carbon-rich films. The effect of dilution gas was also investigated by using argon and hydrogen as dilution gases. Films prepared from hydrogen-diluted gas contained more carbon atoms with fourfold coordination than those prepared from argon-diluted gas.

Optical properties and structrue of SiO2 films prepared by ion-beam sputtering

SiO2 films were prepared by an ion-beam sputtering (IBS) method and their properties were studied using visible-UV absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and IR transmission spectroscopy. The SiO2 films prepared with O2 atmosphere had good transparency in the visible region. Only the XPS signal due to the SiO2 bond was observed, and the film composition was almost stoichiometric. However, the full widths at half maximum of the XPS peak and each IR band of the SiO2 films were larger than those of thermally oxidized SiO2 films. This suggests that the SiO2 films prepared by the IBS were more disordered than the thermally oxidized SiO2 films. The IR spectra showed that the structure of the SiO2 films prepared by the IBS method was mainly coesite like and was different from that of the thermally oxidized SiO2 which was mainly quartz like.

Film Properties of Nanocrystalline 3C–SiC Thin Films Deposited on Glass Substrates by Hot-Wire Chemical Vapor Deposition Using CH4 as a Carbon Source

Nanocrystalline cubic silicon carbide (3C–SiC) thin films have been successfully prepared on glass substrates (at a low temperature of around 325 °C) by hot-wire chemical vapor deposition using CH4 as a carbon source. It was found that using CH4, i.e., a SiH4/CH4/H2 system, is useful for the low-temperature deposition of nanocrystalline 3C–SiC thin films and that filament temperature (Tf) is a significant parameter. The structural transition from hydrogenated amorphous SiC (a-SiC:H) to nanocrystalline 3C–SiC occurred with increasing Tf from 1400 to 1600 °C. The mean crystallite size of the obtained films was 2.6 to 8.4 nm. The IR absorption peak due to Si–C bonds showed a single Lorentzian shape, and with increasing Tf, intensity increased and full width at half maximum decreased. This indicates that the crystallinity of 3C–SiC was improved. The SiH4/CH4/H2 system has enabled us to prepare nanocrystalline 3C–SiC thin films at a low H2 dilution ratio in comparison with the findings of other groups obtained thus far, resulting in a high deposition rate of over 0.15 nm/s.

Properties of hydrogenated amorphous silicon carbide films prepared by a separately excited plasma CVD method

In order to prepare high-quality hydrogenated amorphous silicon carbide () films with a wide band gap, we propose use of a separately excited plasma CVD (SEPCVD) system composed of two independent plasma chambers and one deposition chamber. This method enables control of methane and silane plasmas independently. The optical and electrical properties and structure of films prepared by the SEPCVD method were evaluated with visible - ultraviolet absorption spectroscopy, infrared transmission spectroscopy, x-ray photoelectron spectroscopy and measurements of the photo- and dark conductivities. The carbon content and the optical band gap increased with increasing the rf power on both the methane side and the silane side. films with a carbon content above 0.6 and an optical band gap above 2.8 eV could be prepared by the SEPCVD method even though hydrogen-diluted gas was used. The SEPCVD method proved useful in preparing films with a wide gap. Both fourfold-coordinated carbon atoms and threefold-coordinated carbon atoms existed in films with carbon content from 0.5 to 0.6. However, the atomic percentage of threefold-coordinated carbon in films prepared by the SEPCVD method is smaller than that obtained by the conventional method. was 0.1 - 0.3 and increased with increasing rf power. and decreased with increasing rf power on the methane side, but they were not dependent on the rf power on the silane side. For films with an optical band gap between 1.8 eV and 2.0 eV, the photoconductivity and the photosensitivity were and respectively, and films with high photoconductivity could be prepared. However, the photoconductivity of the films with an optical band gap above 2.2 eV was about .

Properties of Nanocrystalline Cubic Silicon Carbide Thin Films Prepared by Hot-Wire Chemical Vapor Deposition Using SiH4/CH4/H2 at Various Substrate Temperatures

Silicon carbide (SiC) thin films were prepared by hot-wire chemical vapor deposition from SiH4/CH4/H2 gases, and the influence of substrate temperature, Ts (104 < Ts < 434 °C), on the properties of the SiC thin films was investigated. X-ray diffraction patterns and Raman scattering spectra revealed that nanocrystalline cubic SiC (nc-3C-SiC) films grew at Ts above 187 °C, while completely amorphous films grew at Ts = 104 °C. Fourier transform infrared absorption spectra revealed that the crystallinity of the nc-3C-SiC was improved with increasing Ts up to 282 °C and remained almost unchanged with a further increase in Ts from 282 to 434 °C. The spin density was reduced monotonically with increasing Ts.

Preparation of Wide-Gap Hydrogenated Amorphous Silicon Carbide Thin Films by Hot-Wire Chemical Vapor Deposition at a Low Tungsten Temperature

Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) thin films were prepared by hot-wire chemical vapor deposition at a tungsten temperature of 1400°C in methane, silane and hydrogen gas atmosphere, and their properties were investigated. The optical band gap, estimated from Taucs plot, of a-Si1-xCx:H films prepared at a total gas pressure of 1 Torr was 1.79±0.03 eV. On the other hand, the optical band gap of a-Si1-xCx:H films prepared at 4 Torr was 2.18 ±0.05 eV. The infrared absorption spectra showed that a-Si1-xCx:H films prepared at 4 Torr have more Si–C bonds than those prepared at 1 Torr. These findings indicate that the preparation at a high total gas pressure can lead to higher carbon content, consequently, wider-gap a-Si1-xCx:H films, even at a low tungsten temperature.

Dependence on substrate temperature of the film structure of μc-Si:H prepared by RF magnetron sputtering

We prepared hydrogenated microcrystalline silicon (μc-Si:H) films by the RF magnetron sputtering method using an argon/hydrogen gas mixture, and investigated the dependence of the film structure on substrate temperature during deposition. The deposition rate was almost constant when the substrate temperature was between 70°C and 150°C, and also between 200°C and 350°C. However, it decreased by 25% when the substrate temperature was increasing from 150°C to 200°C. The hydrogen concentration in the films showed the same dependence of the deposition rate. These findings suggest that the surface reaction changed with increasing substrate temperature. X-ray diffraction (XRD) spectra revealed that the films prepared below 100°C were amorphous, while the films prepared above 120°C were microcrystalline in nature. The XRD peak intensity and the mean crystalline size, as estimated from the XRD peak width increased with increasing substrate temperature. This suggests that, control of the substrate temperature is very important in order to prepare μc-Si:H films with a high degree of crystallinity.

Mechanism of Hydrogenated Microcrystalline Si Film Deposition by Magnetron Sputtering Employing a Si Target and H2/Ar Gas Mixture

The mechanism of hydrogenated microcrystalline silicon (µc-Si:H) film deposition by magnetron sputtering employing a Si target and H2/Ar gas mixture has been investigated by measuring Si and H atom densities in the gas phase by laser-induced fluorescence spectroscopy. The crystalline volume fraction of the film correlated positively with H atom density. The variation in Si atom density indicated the increase in sputtering yield from the Si target in the H2/Ar discharge. The surface of the Si target immersed in the H2/Ar discharge was hydrogenated. Therefore, it is reasonable to expect the production of SiHx molecules (typically SiH4) from the hydrogenated Si target via reactive ion etching. Since SiHx molecules produced from the target may function as a deposition precursor, the mechanism of µc-Si:H film deposition is considered to be similar to that of plasma-enhanced chemical vapor deposition (PECVD) employing a SiH4/H2 gas mixture. The advantage of magnetron sputtering deposition over PECVD is the production of SiHx molecules without using toxic, explosive SiH4.

Effect of hydrogen radicals on properties and structure of a-Si1−xCx:H films

We investigated the effect of hydrogen radicals on properties and structure of hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films by the use of a preparation system possessing both hydrogen plasma chamber and silane/methane plasma chamber. The deposition rate, the carbon content, the optical band gap and the film structure investigated with IR transmission spectroscopy remained unchanged with changes in rf power on the hydrogen plasma side. However, the refractive index increased with increasing the rf power on the hydrogen plasma side. The Urbach energy decreased from 67 to 53 meV. The photoconductivity of the films prepared with the rf power on the hydrogen plasma side of 100 W was improved to be 3×10−5 S cm−1, which was by about two orders of the magnitude larger than that without hydrogen plasma. For preparing photoconductive a-Si1−xCx:H films, it is important to generate a number of hydrogen radicals and introduce them onto the growing film surface efficiently.