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Effects of nitrogen impurity on ZnO crystal growth on Si substrates have been investigated. The quantitative analysis on the surface morphology deriving height-height correlation function indicates that adsorbed nitrogen atoms suppress the secondary nucleation and enhance adatom migration. The resultant films have smooth surface as well as large grain size up to 24 nm even for small thickness of 10 nm. ZnO films fabricated by using such films as buffer layers possess high crystal quality, where the full width at half maximum of (002) rocking curve is 0.68°, one-fourth of that for films fabricated without nitrogen.
We have recently developed a novel semiconductor, (ZnO)x(InN)1-x (abbreviated to ZION). In this study, we have succeeded in direct epitaxial growth of ZION films on 19–21%-lattice-mismatched c-plane sapphire by radio-frequency (RF) magnetron sputtering. X-ray diffraction analysis showed that there is no epitaxial relationship between ZION films fabricated at room-temperature (RT) and the sapphire substrates, while the films fabricated at 450oC grow epitaxially on the sapphire substrates. From the analysis of time evolution of the surface morphology, the process for the epitaxial growth of ZION on sapphire is found to consist of three stages. They are (i) initial nucleation of ZION crystallites with crystal axis aligned to the sapphire substrate, (ii) island growth from the initially formed nuclei and subsequent nucleation (secondary nucleation) of ZION crystallites, and (iii) lateral growth of ZION islands originated from initially formed nuclei. On the other hand, non-epitaxial ZION films fabricated at RT just grow in 3D mode. From these results, we conclude that the substrate temperature is the key to control of nucleation and subsequent epitaxial growth of ZION films on the lattice-mismatched substrate.
We have produced plasma activated water (PAW) using air, O2, N2, He and Ar atmospheric pressure dielectric barrier discharge plasma irradiation to deionized water. Then, PAW was kept for 1 hour or 1 day at room temperature to reduce concentrations of short lifetime reactive oxygen species and reactive nitrogen species before supplying to plants. O2, air and N2 PAW induces growth enhancement of plants. For 1 hour PAW supply the longest seedling length after 3 days cultivation is 1.62, 1.38, 1.13, 1.12, and 1.04 times long for air, O2, He, N2, and Ar plasmas compared with the length for thecontrol, whereas for 1 day PAW supply it is 1.52, 1.28, 1.13, 1.10, and 1.08 times long for air, O2, He, N2 and Ar. Therefore, long lifetime reactive oxygen nitrogen species in PAW is effective for the growth enhancement.
We have fabricated ZnInON (ZION), which is a pseudo-binary alloy of wurtzite ZnO and wurtzite InN and has a tunable band gap over the entire visible spectrum and a high optical absorption coefficient of 105 cm-1. ZION films grow two dimensionally at Ts = room temperature (RT) and 150°C, whereas they grow three dimensionally at Ts = 250 and 450°C. These films at RT and 150°C show a step-terrace structure with the step height of 0.27 nm, which corresponds to the height of a single-atomic-layer step and the half length of the c-lattice parameter of ZION. ZION film has the same a-lattice parameter of 0.325 nm as ZnO and a longer c-lattice parameter of 0.536 nm, indicating the coherent growth of ZION films on ZnO templates. ZION film grown at RT shows blue (2.89 and 3.08 eV) photoluminescence at RT.
ZnO films were fabricated by RF magnetron sputtering with nitrogen mediated crystallization (NMC) under various gas pressures. X-ray diffraction measurements show that the NMC-ZnO films are highly crystalline regardless of the gas pressure, and the full width at half maximum values of the (0002) rocking curves range from 0.032 to 0.044°. In contrast, atomic force microscopy (AFM) reveals that the gas pressure plays an important role in determining the surface morphology of the films. The root-mean-square (RMS) roughness decreases monotonically from 1.05 to 0.60 nm with increasing pressure from 0.2 to 0.7 Pa. However, the RMS roughness increases with further increases in the pressure, reaching 2.15 nm at 2.1 Pa. The height distribution of the NMC-ZnO films derived from the AFM images is narrowest at 0.7 Pa, indicating that the smooth surface obtained at 0.7 Pa can be attributed to spatially uniform nucleation occurring in a short time period. These results indicate that the sputtering gas pressure is a key parameter for controlling the surface morphology of NMC-ZnO films.
We have investigated plant growth response to atmospheric air plasma treatments of seeds on their growth for 5 plant speces; Radish sprout (Raphanus sativus L.), rice (Oryza Sativa), Zinnia, Arabidopsis L. Thaliana and Plumeri. The average length of Radish sprout, rice, Arabidopsis Thaliana, Plumeria and Zinnia, are 250%, 80%, 60%, 30% and 20% longer than those without plasma treatments, respectively. We have obtained correlation between the growth enhancement and O3 and NOx concentration. The optimum radical dose for the growth enhancement depends on plant species.
We study effects of deposition temperature on growth mode and surface morphology
of hetero-epitaxial (ZnO)x(InN)1-x (ZION) films on ZnO
templates. ZION films deposited at low temperature of RT-250oC grow
two dimensionally, whereas ZION films deposited at high temperature of
350-450oC grow three dimensionally. Growth mode is changed from
two-dimensional growth mode to three-dimensional one, because the critical
thickness where film strain begin to relax decreases with increasing the
deposition temperature. At high deposition temperatures, the number of point
defects in ZION films decreases because migration of adatoms on the growing
surface is enhanced. The strain energy in ZION films increases with increasing
the deposition temperature, since the strain energy is not released by point
defects. Therefore, lattice relaxation for the higher deposition temperature
begins at the smaller film thickness to release the strain energy. As a result,
ZION films with atomically-flat surface were obtained even at RT.
Nanoparticles have great potential for biomedical applications such as early detection, accurate diagnosis, and personalized treatment of cancer. Assessment of bio-compatibility and toxicity of nanoparticles body is an emerging topic for these applications. To study kinetics of nanoparticles in body, we synthesized indium, gold and platinum nanoparticles in aqueous suspension using pulsed electrical discharge plasmas in water. The average size of synthesized primary nanoparticles for indium, gold, and platinum are 6.2 nm, 6.7 nm, and 5.4 nm, whereas the average size of secondary nanoparticles for indium, gold, and platinum are 315 nm, 72.3 nm, and 151 nm, respectively. Synthesized indium nanoparticles are transported from subcutaneous to serum and brain. The indium content in serum for the synthesized nanoparticles is much higher than that for the In2O3 nanoparticles of 150 nm in primary size. For gold and platinum nanoparticles, preliminary examination of intratracheal administration revealed that administration of synthesized nanoparticles with 10 mg/kg BW (body weight) may cause bleedings and/or emphysema in lung.
We studied the pulmonary toxicity of indium hydroxide (In(OH)3), which is produced during a recycling process of indium-tin oxide (ITO), in comparison with that of ITO or indium oxide (In2O3), two raw materials of flat panel displays. One hundred and forty-four male Wistar rats were intratracheally given equivalent doses of 10 mg/kg indium as In(OH)3, ITO, or In2O3 particles, twice a week, for a total of 5 times for 2 weeks. Control rats were given distilled water as a vehicle. After 3 weeks, these rats were serially euthanized, and toxicological effects were determined. Body weight gain was significantly suppressed in the In(OH)3-treated rats compared to that in the control group, but not in the ITO- or In2O3-treated rats. Relative lung weights in all the indium-treated groups significantly increased compared to those in the control group throughout the observation period. Furthermore, lung weights in the In(OH)3 group were significantly higher than those in either the ITO or In2O3 group. Blood indium levels in the In(OH)3-treated rats were much higher, 70- to 200-fold, than those in the In2O3- or ITO-treated rats at each time point. Although the lung indium content decreased gradually during the observation periods, the content in the In(OH)3 group was significantly higher than that in either the ITO or In2O3 group. A histopathological analysis revealed foci indicating a slight to severe pulmonary inflammatory response, including exudation to alveolar spaces, were present in all the indium-treated groups. Interstitial fibrotic proliferation was seen only in the In(OH)3-treated rats. The severity of these lesions in the In(OH)3-treated rats was greater than that in either the ITO- or In2O3-treated rats.
The results of our study clearly demonstrated that In(OH)3 particles caused severe pulmonary toxicity when repeated intratracheal instillations were performed in rats. Furthermore, the toxic potency of In(OH)3 in the lung was much higher than that of ITO and In2O3. Accordingly, the toxicity of In(OH)3 particles should be considered in addition to that of ITO and In2O3 particles when indium exposure occurs.
We succeeded in photovoltaic power generation of p-i-n solar cells utilizing epitaxial ZnInON film with a wide band gap of 3.1 eV as the intrinsic layer, suitable for a top cell of tandem solar cells. The solar cell shows a high open circuit voltage (Voc) of 1.68 V under solar simulator light irradiation of 3.2 mW/cm2. The solar cell performance becomes worse under 100 mW/cm2, which is mainly attributed to the leakage current caused by crystal defects and grain boundaries. X-ray diffraction analysis reveals that the ZnInON film has rather large tilt and twist angles and a high dislocation density of 7.62×1010 cm-2. Such low crystallinity is a bottleneck for high performance of the solar cells. Our results demonstrate a potential of epitaxial ZnInON films as an intrinsic layer of wide band gap p-i-n solar cells with a high Voc.
Effects of surface morphology of buffer layers on ZnO/sapphire heteroepitaxial growth have been investigated by means of “nitrogen mediated crystallization (NMC) method”, where the crystal nucleation and growth are controlled by absorbed nitrogen atoms. We found a strong correlation between the height distribution profile of NMC-ZnO buffer layers and the crystal quality of ZnO films. On the buffer layer with a sharp peak in height distribution, a single-crystalline ZnO film with atomically-flat surface was grown. Our results indicate that homogeneous and high-density nucleation at the initial growth stages is critical in heteroepitaxy of ZnO on lattice mismatched substrates.
We studied effects of atmospheric air dielectric barrier discharge plasma irradiation to seeds of radish sprouts on chlorophyll and carotenoid concentrations in their leaves. Plasma irradiation increases chlorophyll concentration under some irradiation conditions, whereas the irradiation has little effects on carotenoid concentration. These results show that plasma irradiation to seeds has influence on cell activities in a selective way.
We have studied multigeneration effects of plasma irradiation to seeds of Arabidopsis thaliana (L.) and Zinnia peruviana (L.) on their growth using a scalable DBD device. Atmospheric plasma irradiation enhances growth of these plants in multi-generations. For Arabidopsis thaliana (L.) in the third generation, the leaf area is 2 times larger than that without plasma irradiation and the stem length is 1.5 times longer than that without plasma. For Zinnia peruviana (L.) in the second generation, the stem length is 2 times longer than that without plasma.
We present here performance of Li ion batteries with SiC nanoparticle-film anode, which is fabricated by a double multi-hollow discharge plasma chemical vapor deposition (CVD) method. The first cycle of charge/discharge property of the Li ion battery with the SiC nanoparticle-film anode shows a high capacity of over 4,000 mAh/g, which is 12 times higher than the Li ion battery with the conventional graphite anode. The discharge capacity shows high stability for first 10th cycle, and is 3750 mAh/g for the 10th cycle.
We have carried out in-situ measurements of cluster volume fraction in silicon films during deposition by using quartz crystal microbalances (QCM’s) together with a cluster-eliminating filter. The cluster volume fraction in films is deduced from in-situ measurements of film deposition rates with and without silicon clusters using QCM’s. The results show that the higher deposition rate leads to the higher volume fraction of clusters.
We have developed a cluster-eliminating filter which reduces amount of amorphous silicon nanoparticles (clusters) incorporated into a-Si:H films. We have applied the filter to fabricate a-Si:H Schottky solar cells. The cells show a high initial fill factor FF=0.563 and a high stabilized value after light soaking FF=0.552 which light-induced degradation was quite low value of 1.95 %.
We investigated effects of atmospheric pressure dielectric barrier discharge (DBD) plasma irradiation on growth characteristics of bread yeast (Saccharomyces cerevisie). Nitric oxide of 400 ppm and O3 above 200 ppm are produce by the DBD plasmas. DBD plasma irradiation of 50 and 100 s enhances the growth of yeast in the lag phase, whereas 150 s irradiation suppresses the growth. There is an optimum duration of plasma irradiation for the growth promotion.
The aim of this review is to introduce the adverse health effects of indium compounds. This review consists of 2 parts: (1) a study of the toxic effects in indium compounds in humans, and (2) a study of the toxic effects of indium tin oxide (ITO) and copper indium gallium diselenide (CIGS) in animals.
To date, 4 epidemiological surveys have been conducted of indium-handling workers in Japan, and all who were studied showed that exposure to indium compounds caused pulmonary interstitial and emphysematous changes. There were clear dose-response and dose-effect relationships between the serum indium levels and the levels of Krebs von den Lungen-6 (KL-6), which is a serological indicator of interstitial pneumonia up until 2011, 8 cases of interstitial pneumonia in Japanese indium-exposed workers, 2 cases of pulmonary alveolar proteinosis (PAP) in US indium-exposed workers, and 1 case of PAP in a Chinese indium-exposed worker have been reported.
In animals studies, it has been clearly demonstrated that ITO and CIGS particles cause pulmonary toxicity and that the dissolution of ITO and CIGS particles in the lungs is considerably slow when repeated intratracheal instillations were given to experimental animals.
Thus, more studies are needed on the effects of human exposure to indium compounds.
Growth enhancement characteristics of plants are investigated using an atmospheric discharge plasma. Atmospheric pressure plasma torch is consisted of alumina ceramics tube and the steel mesh electrodes wound inside and outside of the tube. The growth enhancement was observed in the length of stem and root of plants after the plasma irradiation to seeds. The stem length increases approximately 2.8 times after the cultivation time of 24 h. And the effect is found to be maintained for 40 h, after sowing seeds. The mechanism of the growth enhancement would be the redox reaction inside plant cells induced by oxygen radicals.
Quantum dot-sensitized solar cells (QDSCs) based on the multiple exciton generation (MEG) of QD are attractive in the field of photochemical cells because the improvement of conventional sensitized solar cells has been stagnant recently. The distinctive characteristics of QDs are their strong photo-response in the visible region and quantum confinement effects. Its theoretical efficiency is much higher than that of solar cell based on the single exciton generation (SEG). Moreover, QDs have tunable optical properties and band-gaps depending on the particle size. But QD materials widely used for QDSC have some disadvantages of toxicity and scarcity. On the other hand, Si as one of good QD materials is abundant and not toxic. Also, Si QD has high stability against light soaking and a high optical absorption coefficient due to quantum size effects. However, the research on Si QD is rare although the quantum effect of Si was already verified. It is one of reasons that the fabrication and collection of Si nano-particles are too difficult. Therefore, this work proposed multi-hollow plasma discharge chemical vapor deposition (CVD). It is possible to collect Si particles unlike conventional CVD and solve the problems of the wet process. The optical properties of Si particles were controlled by varying experimental conditions. In this work, Si particles were fabricated with various sizes and their characteristics were analyzed. Based on the results, Si QD was applied to Si QDSC.