G. Uchida

In situ analysis of size distribution of nano-particles in reactive plasmas using two dimensional laser light scattering method

We have developed a simple in-situ method for measuring the size distribution (the mean size (mean diameter) and size dispersion) of nano-particles generated in reactive plasmas using the 2 dimensional laser light scattering (2DLLS) method. The principle of the method is based on thermal coagulation of the nano-particles, which occurs after the discharge is turned off, and the size and density of the nano-particles can then be deduced. We first determined the 2D spatial distribution of the density and size of the nano-particles in smaller particle size (a few nm) range than ones deduced from the conventional 2DLLS method. From this 2D dataset, we have for the first time been able to determine the size distribution of nano-particles generated in a reactive plasma without ex-situ measurements.

Effects of Atmospheric Air Plasma Irradiation on pH of Water

We have studied the effects of atmospheric air plasma irradiation to water using a scalable dielectric barrier discharge device. Measurements of the pH of water treated by the plasmas have shown the pH decreases due to peroxide molecules generated by plasma irradiation and depends on material of water container. We also found this plasma treated water has little effect on the growth enhancement on Radish sprouts compare with plasma irradiation on dry seeds and the plasma irradiation can affect them through the water buffer of 0.2 mm in thickness.

Contribution of ionic precursors to deposition rate of a-Si:H films fabricated by plasma CVD

We have studied contribution of ionic precursors to deposition rate of a-Si:H films in the downstream region of a multi-hollow discharge plasma CVD reactor using a DC bias grid and QCMs. The deposition rate decreases from 1.1 to 0.93 by applying negative bias voltage to the bias grid. The ionic precursors contribute to 7% of the total deposition rate and the dominant ionic precursors are considered to be negatively charged clusters.

Preparation of Si nanoparticles by laser ablation in liquid and their application as photovoltaic material in quantum dot sensitized solar cell

Quantum dot sensitized solar cell was fabricated using silicon nanoparticles prepared by laser ablation in liquid. The obtained particles are spherical and have an average size of 6 nm. These particles were utilized as photosensitizing material in solar cell with polysulfide as an electrolyte. The conversion efficiency of solar cell with silicon nanoparticles was 5.3 times higher than the one with only TiO2 particles. Electrical impedance spectroscopy also revealed the decrease in resistance in the former case led to higher current density than the latter one.

Growth stimulation of radish sprouts using discharge plasmas

We have investigated growth stimulation of radish sprouts using nonthermal atmospheric pressure He discharge plasmas and low pressure O2 RF discharge plasmas. Seeds of radish sprouts were irradiated by one of these plasmas. After 7 days cultivation, the average length of sprouts with irradiation was 15–60 % longer than those without irradiation. Reactive oxygen species may be involved in the growth stimulation mechanism.

Crystallinity Control of Sputtered ZnO:Al Transparent Conducting Films by Utilizing Buffer Layers Fabricated via Nitrogen Mediated Crystallization

We have developed a fabrication method based on sputtering, “Nitrogen Mediated Crystallization (NMC)”, which enables control of crystal nucleation and growth of ZnO. By utilizing this NMC, ZnO:Al transparent conducting films with low resistivity of 2.8×10-3.2×10 Ω•cm in a film thickness range 20-100 nm have been fabricated. The resistivity is significantly lower than that of ZnO:Al films fabricated by conventional sputtering (6.3×10-1.5×10 Ω·cm). Thus, NMC method opens up a new pathway for development of oxide semiconductors.

Impacts of plasma fluctuation on nanoparticle growth in reactive plasmas

Summary form only given. We are investigating interactions between plasmas and nano-interfaces.1 Our research aims to bring about an explosive development of fabrication technologies of nanomaterials and nanostructures. In the nanoscales there arise four distinctive features of interactions: 1)size effects of properties, 2)fluctuation dominant phenomena, 3)object size below interaction length, and 4) nanostructures of reactive space.

Plasma etching resistance of plasma anisotropic CVD carbon films

Summary form only given. Hard carbon films have attracted much attention due to their high hardness and wear resistance. Deposition profile of hard carbon films on trench substrates is one of the concerns to realize coatings on such substrates. Here we have demonstrated three kinds of deposition profiles of carbon films on substrates with submicron wide trenches using H-assisted plasma CVD of Ar + H2 + C 7 H 8 .1–3) The three deposition profiles are sub-conformal, conformal and anisotropic deposition profile, for which carbon is deposited on top and bottom of trenches without being deposited on sidewall of trenches. Experimental deposition profiles are determined by the balance between deposition of carbon containing radicals and etching by H atoms. Irradiation of ions hardens films and hence decreases the etching rate. When the etching rate surpasses the deposition rate of carbon containing radicals, no deposition takes place there. Therefore, a high H atom flux is the key to anisotropic deposition.