Single-step fabrication of fibrous Si/Sn composite nanowire anodes by high-pressure He plasma sputtering for high-capacity Li-ion batteries.

To realize high-capacity Si anodes for next-generation Li-ion batteries, Si/Sn nanowires were fabricated in a single-step procedure using He plasma sputtering at a high pressure of 100-500 mTorr without substrate heating. The Si/Sn nanowires consisted of an amorphous Si core and a crystalline Sn shell. Si/Sn composite nanowire films formed a spider-web-like network structure, a rod-like structure, or an aggregated structure of nanowires and nanoparticles depending on the conditions used in the plasma process. Anodes prepared with Si/Sn nanowire films with the spider-web-like network structure and the aggregated structure of nanowires and nanoparticles showed a high Li-storage capacity of 1219 and 977 mAh/g, respectively, for the initial 54 cycles at a C-rate of 0.01, and a capacity of 644 and 580 mAh/g, respectively, after 135 cycles at a C-rate of 0.1. The developed plasma sputtering process enabled us to form a binder-free high-capacity Si/Sn-nanowire anode via a simple single-step procedure.

Nanostructured Ge and GeSn films by high-pressure He plasma sputtering for high-capacity Li ion battery anodes.

We fabricated nanostructured Ge and GeSn films using He radio-frequency magnetron plasma sputtering deposition. Monodisperse amorphous Ge and GeSn nanoparticles of 30-40 nm size were arranged without aggregation by off-axis sputtering deposition in the high He-gas-pressure range of 0.1 Torr. The Ge film porosity was over 30%. We tested the charge/discharge cycle performance of Li-ion batteries with nanostructured Ge and GeSn anodes. The Ge anode with a dispersed arrangement of nanoparticles showed a Li-storage capacity of 565 mAh/g after the 60th cycle. The capacity retention was markedly improved by the addition of 3 at% Sn in Ge anode. The GeSn anode (3 at% Sn) achieved a higher capacity of 1128 mAh/g after 60 cycles with 92% capacity retention. Precise control of the nano-morphology and electrical characteristics by a single step procedure using low temperature plasma is effective for stable cycling of high-capacity Ge anodes.

Publisher Correction: Decomposition and oxidation of methionine and tryptophan following irradiation with a nonequilibrium plasma jet and applications for killing cancer cells.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Decomposition and oxidation of methionine and tryptophan following irradiation with a nonequilibrium plasma jet and applications for killing cancer cells.

We present evidence for the decomposition and oxidation of amino acids in aqueous solution following irradiation with a nonequilibrium plasma jet. Of 15 amino acids tested in cell culture medium, plasma irradiation induced a marked chemical change in methionine and tryptophan due to the effective production of reactive oxygen species by plasma-water interaction. We also report that plasma-treated methionine and tryptophan aqueous solutions can kill cancer cells, greatly decreasing the viability of human endometrial carcinoma (HEC-1) cancer cells due to the presence of decomposition or oxidation products generated from the amino acid. Plasma-treated methionine and tryptophan aqueous solutions also induced an anti-cancer effect on cancer-initiating cells.

Plasma-enhanced reactive linear sputtering source for formation of silicon-based thin films.

In this study, an inductively coupled plasma (ICP)-enhanced reactive sputter deposition system with a rectangular target was developed as a linear plasma source for roll-to-roll deposition processes. The longitudinal distribution of the film thickness indicated the feasibility of uniformity control via the control of the power deposition profile of the assisted ICPs. The characteristics of Si films were investigated in terms of the film thickness uniformity and film crystallinity. The results of Raman and X-ray diffraction measurements indicated the crystallization of the Si film with a crystallinity as high as 73%-78% in all the samples of the longitudinal position.

Atmospheric-Pressure Plasma Interaction with Soft Materials as Fundamental Processes in Plasma Medicine.

Molecular-structure variation of organic materials irradiated with atmospheric pressure He plasma jet have been investigated. Optical emission spectrum in the atmospheric-pressure He plasma jet has been measured. The spectrum shows considerable emissions of He lines, and the emission of O and N radicals attributed to air. Variation in molecular structure of Polyethylene terephthalate (PET) film surface irradiated with the atmospheric-pressure He plasma jet has been observed via X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). These results via XPS and FT-IR indicate that the PET surface irradiated with the atmospheric-pressure He plasma jet was oxidized by chemical and/or physical effect due to irradiation of active species.

Plasma Interaction with Organic Molecules in Liquid as Fundamental Processes in Plasma Medicine.

Investigation of plasma-organic materials interaction in aqueous solution with atmospheric pressure plasmas have been carried out. Degradation of methylene blue (MB) in aqueous solution via atmospheric pressure He plasma exposure through gas/liquid interface have been investigated. The optical emission spectrum shows considerable emissions of He lines and the emission of O, OH and N radicals attributed to dissociation of water (H2O) and air has been confirmed. Structure variation of MB in solution treated with the atmospheric-pressure He plasma has been measured by Fourier transform infrared spectroscopy (FT-IR). The results obtained from FT-IR analysis show degradation of MB in solution treated with the atmospheric-pressure He plasma. The pH effect of MB degradation was investigated using controlled pH solutions by an ultraviolet-visible (UV-Vis) spectroscopy and FT-IR. The results show no effect of MB degradation on pH. The results exhibit that the atmospheric pressure plasmas exposure has made it possible to degrade organic materials in solution due to irradiated radicals from plasma through plasma/liquid interface.

Atmospheric-Pressure Gas-Breakdown Characteristics with a Radio-Frequency Voltage.

We present He atmospheric-pressure gas-breakdown phenomena with radio frequency (RF) voltages in the frequency region from a few tens MHz to 100 MHz. The gas-breakdown voltage for RF and very high frequency (VHF) discharges is considerably lower than that for the DC discharge, and the gas-breakdown voltage is effectively reduced to be as low as 160 V in VHF region. The discharge characteristics drastically change with increasing discharge-voltage frequency, and strong emisson is highly loclized in front of the power- and ground-electrode in the VHF discharges. The lowering gas-brakdown voltage and the localized emission-profile are well explained by the effect of the charged-particle confinement in a micro dishcarge-space.

Dynamic Properties of Helium Atmospheric Dielectric-Barrier-Discharge Plasma Jet.

We present here experiments on helium atmospheric dielectric-barrier discharge jet in open air. A long stable plasma plume is realized at high applied voltage and high gas flow rate. Optical emission measurements show that the plasma plume consists of two part: a plume head with high energy electrons and a tail part with low energy electrons. The plasma plume propagates away from the quartz-tube outlet with about 30-80 km/sec along the helium gas flow channel. The propagation velocity of plasma plume is in the time scale of electron drift velocity, and the electric field plays an important role as a driving force of the plasma plume propagation.