Preparation and properties of microcrystalline silicon films using photochemical vapor deposition

microcrystalline silicon films have been prepared through mercury photosensitized decomposition of monosilane at low gas pressures. The dark and light conductivities of the silicon films tend to increase at reactant pressures lower than 65 Pa and become 10^?2Ω^?1· cm^?1 at 26 Pa. From the Raman scattering and x-ray diffraction, silicon films were found to consist of a mixed phase structure including both microcrystalline and amorphous regions.     

Hyperdoping of silicon with deep-level impurities by pulsed YAG laser melting

Hyperdoping with deep-level impurity is a promising method to prepare intermediate band semiconductors. We prepared silicon hyperdoped with deep-level impurities, sulfur and titanium, by ion implantation followed by pulsed YAG laser melting. The processes of sulfur and titanium hyperdoping are comparatively studied. The amorphous sulfur and titanium ion-implanted layers changed to monocrystal by following pulsed laser melting. The depth profile of sulfur impurity after pulsed laser melting is similar to that of ion-implanted sample, while large segregation is observed for titanium hyperdoping. The crystallinity and degree of segregation depend on the laser shot number and initially implanted titanium dose. There is a trade-off between crystallinity and depth profile of impurity for titanium hyperdoping. From a viewpoint material processing, formation of high-quality silicon monocrystal hyperdoped with sulfur is easier than that with titanium. Correlation between the mid-infrared optical absorption and photoconductivity is also discussed for sulfur-hyperdoped sample.     

Isotopic fingerprint of electron-phonon coupling in high-Tc cuprates

Angle-resolved photoemission spectroscopy with low-energy tunable photons along the nodal direction of oxygen isotope substituted Bi(2)Sr(2)CaCu(2)O(8+delta) reveals a distinct oxygen isotope shift near the electron-boson coupling "kink" in the electronic dispersion. The magnitude (a few meV) and direction of the kink shift are as expected due to the measured isotopic shift of phonon frequency, and are also in agreement with theoretical expectations. This demonstrates the participation of the phonons as dominant players, as well as pinpointing the most relevant of the phonon branches.     

An Optochemical Oxygen Scavenger Enabling Spatiotemporal Control of Hypoxia

We present an optochemical O₂ scavenging system that enables precise spatiotemporal control of the level of hypoxia in living cells simply by adjusting the light intensity in the illuminated region. The system employs rhodamine containing a selenium or tellurium atom as an optochemical oxygen scavenger that rapidly consumes O₂ by photochemical reaction with glutathione as a coreductant upon visible light irradiation (560–590 nm) and has a rapid response time, within a few minutes. The glutathione-consuming quantum yields of the system were calculated as about 5 %. The spatiotemporal O₂ consuming in cultured cells was visualized with a hypoxia-responsive fluorescence probe, MAR. Phosphorescence lifetime imaging was applied to confirmed that different light intensities could generate different levels of hypoxia. To illustrate the potential utility of this system for hypoxia research, we show that it can spatiotemporally control calcium ion (Ca²⁺) influx into HEK293T cells expressing the hypoxia-responsive Ca²⁺ channel TRPA1.