Local chemical states and microstructure of photoluminescent porous silicon studied by means of EELS and TEM

Photoluminescent porous Si (PS) layers were formed on low resistivity p-type Si(100) wafers by anodization at a current density (Ia) of 100-350 mA cm(-2) at room temperature. The local chemical states and the microstructures of the PS layers were studied by means of electron energy loss spectroscopy (EELS) and transmission electron microscopy (TEM), and were correlated to the red photoluminescence (PL). The PS layer consists of sponge-like and tree-like structures. The tree-like structure becomes finer with increase of Ia. The fine tree-like structure is shown to be favorable for intensive PL. The EELS analysis reveals that the Si-4O structure, namely the basic structure of SiO2, and Si crystals coexist in the PS layers. The relative content of SiO2 to Si crystallites (R) increases with increase in Ia and decreases with the depth from the top surface of the PS layer. High R corresponds to intensive PL. These results suggest that PL may be connected with some kind of defects in SiO2 and/or defects in the boundary between Si crystallites and SiO2 structure in anodized PS layers, and that PL may be mainly emitted from the layer near the top surface of the PS layers.     

MODELS FOR THE CHROMOPHORE STRUCTURE OF THE PHOTOTRANSFORMATION INTERMEDIATES OF PEA PHYTOCHROME IN VITRO

Abstract— The changes in the chromophore structure of pea phytochrome during phototransformation in vitro from the red-light-absorbing form (P_r) to the far-red-light-absorbing form (P_fr), and from P_fr to P_r, were analysed in terms of wavelength and oscillator strength of absorption, using the zero-differential overlap approximation of the molecular orbital theory for electrons. The effect of a point-charge and a point-dipole on the optical absorption of phytochromobilin intermediates were examined using the stationary perturbation theory for degenerate states. The results indicate that the cis-trans photoisomerization of the pyrrole ring D, if any, occurred within 10 μs after a laser-flash excitation of the phytochrome, and that the conformations of phytochromobilin and the protein moiety of phytochrome were not significantly changed during the period of examination of phototransformation in either direction.     

Characterization of coal fly-ash particles by laser microprobe mass spectrometry

Laser microprobe mass spectrometry (LMMS) was applied to coal fly-ash particles prefractionated to homogeneous composition with respect to particle size and density. For major elements, semiquantitative results (<50% relative standard deviation) were obtained; and the characteristic density dependence found for Si, K, Ca and Fe was in good agreement with that obtained by scanning electron microscopy/energy-dispersive x-ray analysis (EDX). The relative sensitivity coefficients, based on concentrations evaluated from the EDX data, coincided with those obtained for the NBS glass particle standard in previous work.     

Distance-restricted matching extendability of fullerene graphs

A fullerene graph is a 3-connected cubic plane graph whose all faces are bounded by 5- or 6-cycles. In this paper, we show that a matching M of a fullerene graph can be extended to a perfect matching if the following hold: (i) three faces around each vertex in \(\{x,y:xy\in M\}\) are bounded by 6-cycles and (ii) the edges in M lie at distance at least 13 pairwise.     

Young's double-slit interference observation of hot electrons in semiconductors

We have carried out Young's double-slit experiment for the hot-electron wave in man-made semiconductor structures with a 25-nm-space double slit in an InP layer buried within GaInAs, a 190-nm-thick GaInAsP hot-electron wave propagation layer, and a collector array of 80 nm pitch. At 4.2 K, dependences of the collector current on the magnetic field were measured and found to agree clearly with the double-slit interference theory. The present results show evidence for the wave front spread of hot electrons using the three-dimensional state in materials, for the first time, and the possibility of using top-down fabrication techniques to achieve quantum wave front control in materials.     

Microwave spectrum of the HD2O+ ion: inversion-rotation transitions and inversion splitting

Inversion-rotation spectral lines of the dideuterated hydronium ion, HD2O+, have been observed by a source-modulation millimeter- to submillimeter-wave spectrometer. The ion was generated by a hollow-cathode discharge in a gas mixture of D2O and H2O in a free-space cell. Ten inversion-rotation lines were measured precisely for the lowest pair of inversion doublets in the frequency region from 380 to 730 GHz. The observed lines include the most astronomically important transitions, 0(00) (-)-1(10)+ for the para species at 380 538.031(32) MHz and 1(01) (-)-1(11)+ for the ortho species at 728 420.189(34) MHz, which could be used as a radio astronomical probe investigating interstellar chemistry of deuterium fractionation. An analysis of the measured lines has yielded the rotational constants in the ground doublet states and the inversion splitting. The inversion splitting in the ground state was determined to be 808 866(34) MHz, that is, 26.980 87(113) cm(-1), where the numbers in parentheses give uncertainties estimated from the Jacobian matrix of the assumed centrifugal distortion constants. The determined inversion splitting is off by -0.51 cm(-1) from the predicted value of 27.49 cm(-1) by Rajamaki et al. using high-order coupled cluster ab initio calculation [J. Chem. Phys. 118, 10929 (2003)], and by -0.0510 cm(-1) from the observed value of 27.0318(72) cm(-1) by Dong et al. using high-resolution jet-cooled infrared spectroscopy [J. Chem. Phys. 122, 224301 (2005)] beyond the quoted uncertainty.