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The K α resonance fluorescence (RFL) effect via photoabsorptions of inner shell electrons as the element goes through multiple ionization states is studied. We demonstrate that the resonances observed recently in K α (1s–2p) fluorescence in aluminum plasmas by using a high-intensity X-ray free-electron laser [1] are basically K-shell resonances in hollow atoms going through multiple ionization states at resonant energies as predicted earlier for gold and iron ions [2] . These resonances are formed below the K-shell ionization edge and shift toward higher energies with ionization states, as observed. Fluorescence emission intensities depend on transition probabilities for each ionization stage of the given element for all possible K α ( 1 s → 2 p ) transition arrays. The present calculations for resonant photoabsorptions of K α photons in Al have reproduced experimentally observed features. Resonant cross sections and absorption coefficients are presented for possible observation of K α RFL in the resonant energy ranges of 4.5–5.0 keV for Ti ions and 8.0–8.7 keV for Cu ions respectively. We suggest that theoretically the K α RFL process may be driven to enhance the Auger cycle by a twin-beam monochromatic X-ray source, tuned to the K-edge and K α energies, with potential applications such as the development of narrow-band biomedical X-ray devices. [ABSTRACT FROM AUTHOR]

New R-matrix calculations of electron impact excitation rates for transitions among the 2s22p, 2s2p2 and 2p3 levels of Ar xiv are presented. These data are subsequently used to derive the theoretical electron density diagnostic emission-line intensity ratios and for a range of densities and electron temperatures appropriate to solar transition region and coronal plasmas. A comparison of these diagnostics with observational data for solar active regions and flares, obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, reveals that the electron densities determined from are in good agreement with those estimated from line ratios in Fe xiv or Fe xv, which are formed at similar electron temperatures to Ar xiv. However, there are large discrepancies between densities inferred from the ratio and those from Fe xiv or Fe xv, confirming that the Ar xiv 243.78- and 257.40- Å lines are badly blended with Fe xv 243.79 Å and Fe xiv 257.38 Å, respectively. Hence, cannot be employed as a density diagnostic, in contrast to , which does provide reliable estimates. [ABSTRACT FROM AUTHOR]

Thermoelectric properties of single wall carbon nanotubes (SWNT) are quite sensitive to gases in contact with the tube walls. This effect makes possible a thermoelectric chemical sensor. Large, reversible swings in thermoelectric power (S), sometimes even involving sign changes in S, have been observed. Even contact of the SWNTs with He and N 2 and H 2 result in easily detectable and reversible changes in S. Smaller, polar alcohol molecules stimulate a large thermoelectric response, although H 2 O has no effect. For adsorption of six membered ring molecules C 6 H n in SWNTs, the large thermoelectric response observed for Benzene (n=6) is seen to decrease as the π electrons in the molecule are removed, and the coupling between the molecules and the SWNT is thereby reduced. These effects are discussed in terms of the diffusion thermopower for a rope, and a new scattering channel associated with adsorbed molecules. [ABSTRACT FROM AUTHOR]

New R-matrix calculations of electron impact excitation rates for transitions among the 2s[sup 2]2p, 2s2p[sup 2] and 2p[sup 3] levels of Si x are presented. These data are subsequently used, in conjunction with recent estimates for proton excitation rates, to derive theoretical electron density sensitive emission-line ratios involving transitions in the ∼253–356 Å wavelength range. A comparision of these with observations of a solar active region and subflare, obtained during the 1989 flight of the Solar EUV Rocket Telescope and Spectrograph (SERTS), reveals that the electron densities determined from most of the Si x line ratios are consistent with one another for both solar features. In addition, the derived densities are also in good agreement with the values of N[sub e] estimated from diagnostic lines in other species formed at similar electron temperatures to Si x, such as Fe xii and Fe xiii. These results provide observational support for the general accuracy of the adopted atomic data, and hence line ratio calculations, employed in the present analysis. However, we find that the Si x 256.32-Å line is blended with the He ii transition at the same wavelength, while the feature at 292.25 Å is not due to Si x, but currently remains unidentified. The intensity of the 253.81-Å line in the SERTS active region spectrum is about a factor of 3 larger than expected from theory, but the reason for this is unclear, and requires additional observations to explain the discrepancy. [ABSTRACT FROM AUTHOR]

The authors report the fabrication of p-n junctions, consisting of p-type La0.7Sr0.3MnO3 (LSMO) and either n-type ZnO grown on sapphire or n-type Si substrates. The LSMO/ZnO junction exhibits excellent rectifying behavior over the temperature range of 77–300 K with breakdown voltage less than -10 V. LSMO/Si displayed p-n junction characteristics over a temperature region of 77–360 K. Inserting a SrTiO3 layer between LSMO and Si remarkably improved the junction characteristics. All junctions show photocarrier injection effect, illustrating the control of transport properties of LSMO in which electron injection decreases hole concentration following the photoexcitation of both ZnO and Si. [ABSTRACT FROM AUTHOR]

We have demonstrated the fabrication of highly continuous and smooth CdSe semiconductor films containing self-assembled nanocrystals (NCs) using a simple, low cost solution-processed deposition technique. The impact of thermal annealing and ethanedithiol (EDT) treatment on oleate capped CdSe NCs films is illustrated. Post deposition EDT treatment enhances strong electron coupling between NCs by reducing the inter-particle distance, which enhances four orders of magnitude of photocurrent in the pn-device. Mild thermal annealing of NC films cause large redshift and significant broadening. Our findings suggest that NCs with short-range organic ligands are suitable for high-performance Thin-Film-Transistors and next generation high-efficiency photovoltaics. [ABSTRACT FROM AUTHOR]