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Notes: The polarized absorption spectra of oriented films of phase-I and phase-II poly(di-n-hexylsilane), PDHS, have been determined in the visible/UV and in the near-edge regions of the C 1s and Si 1s x-ray ionization potentials. The phase-I absorption band at 360 nm is strongly polarized parallel to the direction of the Si chain, whereas the analog of this band in phase II (317 nm) is only weakly polarized in the same direction; this is consistent with partial trans→gauche isomerization of the Si chain in phase II and delocalization of the excitation in part onto disordered n-hexyl groups. Polarized absorption in the vicinity of the Si 1s ionization limit reveals strong polarization of the discrete and continuum transitions in both phase I and phase II, whereas the equivalent spectra taken in the vicinity of the C 1s limit show strong polarization in phase I but little or no polarization in phase II. The x-ray spectra are interpreted as showing that the Si chain and the n-hexyl groups of the polymer are ordered in phase I and are essentially perpendicular to one another, whereas in phase II the n-hexyl chains are disordered while the Si backbone remains relatively fixed in space. The Si 1s electron-yield spectra also display EXAFS interferences which have been transformed to yield Si–Si and Si–C distances in the polymer of 2.37±0.02 and 1.81±0.03 A(ring), respectively. The various discrete and continuum transitions are assigned according to an orbital model, and the visible/UV thermochromism earlier reported for PDHS is now observed in the Si 1s x-ray near-edge spectrum as well.

Notes: Two-photon cross sections of neat benzene and methyl substituted benzenes at various wavelengths for selective excitation were measured by two-photon induced fluorescence spectra for the first time. The results show that the two-photon rate increases rapidly with the frequency of the photon.

Notes: Two-photon transitions have been examined in argon, krypton, xenon, and molecular hydrogen using a coherent vacuum ultraviolet (VUV) photon at a fixed wavelength of 118 nm and a tunable photon from a dye laser. The 118 nm VUV photon is produced by third harmonic generation in xenon using UV light at 355 nm from a frequency tripled Nd:YAG laser. Though the VUV intensity is very weak, (∼100 nJ per pulse) it was utilized very efficiently since most of VUV photons in the ionization region were absorbed. Spectra were obtained in the region of 12.5 to 13.5 eV and the corresponding two-photon rate constants were calculated. This is the first time that coherent VUV light has been employed with tunable visible light for the production of two-photon spectra and the measurement of two-photon rates. The two-photon ionization rate of xenon was measured using photons at fixed wavelengths of 118 and 355 nm. A new parameter is proposed for direct comparison of the data from various two-photon experiments.

Notes: Abstract: Pharmacologic activation of endogenous protein kinase C (PKC) together with elevation of the intracellular Ca2+ level was previously shown to cause reduction of two voltage-dependent K+ currents (IA and Ica2+-K+) across the soma membrane of the type B photoreceptor within the eye of the mollusc Hermissenda crassicornis. Similar effects were also found to persist for days after acquisition of a classically conditioned response. Also, the state of phosphorylation of a low-molecular-weight protein was changed only within the eyes of conditioned Hermissenda. To examine the role of PKC in causing K+ current changes as well as changes of phosphorylation during conditioning (and possibly other physiologic contexts), we studied here the effects of endogenous PKC activation and exogenous PKC injection on phosphorylation and K+ channel function. Several phosphoproteins (20, 25, 56, and 165 kilodaltons) showed differences in phosphorylation in response to PKC activators applied to intact nervous systems or to isolated eyes. Specific differences were observed for membrane and cytosolic fractions in response to both the phorbol ester 12-deoxyphorbol 13-isobutyrate 20-acetate (DPBA) or exogenous PKC in the presence of Ca2+ and phosphatidylserine/diacylglycerol. Type B cells pretreated with DPBA responded to PKC injection with a persistent reduction of K+ currents. In the absence of DPBA, PKC injection also caused K+ current reduction only following Ca2+ loading conditions. However, the direct effect of PKC injection in the absence of DPBA was only to increase ICa2+_K+. According to a proposed model, the amplitude of the K+ currents would depend on the steady-state balance of effects mediated by PKC within the cytoplasm and membrane-associated PKC. The model further specifies that the effects on K+ currents of cytoplasmic PKC require an intervening proteolytic step. Such a model predicts that increasing the concentration of cytoplasmic protease, e.g., with trypsin, will increase K+ currents, whereas blocking endogenous protease, e.g., with leupeptin, will decrease K+ currents. These effects should be opposed by preexposure of the cells to DPBA. Furthermore, prior injection of leupeptin should block or reverse the effects of subsequent injection of PKC into the type B cell. All of these predictions were confirmed by results reported here. Taken together, the results of this and previous studies suggest that PKC regulation of membrane excitability critically depends on its cellular locus. The implications of such function for long-term physiologic transformations are discussed.

Notes: We have studied the microstructures of epitaxial YbBa2Cu3O7 superconducting films grown on SrTiO3[100] and [110] substrates by a new liquid-gas-solidification processing technique. Films grown on SrTiO3[100] and [110] substrates are epitaxially oriented with [001] and [110] axes normal to the film surface. Twinned domains of ∼200 A(ring) in size are observed in the [001] oriented films. Most defects observed can be attributed to the presence of stacking faults along the c axis. The presence of Cu-O bilayer defects is also observed. Rapid oxygen diffusion in the liquid phase is found to play an important role in the microstructure of the thin films.

Notes: Fluorescence spectra and secondary-ion spectra for laser ablation of high-temperature metal-oxide superconductors are reported. These processes can be used to monitor a thin-film deposition process. The fluorescence spectra are more suitable for Y, Ba, and Ca ions. However, ion spectra can be used to monitor and identify Tl and Ca ions easier than by fluorescence spectra.

Notes: We report microstructures of superconducting YBa2Cu3O7−x thin films epitaxially grown on a SrTiO3(100) substrate. Transmission electron microscopy studies reveal epitaxial, highly ordered grains ∼5000 A(ring) in size for both types of films with either the a or c axis perpendicular to the film. Defects due to out-of-phase boundaries are observed in the former case. The high density of twin boundaries found in the latter case seems to correlate with the higher Jc observed in thin-film samples.

Notes: The number of oxygen atoms in a thermal donor (TD) can be determined directly from the reduction of the concentration of interstitial oxygen in Czochralski (Cz) silicon after annealing at 450 °C for 75 h, when the effect of high-carbon concentration in Si crystals is considered. It is found that on the average a single TD cluster contains eight oxygen atoms. Some TD-inactive large oxygen clusters are produced if the annealing time is longer than the time for TDs to reach their maximum concentration or if the annealing temperature is higher than 475 °C. We also find that the smallest TD cluster contains five oxygen atoms and the largest TD cluster contains 13 oxygen atoms.

Notes: The two-parameter model potential originally proposed by Ning and Sah [Phys. Rev. B 4, 3468 (1971)] for calculating the ground-state energies of group V and group VI impurities in silicon is extended to the variational calculation of the thermal donor ionization energies. In the multivalley effective mass approximation, the theoretical results are in excellent agreement with the reported experimental data. This provides additional evidence for the assumption that thermal donors consist of five to thirteen oxygen atoms, as first proposed by Ourmazd, Schröter, and Bourret [J. Appl. Phys. 56, 1670 (1984)].

Notes: Electron-spin resonance (ESR) has been used to monitor the growth of aluminum-associated trapped-hole centers (i.e., [AlO4 ]0 centers) in high-purity cultured quartz during a sequence of irradiations with 1.7-MeV electrons. Production curves were obtained at three dose rates (3.6, 36, and 360 krad/min) for a series of crystals furnished by three commercial growers of quartz. The shape of each curve depended directly on the dose rate and the origin of the quartz; many of them had an initial rapid growth to a maximum concentration followed by a 5%–25% decrease as the number of defects approached an equilibrium value at a higher dose. We suggest that the complex shapes of these defect production curves, and also their variation between samples, is caused by a competition between the formation of [AlO4 ]0 centers and the formation of [AlO4 /H+ ]0 centers. At higher dose rates, in the 4–40 Mrad/min range, no dependence on dose rate was observed.