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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: The effects of the oxygen dose on the microstructure and the dielectric properties of the buried oxide in oxygen implanted silicon-on-insulator (SOI) structures have been studied. Cross-sectional transmission electron microscopy analyses show that the density of oxygen precipitates at the silicon/buried-oxide interface increases with a decreasing oxygen dose when identical annealing processes are employed. Annealing studies reveal that 1275 °C anneals annihilate the oxygen precipitates. A longer annealing time is required to achieve an oxygen-precipitate-free silicon layer in an SOI substrate implanted with a lower oxygen dose. The inverse relationship between oxygen content in the silicon film and oxygen dose is attributed to the redistribution of oxygen during implantation. In the oxygen dose range studied, the thickness and the breakdown voltage of the buried oxide layer increase with increasing oxygen dose. Higher postimplant annealing temperature improves the isolation properties of the buried oxide layer.

Notes: We have developed a monolithically integrated external feedback laser utilizing a pair of stop-cleaved double channel planar buried heterostructure lasers emitting at 1.3 μm. The external feedback is provided by the stop cleaved facet of the second cavity. A sidemode rejection ratio of 200 : 1 has been obtained with a laser having a 250-μm cavity length and an external resonator length of 200 μm. Since both lasers are fabricated in a self-aligned structure, this device may prove to be a powerful scheme for injection locking to reduce dynamic linewidth.

Notes: Electroluminescent (EL) devices are constructed using multilayer organic thin films. The basic structure consists of a hole-transport layer and a luminescent layer. The hole-transport layer is an amorphous diamine film in which the only mobile carrier is the hole. The luminescent layer consists of a host material, 8-hydroxyquinoline aluminum (Alq), which predominantly transports electrons. High radiance has been achieved at an operating voltage of less than 10 V. By doping the Alq layer with highly fluorescent molecules, the EL efficiency has been improved by about a factor of 2 in comparison with the undoped cell. Representative dopants are coumarins and DCMs. The EL quantum efficiency of the doped system is about 2.5%, photon/electron. The EL colors can be readily tuned from the blue-green to orange-red by a suitable choice of dopants as well as by changing the concentration of the dopant. In the doped system the electron-hole recombination and emission zones can be confined to about 50 A(ring) near the hole-transport interface. In the undoped Alq, the EL emission zone is considerably larger due to exciton diffusion. The multilayer doped EL structure offers a simple means for the direct determination of exciton diffusion length.

Notes: This paper presents results of organometallic vapor-phase-epitaxial growth of low dislocation density GaAs1−xPx on GaAs, utilizing a thin compositionally graded layer (2 μm) and a strained-layer superlattice (SLS) to reduce the dislocation density. The grown structure consists of three sections: (1) a 2-μm GaAs1−xPx graded layer with final phosphorus composition x1 on a GaAs substrate; (2) a GaAs1−yPy /GaAs1−y'Py' SLS; and (3) a 1-μm GaAs1−xPx top layer with x=0.4. Three types of grading layers were investigated: sublinear, hyperlinear, and linear. The linear grading is found to give the lowest dislocation density. However, the 2-μm-thick linearly graded region is definitely too thin to release all the misfit strain. The residual strain produces dislocations after the SLS has been grown, resulting in dislocation generation in the constant composition layer. A novel method has been developed to eliminate this problem. The phosphorus composition at the end of the grading, x1, is made intentionally larger than both the average composition of the SLS and the top layer to prevent residual strain relief during the growth of the top layer. Using this "overshoot grading'' method, the etch pit density in the top layer is reduced from 3×107/cm2 without the special structure to 6.5×105/cm2. The reduction of dislocation density by the SLS has been systematically studied with variation of the SLS parameters, including the thickness of each layer, the number of periods, and the composition change in the SLS. The results show that the SLS itself can reduce the dislocation density by about one order of magnitude. The combination of the SLS with overshoot grading yields the most effective elimination of dislocations. Using the optimum conditions, GaAs0.6P0.4 with good surface morphology, strong visible photoluminescence intensity, and a dislocation density of 6.5×105/cm2 has been obtained.

Notes: Ultrafine particles of nickel-zinc ferrite have been formed from solutions of metal nitrates by coprecipitation with hydrazine, followed by aging at 90 °C. The crystallites either aggregate into much larger clusters or form single particles, depending upon the preparation conditions, and vary in size from 30 to ≈300 A(ring). Saturation magnetizations (Ms) of the ferrites varied from 40 to 65 emu/g and the coercivities from 1 to ≈100 Oe. Increasing hydrazine concentrations tended to produce particles with lower Ms. However, for hydrazine/metal ratios below unity, decreasing the hydrazine concentration dramatically lowered the Ms value. Particles formed without hydrazine (e.g., by aging hydroxides precipitated with potassium hydroxide) did not appear to be magnetic. Variations of the magnetic properties and lattice parameters as a function of preparation conditions will be discussed.

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)].