Solid C60/GaAs contacts were fabricated by growing solid C60 films on both n-type and p-type GaAs(100) substrates through vacuum deposition. The electronic states at C60/GaAs interfaces were studied. Both C60/n-GaAs and C60/p-GaAs contacts were found to be strong rectification junctions with a rectifying ratio higher than 106 at a bias of ± 1.OV. Two distinct traps were also observed at the C60/GaAs interfaces with deep level transient spectroscopy (DLTS); one is the electron trap at 0.35 eV below the GaAs conduction band and the other is a hole trap at 0.45 eV above the GaAs valence band.

The development of high quality indium based III-nitride compounds is lagging behind the corresponding aluminum and gallium based compounds. Potential problems confronting the growth of epitaxial and double heterostructure InGaN will be discussed. A mass balance model is presented describing the competing reaction pathways occurring during the growth of indium containing compounds. Atomic layer epitaxy and metalorganic chemical vapor deposition grown InGaN films will be used to explain this model. Also, the growth parameters leading to the attainment of high InN percentages, reduced indium metal formation, and improved structural and optical properties of indium containing nitrides will be discussed.

Silver has played a critical role for the fabrication of metal/high temperature superconductor composites. Phase equilibrium and microstructure in the ternary PbO-CuO-Ag system have been investigated using differential thermal analysis (DTA), thermogravimetry (TG), scanning electron microscope (SEM), and x-ray diffraction (XRD) techniques. Composition versus temperature diagrams have been established for these systems in air. In the ternary CuO-PbO-Ag system, there is a eutectic reaction CuO + PbO + Ag = L at 750 °C and a composition of 12.04 mol % Ag, 16.35 mol % CuO, and 72.62 mol % PbO. Two immiscible regions near the two binary tie lines PbO-Ag and CuO-Ag were detected. No binary or ternary compound was detected in these systems. SEM and EDS results confirm the presence of two liquid phases and the eutectic point

We have performed photoluminescence (PL) measurements at liquid nitrogen temperature under high pressure up to 5.5 GPa and in the temperature range 10-300 K at atmospheric pressure on {(ZnSe)30(ZnSe0.92Te0.08)30(ZnSe)30[(CdSe)1(ZnSe)2]9}x5 multiple quantum wells. The PL peaks, EB, E1 and Ew corresponding to the band edge luminescence in ZnSe barrier layer, the transitions from the first conduction subband to the heavy-hole subband in ZnSe0.92Te0.08 layers and [(CdSe)1(ZnSe)2]9 ultra short period superlattice quantum well (SPSLQW) layers have been observed. Experimental results show that ZnSe0.92Te0.08/ZnSe forms a type-I superlattice (SL) in contrast to the type-II ZnSe/ZnTe SL. The pressure coefficients of the EB, E1 and Ew exciton peaks have been determined as 67, 63 and 56 meV/GPa, respectively. With increasing temperature (or pressure), the E1 peak-intensity drastically decreases which is attributed to the thermal effect (or the appearance of many defects in ZnSe0.92Te0.08 under higher pressure).

Silver doping into (Bi, Pb)2Sr2Ca2Cu3O10 superconducting composite tapes was found to accelerate the formation process of high-Tc (2223) phase owing to lowering the partial melting point of the samples. The differential thermal analysis (DTA) results showed that the partial melting temperature of the sample was lowered by about 10 °C from 850 °C to 840 °C by silver doping. However, with sufficient sintering both the silver-doped and undoped samples can reach a very high level of high-Tc phase fraction, suggesting that the silver doping only speeds up the rate of high-Tc phase formation, but does not change the final phase assemblage of the materials. The reaction kinetics was analyzed by using the Avrami equation, and the results indicated that the conversion process of low-Tc (2212) phase to high-Tc (2223) phase was a diffusion-controlled, two-dimensional reaction. The correlation of the phase evolution with electrical property inside the superconducting tape during the process of heat treatment was also discussed.

Raman scattering from a (CdSe)m(ZnSe)n-ZnSe strained quantum well structure, composed of (CdSe)m(ZnSe)n as well layers and thick ZnSe as barrier layers, is presented in this report. Two kinds of ZnSe-like LO phonon confined modes were observed by Raman scattering at 10-300 K. Resonance Raman scattering was accomplished by changing sample temperature and incident photon energy and as a results, up to 7 orders of ZnSe-like LO multi-phonon modes were observed. In the discussion, we suggest that anti-Stokes Raman scattering measurements can provide a meaningful way to distinguish the multi-phonon Raman scattering from hot luminescence.

The effect of excess Ca2CuO3 on the superconducting properties in the (Bi, Pb)2Sr2Ca2Cu3Oy, (2223) was investigated through the measurements of ac susceptibility, critical current density, and critical field. All the measurements have been performed on the samples that were identified by x-ray diffraction to consist of the mostly high Tc 2223 phase with varying amounts of excess Ca2CuO3. It was found that when the excess Ca2CuO3 is in the range 0.1 M to 0.3 M the loss peak of ac susceptibility appeared at higher temperature than that for an undoped sample, and the Jc showed a maximum at the excess Ca2CuO3 = 0.2 M, indicating that a proper amount of excess Ca2CuO3 enhanced the flux pinning. The upper critical field, Hc2, determined by using a pulse magnetic field showed a maximum at the excess Ca2CuO3 = 0.1 M, and increased linearly with decreasing temperature within the measurement regime.

Let G be a group with identity e, let λ be a normal supernilpotent radical in the category of associative rings and let λref be the reflected radical in the category of G-graded rings. Then for A a G-graded ring, λref(A) is the largest graded ideal of A whose intersection with Ae is λ (Ae). For λ = B, the prime radical, we compare Bref(A) to BG(A) = B(A)G, the largest graded ideal in B(A).