ALBERT

Notes: A cold-wall rapid thermal processor is used for the wet oxidation of the commensurately grown GexSi1−x layers on Si substrates. The rate of oxidation of the GexSi1−x layer is found to be significantly higher than that of pure Si, and the oxidation rate increases with the increase in the Ge content in GexSi1−x layer. The oxidation rate of GexSi1−x appears to decrease with increasing oxidation time for the time-temperature cycles considered here. Employing high-frequency and quasi-static capacitance-voltage measurements, it is found that a fixed negative oxide charge density in the range of 1011– 1012/cm2 and the interface trap level density (in the mid-gap region) of about 1012/cm2 eV are present. Further, the density of this fixed interface charge at the SiO2/GeSi interface is found to increase with the Ge concentration in the commensurately grown GeSi layers.

Notes: The intersubband infrared absorption of holes in Si1−xGex/Si multiple quantum wells is observed. The quantum well structure consists of 10 periods of 40−A(ring)−thick Si0.6Ge0.4 wells and 300−A(ring)−thick Si barriers. The samples are prepared using molecular beam epitaxy. In the experiment, the infrared absorption as a function of wavelength is measured using a waveguide geometry. An absorption peak near 8.1 μm has been observed, which is due to the transition between first two heavy hole bound states. The polarization dependence spectra are in good agreement with the selection rules for the intersubband transition.

Notes: The intersubband infrared absorption of holes in a GexSi1−x /Si superlattice is observed for the first time. In the experiment, the photocurrent is measured as a function of applied bias which is used to inject holes to the minibands of the superlattice. Two peaks in the photocurrent as a function of bias across the device are observed due to intersubband absorption between the ground to the first and the first to the second light hole minibands. The polarization dependence measurement is used to study the nature of the transitions and is in good agreement with the selection rules.

Notes: The experimental results of the rapid thermal oxidation in the initial oxidation regime of molecular beam epitaxy grown GeSi strained layers are reported. It is shown that the dry oxidation rate of GeSi is the same as that of Si at different temperatures. After a very short initial time (∼10 s), the oxide thickness appears to be a linear function of time, which suggests that the kinetics of oxide growth during dry oxidation is limited by surface reaction controlled mechanisms. Further, the oxidation rate in the thin oxide regime is not affected by the Ge content up to 20% in the GeSi strained layer for dry oxidation. Using secondary-ion mass spectrometry, it is found that Ge is completely rejected out of the SiO2 layer which is formed during oxidation, and a Ge-rich layer is formed at the SiO2/GeSi interface. A significant amount of Ge is found to diffuse into the underlying GeSi layer during the growth of thin oxide films.

Notes: We report on the temperature dependence of the critical current (Ic) near Tc for two Y-Ba-Cu-O thin films having zero-dissipation temperature (Tc) of 81 K and a Y-Ba-Cu-O thin film having Tc of 71 K. At temperatures higher than 0.9Tc, the critical current in a voltage criterion of 1 μV/cm appears proportional to (1−T/Tc)n with n≈2, and n≈1.5 in a 10 μV/cm criterion, exhibiting the dependence of n on the critical current criteria. This observation is in contrast with the report of n=1.5 by Ogale et al. [Phys. Rev. B 36, 7210 (1987)], Yuan et al. [J. Appl. Phys. 64, 4091 (1988)], and Horng et al. [Phys. Rev. B 39, 9628 (1989)], implying that n=2, the value for the superconductor-normal metal-superconductor tunneling junction of BCS superconductors near Tc must be taken into consideration to understand the intergrain tunneling process in polycrystalline high Tc thin films.

Notes: Subspace projection is an algorithm to calculate synthetic long-period seismograms from weakly coupled free oscillations. The algorithm exploits the fact that seismic motion on a slowly rotating, slightly aspherical earth can be represented by a sum of hybrid multiplets that are quasi-isolated in the frequency domain. This method incorporates the coupling interactions between multiplets to first order, and incorporates coupling interaction within each hybrid multiplet with a Galerkin formalism. Subspace projection does not linearize the response of the seismic waveform itself, but rather linearizes the perturbations to the free oscillations that comprise the seismic waveform. The subspace projection method enjoys a computational advantage over full coupled-mode calculations because eigenvalue-eigenvector decompositions are calculated using much smaller matrices. It is valid for times long after the seismic source onset. Subspace projection can be represented by a power series whose speed of convergence depends on the coupling strength parameter εrms. The estimated root-mean-square (rms) relative waveform perturbation caused by intermultiplet coupling is √2εrms. We tested the accuracy of the algorithm with a series of numerical experiments using rotation, hydrostatic ellipticity and upper mantle lateral structure model M84A. Waveforms were constructed from the modes 0Sl, l= 2,…, 56. We found that the subspace projection seismograms, averaged over 300 source-receiver pairs within frequency bands where coupling was significant, represented 92–99 per cent of the waveform variance caused by coupling among nearest neighbours along the 0Sl dispersion branch. If two multiplets are close in frequency, subspace projection may represent the coupled-mode waveform poorly. Closely spaced multiplets dominate the interaction between different free-oscillation dispersion branches, especially spheroidal-toroidal coupling. Numerical tests suggest that problems occur for Δf≳ 0.020 mHz, even for weakly coupled multiplets. These problems can be overcome by combining closely spaced multiplets into a single ‘augmented’ hybrid subspace. Interactions with modes outside the subspace are represented by subspace projection, while interactions within the augmented subspace are calculated using quasi-degenerate coupling. Synthetic vertical-component seismograms for 0Sl, l= 2,…, 60, and 0Tl, l= 2,…, 54, show mixed-mode coupling effects principally at source azimuths near the Love-wave radiation maximum. Perturbations to the free-oscillation spectrum are large for f≲ 4.2 mHz on polar propagation paths due to rotational coupling. However, the smooth lateral structure in M84A generates a smaller amount of spheroidal-toroidal coupling, and causes only modest distortion in the spectrum for f≳ 4.5 mHz.

Notes: The effects of simultaneous incorporation of maximum allowable levels of water and high-oleic sunflower oil (HOSO) on frankfurter properties were investigated. The formulation changes generally had little effect on processing yield. Frankfurters formulated with HOSO were 180-241% higher in the ratio of total monounsaturated fatty acids to total saturated fatty acids when compared to control products with similar total fat levels. Consumer-panel sensory data and instrumental texture profile data indicated that low-fat (14-16%), high-water, HOSO frankfurters- were as acceptable as control frankfurters with 28% fat (all-animal fat) and did not have the texture problems observed previously with low-fat, HOSO frankfurters without extra added water.

Notes: Abstract Electrical conductivity of thermally grown Cr2O3 has been measured as a function of temperature and over a range of oxygen partial pressures from that of air to that of the Cr/Cr2O3 equilibrium. The conductivity showed p-type behavior over the range of the present investigation. At temperatures above 1000°C, the conductivity values were independent of oxygen partial pressure and indicated intrinsic semiconductor behavior. The mobility of holes, determined by measuring conductivity at fixed compositions (i.e., fixed δ in Cr2-δO3), increased with temperature. This behavior can be attributed to hopping-type conduction. For δ ∼ 10−5, the activation energy for hole hopping was 0.248 eV, and the calculated hole mobilities were 5.4x10−2 and 2.4x10−1 V/cm2 · s at 500 and 1000°C, respectively. The oxidation kinetics of Cr were determined by measuring the electrical conductivity and electromotive force across the oxide layer at 875°C. The result agreed well with the oxidation data obtained in thermogravimetric tests.

Notes: Abstract An application of direct bonding method for copper to silicon nitride (Si3N4) joining was investigated. Si3N4 was sintered with 5wt% MgO at 1700 ° C for 30 min in nitrogen atmosphere, and oxidized at various temperatures. The bonding was performed at 1075 ° C in nitrogen atmosphere with low oxygen partial pressure. The direct bonding was not achieved for the Si3N4 oxidized below 1200 ° C or nonoxidized. During oxidation, magnesium ion added as sintering aids, diffused out to the surface of Si3N4 and formed MgSiO3, which seemed to have an important role in the bonding. Fracture of the bonded specimen under tensile stress took place within the oxide layer of Si3N4. The bonding strength was decreased with oxidation temperature and time. Maximum strength was found to be 106 kg cm−2 for the Si3N4 oxidized at 1200 ° C for 1 h.