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Notes: Electrical conductivities (σdc) of the as-quenched Bi3.5Pb0.5Sr3Ca3Cu4Ox+zAg2O (with z=1, 3, 5, and 10 wt %) glassy precursors for high Tc superconductors are found to be much higher (∼10−5−101 Ω−1cm−1) than those of the corresponding Ag2O free Bi3.5Pb0.5Sr3Ca3Cu4Ox (denoted by BPB) precursor glass (∼10−13−10−6 Ω−1cm−1). This unusually high conductivity is attributed to the increase of carrier concentrations caused by the addition of Ag2O (also observed from the Hall effect measurements). The experimentally observed high values of σdc do not follow Mott's variable range hopping model which is in sharp contrast to the behavior of the corresponding pure BPB and many other conventional transition metal oxide glasses having high resistivities. Moreover, the Seebeck coefficients (S) of these glassy precursors show nonlinear variations (from negative at lower temperature to positive at higher temperature) which cannot be clearly explained by phonon drag or electron-phonon interaction. This behavior of S which is also supported from Hall effect measurement is considered to be due to the nonlinear thermal variations of carrier concentrations (both hole and electron) present in the glassy samples. © 1997 American Institute of Physics.

Notes: Nanometer-sized iron particles with diameters in the range 5.5–11.1 nm were grown within a silica gel by an electrodeposition method. Electron diffraction measurements show that some of the iron particles were oxidized to Fe3O4. dc resistivity measurements over the temperature range 110–300 K show a T−1/4 variation indicating a variable range hopping transport. ac conductivity over the frequency range 100 Hz–2 MHz show an overlapping large polaron tunneling mechanism to be operative. The dielectric modulus spectra as a function of frequency were analyzed on the basis of a stretched exponential relaxation function. The values of the exponent β as extracted from this analysis were in the range 0.38–0.46. The activation energies corresponding to the maximum of the imaginary part of the dielectric modulus were in the range 0.13–0.20 eV. These are ascribed to an electron tunneling mechanism. © 1999 American Institute of Physics.

Notes: Nanoparticles of silver with diameters in the range 10.3–25.7 nm were grown within a silica gel medium by an electrodeposition technique. The dc resistivity of the nanocomposites was measured over the temperature range 100–300 K. The resistivity as a function of inverse temperature shows a maximum at around 175 K. This is explained as arising due to the presence of two conduction mechanisms, viz., an electron tunnelling between metal particles and conduction through a percolated metal structure which is fractal in nature. © 1999 American Institute of Physics.

Notes: We report on the effect of annealing on a thin Fe film deposited on a Si(111) substrate, using x-ray reflectivity and secondary ion mass spectrometry (SIMS) techniques. Using Fourier transform of the x-ray reflectivity data, we have estimated the layer thickness of the film. From the estimated thickness and critical value of the scattering vector qc obtained from the reflectivity data, an initial guess model of the electron density profile of the film is made. Using an iterative inversion technique, based on the Born approximation, with the obtained initial guess model, we have extracted the actual electron density profile of the film as a function of depth from the specular x-ray reflectivity data. On annealing, we observe interdiffusion of Fe and Si resulting in an increase in the thickness of the film. We have also carried out a SIMS measurement on the annealed sample to support the result of the annealing effect observed from the analysis of x-ray reflectivity data. The SIMS analysis indicates that the top of the film is rich in Si which has diffused from the substrate to the surface of the Fe film on annealing. © 1999 American Institute of Physics.

Notes: The Navier–Stokes equations have been solved, by a pseudospectral method, for pressure-driven flows between a no-slip wavy wall and a slip flat wall. Periodic boundary conditions were used in the streamwise and spanwise directions. The physical domain is mapped into a computational domain that is a rectangular parallelepiped using a nonorthogonal transformation. The pseudospectral solution procedure employed in previous studies, for example, Lam and Banerjee [Phys. Fluids A 4, 306 (1992)], eliminated the pressure and solved for the wall–normal velocity and vorticity. The other velocity components were calculated using the definition of vorticity, and the continuity equation. This procedure leads to oscillations in the pressure field when solutions were attempted in the mapped computational domain. To overcome the problem, the procedure had to be modified and the pressure solved for directly using a fractional time step technique. For the cases examined here, these modifications resulted in spectral accuracy being maintained. Flow over sinusoidal wave trains has been simulated and the results compare well with available experiments. The simulations show significant effects of the wavy boundary on the mean flow and the turbulence statistics. The mean velocity profile differs substantially from the profile for the flat-wall case, particularly in the buffer region where the fluid is under the influence of both the wavy wall and the slip boundary. The velocity fluctuations in the streamwise direction decrease in the buffer region. This effect becomes more pronounced when the wave amplitude increases. Most of the redistribution of energy, from the streamwise direction to the spanwise and wall–normal directions, occurs in a thin layer close to the boundary, downstream of the wave troughs. The energy primarily redistributes into spanwise fluctuations. High shear stress regions form downstream of the wave troughs, and streaky structures and quasi-streamwise vortices are also seen to initiate in these regions. The length of the streaks, and the extent of the quasi-streamwise vortices, scale with wave length for the two cases investigated. © 1997 American Institute of Physics.

Notes: Particle-laden turbulent flows, at average volume fraction less than 4×10−4, in open channels are numerically simulated by using a pseudospectral method. The motion of particles, that are large compared with the dissipative length scale, is coupled to the fluid motion by a method that generates a "virtual" no-slip boundary on the particle surface by imposition of an external force field on the grid-points enclosed by the particle. Cases for both moving and stationary particles, lying on the wall, are simulated. The investigations focus on particle-turbulence interaction. It is found that particles increase turbulence intensities and Reynolds stress. By examining higher order turbulence statistics and doing a quadrant analysis of the Reynolds stress, it is found that the ejection-sweep cycle is affected—primarily through suppression of sweeps by the smaller particles and enhancement of sweep activity by the larger particles. An assessment of the impact of these findings on scalar transfer is made, as enhancement of wall heat/mass transfer rates is a motivation of the overall work on this subject. In the cases considered, comparison of the calculations with an existing experiment was possible, and shows good agreement. At present, due to limitations in available computational resources, this method cannot be used when the particle diameter is smaller than the smallest turbulence scale (e.g. the Kolmogorov length scale) and the volume fraction is of the same order as studied in this paper, i.e. between 10−3 and 10−4. © 1997 American Institute of Physics.

Notes: This article discusses the electrical characterization of low-temperature intrinsic Si films deposited by remote plasma-enhanced chemical vapor deposition. Metal-oxide-semiconductor (MOS) capacitors were fabricated on films deposited over a range of temperatures. Conventional MOS measurements such as capacitance versus voltage, breakdown voltage, Zerbst plot, and charge-to-breakdown were used to analyze the capacitors. The results of these measurements not only yielded information about the electrical properties of the films, but also led to conclusions regarding structural quality and the presence of metal contamination. This, coupled with the fact that capacitor fabrication requires only a simple, moderate-thermal budget process, makes MOS capacitor measurements an attractive technique for the characterization of low temperature epitaxial Si films. © 1997 American Institute of Physics.

Notes: History-dependent metastable states with different bulk properties are formed in the vortex state of the type-II superconductor 2H-NbSe2. Magnetic measurements demonstrate the difference between the shielding responses of a field- and a zero-field-cooled state, and provide a procedure for switching the system from one state to the other. © 1999 American Institute of Physics.

Notes: The dc characteristics of Si1−x−yGexCy P-channel metal–oxide–semiconductor field-effect transistors (PMOSFETs) were evaluated between room temperature and 77 K and were compared to those of Si and Si1−xGex PMOSFETs. The low-field effective mobility in Si1−x−yGexCy devices is found to be higher than that of Si1−xGex (grown in the metastable regime) and Si devices at low gate bias and room temperature. However, with increasing transverse fields and with decreasing temperatures, Si1−x−yGexCy devices show degraded performance. The enhancement at low gate bias is attributed to the strain stabilization effect of C. This application of Si1−x−yGexCy in PMOSFETs demonstrates potential benefits in the use of C for strain stabilization of the binary alloy. © 1999 American Institute of Physics.

Notes: Ge implantation followed by high-temperature solid phase epitaxy was used to form a relaxed substrate, eliminating need for the growth of relaxed Si1−xGex layers. Upon this film, a 2000 Å buffer layer of Si0.85Ge0.15 followed by a 200 Å strained Si layer was grown by ultrahigh-vacuum chemical vapor deposition. For comparison, unstrained Si epitaxial films and a 2000 Å thick film of Si0.85Ge0.15 (on unimplanted Si) followed by 200 Å of Si were used. n-channel metal–oxide–semiconductor transistors were fabricated and their dc characteristics were examined. Strained Si devices show a 17.5% higher peak linear μFE than control devices as a result of higher electron mobility in the strained Si channel. This work demonstrates a simple method for the formation of strained Si layers. © 1999 American Institute of Physics.