Structural Phase Transitions and Thermoelectric Properties of AgPb<Subscript>18</Subscript>SbTe<Subscript>20</Subscript> Under Compression

The high-figure-of-merit thermoelectric material AgPb₁₈SbTe₂₀ has been investigated by in situ angular-dispersive x-ray diffraction (XRD) and x-ray absorption fine-structure (XAFS) measurements up to 30 GPa. Resistivity and thermopower were measured with Bridgman-type opposed metal anvil cells. The results show that the ambient cubic ( Fm[`3] m ) \left( {Fm\overline{3} m} \right) structure transforms to orthorhombic (Pnma) at 6.4 GPa and then to the CsCl-type ( Pm[`3] m ) \left( {Pm\overline{3} m} \right) structure at 15 GPa. The ambient cubic ( Fm[`3] m ) \left( {Fm\overline{3} m} \right) phase is found to be recoverable on releasing the pressure. The thermoelectric power is found to increase with pressure for the cubic phase. The XAFS studies performed at the Pb L ₃-edge and Ag K-edge along with resistivity studies complement the XRD findings.     

Template-assisted electrohydrodynamic atomization of polycaprolactone for orthopedic patterning applications

This paper presents the development of the novel deposition of biodegradable polycaprolactone (PCL) polymer patterns on a metallic substrate using a jet spraying technique, template-assisted electrohydrodynamic atomization (TAEA), at ambient temperature. The structure of patterns was controlled by systematically varying the polymer concentration (2–15 wt.%) and the flow rate (1–25 μl min^? 1). Polymer deposition was carried out in the stable cone-jet mode to precisely control the surface structure and morphology. The patterns were studied by optical microscopy, scanning electron microscopy and profilometry, and a high degree of control over the pattern geometry and thickness was achieved by varying the spraying time. The hardness and the effective elastic modulus of the polymer patterns were estimated using nanoindentation. The effect of load, loading rate and the holding time on the hardness and effective elastic modulus was derived. Optimal results were obtained with 5 wt.% PCL in DMAC solution sprayed within the stable cone-jet mode operating window at a flow rate of 15 μl min^? 1 for 300 s at 11.1 kV with a working distance of 60 mm. Hexagonal patterns were well-defined and repeatable with thickness of ~ 34 μm. The hardness is 1.6 MPa at a loading rate of 0.1 μN/s and nearly halved when the load rate was increased to 1 μN/s. The effective elastic modulus of ~ 12 MPa is obtained for a load rate of 0.1 μN/s.     

Electrochemical deposition and characterization of cupric oxide thin films

Polycrystalline cupric oxide (CuO) thin films are deposited using an alkaline solution bath employing cathodic electrodeposition method. Thin films are electroplated at various bath temperatures onto conducting indium tin oxide coated glass substrates. The bath temperature effects on the structural, optical and morphological properties of copper oxide films are studied and reported. X-ray diffraction studies revealed mixed phases of monoclinic and cubic for films grown at lower bath temperatures and that the deposited films at temperatures optimized as 75 °C exhibited cubic structure with preferential orientation along a (111) plane. Texture coefficient (T_c) values are calculated for all diffraction lines and the films were highly textured (T_c > 1). The surface morphology and surface roughness are estimated using scanning electron microscopy and atomic force microscopy, respectively and a morphology made up of pyramid shaped grains is presented. Energy dispersive analysis by X-rays revealed that the near stoichiometric CuO thin films are obtained at optimized preparative parameters. The refractive index is calculated using the envelop method. Also, the optical constants of CuO thin films such as complex dielectric constant (ε) and extinction coefficient (k) are also evaluated and reported.     

Spectral properties of aluminium doped zinc oxide thin films prepared by SILAR method

The spectral properties of undoped and Al doped ZnO nano thin films prepared using double dip method otherwise called SILAR method (Successive Immersion Layer Adsorption Reaction) are reported. The thin films were having polycrystalline hexagonal structure. The optical properties of these films are studied and reported. The optical constants like the band gap (E _g ), refractive indices (n, k), dielectric constant (ε), optical conductivity (σ), were estimated using an approximation algorithm developed from established procedures using transmittance spectrum of the thin films. The average excitation energy (E ₀), oscillator strength (E _d ), effective mass (m*), plasma frequency (ω _p ), static dielectric constant (ε_∞) and carrier concentration (N) are also estimated and reported. The highly transparent thin films showed nanowires protruding from stacked nanorods on SEM inspection that signifies the suitability of these thin films for gas sensors.     

LIMITATION OF BOUNDARY LAYER ANALYSES FOR BUOYANT CONVECTION IN STABLY STRATIFIED FLUIDS

Vertical buoyant convection in stably stratified fluids is revisited. The limitation of boundary layer analyses for such flows is quantified. This is accomplished by comparing the results of the present boundary layer numerical study with the published experimental measurements, and full numerical simulations. It is shown that boundary layer analysis underpredicts the heat transfer rates. This is explained with reference to the flow and thermal fields. The boundary layer results are shown to be inadequate for such characteristics as flow reversal and temperature defects. The underlying physical mechanisms are discussed.     

Direct extraction of substrate network parameters for RF MOSFET modeling using a simple test structure

This letter presents a novel test structure to accurately extract the substrate network parameters for RF MOSFET modeling from two-port measurements. The test structure used in the common-gate configuration isolates the gate network to make the substrate network distinctly accessible to measurements. A methodology is developed to directly extract the substrate network from the measured data. The method is further verified and validated by the excellent match obtained between measured and simulated two-port parameters.     

Extraction of SiO2/SiC interface trap profile in 4H- and 6H-SiC metal-oxide semiconductor field-effect transistors from subthreshold characteristics at 25°C and 150°C

The profile of trap density at the SiO₂/SiC interface in SiC metal-oxide semiconductor field-effect transistors (MOSFETs) is critical to study the channel electron mobility and evaluate device performance under various processing and annealing conditions. In this work, we report on our results in determining the interface trap density in 4H- and 6H-SiC MOSFETs annealed in dry O₂, NO, and CO₂, respectively, based on the device transfer and currentvoltage characteristics in the subthreshold region at 25°C and 150°C. We also studied electron field-effect mobility, fixed oxide charge, and gate leakage in those devices.