Analysis of nanoindentation response of diatom frustules

Diatom frustules have been suggested for numerous nanotechnological applications. Experimental studies using nanoindenter have shown that the hardness and the stiffness of the frustules vary with location of indentation. To gain further insight, a computational framework has been developed where the Berkovich nanoindentation experiments were simulated by a rigid-deformable contact process. Three different approaches that provide progressively increasing level of understanding of the deformation behavior of frustules were adopted. The differences in the mechanical responses of the frustule due to variation of indentation location, size of pores, and distribution of pores were analyzed. It has been found that the effective stiffness of the frustule is linearly related to the porosity level and does not depend on the frustule size or its pore architecture. It has been shown that a 3D porous shell computational model is more appropriate to simulate the experimentally obtained mechanical response of diatom frustules.     

Electrical properties of SiO2/TiO2 high-k gate dielectric stack

The trapping/detrapping behavior of charge carriers in ultrathin SiO₂/TiO₂ stacked gate dielectric during constant current (CCS) and voltage stressing (CVS) has been investigated. Titanium tetrakis iso-propoxides (TTIP) was used as the organometallic source for the deposition of ultra-thin TiO₂ films at low temperature (<200 °C) on strained-Si/relaxed-Si_0.8Ge_0.2 heterolayers by plasma-enhanced chemical vapor deposition (PECVD) in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of 66.67 Pa. Stress-induced leakage current (SILC) through SiO₂/TiO₂ stacked gate dielectric is modeled by taking into account the inelastic trap-assisted tunneling (ITAT) mechanism via traps located below the conduction band of TiO₂ layer. The increase in the gate current density observed during CVS from room temperature up to 125 ^oC has been analyzed and modeled considering both the buildup of charges in the layer as well as the SILC contribution. Trap generation rate and trap cross-section are extracted. A capture cross-section in the range of 10⁻¹⁹ cm² as compared to 10⁻¹⁶ cm² in SiO₂ has been observed. A temperature-dependent trap generation rate and defects have also been investigated using time-dependent current density variation during CVS. The time dependence of defect density variation is calculated within the dispersive transport model, assuming that these defects are produced during random hopping transport of positively charge species in the insulating high-k stacked layers. SILC generation kinetics, i.e. defect generation probability under different injected fluences for various high-constant stress voltages in both polarities have been studied. An empirical relation between trap generation probability and applied stress voltage for various injected fluences has been developed.     

Highly conducting transparent nanocrystalline Cd1−xSnxS thin film synthesized by RF magnetron sputtering and studies on its optical, electrical and field emission properties

Transparent conducting Cd_1−xSn_xS thin films have been synthesized by radio frequency magnetron sputtering technique on glass and Si substrates for various tin concentrations in the films. X-ray diffraction studies showed broadening of peaks due to smaller crystal size of the Cd_1−xSn_xS films, and SEM micrographs showed fine particles with average size of 100 nm. Sn concentration in the films was varied from 0% to 12.6% as determined from energy-dispersive X-ray analysis. The room-temperature electrical conductivity was found to vary from 8.086 to 939.7 S cm⁻¹ and corresponding activation energy varied from 0.226 to 0.076 eV. The optimum Sn concentration for obtaining maximum conductivity was found to be 9.3%. The corresponding electrical conductivity was found to be 939.7 S cm⁻¹, and the mobility 49.7 cm² V⁻¹ s⁻¹. Hall measurement showed very high carrier concentrations in the films lying in the range of 8.0218×10¹⁸–1.7225×10²⁰ cm⁻³. The conducting Cd_1−xSn_xS thin films also showed good field emission properties with a turn on field 4.74–7.86 V μm⁻¹ with variation of electrode distance 60–100 μm. UV–Vis–NIR spectrophotometric studies of the films showed not needed the optical band gap energy increased from 2.62 to 2.80 eV with increase of Sn concentration in the range 0–12.6%. The optical band gap was Burstein–Moss shifted, and the corresponding carrier concentration obtained from the shift also well matched with that obtained from Hall measurement.     

Hybrid orientation technology and strain engineering for ultra-high speed MOSFETs

We report here RF MOSFET performance in sub-45-nm hybrid orientation CMOS technology. Based on the combination of hybrid orientation technology (HOT) and process-induced local strain engineering, MOSFET RF performance is investigated using CAD (TCAD) technology. Transistor optimization on (100) substrate via silicon nitride (Si ₃ N ₄ ) cap layer thickness for n-MOSFETs, Ge mole fraction optimization for p-MOSFETs on (110) substrates and channel length scaling have resulted in record RF performance, viz. the cut-off frequency, ${f_{\rm T}}$ .     

Self regulation of photovoltaic module temperature in V-trough using a metal-wax composite phase change matrix

The present study was carried out to take advantage of the enhanced solar insolation in V-trough while limiting the temperature of the photovoltaic (PV) module at around the maximum (ca. 65 °C) observed for conventional usage without any concentration. Paraffin wax of 56-58 °C melting range was chosen as phase change material (PCM) and incorporated at the rear of the module to absorb the excess heat. The problem of low thermal conductivity of the wax was solved with the help of packed metal turnings wherein the wax resided. Two sets of experiments were performed indoor and outdoor. Employing a 0.06 m thick bed of the PCM matrix, the module temperature in the indoor experiment could be maintained at 65-68 °C for 3 h whereas in its absence the temperature rose beyond 90 °C within 15 min. In outdoor studies, the module temperature in V-trough could be reduced from 78 °C to 62 °C with the PCM assembly and operation could be sustained throughout the day. Using the V-trough PV-PCM system, the output power over the day could be enhanced 1.55 times with self regulation of temperature. The molten wax formed during operation re-solidified during the evening and night and could be re-used. A significant finding was the safe operation of the module even under low wind velocity conditions without sacrificing operational simplicity.     

Application of polyamidoamine dendrimer in reactive dyeing of cotton

Cotton is dyed very extensively using reactive dyes. Conventionally, reactive dyeing requires voluminous amount of electrolyte and alkali for dyeing of cellulosic fibres like cotton. But the consumption of electrolyte for reactive dyeing of cellulosic textiles increases the pollution load in the textile wastewater. Moreover, there is a possibility of reactive dye hydrolysis in presence of alkali which is detrimental but unavoidable. Therefore, an attempt has been made to eliminate the use of electrolyte and alkali by modifying the cotton substrate with different generations of PAMAM (polyamidoamine) dendrimer using exhaust and continuous method of application. Subsequently, dyeing was carried out by exhaust method without using electrolyte and alkali. The dyed samples were tested for wash fastness, light fastness and rubbing fastness. Colour strength in terms of K/S was also assessed. The results were comparable to those for dyeing obtained by conventional exhaust method. Therefore, the proposed method demonstrates a promising alternative to the conventional dyeing method by completely eliminating electrolyte and alkali.     

Modeling Growth,Surface Kinetics,and Morphology Evolution in PETN

Pentaerythritol tetranitrate (PETN) is a commonly used energetic material with both military and civilian applications. Good ignition properties mandate a powdered material with a high surface area. However, existing experimental data on PETN powder suggest an active surface that leads to particle coarsening and gradual reduction of the specific surface area over time. In this work we review some of the atomic‐level and coarse‐grained potential models developed for PETN and discuss their applications for studying particle morphology, growth, and surface kinetics, including molecular diffusion and evaporation/condensation rates. Simulation methods include classical molecular dynamics, kinetic Monte Carlo, and transition state calculations.