A new grounded lamination gate (GLG) for diminished fringe-capacitance effects in high-/spl kappa/ gate-dielectric MOSFETs

A grounded lamination gate (GLG) structure for high-/spl kappa/ gate-dielectric MOSFETs is proposed, with grounded metal plates in the spacer oxide region. Two-dimensional device simulations performed on the new structure demonstrate a significant improvement with respect to the threshold voltage roll-off with increasing gate-dielectric constant (due to parasitic internal fringe capacitance), keeping the equivalent oxide thickness same. A simple fabrication procedure for the GLG MOSFET is also presented.     

Cluster-Based Opportunistic Spectrum Allocation in CRWMN’s Using Co-operative Mechanism

With the innovation of Cognitive Radio Wireless Mesh Network’s, Opportunistic Spectrum Allocation can possibly moderate spectrum lack, by letting Secondary User’s a chance to sense and use unused bits of opportunistic licensed spectrum without any unfavourable effect on the Primary User’s. In Cognitive Radio Wireless Mesh Network’s, the Medium-Access-Control protocols characterizes the utilization of spectrum proficiently by allocating the channels among the users. Majority of proposed Medium-Access-Control protocols are utilizing Common-Control-Channel for dealing with the assets of Secondary-Users. The major downsides of these Medium-Access-Control protocols are broadcasting of Control-channel when substantial number of Secondary-User exists. In contrast with these Medium-Access-Control protocols, we develop an algorithm Time-Slotted-Allocation-Medium-Access-Control (TSA-MAC) protocol which is based on Clustered Time-Division-Medium-Access approach, which permits Secondary-User’s to allocate opportunistic spectrum with the help of co-operative decisions by exchange control information. In this approach, we are dividing the channels as different slots on which Secondary-User’s can transfer control and data packets. The TSA-MAC protocol will enhance the throughput for the Secondary-User’s over the communication channel. And also this method will facilitate to decide and allocate free channels for Secondary-User’s without interfering with Primary User’s.     

Aerogels for thermal insulation in high-performance textiles

For many garment applications where protection is needed against hostile environments, part of the requirement is for insulation to shield the wearer from extremes of temperature. For an insulating garment to be fully effective, it needs to allow the wearer to move freely so that they can carry out their intended activity efficiently. Traditional materials achieve their insulation by trapping air within the structure thereby not only limiting heat loss by convection but also making good use of the low thermal conductivity of air to cocoon the wearer within a comfortable environment. To achieve effective protection with conventional textiles, it is usually necessary to have a thick fibrous layer, or series of layers, to trap a sufficient quantity of air to provide the required level of insulation. Several disadvantages arise as a result. For example, thick layers of insulating textile materials reduce the ability of the wearer to move in a normal manner so that the conduct of detailed manual tasks can become very difficult; the layers lose their insulating capacity when the trapped air is lost as they are compressed; the insulating capacity falls rapidly as moisture collects within the fibrous insulator – it does not have to become sensibly wet for this to happen; just 15% moisture regain can give a dramatic reduction in insulating capacity. Not surprisingly therefore, there has been continued interest in developing insulators that might be able to overcome the disadvantages of conventional textile materials and improve the mobility of the wearer by allowing the use of only a very thin layer of extremely-high insulating performance to provide the required thermal protection. One class of materials from which suitable candidates might be drawn is aerogels; their attractiveness derives from the fact that they show the highest thermal insulation capacity of any materials developed so far. Despite sporadic high levels of interest, commercialisation has been slow. Aerogels have been found to possess their own set of disadvantages such as fragility; rigidity; dust formation during working and cumbersome, expensive, batch-wise manufacturing processes. They may well have been destined to become a product of minor interest, confined to very specialist applications where cost was of little concern. However, methods have been developed to combine aerogels and fibres in composite structures which maintain extremely high insulating capacity whilst demonstrating sufficient flexibility for use in garments. Ways have been found to prevent the formation of powder as aerogel composite fabrics are worked. Most significant though, is the achievement, arising from a project supported by the Korean Government, of a simplified one-step production process developed with the express aim of providing a substantial reduction in the cost of aerogels. Suitably-priced aerogel is now available and this should provide fresh stimulus for research and development teams to engage in new product development work utilising aerogels in textiles and garments for thermal insulation. The mechanisms through which aerogels achieve their outstanding thermal insulating ability is unconventional, at least in terms of materials used in textiles. This issue of Textile Progress therefore includes detail about thermal transport in aerogels before reviewing the various forms in which aerogels can now be made, some of their applications and the research priorities that are now beginning to emerge.     

Mechanics and chemistry: single molecule bond rupture forces correlate with molecular backbone structure

We simultaneously measure conductance and force across nanoscale junctions. A new, two-dimensional histogram technique is introduced to statistically extract bond rupture forces from a large data set of individual junction elongation traces. For the case of Au point contacts, we find a rupture force of 1.4 ± 0.2 nN, which is in good agreement with previous measurements. We then study systematic trends for single gold metal-molecule-metal junctions for a series of molecules terminated with amine and pyridine linkers. For all molecules studied, single molecule junctions rupture at the Au-N bond. Selective binding of the linker group allows us to correlate the N-Au bond-rupture force to the molecular backbone. We find that the rupture force ranges from 0.8 nN for 4,4' bipyridine to 0.5 nN in 1,4 diaminobenzene. These experimental results are in excellent quantitative agreement with density functional theory based adiabatic molecular junction elongation and rupture calculations.     

Reversible tuning of plasmon coupling in gold nanoparticle chains using ultrathin responsive polymer film

We demonstrate large and reversible tuning of plasmonic properties of gold nanoparticles mediated by the reversible breaking and making of linear and branched chains of gold nanoparticles adsorbed on an ultrathin (1 nm) responsive polymer film. Atomic force microscopy revealed that at pH below the isoelectric point of the polybase (extended state of the polymer chains), gold nanoparticles adsorbed on the polymer layer existed primarily as individual nanoparticles. On the other hand, at higher pH, the polymer chains transition from coil to globule (collapsed) state, resulting in the formation of linear and branched chains with strong interparticle plasmon coupling. Reversible aggregation of the nanoparticles resulted in large and reversible change in the optical properties of the metal nanostructure assemblies. In particular, we observed a large redistribution of the intensity between the individual and coupled plasmon bands and a large shift (nearly 95 nm) in the coupled plasmon band with change in pH. Large tunability of plasmonic properties of the metal nanostructure chains reported here is believed to be caused by the chain aggregates of nanoparticles and un-cross-linked state of the adsorbed polymer enabling large changes in polymer chain conformation.     

Thermally induced transformations of amorphous carbon nanostructures fabricated by electron beam induced deposition

We studied the thermally induced phase transformations of electron-beam-induced deposited (EBID) amorphous carbon nanostructures by correlating the changes in its morphology with internal microstructure by using combined atomic force microscopy (AFM) and high resolution confocal Raman microscopy. These carbon deposits can be used to create heterogeneous junctions in electronic devices commonly known as carbon-metal interconnects. We compared two basic shapes of EBID deposits: dots/pillars with widths from 50 to 600 nm and heights from 50 to 500 nm and lines with variable heights from 10 to 150 nm but having a constant length of 6 μm. We observed that during thermal annealing, the nanoscale amorphous deposits go through multistage transformation including dehydration and stress-relaxation around 150 °C, dehydrogenation within 150-300 °C, followed by graphitization (>350 °C) and formation of nanocrystalline, highly densified graphitic deposits around 450 °C. The later stage of transformation occurs well below commonly observed graphitization for bulk carbon (600-800 °C). It was observed that the shape of the deposits contribute significantly to the phase transformations. We suggested that this difference is controlled by different contributions from interfacial footprints area. Moreover, the rate of graphitization was different for deposits of different shapes with the lines showing a much stronger dependence of its structure on the density than the dots.     

Evaluation of a LiI(Eu) neutron detector with coincident double photodiode readout

Previous work showed that enriched ⁶Li halide scintillation crystal is a good candidate for portable neutron-sensitive detectors. Photodiode readout is a good alternative to PMT in compact devices. These detectors are often required to work in presence of a strong gamma background. Therefore, great discrimination against gamma rays is crucial. Because of the high Q-value of the ⁶Li(n,α)³H reaction, the light yield of a neutron capture signal corresponds to 3-4 MeV gamma equivalent in spite of the quenching effect of heavily charged particles. As a result, energy discrimination is quite effective against gamma signals generated in thin crystals. However, direct gamma interactions inside the photodiode can create pulses whose amplitude is large enough to interfere with thermal neutron peak. This study shows an innovative design based on coincident readout to solve this problem. In this design, two photodiodes are attached on both sides of the LiI crystal. The output signal is only accepted when both photodiodes give out coincident output. The method is proved to effectively suppress background in the neutron window in a 420 mR/h ¹³⁷Cs field down to the level of natural background.     

Kinetic modeling of high temperature oxidation of Ni-base alloys

The rates of isothermal and cyclic oxidation and the elemental concentration profiles as a function of time of oxidation for a few Ni-base superalloys were determined through a modified Wagner’s oxidation model and the solution of coupled elemental diffusion equations. Thermodynamically calculated interfacial elemental concentrations and oxygen partial pressures for the multi-component Ni-base alloys were used as boundary conditions for the solution of Wagner’s equation and the elemental coupled diffusion equations (for Cr, Al and O). The multiple elemental diffusion and mass conservation equations were solved using a numerical procedure. The dependence of self/tracer-diffusivities of Cr, Al and O in the corundum phase on the oxygen partial pressures was deduced using a genetic algorithm based optimization procedure incorporating the experimental parabolic rate constants for several Ni-base alloys. Rates of cyclic oxidation were then deduced from the deterministic interfacial cyclic oxidation spalling model (DICOSM) developed by Smialek [1]. The calculated oxidation rates were in reasonable agreement with the experimental values for a range of multi-component Ni-base alloys.