A thermal analysis investigation of new insulator compositions based on EPDM and phenolic resin

New rocket insulator compositions have been studied by adding various types and amounts of fillers, such as graphite and asbestos fibres, Al₂O₃, MgZrO₂, Cr₂O₃, SiC, carbon powders and phenolic resin to the base EPDM gum and graphite, kevlar,E type glass fibres to the base phenolic resin in order to improve thermal and ablative efficiency. The degradation of the insulators has been investigated by thermogravimetry (TG) analysis to 900°C and DSC analysis to 500°C. Conversion curves of the insulators at different heating rates were performed and maximum degradation temperatures were found as 646 and 661°C for EPDM P and phenolic resin, respectively. The kinetic parameters for degradation have been evaluated and the lifetime of the rocket insulators has been estimated. Thermal analysis has been conducted on the insulators and the indepth temperature distribution was evaluated in order to find optimum insulation thickness.     

Si-C linked organic monolayers on crystalline silicon surfaces as alternative gate insulators.

Herein, the influence of silicon surface modification via Si-C(n)H(2n+1) (n=10,12,16,22) monolayer-based devices on p-type 100 and n-type 100 silicon is studied by forming MIS (metal-insulator-semiconductor) diodes using a mercury probe. From current density-voltage (J-V) and capacitance-voltage (C-V) measurements, the relevant parameters describing the electrical behavior of these diodes are derived, such as the diode ideality factor, the effective barrier height, the flatband voltage, the barrier height, the monolayer dielectric constant, the tunneling attenuation factor, and the fixed charge density (Nf). It is shown that the J-V behavior of our MIS structures could be precisely tuned via the monolayer thickness. The use of n-type silicon resulted in lower diode ideality factors as compared to p-type silicon. A similar flatband voltage, independent of monolayer thickness, was found, indicating similar properties for all silicon-monolayer interfaces. An exception was the C10-based monolayer device on p-type silicon. Furthermore, low values of N(f) were found for monolayers on p-type silicon (approximately 6 x 10(11) cm(-2)). These results suggest that Si--C linked monolayers on flat silicon may be a viable material for future electronic devices.     

Voltammetry at a three-phase junction

When insoluble insulating crystals adhere to an electrode, the three-phase junction – where electrolyte solution, electrode and crystal meet – is the only feasible site for an electrochemical reaction. Moreover, sustained reaction is possible only if ions from the electrolyte solution are able to enter the crystal through the three-phase junction and disperse within the crystal. Here, order-of-magnitude calculations demonstrate that diffusion to the three-phase junction is well able to support voltammetry under standard experimental conditions. A model is built for cases of adherent cubes of uniform size and thereby the shapes of chronoamperograms, chronograviograms and cyclic voltammograms are predicted. The model assumes that the ion concentration at the three-phase junction plays a crucial role in the voltammetry, being determined by quasi-steady-state ion diffusion from the bulk, the thermodynamics of the electrode reaction, and the extent to which the crystal has already undergone reaction. Depending on the crystal size and scan rate, cyclic voltammograms may mimic solution-phase voltammograms from classical thin-layer experiments or from typical stripping experiments. The effect of size heterogeneity on cyclic voltammetry is simulated for lognormal distributions. Received: 5 January 1998 / Accepted: 17 April 1998     

Reprint of : Transient dynamics of spin-polarized injection in helical Luttinger liquids

We analyze the time evolution of spin-polarized electron wave packets injected into the edge states of a two-dimensional topological insulator. In the presence of electron interactions, the system is described as a helical Luttinger liquid and injected electrons fractionalize. However, because of the presence of metallic detectors, no evidences of fractionalization are encoded in dc measurements, and in this regime the system does not show deviations from its non-interacting behavior. Nevertheless, we show that the helical Luttinger liquid nature emerges in the transient dynamics, where signatures of charge/spin fractionalization can be clearly identified.     

Reprint of : Nanomagnet coupled to quantum spin Hall edge: An adiabatic quantum motor

The precessing magnetization of a magnetic islands coupled to a quantum spin Hall edge pumps charge along the edge. Conversely, a bias voltage applied to the edge makes the magnetization precess. We point out that this device realizes an adiabatic quantum motor and discuss the efficiency of its operation based on a scattering matrix approach akin to Landauer–Büttiker theory. Scattering theory provides a microscopic derivation of the Landau–Lifshitz–Gilbert equation for the magnetization dynamics of the device, including spin-transfer torque, Gilbert damping, and Langevin torque. We find that the device can be viewed as a Thouless motor, attaining unit efficiency when the chemical potential of the edge states falls into the magnetization-induced gap. For more general parameters, we characterize the device by means of a figure of merit analogous to the ZT value in thermoelectrics.     

Far-infrared reflectivity of KI:Cl? and KI:Na+

The far-infrared reflectivity spectra of KI doped with 1% Cl^– and 2% Na⁺ were measured using a dual cavity technique. In addition to the observation of all previously-observed resonant and gap modes, several features were discovered in and near the optic band. A new gap mode at 90 cm^–1 in KI:Cl^– was discovered. In both systems sharp, narrow reductions in reflectivity at 98, 108, 116, and 139 cm^–1 were observed, as was a general reduction in reflectivity between 108 and 139 cm^–1. The structure at 98 and 116 cm^–1 is most-likely due to optical activity induced in normally inactive lattice modes by the high concentration of impurities. The features at 108 and 139 cm^–1 and the reduction in reflectivity between them were shown by a simple model calculation to be due to an increase in damping of the TO phonon.     

Capacitance-voltage behaviour inp-type ɛ-GaSe single crystal ∥c at different temperatures

Summary  Capacitance-voltage measurements have been carried out onp-type ɛ-GaSe single crystal ∥c in the temperature range 300 to 360 K, with applied voltages of -1, 0 and +1 V. TheC-V measurements in this temperature range have shown a shift in capacitanceC and conductanceG to the higher values with an increase in temperature. The depletion layer widthW, the Debye length L_D and the doping densityN _α have been worked out and plots ofN _α vs. W have shown a decrease inW with an increase in temperature. The plots of L_D vs. N _α vary as 1/N_α^1/2, which gives N_αL_D ⋍ 3.3 × 10¹¹ charges/m² for doping density of 10¹⁶m⁻³. The values ofG at different temperatures have been used to obtain the activation energies, which are found to be ΔE ⋍ 0.11 eV for -1 and +1 V applied voltages, and ΔE ⋍ 0.06 eV for zero volt. The authors of this paper have agreed to not receive the proofs for correction.     

Kondo-insulating state in CeNi1−xRhxSn as a function of carrier number

Our systematic study has shown that the gap in doped CeNiSn Kondo insulator is very sensitive to the degree of hybridization V between the f-electron and conduction electron states. In the system CeNi_1−xRh_xSn, the carrier concentration diminishes upon Rh substitution for Ni. The transition from Kondo-insulator region to a metallic region is discussed as a function of variable valence electron number induced by substitution of Rh for Ni and of the accompanying effect of the change hybridization energy V.     

High quality CVD diamond: a Raman scattering and photoluminescence study

High quality synthetic diamonds were grown on single-crystal silicon by microwave plasma enhanced chemical vapour deposition (CVD). A careful optimisation of both the experimental setup and the growth parameters was necessary before that the achievement of the best results was made possible. The films were deposited using a CH₄-H₂ gas mixture at methane concentrations variable in the range 0.6-2.2%, while the substrate temperature was fixed at 750 ^°C. Raman spectroscopy and photoluminescence (PL) were utilised to monitor the quality of the deposited films and to study the spatial distribution of defects, respectively. Micro-Raman analysis shows that linewidths of the diamond peak lower than 2.4 cm^-1 can be easily measured at the growth surface, indicating that the crystalline quality of individual grains is comparable to that of the best natural diamonds. The excellent phase purity of the diamond microcrystals at the growth surface is witnessed by the complete absence of any non-diamond carbon feature and by a very weak luminescence background in the 1.6-2.4 eV spectral range. A worsening of the quality of the diamond particles is found moving from the growth surface towards the film-substrate interface. A photoluminescence feature at about 1.68 eV, commonly associated to Si impurities, is distinctly observed as the exciting laser beam is focused close to the interface. A progressive degradation of the global quality of the films is found with increasing methane concentration in the gas mixture, as witnessed by an increased PL background in the films grown at higher methane concentrations. Received 24 November 2000