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71.
Summary In the present paper we calculate exactly the density of states of an ideal 2DEG in uniform magnetic and electric fields with
parabolic confining potential. From the density of states, we obtain the magnetoconductance oscillations. Consequently, we
get the Hall current by means of the Feynman-Hellman theorem and study its quantization.
Riassunto In questo lavoro si calcola esattamente la densità degli stati di un ideale 2DEG in campi uniformi magnetici ed elettrici con potenziale confinante parabolico. Dalla densità degli stati si ottengono le oscillazioni di magnetoconduttanza. Di consequenza si ricava la corrente di Hall per mezzo del teorema di Feynman-Hellman e si studia la sua quantizzazione.
Резюме В этой работе мы проводим точное вычисление плотности состояний идеального даумерного электронного газа в однородных магнитных и электрических полях с параболическим удерживаущим потенциалом. Из плотности состояний мы получаем осцилляции магнитной проводимости. Таким образом, мы определяем ток Холла с помощью теоремы фейнмана-Гелмана и исследуем его квантование.相似文献
72.
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. 相似文献
73.
Erik J Faber Louis C P M de Smet Wouter Olthuis Han Zuilhof Ernst J R Sudh?lter Piet Bergveld Albert van den Berg 《Chemphyschem》2005,6(10):2153-2166
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. 相似文献
74.
Keith B. Oldham 《Journal of Solid State Electrochemistry》1998,2(6):367-377
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 相似文献
75.
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. 相似文献
76.
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. 相似文献
77.
B. P. Clayman 《International Journal of Infrared and Millimeter Waves》1982,3(5):743-751
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. 相似文献
78.
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 LD 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 LD
vs. N
α
vary as 1/Nα1/2, which gives NαLD ⋍ 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. 相似文献
79.
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 CeNi1−xRhxSn, 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. 相似文献
80.
M.G. Donato G. Faggio M. Marinelli G. Messina E. Milani A. Paoletti S. Santangelo A. Tucciarone G. Verona Rinati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):133-139
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 相似文献