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361.
Karl Zenichowski Tillmann Klamroth Peter Saalfrank 《Applied Physics A: Materials Science & Processing》2008,93(2):319-333
Previous experiments indicate that an STM (scanning tunnelling microscope) can be used to switch a hydrogen atom at a partially
hydrogen-covered Si(100)-2×1 surface, from one Si atom of a Si dimer to a neighbouring, empty Si site [U.J. Quaade et al.,
Surf. Sci. 415, L1037, 1998]. It has been suggested that the switching occurs via a transient positive ion resonance state. In an earlier paper, we have
examined the switching process for the “above threshold” regime when the bias is large enough to directly populate the positive
ion resonance. In the present paper we study the “below threshold” regime instead, where the switching is more appropriately
modelled as a ladder climbing over the barrier, in the ground electronic state.
For this purpose we solve the Liouville–von Neumann equation in Lindblad form, describing a switching H atom on a Si dimer.
STM-induced transition rates between vibrational levels are estimated from cluster calculations, assuming contributions both
from a dipole and a resonance scattering mechanism. Vibrational relaxation is also included, as well as finite temperature
and field effects. The switching rate in a current regime of about 1 to 10 nA scales highly non-linearly with current, and
it is found to be governed by vibrational “ladder climbing” and subsequent tunnelling through the top of the ground state
barrier. Multi-phonon processes also play a role. As a result of tunnelling, pronounced isotope effects are observed when
replacing H with D. It is further argued that resonance-mediated inelastic scattering dominates over dipole excitation, and
that the STM switch is stable also at room temperature. 相似文献
362.
N. Bogdanchikova E. Smolentseva A. Pestryakov M.H. Farias A. Tompos 《Applied Surface Science》2008,254(13):4075-4083
The influence of iron additive on redox, electronic and catalytic properties of gold incorporated into zeolite catalysts has been studied by means of TEM, XPS, XRD, TPR, ICP and AES. The interaction of gold with iron modifier was observed in Y-zeolites and mordenites with different cations and method of Fe incorporation (impregnation or ion exchange). This interaction leads to mutual influence on redox properties of Fe and Au ionic species and facilitates their reduction. Limited diffusion of Au precursor after Fe species deposition in narrow mordenite channels does not permit to incorporate Au in adequate concentration, while in large super-cage of Y-zeolites this limitation is absent. The structure of Y-zeolites favors formation of active gold species. Catalytic tests in CO oxidation show that Fe additive stabilizes the gold active species active at low-temperature (partly charged clusters) and makes them insensitive to redox treatments. 相似文献
363.
Ling-Feng Mao 《Applied Surface Science》2008,254(20):6628-6632
The effects of the interface defects on the gate leakage current have been numerically modeled. The results demonstrate that the shallow and deep traps have different effects on the dependence relation of the stress-induced leakage current on the oxide electric field in the regime of direct tunneling, whereas both traps keep the same dependence relation in the regime of Fowler-Nordheim tunneling. The results also shows that the stress-induced leakage current will be the largest at a moderate oxide voltage for the electron interface traps but it increases with the decreasing oxide voltage for the hole interface traps. The results illustrate that the stress-induced leakage current strongly depends on the location of the electron interface traps but it weakly depends on the location of the hole interface traps. The increase in the gate leakage current caused by the electron interface traps can predict the increase, then decrease in the stress-induced leakage current, with decreasing oxide thickness, which is observed experimentally. And the electron interface trap level will have a large effect on the peak height and position. 相似文献
364.
365.
《The European Physical Journal A - Hadrons and Nuclei》2008,38(2):195-207
The photoproduction of η -mesons off 12C , 40Ca , 93Nb , and
nat
Pb nuclei has been measured with a tagged photon beam with energies between 0.6 and 2.2GeV. The experiment was performed at
the Bonn ELSA accelerator with the combined setup of the Crystal Barrel and TAPS calorimeters. It aimed at the in-medium properties
of the S
11(1535) nucleon resonance and the study of the absorption properties of nuclear matter for η -mesons. Careful consideration
was given to contributions from ηπ final states and secondary production mechanisms of η -mesons, e.g. from inelastic πN reactions of intermediate pions. The analysis of the mass number scaling shows that the nuclear absorption cross-section
for η -mesons is constant over a wide range of the η momentum. The comparison of the excitation functions to data off the
deuteron and to calculations in the framework of a BUU model show no unexplained in-medium modifications of the S
11(1535) . 相似文献
366.
Guoyan Huo Minghui Ren Xiaoqing Wang Hongrui Zhang Pengfei Shi 《Journal of magnetism and magnetic materials》2010,322(5):500-504
The crystal structural, magnetic and electrical transport properties of double perovskite CeKFeMoO6 have been investigated. The crystal structure of the compound is assigned to the monoclinic system with space group P21/n and its lattice parameters are a=0.55345(3) nm, b=0.56068(2) nm, c=0.78390(1) nm, β=89.874(2). The divergence between zero-field-cooling and field-cooling M-T curves demonstrates the anisotropic behavior. The Curie temperature measured from Cp-T curve is about 340 K. Isothermal magnetization curve shows that the saturation and spontaneous magnetization are 1.90 and 1.43 μB/f.u. at 300 K, respectively. The electrical behavior of the sample shows a semiconductor. The electrical transport behavior can be described by variable range hopping model. Large magnetoresistance, −0.88 and −0.18, can be observed under low magnetic field, 0.5 T, at low and room temperature, respectively. 相似文献
367.
The K-matrix approach with effective Lagrangians is used to describe the S and P pion-nucleon partial-wave amplitudes in the energy range E
lab≤ 1 GeV. It is demonstrated, that treating the resonance as K-matrix a pole gives the natural way to separate the resonance and non-resonance parts of the πN amplitude. The model includes all the four-star πN resonances, the non-resonance contributions are calculated from relevant Feynman graphs without any phenomenological form
factors. Different contributions to the inelastic π−
p→ηn amplitude are estimated.
Received: 9 July 1998 相似文献
368.
J. Weis O. Weis 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):135-146
This paper is concerned with the transmission time of an incident Gaussian wave packet through a symmetric rectangular barrier.
Following Hartman (J. Appl. Phys. 33, 3427 (1962)), the transmission time is usually taken as the difference between the time at which the peak of the transmitted packet leaves the barrier of thickness
and the time at which the peak of the incident Gaussian wave packet arrives at the barrier. This yields a corresponding transmission
velocity which appears under certain conditions as a supervelocity, i.e. becomes larger than the corresponding propagation velocity in free space which is the group velocity for electrons or the
velocity of light for photons, respectively. By analysing the propagation of a broadband wave packet (which leads in free
space to an extremely concentrated wave packet at a certain time) we obtain the pulse response function of the barrier and
show that the insertion of the barrier is physically unable to produce a supervelocity. Therefore, the peak of an incident
Gaussian wave packet and the peak of the transmitted wave packet are in no causal relationship. The shape of the transmitted
wave packet is produced from the incident wave by convolution with the pulse response of the barrier. This yields a distortion
of the shape of the wave packet which includes also the observed negative time shift of the peak. We demonstrate further that
the phenomenon of Hartman's supervelocities is not restricted to barriers with their exponentially decaying fields but occurs
for instance also in transmission lines with an inserted LCR circuit.
Received 7 January 1999 and Received in final form 22 April 1999 相似文献
369.
The present status and key issues of surface passivation technology for III-V surfaces are discussed in view of applications to emerging novel III-V nanoelectronics. First, necessities of passivation and currently available surface passivation technologies for GaAs, InGaAs and AlGaAs are reviewed. Then, the principle of the Si interface control layer (ICL)-based passivation scheme by the authors’ group is introduced and its basic characterization is presented. Ths Si ICL is a molecular beam epitaxy (MBE)-grown ultrathin Si layer inserted between III-V semiconductor and passivation dielectric. Finally, applications of the Si ICL method to passivation of GaAs nanowires and GaAs nanowire transistors and to realization of pinning-free high-k dielectric/GaAs MOS gate stacks are presented. 相似文献