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排序方式: 共有163条查询结果,搜索用时 31 毫秒
21.
The shot noise properties in a graphene-based multi-quantum well structure are investigated theoretically. It is found that when the number of the potential barriers (quantum wells) is big enough and the width of the barriers and the wells is shorter than the mean free path, another Dirac-like point at which the Fermi energy equals half of the barrier height appears. The transport is almost forbidden at this new Dirac-like point, the conductivity gets the minimum, and the Fano factor approaches 1/3. With the random potential barrier being taken into consideration, the conductance enhances clearly, meanwhile the Fano factor is suppressed much more. 相似文献
22.
Chengming Wang Toshiyuki Nagahashi Koichi Aoki Jingyuan Chen 《Journal of Electroanalytical Chemistry》2002,530(1-2)
The conductivity, κ, in a suspension of polystyrene sulfonic latex without supporting electrolyte showed a linear dependence on the volume fraction, vf, of the latex for vf<0.03 with a finite intercept. In contrast, this deviated upward from the linear line for vf>0.03. These variations were qualitatively consistent with the dependence of the voltammetric reduction current of H+ on vf without supporting electrolyte. The current values were only a few percent of the theoretical diffusion-controlled current that could be observed in the suspension with supporting electrolyte. This fact indicates the electrostatic immobilization of the hydrogen ions by sulfonic latex particles. A plot of the current against κ at common values of vf showed that the current for vf>0.07 was smaller than the value predicted from the conductivity. This can be explained in terms of a combination of the increase in electrostatically unbounded H+ estimated by conductance measurements and electric migration in which the electrochemical depletion of [H+] also causes the depletion of the latex. 相似文献
23.
基于格林函数方法及Landauer-Büttiker公式, 研究了纳米石墨带异质结的电子输运性质, 石墨带异质结由Z 形石墨带与两个锯齿型石墨带电极构成. 研究发现电导大小依赖其几何构型. 由于电子局域在锯齿型石墨带边缘, 因此在费米能级附近出现了电导隙或电导谷. 调节结间石墨带的宽度, 发现准束缚态的存在诱导许多尖锐的电导峰, 电导峰的数目几乎与结间的石墨带长度无关. 在低能区, 当θ为60°或150°时, 宽度均匀的Z型石墨带仍然保持弹道输运特征. 因此, Z形纳米石墨带可选择地应用于未来的纳微电路. 相似文献
24.
Using the four-point probe method in UHV condition the conductance through a Si(3 3 5)-Au vicinal surface with deposited 6 ML of Pb is investigated in situ during the chain formation process, i.e. as a function of temperature. For the critical temperature, , a local minimum in the conductance is observed which is related to the structural transition of Pb from a two-dimensional film to one-dimensional chains. This process is confirmed by the RHEED technique. To describe theoretically the conductance behavior a tight-binding approach and the Green’s function technique are applied and a satisfactory qualitative agreement with experimental results is obtained. 相似文献
25.
We estimated internal CO2 conductance (gi ) for C3 plant species of different life forms (annual herbs, deciduous trees and evergreen trees) grown in a variety of environments to examine the effect of g i on their leaf carbon isotope ratio (i13C). The purpose of this study was to test the validity of using i13C as an index of photosynthetic water use efficiency (WUE). When comparing deciduous tree species grown in contrasting light environments, there was a strong positive relationship between i13C and WUE. Similarly, i13C was positively correlated to WUE when comparing the different species of evergreen trees. However, the difference in WUE between evergreen and deciduous tree species did not relate to that in leaf i13C. In addition, WUE was similar between highland and lowland herbaceous plants, although the former had a much higher i13C. The positive relationship between i13C and WUE did not hold across different life forms and different altitudes when differences in gi did not relate to those in stomatal conductance, resulting in independence of chloroplast CO2 partial pressure from intercellular CO2 partial pressure. 相似文献
26.
The temperature dependence of capacitance–voltage (C–V) and conductance–voltage (G/w–V) characteristics of Al/HfO2/p-Si metal-oxide-semiconductor (MOS) device has been investigated by considering the effect of series resistance (Rs) and interface state density (Nss) over the temperature range of 300–400 K. The C–V and G/w–V characteristics confirm that the Nss and Rs of the diode are important parameters that strongly influence the electric parameters in MOS device. It is found that in the presence of series resistance, the forward bias C–V plots exhibits a peak, and its position shifts towards lower voltages with increasing temperature. The density of Nss, depending on the temperature, was determined from the (C–V) and (G/w–V) data using the Hill–Coleman Method. Also, the temperature dependence of dielectric properties at different fixed frequencies over the temperature range of 300–400 K was investigated. In addition, the electric modulus formalisms were employed to understand the relaxation mechanism of the Al/HfO2/p-Si structure. 相似文献
27.
C. R. Tench T. M. Fromhold P. B. Wilkinson M. J. Carter R. P. Taylor A. P. Micolich R. Newbury 《Physica E: Low-dimensional Systems and Nanostructures》2000,7(3-4)
We report quantum-mechanical calculations which replicate the self-similar magnetoconductance fluctuations observed in recent experiments on semiconductor Sinai billiards. We interpret these fluctuations by considering the mixed stable-chaotic classical dynamics of electrons in the billiard. In particular, we show that the fluctuation patterns are dominated by individual stable orbits. The scaling characteristics of the self-similar fluctuations depend on the geometry of the associated stable orbit. We find that our analysis is insensitive to the details of the potential landscape, and is applicable to real devices with a wide range of soft-wall profiles. We show that our analysis also provides a possible explanation for the distinct series of magnetoconductance fluctuations observed in recent experiments on carbon nanotubes. 相似文献
28.
We study the electron drift mobility in a metallic nanowire (at low temperature) as a function of both electron energy and electrochemical potential from considerations relative to energy-dependent conductance and carrier spatial density. In fact, a mathematical expression for the electron mobility, when electronic energy equals Fermi energy (resonant states), valid for negative values of the electrochemical potential is derived. 相似文献
29.
We address XOR gate response in a mesoscopic ring threaded by a magnetic flux . The ring, composed of identical quantum dots, is symmetrically attached to two semi-infinite one-dimensional metallic electrodes and two gate voltages, viz, Va and Vb, are applied, respectively, in each arm of the ring which are treated as the two inputs of the XOR gate. The calculations are based on the tight-binding model and the Green’s function method, which numerically compute the conductance–energy and current–voltage characteristics as functions of the ring-electrodes coupling strengths, magnetic flux and gate voltages. Quite interestingly it is observed that, for =0/2 (0=ch/e, the elementary flux-quantum) a high output current (1) (in the logical sense) appears if one, and only one, of the inputs to the gate is high (1), while if both inputs are low (0) or both are high (1), a low output current (0) appears. It clearly demonstrates the XOR behavior and this aspect may be utilized in designing the electronic logic gate. 相似文献
30.
Gui-Bo Zheng Ning-De Jin Xiao-Hui Jia Peng-Ju Lv Xing-Bin Liu 《International Journal of Multiphase Flow》2008
In order to solve the flowrate measurement problem of gas–liquid two phase flow widely existing in gas wells of Daqing oil field in China, a new method has been developed, which is based on the combination instrument of turbine flowmeter and conductance sensor with petal type concentrating flow diverter. The turbine and conductance signals under 104 different flow conditions have been acquired through oil–gas–water three phase flow loop experimental facility. To determine the flow pattern in measurement channel, attractor morphologic characteristics are extracted from the conductance signals. For the total flowrate measurement, based on the turbine fluctuant signals of gas–liquid two phase flow, a statistical model with the average error of 7.9% is set up. With regard to the water cut measurement, the characteristics in time and frequency domains are extracted from the fluctuant conductance signals, and then employing the Support Vector Machine (SVM) soft measurement model used in high-dimension data fitting, the water cut prediction is realized with the average error of 0.038. The results show that the combination instrument of turbine flowmeter and conductance sensor with petal type concentrating flow diverter would be useful in measuring the total flowrate and water cut of gas–liquid two phase flow in gas production wells. 相似文献