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891.
We investigate the longitudinal optical conductivity of spatially separated few-layer graphene analytically and numerically. Each layer could be monolayer or bilayer graphene. The density–density correlation function has been screened by the dielectric function using the random phase approximation, which includes the inter-layer Coulomb coupling. In the presence of the potential function between the layers, the carrier densities in each layer can be tuned respectively. In these two-dimensional layered structures, the main contributions to the optical conductivity are from the intra- and inter-band transition channels in a same layer. In the infrared region, the Drude optical conductivity was observed by the unscreened intra-band transition process. But in the presence of the inter-layer Coulomb interaction, one peak structure of the optical conductivity is observed which can be modified by the dielectric environment. From the number of turning points and the turning positions, the carrier density, the Fermi wavevector, and the layered structure can be determined. 相似文献
892.
Z. P. Niu Z. M. Zheng D. Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):281-287
Four-component Bogoliubov-de Gennes equations are applied to study
tunneling conductance spectra of ferromagnet/ferromagnet/d-wave
superconductor (F1/F2/d-wave S) tunnel junctions and to find
out signs of spin-triplet pairing correlations induced in the
proximity structure. The pairing correlations with equal spins
arises from the novel Andreev reflection (AR), which requires at
least three factors: the usual AR at the F2/S interface, spin
flip in the F2 layer, and superconducting coherence kept up in
the F2 layer. Effects of angle α between magnetizations of
the two F layers, polarizations of the F1 and F2 layers, the
thickness of the F2 layer, and the orientation of the d-wave S crystal on the tunneling conductance are investigated. A conversion
from a zero-bias conductance dip at α = 0 to a zero-bias
conductance peak at a certain value of α can be seen as a
sign of generated spin-triplet correlations. 相似文献
893.
In this study, the axial flow cyclone used in Tsai et al. (2004) was further tested for the collection efficiency of both
solid (NaCl) and liquid (OA, oleic acid) nanoparticles. The results showed that the smallest cutoff aerodynamic diameters
achieved for OA and NaCl nanoparticles were 21.7 nm (cyclone inlet pressure: 4.3 Torr, flow rate: 0.351 slpm) and 21.2 nm
(5.4 Torr, 0.454 slpm), respectively. The collection efficiencies for NaCl and OA particles were close to each other for the
aerodynamic diameter ranging from 25 to 180 nm indicating there was almost no solid particle bounce in the cyclone. The 3-D
numerical simulation was conducted to calculate the flow field in the cyclone and the flow was found to be nearly paraboloid.
Numerical simulation of the particle collection efficiency based on the paraboloid flow assumption showed that the collection
efficiency was in good agreement with the experimental data with less than 15% of error. A semi-empirical equation for predicting
the cutoff aerodynamic diameter at different inlet pressures and flow rates was also obtained. The semi-empirical equation
is able to predict the cutoff aerodynamic diameter accurately within 9% of error. From the empirical cutoff aerodynamic diameter,
a semi-empirical square root of the cutoff Stokes number, , was calculated and found to be a constant value of 0.241. This value is useful to the design of the cyclone operating in
vacuum to remove nanoparticles. 相似文献
894.
895.
B. Doggett S. Chakrabarti R. OHaire A. Meaney E. McGlynn M.O. Henry J.P. Mosnier 《Superlattices and Microstructures》2007,42(1-6):74
Phosphorus-doped ZnO films were grown by pulsed laser deposition using a ZnO:P2O5-doped target as the phosphorus source with the aim of producing p-type ZnO material. ZnO:P layers (with phosphorus concentrations of between 0.01 to 1 wt%) were grown on a pure ZnO buffer layer. The electrical properties of the films were characterised from temperature dependent Hall-effect measurements. The samples typically showed weak n-type conduction in the dark, with a resistivity of 70 Ω cm, a Hall mobility of μn0.5 cm2 V −1 s−1 and a carrier concentration of n3×1017 cm−3 at room temperature. After exposure to an incandescent light source, the samples underwent a change in conduction from n- to p-type, with an increase in mobility and decrease in concentration for temperatures below 300 K. 相似文献
896.
The electrophoresis and electric conduction of a suspension of charged spherical particles in a salt-free solution are analyzed by using a unit cell model. The linearized Poisson-Boltzmann equation (valid for the cases of relatively low surface charge density or high volume fraction of the particles) and Laplace equation are solved for the equilibrium electric potential profile and its perturbation caused by the imposed electric field, respectively, in the fluid containing the counterions only around the particle, and the ionic continuity equation and modified Stokes equations are solved for the electrochemical potential energy and fluid flow fields, respectively. Explicit analytical formulas for the electrophoretic mobility of the particles and effective electric conductivity of the suspension are obtained, and the particle interaction effects on these transport properties are significant and interesting. The scaled zeta potential, electrophoretic mobility, and effective electric conductivity increase monotonically with an increase in the scaled surface charge density of the particles and in general decrease with an increase in the particle volume fraction, keeping each other parameter unchanged. Under the Debye-Hückel approximation, the dependence of the electrophoretic mobility normalized with the surface charge density on the ratio of the particle radius to the Debye screening length and particle volume fraction in a salt-free suspension is same as that in a salt-containing suspension, but the variation of the effective electric conductivity with the particle volume fraction in a salt-free suspension is found to be quite different from that in a suspension containing added electrolyte. 相似文献
897.
运用多重态计算方法研究了在正八面体对称性的晶体场中Co2+离子的2p电子X射线L2,3吸收边光谱, 研究了Co2+离子和周围的配位离子之间的正八面体(Oh)晶体场效应和相应的电荷转移效应对于吸收光谱的影响. 系统讨论了在多重态计算中起作用的所有物理参数对CoO和CoCl2的X射线吸收光谱特性的特定影响及其物理机制. 将计算得出的光谱数据和同样具有Oh对称性结构Co2+离子的CoO和CoCl2实验光谱数据进行了对比, 在实验光谱数据中发现的特征被确定为来自不同自旋态, 并且光谱强度的变化与晶体场的强度相关, 揭示了其中包含的电荷转移效应. 本文为低对称性复杂系统的多重态计算提供了一个基础的参考标准, 可以适用于含有钴元素或其它过渡金属的复杂体系的X射线吸收光谱的理论计算. 相似文献
898.
杂环修饰的萘二酰亚胺(NDI)类化合物由于其独特的光电性能被研究人员广泛关注,并应用于有机场效应晶体管(OFETs)、有机太阳能电池中(OSCs)、传感器等领域。但是含有给受体单元的多元杂环萘二酰亚胺衍生物的合成并不容易,本文通过简单高效的方法设计合成了含有氮、硫原子的11个杂环类萘二酰亚胺衍生物,并通过紫外可见吸收光谱、循环伏安曲线和X射线衍射对其进行了物性研究。通过溶液旋涂法,制备了该材料的底栅底接触场效应晶体管器件,在空气中表现出p型半导体性能,当退火温度为140 ℃时性能达到最优,其空穴迁移率为0.2 cm2?V-1?s-1。 相似文献
899.
Valentinos Mouarrawis Eduard O. Bobylev Prof. Dr. Bas de Bruin Prof. Dr. Joost N. H. Reek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(32):8390-8397
Confinement of a catalyst can have a significant impact on catalytic performance and can lead to otherwise difficult to achieve catalyst properties. Herein, we report the design and synthesis of a novel caged catalyst system Co−G@Fe8(Zn−L ⋅ 1)6 , which is soluble in both polar and apolar solvents without the necessity of any post-functionalization. This is a rare example of a metal-coordination cage able to bind catalytically active porphyrins that is soluble in solvents spanning a wide variety of polarity. This system was used to investigate the combined effects of the solvent and the cage on the catalytic performance in the cobalt catalyzed cyclopropanation of styrene, which involves radical intermediates. Kinetic studies show that DMF has a protective influence on the catalyst, slowing down deactivation of both [Co(TPP)] and Co−G@Fe8(Zn−L ⋅ 1)6 , leading to higher TONs in this solvent. Moreover, DFT studies on the [Co(TPP)] catalyst show that the rate determining energy barrier of this radical-type transformation is not influenced by the coordination of DMF. As such, the increased TONs obtained experimentally stem from the stabilizing effect of DMF and are not due to an intrinsic higher activity caused by axial ligand binding to the cobalt center ([Co(TPP)(L)]) . Remarkably, encapsulation of Co−G led to a three times more active catalyst than [Co(TPP)] (TOFini) and a substantially increased TON compared to both [Co(TPP)] and free Co−G . The increased local concentration of the substrates in the hydrophobic cage compared to the bulk explains the observed higher catalytic activities. 相似文献
900.
Inés Sánchez-Movellán Jorge Moreno-Ceballos Dr. Pablo García-Fernández Prof. Jose Antonio Aramburu Prof. Miguel Moreno 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(54):13582-13590
In the search for new high-temperature superconductors, it has been proposed that there are strong similarities between the fluoroargentate AgF2 and the cuprate La2CuO4. We explored the origin of the possible layered structure of AgF2 by studying its parent high-symmetry phase and comparing these results with those of a seemingly analogous cuprate, CuF2. Our findings first stress the large differences between CuF2 and AgF2. Indeed, the parent structure of AgF2 is found to be cubic, naturally devoid of any layering, even though Ag2+ ions occupy trigonal sites that, nevertheless, allow the existence of a Jahn-Teller effect. The observed Pbca orthorhombic phase is found when the system is cooperatively distorted by a local E⊗e trigonal Jahn-Teller effect around the silver sites that creates both geometrical and magnetic layering. While the distortion implies that two Ag2+−F− bonds increase their distance by 15 % and become softer, our simulations indicate that covalent bonding and interlayer electron hopping is strong, unlike the situation in cuprate superconductors, and that, in fact, exfoliation of individual planes might be a harder task than previously suggested. As a salient feature, these results prove that the actual magnetic structure in AgF2 is a direct consequence of vibronic contributions involved in the Jahn-Teller effect. Finally, our findings show that, due to the multiple minima intrinsic to the Jahn-Teller energy surface, the system is ferroelastic, a property that is strongly coupled to magnetism in this argentate. 相似文献