共查询到20条相似文献,搜索用时 15 毫秒
1.
B. Ya. Balagurov 《Journal of Experimental and Theoretical Physics》2010,110(2):265-274
The electrical conductivity of a two-dimensional structurally anisotropic model for a composite is considered. The model represents
an isotropic matrix with a system of nonconducting inclusions in the form of infinitely thin straight line segments (scratches).
The scratches make an angle θ or −θ with a preferred axis (for definiteness, axis y) at the same probability, and their centers are chaotically distributed. An approximate effective medium method is used to
obtain a general expression for the effective conductivity tensor $
\hat \sigma _e
$
\hat \sigma _e
of this model that is valid over a wide concentration range. In this approximation, both components of tensor are $
\hat \sigma _e
$
\hat \sigma _e
shown to vanish at the same percolation threshold, which is expressed explicitly. The conductivity of the model in a critical
region is considered in terms of the similarity hypothesis. 相似文献
2.
A discussion of electronic conduction in amorphous thin films of Al-In2O3-Al structure is presented. Particular attention is given to the question of film thickness, substrate temperature during
deposition and post-deposition annealing, since these conditions are known to have a profound effect on the structure and
electrical properties of the films. The effects of temperature on the V-I characteristics and effects of frequency on conductivity and capacitance of the Al-In2O3-Al structure are also reported. Activation energies for conduction processes are estimated and the results are discussed
in terms of the hopping model. The conduction at higher temperature is seemingly a contact-limited, i.e. Schottky type process,
so a transition from hopping to free-band conduction takes place. The capacitance decreases with the rise of frequency and
the lowering of temperature. The values of dielectric constants are estimated and the results are discussed in terms of Schottky
type of conduction. The increase in conductivity with the increase in temperature during measurements of electrical properties,
film thickness, substrate temperature and post deposition annealing is reported and results are discussed in terms of current
theory. 相似文献
3.
Temperature-dependent conductivity and thermopower measurements are carried out for undoped and In-doped CuO thin films. We investigate the effects of In-doping on carrier transport properties of CuO thin films in the temperature range of 300?<?T?<?400?K. Carrier transport is dominated by simple thermally activated conduction in the undoped film. On the other hand, small polarons play an essential role in the carrier transport properties in the In-doped films. By increasing the In content, the conduction behaviour transits from adiabatic limit to the non-adiabatic limit, and the conductivity decreases. 相似文献
4.
The conductivity of a two-dimensional composite with natural anisotropy, a thin anisotropic film with a system of randomly distributed nonconducting scratches is considered. An exact expression for the conductivity in the approximation linear in the concentration of scratches is derived. The case of consider-able concentrations is examined using the generalized effective-medium theory. The conductivity near the percolation threshold is treated in the framework of similarity theory. 相似文献
5.
6.
S.Y. Jang N. Nakagawa S.J. Moon T. Susaki K.W. Kim Y.S. Lee H.Y. Hwang K. Myung-Whun 《Solid State Communications》2009,149(41-42):1760-1764
In this study, we investigated the lattice structure, electrical resistivity, and optical conductivity of Nd0.5Sr0.5MnO3 thin films grown on SrTiO3 (001) and SrTiO3 (011) substrates. The thin film on SrTiO3 (001) experiences isotropic tensile strain and shows characteristics of the semiconducting ground state. On the other hand, the thin film on SrTiO3 (011) experiences anisotropic tensile strain, which means that one of the two in-plane lattice axes is fixed by the substrate lattice and the other axis is relaxed. The thin film shows the insulator–metal phase transition at 220 K and characteristics of the charge-ordered insulating ground state below 150 K. By comparing the single crystal data of the lattice along with the resistivity and optical conductivity, we suggest that the substrate strain affects the electronic structure as well as the carrier dynamics of the Nd0.5Sr0.5MnO3 thin films. We propose the possible ground states formed in the thin films. 相似文献
7.
Haoyan Wei 《Journal of Physics and Chemistry of Solids》2009,70(2):459-465
Silver nanoparticles embedded in a dielectric matrix are investigated for their potential as broadband-absorbing optical sensor materials. This contribution focuses on the electrical properties of silver nanoparticles on glass substrates at various morphological stages. The electrical current through thin films, consisting of silver nanoparticles, was characterized as a function of film thickness. Three distinct conductivity zones were observed. Two relatively flat zones (“dielectric” for very thin films and “metallic” for films thicker than 300-400 Å) are separated by a sharp transition zone where percolation dominates. The dielectric zone is characterized by isolated particle islands with the electrical conduction dominated by a thermally activated tunneling process. The transition zone is dominated by interconnected silver nanoclusters—a small increase of the film thickness results in a large increase of the electrical conductivity. The metallic conductivity zone dominates for thicknesses above 300-400 Å. 相似文献
8.
Blanchard F Golde D Su FH Razzari L Sharma G Morandotti R Ozaki T Reid M Kira M Koch SW Hegmann FA 《Physical review letters》2011,107(10):107401
The anisotropic effective mass of energetic electrons in an isotropic, nonparabolic conduction band is revealed using ultrafast THz-pump-THz-probe techniques in a n-doped InGaAs semiconductor thin film. A microscopic theory is applied to identify the origin of the observed anisotropy and to show that the self-consistent light-matter coupling contributes significantly to the THz response. 相似文献
9.
P. Peyla C. Misbah 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):233-247
Elastic interactions between defects is investigated at the surface of thin layers, a question on which we have given a brief
account [P. Peyla et al. Phys. Rev. Lett. 82, 787 (1999)]. Two isotropic defects do not interact in an unlimited medium, regardless of the spatial dimension, a result
which can be shown on the basis of the Gauss theorem in electrostatics. Within isotropic elasticity theory, defects interact
only (i) if they are, for example, at a surface (or at least if they feel a boundary), or if their action on the material
is anisotropic (e.g. they create a non central force distribution, though the material elasticity is isotropic). It is known that two identical
isotropic defects on the surface of a semi-infinite material repel each other. The repulsion law behaves as 1/r
3(r = defects separation). We first revisit the Lau-Kohn theory and extend it to anisotropic defects. Anisotropy is found to
lead to attraction. We show that in thin films defects may either attract or repel each other depending on the local geometric
force distribution caused by the defect. It is shown that the force distribution (or more precisely the forces configuration
symmetry) fixes the exponent in the power law 1/r
n (e.g. for a four-fold symmetry n = 4). We discuss the implication of this behaviour in various situations. We treat the interactions in terms of the symmetries
associated with the defect. We argue that if the defects are isotropic, then their effective interaction in an unlimited 2D
(or a thin film) medium arises from the induced interaction, which behaves as 1/r
4 for any defect symmetry. We shall also comment on the contribution to the interaction which arises from flexion of thin films.
Received 7 October 2002 Published online 4 June 2003
RID="a"
ID="a"e-mail: chaouqi.misbah@ujf-grenoble.fr 相似文献
10.
N-doped CuCrO2 thin films were prepared by using radio frequency magnetron sputtering technique. The XRD and XPS measurements were used to confirm the existence of the N acceptors in CuCrO2 thin films. Hall measurements show the p-type conduction for all films. The electrical conductivity increases rapidly with the increase in N doping concentration, and the maximum of the electrical conductivity of 17 S cm−1 is achieved for the film deposited with 30 vol.% N2O, which is about three orders of magnitude higher than that of the undoped CuCrO2 thin film. Upon increasing the doping concentrations the band gaps of N-doped CuCrO2 thin films increase due to the Burstein-Moss shift. 相似文献
11.
Tsuneya Ando 《Zeitschrift für Physik B Condensed Matter》1976,24(2):219-226
Characteristics of the conductivity tensor are obtained in an anisotropic two-dimensional system where the Fermi surface is given by elliptic form. The anisotropy of the transverse conductivity
xx
and
yy
depends strongly on the range of scattering potentials: It becomes maximum in case of short-ranged scatterers, and decreases with the increase of the range. The conductivity becomes isotropic in the limit of slowly-varying scatterers if the scattering potential is isotropic. The Hall conductivity is, on the other hand, not affected by the anisotropy strongly. 相似文献
12.
13.
In this study, the electrical, optical and mechanical properties of polystyrene (PS) thin films added graphene nanoplatelet (GNP) have been investigated. Surface conductivity (σ), absorbance intensity (A) and tensile modulus of these composite films have increased with increasing the content of GNP in the composite. The increase in the electrical and optical properties of the PS/GNP composite films has been interpreted by site and classical percolation theory, respectively. The electrical and the optical percolation thresholds of PS/GNP composite films were determined as Rσ?=?23.0?wt.% and Rop?=?13.0?wt.%, respectively. While the conductivity results have been attributed to the classical percolation theory, the optical results have attributed to the site percolation theory. The electrical (βσ) and the optical (βop) critical exponents were calculated as 2.54 and 0.40, respectively. The tensile modulus and the tensile strength of the PS/GNP composites increased with the increasing of GNP content in the PS. But, the toughness of the composites fluctuated with GNP addition. 相似文献
14.
Katsu Rokushima Roman Antoš Jan Mistrík Štefan Višňovský Tomuo Yamaguchi 《Czechoslovak Journal of Physics》2006,56(7):665-764
The analytical formalism of Rokushima and Yamakita [J. Opt. Soc. Am. 73, 901–908 (1983)] treating the Fraunhofer diffraction
in planar multilayered anisotropic gratings proved to be a useful introduction to new fundamental and practical situations
encountered in laterally structured periodic (both isotropic and anisotropic) multilayer media. These are employed in the
spectroscopic ellipsometry for modeling surface roughness and in-depth profiles, as well as in the design of various frequency-selective
elements including photonic crystals. The subject forms the basis for the solution of inverse problems in scatterometry of
periodic nanostructures including magnetic and magneto-optic recording media. It has no principal limitations as for the frequencies
and period to radiation wavelength ratios and may include matter wave diffraction. The aim of the paper is to make this formalism
easily accessible to a broader community of students and non-specialists. Many aspects of traditional electromagnetic optics
are covered as special cases from a modern and more general point of view, e.g., plane wave propagation in isotropic media, reflection and refraction at interfaces, Fabry-Perot resonator, optics of thin
films and multilayers, slab dielectric waveguides, crystal optics, acousto-, electro-, and magneto-optics, diffraction gratings,
etc. The formalism is illustrated on a model simulating the diffraction on a ferromagnetic wire grating. 相似文献
15.
L. Turban 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):331-338
Shape-dependent universal crossing probabilities are studied, via Monte Carlo simulations, for bond and site directed percolation on the square lattice in the diagonal direction, at the percolation
threshold. In a dynamical interpretation, the crossing probability is the probability that, on a system with size L, an epidemic spreading without immunization remains active at time t. Since the system is strongly anisotropic, the shape dependence in space-time enters through the effective aspect ratio r
eff = ct/L
z, where c is a non-universal constant and z the anisotropy exponent. A particular attention is paid to the influence of the initial state on the universal behaviour
of the crossing probability. Using anisotropic finite-size scaling and generalizing a simple argument given by Aizenman for
isotropic percolation, we also obtain the behaviour of the probability to find n incipient spanning clusters on a finite system at time t. The numerical results are in good agreement with the conjecture.
Received 10 February 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: turban@lpm.u-nancy.fr
RID="b"
ID="b"UMR CNRS 7556 相似文献
16.
P. V. Gorskii 《Russian Physics Journal》2011,53(10):1072-1085
It is demonstrated that the dependence of Fermi’s energy on the magnetic field causes a set of the Shubnikov – de Haas (SDH)
oscillation frequencies to change, and their relative contribution to the total longitudinal conductivity of layered crystals
depends on whether the scattering of current carriers is isotropic or anisotropic. Owing to the topological transition in
a strong magnetic field, Fermi’s surface (FS) is transformed from open into closed one and is compressed in the magnetic field
direction. Therefore, in an ultraquantum limit, disregarding the Dingle factor, the longitudinal electrical conductivity of
the layered crystal tends to zero as a reciprocal square of the magnetic field for the isotropic scattering and as a reciprocal
cube of the magnetic field for the anisotropic scattering. All calculations are performed in the approximation of relaxation
time considered to be constant versus the quantum numbers for the isotropic scattering and proportional to the longitudinal
velocity of current carriers for the anisotropic scattering. 相似文献
17.
H. E. Roman 《Phase Transitions》2013,86(2):435-461
Dispersed ionic conductors are random mixtures of a solid salt, e.g. AgI, LiI, with fine particles of an insulating second phase, like Al2O3 or SiO2. These composites can show a dramatic increase in ionic conductivity compared to the pure homogeneous system. Generally, this observation is attributed to an increased conductivity along the internal interface between the conducting salt and the insulating material. In this work a three-component random resistor network (RRN) model for dispersed ionic conductors is reviewed. In the model, the ionic conductor is represented by normally conducting bonds, the insulating material by non-conducting bonds and the interface between the two phases by highly conducting bonds. A special feature of the model is the existence of two critical concentrations of the insulating phase, p′c and p″c , for interface percolation and bulk conduction, respectively, where critical transport properties corresponding to conductor/superconductor and conductor/insulator networks are predicted. The model describes satisfactorily the dependence on composition of the conductivity and activation energy of dispersed ionic conductors. Furthermore, the observed effect on the conductivity of the size of dispersed particles can be described qualitatively well by a generalized version of the RRN model, which in addition predicts a sensitive dependence of the critical thresholds on particle size. Non-universality features in the critical exponents for the conductivity are also discussed within a continuum percolation analog of the model. 相似文献
18.
将铁磁共振频率看成外磁场的函数, 讨论了垂直场下磁性膜中的铁磁共振现象. 结果显示: 当外磁场平行于膜面, 并考虑磁膜具有垂直磁晶各向异性情形时, 其磁共振频率随外磁场的变化分为高频支和低频支两种情况, 具体的依赖关系取决于磁膜内磁晶的各向异性; 当外磁场垂直于膜面, 其磁共振频率随外磁场的关系仅存在一支, 一般地, 磁共振频率随外磁场的增加单调地非线性减小, 但当立方磁晶各向异性场Hk1 与单轴磁晶各向异性场Ha之比值介于2/3 < Hk1/Ha <1时, 其磁共振频率随外磁场的增加单调增加, 这与相关的实验结果一致. 研究结果表明: 磁薄膜中有无垂直于膜面的磁各向异性可以通过其磁共振谱的测量进行辨析. 相似文献
19.
B. Ya. Balagurov G. A. Vinogradov 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(6):905-916
The character of electric conduction in a two-dimensional structurally anisotropic composite containing elliptic inclusions with a large ratio of the semiaxis. Dielectric and ideally conducting inclusions were considered. It was demonstrated that the approximation linear in concentration of inclusions fails beginning from rather small concentrations. The region of intermediate concentrations was studied using approximate methods based on the analogy between electric conductivity and the diffusion of a single particle in a nonuniform medium. The conductivity of the model system under study was analyzed over a wide concentration range with the use of the effective medium theory; the results are in close agreement with those obtained by qualitative methods. The behavior of conductivity near the percolation threshold (metal-to-dielectric phase transition) was examined using the similarity. The conductivity of thin composite films with inclusions in the form of carbon nanotubes was examined, as an example. 相似文献
20.
Abstract Measurements of electron paramagnetic resonance, infrared and electrical properties were carried out for the K2SO4—Na2SO4 mixed system before and after γ-irradiation. EPR measurements revealed the presence of a quartet of lines characterized by an isotropic g-value of 2.0034. These lines are mainly attributed to the formation of a SO? 3 center which results from the interaction of γ-rays with the sulfate ion. A decrease in the absorption intensity of the Infrared radiation was observed after γ-irradiation due to radiation damage in the sulfate group. The electrical conductivity, σ, was measured for the K2SO4—Na2SO4 system before and after γ-irradiation in the temperature range from 30 up to 430°C. A considerable decrease in the conductivity value accompanied by an increase in the activation energy was observed after γ-irradiation. The energy of formation of Frenkel defects was estimated to be 2.94eV. The current-voltage characteristics were measured at different temperatures in order to estimate the type of conduction in the samples. Isothermal annealing kinetics was investigated at different temperatures before and after γ-irradiation. The electrical conductivity decreases with increasing time of annealing and the annealing process is dominated by a unique rate process. 相似文献