Direct Current Hopping Conductivity in One—Dimensional Nanometre Systems

A one-dimensional random nanocrystalline chain model is established.A dc electron-phonon-field conductance model of electron tunnelling transfer is set up,and a new dc conductance formula in one-dimensional nanometre systems is derived.By calculationg the dc conductivity,the relationship among the electric field,temperature and conductivity is analysed.and the effect of the crystalline grain size and the distrotion of interfacial atoms on the dc conductance is discussed.The result shows that the nanometre system appears the characteristic of negative differential dependence of resistance and temperature at low temperature.The dc conductivity of nanometre systems varies with the change of electric field and trends to rise as the crystalline grain size increases and to decrease as the distroted degree of interfacial atoms increases.     

Kondo effect for electron transport through an artificial quantum dot

We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper. We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases. The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case. It increases as the external magnetic field increases. We obtain the relation between the coupling coefficient and conductance. If the interaction is big enough to prevent conduction electrons from tunnelling through the dot, the dispersion effect is dominant in this case. In the Kondo temperature regime, we obtain the conductivity of a quantum dot system with Kondo correlation.     

Direct current hopping conductance in one-dimensional diagonal disordered systems

Based on a tight-binding disordered model describing a single electron band, we establish a direct current (dc) electronic hopping transport conductance model of one-dimensional diagonal disordered systems, and also derive a dc conductance formula. By calculating the dc conductivity, the relationships between electric field and conductivity and between temperature and conductivity are analysed, and the role played by the degree of disorder in electronic transport is studied. The results indicate the conductivity of systems decreasing with the increase of the degree of disorder, characteristics of negative differential dependence of resistance on temperature at low temperatures in diagonal disordered systems, and the conductivity of systems decreasing with the increase of electric field, featuring the non-Ohm's law conductivity.     

Electron Dynamics of Atoms in Parallel Electric and Magnetic Fields

Through an analysis of the nearest neighbor level fields, we investigate the evolution of the electron spacing statistics for atoms in parallel electric and magnetic dynamics as electric field strength increases. In the ＇inter-l mixing＇ predominant region, the electron shows complex dynamics while in the ＇inter-n mixing＇ predominant region, its dynamics behaves in a relatively stable way and the characteristic quantity ξ shows a slight oscillation. Comparing the dynamics for hydrogen and barium, we find that the core effect makes the main contribution to the chaotic behavior in non-hydrogen atoms.     

Direct current hopping conductance along DNA chain

This paper proposes a model of direct current (DC) electron hopping transport in DNA, in which DNA is considered as a binary one-dimensional disordered system. To quantitatively study the DC conductivity in DNA, it numerically calculates the DC conductivity of DNA chains with different parameter values. The result shows that the DC conductivity of DNA chain increases with the increase of temperature. And the conductivity of DNA chain is depended on the probability p, which represents the degree of compositional disorder in a DNA sequence to some extent. For p<0.5, the conductivity of DNA chain decreases with the increase of p, while for p\geq0.5, the conductivity increases with the increase of p. The DC conductivity in DNA chain also varies with the change of the electric field, it presents non-Ohm's law conductivity characteristics.     

Characteristics of alternating current hopping conductivity in DNA sequences

This paper presents a model to describe alternating current (AC) conductivity of DNA sequences, in which DNA is considered as a one-dimensional (1D) disordered system, and electrons transport via hopping between localized states. It finds that AC conductivity in DNA sequences increases as the frequency of the external electric field rises, and it takes the form of σ_ac (ω)～ω ²\ln ²(1/ω). Also AC conductivity of DNA sequences increases with the increase of temperature, this phenomenon presents characteristics of weak temperature-dependence. Meanwhile, the AC conductivity in an off-diagonally correlated case is much larger than that in the uncorrelated case of the Anderson limit in low temperatures, which indicates that the off-diagonal correlations in DNA sequences have a great effect on the AC conductivity, while at high temperature the off-diagonal correlations no longer play a vital role in electric transport. In addition, the proportion of nucleotide pairs p also plays an important role in AC electron transport of DNA sequences. For p < 0.5, the conductivity of DNA sequence decreases with the increase of p, while for p ≥ 0.5, the conductivity increases with the increase of p.     

Semiclassical Calculation of Recurrence Spectra of Li Rydberg Atom in Crossed Electric and Magnetic Field

Closed-orbit theory is a semiclassical technique for explaining the spectra of Rydberg atoms in external fields. Using the dosed-orblt theory and classical perturbation theory, we calculate the scaled recurrence spectra of Lithium atom in magnetic field plus a weak perpendicular electric field. The results show when the crossed electric field is added, the recurrence spectra are weakened greatly. As the scaled electric field f increases, the peaks of the recurrence spectra lose strength. Some recurrences are very sensitive and fall off rapidly as f increases, others persist till much higher f. As the electric field is stronger, some of the peaks revive. This phenomenon, caused by the interference among the electron waves that return to the nucleus, can be computed from the azimuthal dependence of the classical closed orbits.     

Pressure influence on the Stark effect of impurity states in a strained wurtzite GaN/AlxGa1-xN heterojunction

A variational method is adopted to investigate the properties of shallow impurity states near the interface in a free strained wurtzite GaN/AlxGa1-xN heterojunction under hydrostatic pressure and external electric field by using a simplified coherent potential approximation. Considering the biaxial strain due to lattice mismatch or epitaxial growth and the uniaxial strains effects, we investigated the Stark energy shift led by an external electric field for impurity states as functions of pressure as well as the impurity position, Al component and areal electron density. The numerical result shows that the binding energy near linearly increases with pressure from 0 to 10 GPa. It is also found that the binding energy as a function of the electric field perpendicular to the interface shows an un-linear red shift or a blue shift for different impurity positions. The effect of increasing x on blue shift is more significant than that on the red shift for the impurity in the channel near the interface. The pressure influence on the Stark shift is more obvious with increase of electric field and the distance between an impurity and the interface. The increase of pressure decreases the blue shift but increases the red shift.     

Effect of Electric Field on Conductivity and Vickers Hardness of an Al－Li Alloy

Static electric fields were applied on an aluminium-lithium alloy during solution treatment. The conductivity and Vickers hardness of the quenched A1-Li alloy is changed with the effect of electric field. The Vickers hardness increases with the applied electric field for a certain solutionizing time but decreases with the time under an electric field. In the absence of the electric field, the Vickers hardness and the conductivity increase synchronously, while reversed after electric field treatment. Positive and negative electric fields had the similar effect. The change of the local electron density in alloy caused by electric field is presented to explain the effect.     

Effect of phonon scattering mechanisms on the lattice thermal conductivity of skutterudite-related compound

We have prepared the skutterudite-related compounds FeCo_3Sb_{12} and La_{0.75}Fe_3CoSb_{12} with different average grain sizes (about 0.8 and 3.9μm) by hot pressing. Samples were characterized by XRD, EPMA and SEM. The lattice thermal conductivity was investigated in the temperature range from room temperature to 200℃. Based on the Debye model, we analyse the change in lattice thermal conductivity due to various phonon scattering mechanisms by examining the relationship between the weighted phonon relaxation time τ(ω/ω_D)^2 and the reduced phonon frequency ω/ω_D. The effect of grain boundary scattering to phonon is negligible within the range of grain sizes considered in this study. The large reduction in lattice thermal conductivity of FeCo_3Sb_{12} compound contributes to the electron－phonon scattering. As for La_{0.75}Fe_3CoSb_{12} compound, the atoms of La filled into the large voids in the structure of the skutterudite produce more significant electron－phonon scattering as well as more substitute of Fe at Co site at the same time. Moreover, the point-defect scattering appears due to the difference between the atoms of La and the void. In addition, the scattering by the rattling of the rare-earth atoms in the void is another major contribution to the reduced lattice thermal conductivity. Introducing the coupling of the electron－phonon scattering with the point-defect scattering and the scattering by the rattling of the rare-earth atom is an effective method to reduce the lattice thermal conductivity of the skutterudite-related compounds by substitution of Fe for Co and the atoms of La filled in the large voids in the skutterudite structure.     

一维二元非对角关联无序体系交流跳跃电导特性

在单电子紧束缚无序模型基础上，建立了一维二元非对角关联无序体系电子跳跃输运交流电导模型，并推导了其交流电导公式，通过计算其交流电导率，探讨了格点能量无序度、格点原子组分、非对角关联及温度、外场对体系交流跳跃电导的影响.计算结果表明，一维二元非对角关联无序体系的交流电导率随格点能量无序度的增大而减小.同时，体系中两种原子的组分的变化实际代表着体系成分无序程度的变化，因而对其交流电导率的影响很大，表现为随A类原子含量p的增加而先减小后增大.当引入非对角关联时，体系出现退局域化现象，电子波函数由局 关键词： 二元无序体系 交流跳跃电导 格点能量无序度 非对角关联     

准一维多链无序体系跳跃电导特性

在单电子紧束缚近似下,建立了准一维多链无序体系直流、交流电子跳跃输运模型,通过计算探讨了无序模式、维度效应、温度及外场对其直流、交流电导率的影响.计算结果表明:准一维多链无序体系的直流、交流电导率随着格点能量无序度的增大而减小,非对角无序具有增强体系电子输运能力的作用.随着链数的增加,体系的直流、交流电导率增大,但格点能量无序度较小时,维度效应的影响不明显.在对角无序情况下准一维多链无序体系的交流电导率随温度的升高而增大,而在非对角无序模式下却随温度的升高而减小,但对于直流情况,体系的直流电导率随温度的升     

Some dielectric properties of novel nano‐s‐triazine derivatives

The evaluation of the dielectric properties of s‐triazine and its mono‐, di‐, tri‐(trityloxy)triazine derivates as a function of temperature from room temperature to 200°C, and frequency varying from 50 Hz to 5 MHz was performed. The dielectric constant increases with the increase of both temperature and frequency. Moreover, from the measured dielectric loss ε″ we found that there are different types of electric energy losses in the presence of an alternating electric field from which we calculate the entropy ΔS and the enthalpy change ΔH of the dielectric relaxation for each sample. The dielectric relaxation was attributed to the phase transition of the s‐triazine derivatives. Additionally, ac‐electrical conductivity as a function of frequency at different temperatures were studied. Analysis of ac conductivity data indicates that the correlated barrier hopping model is the most suitable mechanism for the ac‐conductance behavior. X‐ray diffraction and scanning electron microscopy were performed on the compounds under consideration to determine the grain size of each sample, which was found in the range of 3 to 100 nm.     

一维二元非对角关联无序体系跳跃电导特性

在单电子紧束缚无序模型基础上，建立了一维二元关联无序体系电子跳跃输运直流电导模型，并推导了其直流电导公式，通过计算其直流电导率，探讨了格点能量无序度、非对角关联及温度、外场对体系跳跃电导的影响.计算结果表明，一维二元无序体系的直流电导率随着格点能量无序度的增大而减小；当引入非对角关联时，体系出现退局域化现象，从而使体系的直流电导率增大；温度对体系的电子输运的影响表现为体系的直流电导率随温度的升高而增大；在外加电场的调制下，体系的直流电导率在强场区随电场强度增加而增长很快，呈现出非欧姆定律特性，但在弱场区外场的作用不明显. 关键词： 二元无序体系 跳跃电导 格点能量无序度 非对角关联     

Raman spectra and XPS studies of phase changes in Ge2Sb2Te5 films

Ge_2Sb_2Te_5 film was deposited by RF magnetron sputtering on Si (100) substrate. The structure of amorphous and crystalline Ge_2Sb_2Te_5 thin films was investigated using XRD, Raman spectra and XPS. XRD measurements revealed the existence of two different crystalline phases, which has a FCC structure and a hexagonal structure, respectively. The broad peak in the Raman spectra of amorphous Ge_2Sb_2Te_5 film is due to the amorphous －Te－-Te－ stretching. As the annealing temperature increases, the broad peak separates into two peaks, which indicates that the heteropolar bond in GeTe_4 and the Sb－Sb bond are connected with four Te atoms, and other units such as (TeSb) Sb－Sb (Te_2) and (Sb_2) Sb－Sb (Te_2), where some of the four Te atoms in the above formula are replaced by Sb atoms, remain in crystalline Ge_2Sb_2Te_5 thin film. And from the results of Raman spectra and XPS, higher the annealing temperature, more Te atoms bond to Ge atoms and more Sb atoms substitute Te in (Te_2) Sb－Sb (Te_2).     

Metal particle polarization

The effect of electron collisions with lattice atoms in metals on metal particle polarization in an ac electric field was analyzed. It was shown that, in contrast to collisionless (free) electron gas, an increase in the negative electronic permittivity with decreasing electric field frequency in relaxation metal particles is limited by the conductivity relaxation time. It was shown that the plasma frequency appears in relaxation metal only if the dielectric relaxation time is less than the free path time in metal.