聚烷基芴电场调制光谱研究

有机发光材料和器件中相关物理机制是一个人们普遍关心的问题, 特别是电场作用下的有机半导体激发态的行为格外引起人们的关注。电场调制发光光谱是研究在电场中元激发的产生和发展的非常有效的方法。文章利用电场调制光致发光(PL)方法研究了聚烷基芴的PL电场猝灭效应,得到聚烷基芴激子离化随电场强度变化的规律和载流子平均跳跃距离。研究还显示PL猝灭因子随激发波长的变化,短波长激发光时猝灭因子大。     

Resonant Photon-Assisted Tunneling Through a Coupled Double-Quantum-Dot System

An analytical formula of the tunneling current through a coupled double-quantumdot system in the presence of a time-dependent electric field is obtained by using the Keldysh nonequilibrium Green's function technique. The dependence of the time-averaged current on the frequency of the electric field, as well as the dependence of the multiphoton assisted tunneling on the strength of the electric field are studied. The features of I-V_dc characteristic are also investigated. Besides, we present a simplified formula which can be used to determine the heights of the resonant peaks conveniently.     

Electric field dependence of the Curie temperature and microwave absorption in displacive ferroelectrics with impurities

The electric field dependence of the complex dielectric constant in an anharmonic defect ferroelectric crystal is calculated in its paraelectric phase from the Silverman-Joseph-Hamiltonian augmented with fourth-order phonon coordinates using double-time Green’s functions. The field and impurity dependence of the shift in the Curie temperature is discussed. An expression is obtained for the electric field dependence of dielectric loss at microwave frequencies in defect ferroelectrics. An erratum to this article is available at .     

All-Optical Photorefractive Effect in Carbazole-Based Azo-Side Group Polymer

We observe the photorefractivity without bias voltage or prepoling in a bifunctional photorefractive polymer. The maximum two-beam coupling gain is measured to be 126cm^-1 at zero bias voltage. The sample is considered to be poled by the photoinduced longitudinal electric field, which is formed due to the light intensity gradient along the light path. The expression of the electric field was deduced. The energy transfer direction between two writing beams and light intensity dependence of the two-beam coupling gain coefficient is predicted to be consistent with the experimental results. Furthermore, the dependence of the two-beam coupling gain coefficient on external applied electrical field is measured and this experiment verifies the existence of the photoinduced longitudinal electric field.     

Nonlinear optical absorption in graded quantum wells modulated by electric field and intense laser field

The laser field dependence of the linear and nonlinear intersubband optical absorption in a graded quantum well (GQW) under an applied electric field is investigated in the effective mass approximation. In our calculations, the position and the magnitude of the linear and total absorption coefficients depend on the laser parameter and electric field strength. The resonant peak of total absorption coefficient can be bleached at sufficiently high incident optical intensities. Such a dependence of the exciting optical intensity on the external field strengths in GQWs can be very useful for several potential device applications.     

Non-linear conductivity of one-dimensional charge density wave

A pure system with one-dimensional CDW placed in a homogeneous electric field is considered. Non-linear effects are found to appear due to motion of a soliton superstructure. The dependence of the differential conductivity on the electric field is calculated.     

Strain distribution and electronic structures of the InAs/GaAs quantum ring molecule in an applied electric field

The strain distribution and electronic structures of the InAs/GaAs quantum ring molecule are calculated via the finite element method.In our model,three identical InAs quantum rings are aligned vertically and embedded in the cubic GaAs barrier.Considering the band edge modification induced by the strain,the electronic ground state and the dependence of ground state energy on geometric parameters of the quantum ring molecule are investigated.The change of localization of the wavefunction resulting from the applied electric field along the growth direction is observed.The ground state energy decreases as the electric field intensity increases in a parabolic-like mode.The electric field changes the monotonic dependence of the energy level on the inter-ring distance into a non-monotonic one.However,the electric field has no effect on the relationships between the energy level and other geometric parameters such as the inner radius and outer radius.     

Optimization of ozone generation

The generation of ozone under homogeneous conditions is described by a system of kinetic equations. We supposed a certain time dependence of electric field intensity inside a discharge gap. We computed the dependence of efficiency of the ozone generation on both the width and the maximum intensity of electric pulse.     

Surface superconductivity induced by an external electric field

A theory of surface superconductivity induced by an external electric field in superconducting semimetals, metals and semiconductors is presented. It is shown that the inhomogeneous surface superconducting state deeply penetrates into the bulk of the sample. The dependence of the critical surface temperature and magnetic field on the external electric field is calculated.     

Effect of electric field on diffusion in disordered materials

The effect of electric field on diffusion of charge carriers in disordered materials is studied by Monte Carlo computer simulations and analytical calculations. It is shown how an electric field enhances the diffusion coefficient in the hopping transport mode. The enhancement essentially depends on the temperature and on the energy scale of the disorder potential. It is shown that in one‐dimensional hopping the diffusion coefficient depends linearly on the electric field, while for hopping in three dimensions the dependence is quadratic.     

Self-bending of photorefractive solitons

Self-bending of photorefractive solitons is caused by diffusion in photorefractive crystals and becomes an important effect when the beam size is in the range of the charge carriers diffusion length. In this paper we present an experimental and numerical examination of the beam bending dependence on relevant parameters such as the applied electric field and the beam intensity. We demonstrate that the bending dependence on the electric field in the low saturation regime has the form of a square function at low values of the field and becomes linear for higher values. For stronger saturation the curve gets the form of a square root function. The bending dependence on the beam intensity has a maximum at defined intensity. The experimental data are compared with numerical simulations, giving a good qualitative agreement.     

Electron polarization in quantum wells in a strong variable field

The wave function of an electron in a symmetric double quantum well placed in a strong time-periodic electric field is found, expressions for quasienergy functions are derived, and the dependence of the dipole moment on the average electric field is analyzed for the case where the average field remains constant. In the case of slow monotonic variation of the “constant” component of the electric field, the Schro dinger equation is solved by the WKB method. It is found that the dependence of the dipole moment on the average field is of a clearly nonlinear almost-periodic nature and that in the event of adiabatic monotonic variation of the average field there is a periodic relocation of the electron density from well to well with a small frequency proportional to the rate of variation of the average field. Zh. éksp. Teor. Fiz. 116, 217–235 (July 1999)     

Nernst-Ettingshausen effect in graphene

The Nernst-Ettingshausen effect corresponds to the regime of crossed magnetic and electric fields. In the current theoretical studies of this effect in graphene, the dependence of the Landau levels on the applied electric field is neglected. This dependence takes place in the case of the nonquadratic energy spectrum of the charge carriers. In this work, oscillations of the Nernst coefficient in graphene with a zero and nonzero band gap have been studied taking into account such dependence. The effect of the Coulomb interaction on these oscillations is considered.     

A first study of the infrared emission in argon excited by ionizing particles

We report on the study of infrared emission from gaseous argon excited by MeV protons in the wavelength range 0.7–1.8 μm. The dependence of the light yield on the applied electric field has been measured at different pressures. At zero field (prompt emission) the yield does not depend on pressure. When a field is applied the light emission increases linearly with the field strength above a critical value (drift emission) and a dependence from pressure is observed. Prompt and drift emission are consistent with transitions between the lowest atomic states of neutral argon. Drift emission is generated by electrons which gain energy from the electric field and excite atoms through collisions.     

Thickness-shear vibration of a quartz plate connected to piezoelectric plates and electric field sensing

We study thickness-shear vibration of a quartz plate connected to two piezoelectric ceramic plates with initial deformations caused by a biasing electric field. The theory for small deformations superposed on finite biasing deformations in an electroelastic body is used. It is shown that the resonant frequencies of the incremental thickness-shear vibration of the quartz plate vary with the biasing electric field. The biasing electric field induced frequency shift depends linearly on the field. Therefore this effect may be used for electric field sensing. The dependence of the electric field induced frequency shift on various material and geometric parameters is examined. When the electric field is of the order of 100 V/mm, the relative frequency shift is of the order of 10⁻⁵. The case when the piezoelectric plates are replaced by piezomagnetic plates is also investigated for magnetic field sensing, and similar results are obtained.     

Impact ionization of deep acceptor gold in germanium

We observed the dependence of conductivity on an applied high electric field in compensated gold-doped germanium between 77 and 300K. A slight decrease in conductivity, mainly due to the field-dependent carrier mobility, is followed by a relatively large increase in conductivity. The magnitude of this increase depends on the lattice temperature, being larger at low temperatures, and on the compensation ratio. The increase in conductivity is supposed to be due to impact ionization of the frozen-out neutral acceptor gold in the strong electric field. This interpretation is supported by the temperature dependence of the hole concentration in the gold-doped germanium.     

Electric-field control of electron–hole wave functions in a wide quantum well

The electric field dependence of the electron/hole wave function and the radiation energy of an exciton in a Be-δ-doped 80 nm quantum well (QW) is studied experimentally and compared it with variational calculation. The photoluminescence (PL) spectra show Stark shifts depending on the gate electric field and PL intensity of the exciton of the first excited state has a dip in the electric-field dependence which reflects the node of the electron wave function.     

Electric-field-induced in-plane effective 90° magnetization rotation in Co_2FeAl/PMN-PT structure

The in-plane effective 90° magnetization rotation of Co_2 Fe Al thin film grown on PMN-PT substrate induced by the electric field is investigated at room temperature. The magnetic hysteresis loops under different positive and negative electric fields are obtained, which reveals remanent magnetization can be mediated by the electric field. Moreover, under positive electric fields, the obvious 90° magnetization rotation can be observed, while remanent magnetization is nearly unchanged under negative electric fields. The result is consistent with the electric field dependence of effective magnetic field,which can be attributed to the piezostrain effect in Co_2 Fe Al/PMN-PT structure. In addition, the piezostrain-mediated 90° magnetization rotation can be demonstrated by the result of resonance field changing with electric field in the measurement of ferromagnetic resonance, which is promising for the design of future multiferroic devices.     

Temperature dependence of the electric field gradient in the AgIn2 intermetallic compound

The temperature dependence of the electric field gradient in the AgIn₂ intermetallic compound was measured using the TDPA correlation technique. From 80 K up to 415 K the electric field gradient follows a linear temperature dependence. Below 80 K a change in this behaviour is observed.Work supported in part by FINEP and CNPq.