Effect of an external electric field on two-dimensional nucleation

Summary Two-dimensional nuclei of different possible shapes are considered in the presence of an external electric field which is applied either perpendicular or parallel to the nucleation surface. The additional driving force needed for the formation of a nucleus due to the electric field is found and used in the nucleation theory. The results show that the electric field can either stimulate or inhibit the nucleation process depending on the ratio of the dielectric constants and the orientation of the applied electric field with respect to the nucleation surface. The dependence of the two-dimensional nucleation rate on the intensity of electric field is also determined.

---

Riassunto Si considerano nuclei bidimensionali di differenti forme possibili in presenza di un campo elettrico esterno che è applicato sia perpendicolare che parallelo alla superficie di nucleazione. Si trova e si usa nella teoria di nucleazione l’ulteriore forza guida necesaria per la formazione di un nucleo a causa del campo elettrico. I risultati mostrano che il campo elettrico può sia stimolare che inibire il processo di nucleazione che dipende dal rapporto delle costanti dielettriche e dell’orientamento del campo elettrico applicato rispetto alla superficie di nucleazione. Si determina anche la dipendenza del valore di nucleazione bindimensionale dall’intensità del campo elettrico.

---

Резюме Рассматриваются двумерные ядра различных возможиых форм в присутствии внешнего электрического поля, которое либо перпендикулярно, либо параллельно поверхности вародышеобразования. Определяется и используется в теории зародяшеобразования дополнительная движущая сила, необходимая для образования ядра, всл⪟дствие действия электрического поля. Полученные результатя показяают, что электрическое поле может либо стимулировать, либо тормозить процесс зародышеобразования в зависимости от отношения диэлектричеких постоянных и от ориентации приложенного электричеслог поля отнонительно поверхности зародышеодразования. Такзе определяется зависимость скорости образвания двумерных ядер от интенсивности электрического поля.

     

Adsorption on the surface of ionic crystals and the effect of applied electric field

Adsorption of molecules on an ideal surface of ionic crystals and the effect of an external uniform electric field on this process have been investigated using a model Hamiltonian, which takes account of the Coulomb interaction between electrons and atomic cores of the system under consideration, all valence orbitals of the admolecule, as well as their nonorthogonality to the crystal wavefunctions, the substrate band structure. The binding energy as a function of the adsorbate-to-substrate distance is calculated for H₂O and CO on NaCl and MgO (001) surfaces. The main attention is focused on the contributions of admolecule-substrate interaction of various types to the binding energy.     

横向电场对平面织构胆甾相液晶螺距及反射特性的影响

阐述一种理论模型,讨论共面转换（IPS）模式下横向电场对平面织构胆甾相液晶螺距及扭曲角的影响．利用琼斯矩阵法计算了光正入射情况下未加电场时胆甾相液晶的反射谱．在上述模型基础上,计算了施加电场后胆甾相液晶的反射峰值波长以及反射带宽随场强的变化关系．探讨了忽略锚定与强锚定两种边界条件下横向电场对平面织构胆甾相液晶螺距及反射特性的影响．所得结论在理论上证实：共面转换模式下电场可以调谐胆甾相液晶的反射光颜色,从而为基于电控螺距原理的胆甾相液晶反射式彩色显示方案提供了理论上的依据． 关键词： 胆甾相液晶 电控螺距 共面转换 琼斯矩阵法     

An experimental approach to the analysis of electric field gradients in ionic crystals

The spectrum of a partially oriented sample of ethanol has been analysed by making use of the simpler spectra obtained from the species CD₃CH₂OH and CH₃CD₂OH, together with ¹H?{²H} double resonance. With p-ethoxy-benzylidene-p-n-butylaniline (EBBA) as the nematic solvent the dipolar couplings of CH₃ and CH₂ protons with the OH proton can be observed, and their magnitudes are compared with values calculated assuming different models for C-O-H internal rotation. Information on the quadrupole coupling constant tensor elements for CD₃ and CD₂ deuterium nuclei is obtained.     

Effect of electron exchange on atomic ionization in a strong electric field

Hartree-Fock atom in a strong electric static field is considered. It is demonstrated that exchange between outer and inner electrons, taken into account by the so-called Fock term affects strongly the long-range behavior of the inner electron wave function. As a result, it dramatically increases its probability to be ionized. A simple model is analyzed demonstrating that the decay probability, compared to the case of a local (Har-tree) atomic potential, increases by many orders of magnitude. As a result of such increase, the ratio of inner to outer electrons ionization probability became not too small. It is essential that the effect of exchange upon probability of inner electron ionization by strong electric field is proportional to the square of the number of outer electrons. It signals that in clusters the inner electron ionization by strong field, the very fact of which is manifested by e.g. high energy quanta emission, has to be essentially increased as compared to this process in gaseous atomic objects.     

Effect of electric field on amplitude of scintillations in ZnSAg single crystals

The effect of constant electric field on the amplitude and damping duration of scintillations in ZnSAg single crystals under excitation by -particles was investigated experimentally. Curves for electric quenching as a function of the energy of the -particles were recorded and investigated. If excitation is applied through the negative electrode the amplitude of the scintillation pulse decreases with increase in the strength of the electric field. The observed phenomena are explained by the possibility of electron transition from the valence band to ionized luminescence centers.     

Effect of surface electric field on the anchoring of nematic liquid crystals

We analyse the influence of adsorbed ions and the resulting surface electric field and its gradient on the anchoring properties of nematics with ionic conductivity. We take into account two physical mechanisms for the coupling of the nematic director with the surface electric field: (i) the dielectric anisotropy and (ii) the coupling of the quadrupolar component of the flexoelectric coefficient with the field gradient. It is shown that for sufficiently large fields near saturated coverage of the adsorbed ions, there can be a spontaneous curvature distortion in the cell even when the anchoring energy is infinitely strong. We also discuss the director distortion when the anchoring energy of the surface is finite. Received: 29 September 1997 / Received in final from: 10 November 1997 / Accepted: 18 November 1997     

Effect of weak electric fields on the conduction in thin metal films

The variation of conduction in island metallic Ti, Co, W, and FeNi films in weak electric field is studied. The variation of the differential conductivity of island metallic films with an electric field at temperatures from T = 77 to 300 K is measured, as well as the temperature dependence of the differential conductivity in the same temperature range. It is shown that a thermally activated conduction mode is realized in such structures. The mechanism of variation of conductivity of island metallic films in a weak electric field is discussed.     

Effect of a transverse electric field on the Landau bands in a Weyl semimetal

The Landau bands in crossed magnetic and electric fields are studied for the case of a Weyl semimetal. The expression for the energy spectrum of such a system is obtained using an approach based on the Lorentz shift. It is shown that the electric field leads to a substantial transformation of the Landau bands. At the electric field equal to v_F H/c, the collapse of the Landau levels occurs and the motion becomes completely linear. Under this condition, the wavefunction is nonzero only for the states with p _z = 0. This significantly affects the phenomena related to the unusual surface states, which are characteristic of such materials.     

Hydrogen adsorption on SiC nanotube under transverse electric field

Using density functional theory, we present a model to illustrate that under a transverse electric field the overall amount of hydrogen storage can be increased on the SiC nanotube. Due to the cylindrical shape of the nanotube, an electric field does not have the similar effects on the different adsorption sites. Although it has the desired effects on some sites, the electric field may lead the binding energy to decrease on some other sites. We demonstrate that the binding energy decreases slightly just on the two small areas and increases significantly on the largest part of the nanotube surface.     

外加电场对铁电薄膜相变的影响

采用热力学非线性理论,研究了外加电场对立方基底Pb(Zr_0.3Ti_0.7)O₃(PZT)铁电薄膜相变的影响.通过数值计算,得到了"失配应变-外加电场"相图,及外加电场与极化强度的关系.当外加电场达到186 kV/cm时,能使生长在SrTiO₃ 基底上PZT铁电薄膜从单斜r相转变为c相.在实验上,采用扫描探针显微镜通过对PZT薄膜施加不同的极化电场来研究了它的电畴翻转.从得到的压电响应相图可以看出,绝大多数的电畴是清晰可 关键词： 铁电薄膜 相变 扫描探针显微镜 失配应变     

Effect of ionization of impurity centres by electric field on the conductivity of superlattice

The electric fieldE₀effect on ionization on impurity centres and on the conductivity of superlattices (SLs) has been studied theoretically. It is observed that as the fieldE₀increases the current rises, reaches a maximum, then falls off, i.e. show a negative differential conductivity (NDC). Further increase inE₀leads to an exponential rise of the current. This occurs aroundE₀=3×10⁴ V cm⁻¹. Hence the current density field shows a ‘N’ shape characteristics as against the ‘n’ shape characteristics in the absence of impurity.     

Effect of electric field on reentrance transition in a binary mixture of liquid crystals

Employing a phenomenological mean field theory, we analyze the effect of an electric field on the N ? SmA phase transition for pure liquid crystal and on the reentrant nematic phase in a binary mixture of liquid crystals exhibiting the phase sequence I ? N ? SmA ? N_R on cooling. The basic idea of the work is to explain the phase transition behavior of the system by assuming that certain Landau coefficients associated with the order parameters coupling terms of the free-energy density expansion are field dependent. These parameters play a crucial role and show a rapid variation at the SmA ? N_R transition as compared to the SmA ? N transition.     

Destabilizing effect of a surface electric field generated by ionic adsorption on the molecular orientation of nematic liquid crystals

The destabilizing effect of a surface electric field, produced by selective ionic adsorption, on the molecular orientation of a nematic-liquid-crystal sample is analyzed for a cell in the shape of a slab of thickness d. The electric-field distribution considered in the analysis is the one obtained in the limit in which essentially all the positive ions are adsorbed. Because of the coupling of this surface field with the nematic director, the surface anchoring energy depends on the thickness of the sample as well as on the adsorption energy characterizing the surfaces. A relation connecting the threshold field for the destabilization of the homeotropic pattern to the adsorption energy and to the thickness of the sample is established in closed form, after solving a set of two coupled non-linear equations determining the electric-field distribution across the sample. It is shown that the values of surface electric field generated by adsorbed ions that can lead to a destabilization of the homeotropic alignment can be attained by real samples.     

Effect of electric field on the percolation phase transition in lead scandotantalate single crystals

The effect of a dc electric field on the phase transition process in lead scandotantalate single crystals differing in the degree of ion ordering has been studied by small-angle light scattering (SAS). The spontaneous phase transition occurring in these crystals is shown to be accompanied by a sharp SAS intensity peak indicating the percolation nature of this transition. A phase diagram in the field-temperature coordinates has been constructed for all the PST crystals studied in the work. The electric field and the temperature variation rate have been found to affect the SAS intensity.     

Spin transverse force on spin current in an electric field

As a relativistic quantum mechanical effect, it is shown that the electron field exerts a transverse force on an electron spin 1/2 only if the electron is moving. The spin force, analogue to the Lorentz for an electron charge in a magnetic field, is perpendicular to the electric field and the spin current whose spin polarization is projected along the electric field. This spin-dependent force can be used to understand the Zitterbewegung of the electron wave packet with spin-orbit coupling and is relevant to the generation of the charge Hall effect driven by the spin current in semiconductors.     

静电场对强激光场非序列双电子电离的影响

利用半经典重碰模型计算并研究了He原子在强激光场与静电场的混合场下的非序列双电子电离过程. 由于静电场破坏了激光场电场的反演对称性，在平行于激光场偏振方向的He²⁺离子动量分布不再具有对称双峰结构. 由于超短脉冲具有相似的非对称性，研究静电场对原子在强场中非序列电离的影响，有助于分析超短脉冲非序列电离的过程，进一步了解非序列双电子电离的机理.