Radiofrequency magnetoresistance of Fe/Cr superlattices

The rf magnetoresistance of Fe/Cr superlattices is studied for two orientations of the current: parallel and across the superlattice layers. A mutually single-valued correspondence is established between the relative magnetoresistance measured at dc current and the change in the transmission coefficient of electromagnetic waves in the magnetic field. When rf currents flow across the layers, the relative change in the signal amplitude is proportional to twice the change in the electrical resistance of the superlattice and is of opposite sign. It is shown that the rf losses are determined by the surface resistance which is proportional to the superlattice thickness and inversely proportional to its conductivity. An equation is derived for the rf electric field distribution in the superlattice. It is established that when the thickness of the superlattice is small compared with the skin layer depth, field and current components which penetrate through the entire superlattice exist.     

非晶Si/SiO2超晶格结构的交流电致发光

设计并用磁控溅射方法制备了非晶Ｓｉ／ＳｉＯ２超晶格结构,以高纯多晶Ｓｉ为靶材,当以Ａｒ＋Ｏ２为溅射气氛时,得到ＳｉＯ２膜,仅以Ａｒ为气氛时,得到Ｓｉ膜。重复地开和关Ｏ２气,便交替地得到ＳｉＯ２和Ｓｉ膜。衬底在靶前往返平移,改变平移的速度或者改变溅射的功率,可以控制膜的厚度。通过透民镜的照片可以看出ＳｉＯ２和Ｓｉ膜具有均匀的周期结构,用低角Ｘ－射线反射谱表征了超晶格的周期结构和各层的厚度。透射光谱表     

Energy spectrum and effective mass of carriers in the InSe/GaSe superlattice

Within an effective mass approximation the energy spectrum and mass of carriers in the InSe/GaSe superlattice have been calculated. The superlattice belongs to type II: electrons are primarily confined to the InSe layers whereas the holes are mosfly confined to the GaSe layers. The characteristic feature of electronic structure of the superlattice is the existence of minibands of light carriers at the θ point of the Brillouin zone and minibands of heavy carriers at theM point. The dependence of the miniband structure on thickness of layers has been computed. It is shown that the minibands of light and heavy carriers compete with one another in energy. A general conclusion is made concerning the influence of the competition between the minibands on optic and kinetic properties of the superlattice.     

Energy spectrum and effective mass of carriers in the InSe/GaSe superlattice

Within an effective mass approximation the energy spectrum and mass of carriers in the InSe/GaSe superlattice have been calculated. The superlattice belongs to type II: electrons are primarily confined to the InSe layers whereas the holes are mosfly confined to the GaSe layers. The characteristic feature of electronic structure of the superlattice is the existence of minibands of light carriers at the θ point of the Brillouin zone and minibands of heavy carriers at theM point. The dependence of the miniband structure on thickness of layers has been computed. It is shown that the minibands of light and heavy carriers compete with one another in energy. A general conclusion is made concerning the influence of the competition between the minibands on optic and kinetic properties of the superlattice.     

Plasmon dispersion in a layered structure

Dispersion of plasmons in a superlattice of finite thickness plasma layers is calculated. Good agreement with dispersion from light scattering experiments is obtained.     

PHASE TRANSITION PROPERTIES OF A TWO-COMPONENT FINITE MAGNETIC SUPERLATTICE

We study an (l,n) finite superlattice, which consists of two alternative magnetic materials(components) of l and n atomic layers, respectively. Based on the Ising model, we examine the phase transition properties of the magnetic superlattice. By transfer matrix method we derive the equation for Curie temperature of the superlattice. Numerical results are obtained for the dependence of Curie temperature on the thickness and exchange constants of the superlattice.     

非晶Si/SiO2超晶格结构的交流电致发光

设计并用磁控溅射方法制备了非晶Si/SiO     

周期和准周期超晶格固体薄膜表面吸附原子的共振荧光

本文使用表面修饰的光学Bloch方程,求得周期和准周期超晶格固体薄膜表面吸附原子的共振荧光谱,并研究了压缩效应。对该薄膜各层厚度和介电性质变化所带来的影响进行了讨论。同时,也对整个薄膜不同几何结构的影响进行了比较和分析。 关键词：     

Propagation of light in layered composites with variable thickness of the layers

Propagation of light in a nonideal liquid crystal-silicon superlattice (one-dimensional crystal with two constituent layers in the elementary cell) is considered in terms of the virtual crystal approximation. The influence of the randomly varying layer thickness on the refractive index and lowest stopband of the structure is studied. Layered composites with a variable layer thickness are shown to open up considerable scope for devising new layered materials.     

Luminescence and resonance fluorescence of an adatom near a surface of a superlattice film periodic of quasi-periodic structure

The surface-dressed optical Bloch equations derived from the reservoir theory and Dekker's quantization procedure and the Maxwell equations are used to obtain the spontaneous decay time and frequency shift, the resonance fluorescence spectrum, and squeezing effects of an adatom adsorbed near a surface of a periodic or quasi-periodic superlattice film. The effects of the thickness and dielectric properties of the layers in the film, number of layers, and different geometry structures are discussed, and the results for the two different cases of periodic structure and the quasi-periodic one are compared.     

Co-Zr/Pd多层膜的磁性与结构

Co-Zr/Pd多层膜由高频溅射方法制得．磁性合金Co-Zr层厚度固定为1.8nm，改变Pd层厚度0.5—6nm．由振动样品磁强计测量，发现随Pd层厚度增加，磁化强度发生周期性振荡变化，周期约为1nm，这是由Pd层的极化振荡引起的．经X射线衍射测得Pd层厚度超过1.3nm时，磁性合金Co-Zr层发生晶化，而厚的Co-Zr单层膜是非晶结构．X射线大角衍射图中的超晶格峰表明，在Co-Zr层和Pd层之间存在相关生长．而且还发现，随Pd层厚度增加，样品在垂直膜面方向的晶粒尺寸及fcc（111）面的面间距发生周期性 关键词：     

Domain-enhanced interlayer coupling in ferroelectric/paraelectric superlattices

We investigate the ferroelectric phase transition and domain formation in a periodic superlattice consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. We find that the polarization domains formed in the different FE layers can interact with each other via the PE layers. By coupling the electrostatic equations with those obtained by minimizing the Ginzburg-Landau functional, we calculate the critical temperature of transition Tc as a function of the FE/PE superlattice wavelength Lambda and quantitatively explain the recent experimental observation of a thickness dependence of the ferroelectric transition temperature in KTaO3/KNbO3 strained-layer superlattices.     

极性超晶格中电子—声子的相互作用

本文在Wendler、潘金声研究双层极性晶体时得出的声子振动极化场所满足的微分、积分方程及归一化条件的基础上,讨论周期性排列的层状极性晶体中声子振动极化场所满足的微分、积分方程,得到了SO声子的色散关系,SO声子和LO声子极化强度矢量.用声子产生、湮灭算符表出了声子振动能量及电子—声子的相互作用哈密顿量.     

Effective dielectric and photoelastic tensor components in thin layered superlattices

The effective photoelastic constants of a superlattice composed of thin alternating layers of orthorhombic symmetry are calculated as functions of dielectric, elastic and photoelastic constants of the constituents. In a preliminary step to this calculation, we also obtain the effective dielectric tensor for any symmetry of the layers. It is shown that appropriate combinations of these effective constants are arithmetic averages of the corresponding quantities in the constituents, each layer having a weight equal to its relative thickness.     

Superconducting behaviour of Nb/Co superlattices

We study the superconducting and magnetic behaviour of Nb/Co superlattices, for superconducting Nb layer thickness of 44 nm and Co layer thickness less than 1 nm. In this limit no ferromagnetism is observed for Co. The superlattice behaves as independent superconducting Nb layers. We obtain the penetration depth and superconducting gap of the material, and analyze the results in terms of microscopic models and theories.     

周期或准周期超晶格薄膜表面吸附原子的自发辐射性质

本文把由库理论和耗散系统量子化方法所求得的表面修饰的光学布洛赫方程,同麦克斯韦方程自洽地相结合,求得周期或准周期超晶格薄膜表面吸附原子的自发辐射寿命和频移,讨论了构成该薄膜各层的厚度和介电性质及总层数对上述自发辐射性质的影响。同时,把周期性情况和准周期情况分别求得的结果进行了比较。 关键词：     

Diamond-like and graphite-like carbon states in short-period superlattices

The Raman and luminescence spectra are studied in superlattices consisting of carbon layers separated by thin SiC barrier layers. It is shown experimentally that, upon the avalanche annealing of an initially amorphous superlattice, the carbon layers can crystallize into either a diamond-like or graphite-like structure, depending on the geometrical parameters of the superlattice. A method is proposed for obtaining carbon films with a specified crystal modification within a unified technology.     

Tunable photoluminescence and electroluminescence of size-controlled silicon nanocrystals in nanocrystalline-Si/SiO2 superlattices

We present photoluminescence and electroluminescence of silicon nanocrystals deposited by plasma-enhanced chemical vapor deposition (PECVD) using nanocrystalline silicon/silicon dioxide (nc-Si/SiO₂) superlattice approach. This approach allows us to tune the nanocrystal emission wavelength by varying the thickness of the Si layers. We fabricate light emitting devices (LEDs) with transparent indium tin oxide (ITO) contacts using these superlattice materials. The current-voltage characteristics of the LEDs are measured and compared to Frenkel-Poole and Fowler-Nordheim models for conduction. The EL properties of the superlattice material are studied, and tuning, similar to that of the PL spectra, is shown for the EL spectra. Finally, we observe the output power and calculate the quantum efficiency and power conversion efficiency for each of the devices.     

Modification of the donor-acceptor-pair luminescence in doped multi-thin film structures

A single crystal multi-thin film structure consisting of films with both donor and acceptor doping to almost compensation, and separated by intrinsic semiconductor layers of a thickness governed by the Bohr radius of the donor electron, is analyzed with respect to a possible modification of the Donor-Acceptor-Pair (DAP) luminescence band.Pronounced jumps in the DAP-distribution curve and consequently in the luminescence intensity band with spacings of the intrinsic layer thickness are manifested, which are the result of Coulomb interaction between donors of the one and acceptors of the neighbouring doped films. This photoluminescence property, not yet documented in the literature, can advantageously be used for the analysis of doped superlattice films. Doping layers of the described kind may even be introduced as probes in order to study the initial steps of diffusion or migration of impurity atoms into the bulk in luminescence active semiconductor materials.     

High resolution x-ray diffractometry of the structural characteristics of a semiconducting (InGa)As/GaAs superlattice

A statistical approach is used to construct a kinematic theory of x-ray diffraction on a semiconducting superlattice with a two layer period. This theory takes two types of structural deformations into account: crystal lattice defects caused by microdefects distributed chaotically over the thickness of the superlattice, and periodicity defects of an additional superlattice potential owing to random deviations in the thicknesses of the layers of its period from specified values. Numerical simulation is used to illustrate the effect of structural defects on the development of the diffraction reflection curve. The theory is used to analyze experimental x-ray diffraction spectra of semiconducting In_xGa_1−x As/GaAs superlattices. Zh. Tekh. Fiz. 69, 44–53 (February 1999)