Effect of the vertical correlation of quantum dots on diffuse X-ray scattering

The effect of the vertical correlation of quantum dots (QDs) on diffuse X-ray scattering from multilayer structures has been studied in the framework of a statistical theory of X-ray diffraction. A model of the long-range structural order for the spatial distribution of vertically stacked QDs is considered. Diffuse X-ray scattering in superlattices with QDs has been numerically simulated. The obtained results are applied to a quantitative analysis of heterostructures with QDs using experimental data of high-resolution X-ray diffractometry.     

The influence of the shape and elastic strains of quantum dots on diffuse X-ray scattering

The influence of the shape and elastic-strain fields of buried quantum dots (QDs) on the angular distribution of diffuse X-ray scattering is studied. Elastic lattice displacements were calculated using the Green function method. Diffuse scattering from a semiconductor matrix with QDs having the shape of a cylinder, truncated cone, and spheroid was numerically simulated. It is shown that angular distributions of diffuse scattering for QDs with different shapes have significant distinctions at a small volume density of nanostructures in the crystal. At a large QD density, which is typical for superlattices, these distinctions become weak.     

X-ray diffraction from quantum wires and quantum dots

From the distribution of the scattered intensity in reciprocal space, information on the shape as well as on the strain distribution in nanostructured samples can be obtained. This is exemplified by applying this method to laterally patterned periodic Si/SiGe superlattices as well as to periodic SiGe dot arrays embedded in Si.     

Diffuse X-ray scattering from a crystal with spheroidal pores

A theory of diffuse X-ray scattering from a crystal with spheroidal pores has been developed. Expressions for the Debye-Waller factor, intrinsic correlation function, and correlation volume have been derived. Reciprocal-space maps of the diffuse scattering have been numerically simulated for model crystals with pores having the shapes of spheroids and rectangular parallelepipeds. It is established that the pore size fluctuations influence the angular distribution of X-ray scattering intensity in the reciprocal space.     

Excitonic quantum interference in a quantum dot chain with rings

We demonstrate excitonic quantum interference in a closely spaced quantum dot chain with nanorings. In the resonant dipole-dipole interaction model with direct diagonalization method, we have found a peculiar feature that the excitation of specified quantum dots in the chain is completely inhibited, depending on the orientational configuration of the transition dipole moments and specified initial preparation of the excitation. In practice, these excited states facilitating quantum interference can provide a conceptual basis for quantum interference devices of excitonic hopping.     

A Difference in the change of parameters of silicon-on-sapphire structures upon X-ray irradiation from the sides of epitaxial layer and substrate

The data of atomic force microscopy and ellipsometry reveal a difference in changes of the silicon surface micromorphology, the refractive indices, and the extinction coefficients of silicon and sapphire in the silicon-on-sapphire structures upon pulsed X-ray irradiation at E≤300 keV from the side of the silicon epilayer and from the sapphire substrate.     

Diffuse X-Ray scattering from crystalline systems with ellipsoidal quantum dots

A theory of diffuse X-ray scattering from a semiconductor system with ellipsoidal quantum dots (QDs) has been developed. The elastic strains outside a QD are calculated using the method of multipole expansions. An expression for the lattice displacement field is presented accurate to within the quadrupole term of expansion. Using the proposed approach, an analytical solution for the diffuse scattering from a crystalline medium with ellipsoidal inclusions is obtained. Reciprocal-space maps of the scattering intensity distribution are obtained by numerical calculations for QDs with various ratios of the height to lateral radius.     

In-situ synchrotron X-ray scattering study of thin film growth by atomic layer deposition

We report an atomic layer deposition chamber for in-situ synchrotron X-ray scattering study of thin film growth. The chamber was designed for combined synchrotron X-ray reflectivity and two-dimensional grazing-incidence X-ray diffraction measurement to do a in-situ monitoring of ALD growth. We demonstrate ruthenium thermal ALD growth for the performance of the chamber. 10, 20, 30, 50, 70, 100, 150 and 250-cycled states are measured by X-ray scattering methods during ALD growth process. Growth rate is calculated from thickness values and the surface roughness of each state is estimated by X-ray reflectivity analysis. The crystal structure of initial growth state is observed by Grazing-incidence X-ray diffraction. These results indicate that in-situ X-ray scattering method is a promising analysis technique to investigate the initial physical morphology of ALD films.     

Self-assembly of concentric quantum double rings

We demonstrate the self-assembled formation of concentric quantum double rings with high uniformity and excellent rotational symmetry using the droplet epitaxy technique. Varying the growth process conditions can control each ring's size. Photoluminescence spectra emitted from an individual quantum ring complex show peculiar quantized levels that are specified by the carriers' orbital trajectories.     

Polarized Raman spectroscopy and X-ray diffuse scattering in InGaAs/GaAs(100) quantum-dot chains

Using polarized Raman spectroscopy and high resolution X-ray diffraction we have investigated self-organized In_0.45Ga_0.55As quantum-dot chains in InGaAs/GaAs multilayer structures. It is shown that the formation of InGaAs QDs in InGaAs/GaAs multilayered structures is accompanied by a strong improvement in the uniformity of size and shapes of QDs as well as vertical alignment and lateral ordering. At mean densities, extended chains of QDs (up to 5 μm) appear along the $ [1\bar 10] $ direction; however, increased ordering of QDs along the [110] direction could be observed, too. For the first time, InGaAs dot-chains were investigated using polarized Raman scattering. Observation of optical phonons localized in InGaAs QDs and two-dimensional (2D) layers is demonstrated. An obvious anisotropy in the intensity of Raman modes was observed when the electric field vector of the exciting laser beam is parallel or perpendicular to the wire-like axis $ [1\bar 10] $ of dot-chains. This effect may be related to symmetry lowering effects and real anisotropic geometry of the QDs and 2D wetting layers.     

Small-angle X-ray and neutron scattering studies from multiphase polymers

The thermodynamic understanding of complex polymer systems is presently undergoing important developments. Much of the experimental input is based on structural studies that use small-angle scattering of X-rays and neutrons. These techniques provide important insight into static phase behavior and polymer conformation. In recent years, dynamical aspects have also been probed by in situ studies under time-varying fields. Recent progress has been made in analysing block copolymer systems and complex polymer blends using small-angle scattering.     

Shot noise in resonant tunneling through an interacting quantum dot with intradot spin-flip scattering

We present theoretical investigation of the zero-frequency shot-noise spectra in electron tunneling through an interacting quantum dot connected to two ferromagnetic leads with the possibility of spin-flip scattering between the two spin states by means of the recently developed bias-voltage and temperature-dependent quantum rate equations. For this purpose, a generalization of the traditional generation-recombination approach is made for properly taking into account the coherent superposition of electronic states, i.e., the nondiagonal density matrix elements. Our numerical calculations find that the Fano factor increases with increasing the polarization of the two leads, but decreases with increasing the intradot spin-flip scattering.     

Frequency dependence of the specular and diffuse phonon scattering from silicon surfaces

Phonon backscattering experiments with polished silicon surfaces show that there is no Kapitza anomaly at frequencies corresponding to the aluminum junction detector threshold (80 GHz), whereas at higher frequencies the anomalous transmission into liquid helium or solid nitrogen increases (reduced backscattering by the coverage), closely related to the increase of the diffuse scattering at the uncovered surface.     

缓冲层生长速率对GaSb薄膜二维生长的影响

用分子束外延(MBE)法在GaAs(100)衬底上生长GaSb薄膜,得到了GaSb薄膜的优化生长工艺条件.为了降低因晶格失配度较大所引起的位错密度,采用低温(LT)GaSb作为缓冲层,研究了缓冲层的生长速率对GaSb薄膜二维生长的影响,并以此说明缓冲层在GaSb薄膜生长中所起的作用.通过X射线双晶衍射仪和原子力显微镜测试分析,得到当低温GaSb缓冲层的生长速率为1.43μm/h时,GaSb外延层中的位错密度最小,晶体质量最好.