Search

Photoconductors based on V-grooved Al[sub 0.5]Ga[sub 0.5]As/GaAs multiple quantum wires (QWR) were fabricated. The geometric structure of the QWR was carefully characterized by transmission electron microscopy and spatially resolved microphotoluminescence measurements. Infrared response at 9.2 μm is observed from the photocurrent spectrum measured at 80 K. It is attributed as the intersubband transition in the quantum wire region. Due to the effective quantum confinement from the two (111)-surfaces forming the V groove, the overlapping between the ground state in the QWR and the one in the vertical quantum well is very small. This explains the weak photocurrent signal from the QWR photodetector. Theoretical design for a better wave function overlapping and optical coupling is outlined from the analysis of two-dimensional spatial distributions of the wave functions. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which examined the position of misfit dislocations with respect to the strained interface in [001] In[sub0.1]Ga[sub0.9]As/GaAs single heterostructures using transmission electron microscopy. Results of diffraction contrast investigations from plan-view specimens; Analysis of the effect of the strain associated with interfacial steps; Interaction between neighboring misfit dislocations.

This paper presents annular dark-field scanning transmission electron microscope image simulations of a screw dislocation viewed end-on in a thin single crystal of Mo, taking into account surface relaxation (the Eshelby twist). The image contrast can be understood in terms of the effects of the displacements normal to the dislocation arising from the Eshelby twist on the channelling behaviour and interband scattering of the incident beam. With the beam focussed at the entrance surface, the image peak positions reflect the positions of the atoms at the entrance surface. For atomic columns at distances from the core less than the foil thickness, the image peak positions are predicted to lie between the perfect crystal and actual surface atom positions. The predicted intensity distribution of the image is qualitatively similar to that of a published experimental image of a screw dislocation in GaN [Phys. Rev. Lett. 91 (2003) p. 165501]. An assessment is made of the possibility of imaging core displacements by focussing near the foil centre, where surface relaxation effects should be minimised. [ABSTRACT FROM AUTHOR]

Weak-beam image simulations have been carried out using the CUFOUR programme of a ] edge dislocation in γ-Ti-50 wt% Al, dissociated into three <112] partial dislocations bounding superlattice intrinsic stacking-fault (SISF) and superlattice extrinsic stacking-fault (SESF) ribbons of equal width. The simulations included one of the two core configurations of the composite Shockley partial dislocation found by Kumar et al . to explain their observed image contrast, and two others that involve dissociation into stair-rods. These latter simulated images cannot be distinguished from those for the model proposed by Kumar et al . for the composite Shockley dislocation and therefore account for the observed image contrast equally well. The claim of these workers that configurations consisting of stair-rod dislocations can be ruled out is not substantiated. The core structures involving sessile stair-rod dislocations explain the locked nature of the edge dislocation. The values found by Kumar et al . for the true separation between the pairs of partial dislocations have been used to calculate (on anisotropic elasticity theory) the SISF and SESF energies to be 123 ± 10 mJ m -2 . [ABSTRACT FROM AUTHOR]

The critical thicknesses of InGaAs/GaAs and GaAs/InGaAs/GaAs strained-layer systems were determined by transmission electron microscopy using the lift-off technique. The onset of misfit dislocation generation has been observed for the first time and the geometries of the misfit dislocations in both uncapped and capped layers correspond to the predicted models. A comparison is given between the predicted and experimental critical thicknesses. [ABSTRACT FROM AUTHOR]

Low optical and mechanical loss Ta2O5 amorphous coatings have a growing number of applications in precision optical measurements systems. Transmission electron microscopy is a promising way to probe the atomic structure of these coatings in an effort to better understand the causes of the observed mechanical and optical losses. Analysis of the experimental reduced density functions using a combination of reverse Monte Carlo refinements and density functional theory molecular dynamics simulations reveals that the structure of amorphous Ta2O5 consists of clusters with increased contribution from a Ta2O2 ring fragment. [ABSTRACT FROM AUTHOR]

The misfit dislocations in [001] Ge(Si)/Si islands grown at 700°C were investigated using transmission electron microscopy. 30° partial misfit dislocations are found both in the island/ substrate interface and near the island surface. Since the 30° partial leads the movement of the 60° dissociated misfit dislocation in a (001) compressively strained system such as (001) GeSi/Si, a generation mechanism of misfit dislocations through partial misfit dislocations half loops is proposed. [ABSTRACT FROM AUTHOR]

Ge(Si)/Si(001) coherent islands grown at 700 °C by molecular beam epitaxy were investigated using transmission electron microscopy. [001] on-zone bright-field diffraction contrast imaging and image simulation techniques were used to investigate the structure of these coherent islands. Comparison of simulated and experimental images indicates nonuniform composition distribution within the coherent islands when the islands were grown at high temperatures (700 °C), but uniform composition for growth at lower temperatures (600 °C). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Abnormal grain growth is a commonly observed phenomenon in perovskite materials. In order to study this phenomenon, grain growth experiments were conducted over a temperature range from 1425 to 1600°C for the model system SrTiO3 to analyse the nucleation of abnormal grains and to identify the growth mechanism involved for normal and abnormal grains. Grain boundaries of normal and abnormal grains were investigated in quenched samples by high-resolution transmission electron microscopy and by energy-dispersive spectroscopy in a scanning transmission electron microscope. No amorphous film was observed at the grain boundaries for either normal or abnormal grains. Non-stoichiometry at the grain boundaries was identified as a possible reason for the differences in growth speed. The results are compared to the nucleation and growth of abnormal grains in BaTiO3. [Copyright &y& Elsevier]