Atomic-force-microscopy investigation of the formation and evolution of Ge islands on GexSi1-x strained layers

A constant amount of Ge was deposited on strained GexSi1-x layers of approximately the same thickness but with different alloy compositions, ranging from x = 0.06 to x = 0.19. From their atomic-force-microscopy images, we found that both the size and density of Ge islands increased with the Ge composition of the strained layer. By conservation of mass, this implies that these islands must incorporate material from the underlying strained layer. (C) 2000 American Institute of Physics. [S0003-6951(00)03529-4].

Sequential resonant tunnelling through Landau levels in GaAs/AlAs superlattices

Electron transport in heavily-doped GaAs/AlAs superlattices in parallel electric and magnetic fields is reported. The current-voltage (I-V) characteristic exhibited the feature of negative differential velocity (NDV) and high electric field domain effect at different biases. Under strong magnetic fields, sequential resonant tunnelling through Landau levels in the negative differential velocity regime is observed, which are manifested as oscillations in the conductance-voltage characteristics. (C) 1998 Elsevier Science B.V. All rights reserved.

Transmission electron microscopy study of triple-ribbon contrast features in a ZnTe epitaxial layer

A transmission electron microscopy study of triple-ribbon contrast features in a ZnTe layer grown epitaxially on a vicinal GaAs (001) substrate is reported. The ribbons go through the layer as threading dislocations near the [<(11)over bar 2>](111) or [112](<(11)over bar 1>) directions. Each of these (with a 40 nm width) has two narrow parts enclosed by three partial dislocations (with a 20 nm spacing). By contrast analysis and contrast simulation, the ribbons have been shown to be composed of two partially overlapping stacking faults. Their origin is attributed to a forced reaction between two crossing perfect misfit dislocations.

Characterization of self-organized InAs/GaAs quantum dots under strain-induced and temperature-controlled nucleation mechanisms by atomic force microscopy and photoluminescence spectroscopy

Atomic force microscopy and photoluminescence spectroscopy (PL) has been used to study asymmetric bilayer InAs quantum dot (QD) structures grow by molecular-beam epitaxy on GaAs (001) substrates. The two InAs layers were separated by a 7-nm-thick GaAs spacer layer and were grown at different substrate temperature. We took advantage of the intrinsic nonuniformity of the molecular beams to grow the seed layer with an average InAs coverage of 2.0 ML. Then the seed layer thickness could be divided into three areas: below, around and above the critical thickness of the 2D-3D transition along the 11101 direction of the substrate. Correspondingly, the nucleation mechanisms of the upper InAs layer (UIL) could be also divided into three areas: temperature-controlled, competition between temperature-controlled and strain-induced, and strain-induced (template-controlled) nucleation. Small quantum dots (QDs) with a large density around 5 x 10(10) cm(-2) are found in the temperature-controlled nucleation area. The QD size distributions undergo a bimodal to a unimodal transition with decreasing QD densities in the strain-induced nucleation area, where the QD densities vary following that of the seed layer (templating effect). The optimum QD density with the UIL thickness fixed at 2.4 ML is shown to be around 1.5 x 10(10) cm(-2), for which the QD size distribution is unimodal and PL emission peaks at the longest wavelength. The QDs in the in-between area exhibit a broad size distribution with small QDs and strain-induced large QDs coexisting.

INVESTIGATION OF POROUS SILICON BY SCANNING-TUNNELING-MICROSCOPY AND ATOMIC-FORCE MICROSCOPY

The size and distribution of surface features of porous silicon layers have been investigated by scanning tunneling and atomic force microscopy. Pores and hillocks down to 1-2 nm size were observed, with their shape and distribution on the sample surface being influenced by crystallographic effects. The local density of electronic states show a strong increase above 2 eV, in agreement with recent theoretical predictions.

TRANSMISSION ELECTRON-MICROSCOPY STUDY OF N+-IMPLANTED SILICON ON INSULATOR BY ENERGY-FILTERED IMAGING

We report on the first study of N+ -implanted silicon on insulator by energy-filtered imaging using an Opton electron microscope CEM 902 equipped Castaing-Henry electron optical system as a spectrometer. The inelastic images, energy window set at DELTA-E = 16 eV and DELTA-E = 25 eV according to plasmon energy loss of crystal Si and of silicon nitride respectively, give much structure information. The interface between the top silicon layer and the upper silicon nitride layer can be separated into two sublayers.

A transmission electron microscopy study of microstructural defects in proton implanted silicon

The microstructure of silicon on defect layer, a new type of silicon-on-insulator material using proton implantation and two-step annealing to obtain a high resistivity buried layer beneath the silicon surface, has been investigated by transmission electron microscopy. Implantation induced a heavily damaged region containing two types of extended defects involving hydrogen: {001} platelets and {111} platelets. During the first step annealing, gas bubbles and {111} precipitates formed. After the second step annealing, {111} precipitates disappeared, while the bubble microstructure still remained and a buried layer consisting of bubbles and dislocations between the bubbles was left. This study shows that the dislocations pinning the bubbles plays an important role in stabilizing the bubbles and in the formation of the defect insulating layer. (C) 1996 American Institute of Physics.

Sequential resonant tunnelling through Landau levels in GaAs/AlAs superlattices

Electron transport in heavily-doped GaAs/AlAs superlattices in parallel electric and magnetic fields is reported. The current-voltage (I-V) characteristic exhibited the feature of negative differential velocity (NDV) and high electric field domain effect at different biases. Under strong magnetic fields, sequential resonant tunnelling through Landau levels in the negative differential velocity regime is observed, which are manifested as oscillations in the conductance-voltage characteristics. (C) 1998 Elsevier Science B.V. All rights reserved.

Total-internal-reflection fluorescence microscopy with W-shaped axicon mirrors

A scheme based on a W-shaped axicon mirror device for total-internal-reflection fluorescence microscopy (TIRFM) is presented. This approach combines the advantages of higher efficiency compared with traditional TIRFM, adjustable illumination area, and simple switching between wide-field and TIRF imaging modes. TIRF images obtained with this approach are free of shadow artifacts and of interference fringes. Example micrographs of fluorescently labeled polystyrene beads, of Convallaria majalis tissue, and of Propidium-iodide-labeled Chinese hamster ovary cells are shown, and the capabilities of the scheme are discussed. (C) 2010 Optical Society of America

Multifunctional darkfield microscopy using an axicon

We present a multifunctional darkfield microscopy using an axicon. It combines the functions of a darkfield microscope, fluorescence microscope, and microspectrophotometer in one platform. The advantage of the system over conventional darkfield microscopy includes the high transmittance of the illuminating flux, the high contrast of the image, and the convenient toggle between darkfield and brightfield microscopy. Examples of dark, bright, and fluorescent micrographs as well as concerned spectra of microsized specimens implemented in this apparatus are demonstrated. (C) 2008 Society of Photo-Optical Instrumentation Engineers.