3D APIs in Interactive Real-Time Systems: Comparison of OpenGL, Direct3D and Java3D.

Since the first display of a few computer-generated lines on a Cathode-ray tube (CRT) over 40 years ago, graphics has progressed rapidly towards the computer generation of detailed images and interactive environments in real time (Angel, 1997). In the last twenty years a number of Application Programmer's Interfaces (APIs) have been developed to provide access to three-dimensional graphics systems. Currently, there are numerous APIs used for many different types of applications. This paper will look at three of these: OpenGL, Direct3D, and one of the newest entrants, Java3D. They will be discussed in relation to their level of versatility, programability, and how innovative they are in introducing new features and furthering the development of 3D-interactive programming

Stable and Metastable InGaAs/GaAs Island Shapes and Surfactantlike Suppression of the Wetting Transformation

Contrasting behaviors are observed in InGaAs/GaAs island formation during vapor phase epitaxy: variation of group V partial pressures gives different critical thicknesses for the onset of the Stranski-Krastanow transformation, surface coverages, ratios between coherent and incoherent islands, and dissimilar morphologies upon annealing. The latter experiments show that small lens-shaped islands can be found in equilibrium if InGaAs surface energies are minimized, leading to the conclusion that AsH3 can raise surface energies and act as an impurity-free "morphactant.

Inhibited carrier transfer in ensembles of isolated quantum dots

We report significant differences in the temperature-dependent and time-resolved photoluminescence (PL) from low and high surface density InxGa1-xAs/GaAs quantum dots (QDs). QD's in high densities are found to exhibit an Arrhenius dependence of the PL intensity, while low-density (isolated) QD's display more complex temperature-dependent behavior. The PL temperature dependence of high density QD samples is attributed to carrier thermal emission and recapture into neighboring QD's. Conversely, in low density QD samples, thermal transfer of carriers between neighboring QD's plays no significant role in the PL temperature dependence. The efficiency of carrier transfer into isolated dots is found to be limited by the rate of carrier transport in the InxGa1-xAs wetting layer. These interpretations are consistent with time-resolved PL measurements of carrier transfer times in low and high density QD's. [S0163-1829(99)04748-7]

Strain effect in a GaAs-In0.25Ga0.75As-Al0.5Ga0.5As asymmetric quantum wire

We report a theoretical investigation of the strain effects on the electronic energy band in a GaAs-In0.25Ga0.75As-Al0.5Ga0.5As asymmetric quantum wire formed in a V-grooved substrate. Our model is based on the sp(3)s* tight-binding model. It includes different spatial distributions of the lattice-mismatch-induced strain. We solve numerically the tight-binding Hamiltonian through the local Green's function from which the electronic local density of states (LDOS) is obtained. The detailed energy band structure (discrete localized states and energy bands of extended states) and the spatial distribution of the eigenfunctions (wave function amplitude of nondegenerate states or sum of the wave function amplitudes of degenerate states) are directly reflected in the LDOS. Spatial mapping of the LDOS's shows a reduction of the lowest excitation energies in different regions of the system when the local lattice structure of the In0.25Ga0.75As layer relaxes from completely strained to completely relaxed. By comparing the calculated results with photoluminescence measurement data, we conclude that the strain in the In0.25Ga0.75As layer relaxes linearly from the heterointerface with the Al0.5Ga0.5As buffer layer to the heterointerface with the top GaAs layer

Optical transition in infrared photodetector based on V-groove Al0.5Ga0.5As/GaAs multiple quantum wire

Photoconductors based on V-grooved Al0.5Ga0.5As/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 mum 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. (C) 2001 American Institute of Physics

Field Emission and Radial Distribution Function Studies of Fractal-like Amorphous Carbon Nanotips

The short-range order of individual fractal-like amorphous carbon nanotips was investigated by means of energy-filtered electron diffraction in a transmission electron microscope (TEM). The nanostructures were grown in porous silicon substrates in situ within the TEM by the electron beam-induced deposition method. The structure factorS(k) and the reduced radial distribution functionG(r) were calculated. From these calculations a bond angle of 124° was obtained which suggests a distorted graphitic structure. Field emission was obtained from individual nanostructures using two micromanipulators with sub-nanometer positioning resolution. A theoretical three-stage model that accounts for the geometry of the nanostructures provides a value for the field enhancement factor close to the one obtained experimentally from the Fowler-Nordheim law

Theoretical consideration of equilibrium dissociation geometries of 60° misfit dislocations in single semiconductor heterostructures

Equilibrium geometries of 60°dissociated misfit dislocations are considered theoretically using elasticity theory. The prediction of equilibrium dissociation width and the position of each partial with respect to the interface is given. The experimental results are in excellent agreement with the theory. © 1995 American Institute of Physics

Nanoscale structural analysis of amorphous materials

Reduced density function (G(r)) analysis of energy filtered electron diffraction data provides structural information from small volumes of amorphous materials. Improvements in transmission electron microscopes, energy filters and data recording devices (CCDs) have made it possible to perform G(r) analysis from volumes as small as 1-2 nm in diameter