4,218 publications from this institution
There are two basic requirements for REM imaging of surfaces. The specimen is strongly preferred to be a single-crystalline material so that strong Bragg-reflected beams can be generated. The surface has to be flat enough to permit grazing angle imaging. The foreshortening effect along the beam direction, however, is a major disadvantage of REM, which limits the application of REM for imaging a relatively rough surface. It is thus desirable to enhance the potential of this technique by using it in conjunction with other surface imaging and analytical techniques. We first examine the interaction of an electron beam with the surface.
Abstract The Green's function is a powerful mathematical tool in developing the theory of condensed-matter physics. It is usually easy to write the equation in the form of G(r, r′), but the critical challenge is to find its analytical or numerical solution. In this paper, the Green's function for electron scattering is reviewed, and its general solution is given. The theory is extended into the regimes that are suitable for numerical calculations in different scattering geometries, such as the images in the low-voltage lensless point-projection microscopy. An iterative calculation technique is introduced for computing the Green's function using the Born series, and the result is applied to calculate the optical potential introduced in electron diffraction for recovering the multiple diffuse scattering effects. With the Green's function presented here and the theory reported previously by Wang (1996, Phil. Mag. B. 74, 733), quantitative analysis of electron diffuse scattering due to short-range order of point defects and thermal diffuse scattering is likely to be feasible.
Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.
A method of efficiency calculation and coincidence-summing correction of a germanium detector by using MCNP code is presented. Modeling of the detector geometry is described in detail and differences between the simulated and measured spectra are discussed. Standard point sources traceable to NIST were used to measure the full-energy peak and total efficiencies. A /sup 60/Co point source was placed in five positions above the detector from 0.6 cm to 14.2 cm. For the 1173 keV and 1332 keV gamma rays from /sup 60/Co, their spectra were simulated by MCNP separately. Subsequently, these spectra were combined according to their coincidence relationship to form the simulated /sup 60/Co spectrum. Cs-137 was used to compare a simple measured spectrum with the MCNP simulation. The simulated full energy peak efficiency for non-coincidence gamma rays agreed with the measured value to within 2%, but the simulated total efficiency is about 8% lower for 662 keV. The calculated coincidence summing factors for 1173 and 1332 keV are about 3% lower than the measured values at the closest geometry for a point source due to the underestimation of the total efficiency. This technique will be used in the efficiency calibration of Ge detectors to avoid the difficulties of preparing standard sources.
The utilization of abundant blue energy in the ocean could greatly contribute to achieving carbon neutrality. However, the unsolved economic and technical challenges of traditional technologies for harvesting blue energy have resulted in slow progress. Triboelectric nanogenerators (TENGs), as a new approach for converting mechanical energy into electricity, have great potential for blue energy harvesting, which can be connected as networks with different numbers of units for varying scales of energy harvesting. Here, recent advances of networking strategies of TENGs for harvesting blue energy are reviewed, mainly concerning mechanical and electrical connection designs. Anchoring strategies of devices and networks are also discussed. The development of TENG networks could provide an effective solution for large-scale ocean blue energy harvesting, which can also serve as an in-situ energy station or power source for self-powered systems, supporting various marine equipment and activities.
Abstract Electroluminescence (EL)-based displays are an emerging technology for next generation flat panel displays. ZnS is an important component material for light emitting devices and EL-displays. To make this material useful for high efficiency and low voltage EL applications, the density of dislocations is required to be low. High quality single crystalline ZnS thin films have recently been grown by chemical beam epitaxy [1]. This paper focuses on studying the formation mechanism of stacking faults in the film and its relation with the interface structure between the substrate and the film [2]. Stacking faults are the main defects present in the film (Fig. 1). All four stacking faults (sf) are intrinsic and sf1, growing towards the left-hand side from the interface, is only of short range since after crossing sf2 the defect is terminated by a Shockley partial dislocation and the normal stacking sequence is restored. This is the mechanism that annihilates most of the stacking faults generated from the interface within the first 70 nm thickness range.
