Cathodoluminescence spectroscopy has been performed on silver nanoparticles in a scanning electron microscopy setup. Peaks appearing in the visible range for particles fabricated on silicon substrate are shown to arrive from excitation of out of plane eigenmodes by the electron beam. Monochromatic emission maps have been shown to resolve spatial field variation of resonant plasmon mode on length scale smaller than 25nm. Finite-difference time-domain numerical simulations are performed for both the cases of light excitation and electron excitation. The results of radiative emission under electron excitation show an excellent agreement with experiments. A complete vectorial description of induced field is given, which complements the information obtained from experiments.

We have developed web-based electron microscopy application software (Web-EMAPS) that is designed for both microscopy research and teaching. The software can be accessed via a web browser from anywhere and anytime. The philosophy is to take the advantage of web accessibility and the control afforded by centralized computing to make sophisticated simulation tools available to both experienced researchers and beginners to advance quantitative electron microscopy. The site can be accessed via http://emaps.mrl.uiuc.edu/.The program simulates realistic electron diffraction patterns and images for crystals through a web-browser user interface [ fig. 1]. The simulations are powered by well-tested software developed over several years in JMZ's research, for example, in quantitative CBED. Initial functions include: 1) crystal structure definition and rendering [fig. 2], 2) kinematic diffraction including Kikuchi and HOLZ lines [fig. 3], 3) Convergent beam electron diffraction by the Bloch wave method [fig. 4], 4) HREM image simulation by the Bloch wave method [fig. 5], 5) electron probe propagation and channeling, 6) structure factor and d-spacing calculations, and 7) Coherent electron diffraction.The site has a database of common crystals in modern materials science. Provision is also made for users or students to define their own crystals or upload a CIF (crystallographic information file) file to define a crystal. A crystal is simply defined by the unit cell, atomic positions, and symmetry. Symmetry is defined by the space group number with the origin setting following the convention defined in the international table for crystallography. On the same menu, a crystal drawing function is provided using the open source Java applet, Jmol.Kinematic electron diffraction pattern is simulated based on the diffraction geometry and kinematic intensities. The example shown in Fig. 3 was simulated from GaAs along [111] zone axis at 200 kV. Two diffraction modes are provided, one for selected area electron diffraction and the other for CBED.Dynamic electron diffraction pattern is simulated using the Bloch wave theory [1]. Beams included in the simulation are selected based on the criteria described in ref [2]. The scattering factors are calculated using the Doyle and Turner atomic scattering factors for x-ray listed in the international table for crystallography. The electron adsorption effect is included by calculating adsorption potential using the Einstein model [3]. The simulated diffraction pattern is mapped onto a square pixel area. The mapping is specified by the length of x-axis in number of pixels and the angle relative to the horizontal line. The image is viewed using the NIH ImageJ Java applet or downloaded as a 16-bit image file in TIFF format. An example of a CBED simulation for GaAs is shown in fig.4.Functions for HREM image simulation, coherent CBED and electron probe and probe propagation are also based on the Bloch wave method. An example of HREM image simulation is given in fig. 5. The electron probe simulations ...

Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation.

The Ni∕AlGaN interfaces in AlGaN∕GaN Schottky diodes were investigated to explore the physical origin of postannealing effects in AlGaN∕GaN heterostructures using electron beam induced current (EBIC) and current-voltage characteristics. Black spot density in EBIC images of as-deposited Ni∕AlGaN∕GaN diodes is in the same order of 108cm−2 as the dislocation density of AlGaN∕GaN heterostructures characterized by atomic force microscopy, indicating that recombination sites near Ni∕AlGaN interface are related to dislocations. The EBIC images of the annealed diodes showed that the postannealing reduced the electrically active states at the Schottky metal/AlGaN interfaces. The thermal reaction near Ni∕AlGaN interface due to the postannealing induced passivation effect, leading to decrease in reverse leakage current density, ideality factor, and saturation current density of the diodes and increase in the Schottky barrier height. We suggest that the postannealing process is an effective way to passivate the AlGaN∕GaN heterojunction field effect transistors.

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