Abstract For Abstract see ChemInform Abstract in Full Text.
We propose a microspectromer consisting of a photonic crystal mating directly to a detector array as shown in Figure 1(a). The photonic crystal in this case is a 3D opal structure that is an inhomogeneous quasi-periodic array of microcavities that cause spectral variation in the near field. Advantages of the photonic crystal filter compared to an array of thin film filters are: insensitivity to angle of incidence, ability to characterize large etendue sources, and spectral diversity as a function of position on a small scale less than 10 microns.
Experimental conditions for obtaining high quality core-shell ionization edges in reflec- tion electron energy-loss spectroscopy (REELS) are investigated.Under the (600) specular-"mirror" reflection conditions and using the relative ionization cross-section measured from a MgO thin foil in the transmission geometry for collection semi-angle 03B2 = 1.2mrad, the chemical composition of MgO (100) surfaces is determined to be NO/NMg = 1.5 ± 0.15.This value is not significantly affected by varying the resonance diffraction conditions near the [001] zone axis, under which the spectra were acquired.An incorrect apparent composition will result if channeling effects along the [011] zone axis are not considered properly.Surface microanalysis is limited by the accuracy of the core-shell effective ionization cross-section (EICS), which depends not only on the property of a single atom but also on the dynamical elastic and inelastic scattering and channeling processes of electrons.An experimental method is outlined by which to measure the relative EICS from a thin foil specimen in the transmission case under the equivalent resonance conditions as in reflection geometry.1. Introduction.Reflection electron energy-loss spectroscopy (REELS) combines the techniques of reflection elec- tron microscopy (REM) and electron energy-loss spectroscopy (EELS) in a transmission electron microscope (TEM) [1].The REELS spectra are acquired from reflected electrons under sur- face resonance conditions (see [2] for a review), the electrons having travelled a certain distance along the surface before being reflected [3].Surface compositional microanalysis, an important application of REELS, usually requires the simultaneous detection of two or more atomic inner- shell ionization edges.As a result of strong dynamical scattering effects, however, the signal-tobackground (S/B) ratios of the K ionization edges located above 1 keV are limited in the REM geometry, which may compromise the accuracy of surface microanalysis.In REM, the electrons reflected from the surface can be classified as Bragg-but not resonance, resonance-but not Bragg, and Bragg-resonance.The optimum inelastic signal usually obtained in the last case.In practice, there are many ways to achieve surface resonance, such as axial and
Reflection electron microscopy (REM) is a new technique for real space imaging of bulk crystal surfaces. The REM is performed in a transmission electron microscope (TEM) or a scanning TEM (STEM) using high-energy electrons at a grazing incidence angle. A comprehensive review has been given on basic techniques, fundamental physics, studies of surface reconstructions, and special applications of REM. Theoretical calculations have been described to illustrate the resonance scattering processes of electrons at the bulk crystal surfaces in the geometry of reflection high-energy electron diffraction (RHEED). Fundamental contrast mechanisms of REM have been illustrated to show the surface sensitivity of REM. Applications of REM for in-situ imaging of surface dynamic processes have been summarized for studies of metals, semiconductors, metal-on-semiconductors, semiconductor-on-semiconductors, and ceramics. Inelastic excitations of crystal surfaces in RHEED have been examined to demonstrate a technique, reflection electron energy-loss spectroscopy (REELS), for studying surface electronic structures and determining surface chemical compositions. Finally, novel techniques used in conjunction with REM, such a secondary electron imaging, scanning tunnelling microscopy (STM) and electron holography, have been described to show the future development of REM.
