Monte Carlo Simulation of SEM and SAM Images

Abstract

1.1 Electron microscopic and spectroscopic techniques The electron microscopic and spectroscopic techniques are conveniently and widely used for surface and bulk analysis of materials. These analysis tools use the various types of electron signals that emitted from the specimen irradiated by a beam of mono-energetic primary electrons or X-rays for imaging of surface, and for structural and chemical characterization. Different signals in relevant techniques are secondary electrons (SEs) and backscattered electrons (BSEs) for scanning electron microscopy (SEM), Auger electrons (AEs) for Auger electron spectroscopy (AES) and scanning Auger microscopy (SAM), photoelectrons for Xray photoelectron spectroscopy (XPS) and X-ray photo-emission electron microscopy (XPEEM), elastic scattered electrons for elastic peak electron spectroscopy (EPES), inelastic scattered electrons for electron energy loss spectroscopy (EELS) and reflection electron energy loss spectroscopy (REELS), characteristic X-ray and bremsstrahlung for electron probe microanalysis (EPMA) and analytical electron microscopy (AEM) (Reimer, 1998). Particularly, SEM is more frequently used for a quick sample characterization. Imaging of microstructure of materials with SEs and BSEs plays a very important role in many scientific and technological fields. SE images, formed by SEs of very low energies (<50 eV) emitted from the surface region, provide mainly topographic information of the specimen surface with nanometer resolution with a modern SEM. BSE images can provide more information about the matrix composition for the signal electrons are transported from the sample interior within interaction volume of primary electrons of several keV energy. SAM is a technique that combines AES with SEM and is commercially available as an ultra-high vacuum instrument for chemical investigation of clean surfaces. With SAM it is possible to observe the surface elemental distribution and to obtain chemical state information by detecting AEs that carry characteristic energies representing the specific energy levels of surface atoms ionized by an incident electron beam. The principle of these techniques relies on electron-solid interaction. Therefore, the study of electron transport is very important to these techniques for a detailed understanding of a