A Técnica de Difração de Elétrons Retro-Espalhados (EBSD) em Microscópio Eletrônico de Varredura (MEV) e sua Aplicação no Estudo de Rochas Deformadas

Abstract

The electron backscattered diffraction technique in the scanning electron microscope (EBSD/SEM) is based on the diffraction of a high-energy electron beam by the crystalline structure of a given material, in all possible directions within the sample. Some of the diffracted electrons escape from the specimen with virtually the same initial energy, interact with a phosphorescent screen and the generated EBSP pattern can be picked up with a low-luminosity charge couple device (CCD) camera. These patterns can be indexed using pre-determined patterns for a large variety of minerals, which allows the determination of complete orientation of each single mineral within an aggregate. In this paper we briefly discuss the physical aspects related to the diffraction of an electron beam by crystalline matter and how the EBSP patterns are generated. We also present a short introduction of the necessary instruments to acquire EBSD data, as well as the calibration procedures, acquisition and indexing software of EBSPs. The pitfalls of the technique and possible error sources are also discussed with examples. Considering the scarce availability of literature on geological sample preparation, the polishing method of silicate-rich rocks for EBSP is described in detail in the last part of this paper.The electron backscattered diffraction technique in the scanning electron microscope (EBSD/SEM) is based on the diffraction of a high-energy electron beam by the crystalline structure of a given material, in all possible directions within the sample. Some of the diffracted electrons escape from the specimen with virtually the same initial energy, interact with a phosphorescent screen and the generated EBSP pattern can be picked up with a low-luminosity charge couple device (CCD) camera. These patterns can be indexed using pre-determined patterns for a large variety of minerals, which allows the determination of complete orientation of each single mineral within an aggregate. In this paper we briefly discuss the physical aspects related to the diffraction of an electron beam by crystalline matter and how the EBSP patterns are generated. We also present a short introduction of the necessary instruments to acquire EBSD data, as well as the calibration procedures, acquisition and indexing software of EBSPs. The pitfalls of the technique and possible error sources are also discussed with examples. Considering the scarce availability of literature on geological sample preparation, the polishing method of silicate-rich rocks for EBSP is described in detail in the last part of this paper