**Dr. Devinder Singh**

**1**

**Chapter 1**

*Devinder Singh*

**1. Introduction**

Crystallography

Introductory Chapter: Electron

The different properties of materials are structure dependent. There are many techniques that are developed for the structure analysis. The most common of them is X-ray crystallography for the structural study of periodic ordered structures at atomic scale level. Few years later, after the discovery of X-ray diffraction, electron diffraction of single crystals was invented. The wave nature of electrons was utilized to discover the state of the art instrument, electron microscope. Since then, electron microscope has been extensively used in many fields for the study of micro-/ nanomaterials. Electron crystallography is used to collect different information by electron scattering. This has been used to study crystal structures and defects. After first electron microscopy image taken in 1933, the constant engineering developments from the last 80 years or so made it possible today to record high resolution transmission electron microscopy (HRTEM) images. Moreover, the powerful computers play a very important role in the further improvement of HRTEM images as well as to analyze them quantitatively by using different image processing programs. Modern transmission electron microscope (TEM) can be used for both structure and chemical analysis. The structure analysis is performed by electron diffraction and HRTEM, while the chemical analysis is performed by energy disper-

sive spectroscopy (EDS) and electron energy loss spectroscopy (EELS).

crystallography has some advantages over X-ray crystallography:

be done by electron crystallography.

preserved in the case of HRTEM images.

Although X-ray crystallography is known to be the best technique for the structure determination of unknown crystals, but under certain conditions, electron

• An electron scatters much more strongly than X-rays. Thus, much smaller crystals, million times smaller than those needed for single crystal X-ray diffraction can be studied by electron crystallography. The structure analysis (such as grain boundaries, phases, etc.) of crystals, too small for X-ray diffraction, can

• HRTEM images of crystals can be recorded in electron crystallography while in X-ray crystallography, imaging is not possible. The phase information remains

• The interaction mechanism with the crystal is also different for electron diffraction and X-ray diffraction. Electrons study electrostatic potential distribution in crystals while X-rays study electron density distribution in crystals.

• The X-ray powder diffraction gives results from a sample which may contain millions of small crystals while electron diffraction gives results from a single

Amity School of Applied Sciences, Amity University, Lucknow, India
