Principle of microscopy

The microstructural characterization by microscopic techniques is an essential requirement for materials design as well its materials performance. This paper, starting from historical developments of microscopy, deals with the various methods of optical microscopy, transmission electron microscopy and scanning tunneling microscopy. In optical microscopy emphasis have been given to multiple beam interferometry (MBI) capable of achieving the vertical resolution of I nm while lateral resolution remains to that of optical microscopy. It's capability to unmask microtopographies of surfaces is illustrated by few industrial examples. The operating principles of transmission electron microscopy alongwith various imaging modes illustrated with examples have been described. The capability of Moire fringe in imaging of nanoparticles have been highlighted. The Lorentz microscopy in Fresel imaging and coherent Foucault imaging modes are capable of providing quantitative information about magnetic properties/ substructures. The generic concept of scanning tip microscopies utilizing some physical property of probe-interaction have been described.