Scanning Electron Microscope

Introduction

One of the primary objectives of MNNIT is to provide best research and analytical services facilities, keeping in view the technological needs of the country, for all its undergraduate, postgraduate and research activities. Consequently, MNNIT has set up several facilities, internally known as Centre for Interdisciplinary Research (CIR) facilities. The functioning of each facility is coordinated by a Director of the Institute. Scanning Electron Microscope Central Facility is one such facility. All students, researchers and faculty members from various science and engineering departments of the institute are free to avail the services of SEM as per the guidelines laid by the SEM user Committee of the institute. These guidelines are regularly reviewed from time to time. Whenever it is possible, outside users from Research & Development Organizations and other educational institutions are also allowed to avail the facility against payment. The charges finalized by the SEM User's Committee, are displayed on the SEM website of the institute and are non-negotiable under any circumstances.

The SEM Central Facility is equipped with following equipments:

  • ZEISS EVO Series Scanning Electron Microscope Model EVO15
  • Gold-Palladium sputter coating unit

Scanning Electron Microscope

The scanning electron microscope uses a focused electron beam which is scanned on the surface of the sample to produce high quality images of the surface topography. SEM essentially offers a very high magnification with very high resolution capabilities and a large depth of focus. This characteristic makes it an indispensable tool for analysis of a wide class of conducting, semi-conducting and insulating materials. A strong beam of electrons called primary electron beam is produced by thermionic emission using either tungsten or a Lanthanum Hexaboride (LaB6) filament. LaB6 filaments are preferred because of their long life and reasonable stability of electron beam emission. Lanthanum hexaboride (LaB6) filaments have high thermionic emission characteristics and sufficiently low vapor pressures to be desirable cathode materials for electron microscopy. LaB6 cathodes provide around an order of magnitude higher brightness than tungsten cathodes. The primary beam of electrons thus emitted by therminioc emission interacts with the top atomic layers of surface of the sample. This gives out a variety of signals that can be collected and processed to derive a good quality of information about the morphology of the sample, atomic contrast in the sample and the elemental composition of the top surface of the material. The different possible interactions of the sample with a high energy electron beam are:

  • Primary electrons generate very low energy electrons called secondary electrons from the top atomic layers of the sample that are used to analyze its topographic nature
  • Primary electrons that are backscattered during interaction with sample surface produce images with a high degree of atomic number contrast.
  • Primary beam of electrons can ionize atoms of the sample that stabilize by shell-to-shell transitions of electrons, which causes either emission of X-rays or Auger electron. The X-rays so emitted are characteristic of the elements that make the top surface layers of the sample.

A wide range of materials whose morphology can be routinely analyzed include:

  • Metals, Glass and Ceramics
  • Semiconductors
  • Plastics
  • Fibers (Textile, Glass, Natural)
  • Powders
  • Biological samples (Cells, Microbes, Pollen grains)