Transmission Electron Microscope

Introduction
For analysis of materials of very small dimensions like quantum dots, quantum wires, nano tubes, nano dots, fullerenes etc. we need special kind of microscopes. As photons of light have wavelengths larger than that of most of the nanomaterials, optical microscopes doesn’t have magnification power or resolution capabilities to cater these materials. For this purpose electron microscopes, which uses electrons having shorter wavelengths, like Transmission Electron Microscope (TEM), Scanning Tunneling Microscope (STM), Atomic Force Microscope (AFM) and Scanning Near-Field Optical Microscope are used. These microscopes have the ability to magnify such small dimensions materials, with a higher resolution, for analysis. Microscopes can be used to analyses the following characteristics of a specimen under consideration;
I. Morphology
II. Size
III. Structure
IV. Composition of solids (depending upon the type of microscope)
Basic Characteristics of a Microscope
For getting accurate information for analysis from a microscope, its capabilities regarding its resolution, magnification and depth of focus should be known. These capabilities are discussed below:
Resolution
The ability of a microscope to produce two distinct images of two closely spaced objects is termed as its resolution. Or in other words the
This principle is used in the electron microscopy where electromagnets are used as magnetic equivalent of the lenses to converge electrons over a specimen or magnify the image. In electromagnetic lenses a current is passed through a set of windings to produce a strong magnetic field. This field produces the effect of a convex lens and bring the diverged rays back to focus. The image produced by these lenses is inverted and rotated. The strength of the current controls the focal length of the lenses.