Question

Image formation in electron microscope is based on

• A. ( \text{column length} ) \
• B. ( \text{electron number} ) \
• C. ( \text{differential scattering} ) \
• D. ( \text{specimen size} ) \

Hint:

The fundamental principle of image formation in electron microscopy is that differences in how various parts of the specimen interact with and scatter the electron beam create contrast. This differential scattering allows us to visualize the internal structure (in TEM) or surface topography (in SEM) of the sample.

Answer 1

The Correct Option is C

In an electron microscope (both TEM and SEM), image formation relies on the interaction of the electron beam with the sample.
When the electron beam strikes the specimen, the electrons interact with the atoms of the sample.
These interactions can lead to various phenomena, including elastic scattering (e.
g., Bragg scattering), inelastic scattering (e.g., plasmon excitation, core-level excitations), and electron absorption.
The key principle for image formation is differential scattering.
Different regions of the specimen will scatter the incident electrons differently based on their atomic number, density, and thickness.
In TEM, electrons that are scattered away from the objective aperture contribute to contrast because they are prevented from reaching the detector.
Regions that scatter more electrons appear darker, while regions that scatter fewer electrons appear brighter.
This differential scattering of electrons provides the contrast that forms the image.
Column length, electron number (referring to the total number of electrons in the beam rather than their interaction properties), and overall specimen size do not directly determine the image contrast and formation mechanism in the same way as differential scattering.