1. Scanning Electron Microscopy (SEM)
Main Reference:
Let’s familiarize ourselves with the SEM, Hitachi: Inspire the Next

2. Why do we need the SEM?
human eye can see objects approximately 0.1 mm in size.
resolution of light microscope cannot be small than the half of the wavelength of the visible light ( µm) - with green light (0.5 µm), resolution of light microscope is about 0.2 µm.
Below 0.2 µm, a source with wavelength < 400 nm is needed -> Electron Microscope.
Electron microscopes: transmission electron microscope (TEM), scanning electron microscope (SEM)
TEM is used for observing the inner-structure of a specimen at high magnification, mainly as projected images.
SEM is particularly for observing the fine structure of a specimen surface at high magnification, mainly as scanning images.

4. Principle and Structure of the SEM
Finely converged electron beam scans on sample surface in a vacuum
Information (signals) produced from the sample is detected and presented as an enlarged image of sample surface on the monitor screen.
Secondary electrons, backscattered electrons, characteristic X-rays and light are generated as major signals.
Secondary electron or backscattered electron signals form images.
Secondary electrons (SE) are produced near the sample surface, reflecting the fine topographical structure of the sample.
Backscattered electrons (BE) are those reflected upon striking the atoms of the sample, dependent on the composition of the sample (average atomic number, crystal orientation, etc.) and reflecting the compositional distribution on the sample surface.
X-ray detector can be mounted to the SEM for conducting elemental analysis from characteristic X-rays.
SEM is usable not only for observing the sample structure, but also applicable as an X-ray analyzer for determining what elements qualitatively and quantitatively.