Secondary Electron Imaging:- This mode provides high-resolution imaging of fine surface morphology. Inelastic electron scattering caused by the interaction between the sample's electrons and the incident electrons results in the emission of low-energy electrons from near the sample's surface. The topography of surface features influences the number of electrons that reach the secondary electron detector from any point on the scanned surface.
Backscatter Electron Imaging:- This mode provides image contrast as a function of elemental composition, as well as, surface topography. Backscattered electrons are produced by the elastic interactions between the sample and the incident electron beam. These high-energy electrons can escape from much deeper than secondary electrons, so surface topography is not as accurately resolved as for secondary electron imaging.
Variable Pressure SEM:- By and large, SEM requires an electrically-conductive sample or continuous conductive surface film to allow incident electrons to be conducted away from the sample surface to ground. If electrons accumulate on a nonconductive surface, the charge buildup causes a divergence of the electron beam and degrades the SEM image. In variable-pressure SEM, imaging can be performed on a nonconductive sample when the chamber pressure is maintained at a level where most of the electrons reach the sample surface, Some air is allowed into the sample chamber, and the interaction between the electron beam and the air molecules creates a cloud of positive ions around the electron beam. These ions will neutralize the negative charge from electrons collecting on the surface of a nonconductive material to reduce the charging. Variable pressure SEM is also valuable for examination of samples that are not compatible with high vacuum.
EDAX Technique:-The EDS technique detects x-rays emitted from the sample during bombardment by an electron beam to characterize the elemental composition of the analyzed volume.
Cryo SEM imaging Technique:- Cryo-method has the great advantage wherein the material is so rapidly frozen that vulnerable biological structures are well preserved and thus when using cryo-fracture the material breaks clean along weak edges (e.g. membranes) without causing much malformation to the sample structure. Additionally this technique can be used for observing ‘difficult’ samples, such as those with greater beam sensitivity and of an unstable nature. Soluble materials are retained in this technique. There is almost no exposure to toxic reagents during sample preparation.
Inlens-duo imaging technique:- The Inlens-duo detector allow simultaneous imaging and mixing of a high contrast topography as well as clear compositional contrast .
Scanning transmission electron microscopy (STEM):- STEM combines the principles of transmission electron microscopy and scanning electron microscopy . The STEM technique scans a very finely focused beam of electrons across the sample in a raster pattern. As in the SEM, secondary or backscattered electrons can be used for imaging in STEM; but higher signal levels and better spatial resolution are available by detecting transmitted electrons.