Advantages of Scanning electron microscope
1. Magnification factor
Due to the fixed size of the fluorescent screen of the scanning electron microscope, the change in magnification is achieved by changing the scanning amplitude of the electron beam on the surface of the sample.
If the current of the scanning coil is reduced, the scanning amplitude of the electron beam on the sample will decrease, and the amplification factor will increase. The adjustment is very convenient, and can be continuously adjusted from 20x to around 200000 times.
2. Resolution
Resolution is the main performance indicator of scanning electron microscopy.
The resolution is determined by the diameter of the incident electron beam and the type of modulation signal Co-determination:
The smaller the diameter of the electron beam, the higher the resolution.
The physical signals used for imaging vary in resolution.
For example, SE and BE electrons have different emission ranges and resolutions on the sample surface. The resolution of SE is generally around 5-10nm, while that of BE is around 50-200nm.
3. Depth of field
It refers to the ability range of a lens to simultaneously focus and image various parts of a uneven sample.
The final lens of the scanning electron microscope uses a small Angular aperture and a long focal length, so a large depth of field can be obtained. It is 100-500 times larger than the depth of field of the general optical microscope and 10 times larger than the depth of field of the transmission electron microscope.
The prominent features of SEM are large depth of field, strong three-dimensional sense, and realistic morphology.
The samples used for scanning electron microscopy are divided into two categories:
1 is a sample with good conductivity, which can generally maintain its original shape and can be observed under an electron microscope without or with slight cleaning;
2 is a non-conductive sample, or a sample with water loss, gas release, or shrinkage deformation in vacuum, which needs to be properly treated before observation can be made.
