Transmission electron microscopy sample preparation is a relatively complicated technique, and it is crucial for obtaining a good TEM image or diffraction spectrum. Transmission electron microscopy uses the difference in the ability of the sample to scatter incident electrons to form contrast.
The ability of an electron beam to penetrate a solid sample depends mainly on the acceleration voltage, the thickness of the sample, and the atomic number of the substance. In general, the higher the acceleration voltage and the lower the atomic number, the greater the thickness of the sample that the electron beam can penetrate. For transmission electron microscopes of 100 to 200 kV, the sample thickness is required to be 50 to 100 nm. For high resolution transmission electron microscope, the sample thickness is required to be about 15 nm (the thinner the better).
TEM samples can be divided into: powder samples, thin film samples, surface replicas of metal samples. Different samples have different preparation methods, the following describes the preparation of thin film samples:
The vast majority of TEM samples are thin-film samples. Thin-film samples can be statically observed, such as metallographic structure; precipitated phase morphology; distribution, structure and orientation with the substrate, dislocation type, distribution, density, etc .; dynamic in-situ observation , Such as phase change, deformation, dislocation motion and their interaction. There are four steps to prepare film samples:
a. Cut the sample into thin slices with a SYJ-150 low-speed diamond cutting machine, with a thickness of 100-300 microns. Generally, for tough materials (such as metals), use SYJ-150 saw to cut the sample with silicon carbide saw blade or corundum saw blade to less than 200 micron flakes; for brittle materials (such as Si, GaAs, Sic, MgO), it can be cut into 200-300 micron thick flakes with a SYJ-150 diamond saw.
b. Use the garden (ring) sampler produced by Shenyang Kejing Equipment Manufacturing Co., Ltd. to intercept the φ3mm wafer.
c. For pre-thinning, use UNIPOL-300 small precision grinding and polishing machine produced by Shenyang Kejing Equipment Manufacturing Co., Ltd., which can grind thin wafers to 20-30μm thickness. Grind with a grinder (or use sandpaper), which can be grinded to tens of μm, and use the pit thinner to grind the thin wafer to 10μm thick. The ability of an electron beam to penetrate a solid sample depends mainly on the acceleration voltage, the thickness of the sample, and the atomic number of the substance. In general, the higher the acceleration voltage and the lower the atomic number, the greater the thickness of the sample that the electron beam can penetrate. For transmission electron microscopes of 100 to 200 kV, the sample thickness is required to be 50 to 100 nm. For high resolution transmission electron microscope, the sample thickness is required to be about 15 nm (the thinner the better).
TEM samples can be divided into: powder samples, thin film samples, surface replicas of metal samples. Different samples have different preparation methods, the following describes the preparation of thin film samples:
The vast majority of TEM samples are thin-film samples. Thin-film samples can be statically observed, such as metallographic structure; precipitated phase morphology; distribution, structure and orientation with the substrate, dislocation type, distribution, density, etc .; dynamic in-situ observation , Such as phase change, deformation, dislocation motion and their interaction. There are four steps to prepare film samples:
a. Cut the sample into thin slices with a SYJ-150 low-speed diamond cutting machine, with a thickness of 100-300 microns. Generally, for tough materials (such as metals), use SYJ-150 saw to cut the sample with silicon carbide saw blade or corundum saw blade to less than 200 micron flakes; for brittle materials (such as Si, GaAs, Sic, MgO), it can be cut into 200-300 micron thick flakes with a SYJ-150 diamond saw.
b. Use the garden (ring) sampler produced by Shenyang Kejing Equipment Manufacturing Co., Ltd. to intercept the φ3mm wafer.
d. Final thinning For conductive samples such as metals, electrolytic polishing is used for thinning. This method is fast and has no mechanical damage, but may change the electronic state of the sample surface. The chemical reagents used may be harmful to the body.
For non-conductive samples such as ceramics, ion thinning is used, and the surface of the sample is bombarded with ions to make the sample material sputter out to achieve the purpose of thinning. For ion thinning, the voltage and angle should be adjusted, suitable parameters should be selected, and the thinning speed should be fast. Ion thinning generates heat, which raises the sample temperature to 100-300 degrees, so it is best to use liquid nitrogen to cool the sample. Sample cooling is very important for materials that are not resistant to high temperatures. Otherwise, the material will undergo a phase change. Sample cooling can also reduce pollution and surface damage. Ion thinning is a universal thinning method that can be used for ceramics, composites, semiconductors, alloys, interfacial samples, and even fiber and powder samples can also be ion thinned (after mixing them with resin, into φ3mm metal Tube, after sectioning, then ion thinning). It is also possible to perform ion thinning (FIB) on the designated area, but the FIB is very expensive.
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