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The traditional way of polishing

Polishing is a process to remove the damage layer and strain layer of the material, reduce the surface roughness of the sample and reveal the original morphology of the sample, and is an important method to reveal the internal information of the sample. Traditional polishing methods can be divided into mechanical polishing, chemical polishing, chemical mechanical polishing, electrochemical polishing and electrochemical mechanical polishing. With the development of modern science and industry, material components and structures are developing in the direction of diversification and complexity, and traditional polishing methods are often unable to effectively prepare special materials and samples.

Comparison of the three

Argon ion polishing uses ion beams to etch solids based on the particle bombardment effect, also known as sputtering, which is the process of removing surface atoms by colliding high-energy incident particles with atoms near the surface layer of a solid sample. There are many kinds of techniques derived from ion sputtering effect, among which the closest ones to argon ion polishing are focused ion beam (FIB) and ion thinning.

Compared with FIB, argon ion polishing has a wider ion beam diameter and can be polished over a larger area, while lower ion beam energy can reduce the damage to the sample, in SEM, electron backscattering diffraction (EBSD), cathode fluorescence (CL), EPMA and scanning probe microscopy (SPM). These characteristics have advantages over FIB and ion thinning preparation.
The ion beams used in FIB are mostly focused gallium ion beams, which can realize fixed-point sample preparation at the same time of secondary electron observation, and the processing speed is fast, but the damage to the sample is relatively serious (crystal amorphous, high temperature damage, etc.), and the processing area is relatively small (mostly micron level).
Ion thinning technique uses ion beam to simultaneously bombard both sides of the sample to achieve sample thickness thinning, but only for fixed size (3mm disc) transmission electron microscope samples, but for other sizes of samples can not be thinned.

About argon ion polishing and ion thinning

The similarities and differences between argon ion polishing and ion thinning have been troubling many users, in fact, the basic principles of the two are not different, the difference is the purpose of using them.

Ion thinning reduces the thickness of the material to the desired size by irradiating the surface of the material with an ion beam, causing it to corrode or peel off. The ion beam can be high energy ions or low energy ions, and its energy determines the corrosion rate on the surface of the material. Ion beam irradiation can be uniform or localized, such that only specific areas are thinned.
Ion grinding is to remove surface impurities and non-uniform parts by using the impact and spray effect produced by ion beam on the surface of the material, so that the surface of the material is more smooth. When the ion beam hits the surface of the material, it causes the surface atoms to bounce and diffuse, thereby eliminating the local height difference and making the surface more uniform.
FIB and ion thinning are effective sample preparation methods in the field of transmission electron microscopy (TEM) testing, and argon ion polishing has made up the gap of ion beam sample preparation in other analysis and testing fields besides TEM, and has developed into a new high-quality polishing technology, which has been widely used in the field of geology. However, the use of other materials is still little known and needs to be further expanded.

 Argon ion polishing

Argon ion polishing generally has two polishing functions, cross-section polishing and plane polishing.Among them, an important improvement in section polishing is the use of baffles, as shown in Figure 1a. When the ion beam is emitted, the part shielded by the baffle is not bombarded by the ion beam, while the edge of the exposed part gradually forms a flat cross section perpendicular to the baffle under the action of the ion beam, as shown in Figure 1b.The schematic diagram of plane polishing is shown in Figure 1c. The sample morphology of plane polishing can be more diverse than cross-section polishing, and shaped block and powder polishing can also be applied. The ion beam passes over the surface of the sample at a certain Angle of incidence, and the atoms on the surface of the sample are removed layer by layer from top to bottom, thus forming a flat polished surface.