Desktop Scanning Electron Microscopy—Sampling Method for Magnetic Materials
In this issue, we will talk about the method of using a desktop scanning electron microscope to observe the sample preparation method of magnetic materials. Generally, demagnetization is required before analysis. The main reasons are as follows:
1. Generally, the lens and scanning coil of a desktop scanning electron microscope work by orderly regulating the current flowing through the coil to generate a magnetic field. If the sample itself is magnetic, it will interfere with the work of the electron optical system. If the sample is strongly magnetic, the image will be blurred, the contrast and resolution will be poor, and the astigmatism will not work, and the astigmatism cannot be eliminated.
2. Magnetic samples will deform and distort the electronic image, and will also affect the magnification and the accuracy of microscopic measurements. However, some ferrite materials can still be directly placed in the sample chamber for analysis. First, the sample must be firmly adhered, Tighten to ensure reliability: Secondly, the working distance should be >10mm, and the energy should be >15mm. Use low acceleration voltage and small beam current, because the conductivity of ferrite is poor.
3. The magnetic powder particles that are not firmly pasted on the sample stage are easily adsorbed into the pores of the lower pole piece of the objective lens or the electron optical path. Once these sensitive parts are contaminated, the performance of the electron optics will be destroyed immediately. cleaning. This cleaning and maintenance is much more troublesome than the general cleaning of the lens barrel, because such small magnetic particles are difficult to find and remove. If you really want to analyze this kind of sample, it is recommended to consider demagnetization first, and then consider firing the ceramic block and cleaning it before doing the analysis, otherwise it will bring catastrophic consequences to the desktop scanning mirror.
4. Magnetic materials will also affect the analysis of EDS and WDS. When analyzing a certain point, it is easy to cause difficult positioning such as misalignment and skew, and it will also cause errors in the identification of desktop scanning parameters, resulting in quantitative analysis errors. significantly increased. According to the information of some desktop scanning manufacturers, the objective lens is an objective lens pole piece without magnetic leakage, which can be used for the observation of magnetic samples and EBSD analysis. If some use the design of semi-inner lens, the magnetic flux leakage is relatively small, but it should be used with great care when analyzing magnetic samples.