Types and features of scanning electron microscopes
There are various types of scanning electron microscopes, and different types of scanning electron microscopes have performance differences. According to the type of electron gun, it can be divided into three types: field emission electron gun, tungsten wire gun, and lanthanum hexaboride. Among them, field emission scanning electron microscopy can be divided into cold field emission scanning electron microscopy and hot field emission scanning electron microscopy based on the performance of the light source. Cold field emission scanning electron microscopy requires high vacuum conditions, unstable beam current, short emitter lifespan, and requires regular cleaning of the needle tip, which is limited to single image observation and has a limited application range; The thermal field emission scanning electron microscope not only has a long continuous working time, but can also be combined with various accessories to achieve comprehensive analysis. In the field of geology, we not only need to observe the preliminary morphology of samples, but also need to analyze other properties of samples in combination with analyzers, so the application of thermal field emission scanning electron microscopy is more extensive.
Although scanning electron microscopy is a newcomer in the microscope family, its development speed is very fast due to its many advantages.
The instrument has a high resolution and can observe details of about 6nm on the surface of the sample through secondary electron imaging. By using a LaB6 electron gun, it can be further improved to 3nm.
The instrument has a wide range of magnification changes and can be continuously adjusted. Therefore, different sizes of fields of view can be selected for observation as needed, and clear images with high brightness that are difficult to achieve with general transmission electron microscopy can also be obtained at high magnification.
The depth of field and field of view of the sample are large, and the image is rich in three-dimensional sense. It can directly observe rough surfaces with large undulations and uneven metal fracture images of the sample, giving people a sense of being present in the microscopic world.
The preparation of the 4 samples is simple. As long as the block or powder samples are slightly treated or not treated, they can be directly observed under a scanning electron microscope, which is closer to the natural state of the substance.
5. Image quality can be effectively controlled and improved through electronic methods, such as automatic maintenance of brightness and contrast, correction of sample tilt angle, image rotation, or improvement of image contrast tolerance through Y modulation, as well as moderate brightness and darkness in various parts of the image. By using a dual magnification device or image selector, images with different magnifications can be observed simultaneously on the fluorescent screen.
6 can be subjected to comprehensive analysis. Install a wavelength dispersive X-ray spectrometer (WDX) or energy dispersive X-ray spectrometer (EDX) to enable it to function as an electron probe and detect reflected electrons, X-rays, cathodoluminescence, transmitted electrons, Auger electrons, etc. emitted by the sample. Expanding the application of scanning electron microscopy to various microscopic and micro area analysis methods has demonstrated the multifunctionality of scanning electron microscopy. In addition, it is also possible to analyze the selected micro areas of the sample while observing the morphology image; By installing the semiconductor sample holder attachment, PN junctions and micro defects in transistors or integrated circuits can be directly observed through an electromotive force image amplifier. Due to the implementation of electronic computer automatic and semi-automatic control for many scanning electron microscope electron probes, the speed of quantitative analysis has been greatly improved.
