Introduction to the performance characteristics of scanning electron microscopes
Introduction to the performance characteristics of scanning electron microscopes
There are various types of scanning electron microscopes, and different types of scanning electron microscopes have differences in performance. According to the type of electron gun, it can be divided into three types: field emission electron gun, tungsten wire gun and lanthanum hexaboride [5]. Among them, field emission scanning electron microscopes can be divided into cold field emission scanning electron microscopes and hot field emission scanning electron microscopes according to the light source performance. Cold field emission scanning electron microscopy has high requirements for vacuum conditions, unstable beam current, short service life of the emitter, and the need to clean the tip regularly. It is limited to a single image observation and has a limited application range; while thermal field emission scanning electron microscopy not only continuously It has a long working time and can be used with a variety of accessories to achieve comprehensive analysis. In the field of geology, we not only need to conduct preliminary morphological observations of samples, but also need to combine analyzers to analyze other properties of the samples, so thermal field emission scanning electron microscopy is more widely used.
The scanning electron microscope (SEM) is a large-scale precision instrument used for high-resolution micro-region morphology analysis. It has the characteristics of large depth of field, high resolution, intuitive imaging, strong three-dimensional sense, wide magnification range, and the sample to be tested can be rotated and tilted in three-dimensional space. In addition, it has the advantages of rich types of measurable samples, almost no damage or contamination of the original sample, and the ability to obtain morphology, structure, composition and crystallographic information at the same time. At present, scanning electron microscopes have been widely used in microscopic research in the fields of life sciences, physics, chemistry, justice, earth sciences, materials science, and industrial production. In earth sciences alone, it includes crystallography, mineralogy, and mineral deposits. , sedimentology, geochemistry, gemology, micropaleontology, astronomical geology, oil and gas geology, engineering geology and structural geology, etc.
Although scanning electron microscopy is a rising star in the microscope family, it is developing rapidly due to its many advantages.
1. The resolution of the instrument is high. It can observe details of about 6nm on the surface of the sample through the secondary electron image. Using the LaB6 electron gun, it can be further improved to 3nm.
2 The instrument's magnification has a wide range of changes and can be continuously adjusted. Therefore, you can choose different sizes of fields of view for observation according to your needs. At the same time, you can also obtain high-brightness clear images at high magnification that are difficult to achieve with general transmission electron microscopes.
3. The depth of field for observing the sample is large, the field of view is large, and the image is full of three-dimensionality. The rough surface with large fluctuations and the uneven metal fracture image of the sample can be directly observed, giving people the feeling of visiting the microscopic world in person.
4. The sample preparation is simple. As long as the block or powder sample is slightly processed or not processed, it can be directly placed in the scanning electron microscope for observation, so it is closer to the natural state of matter.
5. Image quality can be effectively controlled and improved through electronic methods, such as automatic maintenance of brightness and contrast, sample tilt angle correction, image rotation, or improvement of image contrast tolerance through Y modulation, as well as the brightness and darkness of each part of the image. Moderate. Using a dual magnification device or image selector, images with different magnifications can be observed on the fluorescent screen at the same time.
6 Comprehensive analysis can be carried out. Equipped with a wavelength dispersive X-ray spectrometer (WDX) or energy dispersive X-ray spectrometer (EDX), it has the function of an electron probe and can also detect reflected electrons, X-rays, cathode fluorescence, transmission electrons, and Auger emitted by the sample. Electronics etc. The expanded application of scanning electron microscopy to various microscopic and micro-area analysis methods shows the versatility of scanning electron microscopy. In addition, you can also analyze selected micro-areas of the sample while observing the morphology image; by installing the semiconductor sample holder accessory, you can directly observe the PN junction and microscopic defects in the transistor or integrated circuit through the electromotive force image amplifier. Since many scanning electron microscope electron probes have realized automatic and semi-automatic control by electronic computers, the speed of quantitative analysis has been greatly improved.
