An introduction to scanning electron microscope performance characteristics
There are various types of scanning electron microscopes, and different types of scanning electron microscopes have different performances. 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 microscopy can be divided into cold field emission scanning electron microscopy and thermal field emission scanning electron microscopy according to the performance of the light source. The cold field emission scanning electron microscope requires high vacuum conditions, the beam current is unstable, the emitter has a short service life, and the needle tip needs to be cleaned regularly, which is limited to a single image observation, and the application range is limited; while the thermal field emission scanning electron microscope is not only continuous It can work for a long time, and it can also be combined with a variety of accessories to achieve comprehensive analysis. In the field of geology, we not only need to observe the preliminary morphology of the sample, but also need to analyze other properties of the sample in combination with the analyzer, so the thermal field emission scanning electron microscope is more widely used.
Scanning electron microscope (SEM) is a large precision instrument for high-resolution micro-domain morphology analysis. It has the characteristics of large depth of field, high resolution, intuitive imaging, strong stereoscopic effect, 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 a wide variety of measurable samples, almost no damage and contamination of the original sample, and simultaneous acquisition of morphology, structure, composition, and crystallographic information. At present, scanning electron microscopy has been widely used in microscopic research in the fields of life science, physics, chemistry, justice, earth science, materials science, and industrial production. , Sedimentology, Geochemistry, Gemology, Micropaleontology, Astrogeology, Oil and Gas Geology, Engineering Geology and Structural Geology, etc.
Although the scanning electron microscope is a rising star in the microscope family, due to its many advantages, the development speed is very fast.
1. The resolution of the instrument is relatively high, and the details of about 6nm on the surface of the sample can be observed through the secondary electron image, which can be further improved to 3nm by using a LaB6 electron gun.
2 The magnification of the instrument has a wide range and can be continuously adjusted. Therefore, different fields of view can be selected for observation according to needs, and at the same time, clear images with high brightness, which are difficult to achieve with general transmission electron microscopes, can also be obtained under high magnification.
3 Observing the sample has a large depth of field, a large field of view, and the image is full of three-dimensionality. It can directly observe the rough surface with large undulations and the uneven metal fracture image of the sample, which makes people feel like they are in the microscopic world.
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 the material.
5 It can effectively control and improve the image quality through electronic methods, such as automatic maintenance of brightness and contrast, sample tilt angle correction, image rotation, or improve the tolerance of image contrast through Y modulation, and the brightness and darkness of various parts of the image Moderate. Using a double magnification device or an image selector, images with different magnifications can be observed on the fluorescent screen at the same time.
6 for comprehensive analysis. Install a wavelength dispersive X-ray spectrometer (WDX) or an energy dispersive X-ray spectrometer (EDX) so that it has the function of an electron probe and can also detect reflected electrons, X-rays, cathodofluorescence, transmitted electrons, Auger electronics etc. Extending the application of scanning electron microscopy to various microscopic and micro-area analysis methods shows the versatility of scanning electron microscopy. In addition, it can also analyze the optional micro-region of the sample while observing the topography image; install the semiconductor sample holder accessory, and 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 electronic probes have realized electronic computer automatic and semi-automatic control, the speed of quantitative analysis has been greatly improved.
