Structure and working principle of scanning electron microscope
From the cathode of the electron gun issued by the diameter of 20 (m ~ 30 (m) of the electron beam, by the cathode and anode between the role of the accelerating voltage, shot to the mirror barrel, through the condenser mirror and the objective lens of the convergence effect, narrowed into a diameter of about a few millimetres of the electron probe. Under the action of the scanning coil on the upper part of the objective lens, the electron probe makes a grating scan on the sample surface and excites a variety of electronic signals. These electronic signals are detected by the corresponding detector, amplified, converted and transformed into a voltage signal, which is then sent to the gate of the picture tube and modulates the brightness of the picture tube. Electron beam in the tube in the fluorescent screen also for raster scanning, and this scanning movement and the sample surface of the electron beam scanning movement is strictly synchronised, so that the degree of liner and the received signal strength corresponding to the scanning electron image, this image reflects the sample surface topographic features. ** section scanning electron microscopy biological sample preparation techniques Most biological samples contain water and are relatively soft, therefore, before carrying out scanning electron microscopy observation, the sample should be treated accordingly. Scanning electron microscopy sample preparation of the main important precision: as far as possible to make the sample surface structure is well preserved, no deformation and contamination, the sample is dry and has good electrical conductivity.
Characteristics of scanning electron microscope
(i) It can directly observe the structure of the sample surface, and the size of the sample can be as large as 120mm×80mm×50mm.
(ii) The sample preparation process is simple and there is no need to cut into thin slices.
(iii) The sample can be translated and rotated in three degrees of space in the sample chamber, so that the sample can be observed from various angles.
(D) The depth of field is large, and the image is rich in three-dimensional sense. The depth of field of the scanning electron microscope is hundreds of times larger than that of the optical microscope, and tens of times larger than that of the transmission electron microscope.
(E) the image of a wide range of magnification, resolution is also relatively high. Can be magnified a dozen times to hundreds of thousands of times, it basically includes from the magnifying glass, optical microscope until the transmission electron microscope magnification range. Resolution between the optical microscope and transmission electron microscope, up to 3nm.
(vi) The degree of damage and contamination of the sample by the electron beam is small.
(vii) While observing the morphology, other signals emitted from the sample can be used for micro-area composition analysis.
