Differences among electron microscope, atomic force microscope and scanning tunneling microscope
Characteristics of scanning electron microscope Compared with optical microscope and transmission electron microscope, scanning electron microscope has the following characteristics:
(1) The surface structure of the sample can be directly observed, and the size of the sample can be as large as 120mm×80mm×50mm.
(2) The sample preparation process is simple and does not need to be sliced.
(3) The sample can be translated and rotated in three dimensions in the sample room, so the sample can be observed from various angles.
(4) the depth of field is large, and the image is full of three-dimensional sense. The depth of field of scanning electron microscope is several hundred times larger than that of optical microscope and dozens of times larger than that of transmission electron microscope.
(5) The image has a wide magnification range and high resolution. It can be magnified ten times to hundreds of thousands of times, which basically includes the amplification range from magnifying glass, optical microscope to transmission electron microscope. The resolution is between optical microscope and transmission electron microscope, which can reach 3nm.
(6) The electron beam has less damage and pollution to the sample.
(7) While observing the morphology, we can also use other signals from the sample for micro-area composition analysis.
atomic force microscope
Atomic Force Microscope (AFM) is an analytical instrument that can be used to study the surface structure of solid materials including insulators. It studies the surface structure and properties of matter by detecting the extremely weak interatomic interaction between the surface of the sample to be tested and a micro force sensitive element. One end of a pair of micro-cantilevers, which are extremely sensitive to weak force, is fixed, and the tiny needle tip at the other end is close to the sample. At this time, it will interact with them, and the force will make the micro-cantilevers deform or change their motion state. When scanning the sample, the force distribution information can be obtained by using the sensor to detect these changes, so as to obtain the surface morphology structure information and surface roughness information with nanometer resolution.
Compared with scanning electron microscope, atomic force microscope has many advantages. Unlike the electron microscope, which can only provide two-dimensional images, AFM provides real three-dimensional surface maps. At the same time, AFM does not need any special treatment on the sample, such as copper plating or carbon plating, which will cause irreversible damage to the sample. Thirdly, the electron microscope needs to operate in high vacuum, and the atomic force microscope can work well under normal pressure and even in liquid environment. This can be used to study biological macromolecules and even living biological tissues. Compared with Scanning Tunneling Microscope, atomic force microscope has wider applicability because it can observe non-conductive samples. At present, the scanning force microscope widely used in scientific research and industry is based on atomic force microscope.
STM
① The high-resolution scanning tunneling microscope has the spatial resolution of atomic level, with the horizontal spatial resolution of L and the vertical resolution of 0.1.
(2) Scanning tunneling microscope can directly detect the surface structure of samples and draw three-dimensional structural images.
③ Scanning tunneling microscope can detect the structure of matter in vacuum, normal pressure, air and even solution. Because there is no high-energy electron beam, it has no destructive effect on the surface (such as radiation, thermal damage, etc.), so it can study the surface structure of biological macromolecules and living cell membranes under physiological conditions, and the samples will not be damaged and remain intact.
(4) Scanning tunneling microscope has the advantages of fast scanning speed, short data acquisition time and fast imaging, so it is possible to carry out dynamic research on life process.
⑤ It doesn't need any lens, and it is small in size. Some people call it a "pocket microscope".
