The difference between an electron microscope, an atomic force microscope and a scanning tunnelling microscope
I. Characteristics of scanning electron microscope Compared with optical microscope and transmission electron microscope, scanning electron microscope has the following characteristics:
(i) the ability to directly observe the structure of the sample surface, the size of the sample can be as large as 120mm × 80mm × 50mm.
(ii) The sample preparation process is simple, without having 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.
(iv) The depth of field is large, and the image is rich in three-dimensional sense. The depth of field of SEM is hundreds of times larger than that of optical microscope and tens of times larger than that of transmission electron microscope.
(E) image magnification range is wide, the 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 damage and contamination of the sample by the electron beam is small.
(vii) While observing the morphology, other signals emitted from the sample can also be used for micro-area composition analysis.
II-Atomic Force Microscope
Atomic Force Microscope (AFM), an analytical instrument that can be used to study the surface structure of solid materials, including insulators. It investigates the surface structure and properties of substances by detecting the extremely weak interatomic interaction forces between the surface of the sample to be tested and a miniature force-sensitive element. A pair of micro-cantilevers, which are extremely sensitive to weak forces, are fixed at one end, and a tiny needle tip at the other end is brought close to the sample, which will then interact with it, and the force will cause the micro-cantilevers to deform or change their state of motion. When scanning the sample, these changes are detected by sensors, and information on the distribution of the force can be obtained, thus obtaining information on the surface morphology and structure as well as surface roughness with nanometre resolution.
AFM has many advantages over scanning electron microscopy. Unlike electron microscopes, which can only provide two-dimensional images, AFM provides true three-dimensional surface maps. Also, AFM does not require any special treatment of the sample, such as copper or carbon plating, which can cause irreversible damage to the sample. Thirdly, while electron microscopes need to operate under high vacuum conditions, AFMs work well at atmospheric pressure and even in liquid environments. This can be used to study biological macromolecules and even living biological tissues. AFM has a wider applicability than Scanning Tunneling Microscope (STM) due to its ability to observe non-conducting samples. Scanning force microscopes, which are currently widely used in scientific research and industry, are based on atomic force microscopy.
Scanning Tunneling Microscope
① high-resolution scanning tunnelling microscope with atomic-level spatial resolution, its horizontal spatial resolution of l, vertical resolution of 0.1, ② scanning tunnelling microscope can be used in the field of atomic force microscopy.
② scanning tunnelling microscope can directly probe the surface structure of the sample, can draw a three-dimensional structural image.
③ Scanning tunnelling microscope can probe the structure of substances in vacuum, atmospheric pressure, air, and even in solution. Since there is no high-energy electron beam, there is no damage to the surface (e.g., radiation, thermal damage, etc.), so it is possible to study the structure of biomolecules and the surface of living cell membranes in a physiological state, and the samples will not be damaged and remain intact.
④ Scanning tunneling microscope has a fast scanning speed, short data acquisition time, and fast imaging, which makes it possible to carry out kinetic studies of life processes.
⑤ It does not require any lens and is small in size, so some people call it a "pocket microscope".
