STM requires the surface of the sample to be conductive, while AFM can test the surface morphology and properties of the insulator. Because the basic principle of STM is to measure the surface morphology by measuring the tunneling current between the probe and the sample surface, while AFM is to measure the interaction force between the probe and the sample surface. AFM consists of four parts: mechanical motion part, optical detection system of cantilever beam deflection signal, control signal feedback system, imaging and information processing software system. The interaction between the probe and the sample deflects the microcantilever upward or downward. The end of the cantilever is irradiated with laser, and the position change of the reflected light is used to measure the offset of the cantilever. This detection method was first proposed by Meyer and Amer. The motion of the mechanical part (up and down and lateral scanning motion of the probe) is controlled by precise piezoelectric ceramics. PSD is used for laser reflection detection. The feedback and imaging system controls the distance between the probe and the sample surface, and finally processes the experimental test results.
AFM working mode of atomic force microscope
With the development of AFM technology, various new applications are constantly emerging. Specifically, it includes the following technologies:
(1) the earliest contact mode, the probe is in direct contact with the sample, and the probe is easy to wear, so the probe is required to be soft, that is, the elastic coefficient of the cantilever is small, generally less than1n/m.
(2) The tapping mode is also called power or intermittent contact. The probe vibrates under the action of external force, and part of the vibration position of the probe enters the repulsive area of the force curve, so the probe contacts the sample surface intermittently. The probe needs a high cantilever elastic coefficient to avoid biting with the micro-layer water film on the surface of the sample. The tapping mode has little force on the sample, which is especially beneficial to improve the resolution of soft samples. At the same time, the life of the probe is slightly longer than that of the contact type.
The above is the most commonly used AFM mode, and there are many other modes, such as
Lateral force microscope (transverse force microscope, which can detect the transverse friction of the micro-area on the surface of the sample to the probe and obtain the mechanical properties of the material),
Non-contact force (non-contact microscope, basically the same as percussion, except that the non-contact probe works in the attractive area of force curve),
Force modulation microscope (force modulation microscope, the probe has great force to detect the micro-area on the surface of the sample, and the mechanical properties such as elastic coefficient of the micro-area of the material can be obtained),
CFM chemical force microscope
Electron microscope force microscope
KFM· kelvin force microscope
MFM magnetic microscope
Scanning thermal microscope
Single chip microcomputer scanning capacitance microscope
SCPM scanning chemical potential microscope
scanning electrochemical microscopy, secm
SICM scanning ion conductivity microscope
SKPM scanning kelvin probe microscope
Scanning thermal microscope
STOS scanning tunnel spectrometer
Various modes and applications require probes with different properties, and the performance index of the probe is the most critical factor to determine the resolution of the microscope.