Atomic Force Microscope Multi-Environment Scanning-Under-Liquid Scanning-TRUTH INSTRUMENTS

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Atomic Force Microscope Multi-Environment Scanning-Under-Liquid Scanning

Release time:

2024-08-20

Atomic Force Microscope (AFM) is a kind of measuring equipment which uses micro-cantilever to sense and amplify the force between the probe tip on the micro-cantilever and the atoms of the sample, so as to characterize the surface morphology of the sample. It not only produces three-dimensional images of samples at atomic resolution in air, but also high-resolution images of sample surfaces in liquid environments.

An article to take you to understand the atomic force microscope under the liquid scanning

Structure diagram of atomic force microscope

Since the atomic force microscope relies on the force between atoms for imaging, it is easily affected by other factors, especially the widening effect of the needle tip. The tip broadening effect means that the probe is affected by electrostatic force and surface capillary action when measuring in air. Charge may accumulate on the solid surface, and the induced charge will also be generated on the probe, and the Coulomb force between the two will affect the accuracy of the AFM test morphology. Capillary action refers to a layer of water film with a thickness of a few nanometers attached to the surface of a microscopic solid. When the probe is close to the sample, the probe will be adsorbed by the water film, which will seriously affect the scanning results. This effect can be greatly reduced by measuring in a liquid environment, which not only provides a more uniform retarding force for the probe, but also helps to measure a more accurate force-distance curve.

Capillary Action and Liquid Imaging

In the process of scanning under liquid, the biggest problem encountered by the general operator is the refraction phenomenon generated by the laser at the gas-liquid junction, which causes the laser to fail to hit the center of the four-quadrant detector, and the fluctuation of the liquid level will also affect the laser. Therefore, the key to the test under the liquid is to design the glass window at the interface with the air and the liquid to reduce the influence of the above factors.

Light path with glass window

In addition to the above advantages, the advantages of liquid scanning are:

(1) For biological samples: When measuring biological samples in the air, the cells are mostly fixed on the solid surface with a fixative, and it is difficult for the cells to have biological activity. Liquid conditions can mimic physiological conditions, allowing AFM to observe the morphology and interactions of biological molecules such as cells, proteins and DNA under physiological conditions. And the effect of the fixative is avoided, making the sample closer to its natural state.

Visualization of human chromosomes using atomic force microscopy^[1]

(2) For material research: liquid phase AFM can study the surface morphology, roughness and mechanical properties of the solid-liquid interface, and help people improve their understanding of the solid-liquid interface.

For example, the characteristics of high-molecular polymers in water are studied.