Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) focus on the surface of a sample: its structure and properties.
A fine probe, invisible to the naked eye, scans the surface of the sample point by point, at a distance of just a few nanometers. The final images are very high-resolution maps (nanometer scale) of the sample surface. They provide information on topography, roughness and various surface properties (magnetic, mechanical and electrical).
AFM allows imaging in air as well as in a liquid environment.
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Local collaboration with CEISAM as part of ANR AZOTICS.
A STM microscope can image a material surface at an atomic scale
The Scanning Tunnelling Microscope (STM)enables imaging the surface of a material at an atomic scale in the direct space and probing the local density of electronic states. To do so, it measures the tunnelling current generated between a metal tip and a conductive sample when there is a potential difference between the two.
The opposite figure shows the STM image of a 1T-TaS2 sample surface obtained in constant-current imaging mode at room temperature. It shows both the atomic lattice and the super lattice of charge density waves.
Sample: IMN, L. Cario and E. Janod.
Images: IMN, P. Bertoncini.
A MFM microscope can determine magnetic domains and magnetic field variations on a sample surface
A Magnetic Force Microscope (MFM) is an Atomic Force Microscope (AFM) with a magnetic tip. The forces being measured result from interactions between the magnetic tip and the surface, and the signal being collected reflects variations in the magnetisation of the sample surface. MFM images are representative of magnetic domains and also reflect variations in magnetic fields at the surface of a sample.
The opposite figure shows the topography of the sample (left) and the mapping of the magnetic domains (MFM phase image) of a Duplex steel.
Sample: IMN, E. Bertrand and P. Paillard.
Images: IMN, P. Bertoncini.
Determining force-distance curves:
AFM allows force-distance curves to be recorded by bringing the AFM tip into contact with the sample surface and then moving it away.
By determining the surface topography, the approach curves can be used to quantify the mechanical deformation and extract the elastic modulus.
Shrinkage curves can be used to measure various adhesion forces between the AFM tip and the sample, interaction forces, stretching of molecules, and so on.
The opposite figure shows an example of approach force (grey) and withdrawal (black) curves. They were recorded when a living cell immobilized on a microlevier was brought into contact with the surface of a Petri dish before being detached.
Curves: IMN, P. Bertoncini.
© IMN – Mentions légales
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