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UPV
 
Atomic force and scanning tunnel microscope
Electron Microscopy Service Atomic force and scanning tunnel microscope  ...

In the atomic force microscope (AFM), a sharp tip at the end of a flexible cantilever passes over the surface of the sample, maintaining a constant, low interaction force. The scanning movement is achieved with a piezoelectric scanner, and tip/sample interaction is monitored by reflecting a laser on the back of the cantilever, which is collected by a photodiode detector. The photodiode is divided into 4 segments and the different voltages between the different segments (general the 2 upper segments compared to the 2 lower segments) accurately determine changes in tip slope or oscillation amplitude.

The UPV Microscopy Service offers the following work modes:

Contact AFM: measures topography by dragging the tip over the surface sample. Can be conducted in air or liquid environments.

Tapping AFM: measures topography by intermittently touching the sample surface with an oscillating tip. Lateral forces and pressure are eliminated; these can damage soft samples and reduce image resolution. Can be conducted in air or liquid environments.

Phase Image: provides a contrasted image caused by differences in the sample surface adhesion and viscoelasticity properties. This is conducted in Tapping mode and measures the delay in the tip oscillation phase measured in the photodiode compared to the oscillation phase value provided by the tip support piezo element.

Scanning Tunnel Microscope: measures the topography of conductive surfaces using a tunnelling current that depends on the separation between the tip and the sample surface.

Magnetic Forces: measures the gradient of magnetic force distribution above the sample surface. It is conducted in Lift Mode to follow the sample topography at a set distance.

Lift Mode: this is a two-step combined technique: on one hand, it measures the sample topography in Tapping mode, and on the other it measures another selected property (magnetic or electrical forces, etc.) using the topographic information to maintain the tip above the sample surface at a constant height.

Lateral Forces: measures friction forces between the tip and the sample surface in Contact mode.

Force-Distance Measurements: measures repulsive, adhesion and attraction forces between the tip and the sample during approach, contact and separation.

Volume Force: takes a series of specific force-distance measurements on a certain area of the sample. It uses these individual force curves at each point to show images of sample force variations and topography.

Electrochemical: measures changes in the surface and properties of the conductive materials immersed in electrolytic solutions by establishing electrical intensity-voltage gradients or cycles.


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