Forskjell mellom versjoner av «Atomic Force Microscopy»

Revisjonen fra 24. mai 2009 kl. 11:24

Fun facts

• High vacuum is not necessary.
• Piezoelectric position control system.
• The cantilever: V-shaped or single beam. V-shaped: high deflection sensitivity, not sensitive to torque. Single beam: vice-versa.
• Material used: diamond, tungsten, silicon.
• Artifacts: drift, non-linear hysteresis of piezoelectric.

Modes of operation

It is the displacement of the probe tip at the end of the cantilever that is measured. The modes have different resolution (can someone explain this?). Problem and material determines which mode is used.

Interaction model lies behind different modes:

• Strong long-range forces: Coulomb forces
• Shorter distances: Van der Waals (kålloidal kemmistri!) These forces decay rapidly, with <math>f \propto d^{-7}</math>
• Strong short range forces: Overlapping of electron shells.

Contact mode

In the contact region of the potential energy curve, repulsive forces dominate. This mode has the best resolution.

Two sub-modes:

• Set height constant and measure repulsive force.
• Set force constant and measure height.

Tapping mode

In the semi-contact region of the potential energy curve. Attractive and repulsive forces have similar magnitude.

Non-contact mode

In the non-contact region of the potential energy curve, attractive forces dominate and are measured. What is observed is a an increase in the amplitude of the oscillations of the vibrating probe, translated into a change in attractive forces.