Forskjell mellom versjoner av «Atomic Force Microscopy»
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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. |
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. |
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| − | Interaction model lies behind different modes: |
+ | Interaction model (surface forces) lies behind different modes: |
| + | *Strongly affected by surface adsorbates and gaseous/liquid environment. |
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| + | Three interaction zones: |
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| + | *Non-contact zone: Only long range forces are experienced. Usually attractive. Coulomb forces - strongest long range forces (can be repulsive as well). |
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| + | *Semi-contact region: Similar magnitude of repulsive and attractive forces. |
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| + | *Contact zone: Attractive forces are negligible. Short range repulsive forces dominate. |
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| + | The forces: |
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* Strong long-range forces: Coulomb forces |
* Strong long-range forces: Coulomb forces |
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* Shorter distances: Van der Waals (kålloidal kemmistri!) These forces decay rapidly, with <math>f \propto d^{-7}</math> |
* Shorter distances: Van der Waals (kålloidal kemmistri!) These forces decay rapidly, with <math>f \propto d^{-7}</math> |
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Revisjonen fra 24. mai 2009 kl. 12:19
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 (surface forces) lies behind different modes:
- Strongly affected by surface adsorbates and gaseous/liquid environment.
Three interaction zones:
- Non-contact zone: Only long range forces are experienced. Usually attractive. Coulomb forces - strongest long range forces (can be repulsive as well).
- Semi-contact region: Similar magnitude of repulsive and attractive forces.
- Contact zone: Attractive forces are negligible. Short range repulsive forces dominate.
The forces:
- 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 highest resolution.
Two sub-modes:
- Set height constant and measure repulsive force.
- Set repulsive 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.
