13-05-2011, 03:12 PM
Presented by:
Dhwani
Varuna
[attachment=13784]
Atomic force microscopy
It is also known as scanning force microscopy.
AFM is a very high resolution type of scanning probe microscopy , with resolution of order of a fraction of nanometer.
AFM is one of the foremost tools for imaging , measuring and manipulating matter at the nanoscale.
Modes of AFM
There are three modes in which AFM can be operated depending on application:-
1. Static mode (contact).
2. Dynamic mode(non contact).
3. Tapping mode.
Static mode
Feedback-static tip deflection.
Attractive forces-strong,causing the tip to ‘snap in’ to the surface.
Force is repusive.
Dynamic mode
In the dynamic mode, the cantilever is externally oscillated at or close to its fundamental resonance frequency or a harmonic . The oscillation amplitude, phase and resonance frequency are modified by tip-sample interaction forces.
Non-contact mode AFM does not suffer from tip or sample degradation effects that are sometimes observed after taking numerous scans with contact AFM. This makes non-contact AFM preferable to contact AFM for measuring soft samples as shown in fig.
Schemes for dynamic mode operation include
frequency modulation and
the more common amplitude modulation .
Tapping mode
In tapping mode, the cantilever is driven to oscillate up and down at near its resonance frequency by a small piezoelectric element mounted in the AFM tip holder similar to non-contact mode.
Due to the interaction of forces acting on the cantilever when the tip comes close to the surface, Van der Waals force, dipole-dipole interaction, electrostatic forces, etc cause the amplitude of this oscillation to decrease as the tip gets closer to the sample.
Dhwani
Varuna
[attachment=13784]
Atomic force microscopy
It is also known as scanning force microscopy.
AFM is a very high resolution type of scanning probe microscopy , with resolution of order of a fraction of nanometer.
AFM is one of the foremost tools for imaging , measuring and manipulating matter at the nanoscale.
Modes of AFM
There are three modes in which AFM can be operated depending on application:-
1. Static mode (contact).
2. Dynamic mode(non contact).
3. Tapping mode.
Static mode
Feedback-static tip deflection.
Attractive forces-strong,causing the tip to ‘snap in’ to the surface.
Force is repusive.
Dynamic mode
In the dynamic mode, the cantilever is externally oscillated at or close to its fundamental resonance frequency or a harmonic . The oscillation amplitude, phase and resonance frequency are modified by tip-sample interaction forces.
Non-contact mode AFM does not suffer from tip or sample degradation effects that are sometimes observed after taking numerous scans with contact AFM. This makes non-contact AFM preferable to contact AFM for measuring soft samples as shown in fig.
Schemes for dynamic mode operation include
frequency modulation and
the more common amplitude modulation .
Tapping mode
In tapping mode, the cantilever is driven to oscillate up and down at near its resonance frequency by a small piezoelectric element mounted in the AFM tip holder similar to non-contact mode.
Due to the interaction of forces acting on the cantilever when the tip comes close to the surface, Van der Waals force, dipole-dipole interaction, electrostatic forces, etc cause the amplitude of this oscillation to decrease as the tip gets closer to the sample.