Atomic force microscopy controller and method

1. A method for determining a loop response for an apparatus for an atomic force microscope, the method comprising:

determining a loop response for an on-surface movement of a cantilever over a frequency range;

determining a loop response for an off-surface movement of the cantilever over the frequency range; and

adjusting an output of the controller at a frequency based on the loop response for the off-surface movement.

2. A method as claimed in claim 1 , wherein the determining the loop response for off-surface movement of the cantilever comprises determining a resonance condition for the cantilever.

3. A method as claimed in claim 2 , further comprising, after the determining the resonance condition, reducing a gain of the controller at a frequency of the resonance condition.

4. A method as claimed in claim 2 , wherein the determining the loop response for the off-surface movement of the cantilever comprises providing a notch filter having a center frequency at the resonance condition.

5. A method as claimed in claim 2 , further comprising, after the adjusting, determining a second resonance condition for the cantilever.

6. A method as claimed in claim 5 , further comprising, after determining the second resonance condition, providing a second notch filter having a center frequency at the second resonance condition.

7. A computer readable medium having a computer readable program code embodied therein, the computer readable program code adapted to be executed by a computer to implement a method for determining a loop response for an apparatus for an atomic force microscope, the method comprising:

determining a loop response for an on-surface movement of a cantilever over a frequency range;

determining a loop response for an off-surface movement of the cantilever over the frequency range; and

adjusting an output of the controller at a frequency based on the loop response for the off-surface movement.

8. A computer readable medium as claimed in claim 7 , wherein the determining the loop response for off-surface movement of the cantilever comprises determining a resonance condition for the cantilever.

9. A computer readable medium as claimed in claim 8 , wherein the method further comprises, after the determining the resonance condition, reducing a gain of the controller at a frequency of the resonance condition.

10. A computer readable medium as claimed in claim 8 , wherein the determining the loop response for the off-surface movement of the cantilever comprises providing a notch filter having a center frequency at the resonance condition.

11. A computer readable medium as claimed in claim 8 , further comprising, after the adjusting, determining a second resonance condition for the cantilever.

12. A computer readable medium as claimed in claim 11 , further comprising, after determining the second resonance condition, providing a second notch filter at the resonance condition.

13. An atomic force microscopy (AFM) system, comprising:

a cantilever;

a probe tip connected at a first end of the cantilever;

an actuator connected to a second end of the cantilever; and

a controller configured to: determine a loop response for an on-surface movement of a cantilever over a frequency range; determine a loop response for an off-surface movement of the cantilever over the frequency range; and adjust an output of the controller at a frequency based on the loop response for the off-surface movement.

14. An AFM system as claimed in claim 13 , wherein the actuator is a piezoelectric actuator.

15. An AFM system as claimed in claim 13 wherein the controller determines a resonance condition for the cantilever.

16. An AFM system claimed in claim 15 , wherein the resonance condition is an off-surface resonance condition.

17. An AFM as claimed in claim 16 , wherein the controller comprises a notch filter at the off-surface resonance condition.

18. An AFM system as claimed in claim 15 , wherein the gain is less than zero at the off-surface resonance condition.