Method and apparatus for measuring electrical properties in torsional resonance mode

1. A method of operating a scanning probe microscope (SPM) including a probe having a cantilever, the method comprising the steps of:

measuring an electrical property between a probe of the SPM and a sample while oscillating the cantilever at or near a resonance of the cantilever, the resonance being at least one of a torsional resonance and a lateral resonance and wherein the cantilever extends along the sample and includes a tip extending substantially orthogonally to the sample; and

maintaining a probe-sample separation less than about 10 nm.

2. The method of claim 1 , wherein the separation is between about 1 and 5 nanometers.

3. The method of claim 1 , further comprising the step of adjusting the probe-sample separation based on a measurement of a property of the torsional oscillation of the cantilever.

4. The method of claim 3 , wherein the torsional resonance frequency is between about 1 kHz and 10 GHz.

5. The method of claim 3 , wherein said adjusting step includes using a feedback loop.

6. The method of claim 1 , wherein the sample is one of a group including a conducting polymer, an organic LED, a biomolecule, a carbon nanotube, a nanowire, a semiconductor, and a biological cell.

7. The method of claim 1 , wherein the electrical property is an electrical current, and said measuring step includes using a pA-amplifier to generate a current output signal.

8. The method of claim 7 , wherein said measuring step includes filtering the current output signal.

9. The method of claim 1 , wherein the probe is conductive and a DC bias voltage is applied between the probe and the sample.

10. The method of claim 1 , wherein the probe is sufficiently stiff to maintain a tip-sample separation of between about 1 nm and 5 nm during operation.

11. The method of claim 10 , wherein the stiffness of the probe is between about 0.1 to 1000 N/m.

12. The method of claim 11 , wherein the stiffness is between 1 to 40 N/m.

13. The method of claim 1 , wherein the probe is a self-actuated probe having a cantilever including an active element.

14. The method of claim 13 , wherein the self-actuated probe includes a piezoelectric drive actuator disposed on a backside of a cantilever of the self-actuated probe.

15. The method of claim 1 , further comprising the step of applying a DC bias voltage between the tip of the probe and a surface of the sample so as to generate a current between the tip and the surface.

16. The method of claim 15 , wherein the current is less than 500 pA.

17. The method of claim 16 , wherein the current is between about 60 fA and 120 pA.

18. The method of claim 15 , further comprising varying at least one of the bias voltage and probe-sample separation.

19. The method of claim 18 , wherein said varying step includes performing a local spectroscopy measurement including varying the bias voltage at a constant probe-sample separation.

20. The method of claim 15 , wherein the bias voltage is a positive bias voltage.

21. The method of claim 1 , wherein the electrical property is a capacitance and is indicative of an SCM measurement.

22. The method of claim 1 , wherein the electrical property is in the frequency range of an electromagnetic field from DC to Tera Hz.

23. The method of claim 1 , wherein the electrical property is based on an optical spectroscopy due to local electromagnetic polarization.

24. The method of claim 1 , further comprising simultaneously measuring topography of the sample.

25. The method of claim 1 , wherein a force between the probe and the sample is maintained at an amount generally less than about 50 nN.

26. The method of claim 25 , wherein the amount is less than about 25 nN.

27. The method of claim 26 , wherein the amount is less than about 1 nN.

28. A method of operating a scanning probe microscope (SPM) including a probe having a cantilever, the method comprising the steps of:

measuring an electrical property between a probe of the SPM and a sample while oscillating the cantilever at or near a resonance of the cantilever, the resonance being at least one of a torsional resonance and a lateral resonance; and

adjusting the probe-sample separation based on a measurement of a property of the torsional oscillation of the cantilever.

29. The method of claim 28 , wherein the sample is one of a group including a conducting polymer, an organic LED, a biomolecule, a carbon nanotube, ananowire, a semiconductor, and a biological cell.

30. The method of claim 28 , wherein said adjusting step includes using a feedback loop.

31. The method of claim 28 , wherein the separation is less than about 10 nanometers.

32. The method of claim 31 , wherein the separation is between about 1 and 5 nanometers.

33. The method of claim 28 , wherein the torsional resonance frequency is between about 1 kHz and 10 GHz.

34. The method of claim 28 , wherein the probe is a self-actuated probe having a cantilever including an active element.

35. A method of operating a scanning probe microscope (SPM) including a probe having a cantilever, the method comprising the steps of:

measuring an electrical property between a probe of the SPM and a sample while oscillating the cantilever at or near a resonance of the cantilever, the resonance being at least one of a torsional resonance and a lateral resonance; and

wherein the probe is a self-actuated probe having a cantilever including an active element, and wherein the self actuated probe includes a piezoelectric drive actuator disposed on a backside of a cantilever of the self-actuated probe.

36. The method of claim 1 , wherein a bias voltage is applied between the probe and the sample so as to measure the electrical property using a tunneling current in a range of about 60 fA and 120 pA.