Method and apparatus for measuring electrical properties in torsional resonance mode
View Patent ↗The preferred embodiments are directed to a method and apparatus of operating a scanning probe microscope (SPM) including oscillating a probe of the SPM at a torsional resonance of the probe, and generally simultaneously measuring an electrical property, e.g., a current, capacitance, impedance, etc., between a probe of the SPM and a sample at a separation controlled by the torsional resonance mode. Preferably, the measuring step is performed while using torsional resonance feedback to maintain a set-point of SPM operation.
1. An apparatus for measuring a sample comprising:
a probe holder supporting a probe having a tip extending substantially orthogonally to the sample;
a torsional resonance mode actuator that couples energy to said probe to oscillate said probe at a torsional resonance thereof;
a conductor, wherein said conductor is in electrical communication with said probe;
an electrical property measuring detector for measuring an electrical property of the sample, wherein the sample is disposed between said probe and said conductor; and
a feedback loop that operates to maintain a probe-sample separation less than about 10 nm based on changes in the torsional oscillation of the probe.
2. The apparatus of claim 1 , wherein the electrical property is a current.
3. The apparatus of claim 1 , wherein the electrical property is a capacitance.
4. The apparatus of claim 1 , wherein the electrical property is in the frequency range of an electromagnetic field from DC to Tera Hz.
5. The apparatus of claim 1 , wherein the electrical property is based on optical spectroscopy of local electromagnetic polarization.
6. The apparatus of claim 1 , wherein the probe-sample separation is less than about 5 nm.
7. The apparatus of claim 1 , wherein the sample has an elastic modulus less than about 1 GPa.
8. The apparatus of claim 1 , wherein the probe holder is shielded.
9. The apparatus of claim 1 , wherein the sample is bound to a surface with a force approximately less than a chemical bounding force between the two.
10. The apparatus of claim 1 , wherein the torsional resonance is between about 1 kHz and 10 GHz.
11. The apparatus of claim 1 , wherein the probe is conductive and a DC bias voltage is applied between the probe and the sample.
12. The apparatus of claim 11 , wherein a current flowing between the probe and the sample is less than about 500 pA.
13. The apparatus of claim 12 , wherein the current is between about 60 fA and 120 pA.
14. The apparatus of claim 1 , wherein a stiffness of the probe is between about 0.1 to 1000 N/m.
15. The apparatus of claim 14 , wherein the stiffness is between 1 to 40 N/m.
16. The apparatus of claim 1 , wherein the probe is a self-actuated probe having a cantilever including an active element.
17. The apparatus 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.