Method and apparatus of operating a scanning probe microscope
Methods and apparatuses are provided for automatically controlling and stabilizing aspects of a scanning probe microscope (SPM), such as an atomic force microscope (AFM), using Peak Force Tapping (PFT) Mode. In an embodiment, a controller automatically controls periodic motion of a probe relative to a sample in response to a substantially instantaneous force determined, and automatically controls a gain in a feedback loop. A gain control circuit automatically tunes a gain based on separation distances between a probe and a sample to facilitate stability. Accordingly, instability onset is quickly and accurately determined during scanning, thereby eliminating the need of expert user tuning of gains during operation.
1. A method for monitoring effectiveness of a scanning probe microscope (SPM), the method comprising:
providing relative motion between a probe and a sample and controlling that motion using a feedback loop in peak force tapping (PFT) mode;
detecting an attractive force between the probe and the sample; and
comparing the attractive force to a predetermined threshold in real time with operation of the controlling step.
2. The method of claim 1 , wherein the attractive force substantially results from an adhesion force between the probe and the sample.
3. The method of claim 2 , wherein the adhesion force is determined according to a maximum adhesion force.
4. The method of claim 2 , wherein the adhesion force is determined according to an integration of a work of adhesion with respect to a departure point from and a return point to a non-interacting zero force baseline.
5. The method of claim 1 , wherein the attractive force substantially results from van der Waals forces.
6. The method of claim 5 , wherein the van der Waals forces are determined according to a slope with respect to a non-interacting zero force baseline.
7. A method for monitoring tip health of a probe of a scanning probe microscope (SPM) during SPM operation, the method comprising:
providing relative motion between a probe and a sample and controlling the motion using peak force tapping (PFT) mode;
providing relative scanning motion between the probe and the sample so the controlling step is performed at multiple pixels along a scan line;
generating a force curve at each pixel; and
automatically determining tip health at each pixel in real time with the controlling step.
8. The method of claim 7 , further comprising detecting an attractive force between the probe and the sample; and
comparing the attractive force to a predetermined threshold.
9. The method of claim 8 , wherein the attractive force substantially results from an adhesion force between the probe and the sample.
10. The method of claim 9 , wherein the adhesion force is determined according to a maximum adhesion force.
11. The method of claim 9 , wherein the adhesion force is determined according to an integration of a work of adhesion with respect to a departure point from and a return point to a non-interacting zero force baseline.
12. The method of claim 8 , wherein the attractive force substantially results from van der Waals forces.
13. The method of claim 12 , wherein the van der Waals forces are determined according to a slope with respect to a non-interacting zero force baseline.
14. The method of claim 13 , wherein the determining step is performed at least every 300 microseconds.
15. The method of claim 7 , further comprising determining a slope of a portion of the force curve corresponding to an attractive force, wherein the slope is indicative of tip health.
16. The method of claim 15 , wherein the attractive force is caused by van der Waals force.