Method and apparatus of operating a scanning probe microscope
View Patent ↗An improved mode of AFM imaging (Peak Force Tapping (PFT) Mode) uses force as the feedback variable to reduce tip-sample interaction forces while maintaining scan speeds achievable by all existing AFM operating modes. Sample imaging and mechanical property mapping are achieved with improved resolution and high sample throughput, with the mode workable across varying environments, including gaseous, fluidic and vacuum.
1. A method of operating a scanning probe microscope (SPM) comprising:
generating relative motion between a probe and a sample,
detecting motion of the probe;
recovering, from the detected probe motion, a probe deflection based on a probe-sample interaction, the recovered probe deflection being substantially independent of parasitic probe deflection, wherein the parasitic probe deflection is caused by the hydrodynamic background associated with operation of the SPM, and wherein the recovering step includes subtracting the hydrodynamic background from the detected probe motion by using a field programmable gate array (FPGA) processor; and
controlling the SPM in real time using the recovering step.
2. The method of claim 1 , where an amplitude of the probe-sample interaction is less than an amplitude of the parasitic probe deflection.
3. The method of claim 1 , further comprising identifying an instantaneous force associated with the interaction.
4. The method of claim 3 , wherein the generating step includes providing relative oscillatory motion between the probe and the sample, and wherein the instantaneous force is identified prior to the completion of one cycle of the oscillatory motion.
5. The method of claim 4 , further comprising using the instantaneous force to maintain a setpoint during imaging.
6. The method of claim 5 , wherein the instantaneous force is a repulsive force.
7. The method of claim 5 , wherein the instantaneous force is a peak force.
8. The method of claim 5 , wherein a minimum controllable force corresponding to the instantaneous force is less than about 1000 μN.
9. The method of claim 8 , wherein the minimum controllable force is less than about 1 nN.
10. The method of claim 9 , wherein the minimum controllable force is less than about 10 pN.
11. The method of claim 8 , wherein the detected probe motion is synchronously averaged to reduce the minimum controllable force.
12. The method of claim 1 , wherein the recovering step comprises determining a probe deflection magnitude resulting from the probe-sample interaction, and wherein the probe deflection magnitude corresponds to a force between the probe and the sample.
13. The method of claim 12 , wherein the magnitude of the probe deflection is less than the magnitude of the parasitic probe deflection.
14. The method of claim 13 , wherein the parasitic probe deflection corresponds to any relative periodic motion between the probe and the sample when the probe is not interacting with the sample.
15. The method of claim 13 , wherein the parasitic probe deflection is caused by the hydrodynamic background associated with operation of the SPM.
16. The method of claim 4 , further comprising using the instantaneous force to initially engage the probe and the sample.
17. The method of claim 4 , wherein a peak force between the probe and the sample is an instantaneous force.
18. The method of claim 5 , wherein the force is an attractive force.
19. The method of claim 1 , further comprising acquiring an image with a resolution of less than 100 nm.
20. The method of claim 19 , wherein the resolution is less than 10 nm.
21. The method of claim 1 , further comprising determining at least one mechanical property of a sample material from the recovering step, wherein the mechanical property is at least one of hardness, stiffness, adhesion, plasticity, and elasticity.
22. The method of claim 1 , further comprising acquiring an image with a maximum tracking force of less than 100 pN.
23. The method of claim 1 , wherein the generating step includes oscillating the probe, and wherein the oscillating probe overcomes an attractive force between the tip and the sample substantially independent of the oscillation energy stored in the oscillating probe, wherein the attractive force is due to adhesion between the tip and the sample.
24. The method of claim 23 , wherein the method is operable with any cantilever having a spring constant between about less than 0.1 N/m and 1000 N/m.
25. The method of claim 1 , wherein the generating step is controlled by a feedback loop using a pre-determined synchronous distance in each interaction period.
26. A method of operating a scanning probe microscope (SPM) comprising:
generating relative motion between a probe mad a sample;
detecting motion of the probe;
recovering, from the detected probe motion, a probe deflection based on a probe-sample interaction, the recovered probe deflection being substantially independent of parasitic probe deflection such that the recovered probe deflection is based substantially only on one or more forces resulting from the probe-sample interaction;
wherein the parasitic probe deflection is caused by the hydrodynamic background associated with operation of the SPM, and wherein the recovering step includes subtracting the hydrodynamic background from the detected probe motion by using a field programmable gate array (FPGA) processor; and
controlling said generating step in real time based on only a part of the recovered probe deflection.
27. The method of claim 1 , wherein the FPGA performs at least one of lock-in amplification and synchronous averaging to subtract the hydrodynamic background.