Method and apparatus of operating a scanning probe microscope
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:
interacting a tip of a probe of the SPM with a sample; then
terminating the interaction, resulting in a decaying probe oscillation;
repeating the interaction before ringdown of the decaying probe oscillation is substantially complete; and
detecting motion of the probe during the interaction step;
determining an instantaneous force on the tip based on the detecting step;
using the instantaneous force as a feedback control parameter to operate the SPM; and
further comprising determining a synchronization distance and using the synchronization distance to determine the instantaneous force.
2. The method of claim 1 , wherein the synchronization distance is determined using one of A) measuring the phase delay between the detected motion and a drive signal of the oscillating step, and B) measuring a distance between initiating a period of the drive signal and an instant of interaction between the probe and the sample.
3. The method of claim 1 , wherein the synchronization distance is determined using a window.
4. The method of claim 1 , wherein the determining step includes subtracting that portion of the detected motion caused by parasitic forces from the detected motion.
5. The method of claim 4 , wherein a minimum controllable force upon performing the subtraction step is at least about an order of magnitude less than a minimum controllable force without perforating the subtraction step.
6. The method of claim 5 , wherein the minimum controllable force is about 1 pN when the cantilever has a length equal to about 100 microns and a spring constant of about 0.01 N/m.
7. The method of claim 4 , wherein the parasitic forces are caused by a hydrodynamic background.