Dynamic activation for an atomic force microscope and method of use thereof
View Patent ↗A scanning probe microscope method and apparatus that modifies imaging dynamics using an active drive technique to optimize the bandwidth of amplitude detection. The deflection is preferably measured by an optical detection system including a laser and a photodetector, which measures cantilever deflection by an optical beam bounce technique or another conventional technique. The detected deflection of the cantilever is subsequently demodulated to give a signal proportional to the amplitude of oscillation of the cantilever, which is thereafter used to drive the cantilever.
1. A method of analyzing a sample in cyclical mode with a probe-based AFM, the method comprising:
providing a cantilever;
oscillating the cantilever at an amplitude of oscillation so as to cause a tip of the cantilever to intermittently contact a surface of the sample;
scanning the cantilever across the sample;
generating a deflection signal in response to said scanning step;
demodulating said deflection signal to generate an amplitude signal indicative of the amplitude of oscillation of the cantilever;
generating, with a first feedback loop, a first control signal in response to the amplitude signal;
using the first control signal as an error signal in a second feedback loop, wherein the first feedback loop is nested within the second feedback loop; and
damping the oscillating voltage with an active drive circuit to actively modify the quality factor (Q) of the cantilever resonant frequency during said scanning step.
2. The method of claim 1 , wherein said demodulating step includes using an amplitude detection circuit.
3. The method according to claim 2 , wherein the amplitude detection circuit includes a gain stage.
4. The method according to claim 1 , further comprising the steps of:
providing a first actuator and a second actuator;
controlling the motion of the first actuator with the first control signal generated by the first feedback loop to keep the amplitude signal substantially constant;
generating with the second feedback loop a second control signal; and
controlling the motion of the second actuator with the second control signal to keep the first control signal substantially constant.