Patent ID: 7845215

Claim:
An atomic force microscope for examining sub-surface features embedded in a matrix material of a sample, the microscope comprising: a cantilever arm having a plurality of contact resonance frequencies; a probe secured to a free end of the cantilever arm; a first oscillator drive coupled to the cantilever arm and configured to oscillate the cantilever arm at a first frequency in response to a first drive signal; a second oscillator drive adapted to be coupled to the sample on an opposite side of the sample from the probe, the second oscillator drive configured to generate a signal at a second frequency in response to a second drive signal, the second frequency differing from the first frequency by an amount substantially equal to one of the contact resonance frequencies; a deflection measuring mechanism configured to measure an amount of deflection of the cantilever arm as a surface of the sample is scanned and configured to generate a deflection signal indicative of the amount of deflection of the cantilever arm, the deflection signal comprising a first frequency component, a second frequency component, and a difference frequency component; and a difference frequency component isolation element configured to isolate the difference frequency component of the deflection signal and to output at least one of (a) a phase of the difference frequency component, (b) a variation of the phase of the difference frequency component, (c) an amplitude of the difference frequency component, or (d) a variation of the amplitude of the difference frequency component.