Material property measurements using multiple frequency atomic force microscopy
View Patent ↗Apparatus and techniques for extracting information carried in higher eigenmodes or harmonics of an oscillating cantilever or other oscillating sensors in atomic force microscopy and related MEMs work are described. Similar apparatus and techniques for extracting information using contact resonance with multiple excitation signals are also described.
1. A method of operating an atomic force microscope which processes a sample, comprising:
using a feedback loop to control a distance between a base of a cantilever of the atomic force microscope which has a probe tip, and a surface of the sample to maintain the probe tip of the cantilever in a pre-established relationship with respect to the surface of the sample while scanning the sample by creating relative movement between the probe tip of the cantilever and the sample;
exciting a chip of the cantilever at two or more synthesized frequencies that have been summed together by a circuit element;
providing each of said synthesized frequencies as a reference signal to a lock-in amplifier; and
measuring cantilever values, including the amplitude and phase of the cantilever at the different excitation frequencies; and
using the measured cantilever values to provide information indicative of a surface of the sample.
2. The method according to claim 1 , comprising:
displaying the measured amplitude and phase of the cantilever.
3. The method of claim 1 where a function of the two measured amplitudes is used in a feedback loop to control the excitation frequencies.