Patent ID: 9453857
Filing Date: 2016-09-27
CPC Classification: G01Q

Claim Text:
1. A method of calibrating an atomic force microscope, which is equipped with a cantilever with a tip, a photodetector and a coarse positioning system and a fine positioning system for controlling a position of the cantilever and a sample, comprising the following steps: turning a drive mechanism off; positioning a detection laser on a side of the cantilever opposite the tip and in a center of the photodetector; calibrating a stiffness of the cantilever from a measured thermal spectrum taken far from the surface of the sample and recording information indicative of the stiffness as representing a natural frequency of the cantilever; approaching the tip of the cantilever to close proximity with the sample, as determined by optical inspection of the tip and the sample using the coarse-positioning system; after said approaching, turning the drive mechanism on; setting a drive frequency equal to the natural frequency of the cantilever as determined from said thermal spectrum; setting a drive amplitude to a desired free oscillation amplitude; approaching the tip of the cantilever to the surface of the sample until contact is established by setting a feedback set point to a desired interaction amplitude that is slightly less than a free oscillation amplitude; fully separating the sample from the tip of the cantilever as determined by optical inspection using the fine-positioning system; acquiring a cantilever tune by either setting the drive frequency to the natural frequency of the cantilever as determined from said thermal spectrum or from setting the drive frequency to a local amplitude maximum of the cantilever near a resonant frequency of the cantilever; turning off the drive mechanism and acquiring an additional thermal spectrum of the cantilever that is closer to imaging conditions; using a simple harmonic oscillator model and the data from the additional thermal spectrum to define a new natural frequency of the cantilever and determine a phase-to-drive-frequency relationship of the cantilever; turning on the drive mechanism and choosing a drive frequency equal either to the new natural frequency of the cantilever or to a local amplitude maximum of the cantilever near the cantilever resonant frequency; choosing a drive amplitude which achieves the desired cantilever free oscillation amplitude; and setting phase from a result of the aforesaid simple harmonic oscillator model.