Patent ID: 8087289

Claim:
A scanning probe system comprising: a probe having a tip that interacts with a specimen; an actuator system that moves said probe relative to said specimen in three directions, two of said directions being in a plane containing said specimen and one of said directions, z, being orthogonal to said plane; a z-axis probe positioning system that sets an average z-position of said probe tip relative to said specimen a shaker element that causes said probe to vibrate at a first frequency; a probe deflection measurement system that generates a probe deflection signal indicative of an oscillation amplitude of said probe; a z-position feedback controller that operates said z-position probe positioning system to maintain an amplitude of said probe deflection signal at said first frequency at a predetermined value; and a probe signal generator that applies a probe signal between said specimen and said probe, said probe signal comprising a DC component and an AC component at a second frequency, said probe signal generator measuring an amplitude of a mixed frequency component of said probe deflection signal at a mixing frequency of said first frequency and said second frequency, wherein said probe signal generator comprises a mixer that mixes said probe deflection signal with a local oscillator signal to generate in phase and quadrature components of said probe deflection signal at said mixing frequency, and wherein said local oscillator signal has a phase chosen such that one of said in phase and quadrature components has an amplitude equal to said amplitude of said probe deflection signal at said mixing frequency.