Scanning force microscope with automatic surface engagement

Abstract

The vibrating probe of a scanning force microscope is brought into engagement with a sample surface in an initial approach process moving the probe toward the sample surface until the amplitude of probe vibration at an excitation frequency is measurably affected by forces between the tip and the sample, an then in a final approach process in which a change in vibration amplitude caused by a dithering vibration superimposed on the excitation vibration exceeds a pre-determined threshold limit. The excitation frequency is reduced if the phase angle of vibrations exceeds another limit, and the amplitude of the excitation driving function is increased as the amplitude or tip vibration falls below a setpoint. During approach and scanning, vibration amplitude is measured through a demodulator having an intermediate reference signal locked in phase with the tip motion signal.