SELF-OSCILLATING MODE FOR FREQUENCY-MODULATION NONCONTACT ATOMIC-FORCE MICROSCOPY

Frequency modulation atomic force microscopy (FM-AFM) has made imaging of surfaces in ultrahigh vacuum with atomic resolution possible. Here , we demonstrate a new approach which simplifies the implementation of FM-AFM considerably and enhances force sensitivity by directly exciti ng the cantilever with the thermal effects involved in the deflection measurement process. This approach reduces the mechanically oscillatin g mass by 6 to 8 orders of magnitude as compared to conventional FM-AF M, because external actuators and oscillating cantilever mounts are no t needed. Avoiding external actuators allows the use of cantilevers wi th very high oscillation frequencies, which results in improved force sensitivity. Further, the implementation and operation of this new tec hnique is significantly simplified, because external actuator, bandpas s filter, and phase shifter are eliminated. (C) 1997 American Institut e of Physics.