Piezo-resistive Ring-shaped AFM Sensors with Piconewton Force Resolution

A new concept of Atomic Force Microscope (AFM) oscillating probes using electrostatic excitation and piezo-resistive detection is presented. The probe is characterized by electrical methods in a vacuum chamber and by mechanical methods in air. The frequency-mixing measurement technique is developed to reduce the parasitic signal level. These probes resonant in the 1MHz range and the quality factor is measured about 53,000 in vacuum and 3,000 in air. The ring probe is mounted onto a commercial AFM set-up and the surface topography of PMMA sample (2 mu m square) is obtained. The force resolution deduced from the measurements is about 10 pN/Hz(0.5).