Scanning Force Microscopy in the Dynamic Mode Using Microfabricated Capacitive Sensors

We report on the first successful operation of a scanning force microscope using microfabricated capacitive force sensors. The sensors which are made from single crystal Silicon on Insulator (SOI) wafers consist of a cantilever spring with integrated tip at the free end and an electrically insulated counter-electrode. Dynamic force gradient sensing is the preferred operating mode. Here, tip-sample interactions are detected by letting the sensor act as a resonator in a phase controlled oscillator set-up and measuring corresponding shifts of the oscillation frequency. Experiments were performed in vacuum using a standard tunneling microscope. A Cr grating on a quartz substrate served as test sample. Topographic images showing details on a 10 nm scale were obtained operating at a constant force gradient of the order of 0.01 N/m. In addition, critical design parameters are discussed based on an analysis of the electro-mechanical properties of the sensors.