Novel high vacuum scanning force microscope using a piezoelectric cantilever and the phase detection method

Abstract

A novel high vacuum scanning force microscope (HV-SFM) using a piezoelectric cantilever and the phase detection method was developed. A self-excited force sensing PZT microcantilever with dimensions of 125×50×3.58 μm is vibrated in vacuum at its resonance frequency by applying an ac voltage to its PZT layer. The piezoelectric microcantilever possesses a spring constant of 16.7 N/m and a vibrational quality factor of 300 in air and 807 in vacuum. As we know, force gradients acting on the vibrating cantilever cause changes in vibration amplitude and phase. The change of the phase of the output piezoelectric current, which corresponds to the phase variation of cantilever vibration, is measured as the controlling signal in this method. The piezoelectric HV-SFM that was constructed has been proved to be stable and easy to handle in vacuum. Its vertical resolution is higher than 1.1 Å. High resolution images of an evaporated Au film can be obtained in vacuum by this new dynamic HV-SFM. Grains of about 5 nm can be seen clearly. The theoretical sensitivity of phase detection with piezoelectric cantilevers is also analyzed and compared with that of amplitude slope detection in this article.