We investigated the surface potential of the ferroelectric domains of the epitaxial PbTiO3 (PTO) films using both Kelvin probe and piezoresponse force microscopy. The surface potential changes as a function of applied biases suggested that the amount and sign of surface potentials depend on the correlation between polarization and screen charges. It also suggested that the trapped negative charges exist on the as-deposited PTO surfaces. Injected charges and their resultant surface potentials are investigated by grounded tip scans. The results unveiled the origin of surface potential changes during ferroelectric switching in the epitaxial PTO films.

Nanoscale manipulation of surface charges and their imaging are essential for understanding local electronic behaviors of polar materials and advanced electronic devices. Electrostatic force microscopy and Kelvin probe force microscopy have been extensively used to probe and image local surface charges responsible for electrodynamics and transport phenomena. However, they rely on the weak electric force modulation of cantilever that limits both spatial and temporal resolutions. Here we present a field effect transistor embedded probe that can directly image surface charges on a length scale of 25 nm and a time scale of less than 125 μs. On the basis of the calculation of net surface charges in a 25 nm diameter ferroelectric domain, we could estimate the charge density resolution to be as low as 0.08 μC/cm(2), which is equivalent to 1/20 electron per nanometer square at room temperature.