Ferroelectricity in thin perovskite films

We report on the investigation of ferroelectricity in thin tetragonal single-crystalline perovskite films of ${\mathrm{Pb(Zr}}_{\mathrm{0.2}}{\mathrm{Ti}}_{\mathrm{0.8}}){\mathrm{O}}_{\mathrm{3}}$ grown by off-axis rf magnetron sputtering. The local ferroelectric properties of atomically smooth films, with thicknesses ranging from a few unit cells to 800 Å, were measured using a combination of electric force microscopy and piezoelectric microscopy. The time dependence of the measured signals reveals a stable ferroelectric polarization in films down to thicknesses of 40 Å.