Local crystal analysis using near-field optical second harmonic microscopy: Application to thin ferroelectric films

Application of near-field optical second harmonic microscopy to nanometer scale crystal and strain analysis of thin polycrystalline ferroelectric films is described. The near-field signal is shown to be sensitive to local crystal orientation by experimental and theoretical studies of polarization properties of second harmonic generation from a poled single crystal of BaTiO3. Spatial resolution of the order of 80 nm has been demonstrated by recovery of the local poling direction of individual ferroelectric domains in polycrystalline thin Pb(ZrxTi1−x)O3 films. Near-field strain induced second harmonic generation from thin BaxSr1−xTiO3 films has also been studied, and an agreement between theory and experiment has been established. Thus, the technique described provides a tool for nanometer scale crystal and strain analysis of polycrystalline samples.