NANOMETER-SCALE OPTICAL STUDIES OF TWIN DOMAINS AND DEFECTS IN LANTHANUM ALUMINATE CRYSTALS

A near-field scanning optical microscope (NSOM) in transmission geomet ry was used to study optical characteristics of twin domains, domain b oundaries, and other defects in lanthanum aluminate (LaAlO3) single cr ystals. Large optical contrast between domains was observed using line arly polarized NSOM light. This domain contrast can be changed and eve n reversed by varying the direction of the polarization axis with resp ect to the local crystallographic axis. We further demonstrate that th e contrast depends critically on the numerical aperture of the collect ion objective lens, enabling us to differentiate between possible cont rast mechanisms. In addition, microscopic stress birefringence associa ted with the domain boundaries was observed under crossed-polar condit ions. Submicron circular optical features on LaAlO3 are attributed to surface terminations of dislocations. (C) 1996 American Institute of P hysics.