OBSERVATION OF AN INCOMMENSURATELY MODULATED STRUCTURE IN DIELECTRICSBY AN ATOMIC-FORCE MICROSCOPE

We report the first direct observation of an incommensurate lattice di stortion in dielectric crystals by an atomic-force microscope. The lay ered crystal (NH3C3H7)(2)MnCl4 has been imaged in the normal and incom mensurate phases. In the normal phase, we observe well-ordered atomic corrugations on a cleavage surface of a crystal. In the incommensurate phase, these atomic corrugations are modulated by a long periodic pla ne-wave distortion.