Abstract
We report the first direct observation of an incommensurate lattice distortion in dielectric crystals by an atomic-force microscope. The layered crystal (NH3C3H7)2MnCl4 has been imaged in the normal and incommensurate 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 plane-wave distortion.