Scanning Tunneling Microscopy Study of the Misfit Layer Compounds (LaSe)_xNbSe₂ and (PbSe)_xNbSe₂

Abstract

Atomic images of the misfit layer compounds (LaSe) x NbSe 2 and (PbSe) x NbSe 2 were obtained with a scanning tunneling microscope (STM) operating in constant height mode in air. It was possible to record pictures of only the NbSe 2 layers of both compounds, the LaSe and PbSe layers could not be observed. Formation of stage-2 portions embedded in the stage-1 crystal and instability of the LaSe and PbSe layers under the scanning conditions are discussed as possible causes. Comparing with the NbSe 2 crystal, the lattice of the NbSe 2 layers of the misfit layer compounds appear deformed. Nonperiodic Moiré-like structures have been observed in the (LaSe) x NbSe 2 surface. We consider that this feature is caused by the STM tip pushing down the surface where it is softer. The nonperiodicity of the patterns might be due to the strain conditions of the crystal growth that would give rise to dislocations and defects.