A scanning tunneling microscopy study of a new superstructurearound defects created by tip–sample interaction on 2H-NbSe2

Abstract

A low temperature scanning tunneling microscope (LT-STM) was usedto investigate a new superstructure on the cleaved surface of a 2H-NbSe2 single crystal after introduction of structural defects through bias voltage pulses duringtunneling at 4.2 K. A charge density wave (CDW) with a reconstruction was observed in the vicinity of the defects and the well-known3 × 3 CDW was observed far from these defects. Multiple layers inside the defectswere also exposed and showed the new modulation of the CDW on all ofthe Se layers. This indicates a local 2H to 1T phase transition for theNbSe2 crystal structure. Two other interesting observations are also included: a disorderedCDW-like phase of the structure near the atomic steps and an anomalous distortion in the underlying atomiclattice revealed by STM images. A local heating mechanism is proposed to explain thecreation of these novel structures.