Different Response of Atomic Force Microscopy and Scanning Tunnelling Microscopy to Charge Density Waves

Abstract
The transition metal dichalcogenides 1T-TaSe2 and 1T-TaS2 have been examined at room temperature by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). STM images are dominated by the charge density wave modulation. In some experiments the underlying atomic lattice can be revealed simultaneously. The AFM operated with a loading in the range of (10−8 ÷ 10−7) N showed only the atomic surface structure. This experimental result shed new light on the relationship between the electronic surface structure and the force response. However, at present we cannot rule out a pressure dependence of the charge density wave state on the AFM results.