Atomic force microscope and scanning tunneling microscope studies of superlattices and density waves in Fe doped NbSe2, TaSe2, TaS2 and in NbSe3 doped with Fe, Co, Cr, and V

Results of atomic force microscope (AFM) and scanning tunneling microscope (STM) studies of superlattices and long‐range modulations induced by impurities in transition metal chalcogenides are presented. Superlattices formed by Fe intercalation into the van der Waals gaps of 2H–NbSe2, 2H–TaSe2 and 2H–TaS2 show ordered occupation of the octahedral holes and STM spectroscopy shows density‐wave energy gaps existing in the antiferromagnetic phases. In NbSe3, interstitial impurities such as Fe, Co, Cr, and V induce long‐range modulated structures that can be detected at room temperature with AFM scans. These modulations modify the charge‐density wave structure forming at low temperature and STM spectroscopy has been used to measure these changes.