Surface structures of layered compounds treated with alkali-metal hydroxide solutions studied by scanning tunneling microscopy

Ordered 2 × 2 and √3 × √3 superstructures with charge density modulation were observed by scanning tunneling microscopy (STM) on highly oriented pyrolytic graphite surfaces treated with MOH (M=Na, K) aqueous solutions. Charge transfer from intercalants to host graphite was observed, as previously seen on stage-1 alkali-metal intercalations. On the other hand, for the MoS2 crystal treated with the same solutions, the host MoS2 lattice was observed together with island structures with low charge density formed by intercalants. Some electronic states seemed to be formed between the MoS2 band gap.