Surface modifications: Nanostructures and nested polyhedra generated by pulsing the STM tip

STM experiments were performed to study modifications on the surface of crystalline and amorphous transition metal chalcogenides. Pulses with different parameters were applied to the STM tip, at predefined locations, while scanning the surface of WSe₂ and MoS₃. Different types of structures were formed on the crystalline WSe₂ surface: (a) holes, (b) mounds, (c) ringlike structures. The three types were formed at different ranges of voltage. In some cases local cleavage of the surface was observed. An explanation is offered for the creation of such a variety of structures. On the amorphous MoS₃ surface the pulses created small, round mounds. The size of the structures grows with the voltage of the applied pulse. I-V characteristics taken on these structures show semiconducting behavior with a gap of 1.1 eV, similar to the gap of bulk MoS₂. TEM Images show that nested polyhedral structures are formed in the STM experiments, with sizes that agree with the observed structures. Similar round crystalline structures are formed on the surface of MoS₂ grown under different conditions. This is the first time that such crystallization is observed by pulsing the STM tip.