Scanning Tunneling Microscope Induced Crystallization of Fullerene-like MoS2

Amorphous precursors, like MoS 3 (WS 3 ), were shown before to be an ideal precursor for the growth of inorganic fullerene-like material in a rather slow crystallization process which lasts anything from 1 h at 800−900 °C 1,2 to a few years at ambient conditions. 3,4 Using a few microsecond short electrical pulses from the tip of a scanning tunneling microscope, crystallization of amorphous MoS 3 (a-MoS 3 ) nanoparticles, which were electrodeposited on a Au substrate into MoS 2 nanocrystallites with a fullerene-like structure (IF-MoS 2 ), is demonstrated. The (outer) shell of each nanocrystallite is complete, which suggests that the reaction extinguishes itself upon completion of the crystallization of the MoS 2 layers. A completely different mode of crystallization is observed in the case of continuous a-MoS 3 films. Here tiny (2−3 nm thick) 2H-MoS 2 platelets are observed after the electrical pulse, suggesting a very rapid dissipation of the thermal energy through the gold substrate, in the continuous domain. Since the reaction mechanism in both cases is believed to be the same, it is likely that the main stimulus for the chemical reaction/crystallization of the IF material results from the slow heat dissipation from the nanoparticle. The exothermicity of the chemical reaction may further promote the rate of the process.