Electronic and vibrational properties of Rb-intercalated MoS2 nanoparticles

Nanoplatelets (diameter about 8 nm) synthesized by laser pyrolysis and bulk powder of MoS2 have been intercalated with Rb to establish the metallic state. The properties of these powders are investigated by Raman scattering, X-ray diffraction, transmission electron microscopy and electron spin resonance (ESR). With increasing time of Rb intercalation the Raman-active interlayer A1g mode is observed to red shift in the nanoplatelet sample and blue shift in the micron-size bulk powder sample. In both samples the Rb doping eventually induces a metallic state and the Raman signal is lost. A broad ESR line was detected for the Rb-saturated MoS2 bulk powder sample, also indicating the metallic character. Owing to the small particle size of the nanoplatelets, no broad line ESR signal was observed for the intercalated nanoplatelets. A low field (ESR) signal was used to search for superconductivity and a Tc = 6.4 K was observed in the bulk, in good agreement with the literature. However, no superconductivity down to 3.5 K was observed in the nanoplatelet sample.