Cluster formation and charge transfer in molecular doping of molybdenum disulfide

Molybdenum disulfide (MoS2) gas sensor prototypes report orders of magnitude higher sensitivity towards nitrogen dioxide (NO2) over ammonia (NH3). Based on the cluster formation model and density functional theory calculation of charge transfer, NO2 is found to form a tightly bound cluster of counter charge upon carrier donation. On the other hand, NH3 forms only a semi-localized cluster of counter charge over wide area MoS2, which should promote recombination of donated carrier. We report the localization of counter charge cluster as an important factor affecting molecular doping efficiency.