  Ubiquitous low frequency 1/f noise can be a limiting factor in the
performance and application of nanoscale devices. Here, we quantitatively
investigate low frequency electronic noise in single-layer transition metal
dichalcogenide MoS2 field-effect transistors. The measured 1/f noise can be
explained by an empirical formulation of mobility fluctuations with the Hooge
parameter ranging between 0.005 and 2.0 in vacuum (< 10-5 Torr). The
field-effect mobility decreased and the noise amplitude increased by an order
of magnitude in ambient conditions, revealing the significant influence of
atmospheric adsorbates on charge transport. In addition, single Lorentzian
generation-recombination noise was observed to increase by an order of
magnitude as the devices were cooled from 300 K to 6.5 K.
