1 Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA 2 Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, USA 3 California Nanosystems Institute, University of California, Los Angeles, California 90095, USA
Two-dimensional (2D) layered transition metal dichalcogenide (TMD) materials (e.g., MoS2) have attracted considerable interest due to their atomically thin geometry and semiconducting electronic properties. With ultrahigh surface to volume ratio, the electronic properties of these atomically thin semiconductors can be readily modulated by their environment. Here we report an investigation of the effects of mercury(II) (Hg2+) ions on the electrical transport properties of few-layer molybdenum disulfide (MoS2). The interaction between Hg2+ ions and few-layer MoS2 was studied by field-effect transistor measurements and photoluminescence. Due to a high binding affinity between Hg2+ ions and the sulfur sites on the surface of MoS2 layers, Hg2+ ions can strongly bind to MoS2. We show that the binding of Hg2+ can produce a p-type doping effect to reduce the electron concentration in n-type few-layer MoS2. It can thus effectively modulate the electron transport and photoluminescence properties in few-layer MoS2. By monitoring the conductance change of few-layer MoS2 in varying concentration Hg2+ solutions, we further show that few-layer MoS2 transistors can function as highly sensitive sensors for rapid electrical detection of Hg2+ ion with a detection limit of 30 pM.