In this study, electrical characteristics of MoTe₂ field-effect transistors (FETs) are investigated as a function of channel thickness. The conductivity type in FETs, fabricated from exfoliated MoTe₂ crystals, switched from p-type to ambipolar to n-type conduction with increasing MoTe₂ channel thickness from 10.6 nm to 56.7 nm. This change in flake-thickness-dependent conducting behavior of MoTe₂ FETs can be attributed to modulation of the Schottky barrier height and related bandgap alignment. Change in polarity as a function of channel thickness variation is also used for ammonia (NH₃) sensing, which confirms the p- and n-type behavior of MoTe₂ devices.

An automated technique is presented for mechanically exfoliating single-layer and few-layer transition metal dichalcogenides using controlled shear and normal forces imposed by a parallel plate rheometer. A thin sample that is removed from bulk MoS₂ or MoTe₂ is initially attached to the movable upper fixture of the rheometer using blue dicing tape while the lower base plate also has the same tape to capture and exfoliate samples when the two plates are brought into contact then separated. A step-and-repeat exfoliation process is initiated using a preprogrammed contact force and liftoff speed. It was determined that atomically thin films of these materials could be obtained reproducibly using this technique, achieving single-layer and few-layer thicknesses for engineering novel two-dimensional transistor devices for future electronic technologies. We show that varying the parameters of the rheometer program can improve the mechanical exfoliation process.