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Strain engineering is an important method for tuning the properties of semiconductors and has been used to improve the mobility of silicon transistors for several decades. Recently, theoretical studies have predicted that strain can also improve the mobility of two-dimensional (2D) semiconductors, e.g., by reducing intervalley scattering or lowering effective masses. Here, we experimentally show strain-enhanced electron mobility in monolayer MoS 2 transistors with uniaxial tensile strain, on flexible substrates. The on-state current and mobility are nearly doubled with tensile strain up to 0.7%, and devices return to their initial state after release of the strain. We also show a gate-voltage-dependent gauge factor up to 200 for monolayer MoS 2 , which is higher than previous values reported for sub-1 nm thin piezoresistive films. These results demonstrate the importance of strain engineering 2D semiconductors for performance enhancements in integrated circuits, or for applications such as flexible strain sensors.

Real-time thermal sensing on flexible substrates could enable a plethora of new applications. However, achieving fast, sub-millisecond response times even in a single sensor is difficult, due to the thermal mass of the sensor and encapsulation. Here, we fabricate flexible monolayer molybdenum disulfide (MoS 2 ) temperature sensors and arrays, which can detect temperature changes within a few microseconds, over 100× faster than flexible thin-film metal sensors. Thermal simulations indicate the sensors' response time is only limited by the MoS 2 interfaces and encapsulation. The sensors also have high temperature coefficient of resistance, ∼1-2%/K and stable operation upon cycling and long-term measurement when they are encapsulated with alumina. These results, together with their biocompatibility, make these devices excellent candidates for biomedical sensor arrays and many other Internet of Things applications.

Metal contacts are a key limiter to the electronic performance of two-dimensional (2D) semiconductor devices. Here, we present a comprehensive study of contact interfaces between seven metals (Y, Sc, Ag, Al, Ti, Au, Ni, with work functions from 3.1 to 5.2 eV) and monolayer MoS 2 grown by chemical vapor deposition. We evaporate thin metal films onto MoS 2 and study the interfaces by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and electrical characterization. We uncover that (1) ultrathin oxidized Al dopes MoS 2 n- type (>2 × 10 12 cm -2 ) without degrading its mobility, (2) Ag, Au, and Ni deposition causes varying levels of damage to MoS 2 (e.g. broadening Raman E' peak from <3 to >6 cm -1 ), and (3) Ti, Sc, and Y react with MoS 2 . Reactive metals must be avoided in contacts to monolayer MoS 2 , but control studies reveal the reaction is mostly limited to the top layer of multilayer films. Finally, we find that (4) thin metals do not significantly strain MoS 2 , as confirmed by X-ray diffraction. These are important findings for metal contacts to MoS 2 and broadly applicable to many other 2D semiconductors.