ACS Nano doi: 10.1021/nn203879f (2011) Bertolazzi - Stretching and Breaking of Ultrathin MoS2

T wo-dimensional crystals, consisting of single or few atomic layers extracted from layered materials such as graphite or MoS2, 1 3 are attracting a great deal of interest due to their promising potential for applications in nanotechnology. Graphene is the best known 2D material because of its high mobility, presence of massless Dirac fermions, and a wealth of interesting physical phenomena such as the fractional quantumHall effect. Other 2Dmaterials such as transitionmetal dichalcogenides or BN could have practical applications and fundamental properties complementary to those of graphene, although they are at this point much less explored. Single-layer MoS2 is a typical two-dimensional semiconductor from the class of layered transition metal dichalcogenides (TMD). Individual layers, 6.5 Å thick, can be extracted from bulk crystals using the micromechanical cleavage technique commonly associated with the production of graphene, lithium-based intercalation, or liquid phase exfoliation and used as ready-made blocks for electronic device fabrication. Bulk MoS2 is an indirect gap semiconductor with a band gap of 1.2 eV (ref 11). Reducing the number of layers modifies the band structure and, as a consequence, monolayer MoS2 becomes a direct gap semiconductor 15 with a band gap of 1.8 eV (ref 14) due to quantum confinement. The presence of a band gap in monolayer MoS2 makes it interesting for applications in nanoelectronics where it allows the fabrication of transistors with low power dissipation and current on/off ratios exceeding 10 at room temperature. Together with the possibility of large-scale liquid-based processing of MoS2 and related 2Dmaterials, MoS2 could also be very interesting for applications in flexible electronics where it would combine high performance with low cost. It is however not clear at this point if monolayer MoS2 would be characterized by mechanical properties necessary for integration with stretchable polymer substrates in order to produce high-end bendable electronics. Previous measurements on MoS2 and WS2 nanotubes, 16,17 which can be thought of as monolayers of MoS2 andWS2 wrapped up in the form of a cylinder, show superior mechanical properties with Young's modulus reaching 255 GPa and strength reaching 11% of its Young's modulus. Subnanometer MoS2 nanowires on the other hand have lower Young's modulus, 120 GPa. Here, we report on the measurement of the in-plane elastic modulus and breaking strength of single and bilayer MoS2. MoS2 consists of a stack of covalently bonded S Mo S layersweakly interactingwith each other via van der Waals forces. The in-plane * Address correspondence to [email protected].