Unconventional cross-step growth of monolayer MoS₂ on sapphire

Regarding thin film growth, it has been widely recognized that the film typically follows the surface texture and high sharp steps potentially lead to growth termination and film discontinuity. Here, we demonstrate an abnormality that monolayer MoS₂ grown on C-plane sapphire is able to cross sharp steps up to ∼10 nm in height. Assisted by theoretical simulations, we unveil that the cross-step growth of monolayer MoS₂ results from the competition between its deformation energy cost and adsorption energy gain. Notably, cross-step growth leads to the formation of one-dimensional (1D) ripples on target substrates after transfer, resulting in symmetry breaking and strain engineering to trigger anisotropic properties and boost transistor performances. The room-temperature mobility (on-state current) along the ripple direction is improved by ∼67.6% (∼118.4%) compared to that perpendicular to the ripple direction. Our work showcases an exotic cross-step growth paradigm to create and manipulate 2D materials, promising the prospect for a broad portfolio of emerging electronic, photonic, and optoelectronic applications.