ABSTRACT
Thin films with large compressive residual stress and low interface adhesion can buckle and delaminate from relatively rigid substrates, which is a common failure mode of film/substrate interfaces. Current studies mainly focused on the geometry of various buckling patterns and related physical origins based on a static point of view. However, fundamental understanding of dynamic propagation of buckles, particularly for the complicated web buckles, remains challenging. We adopt strained two-dimensional MoS2 thin films to study the phenomenon of web buckling because their interface adhesion, namely van der Waals interaction, is naturally low. With a delicately site-controlled initiation, web buckles can be triggered and their dynamic propagation is in situ observed facilely. Finite element modeling shows that the formation of web buckles involves the propagation and multilevel branching of telephone-cord blisters. These buckled semiconducting films can be patterned by spatial confinement and potentially used in diffuse-reflective coatings, microfluidic channels, and hydrogen evolution reaction electrodes. Our work not only reveals the hidden mechanisms and kinematics of propagation of web buckles on rigid substrates but also sheds light on the development of semiconducting devices based on buckling engineering.
ABSTRACT
Two-dimensional semiconducting transition metal dichalcogenides have been employed as key components in various electronic devices. The thermal stability of these ultrathin materials must be carefully considered in device applications because the heating caused by current flow, light absorption, or other harsh environmental conditions is usually unavoidable. In this work, we found that the substrate plays a role in modifying the thermal stability of mono- and few-layer MoS2. Triangular etching holes, which are considered to initiate from defect sites, form on MoS2 when the temperature exceeds a threshold. On Al2O3 and SiO2, monolayer MoS2 is found to be more stable in thermal annealing than few-layer MoS2 either in atmospheric-pressure air or under vacuum; while on mica, the absolute opposite behavior exists. However, this difference due to substrates appears to vanish when using defective, chemical-vapor-deposited MoS2 samples. The substrate modification of the thermal stability of MoS2 with various thicknesses is attributed to the competition between MoS2-substrate interface interaction and MoS2-MoS2 interlayer interaction. Our findings provide important design rules for MoS2-based devices, and also potentially point to a route of controlled patterning of MoS2 with substrate engineering.
