Interface adhesion properties of MoS₂/SiO₂: size and temperature effects

Abstract

The interface adhesion properties are crucial for design and fabrication of two-dimensional materials and related nanoelectronic and nanomechanical devices. Although some progress of the interface adhesion properties of two-dimensional materials has been made, the underlying mechanism on the size and temperature dependence of interface adhesion energy and related physical properties from the perspective of atomistic origin remains unclear. Here, we investigate the effects of size and temperature on the thermal expansion coefficient and Young's modulus of MoS₂ as well as interface adhesion energy of MoS₂/SiO₂ based on the atomic-bond-relaxation approach and continuum medium mechanics. It is found that the thermal expansion coefficient of monolayer MoS₂ is significantly larger than that of its few-layer and bulk counterparts under the condition of ambient temperature due to size effect and its consequence on Debye temperature, whereas the thermal expansion coefficient increases with temperature going up and yet almost tends to a constant as the temperature approaches the Debye temperature. Moreover, the variations of bond identities induced by size and temperature effects will change the mechanical properties of MoS₂. When the temperature is fixed, the Young's modulus of MoS₂ increases with decreasing size. However, the thermal strain induces the volume expansion, resulting in the Young's modulus of MoS₂ being reduced. Furthermore, the size and temperature dependence of lattice strain, mismatch strain of interface, and Young's modulus will lead to the changes of van der Waals interaction energy and elastic strain energy, resulting in the variation of interface adhesion energy of MoS₂/SiO₂. Noticeably, the interface adhesion energy of MoS₂/SiO₂ gradually increases with the decreasing MoS₂ size, while the thermal strain induced by temperature causes interface adhesion energy of MoS₂/SiO₂ decreases with increasing temperature. In addition, we predict the conditions of the interface separation of MoS₂/SiO₂ under different sizes and temperatures. Our results demonstrate that increasing both size and temperature can significantly reduce the interface adhesion energy, which is of great benefit to detachment of MoS₂ from the substrate. Therefore, the proposed theory not only clarifies the physical mechanism regarding the interface adhesion properties of transition metal dichalcogenides (TMDs) membranes, but also provides an effective way to design TMDs-based nanodevices for desirable applications.