Reduction in Modulus of Suspended Sub-2 nm Single Crystalline Silicon Nanomembranes

Ultrathin Si nanomembranes (SiNM) have attracted wide attention due to their potential applications in various fields, including flexible electronics and image sensors for spherical monocentric lens. However, due to silicon's relative high Young modulus, it is quite difficult to perfectly integrate the Si based circuits into these flexible and spherical systems. In this study, we report the reduction in modulus of SiNM when the thickness of SiNM is down to sub-2 nm. The fabrication steps include the Si thinning process by oxidation of the silicon on insulator (SOI) wafers and the suspended process by semiconductor technology. Direct mechanical measurement by atomic force microscope in contact model shows that the Young's modulus of a 1.6-nm-thick SiNMs decreases to 4 Gpa. It is further confirmed by the first-principle theory simulation. It demonstrates that the surface effects play a significant role in SiNM's mechanical properties. The results in this study are significant for the applications of SiNMs on the flexible electronics.