Search

Many applications of graphene can benefit from the enhanced mechanical robustness of graphene-based components. We report how the stiffness of vertical graphene (VG) sheets is affected by the introduction of defects and fluorination, both separately and combined. The defects were created using a high-energy ion beam while fluorination was performed in a XeF2 etching system. After ion bombardment alone, the average effective reduced modulus (Er), equal to ∼4.9 MPa for the as-grown VG sheets, approximately doubled to ∼10.0 MPa, while fluorination alone almost quadrupled it to ∼18.4 MPa. The maximum average Er of ∼32.4 MPa was achieved by repeatedly applying fluorination and ion bombardment. This increase can be explained by the formation of covalent bonds between the VG sheets due to ion bombardment, as well as the conversion from sp2 to sp3 and increased corrugation due to fluorination. [ABSTRACT FROM AUTHOR]

The evolution of crystallographic facets of strained heteroepitaxial Ge islands on Si is investigated. Islands growing on Si(001), (111), (110) and (113) are bound by an equilibrium set of facets that includes only shared stable surfaces between bulk Si and Ge--{105}, {113}, {15 3 23} and {111}. The formation of a stereographic map from these indices facilitates the prediction of Ge faceted-island shapes on any Si substrate at different stages of growth. The analysis presented here can be applied to other heteroepitaxial islanding systems where a finite set of shared equilibrium facets exists for the bulk starting materials. [ABSTRACT FROM AUTHOR]