Mechanism of remote epitaxy using two dimensional materials

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. ; Cataloged from PDF version of thesis. ; Includes bibliographical references (pages 36-40). ; Van der Waals epitaxy (vdWE) has gained great interest as it provides the ability to relax the strict lattice matching conditions required in conventional epitaxy of covalent or ionic single crystal substrates. With the rise of two-dimensional (2D) materials since the isolation of graphene in 2004, vdWE has been attempted on 2D materials, transferred, or grown on substrates. However, there has been the notion that the 2D material is the seed layer in van der Waals epitaxy. Notwithstanding, the substrate below the 2D material may play a role in orienting the crystalline growth of overlayers. This is supported by previous studies of a so called "long range" effect, where the potential field of growth substrates influenced the crystal orientation of overlayers through thin amorphous layers, and the "transparency" of graphene, where the contact angle of a droplet was unchanged by the presence of graphene. Here, we report the ability of the underlying substrate below graphene to assign the epitaxial registry of adatoms despite its presence, and thus form epitaxial layers with the same crystal orientation as the substrate during vdWE. Density functional theory (DFT) calculations are utilized to find that the critical separation gap beyond which a substrate and overlayer will lose electronic interaction is -9 A[angstroms], which allows for the insertion of thin graphene at the substrate-epilayer interface. We experimentally test the interaction as a function of distance by transferring monolayer, bilayer and tetra-layer graphene onto GaAs (001) and performing homoepitaxial growth. The results show that single crystalline GaAs with (001) orientation is only obtained on monolayer graphene, revealing that only monolayer graphene may allow the substrate to have influence over the orientation of the overlayer. The method is applied to ...