Navigation and service

Epitaxial 2D Materials

We investigate the epitaxial growth of two-dimensional materials, with the aim to optimize their quality, such that emergent properties of van der Waals heterostructures can be examined.

Graphene is only the first of a large number of two-dimensional (2D) materials with a broad range of physical properties. This includes insulators, semiconductors, metals as well as superconductors. Some of them moreover exhibit intriguing properties such as strong spin-orbit coupling or non-trivial topologies.

Because 2D materials are held together by van der Waals interactions only, one is relieved from lattice-matching constraints and can create completely new artificial materials, not only by stacking arbitrary (monolayer) sequences, but also by carefully controlling the twist angle between the layers. Through this design principle, van der Waals heterostructures permit a degree of tailoring material properties that is otherwise difficult to achieve. Specifically, we develop new approaches to twisted bilayer graphene on SiC(0001) [1, 2] (for details see Graphene), and study the interfaces between molecules and 2D materials [3].

Hexagonal boron nitride (hBN) is a prominent and frequently studied two-dimensional material, because it has a large bandgap of almost 6 eV, making it an insulator. Growing high-quality hexagonal boron nitride on metal surfaces [4] offers the possibility to fabricate atomically thin insulating layers.

Residual strain in graphene/Ir(111)False-color representation (based on bright-field LEEM) of the residual strain in graphene/Ir(111) after cooling to room temperature. Different thermal expansion coefficients of graphene and Ir cause a rather strong compressive strain in the graphene sheet. The bright-field LEEM image series on the right shows that CuPc islands (dark) overgrow graphene areas with low strain first [3].



Movie 1: The bright-field LEEM movie reveals the dendritic growth of hexagonal boron nitride (hBN) on Cu(111) upon annealing the Cu crystal in borazine atmosphere [4]. The behavior can be explained by different adhesion and dehydrogenation energies for boron and nitrogen.