Theoretical Studies of the Growth and Functionality of Layered Materials

In this thesis, we present several projects on the growth and functionality of layered materials, using density functional theory (DFT) method and phenomenological modeling approach. Beyond the understanding of growth mechanisms and exploration of properties, we propose novel avenues to realize controllable growth processes and layered materials with desirable properties. The contents have three major parts:

(1) Graphene growth on Cu(111) and Ni(111) substrates. We first demonstrate that the inherent multi-orientational degeneracy of the graphene islands on Cu(111) in the early stages of nucleation could result in the prevalence of grain boundaries (GBs). Next, we propose a possible solution to tackle this standing obstacle, by invoking a functionalized Cu(111) surface to lift the orientational degeneracy and consequently suppress the GBs. Following this work, we explore the contrasting mechanisms of graphene bilayer growth on Cu(111) and Ni(111), develop a phenomenological model to predict the critical graphene size for the nucleation of the second layer underneath, and propose ways to substantially enhance the growth rate of the second-layer graphene on Cu.

(2) Contrasting alignment of hexagonal boron nitride (h-BN) and graphene grown on Cu(100). Collaborating with the experimental group, we find that the three-fold symmetric BN exhibits definitive orientation alignments when grown on the four fold-symmetric Cu(100) surface. This is in stark contrast to graphene/Cu(100) epitaxy, despite the crystallographic similarity between graphene and h-BN. Our results reveal that the stronger C-Cu interaction lead to the misalignment, a conclusion runs counter to the conventional wisdom that stronger epilayer-substrate interactions enhance orientational order.

(3) Electronic and chemical properties of monolayer molybdenum disulfide (MoS₂) on metal substrates. We investigate the properties of a single-layer MoS₂ adsorbed on Ir(111), Pd(111), or Ru(0001). We find the contact nature is Schottky type, and the dependence of the barrier height on the work function exhibits a partial Fermi-level pinning picture. Using hydrogen adsorption as a testing example, we further demonstrate that the introduction of a metal substrate can substantially alter the chemical reactivity on the MoS₂ planar surface.