First-principles study of van der Waals interactions and lattice mismatch atMoS2/metalinterfaces

Abstract

We explore the adsorption of MoS2 on a range of metal substrates by means of first-principles density functional theory calculations. Including van der Waals forces in the density functional is essential to capture the interaction between MoS2 and a metal surface, and obtain reliable interface potential steps and Schottky barriers. Special care is taken to construct interface structures that have a mismatch between the MoS2 and the metal lattices of <1%. MoS2 is chemisorbed on the early transition metal Ti, which leads to a strong perturbation of its (electronic) structure and a pinning of the Fermi level 0.54 eV below the MoS2 conduction band due to interface states. MoS2 is physisorbed on Au, where the bonding hardly perturbs the electronic structure. The bonding of MoS2 on other metals lies between these two extreme cases, with interface interactions for the late 3d transition metals Co, Ni, Cu and the simple metal Mg that are somewhat stronger than for the late 4d/5d transition metals Pd, Ag, Pt and the simple metal Al. Even a weak interaction, such as in the case of Al, gives interface states, however, with energies inside the MoS2 band gap, which pin the Fermi level below the conduction band.

Progress in Contact, Doping and Mobility Engineering of MoS2: An Atomically Thin 2D Semiconductor

“…The extent of this interfacial interaction depends on whether the metal is physisorbed (i.e., weakly adsorbed) or chemisorbed (i.e., strongly adsorbed) on the MoS 2 surface, resulting in a small or large density of interface states, respectively. Moreover, the authors showed that by artificially enlarging the physical distance between MoS 2 and the metal, these interface states vanished [150]. Experimentally, this physical separation can be achieved by inserting suitable interfacial tunnel barriers or buffer layers in-between the MoS 2 and the contact metal (more on interfacial contact tunnel barriers is discussed in Section 8).…”

“…This method, widely explored for engineering the contact resistivity in conventional 3D semiconductor FETs based on Si and Ge [226][227][228][229][230][231][232], is based on the incorporation of an ultra-thin insulating material (such as 2D hexagonal boron nitride or hBN, and oxides such as TiO 2 ) in-between the MoS 2 and the contact electrode, to effectively realize a metal-insulator-semiconductor (MIS) configuration at the contact. This thin interfacial insulating "buffer" layer in the MIS structure serves as a "Fermi level de-pinning (FLDP) layer" by increasing the physical separation between the MoS 2 and the contact electrode owing to its finite thickness, thereby, breaking or minimizing the metal/MoS 2 interfacial interaction responsible for the creation of mid-gap interface states that cause FLP [149][150][151]. Once this depinning is achieved, the contact work function can effectively be chosen to line up with or closer to the CBE or VBE of MoS 2 in accordance with the Schottky-Mott rule.…”

The dynamics of copper intercalated molybdenum ditelluride

“…We follow the strategy developed in Ref. [57] to define supercells and minimize strain, chosen to be applied to the metal slab because of the corresponding small effect on the electronic structure of the interface [25]. We develop the in-plane supercell lattice vectors T 1 = n 1 a 1 + n 2 a 2 and T 1 = Table 2: Parameters corresponding to the supercell construction of a Cu/MoTe 2 interface with minimal lattice mismatch (δ).…”

Out-of-plane electron transport in finite layer MoS2

“…To gain better insight into the nature of these peaks, we examine the electronic structure of finite layer MoS 2 . Ignoring the effects of the van der Waals interaction with Au, 34 the band structure and DOS for 2 and 8 ML MoS 2 were calculated using DFT and are plotted in Figs. 4(a) and 4(b).…”