Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Beyond the Energy Band Calculations

Abstract

Although many prototype devices based on two-dimensional (2D) MoS2 have been fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental nature of 2D MoS2-metal contacts has not been well understood yet. We provide a comprehensive ab initio study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au). A comparison between the calculated and observed Schottky barrier heights (SBHs) suggests that many-electron effects are strongly suppressed in channel 2D MoS2 due to a charge transfer. The extensively adopted energy band calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc interface. By contrast, an ab initio quantum transport device simulation better reproduces the observed SBH in 2D MoS2-Sc interface and highlights the importance of a higher level theoretical approach beyond the energy band calculation in the interface study. BL MoS2-metal contacts generally have a reduced SBH than ML MoS2-metal contacts due to the interlayer coupling and thus have a higher electron injection efficiency.

Structural characterization of SnS crystals formed by chemical vapour deposition

“…The resulting cohesive energy is found to be ß0.34 eV per interface atom which is higher than what is typically expected for weak physisorption interactions (Desjonquères & Spanjaard, 1996). This value is however consistent with other modelling works on 2D heterostacks (Zhong et al, 2016) and points towards the presence of a strong interaction at the interface between the two phases (Lefebvre et al, 1998), which leads to a distortion in the atomic structure of the β-SnS layer, leading to the formation of the new β' phase.…”

Defect Dominated Charge Transport and Fermi Level Pinning in MoS2/Metal Contacts

“…Recent experimental 20,61 and theoretical studies 60,62,63 have found a similar discrepancy. According to these studies, the Fermi level is partly pinned as a result of two interface effects: first, due to a metal work function modification resulting from a dipole formation at the interface, and second, by the introduction of gap states due to the weaker Mo–S bonding induced by interface metal–S interactions at the interface.…”

Experimental Route to Scanning Probe Hot‐Electron Nanoscopy (HENs) Applied to 2D Material

“…The bright borders suggest the presence of an enhanced conductivity at the edge, an effect predicted by Density Functional Theory (DFT) calculations. [54] We observe that MoS 2 has a strong conductance anisotropy: the conductivity between two adjacent van der Waals (vdW) bonded S-Mo-S sheets is extremely low with a resistivity that has been measured to be 2200 times larger through the basal planes as compared to that measured along Mo planes. [55] This behavior means that the single layer nanoplatelets are an optimal structure compared to a multilayer crystal because electrons only need to be transferred from the contact to the platelets.…”