Modeling Atomic-Scale Electrical Contact Quality Across Two-Dimensional Interfaces

Abstract

Contacting interfaces with physical isolation and weak interactions usually act as barriers for electrical conduction. The electrical contact conductance across interfaces has long been correlated with the true contact area or the "contact quantity". Much of the physical understanding of the interfacial electrical contact quality was primarily based on Landauer's theory or Richardson formulation. However, a quantitative model directly connecting contact conductance to interfacial atomistic structures still remains absent. Here, we measure the atomic-scale local electrical contact conductance instead of local electronic surface states in graphene/Ru(0001) superstructure, via atomically resolved conductive atomic force microscopy. By defining the "quality" of individual atom−atom contact as the carrier tunneling probability along the interatomic electron transport pathways, we establish a relationship between the atomic-scale contact quality and local interfacial atomistic structure. This real-space model unravels the atomic-level spatial modulation of contact conductance, and the twist angle-dependent interlayer conductance between misoriented graphene layers.

Understanding Interlayer Contact Conductance in Twisted Bilayer Graphene

“…As Φ interface and ρ carrier show opposite trends in affecting the local conductance comparison between AA and AB regions, it is not straightforward to combine the effects of Φ interface and ρ carrier on the moiré‐level modulation of local conductivity as measured by C‐AFM experiments. Atomic‐scale contact quality (ACQ) model, which takes both Φ interface and ρ carrier into consideration as described in our previous work for both graphene/metal and 2D material/2D material interfaces, was utilized here to unravel the modulation of conductance in twisted graphene systems. The individual C–C atom contact conductance ( G atomic )—C–C atom distance ( d C–C ) relationship used in the ACQ model is shown in Figure c (more details can be found in the Supporting Information).…”

Insights into dynamic sliding contacts from conductive atomic force microscopy

“…Specically, there have been several CAFM studies where lateral force and current were measured simultaneously on atomically ordered surfaces. [7][8][9][10]27 In these experiments, both the current and lateral force patterns exhibited the same periodicity as the substrate's atomic lattice. Recently, such studies have shown that current can be used to detect defects in the surface lattice, 9,27 changes in conduction modes or pathways on the surface, 10 and stacking conguration of monolayers on the substrate.…”

“…1,2 Electrically conductive contacts are also relevant to topics such as the mechanical behavior of materials, 3 evolution of the contact formed between two bodies as they are pressed together, 4,5 and friction between sliding surfaces. [6][7][8][9][10] Such phenomena are studied using atomic force microscopy (AFM) which enables spatial, mechanical, and electrical measurements though small, well-dened contacts formed between a nanoscale AFM probe and a substrate. The electrical behavior of these contacts can be studied using conductive AFM (CAFM) where a potential bias is applied between a conductive probe and substrate and the current ow through the contact is measured.…”

“…shortening or lengthening of the distance between atoms in a contact, may be a signicant contributing factor for electron transport. 8,[23][24][25] Finally, the mechanical properties of the substrate, specically the stiffness of a substrate material, can impact the conduction of electrons through the contact. 26 In general, previous studies have shown that the current ow through a nanoscale contact cannot be quantitatively correlated with contact area, except for a general observation that increased contact area sometimes corresponds to increased current ow through the contact.…”

“…Recently, such studies have shown that current can be used to detect defects in the surface lattice, 9,27 changes in conduction modes or pathways on the surface, 10 and stacking conguration of monolayers on the substrate. 8,27 Although these studies suggest strong correlations between conduction and the dynamic structure of the contact, the exact nature of those correlations are just beginning to be explored.…”