Local stiffness and work function variations of hexagonal boron nitride on Cu(111)

Abstract

Combined scanning tunnelling and atomic force microscopy using a qPlus sensor enables the measurement of electronic and mechanic properties of two-dimensional materials at the nanoscale. In this work, we study hexagonal boron nitride (h-BN), an atomically thin 2D layer, that is van der Waals-coupled to a Cu(111) surface. The system is of interest as a decoupling layer for functional 2D heterostructures due to the preservation of the h-BN bandgap and as a template for atomic and molecular adsorbates owing to its local electronic trapping potential due to the in-plane electric field. We obtain work function (Φ) variations on the h-BN/Cu(111) superstructure of the order of 100 meV using two independent methods, namely the shift of field emission resonances and the contact potential difference measured by Kelvin probe force microscopy. Using 3D force profiles of the same area we determine the relative stiffness of the Moiré region allowing us to analyse both electronic and mechanical properties of the 2D layer simultaneously. We obtain a sheet stiffness of 9.4 ± 0.9 N·m−1, which is one order of magnitude higher than the one obtained for h-BN/Rh(111). Using constant force maps we are able to derive height profiles of h-BN/Cu(111) showing that the system has a corrugation of 0.6 ± 0.2 Å, which helps to demystify the discussion around the flatness of the h-BN/Cu(111) substrate.

Formation of an Extended Quantum Dot Array Driven and Autoprotected by an Atom-Thick h-BN Layer

“…Figure displays a series of large-scale STM images of h -BN/Cu­(111) for incremental annealing times. The as grown h -BN (Figure a) displays the characteristic h -BN/Cu­(111) electronic moiré. − Upon annealing for an extended time, we observe the emergence of a quasi-hexagonal network with an average periodicity of 7.7 ± 0.2 nm. As evident from the fast Fourier transforms of the STM images after annealing for 150 min (Figure c) and 330 min (Figure d), the network is highly ordered, but not strictly locked to a specific substrate orientation.…”

Study of the Cu(111) Surface by Scanning Tunneling Microscopy: The Morphology Evolution, Reconstructions, Superstructures and Line Defects

“…This has been experimentally confirmed in several 2D materials such as graphene and MoS 2 [ 20 , 21 , 22 , 23 , 24 ]. In addition, although it is easy to obtain ideal 2D materials, superstructure and regular line defects are frequently observed in the surfaces of 2D materials, and their formation mechanisms are still poorly understood [ 25 , 26 ]. The morphology and structural characteristics of Cu(111) surface are important for understanding the structure and properties of 2D materials because of the close association between the surface structures and properties of 2D materials and the surface structures of the substrates.…”