Reconstruction of a 2D layer of KBr on Ir(111) and electromechanical alteration by graphene.

Zhao Liu,Thilo Glatzel,Stefan Peeters,Maria Clelia Righi,Ernst Meyer,Antoine Hinaut,Sebastian Scherb

doi:10.3762/bjnano.12.35

Abstract

A novel reconstruction of a two-dimensional layer of KBr on an Ir(111) surface is observed by high-resolution noncontact atomic force microscopy and verified by density functional theory (DFT). The observed KBr structure is oriented along the main directions of the Ir(111) surface, but forms a characteristic double-line pattern. Comprehensive calculations by DFT, taking into account the observed periodicities, resulted in a new low-energy reconstruction. However, it is fully relaxed into a common cubic structure when a monolayer of graphene is located between substrate and KBr. By using Kelvin probe force microscopy, the work functions of the reconstructed and the cubic configuration of KBr were measured and indicate, in accordance with the DFT calculations, a difference of nearly 900 meV. The difference is due to the strong interaction and local charge displacement of the K+/Br− ions and the Ir(111) surface, which are reduced by the decoupling effect of graphene, thus yielding different electrical and mechanical properties of the top KBr layer.

Highlights

Many two-dimensional (2D) materials have excellent optical, mechanical, electromagnetic, and other attractive physical properties [1,2]
A novel corrugated reconstruction of KBr was observed on Ir(111) by non-contact atomic force microscopy (nc-AFM) and confirmed by density functional theory (DFT) simulations
The DFT simulations verify these alternating structures and predict repeating KBr clusters that form a double-row structure connected by Br− ions, which are more strongly bound to the Ir substrate, while the K+ ions keep stable

Summary

Introduction

Many two-dimensional (2D) materials have excellent optical, mechanical, electromagnetic, and other attractive physical properties [1,2]. Systems can be created to study the unusual interaction of Dirac fermions, opening up new possibilities for novel electronic and spintronic devices [5]. Another famous 2D insulator is hexagonal boron nitride (h-BN), which cannot only be used as a functional insulating monolayer [8,9,10], but can be stacked with graphene layers [11,12] and has, among other interesting properties, a very stable structural superlubricity [7]. Besides the stacking of different monolayers, the intercalation of a third ma-

Methods

Results

Conclusion