Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure.

Beomyong Hwang,Sungmin Kim,Sungjun Lim,Suklyun Hong,Minjun Lee,Dongchul Sung,Jong Keon Yoon,Gunn Kim,Hongwoo Baek,Joseph A Stroscio,Jeong Hoon Kwon,Jisoon Ihm,Jeongwoon Hwang,Young Kuk

doi:10.1038/srep31160

Abstract

Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk.

Highlights

In a graphene layer mechanically placed on hexagonal boron nitride (h-BN), the valley degree of freedom was found to remain intact[5,8,9,10]; most electronic and transport characteristics of a free-standing graphene layer are preserved
While the above theoretical predictions were derived for a free-standing graphene layer, most previous Scanning tunneling microscopy (STM) studies were performed with graphene flakes epitaxially grown or drop-cast on metal substrates
Most graphene layers were grown on the exposed Cu substrate, while some were grown as graphene nano islands (GNIs) on the h-BN layer

Summary

Introduction

In a graphene layer mechanically placed on h-BN, the valley degree of freedom was found to remain intact[5,8,9,10]; most electronic and transport characteristics of a free-standing graphene layer are preserved. When the spin degree of freedom is considered in[13,14,15,16], a bandgap locally develops at the edge because either a ferromagnetic or an antiferromagnetic state becomes the ground state This edge state with the band gap may decay spatially away from the edge with a finite decay length if there is no corresponding bulk state[17]. While the above theoretical predictions were derived for a free-standing graphene layer, most previous STM studies were performed with graphene flakes epitaxially grown or drop-cast on metal substrates. Energy gaps of 0.2–0.3 eV were reported in a GNR that was drop-cast on Au(111)[18], a graphene monolayer (ML) epitaxially grown on Cu/Ir(111)[19], and a graphene bilayer epitaxially grown on Ru(0001)[20]. Edge states of the graphene layer and bulk gap-like features were observed in this pure and well-defined heterostructure

Methods

Results

Conclusion