Graphene Gets a Good Gap

Abstract

While numerous methods have been proposed to produce semiconducting graphene, a significant band gap has never been demonstrated. The reason is that, regardless of the theoretical gap formation mechanism, subnanometer disorder prevents the required symmetry breaking necessary to make graphene semiconducting. In this work, we show for the first time that semiconducting graphene can be made by epitaxial growth. Using improved growth methods, we show by direct band measurements that a band gap greater than 0.5 eV can be produced in the first graphene layer grown on the SiC(0001) surface. This work demonstrates that order, a property that remains lacking in other graphene systems, is key to producing electronically viable semiconducting graphene. DOI: 10.1103/PhysRevLett.115.136802 PACS numbers: 73.22.Pr, 79.60.Bm, 79.60.Jv, 81.05.ue It is well known that the first graphene layer grown on the SiC(0001) surface is not electronic graphene. That is, the first "buffer" graphene layer does not show the linear dispersing π bands (Dirac cone) expected at the K point of metallic graphene [1][2][3]. The lack of π bands in experimental band maps of the buffer layer [2] supported the theoretical conclusion that sufficiently strong covalent bonds between the buffer layer and the SiC interface would push the graphene π bands below the SiC valence band maximum [4,5]. Aside from these very early studies, research on the SiC graphene buffer layer faded and was subsequently eclipsed by a wide variety of other unsuccessful ideas to open a band gap in exfoliated or chemical vapor deposition (CVD)-grown graphene [6].One method to open a band gap in graphene is by periodic bonding to either all A or all B sites, which breaks graphene's chiral symmetry (referred to as graphene functionalization). The buffer graphene, commensurately bonded to the SiC(0001) surface, should have been an excellent example of a functionalized system. Despite the buffer graphene's potential to be functionalized by a commensurate and, most importantly, ordered array of Si or C atoms at the SiC surface, there was instead a major research shift to functionalize CVD-grown graphene. As of this writing, no functionalized graphene, or graphene modified by any other proposed method, has been developed that produces a workable semiconducting form of graphene. The problem with these methods is the inherent disorder introduced by the functionalization [7,8] and growth processes [6]. In fact, the lack of a graphene band gap was the motivation to shift research to metal dichalcogenides despite the inability to grow them at the level of purity and order required for scalable electronics.In this work, we use furnace-grown graphene to produce a structurally well-ordered buffer graphene (BG) on the SiC(0001) surface. Angle-resolved photoemission (ARPES) measurements show new dispersing π bands that are not observed in samples grown by previous methods. These bands live above the SiC valence band maximum near the Fermi energy E F . The new band structure is a result of impr...

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“…In particular, the D i do not have to be sparse. 5 In this work, all even blocks are diagonal matrices of the form…”

“…for even n, where Âk = (A k ) ij ĉ † i ĉj are the fermionic bilinear operators and A k (without hat) contain matrix elements in the single-particle Hilbert space. The expressions (5) are derived in Refs. [33,58,59] and are also the core of the determinantal Quantum-Monte-Carlo sim-ulations following Blankenbecler, Scalapino and Sugar (BSS).…”

“…[33,58,59] and are also the core of the determinantal Quantum-Monte-Carlo sim-ulations following Blankenbecler, Scalapino and Sugar (BSS). Applying (5) to the expression (3), we obtain…”

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