Understanding the origin of band gap formation in graphene on metals: graphene on Cu/Ir(111)

Vita, Hendrik; Böttcher, Stefan; Horn, Karsten; Voloshina, Elena; Ovcharenko, Roman; Kampen, Th.; Thißen, Andreas; Dedkov, Yuriy

doi:10.1038/srep05704

Cited by 75 publications

(99 citation statements)

References 41 publications

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“…2. For the valence band, the top-most Cu(1) d z 2 band (near -1.6 eV) shows a significant orbital hybridization (see the inset) with the π band of graphene, consistent with the literature [21], and produces large DOS peaks. Such an enhanced DOS for electrons and holes is likely to support an emissive transition due to (i) a significant coupling between C π and Cu d z 2 orbitals, (ii) an optical selection rule and (iii) an insignificant change in momentum (the direct transition).…”

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confidence: 87%

Two-Dimensional Excitonic Photoluminescence in Graphene on a Cu Surface

et al. 2017

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Despite having outstanding electrical properties, graphene is unsuitable for optical devices because of its zero band gap. Here, we report two-dimensional excitonic photoluminescence (PL) from graphene grown on Cu(111) surface, which shows an unexpected remarkably sharp and strong emission near 3.16 eV (full-width at half-maximum ≤ 3meV) and multiple emissions around 3.18 eV. As temperature increases, these emissions blue-shift, showing the characteristic negative thermal coefficient of graphene. Observed PLs originate from significantly suppressed dispersion of excited electrons in graphene caused by hybridization of graphene π and Cu d orbitals of the 1st and 2nd Cu layers at a shifted saddle point 0.525(M+K) of Brillouin zone. This finding provides a new pathway to engineering novel optoelectronic graphene devices, whilst maintaining the outstanding electrical properties of graphene.Graphene has been widely studied due to its remarkable electronic properties [1][2][3][4][5][6]. Nevertheless, owing to zero band gap, graphene has not been considered as useful optical materials [6][7][8][9][10][11]. Excited electron and hole pairs are easily screened by free electrons in metals. This makes the luminescence efficiency of metals very low so that only the band to band transition may be signified, as observed in noble metals [11]. Surprisingly, excitonic features for metallic carbon nanotubes were predicted theoretically and observed in optical absorption experiments [12,13], leading to possible enhancements in luminescence. These were explained by the fact that screening is not effective in one-dimensional metals. For 2-dimensional (2D) materials having intriguing 2D electronic features near the Fermi level like graphene, sharp luminescence was not obtainable. While an exciton in 2D semi-metallic graphene was predicted [14,15], no direct experimental evidence has been reported despite the existence of some signatures [16]. Here we show the photoluminescence (PL) of graphene on Cu, which reveals the presence of an exciton in the quasi 2D system, where Cu is unique in the sense that it interacts weakly with graphene so that the Dirac cone remains.Graphene was grown on Cu single-crystal 7×7×1 mm 3 in a hot furnace consisting of a 25 mm ID quartz tube. The Cu single-crystal disc was first placed in the center of a horizontal quartz tube mounted inside a high temperature furnace, and the tube was then evacuated, back filled with hydrogen (H 2 ) and argon (Ar), and the process was repeated three times to remove the residual air completely from the quartz tube. H 2 (100 sccm) and Ar (200 sccm) were introduced as the carrier gas, when the furnace temperature reached 1323 K. A Cu single-crystal was pre-annealed at 1323 K for 30 mins to remove the native Cu oxide layer in the H 2 and Ar atmosphere. Then, CH 4 (5 sccm) was flowed through the system. In order to know the relation of the PL with graphene, we also prepared pristine Cu(111) and cleaned Cu(111) obtained after annealing without introducing the CH 4 gas. The growth ...

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confidence: 87%

Two-Dimensional Excitonic Photoluminescence in Graphene on a Cu Surface

et al. 2017

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“…[37] authors showed that intercalation of oxygen leads to decoupling of graphene from the substrate with the shift of the Dirac point by 0.57 eV above the Fermi level. On the other hand, Cu intercalated graphene on Ir(111) is characterized by a gap between the π and π * states, opened by lifting the sublattice symmetry due to hybridization of the Cu and graphene bands [38]. At the same time, the result of intercalation of cobalt is the formation of a magnetic moment in the graphene layer [39].…”

Section: Discussionmentioning

confidence: 99%

Variation of the character of spin-orbit interaction by Pt intercalation underneath graphene on Ir(111)

et al. 2015

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The modification of the graphene spin structure is of interest for novel possibilities of application of graphene in spintronics. The most exciting of them demand not only high value of spin-orbit splitting of the graphene states, but non-Rashba behavior of the splitting and spatial modulation of the spin-orbit interaction. In this work we study the spin and electronic structure of graphene on Ir(111) with intercalated Pt monolayer. Pt interlayer does not change the 9.3 × 9.3 superlattice of graphene, while the spin structure of the Dirac cone becomes modified. It is shown that the Rashba splitting of the π state is reduced, while hybridization of the graphene and substrate states leads to a spin-dependent avoided-crossing effect near the Fermi level. Such a variation of spin-orbit interaction combined with the superlattice effects can induce a topological phase in graphene.

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“…Experimentally, graphene on the Cu(111) surface has been well studied by means of angle-resolved photoemission spectroscopy (ARPES) [8][9][10][11][12][13][14] and scanning tunneling microscopy (STM) [4]. The linear dispersion of graphene is found to be preserved.…”

Section: Introductionmentioning

confidence: 99%

“…The top of the d band edge of copper begins at −2 eV below the Fermi level. It is observed that a gap opens within the Dirac cone of graphene of about 50-180 meV [8,[10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Theory of electronic and spin-orbit proximity effects in graphene on Cu(111)

2016

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We study orbital and spin-orbit proximity effects in graphene adsorbed to the Cu(111) surface by means of density functional theory (DFT). The proximity effects are caused mainly by the hybridization of graphene π and copper d orbitals. Our electronic structure calculations agree well with the experimentally observed features. We carry out a graphene-Cu(111) distance dependent study to obtain proximity orbital and spin-orbit coupling parameters, by fitting the DFT results to a robust low energy model Hamiltonian. We find a strong distance dependence of the Rashba and intrinsic proximity induced spin-orbit coupling parameters, which are in the meV and hundreds of μeV range, respectively, for experimentally relevant distances. The Dirac spectrum of graphene also exhibits a proximity orbital gap, of about 20 meV. Furthermore, we find a band inversion within the graphene states accompanied by a reordering of spin and pseudospin states, when graphene is pressed towards copper.

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Understanding the origin of band gap formation in graphene on metals: graphene on Cu/Ir(111)

Cited by 75 publications

References 41 publications

Two-Dimensional Excitonic Photoluminescence in Graphene on a Cu Surface

Two-Dimensional Excitonic Photoluminescence in Graphene on a Cu Surface

Variation of the character of spin-orbit interaction by Pt intercalation underneath graphene on Ir(111)

Theory of electronic and spin-orbit proximity effects in graphene on Cu(111)

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