Sublattice-induced symmetry breaking and band-gap formation in graphene

Skomski, Ralph; Dowben, Peter A.; Driver, M. Sky; Kelber, J. A.

doi:10.1039/c4mh00124a

Cited by 48 publications

(44 citation statements)

References 103 publications

(191 reference statements)

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“…The reduction of symmetry from C6v to C3v, by breaking the equivalency of the graphene sites, leads to the opening of a band gap in the otherwise gapless semiconductor graphene [23]. It should be noted that there is an interplay between the energy cost or strain energy for graphene structural reconstructions and reduction in energy opening up a band gap, but when a reduction of the symmetry is allowed, graphene can lower the total free energy of the system and a band gap will open at the Dirac point.…”

Section: Introductionmentioning

confidence: 99%

“…For this reason, there is considerable activity in search of ways to open and control the band gap in graphene. Several methods have been proposed, in particular (i) adsorption interaction with the substrate and intercalation [7,18,19]; (ii) lattice distortion causing the symmetry reduction [2,3,[20][21][22][23][24]; and (iii) structural confinements (such as in nanoribbons and islands) [25,26]. The produced band gaps were observed in photoemission experiments (in particular, with help of the modern real-time band mapping technique), and thus were considered to prove the Dirac theory due to the observations of cone-like bands.…”

Section: Introductionmentioning

confidence: 99%

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Dirac Cones in Graphene, Interlayer Interaction in Layered Materials, and the Band Gap in MoS2

Yakovkin

2016

Crystals

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Abstract:The 2D outlook of graphene and similar layers has initiated a number of theoretical considerations of electronic structure that are both interesting and exciting, but applying these ideas to real layered systems, in terms of a model 2D system, must be done with extreme care. In the present review, we will discuss the applicability of the 2D concept with examples of peculiarities of electronic structures and interactions in particular layered systems: (i) Dirac points and cones in graphene; (ii) van der Waals interaction between MoS 2 monolayers; and (iii) the issue of a 2D screening in estimates of the band gap for MoS 2 monolayers.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dirac Cones in Graphene, Interlayer Interaction in Layered Materials, and the Band Gap in MoS2

Yakovkin

2016

Crystals

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“…The band gap of graphene oxide 4,9,12,33 makes this material of general interest for a variety of sensor applications. [34][35][36] As noted above, the C 3v symmetry and significant sp 3 character of at least the first two C layers on MgO(111) indicate that spin-orbit coupling should be enabled in these layers.…”

Section: Discussionmentioning

confidence: 99%

“…4,9,12 Moreover, the substantial sp 3 character and three-fold symmetry of the graphene oxide/graphene heterostructure strongly suggest the 'turning on" of spin-orbit coupling 13 , with the potential for a substantial room-temperature spin Hall effect. 14 The reproduction of similar results on both a highly ordered MgO(111) single crystal and heavily twinned thin film indicate that this interfacial arrangement can tolerate a substantial degree of substrate disorder, and suggest that such oxide/graphene heterostructures may be grown on other polar oxides with desirable properties.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3] However, growth on incommensurate polar oxides has also received attention, [4][5][6][7][8][9] including substrates such as MgO 4,[7][8][9] , Co 3 O 4 (111) 5 , and Al 2 O 3 6 . Such incommensurate oxides are attractive because (a) this route to graphene growth would potentially make available a broader variety of substrates for various applications, and (b) substrate-graphene interactions might lead to novel graphene properties, such as a substrate-induced band gap, 9 or induced spin polarization of graphene. 10,11 The practical applications of such properties, however, require a detailed understanding of the graphene-polar oxide interfacial region, and of how the graphene is accommodated to a lattice-mismatched and chemically reactive substrate.…”

Section: Introductionmentioning

confidence: 99%

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Ordered three-fold symmetric graphene oxide/buckled graphene/graphene heterostructures on MgO(111) by carbon molecular beam epitaxy

et al. 2018

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KEYWORDSphotoemission, electron energy loss, low energy electron diffraction, density functional theory ABSTRACT Theory and experiment demonstrate the direct growth of a graphene oxide/buckled graphene/graphene heterostructure on an incommensurate MgO(111) substrate. X-ray photoelectron spectroscopy, electron energy loss, Auger electron spectroscopy, low energy electron diffraction, Raman spectroscopy and first-principles density functional theory (DFT) calculations all demonstrate that carbon molecular beam epitaxy on either a hydroxylated MgO(111) single crystal or a heavily twinned thin film surface at 850 K yields an initial C layer of highly ordered graphene oxide with C 3v symmetry. A 5x5 unit cell of carbon, with one missing atom, forms on a 4x4 unit cell of MgO, with the three C atoms surrounding the C vacancy surface forming covalent C-O bonds to substrate oxide sites. This leads to a bowed graphene-oxide with slightly modified D and G Raman lines and a calculated band gap of 0.36 eV. Continued C growth results in the second layer of graphene that is stacked AB with respect to the first layer and buckled conformably with the first layer while maintaining C 3v symmetry, lattice spacing and azimuthal orientation with the first layer. Carbon growth beyond the second layer yields graphene in azimuthal registry with the first two C layers, but with graphene-characteristic lattice spacing and πàπ* loss feature. This 3 rd layer is also p-type, as indicated by the 5.6 eV energy loss feature. The significant sp 3 character and C 3v symmetry of such heterostructures suggest that spin-orbit coupling is enabled, with implications for spintronics and other device applications.2

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Graphene on Chromia: A System for Beyond‐Room‐Temperature Spintronics

Barut

Yin

et al. 2022

Advanced Materials

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potential of this 2D material for spintronic applications. The weak spin relaxation in graphene can be ascribed to its vanishingly small native spin-orbit coupling [13][14][15][16] (SOC), a property that makes the manipulation of spins in the same material challenging. [4] To resolve this conundrum, various strategies have been explored to introduce magnetic character into graphene, most notably by exploiting proximity effects at its interface with an appropriate magnetic substrate. [17][18][19][20][21][22][23][24] The development of functional room-temperature devices based upon such heterostructures remains an ongoing challenge.Another approach to enhancing SOC in graphene relies on breaking the sublattice symmetry of its pristine crystal. [25,26] By opening a gap between the conduction and valence bands, this distortion effectively adds a SOC term to the Hamiltonian of graphene. In one such approach, hydrogenation has been used to induce sp 2 -to-sp 3 bond conversion, causing a buckling of the graphene structure that yields clear signatures of spin transport at room temperature. [27] Symmetry breaking has also been achieved by supporting graphene on a variety of non-magnetic substrates, such as SiC, [28] Al 2 O 3 , [29] MgO, [30] and BN. [31] While these approaches have their advantages, none of them offer the non-volatility desired to imbue spintronic devices with a potential edge over CMOS. [32] Herein, we describe an approach to achieving robust spindependent transport in graphene, well beyond room temperature, that we realize by supporting this two-dimensional material on a substrate comprised of an antiferromagnetic (AFM) oxide (chromia, Cr 2 O 3 ). One of a small number of materials to exhibit magneto-electric (ME) nature (i.e., coupling of magnetic and electrostatic polarizations) at room temperature (and beyond), [33,34] chromia is antiferromagnetic (AFM) in bulk but exhibits a net alignment of magnetic moments at its (0001) surface. [33,[35][36][37] This boundary magnetism allows chromia to function as a highly spin-polarized substrate, which is ideally suited for combination with a graphene overlayer. [32,38] The excellent dielectric character [39,40] of chromia, along with its ME nature, allows an applied voltage to be used to reverse the direction of its boundary magnetization, at significantly lower energy cost (≈aJ) than that associated with the current-driven switching of ferromagnets. [32] Evidence of robust spin-dependent transport in monolayer graphene, deposited on the (0001) surface of the antiferromagnetic (AFM)/magneto-electric oxide chromia (Cr 2 O 3 ), is provided. Measurements performed in the non-local spin-Hall geometry reveal a robust signal that is present at zero external magnetic field and which is significantly larger than any possible ohmic contribution. The spin-related signal persists well beyond the Néel temperature (≈307 K) that defines the transition between the AFM and paramagnetic states, remaining visible at the highest studied temperature of close to 450 K. This robust...

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Sublattice-induced symmetry breaking and band-gap formation in graphene

Abstract: -induced symmetry breaking and bandgap formation in graphene" (2014). Peter Dowben Publications. 262.

Cited by 48 publications

References 103 publications

Dirac Cones in Graphene, Interlayer Interaction in Layered Materials, and the Band Gap in MoS2

Dirac Cones in Graphene, Interlayer Interaction in Layered Materials, and the Band Gap in MoS2

Ordered three-fold symmetric graphene oxide/buckled graphene/graphene heterostructures on MgO(111) by carbon molecular beam epitaxy

Graphene on Chromia: A System for Beyond‐Room‐Temperature Spintronics

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