Two‐Dimensional Si Nanosheets with Local Hexagonal Structure on a MoS<sub>2</sub> Surface

Chiappe, Daniele; Scalise, Emilio; Cinquanta, Eugenio; Grazianetti, Carlo; Broek, Bas van den; Fanciulli, M.; Houssa, Michel; Molle, Alessandro

doi:10.1002/adma.201304783

Cited by 336 publications

(267 citation statements)

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“…The interior of a 2D topological insulator exhibits a spin-orbit gap, whereas topologically protected helical edge modes exist at the edges of the material [5,6]. The two topologically protected spin-polarized edge modes have opposite propagation directions and therefore the charge conductance vanishes, whereas the spin conductance has a non-zero value.In the past few years various groups have successfully synthesized silicene [7][8][9] and germanene [10-13] on a variety of substrates. To date germanene has only been grown on metallic substrates, such as Pt (111) Here we report the growth of germanene on a band gap material, namely MoS 2 .…”

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Structural and Electronic Properties of Germanene onMoS2

et al. 2016

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To date germanene has only been synthesized on metallic substrates. A metallic substrate is usually detrimental for the two-dimensional Dirac nature of germanene because the important electronic states near the Fermi level of germanene can hybridize with the electronic states of the metallic substrate. Here we report the successful synthesis of germanene on molybdenum disulfide (MoS2), a band gap material. Pre-existing defects in the MoS2 surface act as preferential nucleation sites for the germanene islands. The lattice constant of the germanene layer (3.8 ± 0.2Å) is about 20% larger than the lattice constant of the MoS2 substrate (3.16Å). Scanning tunneling spectroscopy measurements and density functional theory calculations reveal that there are, besides the linearly dispersing bands at the K points, two parabolic bands that cross the Fermi level at the Γ point. The discovery that graphene, a single layer of sp 2 hybridized carbon atoms arranged in a honeycomb registry, is stable has resulted in numerous intriguing and exciting scientific breakthroughs [1,2]. The electrons in graphene behave as relativistic massless fermions that are described by the Dirac equation, i.e. the relativistic variant of the Schrödinger equation. One might anticipate that elements with a similar electronic configuration, such as silicon (Si), germanium (Ge) and tin (Sn), also have a "graphene-like" allotrope. Unfortunately, silicene (the silicon analogue of graphene), germanene (the germanium analogue of graphene) and stanene (the tin analogue of graphene) have not been found in nature and therefore these two-dimensional (2D) materials have to be synthesized. Theoretical calculations have revealed that the honeycomb lattices of the "graphene-like" allotropes of silicon and germanium are not fully planar, but slightly buckled [3,4]. The honeycomb lattices of these 2D materials consist of two triangular sub-lattices that are slightly displaced with respect to each other in a direction normal to the honeycomb lattice. Despite this buckling the 2D Dirac nature of the electrons is predicted to be preserved [3,4]. Another salient difference with graphene is that silicene and germanene have a substantially larger spin-orbit gap than graphene (<0.05 meV). Silicene's spin-orbit gap is predicted to be 1.55 meV, whereas the predicted spin-orbit gap of germanene is even 23.9 meV. This is very interesting because graphene and also silicene and germanene are in principle 2D topological insulators and thus ideal candidates to exhibit the quantum spin Hall effect. The interior of a 2D topological insulator exhibits a spin-orbit gap, whereas topologically protected helical edge modes exist at the edges of the material [5,6]. The two topologically protected spin-polarized edge modes have opposite propagation directions and therefore the charge conductance vanishes, whereas the spin conductance has a non-zero value.In the past few years various groups have successfully synthesized silicene [7][8][9] and germanene [10-13] on a variety of substrates. T...

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confidence: 99%

“…In the past few years various groups have successfully synthesized silicene [7][8][9] and germanene [10-13] on a variety of substrates. To date germanene has only been grown on metallic substrates, such as Pt (111) Here we report the growth of germanene on a band gap material, namely MoS 2 .…”

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confidence: 99%

Structural and Electronic Properties of Germanene onMoS2

et al. 2016

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“…On the other hand, some successfully synthesized graphene-like honeycomb materials, such as silicene [21][22][23][24] , germanene 25 and stanene…”

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“…On the other hand, some successfully synthesized graphene-like honeycomb materials, such as silicene [21][22][23][24] , germanene 25 and stanene 26 , are found to be easily oxidized or chemically absorb other atoms because of their buckling geometries. Obviously, the absorbed atoms will greatly change the hopping energies in the honeycomb lattice.…”

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Semi-Dirac semimetal in silicene oxide

Zhong

Chen

Xie

et al. 2017

Phys. Chem. Chem. Phys.

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Semi-Dirac semimetal is a material exhibiting linear band dispersion in one direction and quadratic band dispersion in the orthogonal direction and, therefore, hosts massless and massive fermions at the same point in the momentum space. While a number of interesting physical properties have been predicted in semi-Dirac semimetals, it has been rare to realize such materials in condensed matters. Based on the fact that some honeycomb materials are easily oxidized or chemically absorb other atoms, here, we theoretically propose an approach of modifying their band structures by covalent addition of group-VI elements and strain engineering. We predict a silicene oxide with chemical formula of Si 2 O to be a candidate of semi-Dirac semimetal. Our approach is backed by the analysis and understanding of the effect of p-orbital frustration on the band structure of the graphene-like materials.2 Dirac Semimetals, as represented by graphene, have been intensively studied in the past decade as a condensed matter platform of massless Dirac fermions [1,2] . The electronic structure of graphene is characterized by two Dirac points, located at K and K', respectively, in the momentum space [3] . In a tight-binding (TB) picture, by tuning the nearest-neighbor hopping energies in a graphene lattice, as illustrated in Figure 1, the two Dirac points can approach each other and merge into one forming the so-called semi-Dirac point, near which the band dispersion exhibits a peculiar feature, i.e., being linear in one direction and quadratic in the orthogonal direction [4][5][6] . Materials possessing semi-Dirac points are called semi-Dirac semimetals, which provide a platform where massless and massive Dirac fermions coexist. Besides the apparent highly anisotropic transport properties [7] , a number of other interesting properties have been predicted for the semi-Dirac semimetals, such as distinct Landau-level spectrum in a magnetic field [8,9] , non-Fermi liquid [10] , Anderson localization [11] and Bloch-Zener oscillations [12] . It is therefore of great interest to search for materials realizing the semi-Dirac semimetals.While the TB picture provides important guidance, the search for semi-Dirac semimetals still relies on non-trivial materials design. A VO 2 /TiO 2 superlattice has been theoretically proposed to hold multiple semi-Dirac points within the first Brillouin zone (BZ) [13] . The formation mechanism of the semi-Dirac points in this material is described by a TB model [14] different from that illustrated in Figure 1. Recently, black phosphorus (BP) has been predicted to exhibit a single semi-Dirac point in the BZ under pressure [15] . An exciting experiment has shown that a giant Stark effect through electron doping on the surface of BP indeed yields a semi-Dirac point [16] , albeit at heavily n-type doped condition with the semi-Dirac point below the Fermi level by about 0.5 eV. A Dirac-to-semi-Dirac transition by merging two Dirac points, as illustrated in Figure 1, still remains 3 to be demonstrated in a solid-...

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“…These properties make silicene ideal for envisaging various types of device functionality related to both spintronics and valleytronics, a quest also significantly fueled by its compatibility with existing Si semiconductor technology. On the experimental side, silicene has already been studied on metallic substrates, including ZrB 2 [6] and notably Ag(111) [7][8][9], as well as for nonmetallic hosts, where a Si nanosheet grown on MoS 2 bulk crystals has recently been reported [10].A particularly exciting prospect is to consider the manifestation of superconducting correlations in silicene, with the unique properties of silicene likely leading to an advanced interplay between spintronics and superconductivity [11]. Recent experimental progress has enabled the study of superconductivity in atomically thin materials, such as in graphene [12][13][14] and transition metal dichalcogenides [15,16], through the proximity effect from external superconductors.…”

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Quantum ground state control in superconductor-silicene structures: 0- π transitions, φ0 -junctions, and Majorana bound states

2016

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We demonstrate theoretically that proximity-induced superconductivity in silicene offers the possibility to exert strong quantum ground state control. We show that electrically controlled 0-π transitions occur in Josephson junctions in the presence of an exchange field due to the buckling of the silicene lattice. We also discover that zigzag-oriented interfaces, featuring intervalley scattering, cause a ϕ0 state with an applied electric field. Finally, we demonstrate that Majorana bound states along the silicene edge are tunable via the edge orientation, electric, and in-plane spin exchange fields.PACS numbers: 74.50.+r, 74.45.+c, 73.61.Wp, 71.10.Pm The discovery of new low-dimensional materials, where the electron bands have topological properties, has attracted a large amount of interest in recent years. A particularly intriguing material is silicene [1], which consists of an atomically thin, buckled layer of Si atoms arranged in a honeycomb lattice. This material has theoretically been shown to host both different topological phases and has individually tunable mass gaps for each spin σ at each valley η [2-5]. These properties make silicene ideal for envisaging various types of device functionality related to both spintronics and valleytronics, a quest also significantly fueled by its compatibility with existing Si semiconductor technology. On the experimental side, silicene has already been studied on metallic substrates, including ZrB 2 [6] and notably Ag(111) [7][8][9], as well as for nonmetallic hosts, where a Si nanosheet grown on MoS 2 bulk crystals has recently been reported [10].A particularly exciting prospect is to consider the manifestation of superconducting correlations in silicene, with the unique properties of silicene likely leading to an advanced interplay between spintronics and superconductivity [11]. Recent experimental progress has enabled the study of superconductivity in atomically thin materials, such as in graphene [12][13][14] and transition metal dichalcogenides [15,16], through the proximity effect from external superconductors. Motivated by this, we set out to determine how superconductivity is manifested in silicene, especially focusing on the external control of unusual phenomena via an electric field.We demonstrate that proximity-induced superconductivity in silicene allows for a strong quantum ground state control. By creating superconductor-ferromagnetsuperconductor (SFS) Josephson junctions in bulk silicene, we find that the exchange field in the F region gives rise to electrically controlled 0-π transitions, due to the buckling of the silicene lattice. We also discover that zigzag-oriented SF interfaces, which host notable intrinsic intervalley scattering, result in an exotic ϕ 0 state, directly tunable by electric field. Finally, we demonstrate that the existence of Majorana bound states (MBS) at SF junctions on silicene edges is controlled by edge orientation and the strength of electric and in-plane exchange fields.First, we compute the supercurrent in bulk silicene S...

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Two‐Dimensional Si Nanosheets with Local Hexagonal Structure on a MoS₂ Surface

Cited by 336 publications

References 42 publications

Structural and Electronic Properties of Germanene onMoS2

Structural and Electronic Properties of Germanene onMoS2

Semi-Dirac semimetal in silicene oxide

Quantum ground state control in superconductor-silicene structures: 0- π transitions, φ0 -junctions, and Majorana bound states

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Two‐Dimensional Si Nanosheets with Local Hexagonal Structure on a MoS2 Surface

Cited by 336 publications

References 42 publications

Structural and Electronic Properties of Germanene onMoS2

Structural and Electronic Properties of Germanene onMoS2

Semi-Dirac semimetal in silicene oxide

Quantum ground state control in superconductor-silicene structures: 0- π transitions, φ0 -junctions, and Majorana bound states

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Two‐Dimensional Si Nanosheets with Local Hexagonal Structure on a MoS₂ Surface