Improving the stability and optical properties of germanane via one-step covalent methyl-termination

Jiang, Shaoquan; Butler, Sheneve; Bianco, Elisabeth; Restrepo, Oscar D.; Windl, Wolfgang; Goldberger, Joshua E.

doi:10.1038/ncomms4389

Cited by 227 publications

(319 citation statements)

References 44 publications

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“…Figure 1a and b present the schematic atomic structure of the methyl-functionalized bilayer films in their most stable configuration. As Figure 1a illustrates, the metal centers have a stable sp 3 configuration analogous to the recently experimentally produced methyl-functionalized germanene, 33 with the chemical functional groups bonding on both sides of the plane in an alternating way. The crystal structures of these thin films present a hexagonal Bravais lattice and can be described by the symmetry point group D 3d , with one pair of M atoms and methyl groups in the unit cell.…”

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confidence: 95%

Robust Two-Dimensional Topological Insulators in Methyl-Functionalized Bismuth, Antimony, and Lead Bilayer Films

et al. 2015

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One of the major obstacles to a wide application range of the quantum spin Hall (QSH) effect is the lack of suitable QSH insulators with a large bulk gap. By means of first-principles calculations including relativistic effects, we predict that methyl-functionalized bismuth, antimony, and lead bilayers (Me-Bi, Me-Sb, and Me-Pb) are 2D topological insulators (TIs) with protected Dirac type topological helical edge states, and thus suitable QSH systems. In addition to the explicitly obtained topological edge states, the nontrivial topological characteristic of these systems is confirmed by the calculated nontrivial Z2 topological invariant. The TI characteristics are intrinsic to the studied materials and are not subject to lateral quantum confinement at edges, as confirmed by explicit simulation of the corresponding nanoribbons. It is worthwhile to point out that the large nontrivial bulk gaps of 0.934 eV (Me-Bi), 0.386 eV (Me-Sb), and 0.964 eV (Me-Pb) are derived from the strong spin-orbit coupling within the p(x) and p(y) orbitals and would be large enough for room-temperature application. Moreover, we show that the topological properties in these three systems are robust against mechanical deformation. These novel 2D TIs with such giant topological energy gaps are promising platforms for topological phenomena and possible applications at high temperature.

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confidence: 95%

Robust Two-Dimensional Topological Insulators in Methyl-Functionalized Bismuth, Antimony, and Lead Bilayer Films

et al. 2015

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“…DRA spectra of (c) GeH and (d) GeCH 3 annealed in Ar/ H 2 gas at various temperatures. 13,14 Accounts of Chemical Research Article dx.doi.org/10.1021/ar500296e | Acc. Chem.…”

Section: ■ Thermal and Air Stabilitymentioning

confidence: 99%

Covalently-Controlled Properties by Design in Group IV Graphane Analogues

et al. 2014

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CONSPECTUS: The isolation of graphene has sparked a renaissance in the study of two-dimensional materials. This led to the discovery of new and unique phenomena such as extremely high carrier mobility, thermal conductivity, and mechanical strength not observed in the parent 3D structure. While the emergence of these phenomena has spurred widespread interest in graphene, the paradox between the high-mobility Fermi-Dirac electronic structure and the need for a sizable band gap has challenged its application in traditional semiconductor devices. While graphene is a fascinating and promising material, the limitation of its electronic structure has inspired researchers to explore other 2D materials beyond graphene. In this Account, we summarize our recent work on a new family of two-dimensional materials based on sp(3)-hybridized group IV elements. Ligand-terminated Si, Ge, and Sn graphane analogues are an emerging and unique class of two-dimensional materials that offer the potential to tailor the structure, stability, and properties. Compared with bulk Si and Ge, a direct and larger band gap is apparent in group IV graphane analogues depending on the surface ligand. These materials can be synthesized in gram-scale quantities and in thin films via the topotactic deintercalation of layered Zintl phase precursors. Few layers and single layers can be isolated via manual exfoliation and deintercalation of epitaxially grown Zintl phases on Si/Ge substrates. The presence of a fourth bond on the surface of the layers allows various surface ligand termination with different organic functional groups achieved via conventional soft chemical routes. In these single-atom thick materials, the electronic structure can be systematically controlled by varying the identities of the main group elements and by attaching different surface terminating ligands. In contrast to transition metal dichalcogenides, the weaker interlayer interaction allows the direct band gap single layer properties such as photoluminescence to be readily observable without the need to exfoliate down to single layers. Furthermore, these materials can be resilient to oxidation and thermal degradation, making them attractive candidates for next generation functional materials for electronic devices and beyond. This class of two-dimensional materials not only are promising building blocks for a variety of conventional semiconductor applications but also provide a pioneering platform to systematically and rationally control material properties using covalent chemistry. The stability and tunability of these versatile materials will push this system toward the forefront of two-dimensional research.

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“…35 Unlike the destruction by hydrogenation and fluorina-tion, the methyl functionalization was observed to be much more moderate reaction kinetics, indicating that the methyl is more suitable for surface passivation. Moreover, methyl functionalization can considerably enhance the thermal stability of system at high-temperature 35 . Consequently, it becomes more interesting to realize large band gap QSH insulators in the methyl functionalized III-Bi films.…”

Section: Two-dimensional (2d) Topological Insulators Also Called Quamentioning

confidence: 99%

Robust large-gap quantum spin Hall insulators in methyl-functionalized III-Bi buckled honeycombs

Lü

Wang

Chen

et al. 2018

Phys. Rev. Materials

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Based on first-principles calculations, we predict that the methyl-functionalized III-Bi monolayers, namely III-Bi-(CH 3 ) 2 (III=Ga, In, Tl) films, own quantum spin hall (QSH) states with band gap as large as 0.260, 0.304 and 0.843 eV, respectively, making them suitable for room-temperature applications. The topological characteristics are confirmed by s-p x,y band inversion, topological invariant Z 2 number, and the time-reversal symmetry protected helical edge states. Noticeably, for GaBi/InBi-(CH 3 ) 2 , the s-p x,y band inversion occurred in the progress of spin-orbital coupling (SOC), while for TlBi(CH 3 ) 2 , the s-p x,y band inversion happened in the progress of chemical bonding. Significantly, the nontrivial topological states in III-Bi-(CH 3 ) 2 films are robust against the mechanical strain and various methyl coverage, making them particularly flexible to substrate choice for device applications. Besides, we find the h-BN is an ideal substrate for III-Bi-(CH 3 ) 2 films to realize large gap nontrivial topological states. These findings demonstrate that the methyl-functionalized III-Bi films may be good QSH effect platforms for topological electronic devices design and fabrication in spintronics.

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Improving the stability and optical properties of germanane via one-step covalent methyl-termination

Cited by 227 publications

References 44 publications

Robust Two-Dimensional Topological Insulators in Methyl-Functionalized Bismuth, Antimony, and Lead Bilayer Films

Robust Two-Dimensional Topological Insulators in Methyl-Functionalized Bismuth, Antimony, and Lead Bilayer Films

Covalently-Controlled Properties by Design in Group IV Graphane Analogues

Robust large-gap quantum spin Hall insulators in methyl-functionalized III-Bi buckled honeycombs

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