Electron-phonon coupling in two-dimensional silicene and germanene

Yan, Jia-An; Stein, Ryan; Schaefer, David; Wang, Xiaoqian; Chou, M. Y.

doi:10.1103/physrevb.88.121403

Cited by 113 publications

(103 citation statements)

References 39 publications

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“…DFT calculations suggest the presence of three optical phonon branches at Γ: a ZO mode, related to out-of-plane optical phonons, and energetically degenerate TO and LO phonons. While the position of the ZO branch at Γ, is close to the experimentally observed A modes, the degenerate TO/LO branches (562 cm −1 [26], ∼550 cm −1 [27], ∼556 cm −1 [28]) do not match the E mode of epitaxial silicene (514 cm ) (see also figure 3(a)). Such a discrepancy can be explained by the significant interaction between the Si adlayer and the substrate, the different atomic arrangement caused by the superstructure formation of´( ) ( ) 3 3 4 4 silicene, and the related modified hybridization state with respect to freestanding silicene [11].…”

Section: Experimental and Theoretical Detailssupporting

confidence: 67%

2D vibrational properties of epitaxial silicene on Ag(111)

et al. 2016

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The two-dimensional silicon allotrope, silicene, could spur the development of new and original concepts in Si-based nanotechnology. Up to now silicene can only be epitaxially synthesized on a supporting substrate such as Ag(111). Even though the structural and electronic properties of these epitaxial silicene layers have been intensively studied, very little is known about its vibrational characteristics. Here, we present a detailed study of epitaxial silicene on Ag(111) using in situ Raman spectroscopy, which is one of the most extensively employed experimental techniques to characterize 2D materials, such as graphene, transition metal dichalcogenides, and black phosphorous. The vibrational fingerprint of epitaxial silicene, in contrast to all previous interpretations, is characterized by three distinct phonon modes with A and E symmetries. Both, energies and symmetries of theses modes are confirmed by ab initio theory calculations. The temperature dependent spectral evolution of these modes demonstrates unique thermal properties of epitaxial silicene and a significant electron-phonon coupling. These results unambiguously support the purely two-dimensional character of epitaxial silicene up to about 300°C, whereupon a 2D-to-3D phase transition takes place. The detailed fingerprint of epitaxial silicene will allow us to identify it in different environments or to study its modifications.

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Section: Experimental and Theoretical Detailssupporting

confidence: 67%

2D vibrational properties of epitaxial silicene on Ag(111)

et al. 2016

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“…Our results clearly show that the in-plane elastic response of bilayer silicene is nearly isotropic with almost the same sound speed, v s = 8.87 km/s, along the Γ-M and Γ-K directions. Such isotropic character in sound speed was also identified in silicene monolayer with v s = 9.49 km/s, 34 suggesting slightly higher in-plane stiffness for silicene monolayer than bilayer silicene. To further verify thermodynamic stability, we also carried out the Born-Oppenheimer molecular dynamics simulations using a relatively large 10 × 10 supercell containing 400 Si atoms.…”

Section: Monolayermentioning

confidence: 60%

“…The highest optical branch is located at the Γ-point, which belongs to a doubly degenerate mode with a frequency of ω Γ = 521 cm −1 . This mode is Raman active and nearly 10 cm −1 higher than the highest optical mode (510 cm −1 in LDA) in bulk silicon 33 while 40 cm −1 lower than the highest optical mode in silicene monolayer, 34 which again suggests stronger sp 3 hybridization in bilayer silicene than silicene monolayer. The slopes of the longitudinal acoustic branches near the Γ-point correspond to the speed of sound, indicating the in-plane stiffness.…”

Section: Monolayermentioning

confidence: 92%

Intrinsic magnetism and spontaneous band gap opening in bilayer silicene and germanene

Wang

2017

Phys. Chem. Chem. Phys.

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It has been long sought to create magnetism out of simple non-magnetic materials, such as silicon and germanium. Here we show that intrinsic magnetism exists in bilayer silicene and germanene with no need to cut, etch, or dope. Unlike bilayer graphene, strong covalent interlayer bonding formed in bilayer silicene and germanene breaks the original π-bonding network of each layer, leaving the unbonded electrons unpaired and localized to carry magnetic moments. These magnetic moments then couple ferromagnetically within each layer while antiferromagnetically across two layers, giving rise to an infinite magnetic sheet with structural integrity and magnetic homogeneity. Furthermore, this unique magnetic ordering results in fundamental band gaps of 0.55 eV and 0.32 eV for bilayer silicene and germanene, respectively. The integration of intrinsic magnetism and spontaneous band gap opening makes bilayer silicene and germanene attractive for future nanoelectronics as well as spin-based computation and data storage.

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“…1). The out-of-plane corrugation of 0.57Å is larger than the ab-initio value of 0.44Å, while the relaxed lattice parameter of 3.83Å is equal to the ab-initio result [3,4,5,16]. The corrugation of silicene is essential for stabilizing the lattice and avoiding imaginary phonon frequencies of the out-of-plane acoustic phonons.…”

Section: Resultsmentioning

confidence: 84%

Comparative study of the two-phonon Raman bands of silicene and graphene

Popov¹,

Lambin²

2016

2D Mater.

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Abstract. We present a computational study of the two-phonon Raman spectra of silicene and graphene within a density-functional non-orthogonal tight-binding model. Due to the presence of linear bands close to the Fermi energy in the electronic structure of both structures, the Raman scattering by phonons is resonant. We find that the Raman spectra exhibit a crossover behavior for laser excitation close to the π-plasmon energy. This phenomenon is explained by the disappearance of certain paths for resonant Raman scattering and the appearance of other paths beyond this energy. Besides that, the electronic joint density of states is divergent at this energy, which is reflected on the behavior of the Raman bands of the two structures in a qualitatively different way. Additionally, a number of Raman bands, originating from divergent phonon density of states at the M point and at points, inside the Brillouin zone, is also predicted. The calculated spectra for graphene are in excellent agreement with available experimental data. The obtained Raman bands can be used for structural characterization of silicene and graphene samples by Raman spectroscopy.

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Electron-phonon coupling in two-dimensional silicene and germanene

Cited by 113 publications

References 39 publications

2D vibrational properties of epitaxial silicene on Ag(111)

2D vibrational properties of epitaxial silicene on Ag(111)

Intrinsic magnetism and spontaneous band gap opening in bilayer silicene and germanene

Comparative study of the two-phonon Raman bands of silicene and graphene

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