Physically founded phonon dispersions of few-layer materials and the case of borophene

Abstract

By building physically sound interatomic force constants, we offer evidence of the universal presence of a quadratic phonon branch in all unstrained 2D materials, thus contradicting much of the existing literature. Through a reformulation of the interatomic force constants (IFCs) in terms of internal coordinates, we find that a delicate balance between the IFCs is responsible for this quadraticity. We use this approach to predict the thermal conductivity of Pmmn borophene, which is comparable to that of MoS 2 , and displays a remarkable in-plane anisotropy. These qualities may enable the efficient heat management of borophene devices in potential nanoelectronic applications. IMPACT STATEMENTThe newly found universality of quadratic dispersion will change the way 2D-material phonons are calculated. Predicted results for borophene shall become a fundamental reference for future research on this material. ARTICLE HISTORY

The electronic, optical, and thermodynamic properties of borophene from first-principles calculations

“…A 7×5×1 supercell with 7×5×1 k-mesh is used to ensure the convergence. Table I lists other typical structures for borophene as predicted in previous studies [20][21][22] . The predicted a corresponds to 1/3 the a observed in Ref.…”

“…[9], while the predicted b is in good agreement with experimental results 9 . Although theoretical studies have proposed various structures for borophene [20][21][22][23][24][25][26][27][28][29][30] , scanning tunneling microscopy measurements have shown that borophene has planar structure with anisotropic corrugation 9 . There is no corrugations along the a direction, while the buckling along the b direction is observed.…”

High anisotropy of fully hydrogenated borophene

“…Two-dimensional (2D) boron sheet (borophene) has attracted much attention [1][2][3][4][5][6] since it was synthesized on a silver substrate under ultrahigh-vacuum 7 . While experimental progress is slow due to difficulty in synthesizing borophene under the strict experimental conditions, many first principles calculations have been performed to study the mechanical properties, electronic structure, phonon dispersion, lattice thermal conductivity, superconducting behavior and optical properties of borophene, as well as borophene nanoribbons and borophene nanotubes [8][9][10][11][12][13][14][15][16][17][18][19] .…”

Intrinsic Charge Transport in Stanene: Roles of Bucklings and Electron–Phonon Couplings

“…The flexural ZA mode of graphene obey a quadratic dispersion ω ZA ∝ |q| 2 , which is attributed to the sixfold rotational symmetry. [47,[55][56][57][58][59][60] The obtained phonon frequency of stanene is about ten times smaller than that of graphene because of the heavier atomic mass. The intersection of LA and ZO in graphene is absent in stanene.…”