Strain engineering is one of the most promising and effective routes toward continuously tuning the electronic and optic properties of materials, while thermal properties are generally believed to be insensitive to mechanical strain. In this paper, the strain-dependent thermal conductivity of monolayer silicene under uniform bi-axial tension is computed by solving the phonon Boltzmann transport equation with force constants extracted from first-principles calculations. Unlike the commonly believed understanding that thermal conductivity only slightly decreases with increased tensile strain for bulk materials, it is found that the thermal conductivity of silicene first increases dramatically with strain and then slightly decreases when the applied strain increases further. At a tensile strain of 4%, the highest thermal conductivity is found to be about 7.5 times that of unstrained one. Such an unusual strain dependence is mainly attributed to the dramatic enhancement in the acoustic phonon lifetime. Such enhancement plausibly originates from the flattening of the buckling of the silicene structure upon stretching, which is unique for silicene as compared with other common two-dimensional materials. Our findings offer perspectives of modulating the thermal properties of low-dimensional structures for applications such as thermoelectrics, thermal circuits, and nanoelectronics.

The thermal transport properties of hexagonal boron nitride nanoribbons (BNNRs) are investigated. By calculating the phonon spectrum and thermal conductance, it is found that the BNNRs possess excellent thermal transport properties. The thermal conductance of BNNRs can be comparable to that of graphene nanoribbons (GNRs) and even exceed the latter below room temperature. A fitting formula is obtained to describe the features of thermal conductance in BNNRs, which reveals a critical role of the T(1.5) dependence in determining the thermal transport. In addition, an obviously anisotropic thermal transport phenomenon is observed in the nanoribbons. The thermal conductivity of zigzag-edged BNNRs is shown to be about 20% larger than that of armchair-edged nanoribbons at room temperature. The findings indicate that the BNNRs can be applied as important components of excellent thermal devices.

A two-dimensional carbon allotrope, Stone-Wales graphene, is identified in stochastic group and graph constrained searches and systematically investigated by first-principles calculations. Stone-Wales graphene consists of well-arranged Stone-Wales defects, and it can be constructed through a 90 • bond-rotation in a √ 8× √ 8 supercell of graphene. Its calculated energy relative to graphene, +149 meV/atom, makes it more stable than the most competitive previously suggested graphene allotropes We find that Stone-Wales graphene based on a √ 8 supercell is more stable than those based on √ 9 × √ 9, √ 12 × √ 12 and √ 13 × √ 13 super-cells, and is a "magic size" that can be further understood through a simple "energy splitting and inversion" model. The calculated vibrational properties and molecular dynamics of SW-graphene confirm that it is dynamically stable. The electronic structure shows SW-graphene is a semimetal with distorted, strongly anisotropic Dirac cones. PACS numbers:Elemental carbon adopts many different allotropes, including the three-dimensional (3D) cubic diamond, hexagonal diamond and graphite, the two-dimensional (2D) graphene 1 and graphynes 2 , the one-dimensional (1D) nanotubes 3 , as well as the zero-dimensional (0D) fullerenes 4 , due to its ability to hybridize in sp, sp 2 and sp 3 . Low-dimensional carbon materials, such as graphene and nanotubes, have attracted much scientific interest in view of their novel electronic and mechanical properties 1,5,6 . In particular, graphene is a well-known Dirac-cone material that exhibits high carrier mobility 1,5,6 and the quantum Hall effect 5,7,8 due to its semi-metallicity contributed from the active π-electrons 8,9 . The successes of isolating graphene 1,10,11 from graphite have spurred many efforts in searching for other 2D carbon allotropes beyond graphene. Graphynes 12,13 are alternative ways to fill the 2D space with mixed sp-sp 2 carbon atoms. They contribute rich electronic properties, including semiconductors, semi-metals and metals. Although graphynes with sp-hybridized bonding are energetically less stable than the pure sp 2 -hybridized graphene, graphite and nanotubes, there are a few graphynes that have been experimentally synthesized 2,14 .The honeycomb-like graphene is not the only way to topologically fill 2D space with sp 2 hybridized carbon. Many other hypothetical graphene allotropes have been previously proposed. For example, the pentaheptites (R 57−1 and R 57−2 ) containing exclusively 5-7 rings proposed in 1996 15 and 2000 16,17 , the Haeckelite sheets (H 567 and O 567 ) proposed by Terrones 17 , the low-energy ψ-graphene previously proposed by Csányi 18 and recently investigated by Li 19 , the dimerites (dimerite I, II and III with metallic property) and octites (metallic octite M 1 , M 2 , M 3 and semiconducting octite SC) constructed through defects patterns 20-23 , the biphenylene sheets (New-W and New-C) containing 4-6-8 rings 24,25 , the T-graphene containing 4-8 rings 26-28 , the PO-graphene con-taining 5-8 rings (OPG-L and...

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Monolayer InP3 is a promising candidate for realizing a multifunctional device that contains both photovoltaic and thermoelectric technologies.

Thermal transport properties of isotopic-superlattice graphene nanoribbons with zigzag edge (IS-ZGNRs) are investigated. We find that by isotopic superlattice modulation the thermal conductivity of a graphene nanoribbon can be reduced significantly. The thermal transport property of the IS-ZGNRs strongly depends on the superlattice period length and the isotopic mass. As the superlattice period length decreases, the thermal conductivity undergoes a transition from decreasing to increasing. This unique phenomenon is explained by analyzing the phonon transmission coefficient. While the effect of isotopic mass on the conductivity is monotone. Larger mass difference induces smaller thermal conductivity. In addition, the influence of the geometry size is also discussed. The results indicate that isotopic superlattice modulation offers an available way for improving the thermoelectric performance of graphene nanoribbons.

Based on first-principles method we predict a new low-energy Stone-Wales graphene SW40, which has an orthorhombic lattice with Pbam symmetry and 40 carbon atoms in its crystalline cell forming well-arranged Stone-Wales patterns. The calculated total energy of SW40 is just about 133 meV higher than that of graphene, indicating its excellent stability exceeds all the previously proposed graphene allotropes. We find that SW40 processes intrinsic Type-III Dirac-cone (Phys. Rev. Lett., 120, 237403, 2018) formed by band-crossing of a local linear-band and a local flat-band, which can result in highly anisotropic Fermions in the system. Interestingly, such intrinsic type-III Dirac-cone can be effectively tuned by inner-layer strains and it will be transferred into Type-II and Type-I Dirac-cones under tensile and compressed strains, respectively. Finally, a general tightbinding model was constructed to understand the electronic properties nearby the Fermi-level in SW40. The results show that type-III Dirac-cone feature can be well understood by the π-electron interactions between adjacent Stone-Wales defects. PACS numbers:The experimental synthesizing of two-dimensional (2D) graphene 1-3 and graphdiynes 4,5 opened the door to the 2D carbon-word and have attracted much scientific efforts to reveal their fundamental properties and potential applications 1,6-9 . With excellent mechanical and electronic properties 1,6,7 , graphene is believed as a potential candidate for replacing silicon in future nano-electronics as new building block 10 . To design pure-carbon nano-divice, 2D carbon allotropes can provide us rich electronic properties for different functional requirements. For example, R 57−1 11 , R 57−2 12 , H 567 12 , O 567 12 , ψ-graphene 13,14 , OPG-L 33 , net-τ 15 and other 2D carbon allotropes 16-24 with normal metallic property can be used as electron conductors. The semiconducting octite SC 19 , pza-C10 25 , Θ-graphene 26,27 and γ-graphyne 28,29 are proper candidates 23,30,31 for building diodes and transistors. The graphene 1-3 , phagraphene 32 , OPG-Z 33 and SWgraphene 23 as Dirac-cone semi-metals 23,30,31 with high carrier mobility can be used to construct high-speed nano-device. Especially, the freedom of rotation in graphene bilayer bring us the surprising phenomenon of superconductivity in some magic degrees [34][35][36][37] , which has set off a new round of research upsurge on low-dimensional carbon systems [38][39][40][41] .

The phonon transport property is a foundation of understanding a material and predicting the potential application in mirco/nano devices. In this paper, the thermal transport property of borophene is investigated by combining first-principle calculations and phonon Boltzmann transport equation. At room temperature, the lattice thermal conductivity of borophene is found to be about 14.34 W/mK (error is about 3%), which is much smaller than that of graphene (about 3500 W/mK). The contributions from different phonon modes are qualified, and some phonon modes with high frequency abnormally play critical role on the thermal transport of borophene. This is quite different from the traditional understanding that thermal transport is usually largely contributed by the low frequency acoustic phonon modes for most of suspended 2D materials. Detailed analysis further reveals that the scattering between the out-of-plane flexural acoustic mode (FA) and other modes likes FA + FA/TA/LA/OP ↔ TA/LA/OP is the predominant phonon process channel. Finally the vibrational characteristic of some typical phonon modes and mean free path distribution of different phonon modes are also presented in this work. Our results shed light on the fundamental phonon transport properties of borophene, and foreshow the potential application for thermal management community.