We report a first-principles study on the elastic, vibrational, and electronic properties of the recently synthesized phosphorene. By calculating the Grüneisen parameters, we evaluate the frequency shift of the Raman and infrared active modes via symmetric biaxial strain. We also study a strain-induced semiconductor-metal transition, the gap size, and the effective mass of carriers in various strain configurations. Furthermore, we unfold the emergence of a peculiar Dirac-shaped dispersion for specific strain conditions including the zigzag-oriented tensile strain. The observed linear energy spectrum has distinct velocities corresponding to each of its linear branches and is limited to the -X direction in the first Brillouin zone.

Elemental 2D materials exhibit intriguing heat transport and phononic properties. Here we have investigated the lattice thermal conductivity of newly proposed arsenene, the 2D honeycomb structure of arsenic, using ab initio calculations. Solving the Boltzmann transport equation for phonons, we predict a highly anisotropic thermal conductivity, of 30.4 and 7.8 W/mK along the zigzag and armchair directions, respectively at room temperature. Our calculations reveal that phonons with mean free paths between 20 nm and 1 µm provide the main contribution to the large thermal conductivity in the zig-zag direction, mean free paths of phonons contributing to heat transport in the armchair directions range between 20 and 100 nm. The obtained low and anisotropic thermal conductivity, and feasibility of synthesis, in addition to other reports on high electron mobility, make arsenene a promising material for a variety of applications, including thermal management and thermoelectric devices. PACS numbers:The discovery of graphene as a stable atomically thin material has led to extensive investigation of similar 2D systems. Its properties such as high electron mobility 1 , and very high thermal conductivity 2-5 make graphene very appealing for applications in electronics, for packaging and thermal management 6-11 . The successful isolation of single-layer graphene fostered the search for further ultra-thin 2D structures, such as silicene, germanene, phosphorene, and transition metal dichalcogenides, e.g. MoS 2 and WS 2 12,13 . These materials are now considered for various practical usages due to their distinguished properties stemming from their low dimensionality. Thermal transport in 2D materials has recently attracted the attention of the scientific community, as anomalous heat conduction has been predicted to occur in systems with reduced dimensionality 14 . Phononic properties and thermal conductivity vary significantly from one 2D system to another [15][16][17][18] . For example, silicene has a buckled structure and a lower thermal conductivity 19,20 compared to graphene 12,21,22 .2D structures of arsenic and phosphorous have been recently investigated [23][24][25][26][27] . Arsenic and phosphorus are in the 5th group of the periodic table and both have different allotropes. Black phosphorus is a layered allotrope of phosphorus similar to graphite, and the stability of its single layer form, named phosphorene has been probed both theoretically and experimentally 13,28 . Gray arsenic is one of the most stable allotropes of arsenic with a buckled layered structure 27,29 . In addition, arsenic has an orthorhombic phase (puckered) similar to black phosphorus 23,25,26 , and its monolayer is called arsenene (see Fig. 1). Experimental observations have shown that gray arsenic undergoes a structural phase transition to the orthorhombic precursor of arsenene at temperatures of about T = 370 K 30 . As a monolayer arsenene has a direct band gap as opposed to the multilayer allotrope, which exhibits an indirect band gap of the order...

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We theoretically investigate the thermoelectric properties of zigzag graphene nanoribbons in the presence of extended line defects, substrate impurities and edge roughness along the nanoribbon's length. A nearest-neighbor tight-binding model for the electronic structure and a fourth nearestneighbor force constant model for the phonon bandstructure are used. For transport we employ quantum mechanical non-equilibrium Green's function simulations. Starting from the pristine zigzag nanoribbon structure that exhibits very poor thermoelectric performance, we demonstrate how after a series of engineering design steps the performance can be largely enhanced. Our results could be useful in the design of highly efficient nanostructured graphene nanoribbon based thermoelectric devices.

The thermoelectric properties of graphene-based antidot lattices are theoretically investigated. A third nearest-neighbor tight-binding model and a fourth nearest-neighbor force constant model are employed to study the electronic and phononic band structures of graphene antidot lattices with circular, rectangular, hexagonal, and triangular antidot shapes. Ballistic transport models are used to evaluate transport coefficients. Methods to reduce the thermal conductance and to increase the thermoelectric power factor of such structures are studied. Our results indicate that triangular antidot lattices have the smallest thermal conductance due to longer boundaries and the smallest distance between the neighboring antidots. Among them, iso-triangular antidot lattices have also a large power factor and as a result a large figure of merit. V

In this paper the effect of biaxial and uniaxial strain on the mobility of single-layer MoS 2 for temperatures T > 100 K is investigated. Scattering from intrinsic phonon modes, remote phonon and charged impurities are considered along with static screening. Ab-initio simulations are utilized to investigate the strain induced effects on the electronic bandstructure and the linearized Boltzmann transport equation is used to evaluate the low-field mobility under various strain conditions. The results indicate that the mobility increases with tensile biaxial and tensile uniaxial strain along the armchair direction. Under compressive strain, however, the mobility exhibits a non-monotonic behavior when the strain magnitude is varied. In particular, with a relatively small compressive strain of 1% the mobility is reduced by about a factor of two compared to the unstrained condition, but with a larger compressive strain the mobility partly recovers such a degradation.

This work presents a more realistic study on the potential of titanium carbide MXene (Ti3C2T x ) for gas sensing, by employing first principle calculations. The effects of different ratios of different functional groups on the adsorption of NH3, NO, NO2, N2O, CO, CO2, CH4, and H2S gas molecules on Ti3C2T x were analyzed. The results indicated that Ti3C2T x is considerably more sensitive to NH3, among the studied gas molecules, with a charge transfer of −0.098 e and an adsorption energy of −0.36 eV. By analyzing the electrostatic surface potential (ESP) and the projected density of states (PDOS), important physical and mechanical properties that determine the strength and nature of gas-substrate interactions were investigated, and also, the significant role of electrostatic effects on the charge transfer mechanism was revealed. Further, the Bader charge analysis for the closest oxygen and fluorine atoms to NH3 molecule showed that oxygen atoms have 60% to 180% larger charge transfer than fluorine atoms, supporting that Ti3C2T x substrate with a relatively lower ratio of fluorine surface terminations has a stronger interaction with NH3 gas molecules. The calculations show that in the presence of water molecules, approximately 90% smaller charge transfer between NH3 molecule and the Ti3C2T x occurs. Ab initio molecular dynamics simulations (AIMD) were also carried out to evaluate the thermal stabilities of Mxenes. The comprehensive study presented in this work provides insights and paves the way for realizing sensitive NH3 sensors based on Ti3C2T x that can be tuned by the ratio of surface termination groups.