First-principles calculations were conducted on armchair graphene nanoribbons (AGNRs) to simulate the elastic behavior of AGNRs with hydrogen-terminated and bare edges. The results show width-dependent elastic properties with a periodicity of three, which depends on the nature of edge. The edge eigenstress and eigendisplacement models are able to predict the width-dependent nominal Young's modulus and Poisson's ratio, while the Clar structure explains the crucial role of edges in the periodically modulated size-dependent elastic properties.
γ graphyne is a new allotrope of carbon that has attracted interest because of its semiconductor characteristics and high mobility. This work investigates the biaxial strain behavior and phonon-limited mobility for single-layer γ graphyne by using first-principles calculations. Ab initio molecular dynamics calculations reveal that γ graphyne is thermodynamically stable at 300 K and can withstand a biaxial strain of ε=10%. The mobility is investigated by using the deformation potential method. We consider the contribution to mobility of three equivalent valence-band maxima and conduction-band minima, which correct the prediction of carrier mobility. The mobility significantly decreases with the biaxial strain. When under strain, the effective mass gradually increases and the elastic modulus decreases. The mobility is mainly determined by scattering from acoustic phonons. With increasing strain, optical phonons play a decisive role in carrier scattering. Finally, phonon-limited mobility is investigated by using the electron–phonon coupling method within the framework of the Boltzmann transport equation. At 300 K, the predicted mobility is as high as 9.04×103cm2V−1s−1 for electrons and 8.64×103cm2V−1s−1 for holes. The results thus give the upper limit of γ graphyne’s mobility.
Motivated by the recent successful synthesis of Janus monolayer of transition metal (TM) dichalcogenides, MXenes with Janus structures are worthy of further study, concerning its electronic structure and magnetic properties. Here, we study the effect of different transition metal atoms on the structure stability and magnetic and electronic properties of M’MCO2 (M’ and M = V, Cr and Mn). The result shows the output magnetic moment is contributed mainly by the d orbitals of the V, Cr, and Mn atoms. The total magnetic moments of ferromagnetic (FM) configuration and antiferromagnetic (AFM) configuration are affected by coupling types. FM has a large magnetic moment output, while the total magnetic moments of AFM2’s (intralayer AFM/interlayer FM) configuration and AFM3’s (interlayer AFM/intralayer AFM) configuration are close to 0. The band gap widths of VCrCO2, VMnCO2, CrMnCO2, V2CO2, and Cr2CO2 are no more than 0.02 eV, showing metallic properties, while Mn2CO2 is a semiconductor with a 0.7071 eV band gap width. Janus MXenes can regulate the size of band gap, magnetic ground state, and output net magnetic moment. This work achieves the control of the magnetic properties of the available 2D materials, and provides theoretical guidance for the extensive design of novel Janus MXene materials.
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