First-principles study on the electronic and optical properties of AlSb monolayer.

Using density functional theory and many-body perturbation theory, we systematically investigate the optoelectronic properties of AlSb monolayer, which has been recently synthesized by molecular beam epitaxy [ACS Nano 2021, 15, 5, 8184-8191]. After confirming the dynamical stability of the monolayer, we analyze its electronic properties at different levels of theory without (PBE, HSE03, HSE06) and with (G[Formula: see text]W[Formula: see text], GW[Formula: see text], and GW) electron-electron interaction. The results show that AlSb monolayer is a semiconductor with a direct quasiparticle band gap of 1.35 eV while its electronic structure is dominated by spin-orbit coupling. Also, we study the optical properties of the monolayer by solving the Bethe-Salpeter equation. In this regard, the effects of spin-orbit coupling, electron-electron correlation, and electron-hole interaction on the optical spectrum of the monolayer are evaluated. Based on the highest level of theory, the first bright exciton is found to be located at 0.97 eV, in excellent agreement with the experimental value (0.93 eV). Moreover, the exciton binding energy, effective mass, and Bohr radius are obtained 0.38 eV, 0.25 m[Formula: see text], and 6.31 Å, respectively. This work provides a better understanding of the electronic, optical, and excitonic properties of AlSb monolayer and may shed light on its potential applications.

Thermoelectric characteristics of X[Formula: see text]YH[Formula: see text] monolayers (X=Si, Ge; Y=P, As, Sb, Bi): a first-principles study.

Ever since global warming emerged as a serious issue, the development of promising thermoelectric materials has been one of the main hot topics of material science. In this work, we provide an in-depth understanding of the thermoelectric properties of X[Formula: see text]YH[Formula: see text] monolayers (X=Si, Ge; Y=P, As, Sb, Bi) using the density functional theory combined with the Boltzmann transport equation. The results indicate that the monolayers have very low lattice thermal conductivities in the range of 0.09-0.27 Wm[Formula: see text]K[Formula: see text] at room temperature, which are correlated with the atomic masses of primitive cells. Ge[Formula: see text]PH[Formula: see text] and Si[Formula: see text]SbH[Formula: see text] possess the highest mobilities for hole (1894 cm[Formula: see text]V[Formula: see text]s[Formula: see text]) and electron (1629 cm[Formula: see text]V[Formula: see text]s[Formula: see text]), respectively. Si[Formula: see text]BiH[Formula: see text] shows the largest room-temperature figure of merit, [Formula: see text] in the n-type doping ( [Formula: see text] cm[Formula: see text]), which is predicted to reach 3.49 at 800 K. Additionally, Si[Formula: see text]SbH[Formula: see text] and Si[Formula: see text]AsH[Formula: see text] are found to have considerable ZT values above 2 at room temperature. Our findings suggest that the mentioned monolayers are more efficient than the traditional thermoelectric materials such as Bi[Formula: see text]Te[Formula: see text] and stimulate experimental efforts for novel syntheses and applications.

Mechanical strength and flexibility in [Formula: see text]-4H borophene.

Very recently, a novel phase of hydrogenated borophene, namely [Formula: see text]-4H, has been synthesized in a free-standing form. Unlike pure borophenes, this phase shows very good stability in the air environment and possesses semiconducting characteristics. Because of the interesting stiffness and flexibility of borophenes, herein, we systematically studied the mechanical properties of this novel hydrogenated phase. Our results show that the monolayer is stiffer (Y[Formula: see text] = [Formula: see text]195 N/m) than group IV and V 2D materials and even than MoS[Formula: see text], while it is softer than graphene. Moreover, similar to other phases of borophene, the inherent anisotropy of the pure monolayer increases with hydrogenation. The monolayer can bear biaxial, armchair, and zigzag strains up to 16, 10, and 14% with ideal strengths of approximately 14, 9, and 12 N/m, respectively. More interestingly, it can remain semiconductor under this range of tension. These outstanding results suggest that the [Formula: see text]-4H is a promising candidate for flexible nanoelectronics.

Thermoelectric properties of hydrogenated Sn2Bi monolayer under mechanical strain: a DFT approach.

Bismuth based structures are among the most promising candidates for thermoelectric applications. Recently, a semiconducting binary compound with stoichiometry of Sn2Bi has been synthesized, showing a strong spin-orbit coupling effect and high electron-hole asymmetry. Motivated by the experiment, we performed a density functional theory calculation combined with the semiclassical Boltzmann transport equation to investigate the thermoelectric properties of the stabilized Sn2Bi monolayer. It is demonstrated that the mobility is strongly dependent on the strain. It is 2389 (186) cm2 V-1 s-1 for hole (electron) in relaxed monolayer, but it becomes 1758 (1758) cm2 V-1 s-1 by applying a 2.5% tensile strain. Spin-orbit coupling (SOC) induces a huge spin splitting in the conduction and valence bands as high as 350 and 270 meV, respectively, coming from p orbitals of bismuth atoms. Also, the thermoelectric efficiency of the monolayer could be directly controlled by doping and strain where the maximum room temperature figure of merit of 1.01 is obtained under the strain of 3% for n-type doping with inclusion of SOC, making it a promising candidate for thermoelectric applications.

Prediction of hydrogenated group IV-V hexagonal binary monolayers.

Group IV and V monolayers are very crucial 2D materials for their high carrier mobilities, tunable band gaps, and optical linear dichroism. Very recently, a novel group IV-V binary compound, [Formula: see text], has been synthesized on silicon substrate, and has shown very interesting electronic properties. Further investigations have revealed that the monolayer would be stable in freestanding form by hydrogenation. Inspired by this, by means of first-principles calculations, we systematically predict and investigate eight counterparts of [Formula: see text], namely [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]. The cohesive energies, phonon dispersions, and AIMD calculations show that, similar to [Formula: see text], all of these freestanding monolayers are stable in hydrogenated form. These hydrogenated monolayers are semiconductors with wide band gaps, which are favorable for opto-electronic purposes. The [Formula: see text] and [Formula: see text] structures possess indirect and direct band gaps, respectively. They represent very interesting optical characteristics, such as good absorption in the visible region and linear dichroism, which are crucial for solar cell and beam-splitting devices, respectively. Finally, the [Formula: see text] and [Formula: see text] monolayers have suitable band gaps and band edge positions for photocatalytic water splitting. Summarily, our investigations offer very interesting and promising properties for this family of binary compounds. We hope that our predictions open ways to new experimental studies and fabrication of suitable 2D materials for next generation opto-electronic and photocatalytic devices.