Two-dimensional (2D) crystals are known to have no bulk but only surfaces and edges, thus leading to unprecedented properties thanks to the quantum confinements. For half a century, the compression of z-dimension has ...Two-dimensional (2D) crystals are known to have no bulk but only surfaces and edges, thus leading to unprecedented properties thanks to the quantum confinements. For half a century, the compression of z-dimension has been attempted through ultra-thin films by such as molecular beam epitaxy. However, the revisiting of thin films becomes popular again, in another fashion of the isolation of freestanding 2D layers out of van der Waals (vdW) bulk compounds. To date, nearly two decades after the nativity of the great graphene venture, researchers are still fascinated about flattening, into the atomic limit, all kinds of crystals, whether or not they are vdW. In this introductive review, we will summarize some recent experimental progresses on 2D electronic systems, and briefly discuss their revolutionizing capabilities for the implementation of future nanostructures and nanoelectronics.展开更多
In this topical review, we discuss the electronic structure of free-standing silicene by comparing results obtained using different theoretical methods. Silicene is a single atomic layer of silicon similar to graphene...In this topical review, we discuss the electronic structure of free-standing silicene by comparing results obtained using different theoretical methods. Silicene is a single atomic layer of silicon similar to graphene. The interest in silicene is the same as for graphene, in being two-dimensional and possessing a Dirac cone. One advantage of silicene is due to its compatibility with current silicon electronics. Both empirical and first-principles techniques have been used to study the electronic properties of silicene. We will provide a brief overview of the parameter space for first-principles calculations.However, since the theory is standard, no extensive discussion will be included. Instead, we will emphasize what empirical methods can provide to such investigations and the current state of these theories. Finally, we will review the properties computed using both types of theories for free-standing silicene, with emphasis on areas where we have contributed.Comparisons to graphene is provided throughout.展开更多
Consequences of an exceedingly strong electric field (E field) on the ground state energetics and transport properties of a 2D spinless electron gas in a perpendicular magnetic field (a Quantum Hall Effect (QHE) confi...Consequences of an exceedingly strong electric field (E field) on the ground state energetics and transport properties of a 2D spinless electron gas in a perpendicular magnetic field (a Quantum Hall Effect (QHE) configuration) are investigated to all orders in the fields. For a conventional semiconductor, we find fractional values of the Hall conductivity and some magnetoelectric coefficients for certain values of E and B fields that do not result from interactions or impurities, but are a pure consequence of a strong enough in-plane E field. We also determine analytically the ground state energy, and response properties such as magnetization and polarization as functions of the electromagnetic field in the strong E field limit. In the case of Graphene, we obtain more complex behaviors leading to the possibility of irrational Hall values. The results are also qualitatively discussed in connection to various mechanisms for the QHE-breakdown.展开更多
In this article, we investigate the predictions of the first principles on structural stability, electronic and mechanical properties of 2D nanostructures: graphene, silicene, germanene and stenane. The electronic ban...In this article, we investigate the predictions of the first principles on structural stability, electronic and mechanical properties of 2D nanostructures: graphene, silicene, germanene and stenane. The electronic band structure and density of states in all these 2D materials are found to be generic in nature. A small band gap is generated in all the reported materials other than graphene. The linearity at the Dirac cone changes to quadratic, from graphene to stenane and a perfect semimetalicity is exhibited only by graphene. All other 2D structures tend to become semiconductors with an infinitesimal band gap. Bonding characteristics are revealed by density of states histogram, charge density contour, and Mulliken population analysis. Among all 2D materials graphene exhibits exotic mechanical properties. Analysis by born stability criteria and the calculation of formation enthalpies envisages the structural stability of all the structures in the 2D form. The calculated second order elastic stiffness tensor is used to determine the moduli of elasticity in turn to explore the mechanical properties of all these structures for the prolific use in engineering science. Graphene is found to be the strongest material but brittle in nature. Germanene and stenane exhibit ductile nature and hence could be easily incorporated with the existing technology in the semiconductor industry on substrates.展开更多
本文基于密度泛函理论(DFT)的第一性原理计算了W、Mn、V、Ti替位掺杂二维MoSi_(2)N_(4)后的几何结构、电子结构以及光学性质的变化.电子结构分析表明W、Mn、W、Ti替位掺杂二维MoSi_(2)N_(4)后的禁带宽度分别为1.806 e V、1.003 e V、1.2...本文基于密度泛函理论(DFT)的第一性原理计算了W、Mn、V、Ti替位掺杂二维MoSi_(2)N_(4)后的几何结构、电子结构以及光学性质的变化.电子结构分析表明W、Mn、W、Ti替位掺杂二维MoSi_(2)N_(4)后的禁带宽度分别为1.806 e V、1.003 e V、1.218 e V和1.373 e V;四种过渡金属掺杂后MoSi_(2)N_(4)的带隙类型没有发生改变,均为间接带隙半导体;W掺杂后的杂质能级靠近价带顶,费米能级靠近价带顶,为p型半导体,杂质能级为受主能级;Mn掺杂后的杂质能级靠近导带底,费米能级靠近导带底,为n型半导体;V和Ti掺杂后杂质能级位于费米能级附近,为复合中心;光学性质分析表明,在2 e V~4 e V的能量区间内,W掺杂结构的吸收波长为336 nm,体系发生红移;Mn、V和Ti替位掺杂后的吸收波长分别为320 nm、358 nm和338 nm,且掺杂体系均发生蓝移.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974357 and U1932151)the State Key Research Development Program of China(Grant No.2019YFA0307800)+1 种基金the Program of State Key Laboratory of Quantum Optics and Quantum Optics Devices,China(Grant No.KF201816)the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation NSFC and CASC,China(Grant No.U1537204).
文摘Two-dimensional (2D) crystals are known to have no bulk but only surfaces and edges, thus leading to unprecedented properties thanks to the quantum confinements. For half a century, the compression of z-dimension has been attempted through ultra-thin films by such as molecular beam epitaxy. However, the revisiting of thin films becomes popular again, in another fashion of the isolation of freestanding 2D layers out of van der Waals (vdW) bulk compounds. To date, nearly two decades after the nativity of the great graphene venture, researchers are still fascinated about flattening, into the atomic limit, all kinds of crystals, whether or not they are vdW. In this introductive review, we will summarize some recent experimental progresses on 2D electronic systems, and briefly discuss their revolutionizing capabilities for the implementation of future nanostructures and nanoelectronics.
文摘In this topical review, we discuss the electronic structure of free-standing silicene by comparing results obtained using different theoretical methods. Silicene is a single atomic layer of silicon similar to graphene. The interest in silicene is the same as for graphene, in being two-dimensional and possessing a Dirac cone. One advantage of silicene is due to its compatibility with current silicon electronics. Both empirical and first-principles techniques have been used to study the electronic properties of silicene. We will provide a brief overview of the parameter space for first-principles calculations.However, since the theory is standard, no extensive discussion will be included. Instead, we will emphasize what empirical methods can provide to such investigations and the current state of these theories. Finally, we will review the properties computed using both types of theories for free-standing silicene, with emphasis on areas where we have contributed.Comparisons to graphene is provided throughout.
文摘Consequences of an exceedingly strong electric field (E field) on the ground state energetics and transport properties of a 2D spinless electron gas in a perpendicular magnetic field (a Quantum Hall Effect (QHE) configuration) are investigated to all orders in the fields. For a conventional semiconductor, we find fractional values of the Hall conductivity and some magnetoelectric coefficients for certain values of E and B fields that do not result from interactions or impurities, but are a pure consequence of a strong enough in-plane E field. We also determine analytically the ground state energy, and response properties such as magnetization and polarization as functions of the electromagnetic field in the strong E field limit. In the case of Graphene, we obtain more complex behaviors leading to the possibility of irrational Hall values. The results are also qualitatively discussed in connection to various mechanisms for the QHE-breakdown.
文摘In this article, we investigate the predictions of the first principles on structural stability, electronic and mechanical properties of 2D nanostructures: graphene, silicene, germanene and stenane. The electronic band structure and density of states in all these 2D materials are found to be generic in nature. A small band gap is generated in all the reported materials other than graphene. The linearity at the Dirac cone changes to quadratic, from graphene to stenane and a perfect semimetalicity is exhibited only by graphene. All other 2D structures tend to become semiconductors with an infinitesimal band gap. Bonding characteristics are revealed by density of states histogram, charge density contour, and Mulliken population analysis. Among all 2D materials graphene exhibits exotic mechanical properties. Analysis by born stability criteria and the calculation of formation enthalpies envisages the structural stability of all the structures in the 2D form. The calculated second order elastic stiffness tensor is used to determine the moduli of elasticity in turn to explore the mechanical properties of all these structures for the prolific use in engineering science. Graphene is found to be the strongest material but brittle in nature. Germanene and stenane exhibit ductile nature and hence could be easily incorporated with the existing technology in the semiconductor industry on substrates.
文摘本文基于密度泛函理论(DFT)的第一性原理计算了W、Mn、V、Ti替位掺杂二维MoSi_(2)N_(4)后的几何结构、电子结构以及光学性质的变化.电子结构分析表明W、Mn、W、Ti替位掺杂二维MoSi_(2)N_(4)后的禁带宽度分别为1.806 e V、1.003 e V、1.218 e V和1.373 e V;四种过渡金属掺杂后MoSi_(2)N_(4)的带隙类型没有发生改变,均为间接带隙半导体;W掺杂后的杂质能级靠近价带顶,费米能级靠近价带顶,为p型半导体,杂质能级为受主能级;Mn掺杂后的杂质能级靠近导带底,费米能级靠近导带底,为n型半导体;V和Ti掺杂后杂质能级位于费米能级附近,为复合中心;光学性质分析表明,在2 e V~4 e V的能量区间内,W掺杂结构的吸收波长为336 nm,体系发生红移;Mn、V和Ti替位掺杂后的吸收波长分别为320 nm、358 nm和338 nm,且掺杂体系均发生蓝移.
