电场作用下P掺杂硅烯选择性吸附CH_4的第一性原理计算

在煤层气中选择性吸附和捕捉甲烷分子,对提高煤矿安全具有十分重要的意义.本文采用第一性原理计算的方法,研究了外加电场作用下P掺杂硅烯对甲烷分子的选择性吸附性能.结果表明:正电场作用下,P掺杂硅烯与甲烷分子之间产生较强的化学吸附,能够快速捕获甲烷分子.当关闭外加电场时,P掺杂硅烯与甲烷分子之间则为微弱的物理吸附,甲烷分子很容易实现脱附.同时还发现,外加电场作用下,P掺杂硅烯与氮气、氧气及水之间的吸附均属于物理吸附,表明P掺杂硅烯可以在这些混合气体中实现甲烷气体的选择性吸附. P掺杂硅烯有望成为选择性好的甲烷传感、捕获新材料.     

Spin-polarized transport induced by photoirradiation in zigzag silicene nanosystem

We study the spin-polarized transport induced by photoirradiation in zigzag silicene nanosystem, based on tight-binding approach, Green's function method and Landauer–Büttiker formula. By applying strong circular polarized light, silicene nanosystem can be transformed into a quantum Hall insulator, where the spin-down subband is gapped while the spin-up subband persists gapless edge state. Therefore, the dc conductance is dominated by the spin-up electrons, and the spin polarization can reach almost 100% around the Fermi energy. The spatial-resolved local density of states confirm that the spin-up electrons transport at two edges of the nanosystem in opposite current directions. Furthermore, because of the topological origin of the edge state, the spin-polarized transport is very robust against the size change of the nanosystem.     

Adsorption studies of dimethyl and methyl-ethyl ester molecules on silicene nanoring: Application of DFT study

The electronic and adsorption properties of dimethyl and methyl-ethyl ester molecules on a silicene nanoring (SiNR) are studied using first-principles calculations. The adsorption properties of dimethyl and methyl-ethyl ester molecules on the surface of a silicene nanoring is investigated in terms of density of states spectrum, adsorption energy, average energy gap variation, Mulliken charge and Bader charge transfer. The structural stability of the SiNR is ensured using formation energy. The variation in the electron density and energy gap is noticed upon adsorption of dimethyl and methyl-ethyl ester molecules in the SiNR base material compared with its isolated counterpart. The highlights of the present work are silicene nanoring is used as a base material for ester molecule adsorption. The adsorption behavior of ester molecules is studied using energy band structure. The DOS spectrum confirms the transfer of electrons between the SiNR and ester molecules. The findings suggest that a SiNR can be used as a base material for the detection of dimethyl and methyl-ethyl ester molecules.     

Electron-phonon coupling in armchair silicene nanoribbons

We report the effects of electron-phonon coupling on the charge density distribution of polarons in armchair nanoribbons of silicene by using an extended tight-binding model with lattice relaxation. The results show that the charge distribution in silicene nanoribbons is analogous to graphene and that the charge localization increases when the intensity of electron-phonon coupling also increases. We further show that silicene nanoribbons may be a conducting or semiconducting material, depending on both the width of the nanoribbon and the possibility of polaron formation. This contribution provides additional insight into the behavior of polarons in silicene nanoribbons, systems of great interest.     

掺杂对硅烯的性能影响

硅烯是单原子层的硅薄膜,具有类石墨烯结构.因此拥有与石墨烯相似的各种奇特的热学、化学、光学和电学性质.近年来,硅烯引起了研究者的广泛关注,作为一种新型的二维狄拉克电子材料,硅烯在理论计算和实验上都取得了不少新的进展.本文主要在前人对硅烯实施边缘钝化、掺杂、外加电场、加应力或者表面官能团修饰和吸附等研究的情况下,结合当前硅烯的研究发展趋势,重点研究了不同掺杂对硅烯性质的影响,并探讨硅烯在未来硅基电子器件的应用前景.     

Electronic and magnetic properties of silicene nanoflakes by first-principles calculations

The geometric, electronic, and magnetic properties of silicene nanoflakes (SiNFs) and corresponding two-dimensional (2D) framework assembled by SiNFs are studied by first-principles calculations. We find that the hexagonal SiNFs exhibit semiconducting behavior, while the triangular SiNFs is magnetic. Although the triangular SiNFs linked directly is antiferromagnetic, the system linked with an odd-number Si chains can exhibit ferromagnetic (FM) behavior, which is ascribed to anti-parallel spin rule on Si atoms, consistent with the Lieb–Mattis criterion. More interestingly, the 2D framework composed of triangular SiNFs linked by a Si atom shows a half-metallic character with an integer magnetic moment. These results provide a better understanding for silicene-based nanoflakes, and expect to pave an avenue to assemble FM silicon materials in spintronics.     

A review on silicene — New candidate for electronics

Silicene-the silicon-based counterpart of graphene-has a two dimensional structure that is responsible for the variety of potentially useful chemical and physical properties. The existence of silicene has been achieved recently owing to experiments involving epitaxial growth of silicon as stripes on Ag(001), ribbons on Ag(110), and sheets on Ag(111). The nano-ribbons observed on Ag(110) were found-by both high definition experimental scanning tunneling microscopy images and density functional theory calculations-to consist of an arched honeycomb structure. Angle resolved photo-emission experiments on these silicene nano-ribbons on Ag(110), along the direction of the ribbons, showed a band structure which is analogous to the Dirac cones of graphene. Unlike silicon surfaces, which are highly reactive to oxygen, the silicene nano-ribbons were found to be resistant to oxygen reactivity.On the theoretical side, recent extensive efforts have been deployed to understand the properties of standalone silicene sheets and nano-ribbons using both tight-binding and density functional theory calculations. Unlike graphene it is demonstrated that silicene sheets are stable only if a small buckling (0.44 Å) is present. The electronic properties of silicene nano-ribbons and silicene sheets were found to resemble those of graphene.Although this is a fairly new avenue, the already obtained outcome from these important first steps in understanding silicene showed promising features that could give a new future to silicon in the electronics industry, thus opening a promising route toward wide-range applications. In this review, we plan to introduce silicene by presenting the available experimental and theoretical studies performed to date, and suggest future directions to be explored to make the synthesis of silicene a viable one.     

Gas-surface interactions on two-dimensional crystals

Two-dimensional (2D) crystals have developed into a popular mainstream research topic which is interesting for basic research and many applications. Gas-surface interactions, as reviewed here, are important for catalysis including noble metal-free catalysts, materials science, and surface science as well as environmental and energy technologies. Basic science concerns fundamental differences of 2D crystals and bulk materials as well as e.g. how the substrate of epitaxial 2D crystals affects their surface properties.Most of the attention so far obtained (gas-phase) water adsorption which always was an evergreen in surface science. However, studies about small inorganic/organic molecule adsorption (CO, CO₂, NO_x, O₂, H, rare gases, H₂S, SO₂, alkanes, benzene, alcohols, thiophene, etc.) and surface reactions on 2D crystals (CO oxidation, ethylene epoxidation, oxygen reduction reaction, SO₂ and H₂SO₃ oxidation) started to appear in the literature as well. This review describes all of these probe molecules, but focuses on experimental and theoretical surface science model studies usually conducted at ultra-high vacuum (UHV).The review focusses on graphene and functionalized graphene (graphene oxide, N-graphene, etc.) since the bulk of the literature deals with that system. However, included in fair detail are also many other 2D crystals such as silicatene, zeolite films (doped silicatene), metal dichalcogenides (such as MoS₂, WS₂), boron nitride, MXenes, germanene, silicene, TiO₂, graphane, graphone, and portlandene.As a prototypical example, in recent projects, the wetting properties of e.g. graphene for water were controversially discussed. Therefore, a long chapter is devoted to water on graphene. That dispute was originally based on contact angle measurements at ambient pressure. In the meanwhile detailed surface science works including theoretical modelling are available. Literature on other carboneous surfaces such as HOPG (see list of acronyms) will be considered as a reference. Related works are also visible for other inorganic 2D crystals such as silicatene, i.e., 2D-SiO₂, or 2D-MoS₂ as well as functionalized 2D crystals (i.e. graphene oxide, N-doped graphene, graphane, etc.). Hydrophobic systems also are interesting for applications.Although included in this review, but not described in very detail are electro chemistry studies, projects in the liquid phase, photo-chemistry, high pressure catalysis, and pure engineering studies (membranes, separation, fuel cells). However, in comparison with 2D crystals and to perhaps motivate related UHV surface chemistry projects in the future many of these projects were included to some extent.As a broader objective, this review summarizes the currently available knowledge needed to extend the use of 2D materials beyond the utilization of their remarkable electronic and mechanical properties.     

Silicene nanoribbon as a new DNA sequencing device

The importance of applying DNA sequencing in different fields, results in looking for fast and cheap methods. Nanotechnology helps this development by introducing nanostructures used for DNA sequencing. In this work we study the interaction between zigzag silicene nanoribbon and DNA nucleobases using DFT and non equilibrium Green's function approach, to investigate the possibility of using zigzag silicene nanoribbons as a biosensor for DNA sequencing.