Study on the electronic structures and transport properties of the polyporphyrin nanoribbons with different edge configurations

Combining the density functional theory with the non-equilibrium Green's function, three kinds of polyporphyrin nanoribbons (PPNRs) with different edge configurations have been considered: 1) all carbocyclic eight-membered rings (C8-Rs) located in edge are broken (M1); 2) all C8-Rs located in edge are perfect (M2); 3) partial C8-Rs located in edge are broken, subject to two kinds of configurations, as illustrated by M3 and M4. Calculation results indicate that the completeness of the C8-Rs can influence the electronic structures and transport properties of the nanoribbons. M1 is a nonmagnetic indirect semiconductor, while M2 and M3 are magnetic metals, M4 behaves as the bipolar magnetic semiconductor. Moreover, the spin-dependent transport properties of the two-lead devices based on PPNRs show that the significant spin-filtering effect can be realized in the device with partially broken C8-Rs in edge. Our results indicate that the PPNRs based devices would be suitable for spintronics devices.     

锯齿型石墨烯纳米带用于锂硒正极材料性能的第一性原理研究(英文)

硒-石墨烯体系是一种新型的锂离子电池正极材料, 引起了广泛的关注. 通过第一性原理的计算, 发现单个Se原子和Sen (n=2,3,4,6,8)团簇都更偏向于吸附在锯齿型石墨烯纳米带(ZGNRs)的边缘位置. 此外, 研究了锂吸附在Sen@ZGNRs (n=1,2)上的理论容量. Se1@ZGNRs系统显现出比Se2@ZGNRs更好的容量. 本文不仅从理论上阐述了Li、Se原子与ZGNRs之间的吸附行为, 而且从Se原子数的角度出发, 为提高锂硒正极材料的性能提供了新的策略.     

The creation of the magnetic and metallic characteristics in low-width MoS2 nanoribbon (1D MoS2): A DFT study

A basic understanding of the catalytic performance is needed to probe the physical properties that change with a reduction in the catalytic clusters size. It has been shown that the edge of low-width MoS₂ nanoribbon has a metallic characteristic, while that of bulk MoS₂ has a semi-conductive characteristic. For probing the observations, we constructed the models representing the surface atoms and the edge atoms of the MoS₂ nanoribbon. The nanoribbon-like model can also be used to model the edge atoms of the nanocluster MoS₂ .Then we calculated the density of states (DOS) of infinitely two-dimensional MoS₂ and of the structure corresponding to the edge atoms of the MoS₂ nanoribbon-like structure with Wien2K software. The magnetic moment of structures was calculated for identifying the magnetic structure. We found that the bulk MoS₂ and infinitely two-dimensional MoS₂ are semi-conductive and not magnetic, while the computation model corresponding to MoS₂ nanoribbon is metallic. The calculation anticipates that the edges of the MoS₂ nanocluster and the low-width MoS₂ nanoribbon are strongly magnetic.     

稀土Gd3+掺杂TiO2纳米带的制备及其光催化性能研究

以水热法制备出的钛酸盐纳米带为原料,利用二次水热反应制备了Gd3+掺杂TiO2纳米带.采用XRD、TEM和N2吸附-脱吸等手段对样品的晶型、微观形貌及比表面积进行了表征,讨论了Gd3+掺杂浓度、二次水热温度对材料结构及性能的影响.研究结果表明,Gd3+的掺杂没有影响原有样品的晶型,样品保持了锐钛矿相,但二次水热温度过高会破坏纳米带的形状,掺杂提高了样品的光催化活性,最佳掺杂量为5.O;.以掺杂量为5.0;、二次水热温度为180°C制备出的样品为光催化剂降解甲基橙,在光照180min后,甲基橙的降解率可达68;.     

Structural stability and electronic properties of Ni-doped armchair graphene nanoribbons

The size dependent electronic properties of armchair graphene nanoribbons (AGNR) with Ni doped atoms have been investigated using spin-unrestricted density functional theory. We predict antiferromagnetic (AFM) ground states for Ni-termination and one edge Ni-doping. The computed formation energy reveals that one edge Ni-terminated AGNR are energetically more favourable as compared to pristine ribbons. One edge substitutional doping is energetically more favourable as compared to centre doping by ∼1 eV whereas both edge doping is unfavourable. The bond length of substitutional Ni atoms is shorter than that of Ni adsorption in GNR, implying a stronger binding for substitutional Ni atoms. It is evident that binding energy is also affected by the coordination number of the foreign atom. The results show that Ni-interaction perturbs the electronic structure of the ribbons significantly, causing enhanced metallicity for all configurations irrespective of doping site. The band structures reveal the separation of spin up and down electronic states indicating towards the existence of spin polarized current in Ni-terminated and one edge doped ribbons. Our calculation predicts that AGNR containing Ni impurities can play an important role for the fabrication of spin filters and spintronic devices.     

石墨烯纳米带量子点中的量子混沌现象

在20 mK的极低温下测量了石墨烯纳米带量子点的电子输运性质,观测到清晰的库仑阻塞菱形块和对应量子点激发态的电导峰.对库仑阻塞近邻电导峰间距和峰值进行了统计分析,发现其统计分布分别满足无规矩阵理论描述的Wigner-Dyson分布和Porter-Thomas分布,说明石墨烯纳米带量子点在低温下出现了量子混沌现象.还讨论了这种长方形量子点中量子混沌的可能成因. 关键词： 石墨烯纳米带 量子点 库仑阻塞 量子混沌     

Spin-polarized transport in a normal/ferromagnetic/normal zigzag graphene nanoribbon junction

We investigate the spin-dependent electron transport in single and double normal/ferromagnetic/normal zigzag graphene nanoribbon (NG/FG/NG) junctions. The ferromagnetism in the FG region originates from the spontaneous magnetization of the zigzag graphene nanoribbon. It is shown that when the zigzag-chain number of the ribbon is even and only a single transverse mode is actived, the single NG/FG/NG junction can act as a spin polarizer and/or a spin analyzer because of the valley selection rule and the spin-exchange field in the FG, while the double NG/FG/NG/FG/NG junction exhibits a quantum switching effect, in which the on and the off states switch rapidly by varying the cross angle between two FG magnetizations. Our findings may shed light on the application of magnetized graphene nanoribbons to spintronics devices.     

O/N替代掺杂对zigzag型硼氮窄纳米带能带及输运特性的影响

用第一性原理非平衡格林函数方法研究了O原子掺杂zigzag型硼氮窄纳米带(z-BNNNRs)的能带结构和电子输运特性.研究结果表明:O原子对N原子的替代掺杂使z-BNNNRs的能带结构出现明显变化,体系由半导体转变为金属;O掺杂明显地改变了z-BNNNRs体系的导电性能,在一定的偏压范围内产生明显的负微分电阻(NDR)现象,边缘掺杂比中间掺杂产生更大的负微分电导,进一步的输运性质计算给出的透射谱也印证了这一点.随着掺杂浓度的增加,负微分电导的极值也随之增大.     

过渡金属原子掺杂的锯齿型磷烯纳米带的磁电子学特性

利用基于密度泛函理论的第一性原理方法,研究了掺杂铁、钴和镍原子的锯齿型磷烯纳米带(ZPNR)的磁电子学特性.研究表明,掺杂和未掺杂ZPNR的结构都是稳定的.当处于非磁态时,未掺杂和掺杂钴原子的ZPNR为半导体,而掺杂铁或者镍原子的ZPNR为金属.自旋极化计算表明,未掺杂和掺杂钴原子的ZPNR无磁性,而掺杂铁或者镍原子的...     

Poly(methyl methacrylate-co-methacrylic amide)-polyethylene glycol/polycarbonate and graphene nanoribbon-based nanocomposite membrane for gas separation

High-performance gas separation membranes were fabricated using 0.5–3wt.% graphene nanoribbon (GNR). Poly(methyl methacrylate-co-methacrylic amide)-polyethylene glycol (PMMA-co-MA-PEG) copolymer was prepared via condensation and blended with polycarbonate to form PMMA-co-MA-PEG/PC. The PMMA-co-MA-PEG/PC and GNR-based nanocomposite possess seamless micro-branched morphological pattern. Tensile strength and Young’s Modulus of PMMA-co-MA-PEG/PC/GNR0.5-3 increased from 64.3–74.7MPa and 76.7–99.9MPa, respectively. GNR loading increased the permselectivity αCO₂/N₂ (25.4–41.6) of nanocomposite membrane relative to blend membrane (20.1). However, permeability P_CO2 was decreased from 163.9 to 139.7 Barrer than blend (174.3 Barrer). PMMA-co-MA-PEG/PC/GNR revealed 51.6% increase and 24.7% decrease in permselectivity and permeability owing to molecular sieving and barricade characteristics of graphene nanoribbon.