Vertically aligned and hexagonal crystal ZnSe nanoribbon arrays on Zn substrates

The vertically aligned and hexagonal ZnSe nanoribbon array can be easily obtained by heating ZnSe: 0.38 en precursors (en = ethylenediamine), while ZnSe precursor nanoribbon arrays are grown directly on Zn foils in en using the solvothermal method. The nanoribbons are mostly about 4 nm in thickness, 100–300 nm in width, and 2 μm in length. The characteristics observed using scanning electron microscopy and X-ray diffraction indicate that the ZnSe precursor as well as ZnSe nanoribbons are vertically aligned on almost the whole zinc foil surface and form a large-scale uniform array. Particularly, ZnSe precursor nanoribbons are hybrid materials of ZnSe and en, while ZnSe nanoribbons are in the from of hexagonal structures. Possible growth mechanisms of the ZnSe precursor nanoribbon arrays are also proposed.     

Possible polaron formation of zigzag graphene nano-ribbon in the presence of Rashba spin–orbit coupling

In this article we study the role of Rashba spin–orbit coupling and electron–phonon interaction on the electronic structure of zigzag graphene nanoribbon with different width. The total Hamiltonian of nanoribbon is written in the tight binding form and the electron–electron interaction is modeled in the Hubbard term. We used a unitary transformation to reach an effective Hamiltonian for nano ribbon in the presence of electron–phonon interaction. Our results show that small Rashba spin orbit coupling annihilates the anti-ferromagnetic phase in the zigzag edges of ribbon and the electron–phonon interaction yields small polaron formation in graphene nano ribbon. Furthermore, Rashba type spin–orbit coupling increases (decreases) the polaron formation energy for up (down) spin state.     

Molecular rectification in triangularly shaped graphene nanoribbons

We present a theoretical study of electron transport in tailored zigzag graphene nanoribbons (ZGNRs) with triangular structure using density functional theory together with the nonequilibrium Green's function formalism. We find significant rectification with a favorite electron transfer direction from the vertex to the right edge. The triangular ZGNR connecting to the electrode with one thiol group at each terminal shows an average rectification ratio of 8.4 over the bias range from ?1.0 to 1.0 V. This asymmetric electron transport property originates from nearly zero band gap of triangular ZGNR under negative bias, whereas a band gap opens under positive bias. When the molecule is connected to the electrode by multithiol groups, the current is enhanced due to strong interfacial coupling; however, the rectification ratio decreases. The simulation results indicate that the unique electronic states of triangular ZGNR are responsible for rectification, rather than the asymmetric anchoring groups. © 2012 Wiley Periodicals, Inc.     

Electronic and magnetic properties of copper-family-element atom adsorbed graphene nanoribbons with zigzag edges

We have investigated the electronic and magnetic properties of copper-family-element (CFE) atom adsorbed graphene nanoribbons (GNRs) with zigzag edges using first-principles calculations based on density functional theory. We found that CFE atoms energetically prefer to be adsorbed at the edges of nanoribbons. Charges are transferred between the CFE atom and carbon atoms at the edge, which reduce the local magnetic moment of carbon atoms in the vicinity of adsorption site and change the electronic structure of GNRs. As a result, Cu adsorbed zigzag GNR is a semiconductor with energy band gap of 0.88 eV in beta-spin and energy gap of 0.22 eV in alpha-spin, while Ag adsorbed zigzag GNR and Au adsorbed zigzag GNR are both half-metallic with the energy gaps of 0.68 eV and 0.63 eV in beta-spin, respectively. These results show that CFE atom adsorbed zigzag GNRs can be applied in nanoelectronics and spintronics.     

带状碳单层与石墨基底之间相互作用的第一性原理计算

利用基于密度泛函理论的第一性原理计算,研究边缘为Armchair型带状碳单层与石墨基底的相互作用,结果发现,其间的相互作用导致双方发生变形,带状碳单层的禁带宽度较其独立存在时有所减小,但石墨基底的作用并不改变其能带结构的基本特征. 关键词： 带状碳单层 第一性原理计算 能带结构     

应变石墨烯纳米带谐振特性的分子动力学研究

从动势能转换与守恒原理出发,在微正则(NVE)系综下,采用COMPASS力场对石墨烯纳米带及其应变传感器的谐振特性进行了分子动力学模拟.研究发现,非线性响应主导了石墨烯纳米带的动态行为,而其超高的基波频率则与长度和边界条件密切相关;单轴拉伸应变对石墨烯纳米带基波频率的影响显著且强烈依赖于边界条件,四边固支型应变石墨烯纳米带具有更高的频移,其灵敏度可高达7800 Hz/nanostrain,远大于相同长度碳纳米管应变传感器的灵敏度;石墨烯纳米带及其应变传感器的谐振特性均与手性无关.本文所得结果表明,由于超低 关键词： 石墨烯纳米带 分子动力学 应变 基波频率     

Magnetoconductance of graphene nanoribbons

The electronic and transport properties of monolayer and AB-stacked bilayer zigzag graphene nanoribbons subject to the influences of a magnetic field are investigated theoretically. We demonstrate that the magnetic confinement and the size effect affect the electronic properties competitively. In the limit of a strong magnetic field, the magnetic length is much smaller than the ribbon width, and the bulk electrons are confined solely by the magnetic potential. Their properties are independent of the width, and the Landau levels appear. On the other hand, the size effect dominates in the case of narrow ribbons. In addition, the dispersion relations rely sensitively on the interlayer interactions. Such interactions will modify the subband curvature, create additional band-edge states, change the subband spacing or the energy gap, and separate the partial flat bands. The band structures are symmetric or asymmetric about the Fermi energy for monolayer or bilayer nanoribbons, respectively. The chemical-potential-dependent electrical and thermal conductance exhibits a stepwise increase behaviour. The competition between the magnetic confinement and the size effect will also be reflected in the transport properties. The features of the conductance are found to be strongly dependent on the field strength, number of layers, interlayer interactions, and temperature.     

Pressure-induced phase transitions in single-crystalline Cu4Bi4S9 nanoribbons

In situ angle dispersive synchrotron X-ray diffraction and Raman scattering measurements under pressure are em- ployed to study the structural evolution of Cu4Bi4S9 nanoribbons, which are fabricated by using a facile solvothermal method. Both experiments show that a structural phase transition occurs near 14.5 GPa, and there is a pressure-induced re- versible amorphization at about 25.6 GPa. The electrical transport property of a single Cu4Bi4S9 nanoribbon under different pressures is also investigated.     

Rectifying performance in zigzag graphene nanoribbon heterojunctions with different edge hydrogenations

Using nonequilibrium Green?s functions in combination with the density functional theory, we investigated the electronic transport behaviors of zigzag graphene nanoribbon (ZGNR) heterojunctions with different edge hydrogenations. The results show that electronic transport properties of ZGNR heterojunctions can be modulated by hydrogenations, and prominent rectification effects can be observed. We propose that the edge dihydrogenation leads to a blocking of electronic transfer, as well as the changes of the distribution of the frontier orbital at negative/positive bias might be responsible for the rectification effects. These results may be helpful for designing practical devices based on graphene nanoribbons.     

Vanadium sulfide nanoribbons: Electronic and magnetic properties

We report the structural, electronic and magnetic properties of zigzag-type 2H-VS₂ nanoribbons based on the first-principles calculations. Our results suggest that the zigzag-type 2H-VS₂ nanoribbons are intrinsic ferromagnetic or ferrimagnetic materials dependent on their edge structures. The S-terminated VS₂ nanoribbons with or without hydrogen saturation at the edges are ferromagnetic, whereas V-terminated VS₂ nanoribbons are ferrimagnetic at their ground states. The average magnetic moment per V atom of VS₂ nanoribbons increases monotonously with their width, but still smaller than that of perfect VS₂ monolayer. These results imply the great potential of VS₂ nanoribbons in spintronics application.