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Register a new userAdsorption properties of dopamine derivatives using carbon nanotubes: A first-principles study
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Detecting dopamine is of great biological importance because the molecule plays many roles in the human body. For instance, the lack of dopamine release is the cause of Parkinsons disease. Although many researchers have carried out experiments on dopamine detection using carbon nanotubes (CNTs), there are only a few theoretical studies on this topic. We study the adsorption properties of dopamine and its derivatives, L-DOPA and dopamine o-quinone, adsorbed on a semiconducting (10, 0) CNT, using density functional theory calculations. Our computational simulations reveal that localized states originating from dopamine o-quinone appear in the bandgap of the (10, 0) CNT, but those originating from dopamine and L-DOPA do not appear in the gap. Therefore, dopamine o-quinone is expected to be detectable using an external electric field but dopamine and L-DOPA should be difficult to detect.
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A type of line defect (LD) composed of alternate squares and octagons (4-8) as the basic unit is currently an experimentally available topological defect in graphene lattice, which brings some interesting modification to magnetic and electronic properties of graphene. The transitional metal (TM) adsorb on graphene with line-defect (4-8), and they show interesting and attractive structural, magnetic and electronic properties. For different TMs such as Fe, Co, Mn, Ni and V, the complex systems show different magnetic and electronic properties. The TM atoms can spontaneously adsorb at quadrangular sites, forming an atomic chain along LD on graphene. The most stable configuration is hollow site of regular tangle. The TMs (TM = Co, Fe, Mn, Ni, V) tend to form extended metal lines, showing ferromagnetic (FM) ground state. For Co, Fe, and V atom, the system are half-metal. The spin-{alpha} electron is insulating, while spin-b{eta} electron is conductive. For Mn and Ni atom, Mn-LD and Ni-LD present spin-polarized metal; For Fe atom, the Fe-LD shows semimetal with Dirac cones. For Fe and V atom, both Fe-LD and V-LD show spin-polarized half-metallic properties. And its spin-{alpha} electron is conducting, while spin-b{eta} electron is insulating. Different TMs adsorbing on graphene nanoribbon forming same stable configurations of metal lines, show different electronic properties. The adsorption of TMs introduces magnetism and spin-polarization. These metal lines have potential application in spintronic devices, and work as quasi-one-dimensional metallic wire, which may form building blocks for atomic-scale electrons with well-controlled contacts at atomic level.
We explore the possibility of using van dar Waals bonded heterostructures of stacked together 2D bilayer black phosphorus (BP) for nanoscale device applications. The electronic property of BP in AA stacking and 90{deg} twisted is studied with density functional theory. Further, we study the homogeneous nanojunction architecture of BP to use its anisotropic properties. Using the first principle simulations along with NEGF approach, we calculate quantum transport properties of the nanojunction setup. The interlayer directionally dependent current characteristics are explained in different setups. Our result revealed that 90{deg} twisted nanojucntion device would be a potential rectifier despite having no p-n junction characteristic only due to the intrinsic anisotropy of the material, making tunneling between armchair- and zigzag-directional BP sheets asymmetric.
First-principles calculations using density functional theory based on norm-conserving pseudopotentials have been performed to investigate the Mg adsorption on the Si(001) surface for 1/4, 1/2 and 1 monolayer coverages. For both 1/4 and 1/2 ML coverages it has been found that the most favorable site for the Mg adsorption is the cave site between two dimer rows consistent with the recent experiments. For the 1 ML coverage we have found that the most preferable configuration is when both Mg atoms on 2x1 reconstruction occupy the two shallow sites. We have found that the minimum energy configurations for 1/4 ML coverage is a 2x2 reconstruction while for the 1/2 and 1 ML coverages they are 2x1.
The heat flux autocorrelation functions of carbon nanotubes (CNTs) with different radius and lengths is calculated using equilibrium molecular dynamics. The thermal conductance of CNTs is also calculated using the Green-Kubo relation from the linear response theory. By pointing out the ambiguity in the cross section definition of single wall CNTs, we use the thermal conductance instead of conductivity in calculations and discussions. We find that the thermal conductance of CNTs diverges with the CNT length. After the analysis of vibrational density of states, it can be concluded that more low frequency vibration modes exist in longer CNTs, and they effectively contribute to the divergence of thermal conductance.
The conductivity of carbon nanotube (CNT) networks can be improved markedly by doping with nitric acid. In the present work, CNTs and junctions of CNTs functionalized with NO$_3$ molecules are investigated to understand the microscopic mechanism of nitric acid doping. According to our density functional theory band structure calculations, there is charge transfer from the CNT to adsorbed molecules indicating p-type doping. The average doping efficiency of the NO$_3$ molecules is higher if the NO$_3$ molecules form complexes with water molecules. In addition to electron transport along individual CNTs, we have also studied electron transport between different types (metallic, semiconducting) of CNTs. Reflecting the differences in the electronic structures of semiconducting and metallic CNTs, we have found that besides turning semiconducting CNTs metallic, doping further increases electron transport most efficiently along semiconducting CNTs as well as through a junction between them.
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