Physics and Astronomy, Department of
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The physical and chemical properties of decorated graphene and graphene ribbons, single-layer III-V systems, three-dimensional carbon and BN foam, and transition-metal-molecular sandwich nanowires have been investigated by first-principle calculations and their potential applications have been predicted. First, it is shown that zigzag graphene nanoribbons (ZGNRs) can be converted into half metal when their edges are decorated by some chemical functional groups, and the half-metalicity is induced by chemical potential difference between two edges when one edge is decorated by electron-donating group like –OH and the other edge is decorated by electron-accepting group like –F, -NH2, -N(CH3)2, -SO2, -NO2 and –CN, or by spin-polarized impurity state induced by isolated SO2 group. In addition, no matter how trivial the potential difference between two edges is, the decorated ZGNR can be half metal as long as the width of ZGNR is sufficiently large. As ZGNRs are decorated by copper atoms, they are shown to be a unique host system for the realization of an extended planar tetracoordinate carbon (ptC) strips due to its highly delocalized in-plane π-electrons and intrinsic rigid structure. When they are decorated by scandium atoms, they are shown to be good candidates for hydrogen storage and the adsorption energy can be controlled by electric field. Second, graphene is also revealed to become half metal through selective chemical decorations, and by selective hydrogenation, it can become magnetic quantum dot arrays and its magnetic coupling or band gap can be tuned, which can be applied for magnetic data storage and light-emitting devices. Third, single-layer BN and some other hexagonal systems like AlN, GaN, BP, SiC, ZnO are studied. It is demonstrated that upon charge-injection some of them like BN and AlN can become magnetic or even half-metallic, which is clarified by using Stoner Criterion. As they are cut into zigzag nanoribbons with one or two edges unpassivated, some of them may become half metals, and the edge-reconstructions of the unpassivated edges are studied. Fourth, two kinds of 3D carbon and BN foam, one with hexagonal holes and the other with triangular holes and only pure sp2 carbon bonds, are designed, and they are shown to be stable and porous low-density carbon and BN allotrope with large internal surface area and strong bulk modulus. Finally, some transition-metal-molecular sandwich nanowires can become magnetic or even half-metallic from nonmagnetic through charge-injection, which is also clarified by using Stoner Criterion. For Ti-benzene nanowires its magnetic coupling can be tuned either by charge-injection or tension.
Adviser: Xiao Cheng Zeng
A Dissertation Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Physics & Astronomy, Under the Supervision of Professor Xiao Cheng Zeng. Lincoln, Nebraska: December, 2011
Copyright (c) 2011 Menghao Wu