Fabrication of nanomaterials

In-situ Characterization

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           Simulation of nano-structure materials

Gold-embedded zigzag graphene nanoribbons as spin gapless semiconductors

         Using density-functional theory calculations, we studied the electronic and magnetic properties of zigzag graphene nanoribbons (ZGNRs) with gold (Au) atoms embedded into different sites of the ZGNRs. Strong site dependence was found, and the system had the ferromagnetic or antiferromagnetic ground state depending on the Au atom position. Spin gapless semiconductor (SGS) behavior was observed when the Au atom was embedded into the center and edge sites of the ZGNRs. The simulations showed that the electronic structure of the ribbon strongly depends on ZGNR width, but the SGS behavior is always present when the Au atom is embedded into the center and edge sites. The SGS properties were also found to be dependent on impurity atom concentration, so that they can be tuned by either selecting the proper positions of Au atoms or changing their concentration. Our results suggest a flexible way of designing SGSs, which could be used in various spintronic, electronic, and optoelectronic applications.
    (a) Atomic structure of a ZGNR. Symbols A to G denote different substitutional sites. (b) Structural model of Au-A-ZGNR. The white, gray, and yellowballs are hydrogen, carbon, and gold atoms, respectively.
Band structures of (a) FM Au-A-ZGNR, (b) FM Au-B-ZGNR, (c) FM Au-C-ZGNR, and (d) AFM Au-D-ZGNR.
Publications: X. H. Hu, W. Zhang, L. T. Sun*, A. V. Krasheninnikov, “Gold-embedded zigzag graphene nanoribbons as spin gapless semiconductors”, Physical Review B 86, 195418-1-7 (2012)
        Materials Studio is one of the most famous softwares to do the simulation in material field. It is the simulation that can mostly guide the real experiment. Via Forcite/Dmol3/ CASTEP, we have discussed properties of various of nanostructures.

Migration of gold atoms in graphene ribbons: Role of the edges

          The migration of gold atoms attached to single vacancies near the edges of graphene ribbons is studied using density-functional theory calculations. The stable position for a single gold atom is found to be on top of a vacancy, as in an infinite graphene sheet. An energy of 5 eV is needed for the Au atom to move through the vacancy to the other side of the sheet, but the Au atom can migrate in lateral direction together with the vacancy, with a migration barrier of about 2.2 eV. The sites near the edges of the graphene layer are energetically more favorable for gold-atom-vacancy pairs than sites in the middle of extended graphene layers. The migration barriers for different pathways show that it is easier for the gold atom to move toward the edge where it can be captured. When the gold atom reaches the edge, it can migrate along the edge with an energy barrier of only 1.4 eV. Our results explain recent experimental observations [Y. Gan et al., Small 4, 587 (2008)] and provide information on the dynamics of metal atoms on substitutional sites in graphene as well as on their agglomeration at defects and at edges of graphene ribbons.

FIG. 5. (Color online) The migration path for the Au atom at the edge site, as found by the NEB method.

Publications: Wei Zhang, Litao Sun*, Zijian Xu, Arkady V. Krasheninnikov, Ping Huai, Zhiyuan Zhu, F. Banhart “Migration of gold atoms in graphene ribbons: role of the edges", Phys. Rev. B 81, 125425-1-5 (2010)
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