Heat and spin transport in graphene based nanostructured materials

Abstract

The monolayer graphene has been successfully synthesized about a decade ago, that have extraordinary electronic, mechanic and thermal properties which have attracted much attention of researchers for versatile applications of this material. Graphene and its allotrope i.e. carbon nanotubes have been proposed as promising materials for heat and electron spin transport. However, these materials are intrinsically non-magnetic in their pristine state, and we need to incorporate the impurities to induce magnetism. In addition to that, with advancement in synthesis techniques and continuous scaling of technology, the integration density in the electronic devices has increased, and it became a matter of extreme interest to manage the heat flow in these low-dimensional materials. In order to make magnetic graphene, we introduce zigzag triangular holes (ZTHs) in graphene by using sublattice engineering. We investigate the availability of ZTHs at experimental thermodynamic conditions and their magnetic properties. After determining the stable and magnetic ZTH configurations in graphene, we further examine spin transport properties of single wall metallic and semiconducting carbon nanotubes with $sp^2$ hydrogen-passivated ZTH. An experimentally reachable transverse external electric field is applied to tune completely spin-polarized transmission at Fermi level and thus carbon nanotube based spin-filters are achieved. Furthermore, to understand the heat transport in the hetero-junctions, graphene and hexagonal boron nitride (BN) heterogeneous interface is studied in the form two dimensional sheets as well as finite width size nanoribbons. We have found that zigzag Graphene/BN interfaces have localized phonon modes developed at the junction, which result in more phonon scattering as compare to armchair interfaces. The interfacial thermal resistance depends on the hardness of materials and thus on available phonon modes, which effect on the phonon transmission probability. Moreover, the role of structural disorders in thermal conductance between graphene and metal interface is also explored for Al/Graphene/Cu thin film. We find that graphene sheet sandwiched between metals, introduces mixing between in-plane and out-of-plane modes and disorders incorporation in the graphene layer enhances the out-of-plane vibrational modes and the phonon mode mixing around the defects site. This defect engineering in graphene sandwiched between metals establishes a new approach to control the heat transport through an interface involving graphene.