Theoretical Studies On Modulations Of Carbon-metal Nanocomposites And Their Applications For Energy Harvesting

Since the1990s, the low-dimensional carbon nanostructures have alreadydrawn quite a lot of attentions in physics, chemistry, materials science andother disciplines. Carbon atoms are densely packed in a regular sp2-bondedhexagonal pattern and form the low-dimensional carbon nanostructures includ-ing the1-dimensional carbon nanotube and2-dimensional graphene. Due to theunique structure, the low-dimensional carbon nanostructures possess outstand-ing properties, such as high tensile strength and elastic modulus, high thermalconductivity, high electronic mobility and high specific surface area. Up to thepresent, the low-dimensional carbon nanostructures have been considered as oneof the most important materials in the post-silicon era. The combination ofgraphene and metals produce nanocomposites, which possess not only both func-tions of graphene and metals, but also some extraordinary synergetic efects. Thenanocomposites spread the applications of graphene in quite a lot of fields, in-cluding electronics, optics, mechanics, catalysis and energy. In this dissertation,we focus our attentions on the theoretical studies on carbon-based nanocom-posites. Based on the density functional theory and molecular dynamics, weinvestigated the structure configuration, electronic doping, spin-orbit coupling ofthe nanocomposites, as well as the modulations of the properties. In addition,the application of graphene-metal nanocomposites in harvesting nuclear energywas also studied.Based on the density functional theory, the properties of graphene/metalinterface and the influences of strain on the interface were studied. It is foundthat the physical adsorption of graphene on metal does not sacrifice graphene’sunique linear dispersion around the Dirac point. However, a huge challenge inthe potential applications is the weak binding (～30meV) at the contacts. Arealizable tensile strain is found to be very efective in enhancing the interfacebinding as well as shifting the Fermi level. Particularly, an enhancement ofthe binding energy up to315%can be achieved because of the dipole-dipole interaction.Based on the full potential linearized augmented plane wave method, thespin-orbit splitting around the Dirac point and its enhancement were studied.We mainly focus our attentions on the roles of the substrate’s atomic numberand the p d interaction between C and metals. It is found that the presenceof light metal substrate Cu generates a small spin-orbit splitting about2meVaround the Dirac point. When a tensile strain of about3%is applied to theinterface, the spin-orbit splitting is greatly enhanced to a maximum value of83meV. The analysis of the compositions of the π-derived band suggests that the Cpzand Cu dz2interaction is responsible for the induced giant spin-orbit splitting.The results confirm, for the first time, that a sufcient spin-orbit splitting canbe achieved in graphene on substrates with small atomic numbers.Using time-dependent density functional theory, the process and mechanismof the conversion from radiation energy into electric power at graphene/metalinterface were studied. It is found that the energetic α particle loses its kineticenergy when it passes through the graphene/metal interface. Most of the αparticle’s energy is absorbed by the metal atoms, resulting in excited electrons.The excited electrons have high enough energy to overcome the potential barrierbetween graphene and metal, and then accumulate at the graphene layer. Dueto the bottleneck that limits electronic energy redistribution into the lattice, theexcited electrons maintain their energies during transport in graphene.The propagation of heat pulses along single-wall carbon nanotube (SWCNT)is also studied by using molecular dynamics. Controlled heat pulses were usedin this work to excite heat wave packets which propagate along SWCNT. It isfound that the propagation of excited wave packets significantly depend on theinitial components of the heat pulses. The excited leading wave packets or heatsignals keep their shapes and amplitudes during propagation and have robustnessagainst vacancy defects, which indicates the stability of the heat wave packetsduring the propagation.