Surface Decoration And Property Tuning Of Noble Metal Clusters And Carbon Nanomaterials

During the last decades, the exploration of low-dimensional nano structures such as metal clusters, carbon nanotubes and graphene, is a hot topic in the fields of physics, chemistry and many other subjects. Intensive investigations of these nanostructures is of key importance to reveal and understand their unique optical properties, electronic structures and band gap, which can help design the novel nano-materials that are technologically promising. In this dissertation, we studied from optical adsorption spectra of the zero-dimensional Ag38and Au38clusters adsorbed with organic molecules, the adsorption behavior of Ru atom or clusters inside and outside carbon nanotubes, to band gap tuning of the two-dimensional hydrogenated graphene.The organic molecules such as polymers, biomolecules and organic ligands, adsorbing on noble metal clusters, not only can avoid the metal clusters aggregating to bigger, but also modify their surface geometry and electronic structures, which can tune their physical and chemical properties. We have investigated the adsorption structures, electronic properties and optical adsorption spectra of the Ag38and Au38clusters adsorbed with different organic molecules by first-principles calculations. Optical adsorption spectra of the noble metal clusters varies with metal elements, functional groups of organic molecules and concentration of adsorption molecules. Due to the d band of Au closer to Fermi level, geometry structures and electronic properties of the Au38cluster are more easily affected by adsorbing organic molecules, which leads to more distinctive optical adsorption spectra comparing with pure gold clusters. Optical adsorption spectra of the noble metal clusters is tuned by such organic molecules, which has higher adsorption energy, leads to stronger surface modifications and transfers more charge to metal clusters, such as2-Pyridinethiol molecule. Adsorption concentration of organic molecules is another important fact to tune optical adsorption spectra of noble mtal cluster. Increasing the numbers of trimethylamine molecules results in the overall red-shift of optical adsorption spectra and the broadening of adsorption peaks for Ag38cluster. After adsorbed with eight TMA molecules, there appears a new adsorption peak at399nm in the visible region for Au38cluster. The simulations of Ag38and Au38clusters can help understand the optical adsorption behavior of noble metal clusters adsorbed with organic molecules, and provide reference to synthesize light-sensitive metal clusters.First-principles calculations were performed to investigate the binding energies, geometric structures, and electronic properties of4d transition metal TM (particularly, Ru), atoms, and clusters adsorbed outside/inside the single-walled or double-walled carbon nanotubes. The equilibrium adsorption structures of the TM atoms depend on the valence electron configuration of the metal atoms. Due to curvature effect, all TM atoms adsorbed inside and outside (6,6) carbon nanotubes donate different amounts of electrons to the nanotube, with a nearly constant difference of about0.5electrons/TM atom. The analysis of electronic density of states revealed hybridization between the n electrons from C and the d electrons from Ru, which results in charge transfer from metal to carbon. The amount of charge transfer shows systematical trend with the electronegativity of4d TMs. When Ru atom or cluster adsorbs on double-walled nanotubes, the effect of charge transfer is slightly enhanced with regard to the single-walled nanotubes.The electronic states of partially hydrogenated graphene (HG) structures are studied by the density functional theory calculations. Several types of HG configurations, including randomly removing of H pair, randomly removing individual H atoms, and ordered H pairs removal, are investigated. We find that the configurations with randomly removingHpairs aremost energetically favorable. More interestingly, the band gap for such configurations decrease with H concentration and approaches zero around67%H coverage. The ability to continuously tune the band gap of hydrogenated graphene from0to4.66eV by different H coverage provides a new pathway for engineering the electronic structure of graphene materials and enhances their applications in electronics and photonics.