Tese de Doutorado #303: Karolline Araújo

In this thesis, studies of transport mechanisms in single-walled carbon nanotubes (SWNT) and photo-assisted electrical response of Retinoic Acid (RA)’s self-assembled monolayers on graphite are presented. Scanning Probe Microscopy (SPM) techniques along with Optical Spectroscopy (Photoluminescence and Raman) and theoretical calculations made possible the detailed study of the physical properties investigated. The charge transfer between neighboring single-walled carbon nanotubes (SWNTs) on a silicon oxide surface was investigated as a function of both the SWNT nature (metallic or semiconducting) and the anode/cathode distance. Two main mechanisms were observed: a direct electron tunneling described by the typical Fowler-Nordheim model, and indirect electron transfer (hopping) mediated by functional groups on the supporting surface. Finally, a highly ordered RA self-assembled monolayer (SAM) on graphite was demonstrated. It was observed by AFM that the molecules are aligned parallel to the graphite with periodicity of 2.7nm. This in agreement with the results from study of the monolayer emission efficiency as a function of temperature. The EFM photo- assisted experiment suggested a graphite doping when decorated with molecules. This result was confirmed by Raman spectroscopy measurements that indicated a p-type doping. The theoretical calculations performed corroborate the experimental results found.