Study of electrostatic shielding and environmental interactions in carbon nanotubes by Resonance Raman Spectroscopy

Abstract

In the last decade, many theoretical and experimental achievements have been made in the photophysics of single wall carbon nanotubes (SWNTs). Such accomplishments allowed us to gain a deep understanding of the physics behind the otical transition energy (Eii) and the radial breathing mode frequency (!RBM) dependence on nanotube chiral indices (n;m). The first part of this work is devoted to assemble and discuss what I have done on the research of the SWNT electronic and vibrational properties, based on the radial breathing mode (RBM)measured by resonance Raman spectroscopy. Attention is directed to the understanding of how a change in the environment changes the correlation between (Eii; !RBM) and (n;m). It will be shown that the changes on the !RBM due to a changing environment makes the frequency to increase. This happens because the SWNTs wall interacts with the environment through Van der Waals interactions, which add an extra spring constant in parallel to the SWNT system. The changes in Eii are explained in terms of changes in the dielectric constant k which, in our model, comprises both, the dielectric constant ktube, that is intrinsically dependent of the SWNT structure, and the dielectric constant env, that depends on the environment. Nowadays, the scientific community faces at the challenge of performing experiments in the nanometer scale. Therefore, to build systems for nano-manipulation (i.e. nanoscaled devices construction and nanoscaled lithography) and nano-characterization (i.e. optical characterization and transportmeasurements) experiments has become a major need. In the second part of this work, a confocal microscopy setup was joined to an atomic force microscopy (AFM) setup. With the confocal system, we are able to perform spectroscopy with optical resolutions coming close to =2, where is the light source wavelength. The AFM system allows us to image and manipulate nano-scaled systems. Together They allow simultaneous experiments of spectroscopy and nanomanipulation.If the AFM tip is metallic, it is possible to perform optical experiments withresolutions delimited only by the tip diameter, going beyond the diffraction limits. Such a system has been utilized to understand the changes on the electronic and vibrational structures of SWNTs due to pressures imposed by a gold tip, and, besides this, to understand the influencesof segments of DNA in the photoluminescence signal of SWNTs@DNA systems.