Optical spectroscopy of 1D nanostructures encapsulated inside carbon nanotubes

Carbon nanotubes (CNTs) represent the most ideal system to confine molecules in a 1D nanospace, due to their hollow structure, their smooth and impermeable sidewalls and the precise tunability of their diameter. These unique characteristics can be exploited to study the behavior of atoms and molecules confined in 1D, or to synthesize and stabilize new 1D nanostructures, overcoming the problem of chemical instability in free space. In this thesis, three 1D structures encapsulated inside CNTs are studied, i.e. graphene nanoribbons (GNR@SWCNTs), linear carbon chains (LCC@DWCNTs) and chains of water molecules (water@CNTs), by means of photoluminescence excitation (PLE) spectroscopy and/or wavelength-dependent resonant Raman spectroscopy. In particular, by analyzing the typical Raman modes of the GNRs together with their corresponding resonant Raman profiles (RRP), both the vibrational and the electronic properties of the encapsulated GNRs can be revealed. This enables us to assign the observed Raman modes to two specific structures of GNRs, namely the 6-armchair GNR and the 7-armchair GNR with widths of 0.61 and 0.74 nm and electronic band gaps of 1.83 and 2.18 eV, respectively. A similar wavelength-dependent analysis is used to study the excited vibronic states of two samples of LCC encapsulated inside DWCNTs. In this case, the analysis of the RRP enables to observe multiple Raman resonances and consequently to estimate the energies of the excited vibronic states. Lastly, the properties of 1D chains of water molecules are studied by probing the variation of the optical properties of the surrounding CNTs as a function of temperature with respect to a reference empty CNT sample. The phase transitions of water encapsulated inside four different CNT chiralities, i.e. (6,5), (7,5), (9,4) and (8,6), with diameters smaller than 1 nm, are observed at temperatures between 110 and 150 K, in agreement with the only observation reported so far in this diameter range.

Publication year:2021

Keywords:Doctoral thesis

Accessibility:Embargoed