Spectroscopic and hyperspectral analysis of singleand double-wall carbon nanotubes

Carbon nanotubes (CNTs) are hollow carbon cylinders with a diameter in the order of one nanometer, while easily reaching macroscopic lengths without any structural defects. This results in a uniquely large aspect-ratio that renders CNTs practically one-dimensional, reflecting in extraordinary electronic, vibrational and optical properties that depend critically on the exact atomic structure of the CNT, so-called chirality. These chirality-dependent characteristics make CNTs promising candidates for many optoelectronic applications. Interestingly, since every carbon atom resides at the surface, these properties are strongly influenced by both the outer and the inner environment, allowing for tuning these peculiar properties even further. However, before CNTs can be implemented in commercially viable devices, first these varying properties must be fully understood. Although the commonly used spectroscopic techniques are incredibly useful for studying these varying properties, they cannot provide information on individual CNTs, let alone along the nanotube's length. Therefore, I developed a hyperspectral fluorescence microscopy setup that is capable of both spatially and spectrally resolving the fluorescence along the length of semiconducting single-wall CNTs (SWCNTs). With this setup, I probed the fluorescence from individual SWCNTs within a chirality-sorted sample using dedicated sample preparation, image correction and image analysis protocols in order to study the inhomogeneous linewidth broadening in the ensemble fluorescence. The resulting statistical dataset contains four distinct emission peaks that can be unambiguously assigned to fluorescence from empty and water-filled versions of the two enantiomer SWCNTs. In a double-wall CNT (DWCNT), which consists of two coaxially aligned SWCNTs, the inter-layer interaction strongly modulates the already peculiar properties of the composing SWCNTs. Together with the many possible inner and outer layer chirality combinations, this makes the macroscopic characterisation of their structure exceptionally complex. In addition, often SWCNTs are unwittingly present in the DWCNT sample that can easily obscure the latter’s characterisation. I demonstrate this with the rapid ultrasonication-induced extraction of inner SWCNT shells from purified DWCNTs. Furthermore, I thoroughly characterised the radial breathing mode vibrations of and the fluorescence from these purified DWCNTs. Through detailed data analysis, employing two-dimensional fit models, I reveal the earlier postulated energy transfer from the inner to the outer shell of the DWCNT, explaining the inner shell fluorescence quenching. Lastly, based on these results, I developed a method with which several inner and outer layer chirality combinations in the macroscopic DWCNT sample can be identified.

Publication year:2021

Keywords:Doctoral thesis

Accessibility:Embargoed