Extreme nanowires : structural and functional properties of filled single walled carbon nanotubes

Extreme nanowires: structural and functional properties of filled single walled carbon nanotubes The development of technology continues to grow and progress at an increasing rate. With the desire for increasing capability and applications, one key area is making smaller, more powerful devices. This has seen the growth of nancomposites, and components at the nanoscale. With this reduced size comes additional considerations for quality control and visualising these materials, which is beyond the resolving limitations of optical microscopy. The research presented in this thesis is primarily based around the experimental synthesis, imaging, and characterisation of Extreme Nanowires by electron microscopy - particularly High Resolution Transmission Electron Microscopy, Scanning Transmission Electron Microscopy, and Scanning Electron Microscopy. Further characterisation techniques, such as Differential Scanning Calorimetry, Thermogravimetric Analysis, and X-Ray Diffraction - have also been reported and provide an insight into the thermal, conduction, and phase change properties of the synthesised nanocomposites. Firstly, this research investigates the structures that form when two different phase change materials - Sb2Te3 and SnSe - are nano-confined inside SWCNTs with diameters of less than _ 2 nm, and how this may affect their phase change behaviour in relation to the bulk. This includes cataloguing, and producing structural models for, the encapsulated nanowires via high resolution (scanning) transmission electron microscopy imaging. Many of the structures have not been observed or published before for these materials, and have no analogue to the bulk structure. In the case of SnSe, this catalogue of nanostructures includes linear chain, zig-zag, 2x1, 2x2, and a novel form that has never been seen before for SnSe but is possibly isometric with that seen for free-standing MoS nanowires. Samples are shown to contain a xv consistently high filling fraction of SWCNTs with the desired phase change material (> 95 % for Sb2Te3, and > 40 % for SnSe) - as confirmed by transmission electron microscopy and energy dispersive x-ray analysis. Next, this research investigates the amorphous-crystalline transformation, and how electron beam irradiation and heat treatment affect the phase of the encapsulated structure. This is primarily conducted via selected area electron diffraction studies of the nano-confined materials. In particular, nano-confined Sb2Te3 has been observed to undergo a reversible amorphous-crystalline phase transition when exposed to beam irradiation and in situ heating. Examination of this transition has shown it to be cyclable under a beam dose of < 25 pA _ c