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Vanadium dioxide (VO2) is a promising material in the development of thermal and electrically sensitive devices due to its first order reversible metal‐insulator transition (MIT) at 68 °C. Such high MIT temperature (TC) largely restricts its widespread application which could be enabled if a straightforward tuning mechanism were present. Here this need is addressed through a facile approach that uses the combined effects of temperature induced strain and oxygen vacancies in bulk VO2 colloidal particles. A simple thermal annealing process under varying vacuum is used to achieve phase transformation of metastable VO2(A) into VO2(M2), (M2+M3), (M1) and higher valence V6O13 phases. During this process, distinct multiple phase transitions including increased as well as suppressed TC are observed with respect to the annealing temperature and varied amount of oxygen vacancies respectively. The latent heat of phase transition is also significantly improved upon thermal annealing by increasing the crystallinity of the samples. This work not only offers a facile route for selective phase transformation of VO2 as well as to manipulate the phase transition temperature, but also contributes significantly to the understanding of the role played by oxygen vacancies and temperature induced stress on MIT which is essential for VO2 based applications. [ABSTRACT FROM AUTHOR]

Harnessing the optical properties of noble metals down to the nanometre scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon properties must be controlled with a challenging high level of precision. Here, we demonstrate that ultimate lateral confinement and delocalization of surface plasmon modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the surface plasmon modes associated with the colloidal superstructures are evidenced by performing monochromated electron energy-loss spectroscopy with a nanometre-sized electron probe. We prepare the metallic bead strings by electron-beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphology and crystallinity but develop very low-energy surface plasmon modes that are capable of supporting long-range and spectrally tunable propagation in nanoscale waveguides. [ABSTRACT FROM AUTHOR]