MacDonald, K.F., Soares, B.F. and Zheludev, N.I.
Nanowatt photonics of structural transformations in a single nanoparticle
At Photon '04 / QEP-16.
06 - 09 Sep 2004.
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Metallic nanoparticles have the potential to play a key role in future, highly-integrated photonic devices, not only as elements of waveguiding structures; (in plasmonic wave-guiding chains, or as scattering centres in band-gap structures), but also as active all-optical switching elements operating at very low power levels. We show that this functionality can be achieved by reversibly controlling the phase composition, and thereby the optical properties, of a nanoparticle with optical excitation at nanowatt power levels. For the first time, phase transition phenomena and associated optical effects have been studied in a single gallium nanoparticle, i.e. without the inhomogeneous broadening associated with size and shape distributions in nanoparticle films. We have been able to dynamically control coexistences between various combinations of galliums crystalline and disordered phases in very narrow temperature intervals and to detect substantial changes in optical properties at very low power levels. The nanoparticle was grown on the aperture at the tip of a gold-coated, tapered silica optical fibre. Its optical characteristics were then studied, at temperatures between 80 and 300 K, using low power infrared diode lasers. Power levels as low as 5 nW were found to be sufficient to substantially alter the particles reflectivity and transmission. The light-induced changes are fully reversible, with relaxation times in the microsecond range, and are critically enhanced near the transition temperatures between gallium’s metastable crystalline phases and the liquid. Such behaviour indicates that structural transformations, including solid-solid transitions between different crystalline forms, occur continuously, through the dynamic coexistence of phases.
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