1 Towards femto-joule nanoparticle

Phase-change functionality in gallium nanoparticles offers an innovative conceptual basis for the development of high density, low energy, non-volatile optical memories. Phase-change materials, wherein structural forms with differing electronic and/or optical properties are used to encode digital information or control signal propagation, have recently attracted great interest due to their potential to address growing challenges of size and power consumption in data storage and memory applications, and to enable innovative photonic and plasmonic functionalities [1-4]. Their functionality may enable the shrinking of optical switching and memory devices all the way down to the nanoscale, thereby helping to achieve the ultimate goal of nanophotonics- that is, to create devices smaller than or comparable in size to the wavelength of the signals they handle (a relationship of proportions that is easily achieved in most electronic circuits). Several problems hinder the nanoscale miniaturization of photonic circuits and data storage technologies: the need to guide optical signals in narrow and sharply bending waveguides; and the need to modulate these signals and encode information in very small active regions. The use of surface-plasmon-polariton waves as information carriers may address the guiding issue [5, 6] but the optical modulation and information storage problems seems to be much more difficult to tackle. In essence, both require very strong changes in the absorption or refraction of nanoscal