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Title: Nanoparticle phase change functionality for photonic switching and optical memory
Author: Soares, Bruno Flavio Nogueira de Sousa
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2007
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Nanoscale photonic functionalities based on light-induced structural transitions in nanoparticles have been investigated, and it has been experimentally shown that nanoparticles caI:l act as both low power nanoscale optical switches and as resonator-less optical memory elements. A system for in-situ growth and characterization of gallium nanoparticles, which combined technologies including atomiC-beam deposition, ultra-high vacuum, cryogenics, and sophisticated fibre instrumentation including diode and ultra-fast lasers, has been developed. Optical switching has been observed in a gallium nanoparticle film on the end of a single mode optical fibre simultaneously in reflection and transmission, and under different regimes of excitation, for the first time. Measurements of the sub-microsecond dynamics of such light-by-light control allowed the first study of the fast kinetics of solid-solid and solid-liquid structural transformations in gallium nanoparticles to be performed. Single gallium nanoparticles have been grown from an atomic beam in the nanoaperture at the tip 'of a tapered optical fibre for the first time. Reversible light-induced reflectivity changes associated with a sequence of transformations between different structural forms (both solid-solid and solid-liquid) stimulated by optical excitation at nanowatt power levels, have been observed in such particles for the first time. The complex temperature hysteresis of the nanoparticle's nonlinear response has been observed and it has been discovered that the extent of overcooling can be controlled by varying the optical pumping regime. The first demonstration of nanoscale all-optical resonator-less memory functionality based on phase transformations has been performed using a film of gallium nanoparticles. It has been shown that single 1/1$ optical pulses of a few mW peak power can be used to 'write' information to the memory by converting the particle$ from a lower energy phase (logic state 0) to a higher energy phase (logic state 1). A high contrast method for 'reading' the state of the particle memory, based on measurements of the reflectivity change induced by a modulated pump beam, has been developed. Both volatile and non-volatile modes of memory operation have been demonstrated. For the first time, an optical memory element based on a single particle has been demonstrated. It has been shown that an 80 nm gallium nanoparticle can act as a fourlevel nanoscale optical memory. Information is encoded on the particle by switching it between phases using single optical pulses with energies as low as 1.5 pJ, and by varying the pulse energy different states can be directly accessed from both ground and intermediate states. A closely packed array of such particles could provide a storage density of about 0.2 Tbjin2 • The experimental work has been underpinned by the development of appropriate qualitative physical models of the processes involved, so as to describe the relationships between excitation controlled phase coexistence in nanoparticles, their optical properties and the demonstrated functionalities.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available