Titanium-assisted growth of silica nanowires: from surface-matched to free-standingmorphologies

Abstract

We report on an oxide-assisted growth technique for silica nanowires which allows tuningthe growth from surface-matched nanowires to free-standing morphologies based on growthcontrol by Ti in the role of a catalyst and surfactant. Using an adjustable Ticoncentration, we grew silica nanowires with lengths ranging from 100 nm up to severalmillimetres whose defect chemistry was analysed by electron microscopy tools,monochromatic cathodoluminescence imaging and time resolved photoluminescencespectroscopy. The knowledge of the luminescence properties and the related defectoccurrence along with their spatial distribution is pivotal for advancing silicananowire growth in order to realize successful device designs based on self-assembledSi/SiOx nanostructures. We demonstrate a core–shell structure of the grown nanowires with ahighly luminescent 150 nm thick shell and outstandingly fast decaying dynamics (≈1 ns) for glass-like materials. The conjunction of the observed efficient and stableluminescences with their attributed decaying behaviours suggests applications forsilica nanowires such as active and passive optical interconnectors and white lightphosphors. The identification of a time domain difference for the spectral regimefrom 2.3 to 3.3 eV, within the confined spatial dimensions of a single nanowire, isvery promising for future, e.g. data transmission applications, employing silicananowires which exhibit achievable compatibility with commonly applied silicon-basedelectronics. A qualitative growth model based on silica particle diffusion andTi-assisted seed formation is developed for the various types of segregated silicananowires which extends commonly assumed oxide-assisted growth mechanisms.