Lenticular Ga-oxide nanostructures in thin amorphous germanosilicate layers - Size control and dimensional constraints

Gallium incorporation in silicate glasses gives rise to compounds in which the nucleation and growth of Ga-oxide nanostructures can be designer controlled so as to obtain a number of functional properties for photonic applications. However, despite planar geometry pertains to a large part of modern technology, no information is available yet on the scalability of Ga-oxide segregation mechanisms in oxide thin films. In fact, incorporated Ga-oxide nanostructures have only been obtained in bulk materials. Here we show that deposition of Ga-alkali-germanosilicate thin films by radiofrequency-plasma sputtering gives rise to Ga-oxide nanostructures incorporated in an amorphous matrix. X-ray diffraction, X-ray reflectivity, small-angle X-ray scattering, and atomic force microscopy data unveil the formation of lenticular nanoaggregates, only a few nm thick, even in as-deposited materials as a result of two-dimensional aggregation of spinel-like Ga2O3 nanoparticles. Importantly, the aggregate size distribution is controlled not only by the temperature but also by the film thickness when it is reduced from 102 nm to only a few nm. The results open the way to the design of oxide-in-oxide thin films with incorporated networks of nanostructures which can act as percolation paths for unconventional electric responses in neuromorphic functional systems.