By combining cross-sectional transmission and scanning electron microscopy with Raman scattering we have investigated the mechanism of nanocrystal formation in ultrathin amorphous SiO2/Ge/SiO2 trilayers grown by e-beam evaporation as a function of annealing temperature and a-Ge layer thickness. We observe that with decreasing a-Ge thickness the amorphous-to-crystalline (a-to-c) transition occurs at considerably higher temperatures, even avoiding crystallisation for very thin films below 2 nm thickness. Furthermore, we demonstrate that the formation of Ge nanocrystals by annealing at around 900 degrees C takes place driven by a liquid-mediated mechanism. As indicated by the observed microstructure, the metallic liquid film dewets from the surface forming droplets that upon cooling and under the influence of the SiO2 capping layer, solidify into barrel-type nanocrystals.
[Show abstract][Hide abstract] ABSTRACT: A simple and silicon process-compatible technique is reported for the synthesis of Ge nanocrystals (Ge-ncs) at low temperatures below 400 °C, which is much lower than the typical growth temperatures. The Ge-ncs were found to form only within a temperature window between 350 and 420 °C. The underlying mechanism has been explained by a competitive process between Volmer–Weber growth and oxidation reaction. We further implemented this technique in the fabrication of multilayered Ge-ncs which exhibited controllable crystallite size with high crystallization quality. The low temperature technique developed in this work would allow production of Ge-ncs and relative devices on low cost substrates, such as glass.
[Show abstract][Hide abstract] ABSTRACT: Design of monodisperse ultra-small nanocrystals (NCs) into large scale patterns with ad hoc features is demonstrated. The process makes use of solid state dewetting of a thin film templated through alloy liquid metal ion source focused ion beam (LMIS-FIB) nanopatterning. The solid state dewetting initiated at the edges of the patterns controllably creates the ordering of NCs with ad hoc placement and periodicity. The NC size is tuned by varying the nominal thickness of the film while their position results from the association of film retraction from the edges of the lay out and Rayleigh-like instability. The use of ultra-high resolution LMIS-FIB enables to produce monocrystalline NCs with size, periodicity, and placement tunable as well. It provides routes for the free design of nanostructures for generic applications in nanoelectronics.
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