Germanium Quantum Dots (Ge QDs) were formed in SiO2 by magnetron sputtering co-deposition of Ge+SiO2, either in form of thick or multilayered films. Deposition temperature, Td, ranged from RT to 973 K. As-deposited samples were subsequently thermally annealed up to Ta = 1000 ^oC. Ge:SiO2 composition ranged from 40 - 60% mol Ge. The substrate was either SiO2 or ‹111› Si. In layered films (Ge+SiO2) these 'active layers', with Ge were separated by layers of pure SiO2, serving as 'spacer' between ‘active’ layers.

Grazing incidence small angle x-ray scattering (GISAXS) was applied for structural characterization of Ge QDs synthesized in SiO2 amorphous matrix. Chemical composition and phase of QDs were determined by Raman spectroscopy and the spatial distribution and concentration of Ge atoms by Rutherford Back Scattering.

The 2D GISAXS patterns were used to reveal the onset of synthesis of Ge QDs in SiO2, to determine their properties, and for QDs ordering, if occurs. The average size of QDs  can be generally controlled by Ta and content of Ge. However, the introduction of spacers brings-in new, independent and better mean to control the size of Ge QDs. Up to Ta=1073 K Ge QDs are fully amorphous and at/above 973 K fully crystalline.  Above Ta= 1073 K, and especially above 1173 K Ge atoms out-diffuse strongly from the sample. For RT deposited samples the best quality, spherical, crystalline, stable Ge QDs were obtained by post-deposition annealing in 973-1073 K range. The quality and possible ordering of Ge QDs was strongly affected by Td. Only for Td around  773 K, combined with proper thicknesses of 'active' and 'spacer' layers, the 3D ordering of Ge QDs into hexagonal superlattice was attainable. For either lower or higher Td only week, in-layer, 2D ordering could be achieved. Around Td = 973 K the deposition of Ge becomes inefficient, and deposited Ge atoms form non-spherical, faceted Ge nanocrystals.

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