Ge NCs have attracted considerable attention because of their potential applications in nonvolatile memory and integrated optoelectronics. A number of groups have already proposed integrate flash memories based on Ge NCs embedded SiO2 matrix.
In this work Ge NCs embedded in alumina thin films were deposited over Si (111) substrates using RF co-sputtering technique. Annealing was performed in order to improve the cristallinity of the Ge phase in the films and achieve control over the NCs size . Ge NCs of suitable size and good crystalline quality were obtained by different techniques, including X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy. The NCs size was estimated from Raman spectra using Fauchet and Campbell model  and from X-ray diffraction using Debye-Scherrer equation. A good agreement between the three techniques for the size estimation was observed for smallest NCs. However, for larger NCs (> 20 nm) there is a discrepancy between XRD and Raman results. For this sample the TO Raman peak presents a blue shift relative Ge bulk and X-ray peaks are shifted for higher angles relative to the Ge diamond structure. A possible explanation for this shift is the compressive stress exerted on Ge NCs by the Al2O3 matrix . Further detailed studies are in course in order to clarify both confinement and stress effects.
 P. Caldelas et al, in press in Journal Nanoscience and Nanotechnology
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This work has been partially supported by FCT-Fundação para a Ciência e a Tecnologia-Portugal, and by the "Programa Operacional Ciência e Inovação 2010-POCI 2010" co-financed by FEDER through the Projects POCTI/FIS/56930/2004 and PTDC/FIS/70194/2006. SRCP thanks FCT for the financial support (grant SFRH/BD/29657/2006).