Stress Evolution during Ge Nanoparticles Growth in a SiO 2 Matrix Branko Pivac,* Pavo Dubč ek, Jasna Dasovic ́ , Jasminka Popovic ́ , and Nikola Radic ́ Materials Physics, R. Bos ̌ ković Institute, Bijenič ka 54, Zagreb 10000, Croatia Sigrid Bernstorff Elettra-Sincrotrone Trieste, SS 14, Km 163.5, in AREA Science Park, Basovizza 34149, Trieste, Italy Janez Zavas ̌ nik Jož ef Stefan Institute, Jamova Cesta 39, Ljubljana 1000, Slovenia Max-Planck-Institut fü r Eisenforschung GmbH, Max-Planck-Straße 1, Dü sseldorf 40237, Germany Branislav Vlahovic North Carolina Central University, Durham, North Carolina 27707, United States * S Supporting Information ABSTRACT: Superstructures are explored that were ob- tained by multilayer magnetron deposition at room temper- ature of 20 SiO 2 and SiO 2 :Ge bilayers, each 2 × 4 nm thick, and subsequently annealed in inert N 2 atmosphere at different temperatures in the range of 500−750 °C. The structural and optical changes induced by annealing and the formation and growth of Ge nanoparticles (nps) from early clusters to their full growth and final dissolution were studied by the simultaneous grazing-incidence small- and wide-angle X-ray scattering, transmission electron microscopy, and (time- resolved) photoluminescence (PL). It is shown that in as- deposited multilayers aggregation of small clusters already occurred, and the clusters were reasonably well intercorrelated in the lateral plane. During annealing at T a = 550 °C or higher temperatures, Ge nps start to form and remain partly amorphous at lower T a but crystallize completely at about 600 °C. At even higher temperatures, the Ge nps dissolve and Ge diffuses out almost completely, leaving voids in the SiO 2 matrix. Visible PL from the samples was detected and attributed to defects in the nps/matrix interface layers rather than to the nps itself because PL persisted even after Ge nps dissolution. 1. INTRODUCTION During the last decades, interest in semiconductor nanocrystals embedded in dielectrics has been continuously growing because of the fact that space confinement drastically affects the properties of matter and thus, e.g., efficient visible photoluminescence (PL) from Si nanocrystals was observed. 1 The properties of such nanoparticles (nps) are critically dependent on their size because of quantum confinement effects, which allow their application in the fields of optoelectonics, 2 semiconductor memories, 3 and photovol- taics. 4 Therefore, such nps are often named quantum dots (QDs). The tunability of QDs affects the efficiency of interaction with light, which is important in the field of photovoltaics. One of the very promising candidates for QDs realization is Si nps confined to a SiO 2 matrix because this approach is compatible with standard Si microelectronic integration technology. 5 Moreover, it was proposed as a good candidate for “all-Si” tandem solar cells. 6 Compared to the intensively studied Si QDs, Ge nanocryst- als have a more prominent quantum confinement effect because of their larger excitonic Bohr radii, 7 i.e., because of the smaller effective masses of electrons and holes. Further, theoretical analysis indicates that indirect-to-direct-band-gap transitions in the Ge energy-band structure occur with size reduction, and the oscillator strengths are expected to be larger in Ge QDs than in Si QDs. 8 This effect is attributed to stronger overlaps of the electron-wave functions in Ge atoms, 9 which enhances light absorption in Ge QDs. Received: September 27, 2018 Article pubs.acs.org/IC Cite This: Inorg. Chem. XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.inorgchem.8b02760 Inorg. Chem. XXXX, XXX, XXX−XXX Downloaded via UNIV PARIS-SUD on November 22, 2018 at 11:48:11 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.