RESEARCH PAPER Structure and electrical transport in films of Ge nanoparticles embedded in SiO 2 matrix Ionel Stavarache • Ana-Maria Lepadatu • Adrian V. Maraloiu • Valentin S. Teodorescu • Magdalena Lidia Ciurea Received: 27 September 2011 / Accepted: 16 May 2012 / Published online: 17 June 2012 Ó Springer Science+Business Media B.V. 2012 Abstract The films containing Ge nanoparticles embedded in SiO 2 matrix were prepared by RF magnetron sputtering and subsequently by thermal annealing. Their structure was investigated by con- ventional transmission electron microscopy and high resolution transmission electron microscopy together with energy-dispersive X-ray spectroscopy. The elec- trical behavior of films was studied by measuring current–temperature and current–voltage characteris- tics. The structure investigation reveals two kinds of features: a low density of big Ge nanoparticles with sizes from 20 to 50 nm and a network of small amorphous Ge nanoregions/nanoparticles (5 nm size or less) with high density, both being embedded in amorphous SiO 2 matrix. The electrical transport was shown to take place through the network of amorphous Ge nanoregions. At low temperature, the T -1/4 dependence of the current was evidenced, while at high temperature, the T -1 Arrhenius dependence was found. At both low and high temperatures, the conductivity is nearly constant. The behavior at low temperature was explained by the hopping mechanism on localized states located in a band near the Fermi energy, while at high temperature by the charge excitation to the extended states. Keywords Nanoparticles  Magnetron sputtering  TEM  Electron irradiation  Conduction mechanisms  Nanostructures Introduction Nanostructures formed by Ge and Si nanoparticles embedded in dielectric matrix, particularly amorphous SiO 2 , have been intensively studied in the last decades for their potential applications in optoelectronics (Tzeng and Li 2008), photovoltaics (Zhang et al. 2011), and non-volatile memory devices (Beyer et al. 2007; Chen et al. 2007; Peibst et al. 2010). In addition, amorphous Ge x Si 1-x O y thin films are investigated for micro-machined uncooled bolometer applications (Ahmed and Tait 2003), and amorphous Ge/SiO 2 multilayered structures are attractive for their property of ferromagnetism at room temperature (RT) (Zhen et al. 2010). Also, metal–insulator–semiconductor photodetector with high efficiency, based on amor- phous Ge quantum dots embedded in a SiO 2 matrix, were reported (Cosentino et al. 2011a). The deposition method commonly used for the preparation of structures formed by Si or Ge nano- particles embedded in amorphous SiO 2 matrix is the All the authors contributed equally to this article. I. Stavarache  A.-M. Lepadatu  A. V. Maraloiu  V. S. Teodorescu  M. L. Ciurea (&) National Institute of Materials Physics, 105 bis Atomistilor Street, 077125 Magurele, Romania e-mail: ciurea@infim.ro 123 J Nanopart Res (2012) 14:930 DOI 10.1007/s11051-012-0930-5