Structural studies of Ge nanocrystals embedded in SiO 2 matrix N. Srinivasa Rao a , S. Dhamodaran a , A.P. Pathak a, * , P.K. Kulriya b , Y.K. Mishra b , F. Singh b , D. Kabiraj b , J.C. Pivin c , D.K. Avasthi b a School of Physics, University of Hyderabad, Central University (P.O.), Hyderabad 500 046, India b Inter University Accelerator Centre, P.O. Box 10502, New Delhi 110 067, India c CSNSM, IN2P3-CNRS, Batiment 108, F-91405 Orsay Campus, France Received 12 April 2007; received in revised form 17 August 2007 Available online 19 September 2007 Abstract Germanium nanoparticles embedded in SiO 2 matrix were prepared by atom beam sputtering on a p-type Si substrate. The as-depos- ited films were annealed at temperatures of 973 and 1073 K under Ar + H 2 atmosphere. The as-deposited and annealed films were char- acterized by Raman, X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). Rutherford backscattering spectrometry was used to quantify the concentration of Ge in the SiO 2 matrix of the composite thin films. The formation of Ge nanoparticles were observed from the enhanced intensity of the Ge mode in the Raman spectra as a function of annealing, the appearance of Ge(3 1 1) peaks in the X-ray diffraction data and the Ge vibrational mode in the FTIR spectra. We have irradiated the films using 100 MeV Au 8+ ions with a fluence of 1 · 10 13 ions/cm 2 and subsequently studied them by Raman and FTIR. The results are compared with the ones obtained by annealing. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.46.Df; 79.20.Rf; 78.30.j Keywords: Ge nanoparticles; Atom beam sputtering; Raman 1. Introduction Si and Ge nanocrystals (nc-Ge, nc-Si) embedded in SiO 2 have recently attracted much attention due to their possible applications in integrated optoelectronic devices [1–3]. In particular it has been suggested that direct optical transi- tions are possible in small size group-IV nanocrystals [4]. Although porous Si is expected to be the most promising Si-based light emitting material, Ge nano crystalline (nc- Ge) embedded in Silica glasses have their own advantages. These Ge dots are useful in infrared detectors [5]. Ge has smaller electron and hole effective masses and larger dielec- tric constant than Si. The effective Bohr radius of the exci- ton in Ge is larger than that in Si. Hence Ge is much easier to change the electronic structure around the band gap than Si due to its larger exciton Bohr radius [6,7]. To date, a series of techniques have been used to prepare nc-Ge, including sol–gel [8], inorganic solution-phase synthetic routes [9], ion-implantation [10,11], UV-assisted oxidation [12] and sputtering [13,14]. The present work investigates the structure of the Ge nanoparticles grown by atom beam sputtering (ABS). This technique has been used to prepare metal nanoparticles embedded in a silica matrix and found to be suitable for synthesis of nanoparticles embedded in silica matrix [15,16]. ABS has been already used to prepare Ge nanoparticles in SiO 2 matrix and to compare the lumi- nescence properties with samples prepared by ion-implan- tation [17]. The present study concentrates on the structural characterization of the films as a function of annealing temperature and ion irradiation induced crystal- lization using Raman, XRD and FTIR. 0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.08.094 * Corresponding author. Tel.: +91 40 23010181/23134316; fax: +91 40 23010181/23010227. E-mail address: appsp@uohyd.ernet.in (A.P. Pathak). www.elsevier.com/locate/nimb Available online at www.sciencedirect.com Nuclear Instruments and Methods in Physics Research B 264 (2007) 249–253 NIM B Beam Interactions with Materials & Atoms