Cathodoluminescence studies of swift heavy ion irradiated Au/SiO 2 /p-Si structures Trupti N. Warang a , P.K. Sahoo b , K.U. Joshi a , D.C. Kothari a, ⁎ , K. Zhang b , V. Milinovic b , K.P. Lieb b , S. Klaumünzer c a Department of Physics, University of Mumbai, Vidyanagari, Santacruz East, Mumbai 400 098, India b II. Physikalisches Institut, Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany c Hahn-Meitner Institut, Glienicker Str. 100, D-14109 Berlin, Germany Available online 12 March 2007 Abstract Cathodoluminescence measurements were performed on swift heavy ion irradiated and annealed Au/SiO 2 /p-Si structures. 5 nm thick Au film was deposited on 500 nm SiO 2 thermally grown on [100] oriented p-type Si wafers. The Au/SiO 2 /p-Si structures were irradiated using 350 MeV Au ions at fluences of 1–4×10 13 cm - 2 and annealed in vacuum at 1050 K for 8 h. The structures were characterised via Rutherford backscattering spectrometry and CL before and after annealing. The CL spectra mainly consist of an ultraviolet peak (4.3 eV) arising from Neutral Oxygen Vacancies (NOVs) and a blue-violet peak (2.7 eV) due to E′ centres as well as NOVs, both of which are oxygen-deficient centres. It is concluded that swift heavy ion irradiations create E′ centres in SiO 2 and annealing transforms E′ centres into NOVs. As NOVs are thought to be precursors to the formation of Si-nanoclusters (Si-nc), the present study leads to the knowledge of a possible synthesis route to form Si-nc. © 2007 Elsevier B.V. All rights reserved. Keywords: Si-nanoclusters (Si-nc); Cathodoluminescence; E′ centres; Neutral oxygen vacancies 1. Introduction Nanometer-sized Si crystallites exhibit unique electrical and optical properties, which are not observed in bulk silicon. Bulk Si is an indirect band gap semiconductor and thus inefficient emitter of light [1]. Silicon in the form of low dimensional system such as porous silicon [2,3], Si nanocrystals [4], Si/SiO 2 superlattices [5], Si nanopillars [6], etc have been found to be efficient light emitters. Si-nanoclusters (Si-nc) have been synthesized by several techniques such as microwave-induced or laser-induced decomposition of silane (SiH 4 )-like precursors [7,8], ion implantation of Si + [9], electrochemical etching of Si wafers [10], low pressure chemical vapor deposition [11], plasma-enhanced chemical vapor deposition [12], pulsed laser deposition (PLD) of Si [13] etc. Si-nc embedded in a SiO 2 matrix is a good system for optoelectronic and photonic applications. High quantum efficiencies of light emission in low dimensional silicon is mainly due to quantum-confinement effects in nm-scale crystalline silicon or due to the Si/SiO 2 interface, which results in an increase in the silicon indirect band gap beyond the crystalline value of ∼ 1.12 eV [14]. This structure will be important to integrate optics with electronics. The present work explores the possibility of forming Si-nc using swift heavy ion irradiation and post-irradiation annealing. Swift heavy ions predominantly loose energy by inelastic collisions. The inelastic component of the ion energy loss is conventionally called as “electronic loss”. In the past, electronic-loss-induced effects have been used for materials modification [15]. Recent studies have shown that in swift heavy ion irradiated substrates, the nucleation of metallic nanoclusters can take place during post-irradiation annealing, via the inelastic “electronic” component of the ion energy loss [16]. It has been known that Neutral Oxygen Vacancies (NOVs) in SiO 2 are precursors to the formation of Si-nc [17]. The presence of Au enhances Si mobility in SiO 2 which also helps in the formation of Si-nc in SiO 2 [18]. It was envisaged that high- energy ion irradiation may help in forming NOVs in SiO 2 and Surface & Coatings Technology 201 (2007) 8503 – 8505 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Tel.: +91 22 2652 6250; fax: +91 22 2652 9780. E-mail address: kothari@physics.mu.ac.in (D.C. Kothari). 0257-8972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.02.071