DOI: 10.1007/s00339-007-3867-2 Appl. Phys. A 87, 709–713 (2007) Materials Science & Processing Applied Physics A p. santhana raman 1,2 k.g.m. nair 2, ✉ r. kesavamoorthy 2 b.k. panigrahi 2 s. dhara 2 v. ravichandran 1 Formation and growth of embedded indium nanoclusters by In 2+ implantation in silica 1 Materials Science Centre, Department of Nuclear Physics, Guindy Campus, University of Madras, Chennai 600025, India 2 Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India Received: 13 September 2006/Accepted: 19 December 2006 Published online: 22 February 2007 • © Springer-Verlag 2007 ABSTRACT Indium nanoclusters are synthesized in an amorph- ous silica matrix using an ion-implantation technique. Indium ions (In 2+ ) with energy of 890 keV are implanted on silica to fluences in the range of 3 × 10 16 –3 × 10 17 cm −2 . The forma- tion of indium nanoclusters is confirmed by optical absorption spectrometry and glancing incidence X-ray diffraction studies. A low frequency Raman scattering technique is used to study the growth of embedded indium nanoclusters in the silica matrix as a function of fluence and post-implantation annealing dura- tion. Rutherford backscattering spectrometry studies show the surface segregation of implanted indium. Photoluminescence studies indicate the formation of a small quantity of indium oxide phase in the ion-implanted samples. PACS 85.40.Ry; 78.67.Bf; 73.20.Mf; 82.75.Fq 1 Introduction Dielectrics containing metal nanoclusters (NCs) are promising materials for optoelectronic devices due to their nonlinear optical (NLO) properties. Field enhancement ef- fects associated with the surface plasmon resonance (SPR), in embedded metal NCs, are important for the femtosecond re- sponse in NLO devices [1]. Ion implantation is an attractive technique for fabricating such nanocomposites. The depth and size selectivity of these embedded NCs can be achieved by varying the energy, fluence and flux of the implanted ions and the temperature during implantation [2]. Arnold and Borders initially reported the use of an ion-beam technique to grow Ag and Au colloids in silicate glasses [3]. Later on, others have used this technique to form a variety of metal colloids in dif- ferent glass substrates [4–11]. Indium NCs in silica form an interesting system because the SPR peak is in the ultraviolet (UV) region. UV-region NLO materials possess a number of applications [1]. There are a few reports on In implantation in silica in the en- ergy range of a few hundred keV. Some of the studies dis- ✉ Fax: +91-44-27480081, E-mail: kgmn@igcar.gov.in cuss the formation of In NCs, although the main interest has been in growing compound semiconductors like InP or InN by sequential implantation of indium and either P or N ions [12–15]. Optical properties alone were discussed as a function of substrate temperatures and fluences in the case of In ion implantation studies by Anderson et al. [14]. Tagliente et al. [15] discussed the phenomena of size-dependent su- perheating and supercooling of indium clusters formed by implantation to a fluence of 2 × 10 17 cm −2 and further growth under different annealing conditions. In the present paper, we report the results of a detailed study on the growth of In NCs in amorphous silica implanted with 890-keV In 2+ ions to different fluences. The cluster for- mation is studied by UV–visible (UV-vis) absorption spec- troscopy, glancing incidence X-ray diffraction (GIXRD), low frequency Raman spectroscopy (LFRS) and photolumines- cence (PL) measurements. Rutherford backscattering spec- troscopy (RBS) is used to study the distribution of the im- planted indium atoms. 2 Experimental procedure Ultrasonically cleaned amorphous silica is im- planted with In 2+ ions of energy 890 keV to various fluences in the range of 3 × 10 16 –3 × 10 17 cm −2 using the 1.7-MV Tandetron accelerator at IGCAR, Kalpakkam, India. The In 2+ beam current is maintained at ∼ 1 μ A with a beam size of 10-mm diameter. The depth profiling of implanted indium in silica is carried out using the RBS technique with 2-MeV He + ions. The optical absorption spectra are recorded using a Shimadzu UV-3101PC spectrophotometer. Scanning is car- ried out in the range of 190–400 nm. The GIXRD pattern is recorded using a Cu K α (λ = 1.54060 Å) source on a STOE powder diffractometer in the (θ –2θ ) scan mode. The inci- dent angle is kept at θ = 0.3 ◦ and data is collected with an acquisition time of 15 s/0.1 ◦ . The variation in size of In clusters is studied by LFRS measurements. The vertically po- larized 488-nm line of an argon-ion laser (Coherent, USA) with 500-mW power is used to record the Raman spectra in the backscattering geometry. The scattered light from the sample is dispersed using a double monochromator (Spex, model 14 018) and detected using a cooled photomultiplier