Electronic transitions in silica glass during heavy-ion implantation O.A. Plaksin a,b, * , Y. Takeda a , N. Okubo a , H. Amekura a , K. Kono a , N. Umeda c , N. Kishimoto a a Nanomaterials Laboratory, National Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan b SSC RF-Institute of Physics and Power Engineering, Obninsk, Russia c University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan Available online 15 July 2004 Abstract Spectra of ion-induced photon emissions (IIPE) of silica glass were measured during implantation of 3 MeV Cu ions at a constant flux of 3 – 10 AA/cm 2 up to a fluence of 9  10 16 ions/cm 2 . Three bands compose the IIPE spectra: a tail of the oxygen-deficient center band, the band of Cu + ions at 2.27 eVand the band of non-bridging oxygen hole center at 1.89 eV. Intrinsic defects of silica glass contribute to the IIPE at the onset of irradiation only. At fluences higher than 5  10 14 ions/cm 2 , the fluence dependence of the Cu + -band of IIPE represents (a) the accumulation of Cu solutes preceding the nanoparticle formation and (b) no change of Cu solute concentration during nanoparticle growth. The intensity of the Cu + -band is proportional to the total concentration of Cu solutes. The balance of Cu solutes and Cu nanoparticles is sensitive to the ion flux. The concentration of Cu solutes necessary for nanoparticle formation cannot be attained at fluxes higher than 10 AA/cm 2 . D 2004 Elsevier B.V. All rights reserved. PACS: 61.46.+w; 78.67.n; 81.07.Bc; 81.16.c Keywords: Heavy-ion implantation; Metal nanoparticles; Silica glass; In-situ measurements; Ion-induced photon emission 1. Introduction Heavy-ion implantation of glasses is a powerful tool for fabricating metal-nanoparticle composites, which are prom- ising for ultra-fast optical devices in the THz region and magneto-optical applications [1,2]. Ion implantation pro- vides superb controllability via variation of the ion beam current, ion energy and fluence. The nanoparticle formation can be monitored by means of in-situ optical measurements. In a recent study [3], spectra of optical absorption of silica glass were measured in the range of the surface plasmon resonance (SPR), during implantation of 3 MeV Cu 2+ ions. The absorption at the SPR is proportional to the number of Cu atoms accumulated in metal nanoparticles. The SPR peak of absorption (2.21 eV) appeared at a fluence of 3.3  10 16 ions/cm 2 , corresponding to the onset of precip- itation. At fluences higher than 4.5  10 16 ions/cm 2 , the growth of nanoparticles predominated, and the fluence dependence of the SPR peak was linear. The formation of Cu nanoparticles is conditioned by various competitive processes induced by implantation of glasses, either by atomic collisions or electronic excitation. The dynamic balance between Cu nanoparticles, Cu sol- utes, charge carriers and intrinsic defects determines the nucleation and growth of Cu nanoparticles. In particular, whether the concentration of Cu solutes necessary for formation of metal nanoparticles is attained or not depends on radiation-induced diffusion. Therefore, along with the measurement of the SPR peak, monitoring of Cu solutes is necessary in order to control the formation of metal nanoparticles. In this study, we conducted measurements of ion-induced photon emission (IIPE) during implantation of Cu into silica glass with the purpose to observe the behavior of Cu solutes during formation of metal Cu nanoparticles. 2. Experimental Disk-shaped substrates of silica glass (OH concentration 800 ppm) were irradiated by 3 MeV Cu 2+ ions at an ion flux of 3–10 AA/cm 2 (9  10 12 –3  10 13 ions/cm 2 s) up to a fluence of 9  10 16 ions/cm 2 . The specimens were placed in 0040-6090/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2004.05.110 * Corresponding author. SSC RF-Institute of Physics and Power Engineering, Russian Federation, Obninsk 249020, Russia. Tel.: +81-29- 863-5477; fax: +81-29-863-5571. E-mail address: plax@mail.ru (O.A. Plaksin). www.elsevier.com/locate/tsf Thin Solid Films 464 – 465 (2004) 264 – 267