Ion implantation into glass has a potential [1, 2] for fabricating photonic or optoelectronic devices on planar glass substrates because it provides control of the dopant concentration and profile. We have measured the changes in optical and magnetic properties of silica glasses implanted with transitionmetal ions [3-5] and structural defects [6-8] produced by the implantation. In previous papers two significant modifications of optical properties of copper-implanted silica glasses have been reported. The first is a large increase in the refractive index [7, 9]. The refractive index, measured at 632 nm (He-Ne laser) increases from 1.47 to 1.65 with doses increasing from 1 x 1016 to 6 x 1016 cm -2. A linear correlation was found between increments in the refractive index and the absorptivity of an induced optical band centred at 2.2eV. The second modification is a very large value (about 4 x 10 -1I m 2 W -I at a wavelength of 532 nm) of the non-linear refractive index [10]. It was suggested that these two properties are due to the formation of copper colloids. In this letter we confirm the presence of Cu nanoscale particles in as-implanted silica glass. Samples used for transmission electron microscopy (TEM) measurements were high-purity type III silica glass discs (Spectrosil; 1 cm in diameter by 0.1 cm thick, OH content 200p.p.m.). The discs were implanted with Cu ÷ to a nominal dose of 6 x 1016 cm -2 at room temperature (acceleration voltage 160 keV and dose rate 2.5/zAcm-2). The depth profile of implanted Cu was measured by backscattering using a 2 MeV beam of a'-particles at current of about 10 A. TEM observation with a Jeol 400EX electron microscope was made on thin leaves peeled by scratching the implanted surface with a diamond pencil. No chemical or physical thinning technique was adopted. The TEM acceleration voltage was 300 kV. Optical absorption spectra were measured with a double-beam spectrophotometer (Jasco 610C) at 300 and 77K using a cryostat (Oxford DN1704). An unimplanted substrate was placed in the reference beam. EPR spectra were measured at 110 and 300 K with a Brucker 200D homodyne spectrometer applying 100kHz field modulation. Fig. la shows the optical absorption spectra of the implanted sample measured at 300 and 77 K. There is a peak at 2.2 eV and inflections around 4.5 and 5.8 eV. Neither shape changes nor further resolution of peaks on the spectrum were observed when