Cu(Ti 27 at.%) alloys on SiO 2 were reacted in NH 3 for 30 min over the temperature range 400-700 °C, Rutherford backscattering spectrometry in conjunction with high resolution transmission electron microscopy were utilized to investigate reaction products. At 400-450 °C, Ti is observed to segregate to the free surface to react with NH 3 , forming an Ti oxynitride layer, Above 500 °C, Ti segregates to both the free surface and to the alloy/SiO 2 interface, leaving relatively-pure Cu layer. Reaction between Ti and SiO 2 results in a TiO/Ti 5 Si 3 bilayer structure. By use of high spatial resolution energy dispersive X-ray spectroscopy, the presence of a Cu-containing layer at the TiO/Ti 5 Si 3 interface is observed. This layer may also contain Ti, Si and/or O. We propose a mechanism for Cu segregation to this interface which requires Cu diffusion across TiO and subsequent dissociation of Ti 5 Si 3 . Thermodynamic calculations support this mechanism.