Effect of ageing in air on morphology and surface-enhanced Raman scattering (SERS) activity of Cu-based amorphous alloys

Changes in morphology and surface-enhanced Raman scattering (SERS) activity due to air ageing of Cu-based amorphous alloys (AAs) were followed by microscopic and vibrational spectroelectrochemical methods. Freshly fabricated ribbons are highly homogeneous and thus SERS-inactive materials. Air ageing results in partial devitrification; Cu-rich domains are formed on the wheel side of Cu-Zr and Cu-Hf ribbons with a ZrO2, or HfO2, supporting layer below. Sporadic small Cu-rich domains are also formed on Cu-Ti ribbons, which however, are generally less susceptible to devitrification. Partially devitrified Cu-Zr, Cu-Hf, and Cu-Ti AAs appear active targets for in situ SERS measurements of adsorbed pyridine. We have found that large SERS signals are measured from the Cu-rich domains, whereas the SERS intensity drops down by as much as two orders of magnitude outside the Cu-rich domains. The effect of electrode potential on the SERS signal for various surface domains varies greatly, suggesting that SERS activity at different sites differs accordingly, probably due to a difference in the degree of local oxidation. (C) 2002 Elsevier Science B.V. All rights reserved.