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.