Figure 2.

Varying thicknesses of amorphous carbon were applied to 42.5 nm gold thin films and monitored with both scanning angle SPR and SPRi. (a) Scanning angle reflectivity curves (8994 cm⁻¹) of gold substrates containing 5, 7.5, 10, and 12.5 nm of amorphous carbon were compared to a bare gold substrate. Experimentally obtained values (circles) were compared to theoretically calculated reflectivity curves for each substrate (lines). The theoretical values were determined with a n-phase Fresnel equation. (b) A series of fixed angle SPRi measurements were made to determine the effect of the amorphous carbon overlayer on binding sensitivity. Each substrate was exposed to two solutions with a 3.4 × 10⁻⁴ index of refraction difference and the change in reflectivity measured. The total change in reflectivity obtained for the bare gold substrate was used to define a range from 0 to 1 (0 = minimum reflectivity; 1 = maximum reflectivity); the total change in reflectivity obtained for the carbon–gold substrates is shown as a fraction of that value.