The surface composition of samples changes monotonically with temperature, as evidenced with the centroids calculated for each sample, shown in Fig. , as well as the relative intensities of the SERS marker bands, shown in Fig. . Fig. presents markerbands-limited regions of SERS spectra collected for samples prepared at 25, 40, 50, 55, and 60 °C with various delays, further illustrating the change in the spectral profiles as a function of temperature. It is evident that the relative intensities of the marker bands approach unity with increasing temperature (Fig. ) and, consequently, the ratio of surface concentrations of the isotopologues follows that trend.