Samples were prepared as described above, and they were dried under vacuum overnight after being transferred either onto a 1-cm 2 piece of silicon wafer for attenuated total reflectance infrared (ATR-IR) spectroscopy, or onto a glass slide for visible Raman spectroscopy. ATR-IR spectra were recorded at 4 cm -1 resolution, 240 scans, with IR Affinity-1S (Shimadzu). Raman spectra were registered using a 532 nm laser (5-10% power) with a Renishaw instrument. For each sample, spectra were recorded with 10-20 accumulations in several spots, using 1 cm -1 resolution.