The mid-IR diffused reflectance spectra, ranging from 2.5 μm to 20 μm, were measured by Thermo Fisher Nicolet™ iS50 FTIR spectrometer with a diffused gold integrating sphere (PIKE Technologies). An e-beam deposited 200 nm gold on a silicon wafer (University Wafer, #1319) was used as the background standard reference. Raman spectroscopy was measured by Horiba LabRAM HR Evolution Confocal Raman Microscope. A 532 nm laser was used to excite the samples on a silicon (111) wafer substrate. All the measurements were performed at room temperature.