Fig. 2: Spectroscopy of the molecular contaminant layer.
From: The composition and structure of the ubiquitous hydrocarbon contamination on van der Waals materials
a Grazing angle infrared spectra on differently covered graphite substrates, revealing the molecular vibrational modes of the adsorbates. The clean HOPG used as reference (black) shows only the E1u graphite band at 1583 cm−1, while the HOPG samples covered with adsorbates (blue, green) or vapor-deposited C32H66 layer show the C–H stretching and scissoring modes of alkanes. Inset: The spectrum of “contaminant layer 2” in the full wavenumber range. There are no other peaks aside from the ones presented in the main panel. b STM measurement of the tunneling conductance (dI/dV) on top of the airborne contaminant layer and C32H66 (temperature 9 K). The spectra show the typical “V shaped” local density of states signal of graphite, with no sign of molecular states. The spectra are normalized to their respective tunneling conductance used for stabilization. Slight differences in the slope are due to different tips being used on the two samples. Both IR and dI/dV spectra are offset for clarity.
