Raman spectra of hydrogenated CnSH (where, n = 3-5,8,9,12, and 18) and C8D17SH SAMs at mechanically polished (MP) Ag indicate monolayer contamination by a small polyaromatic hydrocarbon (PAH). The contaminant source at the unmodified MP Ag surface is identified using Raman spectoscopy, and thus, the contaminant is believed to be placed at this surface during the mechanical polishing procedure. Notably, the PAH contaminant is not completely removed by either solvent dissolution or alkanethiol adsorption, suggesting that it is strongly bound, and more significantly, sequestered within the alkanethiol SAM. Controlled incorporation of pyrene into dodecanethiol SAMs demonstrates that doping of alkanethiol SAMs may be possible for certain systems.