Roman coin, by near-ambient pressure XPS

Near ambient pressure-x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at greater than 2500 Pa. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show survey, O 1s/Ag 3p, Ca 3p/Ag 3d, and extended valence band (0–130 eV) NAP-XPS spectra of an ancient Roman coin at three different positions. A small N 1s signal from N₂ background gas is also observed. On the obverse side, the coin bears the bust of Licinius I. On the reverse side, it bears the image of Jupiter. The Ag 3d region indicates different amounts of silver at different oxidation states in different positions.