A “green” cleaning technique for Si/SiO2 ultrathin films is presented. With the removal of adventitious carbon on the surface, Si/SiO2 ultrathin films can serve as calibration standards in vacuum ultraviolet reflectance characterization (the range from 8 to 60 nm). Data are presented that demonstrate the effect of mild solvents in conjunction with the effect of varying an excimer lamp’s exposure time. Data are determined by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. Additionally, I found that the antechamber of the XPS system deposites hydrocarbon onto the surface of samples. We adapted a plasma cleaner so that it minimized the effects of this instrumental contamination.