The gamma phase of the erbium-hydrogen system is a hexagonal trihydride that is not predicted to be stable at room temperature without an overpressure of hydrogen gas. Herein, we report the creation of both, a thin film and powder of erbium trihydride that is metastable at ambient conditions. The presence of the hexagonal gamma phase was determined by X-ray diffraction (XRD). The ratio of the total moles of hydrogen isotopes (hydrogen and deuterium) to moles of erbium, (H + D):Er, have been confirmed by elastic recoil detection (ERD)/Rutherford backscattering spectroscopy (RBS). Auger electron spectroscopy (AES) depth profiles and X-ray photoelectron spectroscopy (XPS) revealed the presence of an oxide layer that may account for the metastable behavior of the thin film. (c) 2006 Elsevier B.V. All rights reserved.