Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)A detailed investigation concerning the atomic structure of Cr2O3 and Pd/Cr2O3 ultrathin films deposited on a Ag(111) single crystal is presented. The films were prepared by MBE (molecular beam epitaxy) and characterized in situ by LEED (low energy electron diffraction), XPS (X-ray photoelectron spectroscopy), and XPD (X-ray photoelectron diffraction). Evidences of rotated domains and an oxygen-terminated Cr2O3/Ag(111) surface were observed, along with significant contractions of the oxides outermost interlayer distances. The deposition of Pd atoms on the Cr2O3 surface formed a four-monolayer film, fcc packed and oriented in the [111] direction, which presented changes in monolayer spacing and lateral atomic distance compared to the expected values for bulk Pd. 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