We have performed in situ oxide contamination and XUV reflectance vs angle of incidence studies on fresh aluminum and silicon films evaporated in an ultrahigh vacuum system (base pressure 2 x 10(-10)Torr). Our ellipsometric measurements indicate that a surface monolayer of oxide forms on aluminum (1 h at 2 x10(-8) Torr oxygen) and silicon (1 h at 10-(7) -Torr oxygen). The monolayer formation time is inversely proportional to oxygen pressure. Our reflectance vs angle of incidence measurements at 58.4-nm wavelength indicate that unoxidized aluminum and silicon coatings can be used as multifacet retroreflectors with net retroreflectances in excess of 75% for aluminum and 50% for silicon.