The effect of ultrathin oxides on nanocrystallites of luminescent porous silicon is studied using infrared, optical, and Auger spectroscopy. Room-temperature oxidation is performed usingH2O2immersion and UV ozone interactions, producing oxides of ∼5 and ∼10 Å, respectively. TheH2O2oxidized sample is optically active, while the ozone oxidized sample is not active. UV–ozone produces a transverse optical Si–O–Si mode blueshifted by∼90 cm−1from bulk oxide, whichH2O2does not produce. Auger SiLVVspectra show an oxidelike signal for UV/ozone samples and a Si-like signal forH2O2samples. We discuss this in terms of different oxidation behaviors that either preserve or break Si–Si dimers that may be responsible for the optical behavior. ©1998 American Institute of Physics.