We describe the passivation by thioacetamide (TAM) of GaSb and InAs-two III-V semiconductor materials important for fabricating IR devices from Type-II superlattices (T2SLs). We use X-ray photoelectron spectroscopy (XPS) to characterize GaSb and InAs (001) surfaces treated by TAM under both acidic and basic conditions and to analyze the reoxidation of passivated surfaces over time. Both acid-and base-activated TAM treatments produce sulfide layers on GaSb and InAs. The layers produced by base-TAM appear to be of self-limited thickness < 1 nm, whereas acid-TAM creates considerably thicker (1-2 nm) sulfide layers. Passivation by both acid-and base-activated TAM offers significant short-term (< 1 day) protection against reoxidation, but does not prevent oxide formation after exposure to ambient air for 1-3 days. Based on this comparative study and previous literature reports, the chemical effects of TAM treatments on Ga, Sb, In, and As depend not only on the individual element and reaction conditions, but also on the compound. In other words, our results suggest that passivation chemistry for a common element in two different III-V materials should not, in general, be assumed to be the same. (C) 2009 Elsevier B. V. All rights reserved.