Oxide-supported phospholipid bilayers (SPBs) used as biomimetic membranes are significant for a broad range of applications including improvement of biomedical devices and biosensors, and in understanding biomineralization processes and the possible role of mineral surfaces in the evolution of pre-biotic membranes. Continuous-coverage and/or stacked SPBs retain properties (e.g., fluidity) more similar to native biological membranes, which is desirable for most applications. Using neutron reflectivity, we examined the role of oxide surface charge (by varying pH and ionic strength) and of divalent Ca2+ in controlling surface coverage and potential stacking of dipalmitoylphosphatidylcholine (DPPC) bilayers on the (11 (2) over bar0) face of sapphire (alpha-Al2O3). Nearly full bilayers were formed at low to neutral pH, when the sapphire surface is positively charged, and at low ionic strength (I = 15 mM NaCl). Coverage decreased at higher pH, close to the isoelectric point of sapphire, and also at high I >= 210 mM, or with addition of 2 mM Ca2+. The latter two effects are not additive, suggesting that Ca2+ mitigates the effect of higher I. These trends agree with previous results for phospholipid adsorption on alpha-Al2O3 particles determined by adsorption isotherms and on single-crystal (10 (1) over bar0) sapphire by atomic force microscopy, suggesting consistency of oxide surface chemistry-dependent effects across experimental techniques. (C) 2011 Elsevier Inc. All rights reserved.