Surface pressure (II) vs surface area (A) isotherms and Brewster-angle microscopic (BAM) images have been recorded for monolayers, spread on aqueous 1.0 x 10(-3) M Pb(NO3)(2) solutions and prepared from arachidic acid (AA) and octadecylamine (ODA) mixtures. Identical II vs A isotherms and BAM images were obtained for monolayers, prepared from AA:ODA = 1:0, AA:ODA = 5:1, and AA:ODA = 2:1, while II vs A isotherms and BAM images for AA:ODA = 1:1 and AA:ODA = 1:2 monolayers increasingly resembled those obtained from pure ODA (AA:ODA = 0:1). Electron micrographs and diffraction patterns established the epitaxial growth of equilateral triangular PbS nanocrystallites, with their {111} planes parallel to the monolayer, upon exposing AA:ODA = 1:0 (at any surface pressure) and AA:ODA = 5:1 (kept at II = 30 mN/m) monolayers [which were covered with aqueous 1.0 x 10(-3) M Pb(NO3)(2) solutions] to H2S. Similar treatment of AA:ODA = 2.1 monolayers (kept at II = 30 mN/m) resulted in the formation of laminated, irregular shaped, and right-angle triangular PbS nanocrystallites with their {001} planes parallel to the monolayer. In contrast, exposing AA:ODA = 2:1 monolayers (kept at II = 0 and A = 23 Angstrom(2)/molecule) to H2S led to the formation of mostly right-angular Pbs nanocrystallites with their {001} planes parallel to the monolayer. In contrast, exposing AA:ODA = 2:1 monolayers (kept at II = 0 and A = 23 Angstrom(2)/molecule) to H2S led to the formation of mostly right-angular PbS nanocrystallites, epitaxially grown on their {110} faces. TEM images of PbS, grown under AA:ODA = 1:1 (kept at II = 30 mN/m), appeared to be quite similar to images of those that were grown under AA-rich monolayers, but they contained proportionately more right-angular nanocrystallites. PbS, formed under AA:ODA = 1:2 monolayers (kept at II = 30 mN/m), were randomly oriented, rectangularly shaped, and irregularly sized. Finally, no epitaxy occured under AA:ODA = 1:5 monolayers; only irregular brownish-colored particles formed in the bulk solution.