CuO nanocrystallites obtained by oxidation of copper arachidate LB multilayers

Abstract

Copper arachidate (CuA) Langmuir–Blodgett (LB) multilayers were transferred in the subphase pH range 4.6–5.7. FTIR studies of multilayers show a gradual increase in CuA content as subphase pH is increased. X-ray reflection patterns of multilayers show presence of a single layered structure in all the multilayers transferred at different subphase pH. A continuous decrease in bilayer period from 52.5 Å to 47 Å is seen with decrease in CuA content of the multilayers. These observations suggest mixing of CuA and arachidic acid molecules at the molecular level. The precursor CuA multilayers were oxidized at 300 °C–700 °C. The formation of CuO is confirmed by UV–Visible spectroscopy. Atomic force micrographs show the formation of CuO nanocrystallites and their clusters, with the average size, size distribution, height and density of nanocrystallites depending strongly on subphase pH, number of monolayers and oxidation temperature. Typically, 7–11 monolayers CuA transferred at subphase pH of 4.6 and oxidized at 700 °C resulted in isolated and nearly mono-disperse nanocrystallites of size 20–30 nm and height ∼ 1 nm. Crystallites of size 2–10 nm along with few clusters were obtained by oxidation of a 3 monolayer CuA.