Oxidation profiles in Cu and Co oxide nanoparticles

CuO x , CoO y , and bimetallic CoCuO z nanoparticles with diameter between 54.6 and 111.4 nm were synthesized by sol-gel and eroded with Ar ions to identify and quantify the oxide structures formed in the particles. Oxidation was estimated by XPS calculating the respective atomic ratios, x =O/Cu, y =O/Co, and z =O/(CuCo). Five Cu oxides were identified in CuO x , in which x varied from 0.14 to 2.4 with an average of 1. In CoO y , 4 Co oxides were found, in which y varied from 1.6 to 3.8 with an average of 2.8. In CoCuO z , up to 6 Cu and Co oxides were identified, in which x varied from 0.87 to 1.67, y varied between 0.25 and 3.7, and z varied between 2.15 and 1.73. The atomic ratios indicated that oxidation reduced from the surface to the interior in CuO x and CoCuO z and slightly increased in CoO y . The ratios were compared with those indirectly obtained by XRD, finding that they were similar in CuO x with x ≈1, but different in CoOy where y was smaller than that calculated with XPS. The method to identify and quantify oxidation applied here can also be used in other processes.