Copper and copper oxide nanoparticle formation by chemical vapor nucleation from copper (II) acetylacetonate

Crystalline nanometer-size copper and copper (I) oxide particle formation was studied by thermal decomposition of copper acetylacetonate Cu(acac)2 vapor using a vertical flow reactor at ambient nitrogen pressure. The experiments were performed in the precursor vapor pressure range of P_prec = 0.06 to 44 Pa at furnace temperatures of 431.5°C, 596.0°C, and 705.0°C. Agglomerates of primary particles were formed at P_prec0.1 Pa at all temperatures. At 431.5°C the number mean size of the primary particles increased from D_p = 3.7 nm (with geometric standard deviation σ_g = 1.42) to D_p = 7.2 nm (σ_g = 1.33) with the increasing precursor vapor particle pressure from 1.8 to 16 Pa. At 705.0°C the primary particle size decreased from Dp = 24.0 nm (σ_g=1.57) to Dp = 7.6 nm (σ_g = 1.54), respectively.

At furnace temperatures of 431.5°C and 596.0°C only crystalline copper particles were produced. At 705.0°C the crystalline product of the decomposition depended on the precursor vapor pressure: copper particles were formed at P_prec>10 Pa, copper (I) oxide at P_precleq 1 Pa, and a mixture of the metal and its oxide at intermediate vapor pressures. A kinetic restriction on copper particle growth was shown, which leads to the main role of Cu₂ molecule participation in the particle formation. The formation of copper (I) oxide particles occurs due to the surface reaction of the decomposition products (mainly carbon dioxide). For the explanation of the experimental results, a model is proposed to build a semiempirical phase diagram of the precursor decomposition products.