Deposition of gold films and nanostructures from supercritical carbon dioxide

High-purity gold films were deposited onto metal, ceramic, and polymer substrates by the H-2-assisted reduction of dimethyl(acetylacetonate)gold(III) in supercritical CO2 at temperatures between 60 and 125 degreesC. At 125 degreesC and 150 bar, Au deposition proceeded readily on all surfaces studied, including SiO2 and TiN films. By contrast, at 60 degreesC and 138 bar, deposition was highly selective for metal substrates including nickel and palladium films over nongrowth surfaces such as polymers or the native oxide of silicon. Low-temperature deposition on nongrowth surfaces was possible by seeding the substrate with Pt, Pd, or Ni clusters or films. In all cases, Au films deposited from CO2 were conformal. Excellent step coverage on Si wafers was achieved in features ranging from 0.1 to 1.0 mum wide by 1.0 mum deep. Continuous arrays of gold posts were prepared using etched Si wafers backfilled with SiO2 as templates. Following gold deposition at 125 degreesC, the arrays were released from the template by selective etching of the SiO2 layer with HF. The features of the substrate were accurately replicated in the gold film. Postdeposition analysis of the CO2 effluent stream by H-1 NMR revealed that ethane and 2,4-pentanedione were the only major ligand products of precursor reduction.