Rapid Deposition of Gold Nanoparticle Films with Controlled Thickness and Structure by Convective Assembly

We report how convective assembly at high volume fraction combined with thermal treatment allows robust fabrication of gold nanocoatings whose structure can be varied and correlated to their optical properties and conductance. Uniform films of gold nanoparticles were deposited directly from aqueous suspensions, where neither the nanoparticles, nor the substrates, were covered with ligands or pretreated in any way. The number of layers, optical absorbance, and electrical conductance of these nanocoatings could be controlled by the speed of deposition. The electronic, optical, and structural properties of the nanoparticle multilayers could be further tuned by post-deposition heat treatment. Scanning electron microscopy observations and electrical conductance measurements showed that heating leads to a transition from a near-percolated nanoparticle structure (conductivity approaching 2000 Omega(-1)cm(-1)) to a discontinuous insular structure (conductivity <10(-5) Omega(-1)cm(-1)). These structural transitions change the coating transmission spectra, where the surface plasmon resonance peak could be tuned by heating to any value from 800 to 565 nm. The ability to tune the nanocoating structure and spectral and electronic properties may allow for applications such as nonohmic switching, quantum electronics and sensors.