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

Abstract

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 Ω-1cm-1) to a discontinuous insular structure (conductivity <10-5 Ω-1cm-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.

Short-time preparation and electrochemical properties of a single layer of tetraoctylammonium bromide capped Au nanoparticles on dithiol self-assembled monolayer-modified Au electrode

“…But the aggregation is not at so great extent as to exhibit a strong and broad absorption band around 700-900 nm region. The ER signals of both the electrodes are different from that of a bulk polycrystalline Au electrode, indicating that the individual AuNPs are not fused to form a bulk gold on the SAM surfaces [39]. Similar red shifted plasmon resonance bands were noticed for the multilayer assemblies of AuNPs on glass and ITO substrates [14,34].…”

Geometric Model Describing the Banded Morphology of Particle Films Formed by Convective Assembly

“…Structured particle films are of interest in various fields including optics, [1][2][3][4] photonics, [1,5,6] colloidal lithography, [7,8] sensors, [9] separations, [10][11][12] and so forth. Usually, film thickness and film microstructure are of primary concern for the functionality of devices in these applications.…”

“…Increasingly, high-technology applications are requiring controlled microstructures, such as colloidal crystals (such as for photonics) and hierarchical structures (as may be useful in separations). To these ends, we have been studying the method of convective assembly, [1,[3][4][5][13][14][15][16][17][18][19][20][21][22][23][24] rooted in the more general phenomenon of evaporation-induced self-assembly, [25][26][27][28][29][30][31][32] as a coating method for obtaining structured thin films, variously applying the technique to zeolite nanocrystals [33] and silica nanospheres [34] . It is by now well agreed that convective assembly of particles, in addition to yielding continuous films, [1,14,17,35] can also yield films with discrete morphologies [4,19,22,28,30,36] without patterning the substrate (others have patterned the substrate chemically or topologically to control film morphology [37,43] ).…”

Controlled assembly of SERS substrates templated by colloidal crystal films

“…The nanoporosity can be changed by controlled post-deposition fusion of the gold nanoparticles at temperatures between 200 and 500 uC. 43 In order to reliably characterize the effect of the nanoporosity on SERS performance we developed a procedure for making nanoporosity gradient substrates by imposing a monotonically varying thermal gradient onto the backside of the SERS support. 19 This technique produced substrates that had fully fused gold nanoparticles on one end and unchanged discrete aggregated gold nanoparticles on the other, with a variable degree of fusion in the middle.…”