Metal nanoparticles on polymer thin films promise various potential applications as functional coatings in solar cells, biosensors, as reflective or antireflective coatings, and in heterogeneous catalysis. Fabricating such nanocluster films with tailored morphology, their characterization and manipulation at the nanoscale are the essential prerequisites and tools for implementing devices in all of these fields. Here, sputter deposition plays a very important role in industrial and nanostructural processing to tune the size-dependent optoelectronic properties. To obtain full control over the nanostructural evolution at the metal-polymer interface and its impact on optoelectronic properties, we employed an in situ combination of time-resolved surface-sensitive X-ray scattering (GISAXS) with UV/Vis Spectroscopy during sputter deposition of gold (Au) on thin polystyrene films (PS). We monitored the evolution of the metallic layer morphology according to changes in the key scattering features by geometrical modeling and correlate the nanostructural development to optical properties. The morphological characterization is complemented by X-ray reflectivity and electron microscopy. This enables us to identify the different growth regimes including their specific thresholds and permits better understanding of the growth kinetics of gold clusters and their self-organization into complex nanostructures on polymer thin films. During sputter deposition, a change in optical reflectivity of the pristine grey-blue PS film occurred ranging from dark blue color due to the presence of isolated Au nanoclusters at the interface to bright red color from larger Au aggregates. In addition, a surface diffusion coefficient for Au on PS at room temperature according to the interrupted coalescence model was calculated based on a real-time experiment. Furthermore, the role of sputter deposition rate in tailoring metal layer morphologies on polymer thin films has been investigated. The deposition rate affects primarily the nucleation process and the adsorption-mediated growth, whereas rather small effects on diffusion-mediated growth processes are observed. Only at higher rates, initial particle densities are higher due to an increasing influence of random nucleation and an earlier onset of thin film percolation occurs. Thus, our findings are of great interest for applications in organic photovoltaics and organic electronics, which benefit from tailored metal-polymer interfaces.

Tailoring of morphology and optical properties of metal-polymer interfaces during sputter deposition

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.