We develop novel approaches for fabricating dielectric and metallic nanostructured films, and investigate their fundamental optical and plasmonic properties through a combination of experiments and numerical simulations. Fabrication and optical physics are two sides of the same coin: nanostructure architecture is engineered to achieve targeted plasmonic responses, while optical studies feed back into the next generation of designs.
Colloidal Self-Assembly
We exploit the spontaneous organization of colloidal particles to produce large-area nanostructured films on a variety of substrates — rigid (glass, silicon) and flexible (polymer foils). Using convective self-assembly (CSA), we deposit metallic nanoparticles of various morphologies — spherical and star-shaped gold and silver nanoparticles — into ordered or quasi-ordered films with tunable plasmonic properties. For metal oxide nanoparticles (ZnO, TiO₂), we have developed a controlled drop-coating approach that suppresses the coffee-ring effect, yielding uniform disc-like films suitable for optical and photocatalytic applications. Dielectric microspheres (polystyrene, SiO₂) are assembled both by CSA and at the liquid-air interface, forming two-dimensional colloidal crystals that serve as photonic structures or as templates for further processing.
Colloidal Lithography
Two-dimensional periodic arrays of colloidal microspheres serve as versatile lithographic templates for the fabrication of metal and dielectric nanostructured surfaces with precisely controlled morphology. Depositing metal films — by magnetron sputtering or e-beam evaporation — onto these colloidal arrays yields Metal Film over Nanosphere (MFoN) surfaces, a class of plasmonic substrates with tunable resonances determined by sphere diameter and metal film thickness. The morphology can be further tailored through additional processing steps: etching of the nanospheres prior to metal deposition produces quasi-3D MFoN architectures with modified near-field properties; soft lithography using PDMS transfers the colloidal pattern into nanobowl arrays; and nanosphere lithography (NSL) yields triangular nanoparticle arrays. This versatility enables precise control over nanoscale geometry and plasmonic response, with applications in surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF).
Additional Fabrication Capabilities
The group has experience with direct laser writing lithography for the patterning of polymer and other functional films, as well as with molecular beam epitaxy (MBE) for the growth of thin crystalline layers. These capabilities complement the colloidal approaches and broaden the range of material systems and geometries accessible within the group.
Plasmonic and Photonic Resonances: Optical Studies and Simulations
Understanding and predicting the optical response of nanostructured films is a research objective in its own right. We perform optical measurements — transmittance and reflectance spectroscopy, including micro-spectroscopy for spatially resolved studies — across a broad spectral range and in different environments (air, liquid). These experiments are combined with finite-difference time-domain (FDTD) numerical simulations, which provide access to near-field distributions, mode assignments, and the physical mechanisms underlying observed resonances. Together, experiment and simulation allow us to establish clear structure-property relationships, guiding the rational design of nanostructured films for targeted plasmonic and photonic functionality.