Using Particle Lithography to Tailor the Architecture of Au Nanoparticle Plasmonic Nanoring Arrays

The facile assembly of metal nanostructured arrays is a fundamental step in the design of plasmon enhanced chemical sensing and solar cell architectures. Here we have investigated methods of creating controlled formations of two-dimensional periodic arrays comprised of 20 nm Au nanoparticles (NPs) on a hydrophilic polymer surface using particle lithography. To direct the assembly process, capillary force and NP concentration both play critical roles on the resulting nanostructured arrays. As such, tuning these experimental parameters can directly be used to modify the nature of the nanostructures formed. To explore this, two different concentrations of Au NP solutions (∼7 × 10¹¹ or 4 × 10¹² NPs/mL) were used in conjunction with a fixed concentration of polystyrene microspheres (PS MS, ∼6 × 10⁹ PS MS/mL). Assembly at a relative humidity (RH) of 45% with the higher concentration resulted in the formation of well-defined Au nanorings of ca. 23 nm in height and 881 nm in diameter with a pitch of 2.5 μm. Assembly at 65% RH with the lower concentration of NPs resulted in Au nanodonut arrays comprised of isolated single Au NPs. To explore the extent of coupling in the well-defined structures, dark field scattering spectra were collected and showed a broad localized surface plasmon resonance (LSPR) peak with a shoulder, which full-wave electrodynamics modeling (finite-difference time domain (FDTD) method) attributed to be a result of pronounced particle-particle coupling along the circumference of the nanoring array.