Tuning the Optical Properties of Large Gold Nanoparticle Arrays

Abstract

Gold nanoparticles in the mid-nanometer size regime can undergo self-organization into densely packed monoparticulate films at the air-water interface under appropriate passivation conditions. Films could be transferred onto hydrophilic Formvar-coated Cu grids by horizontal (LangmuirSchaefer) deposition or by vertical retraction of immersed substrates. The latter method produced monoparticulate films with variable extinction and reflectance properties. Transmission electron microscopy revealed hexagonally close-packed arrays on the micron length scale. The extinction bands of these arrays shifted by hundreds of nanometers to near-infrared wavelengths and broadened enormously with increasing periodicity. Large particle arrays also demonstrated extremely high surface-enhanced Raman scattering (SERS), with enhancement factors greater than 10 7 . Signal enhancements could be correlated with increasing periodicity and are in accord with earlier theoretical and experimental investigations involving nanoparticle aggregate structures.

Chemoresponsive assemblies of microparticles at liquid crystalline interfaces

“…The possibility of using interfacial nematic fields present within LCs to direct the ordering of microparticle assemblies may enable control of reversible ordering transitions of microparticles at the interfaces of systems with complex geometries, such as at the surface of a droplet (12), which could be used for dynamic tuning of emulsion stability and interfacial rheological properties. The results presented in this paper also guide the design of interfacial assemblies of microparticles that can have tunable mechanical (25), optical (26), and electronic properties (27). For example, precise control over interparticle spacing within chains of microparticles, when combined with control of microparticle orientation, could be used to create tunable media for transport of light.…”

Calixarene‐Encapsulated Nanoparticles: Self‐Assembly into Functional Nanomaterials

“…13). 43,44 The sizedependent shift in the plasmon bands of the 2D arrays are much more pronounced than that of individual metal nanoparticles, because the electromagnetic couplings between 43 Errors are equal to one standard deviation. Fig.…”

“…12(b)). 44,47 These variable reflectivities can be attributed to several effects: size-dependent optical absorption in the visible region for 2D arrays with periodicities below 40 nm; angular-dependent attenuation in reflectance as a function of surface roughness; 48 and size-dependent Mie scattering, which increase in significance for nanoparticles and metal surfaces with roughnesses of 40 nm or more. 8, 51 The 2D nanoparticle arrays exhibited size-dependent SERS activities, with signal intensities varying by two orders of magnitude under identical sampling conditions and surface coverages (see Fig.…”

“…14). 44,47 SERS has attracted widespread interest as a spectroscopic mode of sensing: it can produce vibrational Raman spectra from just a few molecules in the presence of metal nanostructures, and has been shown to be capable of single-molecule detection. 49 SERS is also compatible with water, and its unique combination of high sensitivity and high information content makes it an attractive method for detecting trace levels of analyte in a label-free manner.…”

“…14 SERS spectra of resorcinarene 6 from Au nanoparticle arrays, using an excitation wavelength of 785 nm (10 mW, area = 700 mm 2 , exposure = 30 s). 44 Spectra are shifted for clarity of presentation. resorcinarene-encapsulated nanoparticle arrays were measured to be less than 1 nm.…”