Assembly Dynamics of Plasmonic DNA-Capped Gold Nanoparticle Monolayers.

The self-assembly of nanoparticles in aqueous solutions promises wide applications but requires the careful balance of many parameters not present in organic solvents. While the presence of long-range electrostatic interactions in aqueous solutions may complicate such assemblies, they provide additional parameters through which to control self-assembly. Here, with DNA-capped gold nanoparticles and through the variation of the ionic strength in aqueous solutions, we explored the influence of electrostatic interactions on the adsorption of negatively charged nanoparticles on a positively charged surface. Specifically, we studied the kinetics of nanoparticle adsorption from solution using the quartz crystal microbalance with dissipation (QCM-D). We also characterized the structure of the adsorbed monolayers employing a combination of grazing incidence small-angle X-ray scattering (GISAXS) and scanning electron microscopy. We discovered that adsorption kinetics and monolayer structure were under the control of the DNA ligand length, solution ionic strength, and salt species. We also precisely fit the kinetics to a modified Langmuir model, which converged to the simple Langmuir model at high ionic strengths of magnesium chloride. We demonstrated that increasing the ionic strength and decreasing the DNA ligand lengths increased the surface coverage while decreasing the nanoparticle-nanoparticle spacing. The DNA-capped nanoparticle system reported here provides a readily applicable platform for controlling nanoparticle self-assembly in aqueous solution. Finally, we employ this tunability to create a system with a tunable plasmonic response. Our kinetics studies of the assembly process and further characterizations undertaken will facilitate the construction of nanoparticle arrays with precise structure, and such control will aid in the design of future plasmonic and optoelectronic devices.

Compact matrix formalism for phase space analysis of complex optical systems.

Phase space analysis is a powerful approximate scheme for the analysis of complex optical systems. The matrix formalism introduced makes it possible to determine all important beam characteristics as a function of the distance from the source. An algebraic approach comprising matrix transformations and determinants was consistently employed rather than numerical phase space integrations. While the primary application is x-ray and neutron optics, the approach can be used more generally for characterizing finite-size beams near the optical axis.

Extending the possibilities in phase space analysis of synchrotron radiation x-ray optics.

A simple analytical approach to phase space analysis of the performance of x-ray optical setups (beamlines) combining several elements in position-angle-wavelength space is presented. The mathematical description of a large class of optical elements commonly used on synchrotron beamlines has been reviewed and extended with respect to the existing literature and is reported in a revised form. Novel features are introduced, in particular, the possibility to account for imperfections on mirror surfaces and to incorporate nanofocusing devices like refractive lenses in advanced beamline setups using the same analytical framework. Phase space analysis results of the simulation of an undulator beamline with focusing optics at the European Synchrotron Radiation Facility compare favorably with results obtained by geometric ray-tracing methods and, more importantly, with experimental measurements. This approach has been implemented into a simple and easy-to-use program toolkit for optical calculations based on the Mathematica software package.