Complex-tensor theory of simple smectics.

Matter self-assembling into layers generates unique properties, including structures of stacked surfaces, directed transport, and compact area maximization that can be highly functionalized in biology and technology. Smectics represent the paradigm of such lamellar materials - they are a state between fluids and solids, characterized by both orientational and partial positional ordering in one layering direction, making them notoriously difficult to model, particularly in confining geometries. We propose a complex tensor order parameter to describe the local degree of lamellar ordering, layer displacement and orientation of the layers for simple, lamellar smectics.

Self-assembly and applications of ultraconcentrated nanoparticle solutions.

We demonstrate a highly efficient method for concentrating, purifying and separating gold nanoparticles. The method relies on localized density gradients that can be formed at an aqueous | organic phase interface. We show that this method is able to concentrate aqueous gold nanoparticles to the point where confinement leads to variable interparticle separations.

Self-assembled nanoparticle arrays for multiphase trace analyte detection.

Nanoplasmonic structures designed for trace analyte detection using surface-enhanced Raman spectroscopy typically require sophisticated nanofabrication techniques. An alternative to fabricating such substrates is to rely on self-assembly of nanoparticles into close-packed arrays at liquid/liquid or liquid/air interfaces. The density of the arrays can be controlled by modifying the nanoparticle functionality, pH of the solution and salt concentration.

Plasmonic ruler at the liquid-liquid interface.

We report on a simple, fast, and inexpensive method to study adsorption and desorption of metallic nanoparticles at a liquid/liquid interface. These interfaces provide an ideal platform for the formation of two-dimensional monolayers of nanoparticles, as they form spontaneously and are defect-correcting, acting as 2D "nanoparticle traps". Such two-dimensional, self-assembled nanoparticle arrays have a vast range of potential applications in displays, catalysis, plasmonic rulers, optoelectronics, sensors, and detectors.

Reflection of light by metal nanoparticles at electrodes.

We present model calculations for the reflection spectrum of an ordered two dimensional array of metallic nanoparticles located near an electrochemical interface. We consider three cases, nanoparticles at: (i) a metal electrode, (ii) a transparent semiconductor electrode, and (iii) an electrified liquid/liquid interface. In the case of a metal electrode, the presence of nanoparticles introduces dips in reflection, whose position and depth are affected by the distance and size of the nanoparticles.