Finite-Size Charged Species Diffusion and pH Change in Nanochannels.

Molecular transport through nanofluidic structures exhibits properties that are unique at the nanoscale. The high surface-to-volume ratio of nanometer-sized confined spaces renders particle interactions with the surface of central importance. The electrical double layer (EDL) at the solid-liquid interface of charged surfaces generates an enrichment of counterions and the exclusion of co-ions that lead to a change in their diffusivity.

Gas Flow at the Ultra-nanoscale: Universal Predictive Model and Validation in Nanochannels of Ångstrom-Level Resolution.

Gas transport across nanoscale pores is determinant in molecular exchange in living organisms as well as in a broad spectrum of technologies. Here, we report an unprecedented theoretical and experimental analysis of gas transport in a consistent set of confining nanochannels ranging in size from the ultra-nanoscale to the sub-microscale. A generally applicable theoretical approach quantitatively predicting confined gas flow in the Knudsen and transition regime was developed.

Unexpected behaviors in molecular transport through size-controlled nanochannels down to the ultra-nanoscale.

Ionic transport through nanofluidic systems is a problem of fundamental interest in transport physics and has broad relevance in desalination, fuel cells, batteries, filtration, and drug delivery. When the dimension of the fluidic system approaches the size of molecules in solution, fluid properties are not homogeneous and a departure in behavior is observed with respect to continuum-based theories. Here we present a systematic study of the transport of charged and neutral small molecules in an ideal nanofluidic platform with precise channels from the sub-microscale to the ultra-nanoscale (<5 nm).

Fragmentation approach to the point-island model with hindered aggregation: Accessing the barrier energy.

We study the effect of hindered aggregation on the island formation process in a one- (1D) and two-dimensional (2D) point-island model for epitaxial growth with arbitrary critical nucleus size i. In our model, the attachment of monomers to preexisting islands is hindered by an additional attachment barrier, characterized by length l_{a}. For l_{a}=0 the islands behave as perfect sinks while for l_{a}→∞ they behave as reflecting boundaries.

Nanoparticles heat through light localization.

Aqueous solutions containing light-absorbing nanoparticles have recently been shown to produce steam at high efficiencies upon solar illumination, even when the temperature of the bulk fluid volume remains far below its boiling point. Here we show that this phenomenon is due to a collective effect mediated by multiple light scattering from the dispersed nanoparticles. Randomly positioned nanoparticles that both scatter and absorb light are able to concentrate light energy into mesoscale volumes near the illuminated surface of the liquid.

Scaling and Exponent Equalities in Island Nucleation: Novel Results and Application to Organic Films.

It is known in thin-film deposition that the density of nucleated clusters varies with the deposition rate as a power law, . The exponent α is a function of the critical nucleus size in a way that changes with the aggregation limiting process. We extend here the derivation of the analytical capture-zone distribution function () = · ·exp(-) of Pimpinelli and Einstein to generic aggregation-limiting processes.

Mean-field approximation for spacing distribution functions in classical systems.

We propose a mean-field method to calculate approximately the spacing distribution functions p((n))(s) in one-dimensional classical many-particle systems. We compare our method with two other commonly used methods, the independent interval approximation and the extended Wigner surmise. In our mean-field approach, p((n))(s) is calculated from a set of Langevin equations, which are decoupled by using a mean-field approximation.

Spacing distribution functions for the one-dimensional point-island model with irreversible attachment.

We study the configurational structure of the point-island model for epitaxial growth in one dimension. In particular, we calculate the island gap and capture zone distributions. Our model is based on an approximate description of nucleation inside the gaps.

Effects of impurities on surface morphology: some examples.

Small amounts of impurities are known to have remarkably great influence on surface morphology. We discuss three examples that arise in our research. First, we consider impurities codeposited during epitaxial growth, paying particular attention to Cu(100).

Capture-zone scaling in island nucleation: universal fluctuation behavior.

In island nucleation and growth, the distribution of capture zones (in essence proximity cells) can be described by a simple expression generalizing the Wigner surmise (power-law rise, Gaussian decay) from random matrix theory that accounts for spacing distributions in a host of fluctuation phenomena. Its single adjustable parameter, the power-law exponent, can be simply related to the critical nucleus of growth models and the substrate dimensionality. We compare with extensive published kinetic Monte Carlo data and limited experimental data.

Distinctive fluctuations in a confined geometry.

Spurred by recent theoretical predictions [Phys. Rev. E 69, 035102(R) (2004)10.

Evolution of terrace-width distributions on vicinal surfaces: Fokker-Planck derivation of the generalized Wigner surmise.

We use a Fokker-Planck equation to justify the generalization of the Wigner surmise for the energy-level spacing in quantum systems to the simple expression for the equilibrium terrace-width distribution of steps--with arbitrary-strength repulsions--on a vicinal surface, taking advantage of analogies to one-dimensional models of interacting, spinless fermions. This approach leads to an analytic description of the evolution toward equilibrium of steps from several experimentally relevant initial distributions: step bunches, perfect cleaved crystals, and prequench equilibrated distributions at different temperatures.

New types of unstable step-flow growth on Si(111)-(7 x 7) during molecular beam epitaxy: scaling and universality.

New types of unstable homoepitaxial growth of vicinal surfaces are studied using ex situ atomic force microscopy. The growth features are two types of step bunching with straight step edges between 700 and 775 degrees C and one type of simultaneous bunching and meandering at 800 degrees C. The results of a quantitative size scaling analysis of the straight steps are discussed from the perspective of universality classes in bunching theory.