The growing interest in recent years in gold island films prepared by vapor deposition on transparent substrates is largely attributed to the prominent localized surface plasmon (SP) extinction associated with nanostructured metal films. In the present study, two types of evaporated Au island films were investigated: (i) Au films (2.5, 5.0, and 7.5 nm nominal thickness) evaporated on silanized glass and annealed 20 h at a temperature <250 °C; (ii) Au films (7.5 and 10 nm nominal thickness) evaporated on unmodified glass and annealed 10 h at 550 or 600 °C. The 3D morphology of the Au islands was analyzed using high-resolution scanning electron microscopy (HRSEM), crosssectional transmission electron microscopy (TEM), and atomic force microscopy (AFM) crosssectional profilometry. Annealing at high temperatures, close to the glass transition temperature of the substrate, results in wetting of the Au islands by the glass and partial island embedding. The mechanism of morphology evolution during annealing changes from island coalescence and coarsening (low nominal thicknesses) to dewetting of percolated films (higher nominal thicknesses). The aspect ratio of more than 90% of the islands in annealed films is <1.5; therefore, splitting of the SP band to transversal and longitudinal components is not observed. The bulk refractive index sensitivity (RIS), in terms of SP wavelength shift and plasmon intensity change (PIC) per refractive index unit (RIU) change of the medium, was determined by measuring UV-vis spectra of Au island films in a series of methanol/chloroform mixtures. The RIS values for SP wavelength shift (RIS λ ) and PIC (RIS ext ) are 66-153 nm/RIU and 0.2-0.81 abs.u./RIU, respectively. The RIS shows a strong dependence on the wavelength of the SP maximum extinction, i.e., a higher RIS is measured for Au island films exhibiting a SP band at longer wavelengths. Partial thermal embedding of the Au islands in the glass substrate stabilizes the systems but lowers the RIS. The results presented may be useful for tuning the morphology and optical response of Au island films.

The origin of anomalous or non-Fickian transport in disordered media is the broad spectrum of transition rates intrinsic to these systems. A system that contains within it heterogeneities over multiple length scales is geological formations. The continuous time random walk (CTRW) framework, which has been demonstrated to be an effective means to model non-Fickian transport features in these systems and to have predictive capacities, has at its core this full spectrum represented as a joint probability density psi(s,t) of random space time displacements (s,t) . Transport in a random fracture network (RFN) has been calculated with a coupled psi(s,t) and has subsequently been shown to be approximated well by a decoupled form psi(s,t)=F(s)psi(t) . The latter form has been used extensively to model non-Fickian transport in conjunction with a velocity distribution Phi(xi),xi identical with 1v, where v is the velocity magnitude. The power-law behavior of psi(t) proportional to (-1-beta), which determines non-Fickian transport, derives from the large xi dependence of Phi(xi) . In this study we use numerical CTRW simulations to explore the expanded transport phenomena derived from a coupled psi(s,t) . Specifically, we introduce the features of a power-law dependence in the s distribution with different Phi(xi) distributions (including a constant v) coupled by t=s(xi) . Unlike Lévy flights in this coupled scenario the spatial moments of the plumes are well defined. The shapes of the plumes depend on the entire Phi(xi) distribution, i.e., both small and large xi dependence; there is a competition between long displacements (which depend on the small xi dependence) and large time events (which depend on a power law for large xi). These features give rise to an enhanced range of transport behavior with a broader scope of applications, e.g., to correlated migrations in a RFN and in heterogeneous permeability fields. The approximation to the decoupled case is investigated as a function of the nature of the s distribution.

Diffusion on lattices with random mixed bonds in two and three dimensions is reconsidered using a random walk (RW) algorithm, which is equivalent to the master equation. In this numerical study the main focus is on the simple case of two different transition rates W(1),W(2) along bonds between sites. Although analysis of diffusion and transport on this type of disordered medium, especially for the case of one-bond pure percolation (i.e., W(1)=0 ), comprises a sizable subliterature, we exhibit additional basic results for the two-bond case: When the probability p of W(2) replacing W(1) in a lattice of W(1) bonds is below the percolation threshold p(c) , the mean square displacement r(2) is a nonlinear function of time t . A best fit to the lnr[(2) vs ln t plot is a straight line with the value of the slope varying with p,Delta,d , where Delta identical with W(2)/W(1) and d is the dimension, i.e., r(2) proportional, variant t(1+eta(p,Delta,d)) with eta>0 for Delta>1 . In other terms, all the diffusion (D identical with(r)(2)/2t proportional, variant t(eta)) is anomalous superdiffusion for p1 for d=2,3 . Previous work in the literature for d=2 with a different RW algorithm established an effective diffusion constant D(eff) , which was shown to scale as (p(c)-p)(1/2) . However, the anomalous nature (time dependence) of D(t) becomes manifest with an expanded regime of t , increased range of Delta , and the use of our algorithm. The nature of the superdiffusion is related to the percolation cluster geometry and Lévy walks.