Diffusion in Non-Crystalline Metallic and Organic Media

Computational fluid dynamics modeling of floating treatment wetland retrofitted stormwater pond: Investigation on design configurations

Floating Treatment Wetland (FTW) is a cost-effective and easy-to-retrofit device for stormwater treatment. Its treatment efficiency largely depends on the fraction of inflow entering FTW and the residence time within it. Thus hydrodynamics play a crucial role, which is affected by the design configurations of FTW and stormwater pond. Despite a spike in research on FTWs, very little is known about how various design configurations affect treatment efficiency by an FTW. Our study hypothesizes that relative positions of FTW geometry, FTW position and pond inlet-outlet have impact on the hydrodynamics and as a consequence, treatment efficiency. To explore these design features, we employed computational fluid dynamics (CFD) modeling conducted in ANSYS Fluent, validated by experimental data to examine the impact of the aforementioned design features. The results revealed that circular FTW geometry positioned near inlet coupled with center inlet-side outlet configuration achieved the highest removal (94.8%) for a non-dimensional removal rate of k_rt_HRT = 20 (k_r is the first order removal rate in per day, t_HRT is the nominal hydraulic residence time of the pond in days). Far side inlet-side outlet configuration performed the worst due to profound promotion of short-circuiting. FTW positioned near inlet performed better (61.8% mass removal on an average) than center (42.7%) and near outlet positions (54.1%) for k_rt_HRT = 20. Sensitivity analysis revealed that the treatment efficiency is most sensitive to inlet-outlet configurations. The design implications of this study will help practitioners achieving better water quality and ecological improvement goals.

Fundamental Aspects Of Polymer Metallization

Valuable information on the structure and formation of metal-polymer interfaces originates from radiotracer measurements of metal diffusion at the interface, structural investigations by means of transmission electron microscopy, and computer simulations on the interplay of atomic metal diffusion and aggregation. Moreover, X-ray photoemission spectroscopy has largely contributed to our present understanding of the interfacial chemistry and the early stages of interface formation. While reactive metals always form relatively sharp interfaces with polymers, metals of lower reactivity diffuse into polymers at elevated temperatures and have a very strong tendency to agglomerate. The extent of diffusion appears to be determined by the initial stage of the deposition process. Here sticking coefficients recently measured for metals on virgin polymer surfaces deviate markedly from unity. Diffusion into the polymer increases strongly at low deposition rates. No significant diffusion is expected from a continuous metal film unless metal ions are formed at the interface. Metal ions are highly mobile and do not aggregate due to electrostatic repulsion. The model emerging from these observations allows us to predict the salient features of interface formation between metals and polymers in general and particularly with respect to the new low-k polymers.

Electrical Reliability of Cu and Low-K Dielectric Integration

The recent demonstrations of manufacturable multilevel Cu metallization have heightened interest to integrate Cu and low-K dielectrics for future integrated circuits. For reliable integration of both materials, Cu may need to be encapsulated by barrier materials since Cu ions (Cu+) might drift through low-K dielectrics to degrade interconnect and device integrity. This paper addresses the use of electrical testing techniques to evaluate the Cu+ drift behavior of low-K polymer dielectrics. Specifically, bias-temperature stress and capacitance-voltage measurements are employed as their high sensitivities are well-suited for examining charge instabilities in dielectrics. Charge instabilities other than Cu+ drift also exist. For example, when low-K polymers come into direct contact with either a metal or Si, interface-related instabilities attributed to electron/hole injection are observed. To overcome these issues, a planar Cu/oxide/polymer/oxide/Si capacitor test structure is developed for Cu+ drift evaluation. Our study shows that Cu+ ions drift readily into poly(arylene ether) and fluorinated polyimide, but much more slowly into benzocyclobutene. A thin nitride cap layer can prevent the penetration.

Small isotope effect of diffusion in disordered structures

The isotope effect E of a single jump vacancy diffusion mechanism in statically disordered lattices is investigated by Monte Carlo simulation. It is found that E decreases significantly with increasing disorder. This effect is attributed to percolation processes and ensuing reduction of the effective dimension of space for the diffusing particle.

X-ray reflectivity study on the surface and bulk glass transition of polystyrene

The surfaces of polystyrene (PS) films decorated with gold nanoclusters were investigated by x-ray reflectivity measurements. The thicknesses of the films are much larger than the radii of gyration of the different PS samples. By annealing the films above the glass transition temperature T(g) an embedding process of the clusters into the polymer is detected which is accompanied by a substantial increase in the cluster layer thickness due to Brownian motion. These processes start at a sufficiently low viscosity and may be regarded as a probe of the glass transition in the near surface region of the PS films. Simultaneously the thermal expansion of the entire film and hence its approximate bulk behavior were monitored. Two samples of different molecular weight do not show a significant difference between the surface and bulk T(g) values.

TEM Investigation and Electron Diffraction Study on Dispersion of Gold Nanoparticles into a Nylon 11 Thin Film during Heat Treatment

We have investigated the effect of heat treatment on the changes in the microstructure of nylon 11 thin films containing nanosized Au particles by means of lateral and cross-sectional transmission electron microscopy. It was observed that, on heat treatment, the Au islandlike particles initially deposited on the nylon 11 surface penetrated into the polymer layer to form a composite film consisting of nanosized spherical Au particles dispersed in a polymer matrix, while the initially amorphous nylon 11 matrix crystallized to the alpha-crystalline form. The surface stress coefficient of the Au particles, calculated from the lattice constant determined by the electron diffraction patterns, decreased as the Au particles penetrated into the polymer matrix, which can be due to both coalescence of the particles to a spherical shape and reduction of the surface free energy of the particles by embedding in the matrix. The molecular chain motion of the nylon 11 matrix during the crystallization process is suggested to be responsible for the dispersion of Au particles into the polymer matrix. Copyright 1999 Academic Press.