A model has been developed to predict current distribution in electrodeposition onto substrates that contain lithographic patterns. The aim of the work was to understand the strong effects that substrate patterning can exert on the thickness distribution of plated films. Based on the familiar potential-theory model for secondary current distribution in electrochemical cells, the model is applicable at length scales that are large compared to the individual features of a pattern. The pattern is described entirely as a continuous distribution of"active-area density," a property that reflects any relative change in the electroactive area of the substrate due to the pattern. The active-area density enters the expression that relates the surface overpotential to the current density. An implementation of the model, using the boundary-element method, has been applied to several problems that illustrate the effects of substrate patterning on current distribution. For each example, the dimensionless groups that characterize the current distribution have been identified, general solutions have been obtained over wide parameter ranges, and behavioral trends have been interpreted.

The effect of lithographic patterning on electrodeposit thickness uniformity was investigated in a series of experiments. Copper was electrodeposited from an acid‐sulfate solution onto a specially patterned cathode under controlled agitation provided by a reciprocating paddle. The thickness nonuniformity resulting from a difference in “active‐area‐density” between adjacent zones was measured by profilometry. At current densities far below the mass‐transfer limit, the thickness distributions agreed well with predictions from a recently developed secondary‐current‐distribution model, in which each zone is treated as a continuum. Since this “secondary” model was found to be insufficient to describe behavior at higher current densities, it was extended to include a simple treatment of mass transfer. The resulting “tertiary” model better described the observed behavior. It was discovered that the influence of mass transfer can either decrease or increase the nonuniformity, depending on the importance of radially enhanced diffusion at individual features.

A numerical model is used to examine how the uniformity of current distribution at a flat electrode can be improved using a coplanar auxiliary electrode. A boundary-element code, based on potentialtheory and Tafel kinetics, determines the current that must be passed at a surrounding auxiliary electrode to minimize nonuniformity on a round cathode. Nonuniformity is quantified by the root-mean-square deviation from the mean current density over the cathode surface. The importance of geometric factors such as the size and position of the auxiliary electrode is examined. Applications to plating in the electronics industry and to rotating-disk electrodes are discussed.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.129.120.3 Downloaded on 2015-06-20 to IP

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In this study, dose rate distribution around a spherical 137Cs pellet source, from a low‐dose‐rate (LDR) Selectron remote afterloading system used in gynecological brachytherapy, has been determined using experimental and Monte Carlo simulation techniques. Monte Carlo simulations were performed using MCNP4C code, for a single pellet source in water medium and Plexiglas, and measurements were performed in Plexiglas phantom material using LiF TLD chips. Absolute dose rate distribution and the dosimetric parameters, such as dose rate constant, radial dose functions, and anisotropy functions, were obtained for a single pellet source. In order to investigate the effect of the applicator and surrounding pellets on dosimetric parameters of the source, the simulations were repeated for six different arrangements with a single active source and five non‐active pellets inside central metallic tubing of a vaginal cylindrical applicator. In commercial treatment planning systems (TPS), the attenuation effects of the applicator and inactive spacers on total dose are neglected. The results indicate that this effect could lead to overestimation of the calculated F(r,θ), by up to 7% along the longitudinal axis of the applicator, especially beyond the applicator tip. According to the results obtained in this study, in a real situation in treatment of patients using cylindrical vaginal applicator and using several active pellets, there will be a large discrepancy between the result of superposition and Monte Carlo simulations.PACS number: 87.53.Jw

Accuracy of treatment planning systems may significantly influence the efficacy of brachytherapy. The purpose of this work is a detailed, varied and independent evaluation of an in‐house brachytherapy treatment planning software called STPS. Operational accuracy of STPS was investigated. Geometric tests were performed to validate entry and reconstruction of positional information from scanned orthogonal films. MCNP4C Monte Carlo code and TLDs were used for simulation and experimental measurement, respectively. STPS data were also compared with those from a commercial planning system (Nucletron PLATO). Discrepancy values between MCNP and STPS data and also those of PLATO and STPS at Manchester system dose prescription points (AL and AR) of tandem and ovoid configurations were 2.5%±0.5% and 5.4%±0.4%, respectively. Similar results were achieved for other investigated configurations. Observed discrepancies between MCNP and STPS at the dose prescription point and at 1 cm from the tip of the vaginal applicator were 4.5% and 25.6% respectively, while the discrepancy between the STPS and PLATO data at those points was 2.3%. The software showed submillimeter accuracy in its geometrical reconstructions. In terms of calculation accuracy, similar to PLATO, as attenuation of the sources and applicator body is not considered, dose was overestimated at the tip of the applicator, but based on the available criteria, dose accuracy at most points were acceptable. Our results confirm STPS's geometrical and operational reliability, and show that its dose computation accuracy is comparable to an established commercial TPS using the same algorithm.PACS number: 87.53.Jw

A recent first principles theory for "anomalous" diffusion, which accounts for the effect of a protracted macromolecular response to a perturbation, is used to quantitatively predict the results from successive differential sorption experiments in the benzene/ atactic polystyrene system. The physical constants in the theory are evaluated for the conditions of the experiment without reference to any non-Fickian diffusion data. The theoretical predictions are in reasonable agreement with the experimental observations.