Aberration measurement of photolithographic lenses by use of hybrid diffractive photomasks

In optical lithography the degradation of image quality due to aberrations present in the exposure tool is a serious problem. Therefore it is desirable to establish a reliable aberration measurement procedure based on the analysis of printed images in the photoresist. We present what is to our knowledge a new method for characterizing the aberrations of an exposure tool using a hybrid diffractive photomask. By utilizing each different impact on the aberrated image from each diffracted illumination, we were able to extract the aberration present in the stepper system. We experimentally verified this method with a G-line stepper and verified its spherical aberration astigmatism.     

Synthesis and performance characteristics of methylmethacrylate–divinylbenzene copolymer-based chelating resin for gallium metal recovery

A chelating ion exchange resin based on a methylmethacrylate and divinylbenzene copolymer has been designed through suspension polymerisation and subsequent functionalisation to hydroxamic acid as chelating group. The chelating resin has been characterized by infrared spectroscopy, its particle size, stability in acid/alkaline media, specific gravity and its use in gallium recovery. The use of resin has been demonstrated to effect gallium recovery with an efficiency of about 80%.     

PEDOT-PSSA as an alternative support for Pt electrodes in PEFCs

Poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (styrene sulphonic acid) (PSSA) supported platinum (Pt) electrodes for application in polymer electrolyte fuel cells (PEFCs) are reported. PEDOT-PSSA support helps Pt particles to be uniformly distributed on to the electrodes, and facilitates mixed electronic and ionic (H⁺-ion) conduction within the catalyst, ameliorating Pt utilization. The inherent proton conductivity of PEDOT-PSSA composite also helps reducing Nafion content in PEFC electrodes. During prolonged operation of PEFCs, Pt electrodes supported onto PEDOT-PSSA composite exhibit lower corrosion in relation to Pt electrodes supported onto commercially available Vulcan XC-72R carbon. Physical properties of PEDOT- PSSA composite have been characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. PEFCs with PEDOT-PSSA-supported Pt catalyst electrodes offer a peak power-density of 810 mW cm⁻² at a load current-density of 1800 mA cm⁻² with Nafion content as low as 5 wt.% in the catalyst layer. Accordingly, the present study provides a novel alternative support for platinized PEFC electrodes.     

Stochastic analysis of isothermal cure of resin systems

Curing of catalyzed resin systems is an important and critical processing step in the fabrication of reinforced thermosetting composite materials. Strong uncertainties inherent in the associated process and material parameters, however, pose a stiff challenge to robust commercial manufacturing of quality composites in practice. Although deterministic models have been developed over the years to simulate the cure process, analysis of the effects of the parameter uncertainties on the process performance and the product quality variabilities has been the subject of little attention, and forms the focus of this study. This paper presents a methodology for a systematic analysis of the effects of the process and material parameter uncertainties on the isothermal curing of thermosetting resin systems. A stochastic model is developed, and parameteric studies are presented to systematically examine the effects of the uncertainties in the processing temperature and the kinetic parameters on the process output variabilities. Optimum parameter spaces that minimize the variance of the output parameters are identified, as a first step towards robust manufacturing of composites.     

Optimal cure cycles for the fabrication of thermosetting-matrix composites

Polymer-matrix composites using thermosetting resins as the matrix are increasingly finding use. However, a major impediment to their widespread commercial use is the high cost associated with their manufacture, arising from the long processing cycle times. This paper addresses the problem of determining cure temperature and pressure variations with time for a time-optimal manufacture of thermosetting-matrix composites subject to practical constraints. The optimal cure cycles are determined using the nonlinear programming scheme of sequential quadratic programming combined with a physical model base to simulate the process phenomena. The optimized cycles are shown to improve upon the manufacturer-recomended cycles as well as the improved cycles reported in the literature. The optimization results are reported for a wide range of resin materials, product specifications, and process constraints to illustrate their effects on the optimal cure cycles. Parametric studies are presented in terms of dimensionless groups to assess the combined effects of the product and process variables on the optimal cycles in a generalized manner.     

Production of Nano Talc Material and Its Applicability as Filler in Polymeric Nanocomposites

In the present work, focus is on the production of nano-sized talc particles in a stirred ball mill and their nano talc particles incorporated in the polyamide-6 polymer matrix to form polyamide/talc nanocomposite. The results show that enhancement in the polyamide/talc nanocomposite strength properties such as flexural and tensile strength. The production of nano talc particles is difficult process in wet grinding system; however, the minimum achievable particle size is strongly influenced by the suspension stability. Hence, prior to the wet milling, it is imperative to conduct the ζ potential measurements on the talc sample in order to find out at which pH range a strong repulsive force between the given talc sample particles exists. The desired electrostatic repulsion force is maintained by the adjustment of pH 11 in wet milling. The experiments are conducted at pH 11 conditions which were maintained constant throughout the experiments and nanosized talc particles are obtained consequently.     

Carbon-supported Pt encapsulated Pd nanostructure as methanol-tolerant oxygen reduction electro-catalyst

Pt@Pd/C nanoparticle was prepared by the galvanic displacement reaction between Pt⁴⁺ and Pd. A simple synthesis strategy was followed to prepare carbon-supported Pd nanostructure. Pt modified Pd nanostructure on carbon was characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Cyclic Voltammetry and Linear Sweep Voltammetry. Pt@Pd/C electro-catalyst exhibited higher catalytic activity toward oxygen reduction reaction with excellent methanol tolerance than Pt/C. Pt@Pd/C catalyst showed consistent catalytic activity before and after the durability study. Higher methanol tolerance of Pt@Pd/C with less Pt content than Pt/C suggests that it could be a potential alternative cathode electro-catalyst for DMFCs.     

Impact of Mesoporous and Microporous Materials on Performance of Nafion and SPEEK Polymer Electrolytes: A Comparative Study in DEFCs

Hybrid membranes are prepared from fluoro and non‐fluoro polymer membrane matrices with mesoporous and microporous inorganic materials. Nafion‐Si‐MSU‐F, Nafion‐Al‐MCM‐41, and zeolite 4A‐SPEEK‐MSA hybrid membranes are fabricated by solution casting method. The structural properties of the membranes are characterized using FE‐SEM and AFM techniques. Ion exchange capacity, sorption, proton conductivity, and thermal stability for the membranes have been extensively investigated. Ethanol permeability measurements for the membranes are performed using electrochemical as well as diffusion cell method. Among the membranes that are tested in direct ethanol fuel cells (DEFCs), Nafion‐Al‐MCM‐41 hybrid membrane delivered the highest peak power‐density of 44 mW cm^–2 at 70 °C.