Photoelectrochemical etching of compound semiconductors: Wavelength dependence

Argon-ion-laser photoetching was performed at various wavelengths, around the absorption edge of ZnSe and CdS. The surface etch pit density is observed to decrease with increasing penetration depth of the light. This observation is explained in terms of the recent theory of non-uniform charge flow within semiconductor junctions.Incumbent of Helen and Milton A. Kitmmelman Career Development Chair in perpetuity, established by Helen and Milton A. Kimmelman, N.Y.Formerly: Department of Plastics ResearchIncumbent of Jacob and Alphonse Laniado (Montreal, Canada) Career Development Chair     

Evaluation of yeast strains as possible agents for trace enrichment of metal ions in aquatic environments

Sorption properties of six yeast strains were evaluated for trace enrichment of metal ions; Cd²⁺, Cr³⁺, Cr⁶⁺, Cu²⁺, Pb²⁺, and Zn²⁺ from aqueous environments. Metal concentration was determined by flame atomic absorption spectrometry (FAAS). The results showed that trace enrichment of the metals under study with yeast, was dependent on the pH and available metal ions. Enrichment time of 30 min gave an optimum metal uptake. The presence of Na⁺, K⁺, and Ca²⁺ suppressed the uptake of Pb by less than 5%, but suppressed the uptake of Zn by between 15 and 25%. Mg²⁺, Cu⁺, Cu²⁺, Cr³⁺ Cr⁶⁺, Cd²⁺, and Zn²⁺ suppressed the uptake of Pb by between 25 and 35%, and that of Zn by between 15 and 25%. For both Pb and Zn, Cd had the highest suppression of 35 and 30%, respectively for baker's yeast (Saccharomyces cerevisiae). Baker's yeast achieved enrichment factors (EF) of 23, 4, 100, and 1 for dam water, stream water, treated wastewater, and industrial effluent samples for Cu, Pb, Zn, and Cr, respectively. The recoveries of optimised Cd and Cr samples spiked with 2 μg ml⁻¹ of the metal could reach up to 90%, but never exceeded 66% for 10 μg ml⁻¹ samples. For Cu and Pb, the recoveries generally increased independent of concentration, however they were not as high as those for Zn, which exceeded 90% for all the samples spiked with 10 μg ml⁻¹ of the metal. S. cerevisiae PR 61/3 had the highest EF for Cr as compared to the other yeast strains. S. cerevisiae PRI 60/78 was the only yeast strain which was able to enrich Cd in all the samples. Baker's yeast had the highest EFs for Cu and Zn as compared to the other yeast strains without pH adjustment of the water samples. Candida tropicalis attained the highest EFs for Pb as compared to the other yeast strains. The results indicate that all the yeast strains used had a high affinity for Zn based on the EF values achieved. The results from these studies demonstrate that yeast is a viable trace metal enrichment agent that can be used freely suspended in solution to enrich metal ions at relatively low concentrations. This has ramifications on the traditional methods of sampling, sample collection, and transportation from remote sampling sites.     

Permanent microporosity and enantioselective sorption in a chiral open framework

A homochiral microporous material is presented. The phase has 47% permanently porous void volume and is shown to have >1 nm diameter pores with three-dimensional channels using probe molecule sorption. Enantioselective guest sorption is strongly dependent on guest size. The homochiral microporous phase was identified by reactive selection from a first-generation chiral but nonporous framework. Chiral permanent porosity is established by directional noncovalent interactions between framework-forming and nonframework forming components of the stable second-generation material, which become stronger upon loss of the guests from the pore system.     

Synthesis and characterization of benzimidazolium‐functionalized polysulfones as anion‐exchange membranes

Anion‐exchange membranes containing pendant benzimidazolium groups were synthesized from polysulfone by chrolomethylation followed by nucleophilic substitution reaction with 1‐methylbenzimidazole. The structures of the polymers were characterized by ¹H‐NMR and FTIR analysis. The resulting membranes showed high thermal stability below 200 °C. The values of water uptake and swelling degree increased with the ion‐exchange capacity of the polymeric membrane. The ionic conductivity was measured by means of impedance spectroscopy in aqueous solution of potassium hydroxide (10^?4?10^?1 M). The results show not only a clear correlation between the membrane's electrochemical behavior with the electrolyte solution embedded in the membrane, but also with the degree of the polysulfone's chloromethylation.Thus, the ionic conductivity increased more than two orders of magnitude when the degree of chloromethylation increased from 40 to 140%. Benzimidazolium‐functionalized polysulfones exhibited better thermal, mechanical, and electrochemical properties than the widely used polymeric membranes containing quaternary ammonium groups. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2363–2373     

Nanoscratch behavior of multi-layered films using molecular dynamics

Molecular dynamics simulations are performed to study the plastic deformation, stress and chip formation of scratched multi-layered films. The results showed that stick–slip and work-hardening behaviors were observed during the scratching process. There was a pile-up of amorphous disordered debris atoms and shear rupture ahead of the probe and a clear side-flow on the lateral sides of the probe when the probe moved forward. Both the plastic energy and the adhesion increased with an increase in the scratching depth. The glide band of the interface was on the {111}〈110〉 slip system with a maximum width of the glide band of about 1 nm. The strain energy stored in the deformed structure caused a higher stress region in the material in front of the tool edge, with a maximum stress of about 10 GPa. In addition, the mechanical response and thermal softness phenomenon are discussed. PACS 02.70.Ns; 46.55.+d; 47.11.Mn; 91.55.Ax; 62.40.+i