Molecular dynamics investigations on polishing of a silicon wafer with a diamond abrasive

During the final stages of polishing silicon wafers, much of the interactions between silicon and diamond abrasive takes place at the silicon asperities. These interactions, leading to material removal, were investigated in a MD simulation of polishing of a silicon wafer with a diamond abrasive under dry conditions. Simulations were conducted with silicon asperities of different geometries, different abrasive configurations, and polishing speeds. Under the conditions of polishing, the silicon atoms from the asperities were found to bond chemically to the surface of the diamond abrasive. Continued transverse motion of the diamond abrasive (relative to the silicon asperity) leads to tensile pulling, necking, and ultimate separation of the silicon asperity material instead of conventional material removal in polishing (chip formation) involving cutting/ploughing, which takes place in the absence of chemical bonding between the abrasive and the asperity material. This phenomenon has not been reported previously in the literature. The thrust and cutting forces initially increase due to the increase in the number of asperity atoms affected finally reaching a maximum. This is followed by a decrease of these forces due to tensile pulling and formation of individual strings followed by ultimate separation or breakage of the final string. The ratio of thrust force (F _z ) to the cutting force (F _x ), i.e. |(F _z /F _x )| was found to increase continuously to a maximum of ～0.8 followed by continuous decrease to ～0.25. This is in contrast to a more or less constant value of ～2 in the case of tools with rounded radii or tools with large negative rake angles, where material is removed in the form of chips ahead of the tool. Three regions of the asperity have been identified that are useful in the development of a phenomenological model for polishing that enables computation of material removal rates: (1) the region directly in front of the abrasive for which the probability of the removal of an asperity atom is close to unity, (2) the distant region where this probability is nearly zero, and (3) an intermediate region from which the probability of removal is close to half.     

QSAR Study on Binding Affinity of PATs (Rodenticides) to the [3H]-Mepyramine-Labelled H1 Receptor In Rat and Guinea Pig Brain

Abstract

The binding of a series of PAT analogues (rodenticides) to the [³H]-mepyramine-labelled H₁ receptor in rat and guinea pig brain was investigated topologically using negentropy (N), molecular redundancy (MRI), first-order molecular connectivity (¹X _v ), Wiener (W), and Szeged (Sz) indices. Multiple regression analyses showed that MRI provided excellent results upon introduction of indicator parameters. Predictive ability of the proposed models was discussed using cross-validation parameters.     

An efficient and facile synthesis of Zn(II) complexes with 2-substituted benzothiazoles and glycine- and alanine-based ligands having antifungal and antibacterial activities

We carried out an efficient and facile synthesis of Zn(II) complexes with heterocyclic ligands based on 2-substituted benzothiazole moieties, 2-(2′-hydroxynaphthyl)benzothiazole, 2-(2′-hydroxyphenyl)benzothiazole, and 2-(2′-merceptophenyl)benzothiazole, and amino acids, glycine and alanine, are reported and also examined for antifungal and antibacterial activities. Ligands and complexes were characterized by FTIR, ¹H NMR, and elemental analysis.     

Potential of using plant proteins and chicken feathers for cotton warp sizing

Two plant proteins, soyprotein and wheat gluten, and chicken feathers used to size cotton substrates provided sizing performance similar to starch and were also easily degraded in activated sludge. Sizing is an essential process to impart protection to warp yarns and increase weaving efficiency. Cotton yarns have traditionally been sized with starch, modified starch derivatives, CMC, poly vinyl alcohol (PVA), or a combination thereof along with quite a few other fiber binding ingredients. Although starch and starch derivatives are extensively used for sizing, there can be several limitations including less-than-satisfactory sizing performance and difficulties in desizing starch based size. Plant proteins such as wheat gluten, soyproteins and poultry feathers are available in large quantities at low cost and have limited industrial applications. However, these proteins are known to have excellent film-forming properties, a primary requirement for a warp size, and have also been used as adhesives. Using proteins as warp sizing agents on cotton yarns potentially could provide acceptable sizing performance and be cost-effective, as well. In this research, soyproteins, wheat gluten, and chicken feathers were studied for exploring their feasibility for sizing, desizing, biodegradability, and ability to replace starch and PVA for sizing cotton yarns. It was found that all three proteins provided similar cohesion to fibers and abrasion resistance compared to starch. Protein sizes had significantly high BOD₅/COD ratio compared to PVA, suggesting that the proteins are easily degradable in textile effluent treatment plants.     

222Rn measurements in drinking water and annual effective dose for the adult population around a coal-based and atomic power plant in Uttar Pradesh,India

Journal of Radioanalytical and Nuclear Chemistry - Dissolved radon (222Rn) in drinking water has been measured using SMART RnDuo, a continuous radon monitor. Water samples have been collected from...     

Cl insertion on Si(100)-(2x1): etching under conditions of supersaturation

We use scanning tunneling microscopy to show that Cl2 dosing of Cl-saturated Si(100)-(2x1) surfaces at elevated temperature leads to uptake beyond "saturation" and allows access to a new etching pathway. This process involves Cl insertion in Si-Si dimer bonds or backbonds, diffusion of the inserted Cl, and ultimately desorption of SiCl2. Investigations into the etch kinetics reveal that insertion occurs via a novel form of Cl2 dissociative chemisorption that is mediated by dangling bond sites. Upon dissociation, one Cl atom adsorbs at the dangling bond while the other can insert.     

Curing and thermal behaviour of a flame retardant cycloaliphatic epoxy resin based on phosphorus containing poly(amide–imide)s

The curing behaviour of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate was investigated by the dynamic differential scanning calorimetry (DSC) using phosphorus-containing poly(amide–imide)s (PAIs) having free amine groups, 4,4′-diaminodiphenylmethane (PM) and p-phenylenediamine (PA), in the ratio of 1:1. The PAIs were prepared by co-polymerization of diimide–diacid (DIDA) and phosphorus-containing triamines having phenylene moiety. l-Tryptophan and pyromellitic anhydride were used to synthesize DIDA. Triamines used in the synthesis PAIs were tris(3-aminophenyl) phosphine (TAP), tris(3-aminophenyl) phosphine oxide (TAPO) and bis(3-aminophenyl) aminotolyl phosphine (BAP). TAP-, TAPO- and BAP-containing PAIs were designated as PTAP, PTAPO and PBAP, respectively. These PAIs with free amine groups were characterized by FTIR, ¹H NMR, ¹³C NMR spectroscopic techniques and elemental analysis. The mixture of PAIs and PM or/and PA in the ratios of 0:1, 1:0 and 0.5:0.5 was used for investigation. DSC was used to study the curing of epoxy by recording the DSC scans at heating rates of 10 °C min^?1. Thermal stability of epoxy resin cured isothermally was evaluated by recording thermo gravimetric traces in nitrogen atmosphere at the heating rate of 20 °C min^?1. All samples are highly stable, and the 10 % mass loss found was in the range of 335–520 °C. The percent char yield was highest in case of resin sample E/PM/PTAPO. The flame-retardant properties of cured epoxy resins were investigated by the limiting oxygen index test (LOI) and UL94 test. When phosphorus was incorporated in epoxy resin, the epoxy resin system met the UL94 V-0 classification and the LOI reached at 37.8, because of nitrogen–phosphorus synergistic effect.