RF sputter deposition of poly(tetrafluoroethylene) films as masking materials for silicon micromachining

Polymers have been studied extensively because of their wonderful array of properties. Their properties can be tailored by many means and can be made useful in many ways. Polymers can be crosslinked or branched and can provide different properties, such as conduction and passivation. This study dealt with the RF sputter deposition of poly(tetrafluoroethylene) (PTFE) films with the aim of using them as masking materials during the fabrication of various micromachined structures. The films were deposited on silicon substrates at different plasma powers (100, 150, and 200 W) for a constant deposition time (60 min). To test the masking properties, the deposited films were immersed in a 20 wt % aqueous KOH solution at 80°C for 60 min. The films showed lower contact angles and interfacial tension, and this indicated good adhesion of the films to the silicon substrates. Good adhesion is an essential quality of masking materials during micromachining. The structural properties of the as‐deposited and etched films were studied with Fourier transform infrared and X‐ray photoelectron spectroscopy. These indicated that the bonding groups and binding energies of C? F and C? CF matched the reported values well. Furthermore, the presence of C? F and C? CF bonds, even after the etching of silicon substrates in highly alkaline KOH solutions for 60 min, showed that the PTFE films remained unchanged in the etchant and, therefore, could function as good masking materials during the fabrication of micromachined structures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1183–1192, 2004     

Cover Feature: Superior Proton-Transfer Catalytic Promiscuity of Cytochrome c in Self-Organized Media (7/2021)

Evolutionarily elderly proteins commonly feature greater catalytic promiscuity. Cytochrome c is among the first set of proteins in evolution to have known prospects in electron transport and peroxidative properties. Here, we report that cyt c is also a proficient proton-transfer catalyst and enhances the Kemp elimination (KE; model reaction to show proton transfer catalytic property) by ∼750-fold on self-organized systems like micelles and vesicles. The self-organized systems mimic the mitochondrial environment in vitro for cyt c. Using an array of biophysical and biochemical mutational assays, both acid–base and redox mechanistic pathways have been explored. The histidine moiety close to hemin group (His18) is mainly responsible for proton abstraction to promote the concerted E2 pathway for KE catalysis when cyt c is in its oxidized form; this has also been confirmed by a H18A mutant of cyt c. However, the redox pathway is predominant under reducing conditions in the presence of dithiothreitol over the pH range 6–7.4. Interestingly, we found almost 750-fold enhanced KE catalysis by cyt c compared to aqueous buffer. Overall, in addition to providing mechanistic insights, the data reveal an unprecedented catalytic property of cyt c that could be of high importance in an evolutionary perspective considering its role in delineating the phylogenic tree and also towards generating programmable designer biocatalysts.     

Effect of Extrusion on Physicochemical Properties,Digestibility, and Phenolic Profiles of Grit Fractions Obtained from Dry Milling of Normal and Waxy Corn

Extrusion behavior of grits obtained from 3 successive reductions of dry milling of 2 normal corn types and 1 waxy corn was studied at different extrusion temperatures (ET). The grit from each reduction stage (RS) showed the presence of base‐hydrolyzed bound protocatechuic acid, p‐coumaric acid, sinapic acid, ferulic acid, and quercetin, and the concentrations of these decreased after acid hydrolysis and that of gallic acid increased. African tall grit from all RSs showed the highest average specific mechanical energy (SME) and torque, while waxy corn grit had the lowest. Corn extrudates showed an increase in water solubility index (WSI) and a decrease in water absorption index (WAI), as well as in expansion ratio (ER) with an increase in ET. Extrudates from each corn type showed an increase in rapidly digestible starch (RDS) and a decrease in slowly digestible starch (SDS) and resistant starch with an increase in ET. Most of the phenolics were present in bound form in extrudates, and quercetin, and catechin observed in grit were not present in extrudates. Frying of extrudates showed lower L^* and higher a^* and b^* when compared to color parameters of raw extrudates. Lower expansion of fried extrudates from waxy corn than those from other corn types may be related to its higher protein and fat contents and to lower amylose content.     

A secure multifactor remote user authentication scheme for Internet of Multimedia Things environment

To attain ubiquitous connectivity of everything, Internet of Things (IoT) systems must include “multimedia things.” Internet of Multimedia Things (IoMT) is a heterogeneous network of smart multimedia things connected together and with other physical devices to the Internet so as to achieve globally available multimedia services and applications. Due to the ever increasing amount of multimedia data in IoT environments, securing these systems becomes crucial. This is because these systems are easily susceptible to attacks when information or any service is accessed by the users. In this paper, we propose a secure three‐factor remote user authentication scheme for IoMT systems using ECC. The formal security proof performed using ROR model and BAN logic confirms that an attacker will not be able to extract sensitive user information. Through informal security analysis, we justify the resistance of the scheme against several security attacks. The performance comparison shows that the scheme is efficient in terms of computational cost, security features, and attack resistance. Furthermore, simulation of the scheme using AVISPA and Proverif proves that the scheme is secure against all active and passive attacks.     

Structural,optical, cytotoxicity,and antimicrobial properties of MgO,ZnO and MgO/ZnO nanocomposite for biomedical applications

In this study, MgO nanoparticles were successfully fabricated and incubated inside ZnO NPs to form MgO/ZnO nanocomposite for biomedical applications. The x-ray diffraction analysis of MgO, ZnO, and MgO/ZnO has shown the single-phase x-ray diffraction patterns through X'pert High score. The crystallite sizes were calculated as 18 nm, 42 nm, and 53 nm, respectively. The average particle size of MgO, ZnO, and MgO/ZnO nanopowders depicted from secondary electron images of field emission electron microscopy were 56 nm, 400 nm, and 450 nm, respectively. The presence of MgO NPs inside ZnO NPs was confirmed by transmission electron microscopy. The elemental dispersive spectroscopy of MgO, given the peaks of oxygen and magnesium, also showed only zinc and oxygen peaks in ZnO, which confirms no other impurities in MgO and ZnO powders. The elemental analysis of MgO/ZnO nanocomposite showed the peaks of Zinc and Oxygen, along with a tiny peak of Mg. The photoluminescence and UV–vis spectroscopy revealed the absorbance fluorescence limit of the nanomaterials. Fourier transform infrared spectroscopy confirmed the several groups present in the nanocomposite. The biocompatibility of MgO, ZnO, and MgO/ZnO was observed with human peripheral blood mononuclear cells. The cytotoxicity studies were also performed against human cancer (liver and breast) cell lines. The MgO, ZnO, and MgO/ZnO exhibited the antimicrobial properties against Escherichia coli and Staphylococcus aureus.     

Analysis of GPS-based TEC and electron density by the DEMETER satellite before the Sumatra earthquake on 30 September 2009

An analysis of ionospheric total electron content (TEC) variations obtained using Global Positioning System (GPS) measurements and electron density observations by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER)/ISL before the Sumatra earthquake (magnitude 7.6) on 30 September 2009 is presented. The data used are global TEC maps created in the IONEX format to estimate the spatial scale of ionospheric irregularities associated with this earthquake and DEMETER/ISL observations to analyse plasma parameter changes during earthquakes. This study for the first time integrates ground-based GPS receiver and space-based DEMETER/ISL observations to probe seismo-ionospheric anomalies before a large earthquake. The pre-seismic behaviour of the TEC was detected within a few days before the main event. The anomaly appeared as local TEC enhancement in the vicinity of the forthcoming earthquake epicentre. These structures were generated in the ionosphere at a similar local time at 1, 3 and 5 days prior to the main shock. The equatorial anomaly trough moved northwards (5°) on the earthquake day and 7.5° southwards the next day. The results demonstrate that both enhanced and reduced anomalies in the ionospheric electron density appeared before the Sumatra earthquake. The results from International GNSS Service (IGS) GPS data demonstrate that TEC variations can be used to detect seismo-ionospheric signatures.