• R Kumar

      Articles written in Bulletin of Materials Science

    • Multiple implantation of29Si+ in semi-insulating GaAs and its characterisation

      M B Dutt R Nath R Kumar Y P Khosla

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      Formation of a uniformn-layer by multiple29Si+ implantation on LEC grown semi-insulating GaAs 〈100〉 substrate and its characterisation by differential Hall measurement at room temperature is reported. The implantation energies are 60, 160 and 260 keV with corresponding doses of 1 × 1012, 2·55 × 1012 and 3 × 1012 cm−2. Asimplanted, uncapped substrates were furnace-annealed with face-to-face configuration in an N2 ambient at 850°C with arsenic overpressure. After annealing, the samples were subjected to Hall measurements using Van der Pauw configuration. Experimental and theoretical (LSS) profiles are compared. Electrical activation of the dopant atoms was found to range from 65–90% with average mobility values lying between 2000–2300 cm2 V−1 s−1. Uniform concentration of then-layer ∼ 1017 cm−3 up to a depth of 0·3 µm has been achieved. These layers are used for the fabrication of power MESFETs.

    • Synthesis and characterization of surface-modified and organic-functionalized MCM-41 type ordered mesoporous materials

      S C Laha P Mukherjee R Kumar

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      A new and efficient method for the preparation of MCM-41 type ordered mesoporous phases using phosphate as promoter under reflux conditions is reported. The various mesoporous materials studied were: silica (Si-MCM-41), alumino-silicate (Al-MCM-41), and titanium-silicate (Ti-MCM-41). Our concept of promoter-assisted synthesis of zeolites and related microporous materials was found to be applicable in the synthesis of ordered mesoporous materials as well. The addition of small catalytic quantity of phosphate ions (PO43−), used as promoters, significantly reduced the synthesis time (by a factor of 3–4) of all these mesoporous materials. The synthesis of new MCM-41 type organic-inorganic composite materials with unique properties is also reported.

    • Loss of outer membrane integrity in Gram-negative bacteria by silver nanoparticles loaded with Camellia sinensis leaf phytochemicals: plausible mechanism of bacterial cell disintegration


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      New generation antimicrobial and smart drugs are the needs of the present era in fighting microbial infection and various chronic diseases. Nowadays nanoparticles (NPs) are widely applied in biomedical fields by virtue of their surface modification, which enhances both target selectivity and function. This study is a continuation of our earlier study that demonstrated antimicrobial property of NPs against both Gram-positive and Gramnegative organisms (Goswami et al, 2015). Silver NPs were synthesized using tea leaves (Camellia sinensis) decoction and were characterized using UV-vis spectrophotometry, transmission electron microscopy (TEM) and Fouriertransformed infrared spectroscopy (FTIR). The silver NPs were stable at various environmental conditions. The stability of the particles may be due to various phytochemicals of tea that were bound to the surface of reducedsilver ions as a capping agent. The antimicrobial activity of NP was investigated against three Gram-negative pathogenic bacteria (Shigella dysentriae, Salmonella infestis and Vibrio parahaemolyticus). The outer membrane ofGram-negative bacteria is a lipopolysaccharide (LPS) in nature and provides protection from various stress conditions and antibiotics. But a silver NP destroys its membrane integrity and thus helps in cell killing. Spectral changesconfirmed NP interaction with hydrophobic moiety of LPS. Minimum inhibitory concentrations for S. dysentriae, S. infestis and V. parahaemolyticus were 3.75, 5.25 and 5.25 $\mu$g ml$^{−1}$, respectively. Inhibition of biofilm formationwas significant with the three bacterial strains. Cytoplasmic leakage from each bacterial strain was also demonstrated on account of NP treatment. The particles demonstrated good biocompatibility. No damage of human buccal mucosal cells was recorded even at concentration of 10 mg ml$^{−1}$. Thus, silver NPs would be potential oral therapeutic molecules against Gram-negative bacteria.

  • Bulletin of Materials Science | News

    • Dr Shanti Swarup Bhatnagar for Science and Technology

      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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