• Nemat Tahmasebi

      Articles written in Bulletin of Materials Science

    • Effect of working pressure and annealing temperature on microstructure and surface chemical composition of barium strontium titanate films grown by pulsed laser deposition

      Zahra Saroukhani Nemat Tahmasebi Seyed Mohammad Mahdavi Ali Nemati

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      Barium strontium titanate (BST, Ba1−𝑥Sr𝑥TiO3) thin films have been extensively used in many dielectric devices such as dynamic random access memories (DRAMs). To optimize its characteristics, a microstructural control is essential. In this paper, Ba0.6Sr0.4TiO3 thin film has been deposited on the SiO2/Si substrate by the pulsed laser deposition (PLD) technique at three different oxygen working pressures of 100, 220 and 350 mTorr. Then the deposited thin films at 100 mTorr oxygen pressure were annealed for 50 min in oxygen ambient at three different temperatures: 650, 720 and 800°C. The effect of oxygen working pressure during laser ablation and thermal treatment on the films was investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis methods. X-ray photoelectron spectroscopy analysis was used to determine the surface chemical composition of the samples. The results indicate that the deposited BST film at low working pressure (100 mTorr) in PLD chamber shows a lower surface roughness than other working pressures (220 and 350 mTorr). The as-deposited films show an amorphous structure and would turn into polycrystalline structure at annealing temperature above 650°C. Increase of temperature would cause the formation of cubic and per-ovskite phases, improvement in crystalline peaks and also result in the decomposition of BST at high temperature (above 800°C). In addition, rising of temperature leads to the increase in size of grains and clusters. Therefore more roughness was found at higher temperatures as a result of a more heterogeneous growth and less tensions.

    • Investigation of photodegradation of rhodamine B over a BiOX (X$=$Cl, Br and I) photocatalyst under white LED irradiation

      NEMAT TAHMASEBI SAHAR SEZARI HABIB ABBASI SHAHRAM BARZEGAR

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      In this study, a low temperature precipitation method was applied to prepare BiOX (X$=$Cl, Br and I) nanostructures using HCl, HBr and HI as halogen sources. The as-prepared samples were characterized by various techniques such as X-ray diffraction, field emission scanning electron microscopy, energy dispersive spectroscopy, Fourier-transform infrared spectroscopy, diffuse reflectance spectroscopy and nitrogen adsorption–desorption analysis. The photoactivity of BiOX samples to degrade rhodamine B (RhB) molecules in aqueous solution was investigated under white LED irradiation. The results indicated that BiOCl exhibits a higher photodegradation performance in comparison with BiOBr and BiOI. Ninety six percent of the RhB molecules was degraded over BiOCl after 25 min light irradiation, whereas under the same conditions, the degradation efficiencies of BiOBr and BiOI samples are 62 and 24%, respectively. The enhanced photodegradation activity of BiOCl is ascribed to the higher specific surface area which increases the physical adsorption of RhB molecules on the Vphotocatalyst surface.Moreover, the photodegradation mechanism and the main radical species in the degradation reactionsover BiOCl were investigated.

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    • 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

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      Posted on July 25, 2019

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