Browsing by Author "Othman M.Z."
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Publication Hunting the elusive shallow n-type donor – An ab initio study of Li and N co-doped diamond(Elsevier Ltd, 2021) ;Conejeros S. ;Othman M.Z. ;Croot A. ;Hart J.N. ;O'Donnell K.M. ;May P.W.Allan N.L.We report calculated energetics (at the GGA, and at the B3LYP, HSE06 hybrid density functional levels of theory) and electronic properties (B3LYP, HSE06) of Li and N co-doped diamond containing LiNx clusters (x = 1–4). Defect energies and structural properties at the GGA and hybrid (B3LYP, HSE06) levels of theory are very similar. Our results for isolated Li and N dopants agree with previous work in that they are not suitable candidates for shallow n-type donors. Here, we investigate the effects of addition of N atoms as a co-dopant with Li, which vary with the Li:N ratio and whether Li is interstitial or substitutional. Reaction energies, geometries, bonding and densities of states (DOS) are examined. Nitrogen stabilises substitutional rather than interstitial lithium. Atom-projected DOS show that the chief contributions to the defect states are not from orbitals on the dopant atoms themselves but from states associated with neighbouring carbon atoms. Only the tetrahedral 1:4 cluster, LiCN4, with substitutional Li is likely to behave as a shallow donor. We propose a non-molecular synthetic route for preparation of the LiCN4-doped material via prior generation of the N4V centre at temperatures at which Li is mobile but LiCN4 clusters are not. © 2020 Elsevier Ltd - Some of the metrics are blocked by yourconsent settings
Publication Investigations of the co-doping of boron and lithium into CVD diamond thin films(Elsevier Ltd, 2017) ;Halliwell S.C. ;May P.W. ;Fox N.A. ;Othman M.Z. ;Faculty of Science and Technology ;University of BristolUniversiti Sains Islam Malaysia (USIM)Lithium has been incorporated into heavily boron-doped single-crystal (SCD), microcrystalline (MCD) and nanocrystalline diamond (NCD) films at concentrations up to ~ 2 × 1020 cm−3 using Li3N as a solid-state Li source for in-diffusion and diborane as the B source. The quality, morphology, electrical resistance and concentration of B and Li dopants present in a range of B + Li co-doped SCD, MCD and NCD films have been studied. Analysis of the SIMS depth profiles for Li enabled the diffusion constants, D, to be measured (in units of cm2 s−1) as: 2.5 × 10−15, 1.3 × 10−14 and 7.0 × 10−14 for SCD, MCD and NCD, respectively, at 1100 K. The value for D for SCD agrees closely with that in the literature, while the much larger values for the polycrystalline films provide direct evidence that Li can diffuse rapidly along or through diamond grain boundaries at elevated temperatures. If prolonged diffusion allows the Li to reach the Si substrate, the Si acts as a sink for Li absorbing large quantities and reducing its concentration in the diamond film. - Some of the metrics are blocked by yourconsent settings
Publication Photocatalytic heterostructures-based BiFeO3embedded liquid natural rubber (LNR) for highly removal of cationic dye under direct sunlight(Elsevier Ltd, 2020) ;Ridzuan N.D.M. ;Kaus N.H.M. ;Md Lazim M.A.S. ;Kobayashi T. ;Adnan R. ;Othman M.Z.Kassim M.H.M.In this study, the composite consists of bismuth ferrite (BiFeO3) photocatalyst embedded into macroporous liquid natural rubber (LNR) matrices was fabricated to assess the removal efficiency of methylene blue (MB) dye under direct sunlight. The structural properties and morphology of LNR-BiFeO3 composite were thoroughly characterised using spectroscopic and microscopic methods. X-Ray diffractogram of the composite demonstrated successful inclusion of BiFeO3 into the LNR network. During solar-driven photocatalytic activity of LNR-BiFeO3, the effects of selected operating parameters on removal efficiency, such as catalyst dose, irradiation time, initial dye concentration, and solution pH, were determined. At optimum catalyst dose (0.15 g BiFeO3) and irradiation time (3 h), degradation of 10 ppm MB was remarkably efficient as 98.9+ 0.09 % have been successfully discarded from the system. The composite had managed to degrade up to 75 ppm MB with degradation efficiency exceeding 89.0 %. In order to investigate the mechanism of MB removal using LNR-BiFeO3, monitoring of removal mode, kinetics and scavenger study were carried out. The outcomes revealed that MB removal did fit well with Langmuir-Hinshelwood kinetic model, in which BiFeO3 (Ebg = 1.76 eV) is responsible for photodegradation process using OH-, O2- and h+ with assistance of adsorption by the composite. The composite could be reused for five cycles without any post-treatment or separation step, and most importantly, no significant loss noted in its activity. This eco-friendly and economical approach will render new opportunities for this advanced photocatalyst as great potential in environmental remediation for wastewater treatment. � 2020 Elsevier Ltd.