Browsing by Author "O'Brien, Paul"
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Item Bis(piperidinedithiocarbamato)pyridinecadmium(II) as a Single-Source Precursor for the Synthesis of CdS Nanoparticles and Aerosol-Assisted Chemical Vapour Deposition (AACVD) of CdS thin films(2014) Lewis, David J.; Revaprasadu, Neerish; Mlowe, Sixberth; Malik, Azad; Mubofu, Egid B.; O'Brien, Paul; Raftery, JamesThe synthesis and single-crystal X-ray structure of bis(piperidinedithiocarbamato)pyridinecadmium(II), [Cd(S2C(NC5H10))2(NC5H5)] are reported and its use as a precursor for the synthesis of hexagonal CdS nanoparticles and CdS thin films is presented. Thermogravimetric analysis (TGA) of this complex showed clean decomposition in two steps to give CdS. Thermolysis of the complex in hexadecylamine at different temperatures in the range 190 ¬ 270 °C gave CdS nanostructures including nanorods and oval shaped particles. The band gap of the as-synthesized CdS nanoparticles varied as the temperature was increased. CdS thin films with optical direct band gaps of ca. 2.4 eV were deposited by aerosol-assisted chemical vapour deposition (AACVD) in the temperature range 350 to 450 oC using the same precursor. Powder X-ray diffraction (p-XRD) patterns of CdS nanoparticles and thin films confirmed the hexagonal phase of CdS.Item CdS thin films deposition by AACVD: effect of precursor type, decomposition temperature and solvent.(Journal of Materials Science: Materials in Electronics, 2018-09) Ketchemen, Kevin IY; Mlowe, Sixberth; Nyamen, Linda D; Ndifon, Peter T; O'Brien, Paul; Revaprasadu, NeerishABSTRACT Hexagonal cadmium sulfide (CdS) thin films were deposited on glass substrates by Aerosol Assisted Chemical Vapour Deposition (AACVD) using cadmium(II) dithiocarbamate and xanthate complexes in tetrahydrofuran (THF) and mixed solvents (THF+ chloroform) at 400 and 450 oC. The surface morphology and size of the CdS films determined using scanning electron microscopy (SEM), showed the formation of films of various morphologies depending on the precursor, the deposition temperature and solvent used. An increase in temperature resulted in an increase in particle size and a change in morphology with the formation of CdS films with distorted structures. The CdS films showed an overall blue shift in their absorption band edge (2.35 – 2.49 eV) compared to the bulk CdS. In dithiocarbamates, a slight blue shift was observed with a shift to high wavelengths with the reduction of the carbon chain of the dithiocarbamate and an increase in temperature; while in xanthate, a strong blue shift was observed at both deposition temperatures. The use of mixed THF + chloroform solvent at 450 oC showed the formation of films with irregular structures compared to those deposited using THF solvent alone, indicating the role of the solvent in the shape direction of the films formation. The elemental composition determined by energy dispersive X-ray spectroscopy (EDX) measurements revealed the 1:1 (Cd:S) ratio in all the samples confirming the stoichiometry of the CdS films.Item Deposition of Bi2S3 thin films from heterocyclic bismuth (III) dithiocarbamato complexes.(Polyhedron, 2018) Kun, Walter N; Mlowe, Sixberth; Nyamen, Linda D; Akerman, Matthew P; O'Brien, Paul; Ndifon, Peter T; Revaprasadu, NeerishTwo heterocyclic dithiocarbamate complexes, tris- (piperidinedithiocarbamato)bismuth(III) (1) and tris-(tetrahydroquinolinedithiocarbamato) bismuth(III) (2) were synthesized and characterized by elemental analysis and thermogravimetric analysis. The structure of complex (1) was confirmed by single-crystal X-ray analysis. Both complexes were used as single source precursors for the deposition of bismuth sulfide thin films by aerosol assisted chemical vapour deposition (AACVD) at 350, 400, 450 °C and spin coating followed by thermal treatment at 350 °C, 400 °C and 450 °C. Both deposition methods, gave sulfur deficient polycrystalline films of bismuthinite. Scanning electron microscopy (SEM) images of the films showed morphology was dependent on the solvent mixture, temperature, precursor type and method of deposition. AACVD gave films with hexagonal nanoplatelets, leaf-like platelet, ribbon-like fibre, needle-like fibre morphologies. Films in the form of rods and interwoven nanowires were obtained from spin coating.Item Growth of Nanocrystalline Thin Films of Metal Sulfides [CdS, ZnS, CuS and PbS] at the Water-Oil Interface(2015) Thomas, John; Stansfield, Gemma L.; Komba, Nathaniel; Cant, David J. H.; Ramasamy, Karthik; Albrasi, Enteisar M.; Al Chaghouri, Hanan; Syres, Karen L.; O'Brien, Paul; Flavell, Wendy R.; Mubofu, Egid B.; Bondino, Federica; Magnano, ElenaSimple one pot reactions between thiobiuret complexes [M(SON(CNiPr2)2)2], (M = Cd, Zn, Pb or Cu) in toluene and aqueous Na2S lead to well-defined assemblies of nanocrystals. High quality thin films of CdS, ZnS, CuS and PbS nanoparticulates adhered to the interface are produced and are transferable to glass and other substrates. The effect of reaction parameters on the nature and properties of the deposits are examined. The films are characterized by high-resolution transmission electron microscopy, X-ray diffraction, scanning electron microscopy, transport property measurements, X-ray photoelectron and absorption spectroscopy. The ability to obtain thin films of several nanocrystalline semiconductors from a single precursor set significantly expands the scope of a reaction scheme that is still in its infancy.Item Heterocyclic Dithiocarbamato-Iron (III) Complexes: Single-Source Precursors for Aerosol-Assisted Chemical Vapour Deposition (AACVD) of Iron Sulfide Thin Films(2016) Mlowe, Sixberth; Lewis, David J.; Malik, Mohammad A.; Raftery, James; Mubofu, Egid B.; O'Brien, Paul; Revaprasadu, NeerishThe biomedical potential of flavonoids is normally restricted by their low water solubility. However, little has been reported on their encapsulation into polyamidoamine (PAMAM) dendrimers to improve their biomedical applications. Generation four (G4) PAMAM dendrimer containing ethylenediaminetetraacetic acid core with acrylic acid and ethylenediamine as repeating units was synthesized by divergent approach and used to encapsulate a flavonoid tetramethylscutellarein (TMScu, 1) to study its solubility and in vitro release for potential bioactivity enhancement. The as-synthesized dendrimer and the dendrimer–TMScu complex were characterized by spectroscopic and spectrometric techniques. The encapsulation of 1 into dendrimer was achieved by a co-precipitation method with the encapsulation efficiency of 77.8% ˘ 0.69% and a loading capacity of 6.2% ˘ 0.06%. A phase solubility diagram indicated an increased water solubility of 1 as a function of dendrimer concentration at pH 4.0 and 7.2. In vitro release of 1 from its dendrimer complex indicated high percentage release at pH 4.0. The stability study of the TMScu-dendrimer at 0, 27 and 40 ˝ C showed the formulations to be stable when stored in cool and dark conditions compared to those stored in light and warmer temperatures. Overall, PAMAM dendrimer-G4 is capable of encapsulating 1, increasing its solubility and thus could enhance its bioactivity.Item Heterocyclic lead(II) thioureato complexes as single-source precursors for the aerosol assisted chemical vapour deposition of PbS thin films(Inorganica Chimica Acta, 2018) Ketchemen, Kevin IY; Mlowe, Sixberth; Nyamen, Linda D; Aboud, Ahmed A; Akerman, Matthew P; Ndifon, Peter T; O'Brien, Paul; Revaprasadu, NeerishThe lead N’-benzoylthioureato complexes of N-morpholine (1) and N-pyrrolidine (2) were synthesized and characterized by elemental analysis, Fourier Transform Infra-Red (FT-IR) spectroscopy, proton nuclear magnetic resonance (1H nmr) and thermogravimetric analyses (TGA). The X-ray single crystal structure of complex (1) was determined. The compounds were both used as single source precursors to deposit PbS films on glass substrates at 350, 400 and 450 °C using aerosol assisted chemical vapour deposition (AACVD) The surface morphology of PbS films were determined by scanning electron microscopy (SEM), the crystalline phases established by powder X-ray diffraction (p-XRD) analyses and composition by energy dispersive X-ray spectroscopy (EDX). The particle sizes were found to range between 82 and 85 nm from complex (1) and 70–105 nm for (2) The PbS films were studied by Near Infra-red (NIR) UV–Vis spectroscopy, band gap ranging from 1.46 to 1.55 eV were observed.Item Lead Chalcogenides Stabilized by Anacardic Acid(Elsevier, 2013-04) Mlowe, Sixberth; Nejo, A. A.; Pullabhotla, Rajasekhar; Mubofu, Egid B.; Ngassapa, Faustine; O'Brien, Paul; Revaprasadu, NeerishPbE (E = S, Se and Te) nanoparticles stabilized by anacardic acid in the shape of spheres and cubes have been synthesized employing a simple solution based thermolysis route at moderate reaction temperatures. The route adheres to some of the principles of 'green' chemistry since a naturally occurring capping ligand, anacardic acid, is employed at a relatively low temperature. The lead sources were varied to study their effect on the morphology of the lead chalcogenide particles.Item The Synthesis, Spectroscopy and X-ray Single Crystal Structure of Catena-[(μ-anacardato)-copper(II)bipyridine][Cu2{(μ-O2CC6H3(o-OH)(o-C15H31)}4(NC5H5)2](2013-08) Malik, Azad; O'Brien, Paul; Tuna, Floriana; Pritchard, Robin G.; Buchweishaija, Joseph; Kimambo, Elianaso; Mubofu, Egid B.Hydrogenation of crude anacardic acid gave a transparent crystalline product on recrystallization. When reacted with copper nitrate in the presence of pyridine it produced green crystals of a pyridine adduct of a dimeric copper(ii) anacardate with the copper acetate structure. The X-ray single crystal structures of both anacardic acid and the copper complex were determined. Magnetic studies have confirmed strong antiferromagnetic coupling between copper(ii) centre in the dimer. The exchange coupling constant was determined to be J = -324 cm(-1). The EPR spectra of the polycrystalline product are consistent with spin S = 1. The zero-field splitting parameter and g tensor values are |D| = 0.36 cm(-1), g|| = 2.36 and g⊥ = 2.06.Item Tailoring Shape and Crystallographic Phase of Copper Sulfide Nanostructures Using Novel Thiourea Complexes as Single Source Precursors(Journal of Inorganic and Organometallic Polymers and Materials, 2019-05) Ketchemen, Kevin IY; Khan, Malik D; Mlowe, Sixberth; Nyamen, Linda D; Ndifon, Peter T; O'Brien, Paul; Revaprasadu, NeerishCopper sulfide thin films and nanoparticles have been prepared via aerosol assisted chemical vapour deposition and solvothermal hot injection routes, respectively. Both routes employed heterocyclic amine based benzoylthioureato-copper(II) complexes as single source precursors. Copper sulfide thin films of diverse morphologies ranging from cubic to snowy or irregular crystallites depending on the deposition temperature were observed. Powder X-ray diffraction studies of the as deposited thin films have indicated the formation of hexagonal and cubic phases of copper sulfide. In the case of the nanoparticles, Roxbyite (Cu1.75S) phase was obtained in dodecanethiol at temperatures of 150, 190 and 230 °C. However, a preferred growth of nanoparticles was observed in the presence of oleylamine whereas the roxbyite phase was obtained at temperatures of 150, 200 and 250 °C. Also transmission electron microscopy showed the formation of close to spherical, hexagonal nano-disk and rod shaped nanoparticles.Item Thin Films of Metals, Metal Chalcogenides and Oxides Deposited at the Water-Oil Interface Using Molecular Precursors(2012-10) Thomas, John P.; Mubofu, Egid B.; O'Brien, PaulThe interface between two immiscible liquids is emerging as a powerful medium for the growth and deposition of nanostructured thin films of metals and compound semiconductors. Materials obtained through this exceedingly simple route seem to often adopt fascinating forms and morphologies. In this article, we outline features unique to the interface that shape the striking deposits and highlight the nature and properties of nanostructured films obtained using this technique.