Browsing by Author "Kumar, Promod"

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    Defects induced enhancement of antifungal activities of Zn doped CuO nanostructures
    (2021) Kumar, Promod; Inwati, Gajendra Kumar; Chandra Mathpal, Mohan; Ghosh, Soumya; Roos, W. D.; Swart, H. C.
    CuO nanostructures doped with different concentration of Zn have been synthesized by a simple low-cost combustion method. The prepared samples have been tested by the various techniques such as X-ray diffraction (XRD), Transmission Electron Microscope (TEM), Optical absorption spectroscopy, Photoluminescence, and X-ray photoelectron spectroscopy (XPS). XRD confirmed the presence of the monoclinic phase of CuO along with an extra ZnO phase in the CuO:Zn. TEM results confirmed almost spherical - shaped nanoparticles as well as some irregular shaped NPs for pure CuO and Zn doped CuO with the average size from 24 to 55 nm. The change in morphology revealed a structural change in the CuO:Zn crystal due to different concentration of the Zn. The chemical study was done by XPS and the results were also correlated with XRD based results. The role of localized defects was compared and interpreted for the change in the luminescence spectral bands, micro-stains and oxidation states of the CuO:Zn for the different concentrations. CuO:Zn nanostructures demonstrated significant antifungal activities against two South African plant pathogens, Alternaria alternata CGJM3078 and Alternaria alternate CGJM3006, in comparison to pure CuO samples. The result showed that the pure and Zn doped CuO samples could be used as a good antifungal agent that could have an extensive applications in the agricultural and biotechnological industries.
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    Effects of Pt doping on surface properties and quenching of band edge emission in ZnO
    (2024) Kumar, Promod; Mathpal, Mohan Chandra; Goutaland, F.; Hevia, Samuel A.; Duvenhage, M. M.; Roos, W. D.; Swart, H. C.
    Pt doped ZnO thin films were synthesized on soda-lime glass substrates using a cost-effective sol-gel method, followed by spin coating and thermal annealing at various temperatures. Several characterization techniques such as UV-Vis absorption spectroscopy, photoluminescence (PL), field emission scanning electron microscopy (FESEM), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) are exploited to investigate the Pt doping effects on surface and optical properties of ZnO thin films. UV-Vis analysis demonstrated a slight decrease in the optical band gap from 3.3 eV to 3.2 eV with increased annealing, indicating enhanced suitability for optoelectronic applications. FESEM imaging revealed distinct worm-like structures and small Pt metal nanoparticles in unannealed samples, while thermal treatment supported the formation of spherical Pt nanoparticles and improved conductive pathways in the films. The Wagner diagram, coupled with Auger line transitions from XPS, quantified the oxidation states and chemical environments of Zn and Pt, respectively. Notably, the observed changes in the binding energy of the Zn-2p junction and the kinetic energy of the Zn-LMM Auger junction were significantly influenced by the Pt doping and the electronic properties of the substrate. The Wagner diagram provided a comprehensive visual representation of the parameters, facilitating a deeper understanding of electronic interactions and structural dynamics at the atomic level. XPS results confirmed the presence of ZnO, Zn(OH)(2), Pt-0 and PtO2 phases, indicating stability and constutient's interactions. ToF-SIMS also validated the uniform distribution of Pt nanoparticles within the ZnO thin film, confirming the effectiveness of the sol-gel method. As a result of Pt doping, PL studies revealed a large quenching effect on band edge emission in the UV and visible emission region of ZnO thin film, which is due to Pt acting as a recombination center for photogenerated carriers. Overall, our results highlight the influence of annealing and Pt incorporation on the optical and structural properties of ZnO thin films and highlight their potential applications for photonics and catalysis.
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    Optical limiting applications of resonating plasmonic Au nanoparticles in a dielectric glass medium
    (2021) Kumar, Promod; Chandra Mathpal, Mohan; Jagannath, Gangareddy; Prakash, Jai; Maze, Jero-R; Roos, W. D.; Swart, H. C.
    Plasmonic nanostructures exhibiting high optical nonlinearities are widely used in the rapidly growing modern nanotechnology of nonlinear optics including biomedical applications due to their tunable plasmonic behavior. In this work, we investigate the nonlinear optical properties of uniformly distributed Au nanoparticles (NPs) embedded in pre-synthesized sodium-zinc borate glass by the well-known ion-exchange technique for optical limiting (OL) applications. Various techniques such as optical absorption spectroscopy, x-ray photoelectron spectroscopy, Transmission Electron Microscope (TEM), Photoluminescence, Time of Flight secondary mass spectroscopy and the Z scan technique were used for the characterization of these NPs. TEM confirmed spherically shaped Au NPs with varying sizes of up to 16 nm, in agreement with optical absorption spectroscopy. Nonlinear optical (NLO) properties of these Au NPs were investigated by using an open as well as close aperture Z scan technique which exhibited enhanced optical nonlinearities. The two-photon absorption (2PA) coefficients demonstrated an increasing trend while the OL threshold values demonstrated a decreasing trend as a function of heat treatment. The improved 2PA coefficients and decreased OL threshold values endorsed the Au NPs containing glasses as contending materials for the fabrication of promising optical limiters for the protection of eyes and other sensitive instruments from laser induced damages.
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    Plasmonic Au nanoparticles embedded in glass: Study of TOF-SIMS, XPS and its enhanced antimicrobial activities
    (2022) Kumar, Promod; Mathpal, Mohan Chandra; Ghosh, Soumya; Inwati, Gajendra Kumar; Maze, Jero R.; Duvenhage, Mart-Mari; Roos, W. D.; Swart, H. C.
    The Au nanoparticles (NPs) were formed near the surfaces of pre-synthesized sodium zinc -borate glass by an ion exchange process obtained by thermal heat treatment in an open air environment at various temperatures. The pre-heated Au doped glass samples were extensively tested by the different techniques such as optical absorption spectroscopy, Scanning Electron Microscope (SEM), X-ray photoelectron spectroscopy (XPS), Time of Flight Secondary Ion Mass Spectroscopy (TOF-SIMS), and these Au NPs were used for the antimicrobial applications. SEM confirmed the spherical shaped Au NPs with increasing thermal treatment up to 550 degrees C. The optical absorption findings showed that the as -synthesized Au NPs showed Localized Surface Plasmon Resonance behaviour, giving clear evidence of an Au NPs band formed in the glass matrix. The formation mechanism of the Au doped glass samples was studied theoretically from a thermodynamic point of view during heat treatment. XPS and TOF-SIMS were used to study the chemical state and the thermal stability of the pre-heated Au NPs doped glasses in an ultra-high vacuum. The effect of concentration changes in the line-shape and in binding energy as a function of thermal heat treatment suggests that the Au NPs formed near the glass surfaces and changes in the chemical composition as well as chemical structures of the Au doped glass samples occurred. Antimicrobial activity such as antibacterial as well as antifungal activity of pre-heated Au doped glass samples was tested against different strains by the disk diffusion method. The Au doped glass samples exhibited enhanced antibacterial as well as antifungal activities by the influence of thermal treatment at different temperatures. Thus, the Au doped glass sample could be efficiently explored as a medical tool in pharmaceutical industries, biotechnology industries and chemical laboratories based upon its antibacterial findings.
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    Study of Defect-Induced Chemical Modifications in Spinel Zinc-Ferrites Nanostructures by In-Depth XPS Investigation
    (2023) Kumar, Promod; Mathpal, Mohan Chandra; Inwati, Gajendra Kumar; Kumar, Sanjay; Duvenhage, Mart-Mari; Roos, Wiets Daniel; Swart, Hendrik C.
    Spinel zinc ferrite nanomaterials with exceptional physiochemical properties are potential candidates for various applications in the energy and environmental fields. Their properties can be tailored using several methods to widen their applications. The chemical combustion approach was followed to prepare the spinel zinc ferrite nanomaterials, which were then subjected to thermal treatment at a fixed temperature. Thermal heat treatment at a fixed temperature was used to evaluate the phase and morphological characteristics of the prepared spinel zinc-ferrite nanocomposites. Various techniques were employed to examine the samples, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS and X-ray-induced Auger electron spectroscopy were used to extensively examine the surface characteristics of the zinc-ferrite. To study the actual chemical states of the synthesized spinel zinc ferrite nanomaterials and the defects created during the thermal treatment, an extensive investigation of the kinetic energy of the X-ray-induced Zn L3M45M45 and Fe L3M45M45 was conducted. Finally, a detailed analysis of the Wagner plot using the modified Auger parameter was performed to verify the exact chemical states of Zn and Fe. Thus, the findings of the investigation show that XPS is a promising and powerful technique to study the composition and chemical states of spinel zinc ferrites, providing an understanding of changes in their properties for functional applications.