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Rwenyagila E.R.,African University of Science and Technology | Rwenyagila E.R.,University of Dar es Salaam | Agyei-Tuffour B.,African University of Science and Technology | Zebaze Kana M.G.,Physics Advanced Laboratory | And 4 more authors.
Journal of Materials Research | Year: 2014

This study presents the optical properties of layered ZnO/Al/ZnO composite thin films that are being explored for potential applications in solar cells and light emitting devices. The composite thin films are explored as alternatives to ZnO thin films. They are produced via radio frequency magnetron sputtering. The study clarifies the role of the aluminum mid-layer in a ZnO (25 nm)/Al/ZnO (25 nm) film structure. Multilayers with low resistivity ∼362 Ω cm and average transmittances between ∼85 and 90% (in the visible region of the solar spectrum) are produced. The highest Haacke figure of merit of 4.72 × 10-3 Ω-1 was obtained in a multilayer with mid-layer Al thickness of 8 nm. The combined optical band gap energy of the multilayered films increased by ∼0.60 eV for mid-layer Al thicknesses between ∼1 and 10 nm. The observed shifts in the optical absorption edges to shorter wave lengths of the spectrum are shown to be in agreement with the Moss-Burstein effect. Copyright © 2014 Materials Research Society. Source


Rwenyagila E.R.,African University of Science and Technology | Rwenyagila E.R.,University of Dar es Salaam | Agyei-Tuffour B.,African University of Science and Technology | Zebaze Kana M.G.,Physics Advanced Laboratory | And 4 more authors.
Journal of Materials Research | Year: 2014

This study presents the optical properties of layered ZnO/Al/ZnO composite thin films that are being explored for potential applications in solar cells and light emitting devices. The composite thin films are explored as alternatives to ZnO thin films. They are produced via radio frequency magnetron sputtering. The study clarifies the role of the aluminum mid-layer in a ZnO (25 nm)/Al/ZnO (25 nm) film structure. Multilayers with low resistivity ∼362 Ω cm and average transmittances between ∼85 and 90% (in the visible region of the solar spectrum) are produced. The highest Haacke figure of merit of 4.72 × 10-3 Ω-1 was obtained in a multilayer with mid-layer Al thickness of 8 nm. The combined optical band gap energy of the multilayered films increased by ∼0.60 eV for mid-layer Al thicknesses between ∼1 and 10 nm. The observed shifts in the optical absorption edges to shorter wave lengths of the spectrum are shown to be in agreement with the Moss-Burstein effect. Copyright © 2014 Materials Research Society. Source


Isa M.T.,Ahmadu Bello University | Ameh A.O.,Ahmadu Bello University | Gabriel J.O.,Ahmadu Bello University | Adama K.K.,Physics Advanced Laboratory
Leonardo Electronic Journal of Practices and Technologies | Year: 2012

The extraction and characterization of chitin from four sources of Nigerian origin was investigated. Chemical demineralization and deproteinization was done to obtain the chitin. Proximate analysis, XRD and SEM analysis were conducted on obtained chitins. The investigation revealed that the shrimp had the highest yield of chitin of 8.15%, crab, crayfish and periwinkle had yields of 7.8%, 2.88% and 0.44% respectively. The proximate analysis showed that chitin from shrimp had highest moisture and protein content of 8.70% and 4.16% respectively. Crayfish had the highest ash and fiber content of 7.20% and 6.98% respectively. Crab has the highest lipid content of 1.70%. The SEM analysis showed very uniform structure with a lamellar organization and less dense structure for chitin from shrimp and the surface of chitin from crayfish consists of fibers that form parallel thread networks. XRD analysis showed that chitin from shrimp was more crystalline than others. Source


Momodu D.Y.,African University of Science and Technology | Tong T.,Princeton University | Zebaze Kana M.G.,Physics Advanced Laboratory | Zebaze Kana M.G.,Kwara State University | And 3 more authors.
Journal of Applied Physics | Year: 2014

This paper presents the results of a combined analytical, computational, and experimental study of adhesion and degradation of Organic Light Emitting Devices (OLEDs). The adhesion between layers that are relevant to OLEDs is studied using an atomic force microscopy technique. The interfacial failure mechanisms associated with blister formation in OLEDs and those due to the addition of TiO2 nanoparticles into the active regions are then elucidated using a combination of fracture mechanics, finite element modeling and experiments. The blisters observed in the models are shown to be consistent with the results from adhesion, interfacial fracture mechanics models, and prior reports of diffusion-assisted phenomena. The implications of the work are then discussed for the design of OLED structures with improved lifetimes and robustness. © 2014 AIP Publishing LLC. Source


Fashina A.A.,African University of Science and Technology | Zebaze Kana M.G.,African University of Science and Technology | Zebaze Kana M.G.,Physics Advanced Laboratory | Soboyejo W.O.,African University of Science and Technology | And 3 more authors.
Journal of Materials Research | Year: 2015

This study presents an analytical model of the reflectance of flat and textured silicon substrates. The model was used to study the reflection behavior of textured silicon surfaces under non-normal incidence. By characterizing the incident light and facets of the silicon wafer with vector geometry, dot products and Phong's reflection model (https://cs.oberlin.edu/bob/cs357.08/VectorGeometry/VectorGeometry.pdf) were used to determine the reflection angles between incident light rays and pyramidal facets. The possible optical interactions are considered for a wide range of pyramidal geometries and light incidence angles that are relevant to the exposure of textured silicon surfaces to incident sunlight. Furthermore, the model was used to investigate the possibility of secondary reflection, for the full range of incidence angles to the substrate. The textured silicon surfaces were found to reduce the reflection angles more effectively than flat substrates at lower angles of incidence. Secondary reflection was also found to be experienced or guaranteed, for all pyramid heights, when the angle of incidence to the substrate was less than 19.4°. The predictions are validated with experimental measurements of reflectance from (001)-textured silicon surfaces. The implications of the results are then discussed for the development of micropyramids for improved photoconversion in silicon solar cells. Copyright © Materials Research Society 2015. Source

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