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Lafane S.,Algerian Center de Developpement des Techniques Avancees | Kerdja T.,Algerian Center de Developpement des Techniques Avancees | Abdelli-Messaci S.,Algerian Center de Developpement des Techniques Avancees | Malek S.,Algerian Center de Developpement des Techniques Avancees | Maaza M.,iThemba LABS National Research Foundation
Applied Physics A: Materials Science and Processing | Year: 2010

In this paper, the plume expansion dynamics of an ablated Sm 2O3, Nd2O3 and NiO mixture oxides target by KrF laser into background oxygen atmosphere has been investigated using a fast ICCD imaging. The laser fluence was fixed at 2 J cm-2 and the surrounding ambient gas pressure was varied from vacuum to 50 mbar. Some effects as double plume splitting, plume sharpening and plume stopping were observed. The imaging data were used to create position-time plots of the luminous front. The plume behaviour was found to be influenced by the gas pressure above a certain threshold. Exceeding this pressure threshold, in earlier time the expansion was almost linear independently of the background gas pressure used. However, as time evolves, the plume is decelerated and comes to rest. The plasma plume dynamics was analysed in the framework of a shock-wave model and a drag model. It was found that the shock-wave model is valid in distances range which depends on the gas pressure. At later time, it is rather the drag model which is valid since it predicts exactly the stopping distance observed at high pressures. Using the dimensionless variables, a general description of the plasma plume dynamics was given. Finally, the plasma plume width-time evolution was studied. © 2009 Springer-Verlag. Source


Abdellaoui I.,Abou Bekr Belkaid University Tlemcen | Merad G.,Abou Bekr Belkaid University Tlemcen | Maaza M.,iThemba LABS National Research Foundation | Abdelkader H.S.,Abou Bekr Belkaid University Tlemcen
Journal of Alloys and Compounds | Year: 2016

The energetic, electronic structures and optical properties of Mg-, F-doped and Mg-,F-codoped M1-VO2 systems have been investigated using first-principles calculations with the HSE06 functional theory. The results show that the energetic stability can be easily prepared the desirables Mg-doped at O-rich conditions, and F- and Mg-,F-codoped VO2 at V-rich conditions. In addition, the incorporation of F and Mg into M1-VO2 serves to reduce the absorption under visible-light irradiation. Consequently, the band-gap is widened between lower d|| and π∗sub-bands; this is due to the internal stress induced by Mg atom along a-axis, and the high electronegativity of F atoms compared to that of O atoms. © 2015 Elsevier B.V. Source


Nuru Z.Y.,iThemba LABS National Research Foundation | Nuru Z.Y.,University of the Western Cape | Nuru Z.Y.,University of South Africa | Msimanga M.,IThemba LABS Gauteng | And 4 more authors.
Applied Surface Science | Year: 2014

An AlxOy/Pt/AlxOy multilayer solar absorber for use in solar-thermal applications has been deposited onto copper substrate by electron beam (e-beam) vacuum evaporation at room temperature. Different samples were annealed at different temperatures in air and characterized by spectrophotometry, emissometry, heavy ion elastic recoil detection analysis (HI-ERDA), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The AlxOy/Pt/Al xOy multilayer solar absorbers heated up to 500 C were found to exhibit good spectral selectivity (α/É) of 0.951/0.08. However, beyond 500 C the spectral selectivity decreased to 0.846/0.11, possibly due to thermally activated atomic interdiffusion profiles. HI-ERDA has been used to study depth-dependent atomic concentration profiles. These measurements revealed outward diffusion of the copper substrate towards the surface and therefore, the decrease in the constituents of the coating. The decrease in the intensity of Pt grains and formation of CuO and Cu2O phases at 700 C were confirmed by XRD and EDS. © 2014 Elsevier B.V. Source


Nuru Z.Y.,iThemba LABS National Research Foundation | Nuru Z.Y.,University of the Western Cape | Nuru Z.Y.,University of South Africa | Arendse C.J.,University of the Western Cape | And 6 more authors.
Solar Energy Materials and Solar Cells | Year: 2014

This paper reports the effect of thermal annealing on AlxO y/Pt/AlxOy multilayer solar absorber coatings deposited by an electron beam (e-beam) vacuum evaporator onto copper substrate at room temperature. The samples were annealed at different temperatures for different duration in air. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), Raman spectroscopy, UV-vis spectrophotometer and emissometer. The results showed changes in morphology, structure, composition, and optical properties depend on both temperature and duration of annealing. The XRD pattern showed the intensity of Pt decreased with increasing annealing temperature and therefore, disappeared at high temperature. With increasing annealing temperature, an increase in the size of Pt particles was observed from SEM. The AlxOy/Pt/Al xOy multilayer solar absorber coatings deposited onto Cu substrate were found to be thermally stable up to 500 C in air for 2 h with good spectral selectivity (α/ε) of 0.951/0.09. At 600 C and 700 C, the spectral selectivity decreased to 0.92/0.10 and 0.846/0.11 respectively, which is attributed to the diffusion of Cu and formation of CuO and Cu2O phases. The formation of CuO and Cu2O phases were confirmed by XRD, Raman spectroscopy and optical modelling. Long term thermal stability study showed the coatings were thermally stable in air up to 450 C for 24 h. © 2013 Elsevier B.V. Source


Nuru Z.Y.,University of South Africa | Nuru Z.Y.,iThemba LABS National Research Foundation | Arendse C.J.,University of the Western Cape | Mongwaketsi N.,iThemba LABS National Research Foundation | And 4 more authors.
Renewable Energy | Year: 2015

We report the effects of substrate temperatures on the thermal stability of AlxOy/Pt/AlxOy multilayered selective solar absorber coating (MSSAC). The samples were deposited at different substrate temperatures (from room temperature up to 250°C), and then annealed at various temperatures (300-600°C) in air for 2h. Characterizations are made via X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscopy (AFM), Raman Spectroscopy, UV-Vis and emissometeric measurements. These coatings were found to be thermally stable up to 500°C with good spectral selectivity of 0.930/0.11. Furthermore, the observed decrease in the spectral selectivity 0.883/0.13 at 600°C is attributed to the diffusion of Cu and the formation of CuO phase. Such phase formation was confirmed using XRD and Raman spectral analysis. The insensitiveness of the thermal stability of such coatings on the substrate temperature is demonstrated. © 2014 Elsevier Ltd. Source

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