Browsing by Author "Lushiku, Elias Musa"

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    Study of selectively absorbing surfaces
    (University of Dar es Salaam, 1975) Lushiku, Elias Musa
    The present work was directed towards the production of low cost selective radiation absorbing surfaces. The optical constant n and k of electrode posited thick layers of black nickel (deposited on copper and zinc substrates at current densities ranging from 8A/m2 to 20A/m2) were measured using an ellipsometer of simple construction. Films of Black Nickel of thicknesses ranging from 10nm you 130nm were deposited on different copper and zinc substrates at constant current densities of 10A/m2 and 20A/m2 at 24oC by changing the times of electrode position. For each specimen the values of ellipsometer parameters Y and D were measured before and after electrode position. The curves of Y and D against time of electrode position (i.e. thickness) were compared with calculated variations Y and D versus film thickness using the theory of thin film optics. It was observed that the theoretical predictions were in good agreement with experimental results for black nickel on copper substrates. Hence the thickness of the films could be estimated. Results for zinc substrates were not in agreement with theory. The spectral reflectivity and hence the selectivity of single and double films of black nickel on copper substrates were computed as a function of thickness. Those predicted results were in good agreement with experimental observations of initial temperature rise and maximum temperature reached by specimen placed in simulated solar radiation.