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|Title:||Preferential Sputtering Effects in Nb₂O₅|
|Authors:||Murti, Krishna Dasarao|
|Keywords:||Materials Science and Engineering;Materials Science and Engineering|
|Abstract:||<p>Ion bombardment has been used as a technique for the sputtering of metals for several years; very few studies have, however, been made on alloys and compounds, especially studies where the target itself was analyzed after ion bombardment. In this thesis results are presented concerning the changes in targets of Nb₂O₅ and related systems due to ion bombardment. The targets used were in the form of anodic thin films and sintered pellets. Bombardments were carried out using Kr⁺ and O₂⁺ ions with energies of 2 to 35 keV and at doses varying from 10¹³ to 10¹⁷ ions/cm². The structural changes induced by the bombardment were studied with an electron microscope and the changes in electrical conductivity were studied with a four point probe.</p> <p>The results indicate that an altered layer is formed which has the stoichiometry of NbO when Nb₂O₅ targets are bombarded with 35 keV ions at high doses (≥ 1 x 10¹⁷ ions/cm²). A technique based on the changes in the chemical reactivity of the altered layer as compared to the substrate is used to estimate the thickness of the altered layer. That on Nb₂O₅varies.from 18 nm at very low doses (5x10¹³ ions/cm²) to 23 nm at high doses (1x10¹⁷ ions/cm²). The conductivity of the altered layer formed at high doses is about 4x10³ s/m, an increase by a factor of 2x10⁸. An energy threshold for conductivity changes was found using an oxygen ion beam, whereas Kr ion bombardment reveals conductivity changes at all.</p> <p>Oxygen loss from bombarded Nb₂O₅ can be considered to have three alternative origins based on a vaporization model, an internal displacement model and a preferential sputtering model. The results favour the preferential sputtering of oxygen as the likely mechanism to explain the altered layer in the target. A modified sputtering model explains the energy threshold effect observed when an oxygen beam is used.</p> <p>Several applications of the techniques and results presented here have been considered. They include, among others, dating of minerals, limitations of surface analytical techniques, and preliminary results for Ta₂O₅.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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