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Document Type:Latin Dissertation
Language of Document:English
Record Number:53549
Doc. No:TL23503
Call number:‭3185615‬
Main Entry:Mohammad Omari
Title & Author:The structure of sputter-deposited aluminum trioxide-titanium dioxide nanolaminate films and its effect on film behaviorMohammad Omari
College:The University of Wisconsin - Milwaukee
Date:2005
Degree:Ph.D.
student score:2005
Page No:117
Abstract:The subject of this thesis is the fabrication, structure and optical behavior of Al2O3-TiO2 nanolaminate thin films. Al2O3-TiO2 nanocomposites are of current interest for optical, catalytic, and sensor applications. Five nanolaminate architectures were grown on unheated substrates by sequential reactive sputter deposition of metal targets using Ar-20% O2 radio frequency-excited discharges. For comparison purposes, single layers of TiO2 and Al2O3 were grown under the same deposition conditions used to grow the nanolaminates. TiO2 layer thickness was varied from 2 to 72 nm while Al2O3 layer thickness was kept constant at 7 nm in the nanolaminates. X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and spectrophotometry were used for film analysis. The films were sequentially annealed at 700°C and 1000°C. The x-ray diffraction and Raman spectroscopy results showed that the as-deposited nanolaminates have rutile long range and short range order. No anatase was present, nor was anatase formed by annealing. Al2O3 was amorphous in the as-deposited and annealed films. No significant changes were observed in the nanolaminates annealed at 700°C. Annealing at 1000°C caused significant amorphous to crystalline transitions in the nanolaminates. We proposed that β-Al2TiO 5 phase crystallized from an (Al, Ti)-oxide that formed at bilayer interfaces. The β-Al2TiO5 phase decomposed into α-Al 2O3 and rutile TiO2 in nanolaminates N1, N2, and N3 and retained in N4 and N5. Another scenario was proposed to account for the shift in the XRD peaks of the (Al, Ti)-oxide phase to a lower angle and for the strong XRD peaks from a mixed cation crystalline oxide in Ti-rich nanolaminates. The second scenario suggested phase separation or even a solid solution has occurred in nanolaminates N1, N2, and N3, and a pseudobrookite with a structure isomorphous with Ti3O5 crystallizes at the interfaces of N4 and N5. The optical absorption edge was shifted to lower energy with increasing the TiO2 layer thickness in the asdeposited nanolaminates and after annealing at 700°C. Optical transmission spectra changed slightly after annealing at 700°C. However, spectra for nanolaminates annealed at 1000°C showed a significant decrease in transmission maxima and the optical edge was shifted to a lower energy.
Subject:Applied sciences; Aluminum trioxide; Films; Nanolaminate; Thin films; Titanium dioxide; Materials science; 0794:Materials science
Added Entry:C. R. Aita
Added Entry:The University of Wisconsin - Milwaukee