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Complex Oxide Thin Films from Perovskite to Pyrochlore

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Complex Oxide Thin Films from Perovskite to Pyrochlore University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 8-2018 Complex Oxide Thin Films from Perovskite to Pyrochlore Clayton Russell Frederick University of Tennessee, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Recommended Citation Frederick, Clayton Russell, "Complex Oxide Thin Films from Perovskite to Pyrochlore. " Master's Thesis, University of Tennessee, 2018. https://trace.tennessee.edu/utk_gradthes/5130 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Clayton Russell Frederick entitled "Complex Oxide Thin Films from Perovskite to Pyrochlore." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Physics. Jian Liu, Major Professor We have read this thesis and recommend its acceptance: Norman Mannella, Haidong Zhou Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) Complex Oxide Thin Films from Perovskite to Pyrochlore A Thesis Presented for the Master of Science Degree The University of Tennessee, Knoxville Clayton Russell Frederick August 2018 62 Abstract The world of condensed matter physics is a fascinating field. With all of the many different elements to explore, it seems impossible to discover all of their secrets. Nevertheless, a study of two different materials is covered in this work. The first type of materials are the Perovskites; these materials are commonly used in materials research, but still have hidden treasures left for research scientist to explore. The second type of materials are the Pyrochlores. The Pyrochlores are not as widely studied as the Perovskite materials, thus, leaving even more avenues to venture down in the quest to learn the ways of nature and the properties of these materials. In this work, the valence electron states and the magnetic properties of the Perovskite LMO on STO are reported with the samples varying in thickness from 3 – unit cells to 12 – unit cells were measured and the results reported for their XAS measurements. In addition, the growth of the Pyrochlore YTO on YSZ are, also, investigated using XRD and differing growth conditions to ascertain the ideal growth conditions for the material. Furthermore, an overview of the experimental techniques is included to assist in understanding the results of this thesis. Finally, a summary of the results and an outlook for future work is included. ii Table of Contents Chapter 1: Introduction ................................................................................................................1 1.1 Overview of Thesis ................................................................................................................2 Chapter 2: Experimental Methods ...............................................................................................3 2.1 Pulsed Laser Deposition .........................................................................................................3 2.2 Atomic Force Microscopy ......................................................................................................4 2.3 X-ray Diffraction ....................................................................................................................5 2.4 X-ray Absorption Spectroscopy .............................................................................................8 2.5 X-ray Magnetic Circular Dichroism ....................................................................................10 Chapter 3: Analysis of LMO/STO Growth ..............................................................................14 3.1 Introduction ..........................................................................................................................14 3.2 Substrate Treatment ..............................................................................................................15 3.3 Experimental Details ............................................................................................................17 Chapter 4: Experiment Details and Procedure ........................................................................23 4.1 Introduction ..........................................................................................................................23 4.2 Setup .....................................................................................................................................23 4.3 Growth Conditions ...............................................................................................................24 4.4 Analysis of Growth ..............................................................................................................24 Chapter 5: Outlook and Further Experimental Work ............................................................26 5.1 LMO/STO summary and outlook ........................................................................................26 5.2 YTO growth summary and outlook .....................................................................................26 Bibliography .................................................................................................................................28 Appendices ...................................................................................................................................39 Appendix 1 .................................................................................................................................40 Appendix 2 .................................................................................................................................59 Vita ................................................................................................................................................62 iii List of Tables Table 3.1 Treatment Conditions .................................................................................................60 Table 4.1 Growth Parameters .....................................................................................................61 iv List of Figures Figure 1.1 (a) is the YTO unit cell structure oriented along the (001) direction. (b) is the YTO unit cell oriented along the (111) and is our desired phase for growth ........................40 Figure 2.1 this is a schematic illustration of what the inside of a PLD chamber looks like during the deposition process with all of the different components being represented ........41 Figure 3.1 Illustration of the alternating layers of LMO on STO and the total charge of the each layer. [113] ...........................................................................................................................42 Figure 3.2 (a) is an illustration of a mixed unit cell of STO. (b.) this illustrates the initial mixed terminated state of the substrate before treatment; (c.) illustrates the singly terminated substrate surface after treatment ...........................................................................43 Figure 3.3 (a) AFM image of an STO substrate annealed at 1050°C in air for 2 hrs. (b) Step width (~200nm) and Height (250pm) trace showing single termination.................................44 Figure 3.4 (a.) is an image of an NGO substrate as received; (b.) is an NGO substrate annealed for 3 hours at 1100°C in air. The singly terminated terraces can be seen .............45 Figure 3.5 (a) Mn XMCD spectra for various LaMnO3/SrTiO3 heterostructures. The inset shows a schematic of the experimental configurations for the X-ray spectroscopy studies. Thickness dependence of the XAS spectra of the LaMnO3/SrTiO3 heterostructures at the (b) Ti L2,3, and (c) Mn L2,3 edges with reference spectra for SrTiO3, bulk SrMnO3, LaMnO3, and MnO for comparison. (d) XAS of Mn L2,3 edges for various LaMnO3/NdGaO3 heterostructures where no reconstruction has occurred. .........................................................46 Figure 3.6 XAS spectrum about the Mn L2,3 edges for a 2 unit-cell-thick LaMnO3/SrTiO3 heterostructure. ............................................................................................................................47 Figure 3.7 Thickness dependence of the XAS spectra of the O K edge of LaMnO3/SrTiO3 heterostructures with that for a bare SrTiO3 substrate provided for comparison ...............48 Figure 3.8 Schematic band diagram of LaMnO3/SrTiO3 interface. The electron moving from the top layer of the LMO sample to the bottom layer of the LMO sample is demonstrated by the orange curve ...........................................................................................................................49 v Figure 3.9 (a) Mn L2,3 XAS spectra of the La0.95MnO3/SrTiO3 heterostructures. (b) Mn XMCD spectra for the 3 UC La0.95MnO3/SrTiO3 heterostructure. The XMCD features reverse in sign when the magnetic field is reversed, confirming the reliability of the observation....................................................................................................................................51
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