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Magnetic Properties and Defects in Iron Implanted Strontium Titanate Single Crystals and Thin Films

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Magnetic Properties and Defects in Iron Implanted Strontium Titanate Single Crystals and Thin Films Western University Scholarship@Western Electronic Thesis and Dissertation Repository 4-4-2012 12:00 AM Magnetic Properties and Defects in Iron Implanted Strontium Titanate Single Crystals and Thin films Misha Chavarha The University of Western Ontario Supervisor Lyudmila Goncharova The University of Western Ontario Graduate Program in Physics A thesis submitted in partial fulfillment of the equirr ements for the degree in Master of Science © Misha Chavarha 2012 Follow this and additional works at: https://ir.lib.uwo.ca/etd Part of the Condensed Matter Physics Commons Recommended Citation Chavarha, Misha, "Magnetic Properties and Defects in Iron Implanted Strontium Titanate Single Crystals and Thin films" (2012). Electronic Thesis and Dissertation Repository. 435. https://ir.lib.uwo.ca/etd/435 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. DEFECTS AND MAGNETIC PROPERTIES OF IRON-IMPLANTED STRONTIUM TITANATE AND THIN FIMS (Spine title: Defects and magnetic properties of iron-implanted strontium titanate and thin films) (Thesis format: Monograph) by Misha Chavarha Graduate Program in Physics A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science The School of Graduate and Postdoctoral Studies The University of Western Ontario London, Ontario, Canada © Misha Chavarha 2012 THE UNIVERSITY OF WESTERN ONTARIO SCHOOL OF GRADUATE AND POSTDOCTORAL STUDIES CERTIFICATE OF EXAMINATION Supervisor Examiners ______________________________ ______________________________ Dr. Lyudmila Goncharova Dr. Giovanni Fanchini ______________________________ Supervisory Committee Dr. Jeffrey Hutter ______________________________ ______________________________ Dr. Giovanni Fanchini Dr. Jin Zhang ______________________________ ______________________________ Dr. Peter Simpson The thesis by Misha Chavarha entitled: Magnetic Properties and Defects of Iron Implanted Strontium Titanate and Thin Films is accepted in partial fulfilment of the requirements for the degree of Master of Science Date__________________________ _______________________________ Chair of the Thesis Examination Board ii ABSTRACT Physical vapor deposition was used to grow good quality crystalline stoichiometric SrTiO3 thin films on Si(001) substrates using a systematic approach starting from an understanding of the kinetics and thermodynamics of the system and finishing with the development of a procedure for preparing high quality SrTiO3/Si interface. Growth of optimized SrTiO3 perovskite structures on Si requires careful transformation of a thin interfacial SrSix layer into the initial SrTiO3 lattice cells. The critical aspects of the growth, such as low temperature and low oxidant partial pressure, are identified. Crystallinity and stoichiometry of SrTiO3 were verified using powder x-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS). The SrTiO3/Si(001) interface was examined with X-ray photoemission spectroscopy (XPS) and RBS. The optimum composition can be represented with low concentration (thickness) of strontium silicate phases at the interface (SrxSiyOy) as well as a strong signal from strontium titanate peaks. Thicker samples were grown with the procedure developed and were implanted with iron at 21016 ions/cm2 for future magnetic characterization. In parallel to the thin film growth, (001) SrTiO3 single crystals were implanted with iron at doses ranging from 21014 to 21016 ions/cm2 and magnetic measurements were carried out with a superconducting quantum interference device (SQUID). The results show negative susceptibility, predominately diamagnetic behavior which is characteristic of SrTiO3 and small paramagnetic response at low magnetic fields, indicating the possible presence of oxygen/titanium vacancies. The temperature dependence of magnetization measurements did not reveal phase changes. We note that it was difficult to identify any iii trends between implanted samples most likely due to oxygen contamination of the measurement system. Future experiments are proposed to develop a quantitative and consistent agreement between Fe phases in SrTiO3, SrTiO3 defect concentrations and magnetic responses. Keywords: Strontium Titanate, integration with silicon, ultra-thin films growth, magnetic properties, Rutherford backscattering spectroscopy (RBS), powder x-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), superconducting quantum interference device (SQUID). iv ACKNOWLEDGEMENTS I would like to express my gratitude to the following people: My family for their love and support Dr. Lyudmila Goncharova for the patience, support and guidance through the project Dr. Peter J. Simpson and Dr. Giovanni Fanchini for input during advisory committee meetings Dr. Kanthi Kaluarachchi for being a good boss Jack Handricks for his operation of Tandetron Mark Beisinger for operation of XPS, and helpful professional advises Mike G. Cottam for helpful discussion about nature of magnetic interactions Special thanks to the faculty, staff and students in the Department of Physics and Astronomy at The University of Western Ontario and to my friends Sergey Dedyulin, Eric Barbagiovanni, Arash Akbari-Sharbaf. v TABLE OF CONTENTS CERTIFICATE OF EXAMINATION ii ABSTRACT iii ACKNOWLEDGEMENTS v TABLE OF CONTENTS vi LIST OF ACRONYMS AND ABBREVIATIONS ix LIST OF FIGURES xi LIST OF TABLES xv CHAPTER 1 : INTRODUCTION 1 1.1 Strontium titanate: crystal structure and properties 3 1.2 Progress in growth of epitaxial STO films on Si(001) 5 1.3 Magnetic properties of oxide materials 9 1.4 Magnetic and dielectric properties of strontium titanate. 11 1.5 Ion implantation of STO, damage and its recovery 12 1.6 Thesis overview 14 CHAPTER 2 : EXPERIMENTAL DETAILS 15 2.1 Strontium titanate deposition System overview 15 2.1.1 Physical vapor deposition 15 2.1.2 Strontium and titanium evaporators 19 vi 2.1.3 Quartz crystal microbalance 21 2.1.4 Deposition rate calibration 22 2.2 Iron ion implantation 23 2.2.1 Ion beam implantation 23 2.2.2 SRIM simulation of ion implantation 26 2.3 Rutherford Backscattering Spectroscopy 27 2.4 X-ray photoelectron spectroscopy 30 2.6 SQUID (Superconducting Quantum Interference Device) 32 2.7 X-ray powder diffraction. 32 2.8 Experimental procedure 33 CHAPTER 3: ESTABLISHING HIGH QUALITY STO/SI INTERFACE 35 3.1 Investigation of SrO/Si interface 38 3.1.1 XPS results for silicon 2p region 41 3.1.2 XPS results for strontium 3d peaks 43 3.2 Investigations of SrTiO3/Si interface 46 3.2.1 XPS and RBS results of SrTiO3 films on Si 46 Comparison of the interface model of SrTiO3/Si and reference 3.2.2 sample 48 3.2.3 XPS results of STO reference sample and single crystal STO 49 3.2.4 XPS results of deposited SrTiO3 thin films 54 vii CHAPTER 4: DEFECTS AND MAGNETISM IN IRON IMPLANTED STO 63 4.1 Magnetic properties of oxide materials 65 4.1.1 Diamagnetism, paramagnetic and ferromagnetism 65 4.1.2 Superexchange, itinerant exchange interaction and spin glasses 68 4.2 Experimental Details 70 4.2.1 RBS and XRD analysis of SrTiO3 film on Si 71 4.2.2 XPS results of iron-implanted SrTiO3 single crystals 73 4.3 Magnetic properties of Fe-implanted SrTiO3 74 CHAPTER 5: CONCLUSIONS AND FUTURE WORK 90 References 92 VITA 97 viii LIST OF ACRONYMS AND ABBREVIATIONS AIL Amorphous interface layer BE Binding Energy FC Field Cooled FWHM Full Width at Half Maximum IMFP Inelastic Mean Free Path MBE Molecular Beam Epitaxy MEIS Medium Energy Ion Scattering ML Monolayer PVD Physical Vapour Deposition QCM Quartz Crystal Microbalance RBS Rutherford Backscattering Spectroscopy SC Single Crystal SQUID Superconducting Quantum Interference Device SRIM Stopping and Range of Ions in Matter ix STO Strontium Titanate TC Thermocouple XPS X-ray Photoemission Spectroscopy XRD X-ray Diffraction UHV Ultra High Vacuum ZFC Zero Field Cooled x LIST OF FIGURES Chapter 1 Figure 1.1 Crystal structure of cubic strontium titanate. 3 Figure 1.2 Crystal structure of tetragonal strontium titanate. 4 Figure 1.3 Si surface rotated by 45o around z axis (top) and SrO terminated (001) SrTiO3 surface (bottom). 6 Figure 1.4 High-resolution transmission electron microscopy Z-contrast image of SrTiO3 on (001) silicon. 8 Chapter 2 Figure 2.1 Physical vapor deposition system. 16 Figure 2.2 Schematics of strontium and titanium deposition sources. 20 + Figure 2.3 RBS spectra for 60Å SrTiO3/Si(001) measured with 0.5MeV He beam. 24 Figure 2.4 The schematics of Tandetron accelerator. 25 Figure 2.5 SRIM simulation of the distribution of implanted iron at 30keV and normal incidence geometry (bottom). 27 xi Chapter 3 Figure 3.1 a) XPS spectra from reference [36] (top left); b) reference [37] (top right); c) reference [38] (bottom). 36 Figure 3.2 XPS spectra of a) Sr 3d region (top) and Si 2p region (bottom) for SrO/Si (Sample 1, Table 3.2). 42 Figure 3.3 XPS spectra of a) Si 2p region (top) and b) Sr 3d region (bottom) for SrO/Si (Sample 2, Table 3.2). 44 Figure 3.4 XPS spectra of a) Si 2p region (top) and b) Sr 3d region (bottom) for SrO/Si (Sample 4, Table 3.2). 45 Figure 3.5 RBS spectra for SrTiO3/Si (Sample 3, table 3.7) in random geometry. 50 Figure 3.6 RBS spectra (red scatters) and RBS fits (blue line) for sample #3 in aligned geometry. a) Top figure corresponds to the model consisting of 20Å SrTiO3 on silicon. b) Bottom figure corresponds to 20Å SrTiO3 / 20Å SrSiO3/Si 51 Figure 3.7 XPS spectra of Sr 3d region for SrTiO3 thin film in a) reference sample (top) and b) STO SC (bottom). 52 Figure 3.8 XPS spectra of O 1s region for STO thin film in a) reference sample (top) and b) STO SC (bottom). 53 xii Figure 3.9 Summary of energies of silicon peaks (pink) and silicon in 56 strontium silicate (blue). Figure 3.10 XPS spectra of a) Si 2p region in reference sample (top) and b) SrTiO3/Si (Sample 3, table 3.7) (bottom). 57 Figure 3.11 XPS spectra of a) Si 2p region for sample 1(top) and b) O 1s region for SrTiO3/Si (Sample 3) (bottom).
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