Ferromagnetism in wide band gap materials Mn-ZnO and Mn-Si3N4 thin films

Resumen

Contents 1. Introduction ..................................................................................1 1.1. State of the art ............................................................................1 1.2. Outlook of this dissertation ..........................................................................6 1.3. Dissertation structure .....................................................................................7 2. Thin Film Preparation Method and Experimental Techniques ...........................................................13 2.1. Sputtering technique ............................................................................................13 2.1.1. Experimental equipment .....................................................................17 2.2. SQUID magnetometry ...............................................................................20 2.3. X-Ray Diffraction (XRD) .............................................................................................21 2.4. X-Ray Reflectivity (XRR) ..............................................................................................22 2.5. Rutherford Backscattering Spectroscopy (RBS) .........................................................25 2.6. X-ray Absorption Spectroscopy (XAS) .........................................................26 2.6.1. XAS experiments at the Mn and Zn K -edges .............................................................27 2.6.1.1. X-Ray Absorption Near-Edge Structure (XANES)................................................................28 2.6.1.2. Extended X-Ray Absorption Fine Structure (EXAFS) ............................................29 2.6.2. XAS at the Mn L3,2 .edge..................................31 2.6.3. X-ray Magnetic Circular Dichroism (XMCD) .........................................................34 I. Mn-ZnO system 3. Mn/ZnO Multilayers .....................................................................................41 3.1. Motivation ................................................................................41 3.2. Preparation of multilayers ...............................................................42 3.3. Magnetic properties ......................................................................43 3.4. X-Ray Reflectivity (XRR) ..........................................................46 3.5. Rutherford Backscattering Spectroscopy (RBS) .........................................................50 3.6. X-Ray Diffraction (XRD) .................................................................................53 3.7. Transmission Electron Microscopy (TEM) ............................................................................58 3.8. X-Ray Absorption Spectroscopy (XAS) ...............................................................61 3.8.1. X-Ray Absorption Near-Edge Structure (XANES) ......................................................61 3.8.2. Extended X-Ray Absorption Fine Structure (EXAFS) ..........................................64 3.9. Structural and magnetic scheme .................................................................73 3.10. Conclusions .........................................................................................77 4. MnOx/ZnO Multilayers.....................................................................81 4.1. Motivation....................................................................................81 4.2. Preparation of multilayers ..................................................................................81 4.3. Magnetic properties ...............................................................................82 4.4. Rutherford Backscattering Spectroscopy (RBS) ..................................................................83 4.5. X-Ray Reflectivity (XRR) ...............................................................85 4.6. X-Ray Diffraction (XRD) .......................................................................86 4.7. X-Ray Absorption (XAS) ........................................................................88 4.7.1. XANES at the Mn K-edge ..................................................89 4.7.2. XAS at the Mn L3,2-edge .............................................................90 4.8. Thermal post-deposition annealing ......................................................91 4.9. Discussion and remarks: The origin of FM in MnOx/ZnO multilayers versus the origin in the so-called Mn/ZnO multilayers ...................................................92 4.10. Conclusions ...........................................................98 5. Mn:ZnO Thin Films ........................................................101 5.1. Motivation .............................................................................101 5.2. Preparation of Mn:ZnO films ......................................................102 5.3. X-Ray Reflectivity (XRR) .............................................................104 5.4. Rutherford Backscattering Spectroscopy (RBS) ................................................106 5.5. X-Ray Diffraction (XRD)..........................................................107 5.6. Magnetic properties ............................................................109 5.7. X-Ray Absorption Near-Edge Structure (XANES).....................................................111 5.8. UV-VIS Absorption .........................................................................115 5.9. Conclusions .........................................117 A. Effect of Thermal Treatments and Substrate Temperature on Mn/ZnO Multilayers..................................................................121 B. ZnO Crystal Structures ...............................................143 II. Mn-Si3N4 system 6. Mn/Si3N4 Multilayers ....................................................147 6.1. Motivation ...............................................147 6.2. Preparation of multilayers ....................................................149 6.3. X-Ray Reflectivity (XRR) ......................................................150 6.4. Transmission Electron Microscopy (TEM) .........................................153 6.5. Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) .................................................................154 6.6. Magnetic properties .............................................................156 6.7. X-Ray Photoemission Spectroscopy (XPS) .....................................................159 6.8. X-Ray Absorption Spectroscopy (XAS) ......................................................161 6.8.1. X-Ray Absorption Near-Edge Structure (XANES) ...........................................162 6.8.2. Computational methods: XANES simulations ....................................................164 6.8.3. Extended X-Ray Absorption Fine Structure (EXAFS) ........................................................169 6.8.4. XAS at the Mn L3,2-edge and XMCD .....................................................172 6.9. Remarks and discussion ....................................................................175 6.10. Conclusions ..................................................................178 C. From Ferromagnetism to Noble Metal Nanoparticles Formation in Si3N4 and ZnO Systems .................................................. 183 C.1. Au/Si3N4 Multilayers .....................................................................................................183 C.1.1. Motivation ...............................................................................................................183 C.1.2. Preparation of samples ..........................................................................................185 C.1.3. X-Ray Reflectivity (XRR) .....................................................................................186 C.1.4. Rutherford Backscattering Spectroscopy (RBS) .............................................188 C.1.5. X-Ray Absorption Spectroscopy (XAS) ............................................................190 C.1.5.1. X-Ray Absorption Near-Edge Structure (XANES) .........................190 C.1.5.2. Extended X-Ray Absorption Fine Structure (EXAFS) ....................191 C.1.6. Grazing Incidence Small Angle X-ray Scattering (GISAXS) .........................193 C.1.7. UV-VIS Absorption ................................................................................................198 C.1.8. Conclusions ..............................................................................................................203 C.2. Au/ZnO Multilayers .......................................................................................................207 C.2.1. Motivation ...............................................................................................................207 C.2.2. Preparation of samples ...........................................................................................207 C.2.3. X-Ray Reflectivity (XRR) ......................................................................................209 C.2.4. Rutherford Backscattering Spectroscopy (RBS) ..............................................212 C.2.5. X-Ray Absorption Spectroscopy (XAS) .............................................................213 C.2.5.1. X-Ray Absorption Near-Edge Spectroscopy (XANES) ..................213 C.2.5.2. Extended X-Ray Absorption Fine Structure (EXAFS) ....................213 C.2.6. X-Ray Diffraction (XRD) ......................................................................................215 C.2.7. Grazing Incidence Small Angle X-ray Scattering (GISAXS) .........................218 C.2.8. UV-vis Absorption ..................................................................................................221 C.2.9. Conclusions ..............................................................................................................223