Studies of Nanoconstrictions, Nanowires and Fe3O4 Thin Films (eBook)

Studies of Nanoconstrictions, Nanowires and Fe3O4 Thin Films 3
Supervisors’ Foreword 5
Contents 6
Acronyms 11
1 Introduction 14
1.1…Introduction to Nanotechnology 14
1.2…Introduction to Nanoelectronics 16
1.2.1 Information Technology: Current Limits 16
1.2.2 GMR Heads: Impact on the Information Storage 17
1.3…Comparison of the Nanostructures Studied in the Thesis from a Dimensional Point of View 20
1.4…Epitaxial Fe3O4 Thin Films 21
1.5…Dual Beam System for the Fabrication of Nanostructures 24
1.5.1 Focused Electron Beam (or SEM) 25
1.5.2 Focused Ion Beam 26
1.5.3 Focused Electron/Ion Beam Induced Deposition 26
1.6…Atomic-Sized Nanoconstrictions 29
1.6.1 Theoretical Background for Atomic-Sized Constrictions 29
1.6.1.1 Introduction 29
1.6.1.2 Conduction Regimes for Metals 30
1.6.1.3 Typical Methods for the Fabrication of Atomic Contacts 31
1.6.2 Atomic Constrictions in Magnetic Materials 32
1.6.2.1 Introduction 32
1.6.2.2 Ballistic Magnetoresistance 32
1.6.2.3 Ballistic Anisotropic Magnetoresistance 33
1.7…Functional Nanowires Created by FEBID/FIBID 34
1.7.1 Pt--C NWs Created by FEBID/FIBID 34
1.7.2 Superconducting W-Based NWs Created by FIBID 35
1.7.3 Magnetic Co NWs Created by FEBID 36
1.8…Structure of the Thesis 37
1.9…Reproduction of Material 38
References 40
2 Experimental Techniques 45
2.1…Lithography Techniques 45
2.1.1 Optical Lithography 46
2.1.2 Dual Beam System 50
2.2…Electrical Measurements 52
2.2.1 Magnetotransport Measurements as a Function of Temperature 52
2.2.2 ‘‘In Situ’’ Electrical Measurements 53
2.3…Spectroscopic Techniques 54
2.3.1 Energy Dispersive X-Ray Spectroscopy 54
2.3.2 X-Ray Photoelectron Spectroscopy 55
2.4…Spatially Resolved MOKE Magnetometry 56
2.5…Atomic Force Microscopy 58
2.6…High Static Magnetic Fields 59
2.7…Other Techniques 59
References 61
3 Magnetotransport Properties of Epitaxial Fe3O4 Thin Films 62
3.1…Introduction 62
3.1.1 General Properties of Fe3O4 62
3.1.2 Properties of Epitaxial Fe3O4 Thin Films 64
3.2…Experimental Details 65
3.2.1 Growth of the Films 65
3.2.2 Types of Electrical Measurement: Van Der Pauw and Optical Lithography 65
3.3…Structural and Magnetic Characterization 65
3.4…Resistivity 68
3.4.1 Resistivity as a Function of the Film Thickness (Room Temperature) 68
3.4.2 Resistivity as a Function of Temperature 68
3.5…Magnetoresistance and Anisotropic Magnetoresistance 69
3.5.1 Geometries for MR Measurements 69
3.5.2 MR as a Function of Film Thickness (Room Temperature) 70
3.5.3 MR as a Function of Temperature 72
3.6…Planar Hall Effect 74
3.6.1 Introduction to the Planner Hall Effect 74
3.6.2 PHE as a Function of Film Thickness (Room Temperature) 75
3.6.3 PHE as a Function of Temperature 77
3.7…Anomalous Hall Effect 79
3.7.1 Introduction to the Anomalous Hall Effect 79
3.7.2 AHE as a Function of the Film Thickness (Room Temperature) 81
3.7.3 AHE as a Function of the Temperature 82
3.7.4 AHE in Fe3O4: Universal Behavior 83
3.7.5 Fe3O4 Inside the AHE Dirty Regime of Conductivities 85
3.8…Ordinary Hall Effect 85
3.8.1 OHE as a Function of the Film Thickness (Room Temperature) 87
3.8.2 OHE as a Function of Temperature 88
3.9…Conclusions 89
References 90
4 Conduction in Atomic-Sized Magnetic Metallic Constrictions Created by FIB 94
4.1…Introduction 94
4.2…Experimental Procedure. Example for a Non-Magnetic Material: Chromium 95
4.3…Iron Nanocontacts 101
4.3.1 Creation of Fe Nanoconstrictions Inside the Chamber 101
4.3.2 Measurement of One Constriction in the Tunneling Regime of Conduction 102
4.3.2.1 Creation of the Constriction 102
4.3.2.2 Magnetoresistance Measurements 103
4.4…Conclusions 106
References 107
5 Pt--C Nanowires Created by FIBID and FEBID 109
5.1…Nanowires Created by Focused-Ion-Beam-Induced-Deposition 109
5.1.1 Previous Results in Pt--C Nanodeposits Grown by FIBID 109
5.1.2 Experimental Details 110
5.1.2.1 Deposition Parameters 110
5.1.2.2 ‘‘In Situ’’ Measurement of the Resistance During the Growth Process 112
5.1.2.3 Compositional Analysis by EDX 113
5.1.2.4 Structural Analysis via Scanning-Transmission-Electron-Microscopy 113
5.1.2.5 XPS Measurements 113
5.1.2.6 Transport Measurements as a Function of Temperature 114
5.1.3 Results 114
5.1.3.1 Compositional (EDX) and Structural (STEM) Analysis of the Deposits 114
5.1.3.2 XPS Measurements 115
5.1.3.3 ‘‘In Situ’’ Measurements of the Resistance as the NWs are Grown 118
5.1.3.4 Temperature Dependence of the Electrical Properties 120
5.1.4 Discussion of the Results 124
5.2…Comparison of NWs Created by FEBID and FIBID 128
5.2.1 Experimental Details 128
5.2.1.1 Deposition Parameters 129
5.2.1.2 ‘‘In Situ’’ Electrical Measurements 129
5.2.1.3 HRTEM Analysis 129
5.2.2 Results 129
5.2.2.1 EDX 129
5.2.2.2 ‘‘In Situ’’ Measurements of the Resistance as the NWs are Grown 129
5.2.2.3 Temperature Dependence of the Electrical Properties 131
5.2.2.4 HRTEM Images 133
5.3…Conclusions 134
References 135
6 Superconductor W-based Nanowires Created by FIBID 138
6.1…Introduction 138
6.1.1 Previous Results in FIBID-W 138
6.1.2 Transition Superconductor Temperatures in W Species 139
6.2…Experimental Details 139
6.2.1 HRTEM Analysis 140
6.2.2 XPS Measurements 140
6.2.3 Electrical Measurement in Rectangular (Micro- and Nano-) Wires 140
6.3…HRTEM Analysis of FIBID-W 140
6.4…XPS Study of FIBID-W 141
6.5…Superconducting Electrical Properties of Micro- and Nanowires 143
6.5.1 Critical Temperature of the Wires 143
6.5.2 Critical Field of the Nanowires 146
6.5.3 Critical Current of the Nanowires 147
6.6…Study of FIBID-W by Scanning-Tunneling-Spectroscopy 147
6.7…Conclusions 149
References6.7…Conclusions 150
7 Magnetic Cobalt Nanowires Created by FEBID 152
7.1…Previous Results for Local Deposition of Magnetic Materials Using Focused Beams 152
7.2…Experimental Details 153
7.2.1 Compositional Analysis by EDX 153
7.2.2 HRTEM 153
7.2.3 Electrical Measurements of Wires 154
7.2.4 Spatially-Resolved MOKE Measurements 154
7.2.5 AFM Measurements 154
7.3…Compositional (EDX) and Microstructural (HRTEM) Characterization 154
7.4…Magnetotransport Measurements of FEBID-Co Nanowires 156
7.4.1 Magnetotransport Properties of Cobalt NWs Grown at High Currents 157
7.4.2 Magnetotransport Properties of Cobalt NWs Grown at Low Beam Currents 160
7.5…Systematic Study of Rectangular Wires 161
7.5.1 Types of Structures Grown. Maximum Resolution Obtained 162
7.5.2 AFM Investigation of the NWs Topography 163
7.5.3 Magnetization Hysteresis Loops 165
7.5.4 Micromagnetic Study in FEBID-Co NWs 169
7.5.4.1 Introduction to Micromagnetic Simulations 169
7.5.4.2 Micromagnetic Study 169
7.6…Domain Wall Conduit Behavior in FEBID-Co 172
7.6.1 Domain Wall Conduit: The Concept 172
7.6.2 Creation of L-Shaped Nanowires 173
7.6.3 MOKE Measurements and Field Routines 174
7.7…Conclusions 179
References 180
8 Conclusions and Outlook 183
8.1…General Conclusions 183
8.2…Fe3O4 Epitaxial Thin Films 184
8.3…Creation of Atomic-sized Constrictions in Metals using a Focused-Ion-Beam 185
8.4…Nanowires Created by Focused Electron/Ion Beam Induced Deposition 186
Curriculum Vitae 188
Sec1 188
Scientific Background 188
Prizes 189
Grants 189
Stays in Scientific Institutions and Large Facilities 189
Scientific Schools 190
Technical Skills 190
Publications 191
Contributions to Conferences and Workshops 193
Participation in Research Projects 194
Teaching 195
Other Merits 195