Atomic resolution studies of In_1tn2O_1tn3ZnO compounds on aberration-corrected electron microscopes [Elektronische Ressource] / vorgelegt von Wentao Yu
144 Pages
English
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Atomic resolution studies of In_1tn2O_1tn3ZnO compounds on aberration-corrected electron microscopes [Elektronische Ressource] / vorgelegt von Wentao Yu

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144 Pages
English

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Atomic-resolution studies of In O –ZnO compounds 2 3on aberration-corrected electron microscopes Dissertation zur Erlangung des Doktorgrades ( Dr. rer. nat. ) der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn vorgelegt von Wentao Yu aus Hangzhou, V. R. China Bonn, Juli 2009 Tag der Promotion: 23.10.2009 Angefertigt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn. 1. Gutachter: Prof. Dr. Werner Mader 2. Gutachter: Prof. Dr. Karl Maier i Contents I. Electron microscopy and interaction of electrons with matter ......... 1 Chapter 1 Transmission electron microscope ............................................. 3 1.1 Introduction ............................................................................... 3 1.2 Elements of the transmission electron microscope [3] .............................................. 4 1.2.1 Electron gun ....................................................................... 4 1.2.2 Illumination system ............................ 4 1.2.

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Published 01 January 2009
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Atomic-resolution studies of In O –ZnO compounds 2 3
on aberration-corrected electron microscopes








Dissertation
zur
Erlangung des Doktorgrades ( Dr. rer. nat. )
der
Mathematisch-Naturwissenschaftlichen Fakultät
der
Rheinischen Friedrich-Wilhelms-Universität Bonn






vorgelegt von
Wentao Yu

aus
Hangzhou, V. R. China

Bonn, Juli 2009





































































































Tag der Promotion: 23.10.2009




Angefertigt mit Genehmigung der Mathematisch-Naturwissenschaftlichen Fakultät
der Rheinischen Friedrich-Wilhelms-Universität Bonn.

1. Gutachter: Prof. Dr. Werner Mader
2. Gutachter: Prof. Dr. Karl Maier




























i
Contents

I. Electron microscopy and interaction of electrons with matter ......... 1
Chapter 1 Transmission electron microscope ............................................. 3
1.1 Introduction ............................................................................... 3
1.2 Elements of the transmission electron microscope [3] .............................................. 4
1.2.1 Electron gun ....................................................................... 4
1.2.2 Illumination system ............................ 4
1.2.3 Specimen stage ................................................................................................... 5
1.2.4 Imaging system .. 6
1.2.5 Electron detectors ............................................................................................... 6
1.3 Lens aberrations......................................... 6
1.3.1 Spherical aberration (fig.1-3a) ........................................... 6
1.3.2 Defocus............................................................................... 7
1.3.3 Axial astigmatism ............................................................................................... 7
1.3.4 Chromatic aberration .......................... 7
1.4 Aberration correctors ................................................................................................. 9
1.5 Diffraction and imaging mode of CTEM .. 9
Chapter 2 Kinematic and dynamic theory of electron diffraction ............ 12
2.1 Kinematic theory of electron diffraction ................................................................. 12
2.2 Dynamic theory of electron diffraction ... 13
2.2.1 Bloch wave formalism ..................................................................................... 14
2.2.2 Multi-slice method [18,19] ............... 15
2.2.3 Dynamic calculation with absorption and specimen or beam tilt ..................... 17
Chapter 3 Wave-optical theory of imaging .............................................. 19
3.1 Contrast transfer theory ........................................................... 19
3.1.1 PCTF and delocalization .................. 19
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3.1.2 Conventional settings of defocus of the objective lens .................................... 19
3.1.3 Dark-atom and bright-atom contrast conditions [29,30] .. 20
3.2 Image formation theory ........................................................................................... 22
3.2.1 Weak phase object approximation (WPOA) in BF-TEM ................................ 22
3.2.2 Image formation theory .................................................................................... 23
3.2.3 Linear image approximation ............ 25
3.2.4 Non-linear image formation ............................................................................. 27
3.3 2D displacement field and strain measurements ..................... 28
3.3.1 ‘Peak-finding’ method ...................................................................................... 29
3.3.2 Geometric phase analysis (GPA) ..................................................................... 29
3.3.3 Strain measurement .......................................................... 30
Chapter 4 Wave aberrations in HRTEM .................................................. 31
4.1 Wave aberrations by lens system ............................................ 31
4.2 Description of wave aberrations including higher order aberrations ....................... 32
4.3 Aberration corrections ............................................................................................. 35
Chapter 5 Analytical electron microscopy [58] ........................................ 36
5.1 Inelastic scattering processes ................................................... 36
5.1.1 Phonon creation ................................................................ 36
5.1.2 Plasmon excitation ........................................................... 36
5.1.3 Core electron excitation ................................................... 36
5.2 X-ray microanalysis by Energy-dispersive spectrometer (EDS) ............................. 37
5.3 Energy-Loss spectroscopy and Energy-Selecting imaging ..................................... 38
Chapter 6 HAADF /STEM Imaging ......................................................... 40
6.1 Introduction ............................................................................. 40
6.2 Optical system of ADF /STEM ............... 40
6.3 HAADF /STEM image contrast .............................................................................. 41
6.3.1 Effects that influence the contrast of HAADF imaging ... 42
6.4 HAADF image simulations ..................................................................................... 43
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6.4.1 TDS approaches ............................................................................................... 43
6.4.2 ‘qSTEM’ (quantitative STEM) package .......................... 44
6.5 Extraction of information with the intensity line profile ......................................... 45
II. Experimental part ............................................................................47
Chapter 7 Indium doped Zinc Oxide compounds (In O (ZnO) ) ............ 49 2 3 m
7.1 Introduction ............................................................................................................. 49
7.2 Appearance of the pyramidal IDBs for m ≥ 7 ......................... 50
7.3 Goals of the structure studies of In O (ZnO) compounds for m ≥ 7 ...................... 54 2 3 m
Chapter 8 Experimental procedures and methods .................................... 55
8.1 Sample preparation .................................................................. 55
8.2 HR-TEM and image simulations ............. 55
8.3 Z-contrast imaging and HAADF image simulations ............................................... 56
Chapter 9 Displacement field and strain field mapping in TEM .............. 57
9.1 Displacement field measurement by the ‘peak finding’ method ............................. 58
9.1.1 Error analysis.................................................................................................... 61
9.2 The strain field ......... 65
9.3 Determination of the local lattice distortion by GPA .............................................. 68
Chapter 10 HR-TEM phase imaging ........................................................ 71
10.1 Structure of the basal IDB ....................... 71
10.1.1 HR-TEM imaging in both zone axes ................................ 71
10.1.2 Structure model for the basal IDB .................................... 72
10.1.3 Structure refinement of the basal IDB .............................. 74
10.1.4 Bending of the specimen .................................................................................. 76
10.2 Atomic structure of the pyramidal IDB ................................................................... 76
10.2.1 HR-TEM imaging of the pyramidal IDB in the m axis .... 76
10.2.2 Focal series reconstruction of the pyramidal IDB in the a axis ....................... 77
10.2.3 Structure models of the pyramidal IDB ........................................................... 78
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10.2.4 Image simulations of the pyramidal IDBs ........................................................ 80
Chapter 11 Z-Contrast Imaging ................................................................82
11.1 Experimental HAADF imaging and intensity extraction ........ 82
11.1.1 Experimental HAADF images ......... 82
11.1.2 Information extraction ...................................................................................... 89
11.2 HAADF image simulations of the pyramidal IDBs ................ 94
11.2.1 HAADF image simulations by different atomic structure models ................... 94
11.2.2 Investigation of specimen thickness effects on intensities ............................... 97
11.2.3 Investigation of the intensity ratios for different models of In content .......... 100
11.2.4 Determination of In contents at the pyramidal IDB ....................................... 101
11.2.5 Effect of contrast variations by specimen tilt ................. 102
11.2.6 Proposed structure model of the pyramidal IDB ............................................ 105
11.3 Discussion of the domain microstructures ............................................................. 106
3+11.3.1 In in trigonal bi-pyramids ............................................................................ 107
11.3.2 Formation of zig-zag shaped pyramidal IDBs ............... 107
Summary ..............................................................................................1 09
References 1 12
Appendix A .............................................................................................1 19
Appendix B 1 19
Appendix C .............................................................................................1 21
Appendix D 1 23
Appendix E .............................................................................................1 24
Appendix F ..............................1 30
Appendix G .............................................................................................1 31
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Acknowledgement ..................................................................................1 33
Curriculum Vitae ....................1 35































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