Quantitative TEM analysis of crystalline and amorphous GeTe-based chalcogenides [Elektronische Ressource] / vorgelegt von Galyna Laptyeva

Glaptyeva

Sujets

• Naturwissenschaften

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2009
• Nombre de lectures: 48
• Langue: Deutsch
• Poids de l'ouvrage: 2 Mo

Extrait

Quantitative TEM analysis of crystalline and
amorphous GeTe-based chalcogenides



Von der Fakultät für Mathematik, Informatik und Naturwissenschaften
der RWTH Aachen University zur Erlangung des akademischen Grades
einer Doktorin der Naturwissenschaften genehmigte Dissertation


vorgelegt von

M.Sc. in Metallurgical Engineering Galyna Laptyeva

aus Kramatorsk, Ukraine



Berichter: Universitätsprofessor Dr. Joachim Mayer
Universitätsprofessor Dr. Matthias Wuttig


Tag der mündlichen Prüfung: 24. September 2009

Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek
online verfügbar





Contents
ACKNOWLEDGMENTS ....................................................................................................... 6
SUMMARY............................................................................................................................ 7
1 MOTIVATION AND BACKGROUND ................................................................................. 9
1.1 Devices for phase-change recording..........................................................................10
1.1.1 Optical recording......................................................................................................11
1.1.2 Electrical recording ..................................................................................................11
1.2 Structural aspects of binary GeTe and quasibinary GeTe-Sb Te ............................12 2 3
2 THEORETICAL BACKGROUND OF ELECTRON DIFFRACTION ANALYSIS ................15
2.1 Scattering of a wave.....................................................................................................15
2.1.1 Wavefunction...........................................................................................................16
2.1.2 Coherent and incoherent scattering .........................................................................18
2.1.3 Elastic and inelastic scattering.................................................................................19
2.1.4 Atomic scattering factors..........................................................................................20
2.2 Electron diffraction.......................................................................................................21
2.2.1 Electron diffraction from crystalline materials...........................................................21
2.2.2 Geometrical relationships ........................................................................................23
2.2.3 Electron diffraction from amorphous materials .........................................................25
2.3 Quantitative electron diffraction analysis...................................................................25
2.3.1 Scattering amplitude and diffraction intensity...........................................................25
3

2.3.2 Atomic Pair Distribution Function Analysis...............................................................27
2.3.3 Limitations of the atomic PDF method .....................................................................29
2.3.4 Accuracy and resolution of PDF...............................................................................31
2.3.5 Comparison of reduced PDF with other correlation functions...................................32
3 TRANSMISSION ELECTRON MICROSCOPY .................................................................33
3.1 Conventional TEM (CTEM)...........................................................................................34
3.1.1 CTEM operation modes...........................................................................................34
3.1.2 Contrast formation in CTEM images ........................................................................37
3.2 Phase contrast and High Resolution TEM (HRTEM) imaging....................................40
3.3 Chemical mapping in TEM ...........................................................................................43
4 MATERIALS.................................................................................................................46
4.1 Samples overview...................................................................................................46
4.2 Sample preparation techniques.............................................................................47
4.2.1 Sputtering technique..............................................................................................48
4.2.2 Ion milling for plane view sample preparation ........................................................50
4.2.3 FIB technique for cross-sectional specimen preparation........................................50
4.3 Sample characterisation.........................................................................................52
4.3.1 Quantification of sample composition by EPMA.....................................................52
4.3.2 Estimation of sample thickness..............................................................................54
5 CRYSTALLIZATION MORPHOLOGY IN SINGLE- AND MULTI-LAYER GST225
SAMPLES............................................................................................................................56
5.1 Nucleation and growth process during solid state phase transformation ...............56
4

5.2 TEM results...................................................................................................................59
5.2.1 Single-layer GST225 samples...........................................................................59
5.2.2 Double-layer GST225 samples .........................................................................61
5.2.3 Three-layer GST225 samples ...........................................................................62
5.3 Discussion and conclusions of the crystallization experimets.................................65
6 AMORPHOUS TO CRYSTALLINE TRANSITION IN BINARY MONOLAYER GE-TE
SAMPLES............................................................................................................................69
6.1 TEM results...................................................................................................................69
6.1.1 Crystallization morphology ................................................................................69
6.1.2 Phase separation during crystallization .............................................................71
6.1.3 Ordered regions in amorphous GeTe samples .......................................................74
6.2 Discussion and conclusions, amorphous to crystalline transition in binary GeTe.75
7 SHORT RANGE ORDER IN BINARY GE-TE- AND QUASI-BINARY GST124
SAMPLES............................................................................................................................76
7.1 Short range order in amorphous and crystalline GeTe samples.........................78
7.2 Short range order in amorphous and crystalline GST124 samples ....................79
7.3 Discussion and conclusions of short range order measurements...........................81
8 FINAL CONCLUSIONS................................................................................................83
BIBLIOGRAPHY..................................................................................................................86
CURRICULUM VITAE..........................................................................................................89


5 Acknowledgments

Acknowledgments
This thesis would not have been possible without the support of many people whom I would
like to express my gratitude:
I owe the deepest gratitude to Professor Joachim Mayer, supervisor of my PhD, for making it
possible for me to learn more about TEM not only in theory but also in practice. I appriciate
very much his constant support of my work during my three years in GFE and his many
useful comments on this work during the final stages of the dissertation.
Prof. Matthias Wuttig for putting his valuable time into reading the final version of the thesis.
Julia van Eijk, Michael Woda and Helmut Kölpin for sample preparation and for an excellent
cooperation during the whole project.
I would like to thank Dr. Thomas Weirich and Dr. Joseph Penkalla for a number of critical
advices on quantification of diffraction data and for the valuable discussions.
Dr. Alla Sologubenko, Dr. Arbi Dimyati, Dr. Cleo Herwartz and Falk Dorn for a great support
during my practical TEM sessions.
Dr.Silvia Richter for being very interested in my work and for discussing with me a lot of
ESMA related questions.
I would like to thank Achim Herwartz and Helga Mainz for helping me to make a lot of my
TEM-images visible.
Steffi Stadler and Evi Münstermann for keeping a lot of things organized and allways having
the right advice.
I am grateful my roommate Manuela Reichelt and all GFE team for a sence of humor.
Last but not least I would like to thank Robert, my parents Tamara&Alexander for always
supporting and inspiring me.
6 Summary


Summary
The present dissertation reports the results of investigations of (i)