FU Berlin Digitale Dissertation
Gerd Wedler : Influence of Stress on Morphology and Magnetism of Heteroepitaxial Thin Films Mechanische Spannung bei Heteroepitaxie: Einfluss auf Struktur und Magnetismus
|Abstract| |Table of Contents| |More Information|

Abstract In this thesis a cantilever beam method and scanning tunneling microscopy are employed to investigate the influence of stress on the morphology and magnetoelastic coupling of various epitaxial thin film systems. SixGe1-x-alloy films with a Si content <20% deposited onto Si(001) substrates at 900 K grow by the well established Stranski-Krastanow growth mode. The stress of the initial layer by layer regime is dominated by high misfit strain, which is partially relieved when 3D islanding sets in. As indicated by striking differences in the stress evolution the film growth changes to a pure 3D island mode (without wetting layer!) at Si concentrations >20%. The 3D island mode is confirmed by in situ scanning tunneling microscopy investigations, which reveal small islands with narrow size distribution already at a film thickness of 1 nm. To describe this surprising switching of growth mode a kinetic growth model is proposed. Furthermore, the first stress measurements of Fe/GaAs(001) are presented. In accordance with previous studies a few nm thick interdiffusion layer is indicated by the stress evolution at 450 K. Though reduced by 30%, interdiffusion cannot be neglected even at 300 K. The growth of Fe on different substrates [MgO(001), low-stress Cr(001) buffer-layers, GaAs(001)] provides a general picture of the stress dependence of the magnetoelastic coupling B1 and B2 in the thickness range of 2-100 nm. Both constants exhibit a strong dependence on the film stress above 0.1 GPa and even change sign at stress values in the GPa range. Whereas B2 decreases linearly with film stress up to 6 GPa, B1 saturates after a steep linear increase at 2-3 GPa. Stress-free Fe(001) films exhibit bulk behavior. Magnetization and magnetic anisotropy, on the contrary, are bulk-like in the entire thickness range independent of the stress.

Table of Contents Download the whole PhDthesis as a zip-tar file or as zip-File For download in PDF format click the chapter title Titelblatt 1 Inhaltsverzeichnis 3 1 Einleitung 5 2 Theoretische Grundlagen 9 2.1 Grundlagen des Filmwachstums 9 2.1.1 Kategorien des Filmwachstums 9 2.1.2 Wachstum der untersuchten Materialsysteme 14 2.2 Intrinsische Spannung dünner Filme 18 2.3 Die magnetoelastische Kopplung 22 2.3.1 Magnetismus und Kristallenergie 22 2.3.2 Magnetostriktion und magnetoelastische Kopplung 24 2.4 Experimentelle Methoden 29 2.4.1 Das Biegebalkenmessverfahren 29 2.4.2 Der Biegebalken als Magnetometer 33 2.5 Rastertunnelmikroskopie 39 3 Experimenteller Aufbau 41 3.1 Die UHV-Anlage 41 3.2 Biegebalkenmessanordnung 47 3.3 Versuchsdurchführung und Probenpräparation 52 4 Resultate: Filmwachstum 55 4.1 SixGe1-x/Si(001) 55 4.2 Fe/MgO(001) 62 4.3 Fe/GaAs(001) 67 4.4 Zusammenfassende Diskussion 72 5 Resultate: Filmmagnetismus 77 5.1 Fe/MgO(001) 77 5.2 Fe/GaAs(001) 83 5.3 Zusammenfassende Diskussion 91 6 Zusammenfassung 99 Literaturverzeichnis 103 Publikationsliste 111 Anhang 115

More Information:
Online available:	http://www.diss.fu-berlin.de/2001/110/indexe.html
Language of PhDThesis:	german
Keywords:	stress, Fe, GaAs, MgO, Cr, Ge, Si, cantilever beam magnetometer, morphology, magnetoelastic coupling
DNB-Sachgruppe:	29 Physik, Astronomie
Classification PACS:	68.60.Bs, 68.55.Ac, 75.70.-i, 75.80.+q
Date of disputation:	19-Jun-2001
PhDThesis from:	Fachbereich Physik, Freie Universität Berlin
First Referee:	Prof. Karl Heinz Rieder
Second Referee:	Prof. Paul Fumagalli
Contact (Author):	wedler@physik.fu-berlin.de
Contact (Advisor):	koch@pdi-berlin.de
Date created:	03-Jul-2001
Date available:	04-Jul-2001

 

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