Stacking faults and twinning in homoepitaxial thin films on Ir(111) [Elektronische Ressource] / vorgelegt von Sebastian Bleikamp

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• Physik

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• Publié par: universitat_zu_koln
• Publié le: 01 janvier 2010
• Nombre de lectures: 33
• Langue: English
• Poids de l'ouvrage: 10 Mo

Extrait

Stacking Faults and Twinning
in Homoepitaxial Thin Films
on Ir(111)
Inaugural-Dissertation
zur
Erlangung des Doktorgrades
der Mathematisch-Naturwissenschaftlichen Fakultät
der Universität zu Köln
vorgelegt von
Sebastian Bleikamp
aus Oberhausen
Köln, 2010Berichterstatter: Prof. Dr. Thomas Michely
Prof. Dr. Mohsen Abd-Elmeguid
Vorsitzender
der Prüfungskommission: Prof. Dr. Ladislav Bohatý
Tag der mündlichen Prüfung: 12. April 2010Abstract
The growth and annealing behavior of thin Iridium films on the Ir(111)
surface was studied with respect to stacking fault and twin formation by
means of scanning tunneling microscopy (STM), low energy electron diffrac-
tion (LEED) and surface X-ray diffraction (SXRD).
It was found that by heterogeneous nucleation of new faults at phase
boundariesbetweenareasofregularandfaultedstacking,initialfaultedareas
spread into their surrounding (proliferationeffect). Inthe process, thephase
boundary is stabilized and evolves to a persistent fault structure, and a
transition from layer-by-layer growth to a defect dominated growth with
a fixed length scale takes place. During this transition, the majority of
the surface area becomes twinned. A step-influenced enhancement of the
stacking fault probability initially supports the effect.
By the supply of additional energy in the order of 50eV per deposited
atom using ion beam assisted deposition (IBAD), stacking fault and twin
formation can be effectively lifted. Various strategies of IBAD have been
tested.
The stronglytwinned Ir/Ir(111) films exhibit a high stability against ther-
mal annealing. Annealing is found to take place in a two step process: At
800K-1000K the boundaries between areas of different stacking are dimin-
ished. Only beyond 1200K also the twins themselve heal. Structure models
of the boundaries involved are presented. The boundaries between different
stackingareasareidentifiedtoconsistof{111}/{115}boundariesdissociated
into coherent {111}/{111} and {112}/{552} boundaries.
TheinfluenceofadsorbatesonthegrowthofIr/Ir(111)wasstudiedforCO
andO.ItwasfoundthatexposureofthesampletoCOorOduringdeposition
prevents coalescence, leads to columnar growth and multiple twinning. For
bothadsorbates,theislandnumberdensityisincreased, indicatingareduced
mobility on the surface.
3Contents
1 Introduction and Motivation 19
2 Background and Review of Previous Works 21
2.1 Thin Film Growth . . . . . . . . . . . . . . . . . . . . . . . 21
2.2 CrystalDefects: StackingFaults,PartialDislocationsandTwins 26
2.3 Thin Film Growth with Stacking Faults. . . . . . . . . . . . 28
2.4 Homoepitaxy on Ir(111) . . . . . . . . . . . . . . . . . . . . 34
2.5 Self-Healing of Stacking Faults in the System Ir/Ir(111) . . . 38
3 Experimental Details and Methods 41
3.1 Experimental Setup for the STM and LEED Experiments:
UHV Systems Tuma III and Athene . . . . . . . . . . . . . . 41
3.2 Experimental Setup for the SXRD Experiments at the Beam-
line BM32 of the ESRF . . . . . . . . . . . . . . . . . . . . . 43
3.3 Experimental Procedure . . . . . . . . . . . . . . . . . . . . 45
3.4 SXRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.4.1 Penetration Depth . . . . . . . . . . . . . . . . . . . 46
3.4.2 Basics of Surface X-ray Scattering . . . . . . . . . . . 48
3.4.3 Application to Ir(111) . . . . . . . . . . . . . . . . . 50
3.5 Ion Beam Assisted Deposition . . . . . . . . . . . . . . . . . 53
4 Evolution of Stacking Faults and Twinned Areas in Thin Films 57
4.1 Growth at 350K . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2 The Proliferation Effect . . . . . . . . . . . . . . . . . . . . 64
4.3 Methods of Stacking Fault and Twin Detection . . . . . . . . 67
4.3.1 DirectObservationofStackingFaultsintheFirstMono-
layer by STM . . . . . . . . . . . . . . . . . . . . . . 67
4.3.2 Stacking Fault Detection after Deposition of a Few
Monolayers by STM . . . . . . . . . . . . . . . . . . 68
4.3.3 Measuring the Surface Area of Twin Crystallites by
LEED . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5Contents
4.3.4 Twin Crystallite Identification in Annealed Films by
STM through Post Decoration . . . . . . . . . . . . . 72
4.3.5 QuantitativeComparisonofLEEDandSTMMethods
Applied to Annealed Films . . . . . . . . . . . . . . . 73
4.4 Influence of Stacking Faults and Twinning on the Growth Be-
yond the First Monolayer . . . . . . . . . . . . . . . . . . . . 74
4.4.1 Layer Dependence of P and θ . . . . . . . . . . . . 76F F
4.4.2 Influence of the Proliferation Effect . . . . . . . . . . 78
4.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5 Annealing Behavior and Stability of Twinned Films 83
5.1 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.1.1 STM Experiments . . . . . . . . . . . . . . . . . . . 84
5.1.2 SXRD Experiments . . . . . . . . . . . . . . . . . . . 88
5.1.3 Comparison . . . . . . . . . . . . . . . . . . . . . . . 92
5.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
5.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6 SuppressionofTwinCrystalliteFormationbyIonBeamAssisted
Deposition 101
6.1 IBAD Strategies to Suppress Twinning . . . . . . . . . . . . 101
6.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
6.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
7 Effect of Adsorbates on Twin Crystallite Formation 115
7.1 Adsorbates Used and Their Adsorption Sites . . . . . . . . . 115
7.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . 116
7.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
8 Summary 121
Bibliography 123
List of Publications 133
Deutsche Kurzfassung 135
Danksagung 137
6Contents
Offizielle Erklärung 139
Lebenslauf 141
7List of Figures
2.1 Growth modes in epitaxy close to the thermodynamical equi-
librium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2 Growth regimes in homoepitaxy . . . . . . . . . . . . . . . 24
2.3 Schematic representation of stacking sequences . . . . . . . 27
2.4 Schematic structure of an embedded twin . . . . . . . . . . 28
2.5 Homoepitaxy of Ag/Ag(111) . . . . . . . . . . . . . . . . . 29
2.6 Homoepitaxy of Cu/Cu(111) . . . . . . . . . . . . . . . . . 30
2.7 STM images of Co/Cu(111) . . . . . . . . . . . . . . . . . . 31
2.8 STM images of Co/Pt(111) . . . . . . . . . . . . . . . . . . 32
2.9 Twin boundary movement of Ag/Ru(0001) . . . . . . . . . 33
2.10 Atomistic model of stacking fault nucleation . . . . . . . . . 34
2.11 STM images of Ir islands on Ir(111) at various growth tem-
peratures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.12 Island density for Ir/Ir(111) . . . . . . . . . . . . . . . . . . 36
2.13 Relative stacking fault probability for Ir/Ir(111) . . . . . . . 37
2.14 Ball model of the self-healing effect . . . . . . . . . . . . . . 38
2.15 Self-healing effect at intersecting A-gaps . . . . . . . . . . . 39
2.16 STM image of decoration rows on Ir/Ir(111) . . . . . . . . . 40
3.1 Sketch of the vacuum chamber Athene . . . . . . . . . . . . 42
3.2 Experimental setup at the beamline BM32 of the ESRF . . 44
3.3 Scheme of the main movements of the diffractometer . . . . 45
3.4 X-ray attenuation length . . . . . . . . . . . . . . . . . . . 48
3.5 CTR maps for fcc crystals . . . . . . . . . . . . . . . . . . . 52
3.6 Island number densities for Pt/Pt(111) . . . . . . . . . . . . 53
4.1 STM topographs after deposition of 0.20 ML - 5.00ML of Ir
on Ir(111) at 350K . . . . . . . . . . . . . . . . . . . . . . . 58
4.2 STM topographs after deposition of 10 ML - 90 ML of Ir on
Ir(111) at 350K . . . . . . . . . . . . . . . . . . . . . . . . 59
4.3 Ball model of the Ir(111) surface . . . . . . . . . . . . . . . 60
4.4 RMS roughness for coverages up to 90 ML . . . . . . . . . . 62
9List of Figures
4.5 Averagelaterallengthscaleandaveragedistanceofdecoration
rows for coverages up to 90 ML . . . . . . . . . . . . . . . . 63
4.6 STM topograph and schematic drawing illustrating the pro-
liferation effect . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.7 Ball model of the proliferation effect . . . . . . . . . . . . . 65
4.8 STMtopographsafterdepositionof2.18MLat350K,colored
with respect to the stacking sequence . . . . . . . . . . . . . 68
4.9 LEED I/V spectra . . . . . . . . . . . . . . . . . . . . . . . 71
4.10 Illustration of the post decoration method . . . . . . . . . . 72
4.11 Comparison of θ for a 90ML Ir film between LEED and STM 74F
4.12 Fraction of surface area covered by stacking faults θ versus Θ 75F
4.13 Comparison of STM topographs of films grown at 350K and
below 210K . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.14 STM topographs after sputtering and successive deposition 78
4.15 Ball model of the proliferation effect for up to four layers . . 80
5.1 STM topographs of 90ML Ir/Ir(111) after annealing to dif-
ferent temperatures . . . . . . . . . . . . . . . . . . . . . . 84
5.2 STM topographs and linescans showing fractional steps after
annealing . . . . . . . . . . . . . . . . . . . . . . . . . . .