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FU Berlin
Digitale Dissertation

Jens J. Schulz :
Scanning Tunneling Microscopy of Mobile Single-Crystal Surfaces
Rastertunnelmikroskopie an mobilen Einkristalloberflächen

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Abstract

In the present thesis the fcc(110) surfaces of silver, gold and iridium as well as the (001) surface of silicon were investigated by scanning tunneling microscopy (STM) at different sample temperatures.

For Ag(110), self diffusion is strongly influenced by the scanning tip even under mildest imaging conditions. Along the hard diffusion direction, atoms may follow the tip a few lattice distances via an energetically favourable atom exchange mechanism. The emerging metastable dumbbell structure - exhibiting a characteristic scan profile - has been imaged with the STM for the first time. Along the easy diffusion direction, atoms may be pulled out of step edges and follow the tip for several nanometres with a characteristic sequence of detachment and reattachment. Thus, diffusion is suppressed by the tip influence by orders of magnitude.

For (1×2) missing row reconstructed Au(110) it is shown that [1-10] oriented step edges are stable under the influence of the scanning tip even at temperatures as high as 500 K. The fjordlike structures observed previously at higher temperatures has been investigated. An unequivocal decision whether this structure is real or just an artefact due to kink diffusion is not yet possible. Nevertheless, observations seem to contradict an artefact interpretation.

Ir(110) is investigated in the temperature range from 300 K to 890 K. The results are compared with the apparently inconsistent literature data. At 300 K the surface shows {331} facets. With increasing temperature (520 K) it flattens, resulting in a (1×3)/(1×1) structure. In addition, quantum dot structures are observed. STM and LEED reveal at still higher temperatures (890 K) a flat surface with (1×2) missing row structure. Temperature dependent surface stress is suggested as the driving force.

Different low temperature methods for Si(001)-(2×1) sample preparation (Ishizaka-Shiraki-Method and SPM) are characterized for the first time with the STM under ultra high vacuum conditions. Compared with surfaces prepared by a high temperature "standard procedure" typically used in scientific investigations, the resulting surfaces at low temperatures show a sufficiently higher defect concentration, particularly dimer vacancies.

Table of Contents

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Titel 1
Inhaltsverzeichnis 3
1 Einleitung 5
2 Grundlagen 9
2.1 Struktur und Stabilität von Ag(110), Au(110), Ir(110) und Si(001)
10
2.2 Das STM als Sonde und Werkzeug
17
2.3 Einsatz des STMs bei höheren Temperaturen
21
3 Experiment 23
3.1 Versuchsaufbau
23
3.2 Einfluss der STM-Spitze
30
3.3 Thermische Drift
33
3.4 Scan-Modi
33
4 Ag(110) 35
4.1 hcp-Plätze beim fcc-Gitter
35
4.2 Typische Strukturmerkmale und Mess-Artefakte
36
4.3 Der spitzeninduzierte Atom-Austausch
38
4.4 STM-kontrollierte Diffusion entlang der Atomreihen
45
4.5 Diagonal-Scans
51
5 Au(110) 53
5.1 Typische Strukturmerkmale
54
5.2 Die Stabilität von Stufenkanten
55
6 Ir(110) 59
6.1 Weitere Rekonstruktionen der 5d Metalle
59
6.2 STM-Resultate
61
6.3 Diskussion
66
7 Si(001) 71
7.1 Einfluss der Präparation
71
7.2 Hochtemperatur-Untersuchungen
76
8 Zusammenfassung 79
9 Anhang 83
9.1 Abkürzungen
83
9.2 Symbole
85
9.3 Eigenschaften der untersuchten Systeme
85
Literaturverzeichnis 87
Publikationsliste 99
Danksagung 101

More Information:

Online available: http://www.diss.fu-berlin.de/2001/268/indexe.html
Language of PhDThesis: german
Keywords: High Temperature Scanning Tunneling Microscopy; Surface Diffusion; Surface Reconstruction; Silver; Gold; Iridium; Silicon
DNB-Sachgruppe: 29 Physik, Astronomie
Classification PACS: 68.37.Ef, 66.10.Cb, 68.35.Bs, 68.35.Fx, 61.50.Ks
Date of disputation: 21-Nov-2001
PhDThesis from: Fachbereich Physik, Freie Universität Berlin
First Referee: Prof. Dr. Karl-Heinz Rieder
Second Referee: Prof. Dr. Klaus H. Ploog
Contact (Author): jens.schulz@pdi-berlin.de
Contact (Advisor): koch@pdi-berlin.de
Date created:13-Dec-2001
Date available:19-Dec-2001

 

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