DARWIN Digitale Dissertationen German Version Strich

FU Berlin
Digitale Dissertation

Jascha Repp :
scanning tunneling microscopy and spectroscopy of adsorbates on metal and insulator surfaces
Rastertunnelmikroskopie und -spektroskopie an Adsorbaten auf Metall- und Isolatoroberflächen

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Abstract

In this thesis investigations of adsorbates on metal and insulator surfaces are presented using low temperature scanning tunneling microscopy and spectroscopy.
With the study of Cu/Cu(111) a long-ranged oscillatory interaction could be identified for the first time that is mediated by a surface state band. Single copper adatoms have a low diffusion barrier of (37 ± 5)meV and occupy only hcp adsorption sites. In agreement with theoretical predictions the pair potential oscillates with half the Fermi wavelength and the envelope falls off as 1/d with distance d. The difference between the first potential minimum and maximum is about 1meV. In the case of a potential minimum/maximum the local density of states at the Fermi level directly between the adatoms is reduced/increased. The diffusion of single adatoms in artificial nanostructures can be forced into discrete diffusion channels. The copper adatoms within a dimer can occupy either fcc or hcp adsorption sites at a temperature of 8K. In long chains of adatoms adsorption could be observed on fcc sites only.
NaCl(100)/Cu(111) shows an interface state band. The dispersion is shifted towards higher energy compared to the surface state band of the clean Cu(111) surface. A simple model is proposed that gives a qualitative understanding of the observed features. The interface state band shows a one dimensional band gap that appears in the images as standing waves. Moiré patterns arise from the incommensurate growth. These patterns cause a modulation of the potential and thereby split up the interface state band. At chlorine vacancies a bound state can be found. At NaCl island edges the refraction of electrons in the interface state band can be observed.
Single silver, copper and gold adatoms on NaCl(100) appear as protrusions in the scanning tunneling microscopy images. For these adatoms the adsorption site is found to be on top of the chlorine ions. This falsifies all previous theoretical studies in this regard. Gold adatoms have a diffusion barrier of (147 ± 15)meV on NaCl(100). Atomic manipulation can be performed applying a voltage puls that switches single gold adatoms into a different stable state. This manipulation does not change the adsorption site. The adatoms can be switched back to the primary state by an additional suitable voltage pulse.
A digital control unit was designed, which will be used in a future combined low temperature scanning tunneling and atomic force microscope.

Table of Contents

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Titel 1
Inhaltsverzeichnis 9
1 Einleitung 11
2 Grundlagen 13
2.1 Das Rastertunnelmikroskop 13
2.2 Zur Theorie der Rastertunnelmikroskopie 14
2.3 Spektroskopie mit dem Rastertunnelmikroskop 16
2.4 Oberflächenzustände der Elektronen im NFE-Modell 18
3 Experimentelles 25
3.1 Die verwendete Meßapparatur 25
3.2 Eigenschaften der verwendeten Materialien 26
3.3 Probenpräparation 27
4 Entwicklung einer digitalen DFM-Steuerung 29
4.1 Der prinzipielle Aufbau 30
4.2 Realisierung 31
4.3 Testmessungen 33
5 Substratvermittelte langreichweitige Wechselwirkung 35
5.1 Diffusion einzelner Cu-Adatome auf Cu(111) 36
5.2 Bestimmung des Paarpotentials zwischen Cu-Adatomen 43
5.3 Lokale Zustandsdichte für unterschiedliche Adatomabstände 48
5.4 Zur Theorie dieser Wechselwirkung 53
5.5 Kinetische Monte-Carlo-Simulationen 56
5.6 Das reine Paarpotential 59
5.7 Die Wechselwirkung zwischen Monomeren und Adatom-Ketten 59
5.8 Platzbestimmung von Cu-Monomeren und -Dimeren 65
5.9 Diffusion in künstlichen Nanostrukturen 70
6 Grenzflächenzustände von NaCl(100) auf Cu(111) 71
6.1 Wachstum von NaCl(100) auf Cu(111) 71
6.2 I(z)-Spektroskopie 77
6.3 Elektronische Grenzflächenzustände 79
6.4 Zur Theorie des Grenzflächenzustandsbandes 83
6.5 Aufspaltung des Grenzflächenzustandsbandes 89
6.6 Brechung an NaCl-Stufenkanten 94
6.7 Cl-Fehlstellen und gebundene Zustände 95
7 Einzelne Metallatome auf NaCl(100)/Cu(111) 99
7.1 Abbildung von Gold-Monomeren und -Dimeren 99
7.2 Platzbestimmung einzelner Gold-Adatome 102
7.3 Diffusion von Au/NaCl(100) 103
7.4 Manipulation einzelner Gold-Adatome 105
7.5 Theoretisches Modell zur Manipulation 109
7.6 Desorption von Gold-Adatomen 112
7.7 Gezielte Erzeugung einzelner Cl-Fehlstellen 112
7.8 Messungen an einzelnen Ag- und Cu-Adatomen 114
7.9 Weiterführende Messungen 123
8 Zusammenfassung 125
9 Ausblick 129
Literaturverzeichnis 131
Curriculum Vitae 139
Veröffentlichungen 141
Danksagung 143

More Information:

Online available: http://www.diss.fu-berlin.de/2002/84/indexe.html
Language of PhDThesis: german
Keywords: STM, insulator, thin film, Cu(111), atomic manipulation
DNB-Sachgruppe: 29 Physik, Astronomie
Classification PACS: 68.55.-a, 68.35.Fx, 61.16.Ch
Date of disputation: 13-May-2002
PhDThesis from: Fachbereich Physik, Freie Universität Berlin
First Referee: Prof. Dr. Karl-Heinz Rieder
Second Referee: Prof. Dr. Frank Forstmann
Contact (Author): jascha.repp@epost.de
Contact (Advisor): rieder@physik.fu-berlin.de
Date created:16-May-2002
Date available:06-Jun-2002

 

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