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FU Berlin
Digitale Dissertation

Dino Tonti :
Photoelektronspektroskopie zur Interkalationsreaktion von Alkalimetallen in Übergangsmetalldichalkogeniden
Photoelectron Spectroscopy Study of the Intercalation Reaction of Alkali Metals in Transition Metal Dichalcogenides

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Abstract

The insertion of alkali atoms into appropriate solid materials, also known as intercalation, is thermodynamically strongly favored for certain host-guest combinations, and advanced batteries are based on this process. Goal of the present work was a systematic investigation by photoelectron spectroscopy of the intercalated phase as a function of the host, the guest and its concentration.

Na has been deposited onto layered dichalcogenides of formula MX2, using transition metals of the groups IVb (Ti) and Vb (Ta) and chalcogens of different size (S and Se). In spite of the different electronic properties of the host, only similar general features could be observed between TiX2 and TaX2: shift of the chalcogen levels to higher binding energies, broadening of the transition metal levels, and a small decrease of the work function. Instead, whereas the opening of a large gap was induced between the valence states Ti 3d and S 3p states of TiS2 no comparable effect was observed in the corresponding states of TiSe2.

Alkali metals of different size have been compared by co-deposition onto the same host sample. It has been found that in general smaller atoms have a higher intercalation driving force, even being able to induce the deintercalation of larger species if previously deposited.

Due to fast alkali diffusion into the bulk of the crystals it was not possible to study highly intercalated samples. For this purpose an UHV preparation of TiS2 thin films has been developed. With TiS2 thin films as substrate no limiting alkali concentration was observed, demonstrating the possibility to in-situ prepare fully intercalated materials.

With the same preparation TiS2 thin films could be deposited onto Na-b ''-Al2O3, a well-known solid Na+ ion conductor. Therefore it was possible to in-situ prepare a solid-state electrochemical cell, which could be operated in UHV in a coupled electrochemical and PES measurement. Thus, not only the guest concentration can be controlled at unparalleled level by keeping the electronic structure under control. Since the electrode potential depends on the chemical potential of the guest in the host matrix, a correlation between thermodynamic data and electronic structure is possible. The chemical potential of the guest atom is considered to split in an electronic and an ionic contribution corresponding to the separated interactions of inserted electrons and ions with the host. Both contributions vary along intercalation following the potential drop. The ionic component contributes for about one third to the battery voltage. A detailed analysis of the shifts of binding energies suggests a partial charge transfer from the intercalated alkali metal to the transition metal, but also to the chalcogen.


Table of Contents

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Cover and Abstracts

Table of contents

1 Introduction

2 Fundamentals

2.1 Transition metal dichalcogenides
2.2 The intercalation reaction
2.3 Motivation and outline of the present work

3 Experimental

3.1 Photoelectron spectroscopy
3.2 UHV equipment and spectrometer systems
3.3 Preparative methods
3.4 Ex-situ characterization techniques

4 Thin film synthesis

4.1 Low-pressure growth techniques
4.2 The electronic structure of TiX2
4.3 Optimization
4.4 The reaction mechanism
4.5 Ex-situ characterizations

5 Intercalation

5.1 Deposition on single crystals
5.2 Co-deposition experiments
5.3 Deposition on thin films
5.4 In-situ electrochemical intercalation

6 Discussion and conclusions

6.1 Binding energy shifts and charge transfer
6.2 The ionic and electronic contributions to the electrochemical potential
6.3 Summary of results and perspectives

References

List of abbreviations

Publications


More Information:

Online available: http://www.diss.fu-berlin.de/2000/145/indexe.html
Language of PhDThesis: english
Keywords: Intercalation, XPS, UPS, Chemical Beam Epitaxy, TiS2, Na, chemical potential
DNB-Sachgruppe: 30 Chemie
Classification PACS: 71.20, 73, 81.15.Hi, 81.15.-z, 81.20.-n, 81.70.-q, 82.30.-b, 82.45.-h, 82.80.Fk, 82.80.Ms, 82.80.Pv
Date of disputation: 24-Oct-2000
PhDThesis from: Fachbereich Biologie, Chemie, Pharmazie, Freie Universität Berlin
First Referee: Prof. Dr. Wolfram Jaegermann
Second Referee: Prof. Dr. Helmut Tributsch
Contact (Author): dino.t@gmx.net
Contact (Advisor): jaegerw@surface.tu-darmstadt.de
Date created:12-Dec-2000
Date available:02-Feb-2001

 


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