HCl Nanoscience at Copper and Copper/Gold Alloy Surfaces

202 Pages·2013·17.23 MB·English

HCl Nanoscience at Copper and Copper/Gold
Alloy Surfaces

Hatem Muhmad Altass

Thesis submitted to Cardiff University
in candidature of the degree of Doctor of Philosophy in Chemistry

Department of Chemistry, Cardiff University, Cardiff, Wales, U.K.
April 2013

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DECLARATION
This work has not been submitted in substance for any other degree or award at this or any
other university or place of learning, nor is being submitted concurrently in candidature for
any degree or other award.
Signed ……………………………………(Hatem M Altass) Date …...25/04/2013…………
STATEMENT 1
This thesis is being submitted in partial fulfilment of the requirements for the degree of
………PhD…………………

Signed ……………………………………(Hatem M Altass) Date …...25/04/2013…………

STATEMENT 2
This thesis is the result of my own independent work/investigation, except where otherwise
stated. Other sources are acknowledged by explicit references. The views expressed are my
own.
Signed ……………………………………(Hatem M Altass) Date …...25/04/2013…………
STATEMENT 3
I hereby give consent for my thesis, if accepted, to be available for photocopying and for
inter-library loan, and for the title and summary to be made available to outside organisations.
Signed ……………………………………(Hatem M Altass) Date …...25/04/2013…………

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This thesis is dedicated to my parents, wife, children, sister, and brothers
for their love, endless support and encouragement.

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Abstract

The reaction of HCl with clean, Cu(100) and (111), and Au/ Cu(100) surfaces was
investigated using x-ray photoelectron spectroscopy (XPS) and scanning tunneling
microscopy (STM) under ultra high vacuum (UHV) conditions. Exposure of the Cu(100) and
(111) samples to HCl at room temperature leads to the formation of a saturated copper
chloride monolayer. In the case of Cu(100), the saturated coverage was half monolayer
corresponding to a c(2x2)-Cl reconstruction (half monolayer is 7.25x1014 cm-2) while for
Cu(111) it was one third monolayer consistent with the reconstruction of (√3x√3)R30o (one
third monolayer 5.9x1014 cm-2).

The interaction of HCl with preoxidised Cu(100) and (111) showed different behaviour from
those of clean copper surface depending on the way of interaction of oxygen with copper
surface. Interaction of HCl with peroxidised Cu(111) at saturation oxygen coverage leads to
the adsorption of chlorine on top of the copper surface with one third coverage. In contrast,
presence of oxygen on Cu(100) surface at saturation coverage or less leads to adsorb chlorine
but with an excess in chlorine concentration (more than the expected c(2x2) coverage).

Oxidized Cu(100) and (111) surface at elevated temperature leads to the formation multi
oxide layer. The two oxide surfaces („‟44‟‟ and „‟29‟‟) observed at the Cu(111) depend on the
temperature of the substrate at the time of oxidation. The (√2x2√2)R45o structure was
observed on the Cu(100) surface on heating which is the same structure formed at saturation
coverage at room temperature. Interaction of HCl with Cu(100) and (111) surfaces covered
by multilayers of oxide lead to adsorption of chlorine on top of the copper surface with a
coverage more than more than the saturation coverage.

Interaction of HCl with Au/Cu(100) showed two different behaviour depending on the gold
coverage. Au/Cu(100) alloy formed at half monolayer of gold coverage, forming c(2x2)
structure. Exposure of the Au/Cu(100) alloy at half monolayer of gold coverage to HCl leads
to the formation of c(2x2)-Cl structure with saturation coverage of half monolayer in similar
manner of interaction of HCl with the clean cu(100) surface. Interaction of HCl with
Au/Cu(100) surface at gold coverage more than half monolayer leads to a dealloying of the
gold from the copper surface and forming the Au(111) surface. Cu-Cl formed underneath the
Au(111) surface with excess of chlorine concentration.
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Acknowledgments

The realization of this work was only possible due to the several people's collaboration, to
which desire to express my gratefulness.

To Dr Philip Davies and Dr Albert Carley, my supervisors, I am grateful for the trust
deposited in my work and for the motivation demonstrated along this arduous study. Their
help was endless, no matter what the issue and time. They give me a lot of knowledge about
handling the complicated UHV system. Your guidance was the best guide during the period
that I spent with you and I hope this cooperation will continue even after my return to home. I
am very grateful to both of them for their supervision and friendship.

I would like to thank from a special way Dr Robert Davies for his help for all the time of my
work and when we travel together to attend the scientific conferences. I am very glad to have
a friendship with such a man.

I would like to thank Dr David Morgan for his continuous help for solving the UHV system
problem, advices and suggestions.

To all my colleagues and researchers in surface science group, for the encouragement, advice
suggestions and friendship.

I must also thank all the staff of the School of chemistry for their help and assistance during
the time of my work. Special thanks as well for the staff of the mechanical workshop for their
help to fix the engineering issues and amazing solutions which they suggested.

I would also to express my appreciation to my friend, Dr Mohammed Baashen and all my
friends in Saudi Chemists Group in Cardiff for their enthusiasm, encouragement and
fascinating friendship.

Finally, I would like to thank to my family, their love gave me forces to make this work.

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Contents
Chapter 1 Introduction ......................................................................................................................... 10
1.1 Single Crystal of metal surface ....................................................................................................... 11
1.2 Miler indices ................................................................................................................................... 11
1.3 Surface structures and reactivity ..................................................................................................... 12
1.4 Atomic densities of atoms in the surface plane ............................................................................... 14
1.5 Adsorption....................................................................................................................................... 14
1.5.1 Physisorption............................................................................................................................ 15
1.5.2 Chemisorption .......................................................................................................................... 15
1.5.3 Adsorption isotherm ................................................................................................................. 17
1.6 Surface science and heterogeneous catalysis .................................................................................. 18
1.7 Copper and gold as a catalyst .......................................................................................................... 20
1.8 References ....................................................................................................................................... 24
2.1 Introduction ..................................................................................................................................... 28
2.2 Binding energy ................................................................................................................................ 29
2.3 Koopmans‟ Theorem ...................................................................................................................... 30
2.4 Initial state effect ............................................................................................................................. 31
2.5 Final state effects ............................................................................................................................ 31
2.6 Spectral features .............................................................................................................................. 31
2.6.1 Inelastic background ................................................................................................................ 31
2.6.2 Spin-orbit splitting ................................................................................................................... 32
2.6.3 X-ray Satellites ......................................................................................................................... 34
2.6.4 Auger peak ............................................................................................................................... 34
2.7 Instrument ....................................................................................................................................... 34
2.7.1 X-ray source ............................................................................................................................. 35
2.7.2 Analyzer ................................................................................................................................... 37
2.8 Quantification analysis .................................................................................................................... 38
2.9 References .......................................................................................... Error! Bookmark not defined.
3.1- Introduction ................................................................................................................................... 43
3.2 Quantum Tunnelling ....................................................................................................................... 43
3.3 Instrumentation ............................................................................................................................... 44
3.3.1 Overview of the Design ........................................................................................................... 45
3.3.2 Tip ............................................................................................................................................ 45
3.3.3 Piezodrive ................................................................................................................................ 48
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3.3.4 Type of scan ............................................................................................................................. 48
3.3.5 Vibration isolation ................................................................................................................... 49
3.4 References ....................................................................................................................................... 51
4.1 The ultra high vacuum system (UHV) systems .............................................................................. 53
4.1.1 Main overview ......................................................................................................................... 53
4.1.2 The need for UHV system ....................................................................................................... 54
4.2 Achieving the UHV condition ........................................................................................................ 56
4.2.1 Mechanical pump ..................................................................................................................... 56
4.2.1.1 Rotary pump .......................................................................................................................... 56
4.2.1.2 Turbo molecular pump .......................................................................................................... 57
4.2.2 Entrapment pump ..................................................................................................................... 58
4.2.2.1 Ion pump ............................................................................................................................... 58
4.2.2.2 Titanium sublimation pump TSB .......................................................................................... 59
4.2.3 Bakeout and degas ................................................................................................................... 60
4.3 Pressure measurements ................................................................................................................... 60
4.3.1 Pirani gauge ............................................................................................................................. 60
4.3.2 Ion gauge .................................................................................................................................. 60
4.3.3 Residual gas analyser ............................................................................................................... 61
4.4 Sample processing .......................................................................................................................... 62
4.4.1 Polishing the sample ................................................................................................................ 62
4.4.2 Transferring the sample to UHV and in situ cleaning .............................................................. 63
4.5 Gold evaporator .............................................................................................................................. 64
4.6 Gas line ........................................................................................................................................... 64
4.7 References ....................................................................................................................................... 65
5.1 Introduction ..................................................................................................................................... 67
5.1.1 Interaction of oxygen with Cu(100) ......................................................................................... 67
5.1.2 Interaction of chlorine with Cu(100) ....................................................................................... 70
5.2 Experimental ................................................................................................................................... 72
5.3 Results and discussion .................................................................................................................... 73
5.3.1 XPS and STM of the clean Cu(100) surface ............................................................................ 73
5.3.2 Interaction of HCl with clean Cu(100) surface at room temperature ....................................... 75
5.3.3 Interaction of oxygen with clean Cu(100) surface at room temperature .................................. 80
5.3.4 Interaction of oxygen with clean Cu(100) surface at 100 oC ................................................... 83
5.3.5 Interaction of oxygen with clean Cu(100) surface at 250 oC ................................................... 87
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5.3.6 Interaction of Cu(100)-O surface with HCl at room temperature ............................................ 91
5.3.6.1 Interaction of preoxidised Cu(100) surface at room temperature with HCl. ..................... 91
5.3.6.2 Interaction of oxygen saturated Cu(100) surface at room temperature with HCl. ............ 97
5.3.7 Interaction of Cu(100) surface oxidised at 250 oC, with HCl at room temperature. .............. 107
5.4 Conclusions ................................................................................................................................... 111
5.5 References ..................................................................................................................................... 114
6.1 Introduction ................................................................................................................................... 119
6.1.1 Interaction of oxygen with Cu(111) ....................................................................................... 119
6.1.2 Interaction of Cu(111) with chlorine. .................................................................................... 122
6.2 Experimental ................................................................................................................................. 123
6.3 Results and discussions ................................................................................................................. 125
6.3.1 XPS and STM of clean Cu(111) surface ................................................................................ 125
6.3.2 Interaction of oxygen with clean Cu(111) at room temperature. ............................................... 126
6.3.3 Interaction of oxygen with Cu(111) sample at 380 oC ............................................................... 133
6.3.4 Interaction of oxygen with Cu(111) sample at 450 oC ............................................................... 139
6.3.5 Interaction of HCl with clean Cu(111) surface at room temperature ......................................... 140
6.3.6 Interaction of HCl with O/Cu(111) surface at room temperature .............................................. 144
6.3.7 Interaction of HCl with „‟44‟‟ structure of oxygen at a Cu(111) surface at room temperature . 152
6.3.8 Interaction of HCl with „‟29‟‟ structure of oxygen on top of the Cu(111) surface at room
temperature ......................................................................................................................................... 155
6.4 Conclusion .................................................................................................................................... 160
6.5 References ..................................................................................................................................... 163
7.1 Introduction ................................................................................................................................... 166
7.2 Experimental ................................................................................................................................. 171
7.3 Results and discussion .................................................................................................................. 171
7.3.1 Interaction of clean Cu(100) with gold low coverage to half monolayer) ............................. 171
7.3.2 Interaction of clean Cu(100) with gold at a coverage more than half monolayer .................. 174
7.3.3 Interaction of HCl with Au/Cu(100) alloy at half monolayer coverage of gold .................... 176
7.3.4 Interaction of HCl with Au/Cu(100) alloy at more than half monolayer coverage of gold ... 180
7.3.5 Interaction of oxygen with Au/Cu(100) alloy at half monolayer coverage of gold ............... 184
7.3.6 Interaction of gold with Cu(100) precovered with (√2x2√2)R45o of oxygen reconstruction 188
7.4 Conclusions ................................................................................................................................... 194
7.5 References ..................................................................................................................................... 197
8.1 Introduction ................................................................................................................................... 200
8.2 Interaction of HCl with Cu(100) and (111)................................................................................... 200
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8.3Influence of oxygen on the interaction of Cu(100) and (111) with HCl ........................................ 200
8.4 Influence of gold on the interaction of Cu(100) with HCl ............................................................ 201
8.5 Summary ....................................................................................................................................... 202
8.6 Future work ................................................................................................................................... 202

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Chapter 1 Introduction
Contents
1.1 Single Crystal of metal surface .......................................................................................... 11
1.2 Miler indices ...................................................................................................................... 11
1.3 Surface structures and reactivity ........................................................................................ 12
1.4 Atomic densities of atoms in the surface plane ................................................................. 14
1.5 Adsorption.......................................................................................................................... 14
1.5.1 Physisorption ............................................................................................................... 15
1.5.2 Chemisorption ............................................................................................................. 15
1.5.3 Adsorption isotherm .................................................................................................... 17
1.6 Surface science and heterogeneous catalysis ..................................................................... 18
1.7 Copper and gold as a catalyst ............................................................................................. 20
1.8 References .......................................................................................................................... 24

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