Abstract
Contents
Abstract 1
Zusammenfassung 3
1 Introduction: the role of in situ studies in surface science 5
1.1 In situ vs ex situ studies ................................................................................................. 6
1.2 Scope and contents of the thesis................................................................................... 8
2 Metal Oxide Surfaces 11
2.1 The TiO2(110) surface.................................................................................................... 11
2.1.1 Structure of the TiO2( 110) surface................................................................. 12
2.1.2 Preparation of the TiO2(110) surface.............................................................. 14
2.1.3 Water adsorption on the TiO2(110) surface.................................................. 15
2.1.4 Adsorption of HCOOH on the TiO2(110) surface......................................... 16
2.1.5 Photocatalysis on the TiO2(110) surface: photocleaning and photoswitching 18
2.2 The Fe3C>4(001) surface................................................................................................. 20
2.2.1 Structure of the Fe304(001) surface................................................................. 21
2.2.2 Preparation of a Fe304(001)-(v/2 x \/2)R45o surface................................... 23
2.2.3 Adsorption of gas molecules on the Fe304(001) SCV surface..................... 24
2.2.4 Single metal atom adsorption on Fe304(001) ............................................... 26
3 Experimental methods and techniques 29
3.1 X-ray Photoelectron Spectroscopy (XPS).................................................................... 29
3.1.1 Basic theory of XPS........................................................................................... 29
3.1.2 XPS and instrumentation.................................................................................. 32
3.1.3 Quantification of XPS spectra.......................................................................... 34
3.2 APXPS and the sample environment .......................................................................... 37
3.3 LEED................................................................................................................................. 43
3.4 Density Functional Theory and Molecular Dynamics................................................ 45
4 The SLIC endstation for APXPS at the SwissLightSource 49
4.1 The SLIC endstation...................................................................................................... 49
4.1.1 Analyzer and light sources................................................................................ 50
4.1.2 Analysis chamber................................................................................................. 51
4.1.3 Load-lock / transfer chamber ............................................................................ 53
4.1.4 Preparation chamber ........................................................................................... 54
4.2 Endstation commissioning: potential control and possible experiments ............... 55
5 Carbon contamination in APXPS experiments 61
5.1 Experimental materials and methodology...................................................................... 62
5.1.1 Additional materials and details......................................................................... 62
5.1.2 Fitting procedure and parameters...................................................................... 63
5.2 Experimental results and discussion............................................................................... 65
5.2.1 In situ vs ex situ sample preparation................................................................... 65
5.2.2 The synchrotron beam influence over carbon contamination ..................... 67
5.2.3 The role of gas pressure in carbon contamination........................................... 68
5.2.4 The role of molecular oxygen gas in APXPS experiments........................... 70
5.3 Conclusion - the role of H2O, O2 and impinging photons in TiO2(110) surface
cleaning .............................................................................................................................. 75
6 Dynamic equilibrium at the HCOOH-saturated TiO2(110)-water interface 77
6.1 Additional material and methodology details................................................................ 78
6.1.1 Additional material and experimental methodology .................................... 78
6.1.2 Computational model and methodology......................................................... 79
6.2 Experimental results (XPS and LEED)........................................................................ 83
6.3 Computational results........................................................................................................ 87
6.4 Conclusions.......................................................................................................................... 90
7 Ir single atoms on the FesO^OOl) surface in near-ambient conditions 93
7.1 Experimental materials and methodology....................................................................... 95
7.1.1 Additional material and experimental details................................................ 95
7.1.2 Data acquisition and fitting procedure.............................................................. 95
7.2 Experimental results and discussion................................................................................ 97
7.2.1 Benchmark spectra under HV conditions......................................................... 97
7.2.2 Exposure to CO,O2and Ar.....................................................................................IOO
7.2.3 Exposure to H2.........................................................................................................I04
7.2.4 Exposure to N2.........................................................................................................105
7.2.5 Exposure to watervapor.........................................................................................107
7.2.6 Gas exposure at elevated temperatures................................................................108
7.3 Conclusions........................................................................................................................... HI
8 Closing statements 113
Comini, Nicolo