A novel technique to monitor ultrafast photoinduced chemical reaction dynamics at surfaces [Elektronische Ressource] : the femtochemistry of methyl halide molecules adsorbed on oxides, metals and oxide supported metal clusters / vorgelegt von Mihai Emilian Vaida

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A novel technique to monitor ultrafast photoinduced chemical reaction dynamics at surfaces: The femtochemistry of methyl halide molecules adsorbed on oxides, metals and oxide supported metal clusters Dissertation zur Erlangung des Doktorgrades Dr. rer. nat. der Fakultät für Naturwissenschaften der Universität Ulm vorgelegt von Mihai Emilian Vaida aus Deva, Rumänien 2010 Amtierender Dekan: Prof. Dr. A. Groß 1. Gutachter: Prof. Dr. T. M. Bernhardt 2. Gutachter: Prof. Dr. H. Jones Tag der Promotion: 21.07.2010 Contents ABBREVIATIONS .................................................................................................................. 7 ABSTRACT .............................................................................................................................. 9 1 INTRODUCTION AND MOTIVATION ................................................................ 11 2 EXPERIMENTAL: GENERAL ASPECTS ............................................................ 15 2.1 Vacuum apparatus ................................................................................................................................ 16 2.1.1 Surface science chamber .................................................................................................................... 18 2.1.2 Sample holder .......................................................................
Publié le : vendredi 1 janvier 2010
Lecture(s) : 22
Source : VTS.UNI-ULM.DE/DOCS/2010/7401/VTS_7401_10507.PDF
Nombre de pages : 217
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A novel technique to monitor ultrafast photoinduced
chemical reaction dynamics at surfaces:
The femtochemistry of methyl halide molecules
adsorbed on oxides, metals and oxide supported
metal clusters







Dissertation
zur Erlangung des Doktorgrades
Dr. rer. nat.
der Fakultät für Naturwissenschaften
der Universität Ulm




vorgelegt von
Mihai Emilian Vaida
aus Deva, Rumänien

2010

























Amtierender Dekan: Prof. Dr. A. Groß
1. Gutachter: Prof. Dr. T. M. Bernhardt
2. Gutachter: Prof. Dr. H. Jones
Tag der Promotion: 21.07.2010







Contents
ABBREVIATIONS .................................................................................................................. 7
ABSTRACT .............................................................................................................................. 9
1 INTRODUCTION AND MOTIVATION ................................................................ 11
2 EXPERIMENTAL: GENERAL ASPECTS ............................................................ 15
2.1 Vacuum apparatus ................................................................................................................................ 16
2.1.1 Surface science chamber .................................................................................................................... 18
2.1.2 Sample holder ..................................................................................................................................... 19
2.2 Analytical tools ...................................................................................................................................... 21
2.2.1 Surface investigation by electron-based analytical methods .............................................................. 21
2.2.1.1 Low energy electron diffraction ..................................................................................................... 22
2.2.1.2 Auger Electron Spectroscopy ......................................................................................................... 25
2.2.1.3 Electron energy loss spectroscopy ................................................................................................. 26
2.2.2 Photoemission spectroscopy ............................................................................................................... 27
2.2.3 Temperature programmed desorption ................................................................................................. 30
2.2.3.1 Kinetics of temperature programmed desorption ........................................................................... 32
2.2.3.2 Redhead equation ........................................................................................................................... 33
2.3 Cluster sources ...................................................................................................................................... 34
2.3.1 Gold evaporator .................................................................................................................................. 34
2.3.2 Production of mass-selected Au clusters ............................................................................................ 35
2.4 Laser system .......................................................................................................................................... 37
2.4.1 Ti:Sapphire active medium ................................................................................................................. 38
2.4.2 Femtosecond oscillator ....................................................................................................................... 38
2.4.3 Pulse amplification ............................................................................................................................. 41
2.4.4 Wavelength conversion ...................................................................................................................... 43
2.4.5 Pulse characterization ......................................................................................................................... 46
2.4.5.1 Spectral measurements ................................................................................................................... 46
2.4.5.2 Pulse temporal profile .................................................................................................................... 46
3 SURFACE FS PUMP-PROBE MASS SPECTROMETRY ................................... 49
3.1 Time-of-flight mass spectrometry: General aspects ........................................................................... 50
3.2 SFsMS: Experimental realization ........................................................................................................ 53
3.3 Molecular adlayer preparation ............................................................................................................ 54
3.4 Fs-laser excitation and ionization of molecules at the surface .......................................................... 55
3.4.1 Wavelength ......................................................................................................................................... 55
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3.4.2 Polarization ......................................................................................................................................... 58
3.4.2.1 Polarization in direct surface photodissociation ............................................................................. 64
3.4.2.2 Polarization in substrate mediated dissociation .............................................................................. 65
3.4.3 Intensity .............................................................................................................................................. 66
3.4.3.1 Pump intensity ................................................................................................................................ 66
3.4.3.2 Probe intensity ................................................................................................................................ 66
3.5 Mass, time, and velocity resolved measurements ............................................................................... 69
3.5.1 Pump-probe schema ........................................................................................................................... 69
3.5.1.1 Surface photoexcitation .................................................................................................................. 69
3.5.1.2 REMPI detection ............................................................................................................................ 71
3.5.2 Transient recording routine ................................................................................................................ 71
3.5.3 Time zero determination ..................................................................................................................... 73
3.5.4 Evaluation of the SFsMS data ............................................................................................................ 75
3.5.4.1 Potential energy diagram ................................................................................................................ 75
3.5.4.2 Fitting procedure ............................................................................................................................ 77
4 SURFACE PREPARATION AND CHARACTERIZATION ............................... 79
4.1 MgO(100) on Mo(100) .......................................................................................................................... 80
4.1.1 Preparation of ultrathin MgO films on Mo(100) ................................................................................ 80
4.1.2 Geometric structure of ultrathin MgO films on Mo(100) ................................................................... 83
4.1.3 PES of Mo(100) covered by ultrathin MgO(100) films of variable thickness .................................... 85
4.1.3.1 Excitation energy dependent photoemission .................................................................................. 85
4.1.3.2 Coverage dependent photoemission ............................................................................................... 90
4.2 Gold films on a molybdenum single crystal surface ........................................................................... 93
4.2.1 Preparation of Au films on Mo(100) .................................................................................................. 93
4.2.2 Structure of Au films grown on Mo(100) ........................................................................................... 97
4.3 Magnesia supported gold clusters ...................................................................................................... 100
4.3.1 Fs-Laser photoemission from magnesia supported gold clusters ..................................................... 101
4.3.2 Estimation of the gold particle size .................................................................................................. 104
5 METHYL IODIDE ................................................................................................... 107
5.1 Methyl iodide on magnesia ................................................................................................................. 108
5.1.1 Temperature programmed desorption ............................................................................................... 108
5.1.2 Real-time photoreaction dynamics ................................................................................................... 109
5.1.2.1 Unimolecular reaction .................................................................................................................. 109
5.1.2.2 Bimolecular reaction .................................................................................................................... 117
5.1.3 Influence of magnesia thin film layer thickness on the methyl iodide photochemistry .................... 121
5.1.4 Influence of the MgO stoichiometry and composition on the methyl iodide thermal desorption and
photodissociation .............................................................................................................................. 124
5.2 Methyl iodide on gold ......................................................................................................................... 131
5.2.1 Temperature programmed desorption and reaction .......................................................................... 131
5.2.2 Photoemission spectroscopy ............................................................................................................. 132
5.2.3 Methyl iodide photochemistry on gold ............................................................................................. 135
5.2.3.1 Methyl iodide photodissociation on a gold surface ...................................................................... 135
5.2.3.2 Trapping of the I atoms at the surface subsequent to CD I photodissociation on Au .................. 136 3
5.3 Methyl iodide on magnesia supported gold nanoparticles .............................................................. 141
5.3.1 Methyl iodide adsorption on magnesia supported gold nanoparticles .............................................. 141
5.3.2 Photodissociation dynamics ............................................................................................................. 142
5.3.3 Methyl iodide reactivity with very small gold clusters ..................................................................... 144
5.4 Conclusions .......................................................................................................................................... 146
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6 METHYL BROMIDE .............................................................................................. 147
6.1 Methyl bromide on magnesia ............................................................................................................. 148
6.1.1 Temperature programmed desorption ............................................................................................... 148
6.1.2 Real-time photodissociation dynamics ............................................................................................. 149
6.1.3 Influence of the magnesia film thickness on the methyl bromide photodissociation dynamics ....... 155
6.2 Methyl bromide adsorption and photodissociation on gold ............................................................ 160
6.2.1 Temperature programmed desorption ............................................................................................... 160
6.2.2 Photodissociation dynamics ............................................................................................................. 161
6.3 Methyl bromide adsorption and photodissociation on magnesia supported gold clusters ........... 164
6.3.1 Temperature programmed desorption ............................................................................................... 164
6.3.2 Photodissociation dynamics ............................................................................................................. 167
6.3.3 Gas-phase reactivity measurements .................................................................................................. 171
6.4 Conclusions .......................................................................................................................................... 172
7 METHYL HALIDE ADSORPTION AND SURFACE FEMTOCHEMISTRY:
COMPARISON AND CONCLUSIONS ................................................................ 175
7.1 Electronic structure ............................................................................................................................ 176
7.2 Adsorption behavior ........................................................................................................................... 176
7.2.1 Adsorption on MgO films on Mo(100)............................................................................................. 177
7.2.2 Adsorption on Au films on Mo(100) ................................................................................................ 177
7.2.3 Adsorption on magnesia supported gold clusters ............................................................................. 177
7.3 Photochemistry .................................................................................................................................... 178
7.3.1 Photochemistry on MgO films on a Mo(100) ................................................................................... 178
7.3.1.1 8-10 ML MgO/Mo(100) ............................................................................................................... 178
7.3.1.2 Mo(100) and 1-6 ML MgO/Mo(100) ........................................................................................... 179
7.3.2 Photochemistry on Au films on Mo(100) ......................................................................................... 180
7.3.3 Photochemistry on Magnesia supported gold clusters ...................................................................... 180
7.3.3.1 Small gold clusters and nanoparticles .......................................................................................... 180
7.3.3.2 3D gold nanoparticles .................................................................................................................. 180
7.4 Conclusions and future directions ..................................................................................................... 183
ZUSAMMENFASSUNG ..................................................................................................... 185
BIBLIOGRAPHY ................................................................................................................ 187
CURRICULUM VITAE ...................................................................................................... 205
LIST OF PUBLICATIONS ................................................................................................. 207
CONFERANCE CONTRIBUTIONS ................................................................................. 209
ACKNOWLEDGEMENTS ................................................................................................. 213


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Abbreviations
2D Two dimensional
2PPS Two-Photon Photoemission Spectroscopy
3D Three dimensional
AES Auger Electron Spectroscopy
AOM Acousto Optical Modulator
BBO β-Barium Borate
bcc Body Centered Cubic
CCD Charge Coupled Device
CORDIS Cold Reflex Discharge Ion Source
CPA Chirped Pulse Amplification
cw Continuous Wave
DEA Dissociative Electron Attachment
EELS Electron Energy Loss Spectroscopy
E Fermi Level F
E Primary Energy P
EPR Electron Paramagnetic Resonance
E Vacuum Level VAC
fcc Face Centered Cubic
fs Femtosecond
FWHM Full Width at Half Maximum
GPIB General Purpose Interface Bus
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GVD Group Velocity Dispersion
IR Infrared
HREELS High Resolution Electron Energy Loss Spectroscopy
L Langmuir
LEED Low Energy Electron Diffraction
LN Liquid Nitrogen 2
MCP Micro Channel Plate
MCS Multi-Channel Scaler
MIES Metastable Impact Electron Spectroscopy
ML Monolayer equivalent
OPA Optical Parametric Amplifier
PES Photoemission Spectroscopy
PID Proportional-Integral-Differential
rf Radio Frequency
RGA Residual Gas Analyzer
SFsMS Surface Femtosecond Mass Spectrometry
SFM Sum Frequency Mixing
SHG Second Harmonic Generation
STM Scanning Tunneling Microscopy
TPD Temperature Programmed Desorption
THG Third Harmonic Generation
TOF-MS Time-of-Flight Mass Spectrometer
TOF-PES Time-of-Flight Photoelectron Spectrometer
UHV Ultra High Vacuum
UV Ultraviolet

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