Nanoparticles ofScandium Oxide, Zirconium Oxide and Hafnium Oxide in Alcoholic Medium, used ...

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Nanoparticles of Scandium Oxide, Zirconium Oxide
and Hafnium Oxide in Alcoholic Medium, used
for High Index Optical Coatings at 351nm
Thesis submitted to the University of Surrey
for the Degree of
Doctor of Philosophy in Chemistry
by David Grosso
Key words: Scandium oxide
Sol-gel chemistry
Thin optical films
Department of chemistry
School of physical science
University of Surrey,
Guilford, GU2 5XH, United Kingdom. Date: December 1998
a
Sebastien
Acknowledgements
I acknowledge the support by the United Kingdom Ministry of Defence.
I would like to thank my supervisor Professor P. A. Sermon for accepting me in his
research group and supervising me in my research.
I would like to thank (i) J. Andrew and N. Bazin (AWE) for damage testing and XPS
analysis, (ii) M. Commandre (Laboratoire d'Optique de Surface et Couches Minces of
a
Marseille) for photothermal deflection analysis, (iii) A. Fomier (Commissariat
l'Energy Atomic of Limeil-Valenton) for laser damage testing and useful advice, (iv)
Prof. P. Foot (University of Kingston) for access to XRD, and (v) M. Vickers
(Department of Materials Science and Metallurgy of Cambridge University) for SAXS
analyses, (vi) R. Badheka for the preparation of Si02 and MgF2 sol coatings (used to
support scandia coatings whose use is described in VII-2-1», and (vii) the staff in the
University of Surrey for their assistance.
I would like to acknowledge the support, help and friendship of S. Camus, N. Quentel,
J. Mendez-Vivar, R. Badheka, S. Roesch, T. Salvesen and F. Getton during these two
and a half years.
Finally, I would like to thank my parents without whom, despite the geographical
distance, this would not have been possible.
Abstract
SC203, Hf02 and Zr02 colloidal nanoparticles have been synthesised by sol-gel
chemistry from organometallic precursor in alcoholic medium. Hafnia and zirconia
particles were spherical and less than 5nm in diameter. Scandia particles were lozenge
shaped platelets of 70 x 40 x 8nm in dimension. Sol stability was analysed by viscosity
measurement. Particle morphologies were characterised by TEM, XRD and SAXS
analyses. Scandia, hafnia and zirconia xerogels were obtained by solvent evaporation at
room temperature and pressure. Bulk materials had structures, thermal stabilities and
compositions deduced by XRD, TGA-DSC, EDX, N2-BET adsorption-desorption and
FfIR spectrometry. Elementary analyses were undertaken to study the mechanisms of
synthesis. Present and potential applications of the so formed xerogel materials are
discussed. Optical coatings to be used at 351nm were produced on fused silica
substrates by dip coating from stable scandia hafnia and zirconia sols. Coatings
containing organic impurities were purified via chemical or thermal treatment, or
solvent extraction. The optical properties (absorption, scattering, reflection,
transmission, refractive index), compositions, homogeneity and surface topologies of
these thin films were obtained by UV transmission, photothermal deflection at 520nm,
XPS and AFM investigations. Resistance to laser radiation at 351nm was also measured
for xerogel coatings of quarter wavelength thick. These coatings exhibited high
refractive indices, good structural homogeneity and good resistance to laser damage.
Future uses of such coatings are considered.
CONTENT page 1
Acknowledgement
Abstract
7
Introduction and aims of the work
10
References
.
Chapter I FUNDAMENTALS OF SOL-GEL CHEMISTRY
1-1 The Chemistry of Metal Oxides 12
1-2 The Partial Charge Distribution Model 13
1-2-1 Electronegativity Equalisation 15
1-2-2 Determination of the Mean Electronegativity X 15
1-2-3 Determination of Coordination Number 16
1-3 The Sol-Gel Transition 17
1-4 The Sol-Gel Chemistry of Transition-Metal Oxides in Aqueous Media 20
1-4-1 Mechanisms of Hydrolysis 20
1-4-2 Mechanisms of Condensation 21
1-4-3 Influence of the Counter Ion 25
1-5 The Sol-Gel Chemistry ofTransition Metal Oxides in Organic Media 25
1-5-1 Mechanisms of Hydrolysis 26
1-5-2 Mechanisms of Condensation 27
1-5-3 Ligand Exchange Reactions 28
1-5-4 Influence of the Metal Atom 29
1-5-5 Nature of the Organic Ligand 30
1-5-6 Precursor Concentration 30
1-5-7 Nature of the Solvent 31
1-5-8 Water Content 32
1-5-9 Catalysts 33
1-5-10 Temperature 33
1-5-11 Agents of Chemical Modification 33
1-5-12 Phenomenon of Aggregation 34
CONTENT page2
1-6 Types of Gel 35
1-6-1 Aerogel 36
1-6-2 Xerogel 36
1-6-3 Sonogel 37
1-6-4 Cryogel 37
1-6-5 Additional gels 37
1-7 Types of Ceramic Preforms 37
1-7-1 Fibres 38
1-7-2 Films and coatings 38
1-7-3 Monoliths 39
1-8 Techniques of Characterisation 39
1-8-1 Sols 39
1-8-2 Gels 40
1-8-3 Coatings 40
References 41
Chapter II THE SOL-GEL CHEMISTRY OF SCANDIA
II-I Scandium Oxide 44
U-l-l Interesting Properties 44
U-I-2 General Chemistry 44
U-I-3 Fields of Application 46
11-2 Sol-Gel Processing of Lozenge-Shaped Nanoparticles 48
U-2-1 Introduction on Scandium Acetylacetonate (ACAC) 48
U-2-2 Experimental Synthesis of Scandia Lozenge Particles 51
11-2-3 Viscosity of Scandia Sols 51
U-2-4 Characterisation of Scandia Particles by TEM 52
U-2-5 Characterisation of Scandia Particles by SAXS 54
U-2-6 Characterisation of Scandia Xerogels by FTIR 57
U-2-7 Characterisation of Scandia Xerogels by TGA-DSC 59
11-2-8 Characterisation of Scandia Xerogels by XRD 60
11-2-9 Characterisation of Scandia Xerogels by N2-BET 63
CONTENT page 3
II-2-10 Influence of Refluxing Time and Water Content
on the Scandia Particle Composition, Measured by Elemental Analysis 65
11-3 Discussion and Proposed Mechanism of Formation
of Scandia Lozenge Particles 70
11-4 Sol-Gel Processing of SC203(extension of the chemical investigation) 73
II-4-1 Acid Catalysis 73
II-4-2 Base Catalysis 76
11-5 Conclusions on Scandia Sol-Gel Chemistry 77
References 78
Chapter III THE SOL-GEL CHEMISTRY OF HAFNIA
82
111-1 Hafnium Oxide
Ill-l-l Interesting Properties 82
III-1-2 General Chemistry 83
III-1-3 Fields of Application 84
111-2 Sol-Gel Processing of Hf02 from a Hf(OPr)4 Precursor 84
III-2-1 Introduction on Hafnium n-Propoxide 84
III-2-2 Experimental Synthesis of Spherical HafniaParticles 85
III-2-3 Characterisation of Hafnia Particles by TEM 87
III-2-4 Characterisation of Hafnia Xerogels by FfIR 89
III-2-5 Characterisation of Hafnia Xerogels by TGA-DSC 91
III-2-6 Characterisation of Hafnia Xerogels by XRD 92
III-2-7 Determination of the Average Hafnia Particle Sizeby XRD 94
III-2-8 Characterisation of Hafnia Xerogels by NrBET 94
95
III-3 Conclusions on Hf02 Sol-Gel Chemistry
References 97
Chapter IV THE SOL-GEL CHEMISTRY OF ZIRCONIA
100
IV-1 Zirconium Oxide
100
CONTENT page4
IV-l-l Interesting Properties
IV-I-2 General Chemistry 100
IV-I-3 Fields of Application 101
IV-2 Sol-Gel Processing of Zr02 from a Zr(OPr)4 Precursor 102
IV-2-1 Introduction on Zirconium n-Propoxide 102
IV-2-2 Experimental Synthesis of Spherical Zirconia Particles 103
IV-2-3 Characterisation of Zirconia Particles by TEM 104
IV-2-4 Characterisation of Zirconia Xerogels by FTIR 105
IV-2-5 Characterisation of Zirconia Xerogels by TGA-DSC 107
IV-2-6 Characterisation of Zirconia Xerogels by XRD 108
IV-2-7 Determination of the Average Zirconia Particle Size by XRD 109
IV-2-8 Characterisation of Zirconia Xerogels by N2-BET 110
IV-3 Conclusions on ZrOz Sol-Gel Chemistry 110
References 111
Chapter V PROCESSING OF OPTICAL COATINGS
V-I Fundamental Aspects of Liquid Deposition Methods 114
V-l-l Spray Coating 115
V-I-2 Meniscus Coating 115
V-I-3 Spin Coating 116
V-I-4 Dip Coating 116
V-2 Optical Properties of Coatings 119
VI-2-1 Dielectric Films 119
VI-2-2 Periodically Stratified Media 123
VI-2-3 Determination of nn and h of a Thin Film 125
V-3 Experimental Dip Coating 127
V-3-1 Substrate Preparation for Dip Coating 127
V-3-2 Sols and Method of Dip Coating 129
V-3-3 Adjustment of the Withdrawal Rate 131
V-3-4 Thermal Treatment of Scandia Coatings 131
V-3-5 Solvent Extraction of Scandia Coatings 132
pageS
CONTENT
V-3-6 Chemical Treatment of Scandia Coatings 133
References 133
Chapter VI CHARACTERISATION OF COATINGS
VI-l AFM Characterisation of Coatings 136
VI-l-l Determination of Cracks in aSilica Gel Coating by AFM 136
VI-1-2 Scandia Coatings 137
VI-I-3 Zirconia Coatings 140
VI-1-4 Hafnia Coatings 142
VI-I-5 Discussion on Surface Topography 144
VI-2 XPS Characterisation of Coatings 146
VI-2-1 Experimental Results 147
VI-2-2 Scandia Coatings 150
VI-2-3 Zirconia Coatings 153
VI-2-4 Hafnia Coatings 155
VI-2-5 Discussion on Coating Composition 157
VI-3 UV-Transmission Characterisation of Coatings 157
VI-3-1 Scandia Coatings 158
VI-3-2 Zirconia Coatings 161
VI-3-3 Hafnia Coatings 163
VI-3-4 Discussion on Coating Optical Properties 164
VI-4 PD Characterisation of Coatings 165
VI-4-1 Scandia Coatings 168
VI-4-2 Zirconia Coatings 169
VI-4-3 Hafnia Coatings 169
VI-4-4 Discussion on Absorption and Scattering ofCoatings 169
VI-S Conclusions on Characterisation of Coatings 170
References 172
CONTENT page 6
Chapter VII APPLICATION OF COATINGS to
3m LASER OPTICAL DEVICES
VII-l LIDT Measurement Techniques 175
VII-l-l The Inertial Confinement Fusion Program: the Nova Facility 175
VII-l- 2 Measurement of the Laser Induced Damage Threshold (LIDT) 177
VII-I-3 Experimental Procedure of LIDT Measurement 177
VII-I-4 Mechanisms of Damage Formation 178
VII-2 Analysis of Damage and Laser Resistance 180
VII-2-1 Scandia Coatings 181
VII-2-2 Zirconia Coatings 188
VII-2-3 Hafnia Coatings 189
VII-3 Conclusion, Comparison Between Scandia, Zirconia and Hafnia LIDT 189
References 190
Conclusions and Further work
192
Annexes A: Princil!les of Technigues
A-I Transmission Electron Microscopy (TEM) and Shadowing
1
A-2 X-Ray Probe Analysis (EDX)
2
A-3 Small Angle X-Ray Scattering (SAXS)
3
A-4 Spectrophotometry IR (FfIR)
4
A-5 Thermogravimetry (TGA-DSC)
5
A-6 X-ray Diffraction (XRD)
5
A-7 Determination of Particle Sizes by XRD 6
A-8 UV spectrophotometry 7
A-9 Nitrogen Adsorption-Desorption Analysis (N2-BET) 8
A-1O Atomic Force Microscopy (AFM) 9
A-ll X-ray Photoelectron Spectroscopy (XPS) 10
A-12 Photothermal Deflection (PD) 11
A-13 Viscosity 15
Annexes B: Additional Figures 17