Synthesis of novel single-source precursors for CVD of mixed-metal tungsten oxide Hamid Choujaa A thesis submitted for the degree of Doctor of Philosophy University of Bath Department of Chemistry March 2008 COPYRIGHT Attention is drawn to the fact that copyright of this thesis rests with its author. This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognize that its copyright rests with its author and that no quotation the thesis and no information derived from it may be published without the prior written consent of the author. This thesis may be made available for consultation within the University Library and may be photocopied or lent to other libraries for the purposes of consultation. TABLE OF CONTENTS Abstract ....................................................................................................................................... i Acknowledgements .................................................................................................................... iii Abbreviations and Acronyms .................................................................................................... iv 1. INTRODUCTION .................................................................................................................. 1 1.1 Generality about tungsten(VI) oxide ............................................................................. 1 1.1.1 The different lattice structures of tungsten oxide ........................................... 1 1.1.2 Electronic and surface structure of WO3 ........................................................ 3 1.1.3 Properties and Applications ........................................................................... 5 1.1.3.1 Electrochromism, photochromism and thermochromism .............. 5 1.1.3.2 Photocatalysis .................................................................................. 7 1.1.3.3 Gas sensor ..................................................................................... 10 1.2 Fundamentals of Chemical Vapour Deposition (CVD) .............................................. 11 1.2.1 Basic principle of CVD ................................................................................ 11 1.2.2 CVD growth modes ...................................................................................... 12 1.2.3 Reactor design .............................................................................................. 13 1.2.3.1 Hot- and cold-wall reactors ........................................................... 13 1.2.3.2 Parameters influencing the film growth ........................................ 14 1.2.4 Precursor design ........................................................................................... 15 1.2.4.1 Requirements ................................................................................. 15 1.2.4.2 Molecular design ........................................................................... 16 1.2.4.3 Single-source approach for multi-components compounds .......... 18 1.2.5 Film deposition techniques ........................................................................... 20 1.2.5.1 Others variants of CVD ................................................................. 20 1.2.5.2 Comparison ................................................................................... 22 1.3 Chemical background .................................................................................................. 23 1.3.1 Tungsten chemistry ...................................................................................... 23 1.3.2. Electronic and structural aspects of metal ligand bonding .......................... 25 1.3.2.1 Bonding modes of ligands ............................................................. 25 1.3.2.2 Alkoxo ligand ................................................................................ 26 1.3.2.3 Amido ligand ................................................................................. 27 1.3.2.4 Imido ligand .................................................................................. 28 1.4 CVD chemistry of WO3 and mixed-metal tungsten oxide: WMxOy ........................... 29 1.4.1 Inorganic precursors: tungsten(VI) halides .................................................. 29 1.4.2 Metal organic precursor............................................................................... 29 1.4.2.1 Tungsten(VI) alkoxides and polyoxotungstate complexes ........... 29 1.4.2.2 Tungsten(VI) amides ..................................................................... 31 1.4.3 Organometallic precursors ........................................................................... 32 1.4.3.1 Tungsten carbonyl and derivatives ................................................ 32 1.4.3.2 Tungsten allyl ................................................................................ 33 1.5 Motivations, objectives and strategies ........................................................................ 33 1.6 References ................................................................................................................... 35 2 HOMO-METALLIC TUNGSTEN AMINO-ALKOXIDE COMPLEXES .......................... 39 2.1 Introduction ................................................................................................................. 39 2.2 Results and discussion ................................................................................................. 44 2.2.1 Synthesis of mononuclear tungsten amino-alkoxides .................................. 44 2.2.2 Synthesis of polynuclear tungsten amino-alkoxides .................................... 49 2.2.2.1 Crystal structures ........................................................................... 50 2.2.2.2 NMR spectroscopy ........................................................................ 63 2.2.3 Thermal decomposition studies and applications ......................................... 64 2.2.3.1 TGA measurements ....................................................................... 64 2.2.3.2 Thermal decomposition applications ............................................ 65 2.2.3.3 Characterisations ........................................................................... 67 2.3 Conclusion ................................................................................................................. 81 2.4 Experimental section ................................................................................................. 82 2.5 References ................................................................................................................. 86 3. HETERO-METALLIC TUNGSTEN ALKOXIDE COMPLEXES .................................... 88 3.1 Introduction ............................................................................................................... 88 3.2 Results and discussion ............................................................................................... 94 3.2.1 Synthesis of heterobimetallic tungsten amino-alkoxides ............................. 94 3.2.1.1 Crystal structures ........................................................................... 95 3.2.1.2 NMR spectroscopy ...................................................................... 107 3.2.2 Synthesis of heterobimetallic tungsten acetylacetonate alkoxide .............. 111 3.2.2.1 Crystal structures ......................................................................... 113 3.2.2.2 NMR spectroscopy ...................................................................... 116 3.2.3 Thermal decomposition studies and applications ....................................... 118 3.2.3.1 TGA measurements ..................................................................... 118 3.2.3.2 Thermal decomposition applications .......................................... 121 3.2.3.3 Characterisations ......................................................................... 122 3.3 Conclusion and future work .................................................................................... 133 3.4 Experimental section ............................................................................................... 134 3.5 References ............................................................................................................... 140 4 HOMO- AND HETERO-METALLIC TUNGSTEN AMIDES COMPLEXES ................ 142 4.1 Introduction ............................................................................................................. 142 4.2 Results and discussion ............................................................................................. 146 t t 4.2.1 Synthesis and structure of W( BuNH)2( BuN)2 .......................................... 146 t t t 4.2.2 Synthesis and structure of MeZn(NH2 Bu)(N Bu)2W(N Bu)Me ................ 149 4.2.3 Tungsten-picnogen amido compounds ....................................................... 152 t t t 4.2.3.1 Synthesis of Sb2W(NBu )(2-NBu )(3-NBu )2Cl3(2-Cl) ......... 152 t t t 4.2.3.2 Structure of Sb2W(NBu )(2-NBu )(3-NBu )2Cl3(2-Cl) .......... 153 t t t 4.2.3.3 NMR spectrum of Sb2W(NBu )(2-NBu )(3-NBu )2Cl3(2-Cl) 155 4.2.3.4 Hydrolysis products ..................................................................... 156 4.2.3.5 Crystal structures of the hydrolysis products .............................. 158 4.3 Conclusion ..............................................................................................................