Prof Claire Carmalt - Materials and Inorganic Chemistry

Materials Main group chemistry Transition chemistry Amido complexes Alkoxide complexes

Publications list tel: +44 (0)20 7679 7528 fax: +44 (0)20 7679 7463 internal: 27528 email: c.j.carmalt@ucl.ac.uk Biographical Details

Research within our group is based around the development of molecular precursors to a range of materials including transition metal nitrides, phosphides, sulfides and selenides and Group III nitrides and oxides. The research involves the development of innovative new routes to inorganic materials via chemical vapour deposition (CVD) and 'sol-gel' processes. A number of CVD rigs have been designed and built for the deposition of thin films. Films can be grown under a number of conditions using these rigs, for example at low pressure and aerosol-assisted. Most of the work involves the synthesis of air and/or moisture sensitive complexes and therefore extensive use of Schlenk and dry-box techniques. Characterisation of the complexes involves NMR, Mass Spec, FTIR, elemental analysis, TGA and X-ray crystallography. Thin films are characterised by SEM/EDAX, WDX, XPS, powder XRD, FTIR and Raman spectroscopy. Current research focuses on:

• Molecular Precursor routes to Group III oxides.
• Transition Metal Nitrides and Carbonitrdes.
• CVD routes to Transition Metal Sulfides and Selenides in collaboration with Professor Ivan Parkin.
• Formation of novel solid-state materials by combining organometallic molecular precursor chemistry with high pressure-high temperature materials synthesis in collaboration with Professor Paul McMillan.

Molecular Precursor Routes to Group III Oxides

Gallium oxide (Ga₂O₃) is considered to be one of the most ideal materials for application as thin film gas sensors at high temperatures. Indium oxide films are both transparent to visible light and conductive. Current work is concerned with developing new highly volatile CVD precursors to deposit oxide films free from contamination (e.g. C, F) . Recently, crystalline gallium oxide films have been deposited by low pressure CVD at 600^oC using the gallium sesquialkoxide shown in Figure 1. This is the first time that crystalline gallium oxide films have been deposited below 700^oC - probably achieved due to the correct ratio of Ga : O (2:3) for Ga₂O₃being present in the core of the molecular precursor.

Figure 1. Molecular Structure of the sesquialkoxide, [Ga{MeGa(OCH 2C 6H 4Me-4) 3} 3]

Transition Metal Nitrides and Carbonitrdes

We have been studying the reactivity of metal halides with silylamines and the formation of metal guanidinates in an attempt to isolate volatile single-source precursors to metal nitrides. The motivation for this work is to prepare good quality metal nitride/carbonitride films from a non-ammonia nitrogen source. Low pressure CVD produced metal nitride or metal carbonitride films on glass. The films produced have potential as decorative reflective coatings (Figures 2 and 3).

CVD routes to Transition Metal Sulfides and Selenides

Atmospheric pressure chemical vapour deposition (APCVD) of NbCl₅ and S(SiMe ₃) ₂, tBu₂S₂, tBuSH or HSCH₂CH₂SH at 250–600^oC afforded thin-films of niobium sulfide on glass. The sulfur precursor used is fundamental to the polytype of NbS₂ obtained; APCVD reaction of NbCl₅ and S(SiMe₃)₂ or tBu₂S₂ at 500–600^oC crystallize into the IT structure whereas those grown from the APCVD reaction of NbCl₅ and tBuSH or HSCH₂CH₂SH at 500–600^oC crystallize into the 3R structure. This work has recently been extended to metal selenides in collaboration with Professor Ivan Parkin.

Figure 4. SEM of the film deposited at 50oC from NbCl5 and tBu2S2(1T).	Figure 5. Structure of 1T-NbS2 as refined from grazing incidence PXD data. Thermal ellipsoids are shown at the 50% probability level.

High purity TiS₂ films have also been grown on glass from the in situ aerosol-assisted CVD reaction between [Ti(NMe₂)₄] and tert-butylthiol in a range of solvents. The in situ reaction eliminates the requirement to synthesise and purify a precursor. This discovery represents an expedient approach, which also reduces costs.

Acknowledgements

We thank EPSRC and SAFC Hitech for financial support. Professor Derek Tocher and Dr Sarah Barnet are thanked for X-ray crystallography.

Selected Publications

1. "Synthesis of Group 13 Sesquialkoxides and their Application as Precursors to Crystalline Oxide films". S. Basharat, W. Betchley, C. J. Carmalt,* S. Barnett, D. A. Tocher and H. O. Davies, Organometallics, 2007, 26, 403–407
2. " Molecular Precursors to Gallium Oxide Thin Films ". S. Basharat, C. J. Carmalt,* S. J. King, E. S. Peters and D. A. Tocher, Dalton Trans, 2004, 3475–3480
3. "Synthesis of Titanium(IV) Guanidinate Complexes and the Formation of Titanium Nitride via Low Pressure CVD". C. J. Carmalt,* A. C. Newport, S. A. O'Neill, I. P. Parkin, A. J. P. White and D. J. Williams, Inorg. Chem., 2005, 44, 615–619
4. "NbS 2 Thin Films by Atmospheric Pressure Chemical Vapour Deposition and the Formation of a New 1T Polytype". C. J. Carmalt,* T. D. Manning, I. P. Parkin, E. S. Peters, and A. L. Hector, Thin Solid Films, 2004, 469–470, 495–499
5. "Dual-Source Chemical Vapour Deposition of Titanium Sulfide Thin Films from Tetrakisdimethylamidotitanium and Sulfur precursors". E. S. Peters, C. J. Carmalt* and I. P. Parkin, J. Mater. Chem., 2004, 14, 3474–3477

This page last modified 20 October, 2009