Prof Claire Carmalt

Research Overview

Research in my laboratory is based around the application of organometallic chemistry to problems in materials deposition, most notably in connection with the development of "designed" molecular precursors targeted for thin film growth by chemical vapour deposition (CVD). CVD is often the preferred industrial method for thin film growth to materials with important industrial applications (e.g. photovoltaics), but is limited by the availability of suitable precursors. We have built a number of CVD rigs for the deposition of thin films using the novel precursors developed. We are particularly interested in the use of solution based CVD and often use aerosol-assisted (AA)CVD. AACVD uses a liquid-gas aerosol to transport soluble precursors to a heated substrate and is a useful method when a conventional atmospheric pressure CVD precursor proves involatile or thermally unstable.

Current research focuses on:

  • Synthesis of Molecular Precursors.
  • Aerosol-assisted chemical vapour deposition.
  • Low pressure chemical vapour deposition.
  • Combinatorial CVD routes to metal oxides in collaboration with Professor Ivan Parkin.

Synthesis of Molecular Precursors

Designing the ideal precursor is a significant challenge since it must be volatile, non-toxic, low melting and thermally stable. The synthesis of these precursors is difficult, involving highly air- and moisture-sensitive reagents, which require demanding researcher skills. We have developed new precursors, with significantly improved physical properties and decomposition characteristics, particularly for oxides, sulfides, selenides and nitrides. Characterisation of the complexes involves NMR, Mass Spec, FTIR, elemental analysis, TGA and X-ray crystallography.

Metal Oxides

Metal oxide films have attracted attention because of their potential for a range of applications. For example, thin films of gallium oxide have been tested as gas sensors. In contrast, indium oxide films find application as transparent conductive oxide (TCO) coatings, which exhibit high transmittance in the visible spectral region, high reflectance in the Infrared region and nearly metallic conductivity. Work has focused on the development of modified metal alkoxides, using donor functionalized ligands, which have an increased coordinative saturation at the metal centre and result in precursors with improved volatility and solubility.

Molecular Structure of a monomeric gallium bis(alkoxide)Molecular Structure of a dimeric indium mono(alkoxide)

Figure 1. Molecular Structure of a monomeric gallium bis(alkoxide) and a dimeric indium mono(alkoxide).

Transition Metal Nitrides and Carbonitrdes

Compounds containing guanidinate ligands are of interest as precursors to metal nitride thin films, due to their nitrogen content, potential to increase the volatility of the compound and their ability to stabilise the metal centre due to their electronic flexibility. We have developed some zirconium guanidinate compounds as LPCVD precursors to zirconium carbonitride.

Synthesis of zirconium guanidinate complexesStructure of zirconium guanidinate complexes

Figure 2. Synthesis and structure of zirconium guanidinate complexes.

We have also developed a range of tungsten imido complexes to produce precursors with the best thermal properties for CVD of tungsten carbonitride. We successfully tuned the ligands surrounding the tungsten centre to optimise the thermal properties of the precursors to produce the tungsten carbonitride thin films, which are used as barrier layers.

Synthesis of tungsten imido complexes


Figure 3. Synthesis of tungsten imido complexes.

Aerosol-assisted chemical vapour deposition

Transparent, unreflective films of Ga2O3 have been produced from [Ga(NMe2)3]2 and ROH (R = donor-functionalised ligand) by AACVD on glass. Due to the influence of the solvent on the deposition, AACVD can lead to unique or different morphologies that could potentially result in improved properties.

AACVD route to Ga 2 O3AACVD route to Ga2O3 highlighted on front cover of Dalton Transactions

Figure 4. AACVD route to Ga­2­O3 as highlighted on front cover of Dalton Transactions.

The in situ reaction of the reagents eliminates the need for the synthesis, isolation and purification of a single-source metal alkoxide precursor and represents a facile method for the formation of these films, without the necessity of oxygen carrier gas.

Thin films are characterised by SEM/EDAX, WDX, XPS, powder XRD, UV-vis, FTIR and Raman spectroscopy.

Low Pressure chemical vapour deposition

Low pressure chemical vapour deposition of four closely related precursors: [W(µ-NtBu)(NtBu)Cl2(H2NtBu)]2, [W(NtBu)2Cl2(TMEDA)], [W(NtBu)2Cl2(py)2] and [W(NtBu)2Cl(N{SiMe3}2)] resulted in the deposition of grey mirror-like crystalline films of b-WNxCy at 550 oC . In all cases the chlorine content of the deposited film was less than 1 at.% and the films were deposited with either a nitrogen or ammonia bleed. The presence of ammonia reduced the oxygen content of the films, but surprisingly did not change the carbon content of the resulting films.

LPCVD of WNxCy as highlighted on front cover of Dalton TransactionsLPCVD of WNxCy


Figure 5. LPCVD of WNxCy as highlighted on front cover of Dalton Transactions

Acknowledgements

We thank EPSRC, Applied Materials and SAFC Hitech for financial support. 

Selected Publications

  1. “Syntheses, X-ray structures and CVD of titanium(IV) arsine complexes”. Thomas T., Pugh D., Parkin I. P., Carmalt C. J.,* Dalton Trans, 2010, 5325-5331.
  2. “Synthesis of Zirconium Guanidinate Complexes and the Formation of Zirconium Carbonitride via Low Pressure CVD”. Potts S. E., Carmalt C. J.,* Blackman C. S., Abou-Chahine F., Pugh D., Davies H. O., Organometallics, 2009, 28, 1838-1844
  3. “Dimethylalkoxygallane incorporating a donor-functionalised alkoxide: the monomeric gas-phase structure”. Knapp C. E., Carmalt C. J.,* McMillan P. F., Wann D. A., Robertson H. E., Rankin D. W. H., Dalton Trans, 2008, 6880-6882.
  4. “Tungsten imido complexes as precursors to tungsten carbonitride thin films”. Potts S. E., Carmalt C. J.,* Blackman C. S., Leese T., Davies H. O., Dalton Trans, 2008, 5730-5736.
  5. “Gallium oxide thin films from the AACVD of [Ga(NMe2)3]2 and donor functionalised alcohols”. Basharat, S., Carmalt, C. J.,* Binions, R., Palgrave, R., Parkin, I. P., Dalton Trans. 2008, 591-595.
  6. “Aerosol assisted chemical vapor deposition of In2O3 films from Me3In and donor functionalized alcohols” Basharat S., Carmalt C. J.,* Barnett S. A., Tocher D. A., Davies H. O. Inorg. Chem. 2007, 46, 9473-9480.