Peter T. DawsonProfessor
B.Sc. (Birmingham), Ph.D. (Cambridge)
Surface Science of Heterogeneous Reactions and Thin Film Growth
Studies of the surface intermediates formed by reactions between gases and metal surfaces are important for two reasons. First, they represent the molecular stepping stones whereby the products of chemical industry are produced economically by heterogeneous catalysis. Second, the formation of these surface intermediates is the first stage in the growth of thin surface films. These films endow a bulk material with useful environmental properties such as corrosion and wear resistance. Surface films are the high-value-added products of the modern materials industry.
Our specific research interests are in studies of the interaction of ammonia or nitrogen gas with single crystal transition metal surfaces using Auger electron spectroscopy (AES) to monitor the surface composition and electronic structure, low energy electron diffraction (LEED) to determine surface geometrical structure, and thermal desorption mass spectrometry (TDMS) to measure kinetic parameters of adsorption and desorption reactions.
The activation energy for a dissociation reaction, e.g. breaking the N N bond in nitrogen fixation, is lower in a surface catalysed reaction because of participation of surface metal atoms in the creation of new bonds in order to compensate for the energy required to break the molecular bond. Therefore the activation energy is expected to depend critically on the symmetry and spacing of the metal atoms on the catalyst surface. These effects are under active investigation in our laboratory by studying reactions on surfaces of single crystals of a series of b.c.c. metals, V, Cr, Ta and W, with different low index orientations, (100), (110) and (111), in order to vary the site symmetry and site spacing.
In recent work the effect of electron stimulation of the surface reactions has added an interesting new dimension to our research. Important differences between ground state and excited ammonia and dinitrogen have led to proposals for increasing the efficiency of the production of nitride films. It is anticipated that this work will stimulate considerable further interaction between our research group and the industrial research community.
- P.T. Dawson and S.A. Petrone, "Studies on Cr-Mo binary alloys: II. Cross-over surface segregation for chromium rich alloys", Surface Science 304 (1994) 119-130; "Crystal orientation effects on the surface morphology produced by ion bombardment of a pure element: Implications for quantitative surface analysis", J. Surf. Int. Anal., 17, (1991) 273-281; "Quantitative surface analysis with elemental standards: Surface roughness limitations", J. Vac. Sci. Technol., A9 (1991) 1234-1236; "Studies on Cr-Mo binary alloys: I. Surface composition modifications induced by ion bombardment", Radiation Eff. and Defects in Solids, 115 (1991) 315-333.
- P.T. Dawson, "Periodic variations in the nitrogen KLL Auger intensity from interstitial nitride films", J. Surf. Int. Anal., 17 (1991) 335-342.
- P.T. Dawson and K.K. Tzatzov, "New features in the very low energy Auger spectra of transition metal nitrides", Surface Science, 249 (1991) 223-232; "Low energy Auger electron spectroscopy of vanadium nitrides", Surface Science, 234 (1990) 339-354; "Nitrogen sorption on titanium: An iterative reconstruction of the subsurface composition profile using low and high energy Auger data", J. Vac. Sci. Technol., A5 (1987) 1345-1351; "Plasma enhanced CVD growth of TiN films", Final Report; WESTAIM - Sherritt October (1993).
Dr P.T. Dawson
Department of Chemistry
Hamilton, Ont., Canada
Voice (905) 525-9140, ext. 24717
FAX (905) 522-2509
Laboratory: ABB-334, 335
Department of Chemistry