Figure 1 : A pyramidal copper nanocrystal, deposited from copper guanidinate.

Chemical Vapour Deposition (CVD) is a chemical method of depositing thin films of materials. In figure 1, careful control over the thermolysis of a copper guanidinate allowed deposition of crystalline copper nanoparticles:

[Me₂N-guanCu]₂ + H₂ --> 2 Hguan + 2 Cu⁰

A modification of CVD, Atomic Layer Deposition (ALD) allows very careful control of film thickness by allowing deposition of one atomic layer at a time. We try to tailor the characteristics of the precursor to allow selection between continual growth by CVD, and self-limited growth by ALD. We also endeavour to control melting point, volatility, thermal stability, and chemical reactivity. It is through the careful design of the volatile precursor that we can try to affect not only the nature of the precursor in the gas phase, but also control its reactivity with the deposition surface.

Figure 2 : A bis-Cp guanidinato titanium precursor.

We work with amidinates and guanidinates to design precursors for ALD. A typical precursor is shown in Figure 2. The process allows the deposition of thin films on surface one atomic layer at a time, and has tremendous impact on both microelectronics and nanotechnology.

ALD is presently being introduced in industrial processes for the production of microelectronics, and will see employment in the future in magnetic memory and optical components.

Although we make these ligands by carbodiimide insertion (Figure 3a), we have discovered there is a very important competing mechanism of ligand exchange (Figure 3b). This allows us the versatility to easily make mixed ligand systems to tune our precursors for thermal reactivity, volatility, melting point, and steric protection of the metal centre.

Figure 3 : Mechanisms for a) carbodiimide insertion and b) ligand exchange for the formation of aluminum amidinates

The heteroleptic nature of the precursor also allows us to design reactivity specific for the deposition surface (through an "anchor ligand") while controlling self-limiting growth through steric bulk.

With a grant from the Canadian Foundation of Innovation and the Ontario Innovation Trust, we are installing an ALD reactor to test our precursors. This will give us the versatility to design the process as well as the precursor, and this uncommon combination of scientific skills should help us understand ALD in a more fundamental way.

If you have any questions, please direct them to Sean or the research group .