Determination of diffusion in polycrystalline platinum thin films (original) (raw)

Grain boundary diffusion of titanium through platinum thin films has been carried out in the temperature range from 200 to 600°C. Five different platinum/titanium bilayer thicknesses, from 35 to 800 Å Pt, were annealed in 5% O 2 /95% N 2. The accumulation of titanium at the platinum surface layer was measured by x-ray photoelectron spectroscopy ͑XPS͒ to determine the grain boundary diffusion coefficient (D b). Diffusivity values were calculated based on two different analysis methods assuming type C kinetics. For Pt layers thicker than 200 Å, the activation energy (Q b) for titanium diffusion was found to be 118Ϯ15 kJ/mol ͑1.22Ϯ0.16 eV͒. For Pt layers thinner than 200 Å, there was a thickness dependence on the diffusion kinetics, resulting in activation energies as low as 20Ϯ4 kJ/mol ͑0.21Ϯ0.04 eV͒. XPS results gave no evidence for any Pt-Ti alloy formation in these layers. The suppression of alloy formation may be attributed to the presence of oxygen at the Pt/Ti interface during layer deposition. The quantitative analysis of titanium interdiffusion in platinum provides valuable information regarding Pt/Ti surface concentrations in thin-film chemical sensors, and for understanding changes in operational characteristics of platinum electrodes.