Optically thin palladium films evaporated on silicon substrates are investigated following exposure to low concentrations of hydrogen gas in nitrogen using spectroscopic ellipsometry. Changes in the parameters tan Ψ and cos Δ are observed for concentrations as low as 0.01% hydrogen in nitrogen. A nonlinear behavior of the change in the ellipsometry parameters as a function of hydrogen concentration is demonstrated, with saturation occurring at a flow of 0.05% hydrogen in nitrogen.
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