The Optical Constants of CuO0.67 from 400 to 800 mμ

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Abstract
At temperatures below 200 °C, copper films less than 1085 Å thick oxidize in 100 Torr of oxygen to form CuO0.67 before nucleation to CuO sets in. The oxidation of copper to CuO0.67 can be described by two parallel absorbing layers. During the oxidation, the transmittance, T, at normal incidence has been measured as a function of the wavelength λ while the mass change of the copper film has been simultaneously recorded with a vacuum ultramicrobalance. The thickness of the two absorbing layers, d1 and d2, has been calculated from the mass data. Using the measured values of T, λ, d1, and d2 and known values for the optical constants, n and k, for annealed copper films, trial values for n and k for the oxide have been inserted into rigorously derived equations for two parallel homogeneous absorbing films on a nonabsorbing substrate. By comparing the values of the transmittance calculated by a computer with the experimental values, k–n pairs are found that yield the measured transmittance. When the k–n pairs are plotted for several thickness combinations, a unique set of n and k is determined from the convergence or clustering of the n and k curves in a narrow region. Each set of n and k has a variable percentage error associated with it at any wavelength depending on how closely the curves cluster when they are plotted in the k–n plane. A narrow range of values of n and k are reported for CuO0.67 layers on copper in 50-mμ intervals for 400 to 800 mμ. The values reported are valid for oxide thicknesses exceeding about 800 Å.

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