Spectroscopic Ellipsometric Studies On Electrodeposition Of Cuprous Oxide

As the silver-white appearance of Ni is not satisfactory for decoration applications, the cuprous oxide(Cu2O) layer is coated on the Ni substrates by electrodeposition method for creating rich colors. Cuprous oxide is normally a red color in the bulk, however, when the Cu2 O film is sufficiently thin, then the “thin film interference” effect becomes apparent and a variety of colors changing with the thicknesses will be observed. However, the Cu2 O film is too thin to measure. In this article, spectroscopic ellipsometry(SE) with high-precision and high sensitivity was used to characterize the films, and the affects of the experimental conditions on the thickness and color of the film were studied.SEM proved that the surface of Ni substrate and the deposited were rough. And the XPS showed that the deposited were Cu2 O and the content of Cu2 O was gradual change near rough surface of Ni substrate. Based on the results metioned above, a three-layer model was constructed: EMA was used to simulate the sample surface roughness as a mixed layer involved Cu2 O and air; the second layer is a pure Cu2 O film; and the last layer was also a mixed layer involved Cu2 O and Ni that the gradient distribution of Cu2 O was simulated by Graded model. The theoretical curves generated from the three-layer model were agreed well with the experimental curves.Firstly, direct current Hull cell coupled with SE were applied to research the influence of two kinds of additivies, sodium citrate and potassium sodium tartrate, on the color plating. The results showed that additivies can improve the coverage and dispersing ability of electrolyte, so as to improve the effect of color plating, and in a certain range with the increase of the content of additives the apparent of sample became better. Compared with sodium citrate, potassium sodium tartrate can more significantly improve the electrolyte plating ability, and achieve the uniform colored sample. In this experiment, when the concentration of potassium sodium tartrate added to 20g/L, the color plating effect was the best. Secondly, according to the condition optimized by the Hull cell test, another experiment was conducted to study the dependency relationship between the colors and the thickness of films. Adjusting the deposition time, cuprous oxide thin films were deposited on planar electrode by direct current electrodeposition. It was easy to find the colors of films changed with the deposition time, and colors also exhibited cyclic transformation increasing with time. The color is determined by the thickness. And the ellipsometric measurements revealed that the film thickness and the deposition time were linear relationship. The fitting equation was shown as follow: dtotal =9.232+0.434t(nm).Changing the electrodeposition methods, use the pulse current Hull cell to study the pulse duty ratio on the color plating effect. Results showed that, with the decrease of duty ratio the bright range of the colored layer became wider, but the surface colors of the Hull cell samples deposited with different duty ratio were not uniform due to the thickness distribution of the deposition layers were not uniform. Then, adjusting the deposition time, cuprous oxide thin films were deposited on planar electrode by pulse current electrodeposition. It was also to find that the colors and the thickness of films changed with the deposition time. And the film thickness and the deposition time were linear relationship, too. The fitting equation was shown as follow: dtotal= 0.554t-0.143(nm).