AN OPTICAL-EMISSION-SPECTROSCOPY CHARACTERIZATION OF OXYGEN PLASMA DURING THE OXIDATION OF ALUMINIUM FOILS

A highly reactive oxygen plasma was applied for the oxidation of aluminium foils. The plasma was created within a radio frequency discharge operating at a power of 300 W and a frequency of 27.12 MHz. Samples of Al foils with dimensions of (20 x 40) mm were placed into the discharge chamber. During the treatment of the foils with oxygen plasma, the optical spectra were measured simultaneously with,in optical spectrometer. The predominant spectral features observed during the treatment were atomic oxygen lines at 777.4 nm and 844.6 nm, atomic hydrogen lines and in OH band at 309 nm. As the oxidation took place other spectral features appeared. The major lines were Na at 589.35 nm and K at 766.5 nm and 769.9 nm, The time evolution of the Na and K peaks showed well-defined maxima after about a minute of plasma treatment. These maxima depended on the pressure in the discharge chamber. At the lowest pressure of 30 Pa the maxima appeared after about 100 s, while at a pressure of 80 Pa the maxima appeared after about 50 s. At a pressure of 120 Pa these maxima appeared after about 125 s. This behaviour was explained by the segregation of Na and K on the surface of the foil and the rapid desorption into the gas phase.