Determination of atomic oxygen density with a nickel catalytic probe

Abstract

A nickel catalytic probe was used to determine the density of neutral oxygen atoms in a glass tube. The O source was a low pressure weakly ionized inductively coupled rf oxygen plasma. The recombination coefficient for polycrystalline nickel (purity 99.8 at. %) was determined experimentally by use of a nickel tube with a well activated surface, recombining almost all the atoms entering the experimental chamber. The recombination coefficient was found to be constant over the temperature range of 500–1100 K with a value of 0.27±0.04. The catalytic probe was a disk with a diameter of 2 mm and thickness of 0.2 mm made of the same material. The O density was measured along a glass tube (Schott 8250) with an inner diameter of 3.6 cm and length of 40 cm. The density depended on the pressure in the experimental chamber and was found to decrease exponentially along the glass tube. The characteristic penetration depth depended slightly on pressure and was 60±16 cm. Comparison of the experimental data with theoretical predictions allowed estimation of the recombination coefficient for O atoms on a Schott 8250 glass surface: γ=(1.9±0.5)10−4.