Interactions of N 2O, NO and CO 2 with (100) nickel using combined LEED and mass spectrometer measurements

Abstract

Results were obtained with combined LEED and Mass Spectrometer equipments. On first admission of N 2O to the outgassed system in the pressure range 2 to 5 × 10 −8 Torr, nitrogen was formed by decomposition but no oxygen was observed. In addition to some dissociation of N 2O on (100) Ni, some adsorption of N 2O occurred in a lattice structure similar to that of the nickel substrate. Subsequent heating at 200–300°C caused weak desorptions of CO and N 2O, the oxygen being removed as CO. The adsorbed N 2O was easily replaced by CO at room temperature. The work function of the clean surface was increased 0.1 eV by exposure to N 2O, probably due to adsorbed oxygen as a decomposition product of N 2O as well as adsorbed N 2O. On first admission of NO, substitutional desorption of CO from tube components occurred and the resulting CO adsorbed on the crystal surface was later substitutionally desorbed by NO. NO was strongly adsorbed on the crystal surface primarily in an amorphous form but with some lattice structure similar to that of the nickel substrate. The adsorbed NO was removed as CO and N 2 by heating. NO was strongly adsorbed on both clean and slightly contaminated surfaces. There was no evidence of a surface reaction between adsorbed NO and oxygen atoms to form NO 2. Adsorption of NO caused a maximum decrease in work function of 0.38 eV. Admission of CO 2 to the system caused no substitutional desorption of CO. Adsorbed CO 2 molecules were dissociated on the clean crystal surface at room temperature to form adsorbed CO and O when the exposure reached a rather critical value of about 10 −6 Torr-min, as indicated by both sharp decreases in LEED intensity and increases in work function. Heating the crystal at 200 to 300°C caused desorption of both CO and CO 2. A slightly contaminated surface, produced by heating the crystal at 850°C for a few hours, was very inactive for CO 2 adsorption or dissociation.