Chemisorption of N 2 and no on polycrystalline molybdenum

Abstract

The adsorption of nitric oxide and nitrogen on a polycrystalline Mo filament at room temperature has been studied by thermal desorption spectroscopy (TDS), field-emission microscopy (FEM) and work function measurements, using 15NO and 15N 2. The chemisorption behavior of N 2 on molybdenum resembles that of tungsten. At low coverage, 15NO and 15N 2 adsorb dissociatively on the Mo surface and molecular adsorption becomes dominant at higher coverage. At higher coverage in the NOMo system, the peak temperature of the desorption of 15N 2 from the 15NO layer on Mo shifts to higher value. The retrograding behavior of the desorption peak temperature is attributed to the lateral molecule interactions on the molybdenum surface. The attractive interaction energy, ε, is about 8.4 kcal/mol. The variations in the FEM pattern and in the work function of the 15NO chemisorbed Mo tip with heating to about 1400 K are similar to the results of the O 2 chemisorbed Mo tip which appeared above 1400 K. In the temperature range of 300–1350 K, the regions around the (112) of the NO- and N 2-covered Mo tip become brighter and show similar changes in the FEM pattern. It is also found that the oxygen resulting from the dissociation of 15NO chemisorbed on the Mo surface plays a similar role as the oxygen in the O 2Mo system.