From the experimental data points, the plot of 1/(number of extinct Si adatoms) versus the duration of exposition to N2 at a given pressure is a straight line (Figure ), supporting a partial second order in terms of kinetics law. Finally, we have investigated the role of the temperature. STM images in Figure compare the number of extinct adatoms of a Si(111)-7x7 surface exposed to 3•10 -6 mbar of N2 for 20 minutes at 120 K (Figure ) and 300 K (Figure ).The number of extinct silicon adatoms strongly decreases from 36% to 4.5% when the temperature increases from 120 K to 300 K. Hence, the number of extinct silicon adatoms increases with the N2 pressure and the exposition duration but it decreases with the temperature of the substrate.