Adsorption and decomposition of NO and NH 3 on Ru(001) and Ru(1,1,10) surfaces

Abstract

Adsorption and decomposition of NO and NH 3 on a Ru(001) flat surface and a Ru(1,1,10) stepped surface which possesses one step per five terrace widths have been investigated by means of XPS and UPS measurements. Adsorption of NO on the Ru(001) surface at 120 K exhibited two molecularly adsorbed NO states which were distinguished by O 1s core levels at 530.7 and 531.8 eV. On the Ru(1,1,10) surface the concentration of molecular NO states characterized by the O 1s level at 530.7 eV was quite smaller than that on the Ru(001) surface after saturated adsorption (above 7 L exposure), while the concentration of molecular NO characterized by 531.8 eV O 1s emission did not change. Therefore, the total amount of adsorbed NO on the Ru(1,1,10) surface was less than that on the Ru(001) surface. As a result, the dissociation of adsorbed NO occurred at temperatures as low as 200 K on Ru(1,1,10), while molecular NO was stably adsorbed on Ru(001) surface above 300 K. The formation of surface nitrogen complexes, NH x ( a) ( x = 0–3) could be characterized on the Ru(1,1,10) stepped surface by the successive shift of the N 1s core and valence level, whereas intermediate adsorbed species except for atomic nitrogen could not be detected on the Ru(001) flat surface. In the adsorption at 120 K molecular ammonia was adsorbed on both surfaces which exhibited a core emission at 400.0 eV and valence levels at 6.7 and 11.0 eV. Upon heating NH 2(a) species was formed at 300 K which caused a shift of the N 1s core level to 398.1 eV and of the valence level to 7.4 eV, respectively. Furthermore, under ammonia flow condition, NH(a) species giving the emission at 8.8 eV in the valence region was populated on the stepped surface at 380 K. Further heating to above 500 K resulted in atomic nitrogen on both surfaces which represented the N 1s core level at 397.3 eV and the 5.6 eV in valence level.