Self-organisation of adsorbed nitrogen on (100) and (410) copper faces: a SPA-LEED study

The self-organisation of nitrogen nanostructures at different coverages on a (100) copper surface is studied by spot profile analysing low energy elec tron diffraction (SPA-LEED). The existence of two surface states with a dom ain of coverage leading to coexistence of the two states as already observe d by scanning tunneling microscopy (STM) [Leibsle and Robinson, Phys. Rev. B 47 (1993) 15 865; Leibsle et al., Surf. Sci. 317 (1994) 309; Leibsle, Sur f. Sci. 440 (1999) L835] and low energy electron diffraction (LEED) [Sotto et al., Surf. Sci. 371 (1997) 36] is confirmed. In the first state, the sur face is organised in square shape islands separated by bare copper [100] ro ws. This work shows that the surface periodicity depends on the preparation of the nitrogen overlayer. When nitrogen coverage is obtained by adsorptio n with a sample temperature near 320 degrees C, the periodicity does not va ry with coverage and is found to be equal to 55 +/- 2 Angstrom. At coverage s below 0.75 +/- 0.05 and if the nitrogen is deposited at room temperature followed by an anneal at 320 degrees C, during long periods of time, the pe riodicity evolves to large values (similar to 97 +/- 3 Angstrom). During th ermal desorption, the long range order with decreasing coverage is maintain ed but the surface periodicity also evolves continuously to large values (s imilar to 100 Angstrom). However, a surface periodicity of 55 +/- 2 Angstro m seems to be a characteristic length of this system. The second surface st ate corresponds to large c(2 x 2)N domains separated by [110] trenches [Lei bsle and Robinson, Phys. Rev. B 47 (1993) 15 865; Leibsle et al., Surf. Sci . 317 (1994) 309; Leibsle, Surf. Sci. 440 (1999) L835]. Nitrogen adsorption on a (410) stepped face induces a reconstruction into a (810) face with do uble step height. The complex behaviour of this film growth is discussed in the light of existing theories about the driving force leading to nanostru cturation. (C) 2000 Elsevier Science B.V. All rights reserved.