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

摘要

The self-organisation of nitrogen nanostructures at different coverages on a (100) copper surface is studied by spot profile analysing low energy electron diffraction (SPA-LEED). The existence of two surface states with a domain of coverage leading to coexistence of the two states as already observed by scanning tunneling microscopy (STM) Leibsle and Robinson, Phys. Rev. B 47 (1993) 15 865; Leibsle et al., Surf. Sci. 317 (1994) 309; Leibsle, Surf. 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 surface is organised in square shape islands separated by bare copper 100 rows. This work shows that the surface periodicity depends on the preparation of the nitrogen overlayer. When nitrogen coverage is obtained by adsorption with a sample temperature near 320 degrees C, the periodicity does not vary with coverage and is found to be equal to 55 +/- 2 Angstrom. At coverages 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 periodicity evolves to large values (similar to 97 +/- 3 Angstrom). During thermal desorption, the long range order with decreasing coverage is maintained but the surface periodicity also evolves continuously to large values (similar to 100 Angstrom). However, a surface periodicity of 55 +/- 2 Angstrom seems to be a characteristic length of this system. The second surface state corresponds to large c(2 x 2)N domains separated by 110 trenches Leibsle 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 double step height. The complex behaviour of this film growth is discussed in the light of existing theories about the driving force leading to nanostructuration. (C) 2000 Elsevier Science B.V. All rights reserved. References: 20