Self-ordering in two dimensions: nitrogen adsorption on copper (100) followed by STM at elevated temperature

We have followed the adsorption and the desorption of nitrogen on the coppe r (100) surface in real time using scanning tunneling microscopy at elevate d temperatures. This gives an unprecedented view, especially of the adsorpt ion behavior at very low coverage. Growth proceeds by splitting of square-s haped islands of critical size without loss of C-4 symmetry. The equilibriu m structures are analyzed in terms of their dimensionality and shape showin g that the phase diagram comprises two periodic domain morphologies as a fu nction of nitrogen coverage: two-dimensional (2D) array of compact nitrogen islands at low and high coverage and a quasi 1D arrangement of striped dom ains (rows of squares) at intermediate coverages. Furthermore, we investiga ted the sensitivity of the system to small changes in the elastic propertie s of the substrate by pre-deposition of gold on the bare copper surface. Fi nally, the comparison all our observations in the light of existing model p redictions for long-range interactions in 2D systems reveals crucial differ ences and, therefore, these models have to be extended to include short ran ge relaxation and interactions in order to reproduce the fundamental aspect s of this system. (C) 2001 Elsevier Science B.V. All rights reserved.