Using a combination of photoelectron diffraction and scanning tunnelling mi
croscopy the Cu(100)c(2 x 2)-N surface is shown to undergo a symmetry-lower
ing reconstruction with a strong (0.34 Angstrom) periodic distortion of the
outermost Cu layer perpendicular to the surface. The rumpling reconstructi
on is shown to account for N-N attractions which create c(2 x 2) islands an
d the systematic behaviour of inter-island boundary widths in the mesoscopi
c self-organization of this surface.