[1] Adsorbed species on single crystal surfaces are frequently found to exhibit long-range ordering; that is to say that the adsorbed species form a well-defined overlayer structure.
Each particular structure may only exist over a limited coverage range of the adsorbate, and in some adsorbate/substrate systems a whole progression of adsorbate structure are formed as the surface coverage is gradually increased.
[2] The periodicity of the overlayer (which often is larger than that of the substrate unit cell) can be determined by low-energy electron diffraction (LEED), because there will be additional diffraction beams associated with the overlayer.
[5] Wood's notation takes the form where M is the chemical symbol of the substrate, A is the chemical symbol of the overlayer,
matrix that describes the overlayer primitive vectors in terms of the substrate primitive vectors: and so hence matrix notation has the form