Figure 2.

(a) LEED pattern of PTCDA on Cu(100) observed after deposition at a sample temperature of 400 K (62.5 eV, θ ≈ 0.5 ML). Left hand side: Corresponding calculated LEED pattern. The reciprocal unit cells of the Cu(100) surface (black) and of the two symmetry equivalent domains of the commensurate (4√2 × 5√2)R45° superstructure (blue and red) are indicated. (b) LEED pattern of PTCDA on (√2 × 2√2)R45° – 2O/Cu(100) (16.6 eV, θ ≈ 0.5 ML). Left hand side: Corresponding calculated LEED pattern. The reciprocal unit cells of the (√2 × 2√2)R45° – 2O/Cu(100) (blue and red) and the four symmetry equivalent domains of the incommensurate superstructure of PTCDA according to the matrix M₀ (see third column of Table 1) are indicated. Note that the unit cells of the (√2 × 2√2)R45° – 2O/Cu(100) surface do not fit completely into the depicted area of the reciprocal space.