“…The 3 · 3 pattern can result from an arrangement in which one Sn atom is higher than the other two in the unit cell (1U2D), or from the opposite geometry (2U1D). The 1U2D configuration appears the most stable from a theoretical point of view [6,7] and is the one resulting from the analysis of X-ray standing wave measurements [8]. On the other side, other experimental investigations consisting in a doping of the Sn/Ge(1 1 1) surface to assign the two Sn 4d components in the core levels [9], or based on a combination of X-ray standing waves and photoemission [10], lead to favor the 2U1D geometry.…”