Geometric and Electronic Structure of Potassium on Rh(111)

The interaction of potassium with Rh(111) was studied by AES, REELS, LEED, TDS, UPS and work function (WF) measurements. At low coverages (ΘK < 0.1) Φ decreases linearly followed by a shallow minimum at ΘK ≈ 0.2 and a slight reincrease. Three different LEED K-superstructures at ΘK = 0.25 (2 × 2), ΘK = 0.33 (√3 × √3 R30°) and at ΘK = 0.5 (2 × 2) have been observed corresponding to a nearest K–K neighbour distance for the first two structures of 5.38A and 4.66A, respectively, The √3 × √3 R30° structure is compressed by 6% compared to the surface density of (110) K planes. The multilayer desorption in TDS is observed only at K-coverages beyond 0.5 which is generally correlated with a metallic (potassium like) character of the overlayer. In the K-coverage range 0–0.33 the electronic binding energy of the K(3p) level shifts to lower binding energy (18.4–17.8 eV). Above ΘK = 0.5 a new K(3p) peak develops at the sane energetic position as it is observed for a thick potassium film (18.6 eV). The transition of the electronic properties of the K-overlayer character is also ionic (low coverage) to a covalent (high coverage) bonding character is also reflacted in the electron loss experiment. Only above ΘK = 0.5 the plasmon loss characteristic of thick metallic K at 2.5 eV can be detected, even though already around 0.33 the K–K nearest neighbour distance corresponds to the covalent value.