K adsorption on Fe(100) studied by X-ray standing waves

The K covered Fe(100) surface has been studied by X-ray standing waves. The measurements were performed using (200) symmetric Bragg diffraction planes with an incidence angle of 85°. Iron L and potassium K fluorescence lines were detected as secondary yield signals. In the case of the Fe(100)(3 × 3)-K reconstructed surface we assumed the substitutional adsorption site for the K as determined in a previous TOF-SARS study and no relaxation of the Fe. This resulted in a KFe bond length of 2.92 ± 0.04 A ̊ corresponding to an effective radius for the K of 1.67 ± 0.04 A ̊ . For the room temperature K saturated Fe(100) surface evidence is obtained for multiple adsorption sites and a larger K radius. The KFe interaction for the saturated and Fe(100)(3 × 3)-K reconstructed surface is discussed and compared to the general phenomena reported for alkali adsorption on metal surfaces.