Condensation and epitaxial growth of K on W(001)

The growth of K layers on W(001) from the first adsorption phases up to the deposition of thick films has been investigated by means of a RHEED camera, in the temperature range 143 ? T ? 273 K. At first the deposited potassium atoms form a W(001)-c(2 × 2)K⁺ structure, upon which a non-ionized but polarized adstructure grows. Further condensation is characterized by a very low binding energy of 0.09 eV to the substrate layer and consequently by a low condensation coefficient. The transition layer grows out of single adsorption events without the formation of nuclei, while the epitaxial layers growing upon it are initiated by three-dimensional nucleation. For these layers, epitaxial orientations $\text{K}\text{(001)}\text{W}\text{(001)}\text{with}\text{K}\text{001]}\text{W}\text{010]}$ or $\text{K}\text{001]}\text{W}\text{100]}$ were observed.