Surface Structure and Growth Mode of PdDeposited on Mo(110) Surface

The surface structure and growth mode of Pd/Mo(110) have been studied using reflection high energy electron diffraction (RHEED). The surface diagram of Pd on the Mo(110) substrate for deposition thickness versus substrate temperature was obtained. Four kinds of surface structures, namely α1, α2, β and γ, were observed. At less than 1 ML, α2appeared in temperatures ranging from 400 to 1050°C and α1appeared from RT to 400°C. α2has a structure intermediate between those of Pd(111) and Mo(110), in which the dense direction of the layer is parallel to the [111]Moorientation and their atomic row distances are coincident, resulting in formation of a long-period structure with a Mo surface, namely a coincident site lattice. The α1structure is similar to the 1 × 1 structure. At more than 1.0 ML, β and γ structures appeared simultaneously in the temperature region from 500 to 950°C. However, at a high temperature region from 950 to 1050°C, the α2structure was observed. β shows a one-dimensional ordered structure, in which Pd atoms line along [111]Mo. γ exhibits a 3 × 1 structure with the same atomic arrangement as the Mo(110) plane rotated at 70.5°. At greater than 2.0 ML, the Pd film grows in the Frank–van der Merwe growth mode at a low temperature with accumulation of a Pd(111) layer, and in the Stranski–Krastanov growth mode at a high temperature with two-dimensional growth of the γ structure followed by formation of flat crystallites.