Growth and Morphology of Calcium-Oxide Films Grown on Mo(001)

Crystalline calcium-oxide films of various thicknesses have been grown on a Mo(001) support. The growth behavior and resulting film morphology have been characterized with low-energy electron diffraction, Auger spectroscopy, and scanning tunneling microscopy. At low film thickness, a considerable interdiffusion of Mo ions from the support into the ad-layer is revealed, giving rise to the development of a sharp (2 × 2) superstructure with respect to the Mo(001). The Ca/Mo mixed oxide has a similar lattice parameter as the metal substrate and therefore grows pseudomorphically with a very low defect concentration. At 4−5 ML thickness, the supply of Mo from the support is interrupted and pristine CaO patches start to grow on the surface. The reemerging lattice mismatch drives the system into the Stranski-Krastanov mode, as reflected by the formation of three-dimensional oxide islands. Above 15 ML nominal thickness, the islands merge into a closed film with high surface quality and low defect concentration. Th...