A planar CrOx(/)SiO(2)/Si (100) model for the Phillips ethylene polymerization catalyst, prepared by spin-coating impregnation from an aqueous solution of CrO3, polymerizes ethylene in the gas phase at 160 degrees C with a significant and constant activity. After polymerization for 5 min and cooling to room temperature, an approximately 40 nm thick high-density polyethylene layer was formed that exhibits a morphology of regions with almost parallel aligned edge-on lamellar crystals. These lamellae show a distinct blocklike submorphology, which is discussed in detail. The work demonstrates that controlled polymerization and crystallization using a surface science model catalyst on a flat surface offers an excellent approach for fundamental studies of polymer physics, e.g., the study of the origin of crystal formation.