Pseudomorphic growth of thin Cu films on Pd(110)

Abstract

The growth of thin Cu films on Pd(110) has been studied by variable temperature scanning tunneling microscopy in the temperature range 250 ⩽ T s ⩽ 900 K. Cu adatom diffusion on the substrate is highly anisotropic and determines the submonolayer Cu island shapes. This leads at low deposition temperatures ( T s ⩽ 300 K) and low Cu coverages (θ < 0.1 ML) to the formation of monatomic Cu chains oriented along [11̄0]. At higher coverages and/or deposition temperatures two-dimensional (2D) islands of anisotropic shape grow. At 300 K the 2D Cu-islands are arranged in a semi-ordered striped domain structure along the [001] direction. In the Cu multilayer range, the film growth mode can be varied through deposition temperature control. Microrough Cu films consisting of small 3D clusters grow below 400 K. Between 400 and about 550 K, Stranski-Krastanov growth with a critical thickness of one monolayer takes place. At 550 K, a transition to a layer-by-layer step-flow mode occurs. Flat Cu multilayers are found to be (1 × 1) pseudomorphic up to a critical thickness of 5 ML. Thicker films partially relieve their misfit strain through uniaxial relaxation into a (29 × 1) high-order commensurate structure. At temperatures above 750 K, we observe CuPd intermixing.