O-mediated layer growth of Cu on Ru(0001)

Abstract

The film growth of Cu on clean and O-precovered Ru(0001) at different growth temperatures form 300 K to 450 K was investigated by scanning tunnelling microscopy (STM). Cu films on clean Ru(0001) grow in a multilayer mode at these temperatures. By using an O precoverage in the range of 0.1 monolayers (ML) up to a saturation coverage of 0.5 ML on clean Ru(0001), at 400 K different growth regimes are obtained. For ML a multilayer mode is preserved which changes into an O-induced two-dimensional (2D) growth for higher (0.2-0.5 ML). STM reveals the formation of an O/Cu surfactant structure on the surface due to migration of O initially located at the Ru surface. Its surface coverage rises linearly with O precoverage up to ML where it covers the surface completely. By increasing up to 0.5 ML, a drastic change in the morphology and density of the 2D islands occurs, which is accompanied by a change of the O/Cu surfactant structure. The O/Cu surfactant structure displays some order on a local scale for low , which changes into a disordered structure for ML. Structural similarities to oxidized surfaces of Cu(111) and the structures induced by postadsorption on Cu/Ru(0001) are discussed. Different models of surfactant mechanisms are presented to explain the observations. The locally ordered O/Cu surfactant structure (for ML) together with specific Cu film defects induce a heterogeneous nucleation of Cu with a high island density. Different mobilities of migrating Cu adatoms are established on top of the small islands and on the O/Cu structure resulting in enhanced interlayer diffusion explaining the observed 2D growth. The average island density only slightly changes within the temperatures investigated. In contrast, the saturated and disordered O/Cu surfactant structure (for = 0.4 - 0.5 ML) causes homogeneous nucleation. For this structure, the island density strongly depends on temperature and gives rise to an Arrhenius-like behaviour. The observed 2D growth is attributed to a reduction of the interlayer diffusion barrier. Cu growth on a formerly annealed Cu/O/Ru(0001) film system yields an almost perfect layer-by-layer growth caused by heterogeneous nucleation at periodically arranged Cu film defect sites. The relationship of the O/Cu surfactant structures to the ordered O/Cu bilayer on Ru(0001) - interpreted as a disrupted -like oxidized surface - was revealed.

Oxidation electronics: bond–band–barrier correlation and its applications

“…AES [363], ICISS [242], work function measurements [198,364] and STM observations [241,365] have revealed that oxygen atom is always present on the surface of the grown Cu films deposited on an oxygen pre-covered Ru(0001) surface. Under certain conditions (Y O =0.2-0.4 ML, T $ 400 K), the work function, monitored during film deposition, oscillates with a period of one monolayer of copper epitaxial growth.…”

“…If the tetrahedron is destroyed, oxygen will seek new partners for a new tetrahedron-a process of re-bonding or bond switching. This may provide a mechanism for O-penetrating in bulk oxidation and O-floating in the epitaxial growth of metals on the oxygen pre-covered metal surfaces [241,242].…”

“…The structure also consists of O-Cu-O strings inducing the observed corrugation. One possible mechanism proposed by Wolter et al [241] is that the strain of the first Cu layer promotes the formation of the Cu 2 O-like (3Â2 p 3) structure. Once the structure is formed, elements of it float onto the top of the growing film and act as a surfactant layer for further Cu film growth.…”

“…Therefore, oxygen floating in the process of Cu/O/Ru(0001), Cu/O/Cu(111) and Cu/O/Cu(001) growth and Ni cluster on O-W(110) surface is driven by a common, yet poorly known, mechanism. As pointed out by Wolter et al [241] the detailed mechanism of oxygen segregation on the top of a metal surface is still an open question.…”

Kinetics of Bond Forming and Bond Switching

“…AES [3], ICISS [4], work function measurements [5,6], and STM observations [7,8] revealed that oxygen atom is always present on the surface of the grown Cu films deposited on an oxygen pre-covered Ru(0001) surface. Under certain conditions (H O = 0.2-0.4 ML, T * 400 K), the work function, monitored during film deposition, oscillates with a period of one monolayer of copper epitaxial growth.…”