M. Schick

Investigation of thin Ag/Cu‐alloy films on Ru(0001)

Thin Ag/Cu‐alloy films on a Ru(0001) substrate were investigated with respect to the two‐dimensional miscibility properties of the two component metals using thermal desorption spectroscopy (TDS), low‐energy electron diffraction spectroscopy (LEED), Auger‐electron spectroscopy, angle resolved ultraviolet photoemission spectroscopy (ARUPS), and Xe adsorption. The desorption of pure Ag and pure Cu submonolayers from Ru(0001) proceeds with zeroth order kinetics around 1000 and 1200 K, respectively. The Ag‐TD spectra from the alloy films show a change from zeroth to first order kinetics as the Cu concentration [ΘAg+ΘCu≤1 ML (monolayer)] increases between 0≤ΘCu≤0.5 ML. TD spectra of adsorbed Xe, in which one clearly can distinguish between submonolayer islands of pure Ag and pure Cu on Ru do not exhibit a distinct heterogeneity in the case of Ag/Cu‐alloy films. Instead the desorption peaks shift continuously depending on film composition. Furthermore no Ag induced LEED superstructure typical for pure Ag on Ru(...

Thin film growth on an O-precovered Ru(0001) surface

Abstract The growth of Cu on an O-precovered Ru(0001) surface was studied at various substrate temperatures by Auger electron spectroscopy, thermal desorption spectroscopy and sputter profiling. In contrast to the Volmer-Weber growth mode of Au films on O-precovered Ru(0001) the initial growth of Cu films is layer-by-layer at moderate temperatures (300 K–450 K). During the deposition of Cu, O is displaced from the Ru surface and transported to the top of the surface of the growing film. This can be observed up to Cu coverages of 9 ML and even higher, independently of the evaporation rate and substrate temperature. The thermal deposition spectra of Cu and O2 indicate the existence of an oxidized Cu layer.

Coadsorption of Cu and O2 on a Ru(0001) surface

The adsorption behavior of oxygen on Cu submonolayer, monolayer and multilayer films epitaxially grown on a Ru(0001) substrate is studied by AES, LEED, TDS and Δφ-measurements. In the presence of coadsorbed oxygen and below 500 K the Cu films preserve a layered structure. In the case of θCu < 1 ML the interaction is dominated by the free Ru(0001) sites. Annealing of the Cu film after adsorption of oxygen destabilizes the Cu structure and Cu clusters are formed; the O atoms are then distributed among the free Ru areas and the Cu clusters. Up to ∼ 6 ML the adsorption of oxygen is influenced by the presence of the underlying Ru(0001) substrate, possibly in two ways: (a) by direct mutual influence between both metals and (b) by the presence of relatively high oxygen concentration within the thin Cu films (Ru acts at this temperature as diffusion barrier for oxygen). The adsorption is accompanied by diffusion into the Cu overlayer as evidenced by a comparison of AES and TDS data for θCu≥6 ML.

Compression phases in copper/oxygen coadsorption layers on a Ru(0001) surface

Abstract The adsorption of Cu on an oxygen-precovered Ru(0001) surface and the interaction within the O-Cu coadsorption layer have been studied at substrate temperatures of 640 and 400 K using dynamical work function change measurements with a Kelvin-probe, LEED observations as well as Cu thermal desorption spectra. The results are consistently explained in terms of a “compression model” according to which adsorbing Cu compresses any oxygen surface structure which is less dense than the p(2 × 1) phase, e.g. the p(2 × 2) structure, into a p(2 × 1) structure.

Aluminum thin film growth on a Ru(0001) surface

Abstract The growth of thin Al films on a Ru(0001) substrate has been investigated by means of AES, LEED, TDS, and PAX measurements. A plot of the Ru and Al AES intensities versus evaporation time for a deposition temperature of 300 K reveals a distinct break at θ Al = 1, while for higher coverages the Ru intensity decays exponentially indicating a three-dimensional growth of Al clusters. From this behavior we deduce a Stranski-Krastanov growth mechanism. This behavior persists up to 650 K. For higher deposition temperatures a diffusion of Al into the substrate and a partial desorption of the Al film is found. At low Al coverage the LEED pattern reveals an initial film growth with Al(111) structure and an expansion of the interatomic spacing of 2% compared to the Al(111) bulk plane. This superstructure persisted up to ∼ 2.5 ML. In the submonolayer regime CO and Xe TD-spectra as well as Xe 4d PAX-spectra suggest together with LEED an island growth.

Influence of substrate steps on the properties of epitaxial noble-metal films

In this work we report on the influence of surface steps on the growth structure, the energetics and the electronic-properties of Ag on a stepped Ru(10117) surface as deduced from TDS, AES, LEED, ARUPS and PAX measurements. Increased desorption temperatures as well as PAX data suggest a selective “decoration” of the surface step sites at low Ag coverages. In particular no Ag island formation is detected neither with PAX, nor with LEED, nor with ARUPS for θAg < 0.2 ML, in contrast to the findings on flat Ru(0001). As an interesting consequence, a significant change in the Ag valence band spectra is observed. While already 0.05 ML Ag on a flat Ru(0001) surface exhibit a clear 4d-spin-orbit- and crystal-field-splitting of 1.35 eV no such splitting is detectable for up to 0.15 ML Ag on the stepped surface. Furthermore, a quasi-one-dimensional Ag band structure is suggested by ARUPS data for these low Ag coverages showing a dispersion of the Ag d-states only parallel but not perpendicular to the substrate steps.

Effects of thermal healing in cold deposited Cu films on a Ru (0001) surface

Abstract The influence of defects in thin metal films was studied for Cu films deposited on a Ru (001) surface at 40 K by means of angular resolved photoelectron spectroscopy (ARPES), photoemission of adsorbed xenon (PAX) and work function measurements. The cold deposited films are dominated by defects and the defect concentration at their surfaces is hardly inffluenced by annealing up to 150 K. Above 150 K defects are healed out resulting in strong shifts in the PAX spectra and work function changes. An annealed 8 nm films exhibits a clear Cu(111) valence band structure and angular integrated photoemission spectra show the density of state (DOS) of bulk copper. The coldly deposited 8 nm Cu film is characterized by a drastically reduced DOS at electron binding energies larger than 3 eV as well as by a lower dispersion of the Cu (3d) bands. The properties of a 3 ML Cu film, as obtained by PAX, are at all temperatures identical to the properties of a thick Cu film (8 nm).

Studies of the Facetting of the Polished (100) Face of CaF2

The present paper deals with studies of the facetting of the polished (100) surface of CaF2 during annealing and growth in UHV using low energy electron diffraction (LEED), atomic force microscopy (AFM), and transmission electron microscopy (TEM). First morphological modifications of the polished surfaces become visible at temperatures of T = 874 K. Surfaces annealed at T = 974 K exhibit a micro‐roughening with pyramidal protrusions and corresponding depressions. LEED studies indicate the evolution of {111} facets. Reflexes from the (100) surface are not seen. After growth of about 660 monolayers of CaF2 at T = 1093 K and a saturation ratio S = 33 from the vapor phase, larger pyramid‐like or hip roof‐like crystallites are developed. The results of AFM height profiles as well as of the LEED investigations indicate again the formation of {111} facets as proved by their angles of 54.7° with the base (100) surface. This shows that the crystallites are homoepitaxially grown on the underlying CaF2 substrate.