K. Markert

Thermal desorption of strained monoatomic Ag and Au layers from Ru(001)

Model‐independent or complete analysis of thermal desorption spectra suggests, in agreement with low‐energy electron diffraction, that attractive lateral interactions between Ag atoms on a Ru(001) substrate lead to island formation for Ag coverages above 0.15 ML, with zeroth‐order desorption kinetics and coverage‐independent activation energy of desorption E, and preexponential factor ν. For the system Au/Ru(001), on the other hand, E and ν decrease monotonically with coverage, indicating that Au–Au interactions on Ru(001) are repulsive. For ΘAg<0.15 and ΘAu<1 the systems exhibit a clear compensation effect between E and ν.

The compensation effect and the manifestation of lateral interactions in thermal desorption spectroscopy

Abstract If thermal desorption spectra are analysed in terms of the Polanyi-Wigner equation lateral interactions between the adsorbates may lead to coverage (θ) dependent pre-exponential factors, v, and activation energies of desorption, E. Evidence from the literature shows that E and v often satisfy the well-known compensation effect 1n v(θ) = bE(θ) + c, with constants b and c. Here we insert this compensation effect into the rate equation of desorption and simulate spectra which illustrate the influence of the compensation effect in thermal desorption spectra of adsorbate systems where pairwise lateral interactions prevail.

The short range of the electronic promoter effect of potassium

Abstract Photoemission of Adsorbed Xenon atoms (PAX) as a local work function probe is used to investigate the range of the electronic promoter effect of potassium submonolayers on a Ru(001) surface. Three Xe states on these bimetallic K/Ru surfaces are clearly distinguishable by their 5p photoemission and are associated with Xe probe atoms at basically unmodified Ru sites, at “mixed” K.Ru sites next to K ions, and on top of potassium, respectively. From the relative intensities of these three states as well as from their 5p electron binding energies as a function of potassium coverage it is concluded that the radius of the “sphere” of modified charge density around one K ion is ∼ 6 A.

Two‐dimensional gas–solid phase transition of xenon adsorbed on different metal substrates

Coexisting two‐dimensional (2D) gas and 2D solid phases of Xe adsorbed on Ag(111), Cu(111), and Ru(001) can be distinguished by means of their Xe(5p) photoemission. The relative equilibrium concentrations (at a given temperature) are substrate dependent and correlate with the xenon–metal interaction strength. Namely, the maximum gas concentration just before 2D phase separation grows with increasing Xe adsorption energy as well as adsorption induced xenon dipole moment in the order Ag(111)

Thermal stability of atomic Ag/Au and Au/Ag interfaces on A Ru(001) substrate

Abstract The thermally activated intermixing in Ag/Au and Au/Ag bilayers supported on a Ru(001) substrate has been studied using the PAX-technique (photoemission of adsorbed xenon). It is found that the Ag/Au interface (on Ru) is thermally more stable than the Au/Ag interface. In the first case Ag atoms do not penetrate into the Au underlayer at 275 K, while in the second case An atoms do penetrate into the Ag underlayer at this temperature. These investigations also represent a very successful model study which may be carried over the other metal/metal combinations.

Microscopic pooperties of two-dimensional silver and gold metal- and alloy-films on Ru(001)

Structural changes in submonolayer codeposits of gold and silver on Ru(001) are studied using the PAX technique. It is shown that the formation of two-dimensional AgAu alloys from Ag islands and co-deposited Au atoms is a two-step process: first the Au atoms diffuse from the Ag silands, only then the Au atoms interalloy from island boundaries.

Mechanism of two‐dimensional AgAu alloy formation on Ru(001)

Using the photoemission of adsorbed xenon technique we demonstrate that the two‐dimensional alloy formation between ordered Ag islands on Ru(001) and Au atoms deposited on top of these islands proceeds via a two‐step mechanism: The Au atoms do not penetrate the Ag layer directly, but first migrate from the islands onto the Ru substrate, from where they then ‘‘attack’’ the Ag islands to form a two‐dimensional AgAu alloy.

Structural and electronic properties of Ag/Si(111) and Au/Si(111) surfaces

The structural and electronic properties of thin Ag and Au films adsorbed on a Si(111)‐7×7 surface were studied using thermal desorption spectra of xenon, work function measurements, and photoemission spectra of the clean Si(111)‐7×7 and the Ag/Si(111) and Au/Si(111) surfaces at 300 and 60 K. Similarities and differences with Au/Si(111) results are noted.

Site-exchange processes across an atomic Ag/Au interface

Abstract The thermally activated intermixing between Ag submonolayer deposits and a complete Au monolayer supported on a Ru(001) substrate was studied using the PAX (photoemission of adsorbed xenon) technique. At 275 K 2D Ag islands exist on the Au monolayer. At 350 K AgAu atom exchange occurs only within the area of the previous Ag islands. Only at even higher temperatures a homogeneous AgAu alloy double layer is formed. This study may, of course, serve as model for other metal/metal combinations.

Site exchange of atoms across atomically sharp Ag–Au interfaces

The thermally activated site exchange between Ag/Au and Au/Ag double layers on a Ru(001) substrate has been studied with photoemission of adsorbed xenon (PAX). The Au/Ag interface is less stable than the Ag/Au interface on Ru, penetration of Au atoms in a Ag underlayer occurs at lower temperatures than penetration of Ag atoms in a Au underlayer. The work serves as a model for other metal–metal interfaces and illustrates the usefulness of PAX in the characterization of surfaces on a subnanometer scale.