J. Kołaczkiewicz

The adsorption of Eu, Gd and Tb on the W(110) surface

Abstract The adsorption of Eu, Gd and Tb on the W(110) surface is studied by AES, LEED, TDS and work function change (Δφ) measurements with the goal of understanding growth mode, structure and bonding as a function of coverage and adsorbate. Significant differences between Eu on the one hand and Gd and Tb on the other hand are found and related to atomic diameter and electronic structure. The structural and TDS results point to a strong compensation of the repulsive dipole-dipole interactions by attractive, presumably indirect electronic interactions.

Thermal desorption spectroscopy of Ni, Cu, Ag and Au from W(110)

Abstract Ni, Cu, Ag and Au on W(110) in the submonolayer range are studied by thermal desorption spectroscopy with the goal of obtaining information on lateral interactions and on the phase state of the adsorption layer in the temperature range in which desorption occurs. Ni, Cu and Ag are found to desorb over a wide coverage range from the two-phase (vapor-condensate) region while Au desorbs only from the single-phase vapor region. Segments of the coexistence curve are determined. The desorption energies have the following limiting values: 4.35–4.95. 3.2–3.85, 2.8–3.55 and 3.3–4.1 eV for Ni, Cu, Ag and Au, respectively.

The law of corresponding states for chemisorbed layers with attractive lateral interactions

Abstract Chemisorbed layers which form two-dimensional islands at low temperature consist in general of two phases: condensed phase and a gaseous phase. The coexistence region of the two phases is derived from work function change data of Ni, Cu, Pd and Ag on W(110). The experimental coexistence lines are compared with those obtained from various equations of state with the result that a law of corresponding states is found in the form of the reduced Van der Waals equation or of the quasichemical approximation.

The dipole moments of noble and transition metal atoms adsorbed on W(110) and W(211) surfaces

Abstract The dipole moments of Cu, Ag, Au, Ni and Pd on W(110) and of Ag, Au and Ni on W(211) surfaces are derived from work function change ( Δφ ) measurements at low coverages θ and high temperatures at which the adsorption layer is a two-dimensional gas of monomers and Δφ is proportional to θ. The dipole moments decrease linearly with increasing Wigner-Seitz radius of the adsorbed metals and have a strong linear temperature dependence. The temperature coefficient increases with decreasing binding energy of the adsorbate. Au makes an exception to both relationships. Qualitative explanations are proposed for the observed phenomena.

The adsorption of europium and terbium on the tungsten (211) surface

Abstract The adsorption of Eu and Tb on W(211) is studied with AES, LEED, work function change (Δφ) measurements and thermal desorption spectroscopy (TDS). Although both atoms differ in electron configuration, in ionic and atomic diameter significant differences in the adsorbate structure occur only at higher coverages. Both adsorbates show the general behaviour of electropositive adsorbates but differ from those studied up to now in the coverage dependence of the desorption energy, in particular Tb.

The interaction of Al and O atoms on W(110) studied with metastable impact electron spectroscopy (MIES) and UPS

Al layers (< 2.5 adlayers thickness) are grown on W(110) under the “in situ” control of metastable impact electron spectroscopy (MIES) and photoelectron spectroscopy (UPS). The adlayer thickness was determined by combining LEED and work function measurements. The interaction of oxygen with the Al adlayers is studied. In order to analyze the adsorbed-oxygen/oxide transition, thin layers of alumina are grown by coadsorbing Al and oxygen on a 750 K hot W(110) surface. The resulting MIE and UP spectra are compared with those obtained during the oxygenation of the Al layers. Finally, the MIE spectra for Al/W, Al/W + O2 and alumina are simulated by taking into account information on the electronic structure available from previous studies.

Growth and thermal stability of Fe, Ni, Rh and Pd layers on the (111)W crystal face

Abstract LEED, AES and Δ φ measurements were used to investigate the growth of Fe, Ni, Rh and Pd layers on the tungsten (111) surface. The thermal stabilities of the layers and of the substrate were also examined. Both were found to be thermally unstable at coverages above one monolayer. In addition, Rh and Pd were found to cause faceting of the substrate surface. In thick Fe layers, a non-wetting-wetting transition was observed.

Ultrathin films of Rh, Ir and Pt on tungsten (110)

Abstract The initial growth of rhodium, iridium and platinum on W(110) was studied at several temperatures by low-energy electron diffraction, Auger electron spectroscopy, thermal desorption spectroscopy and work function change measurements. At room temperature Frank-van der Merwe-type growth was observed, at temperatures in excess of 600–800 K, however, Stranski-Krastanov-type growth. Several metastable structures were observed in all the adsorbates.

Investigation of the temperature dependent changes of work function induced by adsorption of Ag on W(011)

Abstract The adsorption of silver on the (011) face of tungsten has been studied at temperatures from 78 to 1200 K. Investigations were performed using LEED, AES and work function measurements. The work function changes appeared to depend on the nature of the adlayer, and its arrangement with respect to the substrate. An absolute coverage scale was determined for room temperature, and this scale was related to the work function changes observed at this temperature. An interpretation of the obtained curves of the work function changes is presented.

LEED, AES, Δφ and EELS study of Al on Mo(110)

Abstract The mechanism of layer growth upon Al adsorption was investigated with increasing temperature of the Mo sample. It has been found that a layer-by-layer growth mechanism of the adsorbate is primary at room temperature.