L. Surnev

Comparative study of hydrogen adsorption on Ge(100) and Ge(111) surfaces

Abstract In this study, the work function changes, Δφ, surface conductivity, Δσ, and electron energy loss spectra (ELS) have been obtained as a function of relative hydrogen coverage, θ, determined by thermal desorption (TD) measurements. A comparative measurement has been performed. The Δφ and Δσ data favour the ionic type models of a Ge(100) surface and the covalent type models of a Ge(111) surface. However, the adsorption kinetics and ELS data are almost the same for both the Ge(111) and Ge(100) surfaces.

Interaction of oxygen with a Ru(OO1) surface

Abstract The interactions of oxygen with a Ru(001) surface were investigated at 300–1300 K by AES, thermal desorption spectroscopy (TDS) and work function measurements. A single second-order TD peak was observed at coverages θ lower than 0.25. The considerable changes in the shapes of the TD curves recorded at θ

Oxygen adsorption on a Pd(111) surface

The interaction of oxygen with Pd(111) has been studied by means of AES, ELS, thermal desorption (TD), electron stimulated desorption (ESD) and work function measurements. It was found that a very small part ( ∼ 2–3%) of the available adsorption sites are contributing to the O+ electron stimulated yield, the population of the latter being accompanied by enormously large work function changes (up to ∼ 0.9 eV). A mechanism of adsorption and depopulation of these sites involving oxygen bulk and surface diffusion has been proposed.

Oxygen adsorption on an alkali metal-covered Ni(100) surface

The oxygen chemisorption on an alkali (Na, K, Cs) covered Ni(100) surface and its initial oxidation were studied by Auger and electron energy loss spectroscopy (ELS). It was found that in the presence of an alkali metal, the sticking coefficient S remains unity up to a given oxygen coverage of θOcwhose value depends on the alkali overlayer concentration and the ionicity of the Ni-alkali metal bond. At a given oxygen coverage, the line shapes of Auger and loss spectra are almost the same for alkali-covered and clean Ni(100), which suggests that alkali metals cause no change in the character of the Ni-O bond. The effect of alkali metals is associated with increasing electron charge in the surface region, which facilitates oxygen chemisorption. The enhanced surface oxygen concentration in the presence of an alkali metal results in the formation of an oxide phase at lower oxygen exposures than is the case of clean Ni surfaces.

Interaction of oxygen with an alkali modified Ru(001) surface

Abstract The interaction of oxygen with potassium predosed Ru(001) has been studied by means of thermal desorption (TD), Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and work function (WF) measurements. These results were compared with those reported earlier on Na and Cs precovered Ru(001). It was found that the initial sticking coefficient, S 0 , increased linearly with alkali coverages θ am , in the sequence Na-K-Cs. The TD, WF and EELS data indicated predominance of the strong oxygen-ruthenium interactions over the alkali-oxygen interactions at low potassium and oxygen coverages (θ K and θ O , respectively). Above certain θ K and θ O (θ K > 0.12 and θ O > 0.6), the coincident O 2 , K and K 2 O TD peaks at 890 K, the EL feature at ~ 28 eV, and the appearance of a shoulder in the WF I–V curves were interpreted as the formation of K-O-Ru complexes gathered in patches on the Ru(001) surface. This behaviour was common for the three alkali metals when coadsorbed with oxygen.

Alkali metal adsorption on Ru(001)

The adsorption of Na, K and Cs on Ru(001) was studied by thermal desorption (TD), work function (WF) measurements, and electron energy loss spectroscopy (EELS). The coverage dependences of the desorption energy, Ed () and the mean dipole moment 2 μ-() were found to be similar for all alkali metals under investigation. Therefore, the dipole depolarization interactions determined the slope of the Ed() curves. These interactions also determined the energy changes of the Na 2p, K 3p and Cs 5p core level excitations with increasing . The one-electron transitions involving alkali valence orbitals and the appearance of plasmon excitations in the alkali overlayer are also discussed.

Sodium adsorption on a Si(001)-(2 × 1) surface

Abstract The adsorption of Na on a Si(001)-(2 × 1) surface has been studied by means of AES, LEED, EELS, Temperature Programmed Desorption (TPD), and work function (Δφ) measurements. Four peaks are observed in the Na TPD spectra. The lowest temperature peak corresponds to a multilayer Na structure. The observed weak coverage dependence of the Na desorption energy suggests a predominantly covalent character of the NaSi bonding. Our TPD data show that with Na in the first layer (θNa = 0.68), no metallization of the Na overlayer takes place. The AES, LEED, EELS and Δφ data give strong evidence of 3D clustering (Stranski-Krastanov growth mode), which at 300 K occurs for θNa ⩾ 0.5.

Interaction of oxygen with Na-covered Si(100)

Abstract Oxygen interaction with Na-dosed Si(100) has been studied by thermal desorption (TD), Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), LEED and work function (Δφ) measurements. It is found that Na-dosing increases drastically the oxygen uptake rate. However, no Na-promoted oxidation of Si(100) occurs with Na in the first layer. Oxidation of Si(100) is observed only for a multilayer Na structure. Linear enhancement of the Si oxidation activity with increasing Na coverage, θ Na , is obtained for θ Na > 0.5. The inhomogeneous oxidation of Si(100) is associated with the formation of NaO 2 3D clusters.

Oxygen adsorption on Ge(111) surface: I. Atomic clean surface

Abstract Oxygen adsorption on a clean Ge(111) surface has been studied in the temperature range 300–560 K by means of Auger electron spectroscopy (AES), thermal desorption (TD), work function (WF) measurements, and electron energy loss spectroscopy (ELS). The adsorption and WF kinetics at 300 K exhibit a shape different from those observed at higher adsorption temperatures. At 300 K oxygen only removes the empty dangling bond surface state, whereas at higher temperature new loss transitions involving chemically shifted Ge 3d core levels appear. The findings imply that at 300 K only a chemisorption oxygen state exists on the Ge(111) surface whereas the formation of an oxide phase requires higher temperatures. The shapes of the TD curves show that the desorption of GeO follows 1 2 order desorption kinetics.

Oxygen adsorption on Ge(111) surface: II. Alkali metal-covered surfaces

Abstract Oxygen adsorption on an alkali metal (a.m.)-covered Ge(111) surface has been studied by means of Auger electron spectroscopy (AES), electron energy loss spectroscopy (ELS), thermal desorption (TD), and work function measurements (WF). It was found that the presence of a.m. results in enhancement of the oxygen adsorption rate. The initial values of the sticking coefficient, S 0 , are exponential functions of the work function changes caused by the a.m. adsorption. It was shown that no germanium oxide phases are formed on an alkali-covered Ge surface at 300 K. The oxidation rate at high temperatures is limited by the rearrangement processes taking place in the surface GeO layer. The results obtained show that the alkali metal perturbs the GeO bond to a certain extent but no alkali oxide formation was observed at a.m. covertages under investigation.