M. Tikhov

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.

Growth, structure and energetics of ultrathin ferromagnetic single crystal films on Mo(110)

Abstract The growth mode, structure and thermal stability of ultrathin Fe, Co and Ni films on Mo(110) surfaces is studied by Auger electron spectroscopy, low energy electron diffraction, work function change measurements at various temperatures at and above room temperature and by thermal desorption spectroscopy. In all cases pseudo-Frank-van der Merwe growth is found near room temperature, Stranski-Krastanov growth at intermediate temperatures and alloying at higher temperatures. In Co and Ni films structural rearrangements during growth occur already in the submonolayer range, in Fe films only towards the end of the second monolayer. Implications for the study of magnetic properties are discussed.

The interaction of Pb and Sn with the Mo(110) surface

Abstract The adsorption, initial film growth, alloying and desorption of Pb and Sn on Mo(110) is studied by Auger electron spectroscopy, low energy electron diffraction, work function change measurements and thermal desorption spectroscopy. In the submonolayer range attractive lateral interactions are found in Pb layers, repulsive interactions in Sn layers. In Pb three-dimensional growth begins after completion of one monolayer, in Sn after two monolayers. No alloying occurs between Pb and Mo at any coverage and temperature while Sn reacts with Mo already in the submonolayer range at temperatures as low as 600 K. It is concluded that unusually strong electronic interactions occur in the system Sn-Mo.

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.

Interaction of oxygen with a Cs-covered Si(111)7 × 7 surface

Abstract The influence of submonolayer Cs coverages, θCs, on Si(111)7 × 7 at varying surface temperatures, Ts, on the initial oxygen uptake and Si oxide growth has been studied by means of thermal desorption, work function and Auger electron spectroscopy. The experimental data have shown that the presence of Cs always causes an increase of the oxygen initial uptake whereas promotion of the Si oxide growth is observed only at θCs above half a monolayer. It was found that in the presence of Cs the oxygen initial sticking coefficient becomes independent of Ts (in the range 300–700 K) and the oxygen uptake rate remains constant up to a certain oxygen coverage. The value of this oxygen coverage increases with increasing θCsand Ts. Experimental evidence is given from the thermal desorption data that at θCs > 0.5, Cs participates in the formation of an intermediate with oxygen which is thermally stable at temperatures below 500 K. The mechanism of the Cs-promoted Si oxide growth and the conditions when Cs can act as a catalyst for Si oxidation are discussed.

Adsorption of CO on Ru(1010) doped with different amounts of K and Cs

Abstract The interaction of CO with K and Cs doped Ru(10 1 0) has been studied by means of Auger electron spectroscopy (AES), thermal desorption (TD), electron energy loss spectroscopy (EELS), LEED and work function (WF) measurements. It was found that both alkali metals (AM) induce similar changes in the CO adsorption kinetics and energetics, with preferential filling of the promoted sites. The initial heat of CO adsorption, Δ H CO 0 , associated with promoted CO ∗ , increases linearly from 145 up to 224 kJ/mol with increasing alkali coverage, θ AM , the maximum Δ H CO 0 value being reached when coincident CO and AM desorption is detected. LEED and WF data for coadsorbate systems indicate formation of patches with different WF and compositions on the surface. EELS results show that the presence of AM causes an energy shift of the CO 2 π b → 2 π a transitions from 6.3 to ∼7.0 eV, removal of the AM ns valence transitions and plasmon excitations and appearance of new loss structures. Comparing the present data with the results on CO adsorption on Na doped Ru(10 1 0) the type and contribution of the possible direct COAM interactions are discussed.

Adsorption and electric measurements on germanium (111) surfaces covered with potassium and cesium

Abstract Potassium and cesium adsorption on a Ge(111) surface and its effect on the surface conductivity, Δσ, surface recombination velocity, S, and work function changes, Δϕ, has been studied. The K and Cs Thermal desorption spectra consist of multiple peaks. To each peak corresponds a straight line segment of the Δϕ versus coverage curves. The surface conductivity versus coverage curves successively pass through a minimum and a maximum. The decreasing parts of these curves are attributed to the appearance of alkali-metal-induced extrinsic surface states, whereas the increasing one are ascribed to the disappearance of the intrinsic states of the clean Ge(111) surface. The surface recombination velocity has been found to be multi-valued function of the surface potential. At a K overlayer coverage close to one monolayer new high-temperature peaks appear in the TD spectra due to irreversible surface reconstruction.

Thermal disordering of the Al(110) surface

The thermal disordering of the Al(110) surface is studied by video LEED, work-function change and electron energy loss spectroscopy measurements. It is found that the disordering of the Al(110) surface is similar to that of the (110) surface of a stress-free Pb crystal, though with lower disordering temperatures relative to the melting point.

Na-promoted oxidation of Si(111)

Abstract The effect of Na on the oxidation of a Si(111)-7 × 7 surface has been studied by Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), thermal programmed desorption (TPD), LEED and work-function measurements. Two modes of Na-promoted oxidation were used. It was found that the drastic increase of the initial oxygen adsorption rate, observed for sodium coverages, θ NA , in the submonolayer coverage range was not accompanied by a parallel enhancement of the oxidation rate. Na-promoted oxidation of Si(111) occurred only for θ NA > 0.5. The formation of NaO 2 and the resulting oxidation of the Si surface was studied thoroughly.