The influence of an electric double layer on the surface of nanometer-thick ytterbium films grown on a Si(111) substrate on their adsorption and catalytic properties has been studied. It is shown that charge density waves (Friedel oscillations) generated in such nanofilms by the Si interface cause nonmonotonic changes of the distance in the double layer with increasing thickness. In turn, compression and expansion of the double layer lead to size dependences of the adsorption-catalytic properties of the film surface. In particular, as the film thickness increases, the adsorption character and decomposition rate of ammonia molecules on the ytterbium surface change.

The effect of standing waves of charge density (Friedel oscillations) generated by an interface of the metallic ytterbium nanofilm single-crystal silicon substrate type on the work function of ytterbium nanolayers has been studied. It is shown that in the range of nanofilm thicknesses from 0 to 8 monatomic layers, the work function has an oscillating character. This feature of the dependence of the work function on the nanofilm thickness is a consequence of the fact that the standing waves change nonmonotonically the power (momentum) of the electric double layer, which exists on the metal surface and affects the work function of the metal. This ultimately determines the oscillating nature of the dependence of the work function on the thickness of the nanofilms. Keywords: surface, nanofilm, work function, Friedel oscillations, electric double layer, ytterbium.

The influence of an electric double layer on the surface of nanometer-thick ytterbium films grown on a Si(111) substrate on their adsorption and catalytic properties has been studied. It is shown that charge density waves (Friedel oscillations) generated in such nanofilms by the Si interface cause nonmonotonic changes of the distance in the double layer with increasing thickness. In turn, compression and expansion of the double layer lead to size dependences of the adsorption-catalytic properties of the film surface. In particular, as the film thickness increases, the adsorption character and decomposition rate of ammonia molecules on the ytterbium surface change.

A model is proposed for interpreting the results of Auger electron spectroscopy in the case of film systems with reactive interfaces. A quantitative relationship has been established between the parameters of the transition layer and the shape of dependences of the Auger signal of the substrate on the film thickness in such systems. The model was tested for three rare-earth metal (Yb, Sm, Gd) – Si(111) interfaces. Quantitative data have been obtained concerning their structure and stoichiometric composition, as well as the dependence of these characteristics on the thermodynamic properties of the studied rare earth metals.

The effect of standing waves of charge density (Friedel oscillations) generated by an interface of the ‘metallic ytterbium nanofilm  single-crystal silicon substrate’ type on the work function of ytterbium nanolayers has been studied. It is shown that in the range of nanofilm thicknesses from 0 to 8 monatomic layers, the work function has an oscillating character. This feature of the dependence of the work function on the nanofilm thickness is a consequence of the fact that the standing waves change nonmonotonically the power (momentum) of the electric double layer, which exists on the metal surface and affects the work function of the metal. This ultimately determines the oscillating nature of the dependence of the work function on the thickness of the nanofilms.

The effect of nondissociative adsorption of oxygen molecules on the electronic structure of ytterbium films with a thickness of 16 monolayers (6.08 nm) is investigated for the first time using scanning tunnelling spectroscopy. It is found that the adsorption of O 2 molecules induces a metal–semiconductor transition in ytterbium. As a result of this transition, quantum states in nanofilms disappear, indicating a change in the type of coupling in the ytterbium crystal lattice, and a bandgap with a width of about 0.72 eV is opened.

X-ray photoelectron spectra of nanoscale-thickness ytterbium films along with adsorbed oxygen layers have been studied for the first time. It is found that the spectra include features from both divalent and trivalent ytterbium. The intensity ratio of these features raises upon increasing the film thickness (the size effect). It is shown that the above behavior is due to the formation of two final states related to divalent and trivalent ytterbium at the photoionization of 4f-level by photons with the energy of 1253.6 eV, while only the trivalent state is realized by using the photons with the energy of 142 eV. Keywords: Ytterbium, nanofilms, adsorbed molecules, electronic state, X-ray photoelectron spectroscopy.

X-ray photoelectron spectra of nanoscale-thickness ytterbium films along with adsorbed oxygen layers have been studied for the first time. It is found that the spectra include features from both divalent and trivalent ytterbium. The intensity ratio of these features raises upon increasing the film thickness (the size effect). It is shown that the above behavior is due to the formation of two final states related to divalent and trivalent ytterbium at the photoionization of Yb 4f level by photons with the energy of 1253.6 eV, while only the trivalent state is realized by using the photons with the energy of 142 eV.

Influence of adsorbed carbon monoxide molecules on the thermal properties of rare-earth metal ytterbium films of nanoscale thickness has been studied. The films are produced at room temperature by metal deposition on single-crystal silicon substrates with the Si(111) surface orientation or textured tungsten ribbons with the predominant (100) face. It is shown that the adsorbed molecules hinder evaporation of ytterbium. The strength of such hindering is dependent on the chemical nature of substrate material. It is established that the substrates affect the state of adsorbed molecules through the nanofilms. This in turn influences on the evaporation rate of nanolayer material.

The adsorption of oxygen molecules on ytterbium nanofilms of various thicknesses has been studied by X-ray photoelectron spectroscopy and contact potential difference measurements. It has been established that the maximum number of O2 molecules that can be adsorbed on the films increases with the film thickness. Such behavior is observed at thicknesses less than 10 monolayers. This size effect is ultimately due to the fact that an indispensable condition for the adsorption process at high doses of oxygen is the electron transfer from the film to molecules, and that the maximum number of electrons that can participate in this process depends on the nanolayer thickness. Localization of a negative charge on O2 molecules occurring in at high doses of adsorbate, causes a weakening of the bonding of 1s electrons in these molecules. In addition, it should lead to a weakening of the bond between oxygen atoms in O2 molecules.

Influence of adsorbed carbon monoxide molecules on the thermal properties of rare-earth metal ytterbium films of nanoscale thickness has been studied. The films are produced at room temperature by metal deposition on single-crystal silicon substrates with the Si(111) surface orientation or textured tungsten ribbons with the predominant (100) face. It is shown that the adsorbed molecules hinder evaporation of ytterbium. The strength of such hindering is dependent on the chemical nature of substrate material. It is established that the substrates affect the state of adsorbed molecules through the nanofilms. This in turn influences on the evaporation rate of nanolayer material.

The adsorption of oxygen molecules on ytterbium nanofilms of various thicknesses has been studied by X-ray photoelectron spectroscopy and contact potential difference measurements. It has been established that the maximum number of O 2 molecules that can be adsorbed on the films increases with the film thickness. Such behavior is observed at thicknesses less than 10 monolayers. This size effect is ultimately due to the fact that an indispensable condition for the adsorption process at high doses of oxygen is the electron transfer from the film to molecules, and that the maximum number of electrons that can participate in this process depends on the nanolayer thickness. Localization of a negative charge on O 2 molecules occurring in at high doses of adsorbate, causes a weakening of the bonding of 1s-electrons in these molecules. In addition, it should lead to a weakening of the bond between oxygen atoms in O 2 molecules. Keywords: oxygen, ytterbium, adsorbed molecules, nanofilms, X-ray photoelectron spectroscopy, work function.

Using the energy diagrams of asymmetric potential barriers, which are formed during the contact of two metals with different work functions, the effect of the contact potential difference on the current–voltage characteristics and differential conductivity spectra obtained using scanning tunneling spectroscopy is considered. It is shown that the obtained conclusions agree qualitatively with the experimental results for ytterbium nanofilms with a thickness of 16 monolayers (6.08 nm). However, they differ significantly quantitatively. An analysis of these differences is carried out.

Using the energy diagrams of asymmetric potential barriers formed at the contact of two metals with different work functions, the influence of contact potential difference on the current-voltage characteristics and differential conductivity spectra measured by scanning tunneling spectroscopy is considered. It is shown that the obtained conclusions are in qualitative agreement with the experimental results for ytterbium nanofilms with the thickness of 16 monolayers (6.08 nm). However, they significantly differ quantitatively. The analysis of such diffrences is performed.

The influence of nondissociative adsorption of oxygen molecules on the electronic structure of ytterbium films with the thickness of 16 monolayers (6.08 nm) has been studied for the first time by using scanning tunneling spectroscopy. It is established that the adsorption of O2 molecules induces the metal-semiconductor transition in ytterbium. As a result of this transition, the quantum states have disappeared in the films, which evidences for a change of bonding type in the ytterbium crystal lattice, as well as the band gap of ~0.72 eV has opened.

–The influence of oxygen molecules adsorbed on the surface of ytterbium nanofilms with a thickness of 16–200 single layers (6.1–76 nm) on the state of these films is studied. It is found that the adsorption of molecules is accompanied by the formation of an adjacent modified ytterbium layer. One of the features of the modified layer is that it contains trivalent ytterbium. The minimum thickness of this layer is estimated. It is 16 single layers (6.1 nm). Based on results previously obtained by us, it is suggested that the modified layer protects the ytterbium bulk from corrosion when exposed to air.

The surfaces of Yb–Si(111) and O–Yb–Si(111) structures (with a thickness of ytterbium nanofilms of 16 monolayers (6.08 nm)) have been investigated for the first time using scanning tunnel microscopy, which has provided data on the morphology and phase composition of these surfaces. It is found that, prior to oxygen adsorption, the nanofilms exhibit a high degree of homogeneity over their thickness, grow in accordance with a mechanism very close to the layer-by-layer growth, and have a homogeneous crystalline structure. After oxygen adsorption, an island layer of oxygen molecules is formed with a thickness of 0.112 nm. It is shown that the nanofilms morphology in the regions of the film surface coated by a monomolecular oxygen film changes significantly, while the morphology of the surface regions uncoated with the adsorbed layer remains unchanged.

Using scanning tunneling microscopy, surfaces of Yb-Si(111) и O-Yb-Si(111) structures (the Yb nanofilm thickness is 16 monolayers (6.08 nm)) have been studied for the first time, and the information about the morphology and phase composition of these surfaces has been gained. It is established that before the oxygen adsorption, the nanofilms have a high degree of uniformity in thickness, the groth mechanism which is very similar to the layer-by-layer fashion, and the uniform crystallographic structure. Upon the oxygen adsorption a layer composed of islands of oxygen molecules is formed. The height of this layer is 0.112 nm. It is shown that the morphology of the nanofilm within the surface areas which are covered by the monomolecular oxygen film is significantly changed. At the same time the morphology of surface areas which are not occupied by adsorbed layer has still remained intact.

The adsorption of carbon monoxide (CO) molecules on ytterbium nanofilms composed of 16–200 single layers (6.1–76 nm-thick) is studied. The films are grown on grain-oriented tungsten ribbons with the preferential surface orientation (100). It is shown that, prior to the adsorption of CO molecules, ytterbium is divalent, possessing the [Xe]4f146s2 electron configuration. The adsorption of gas molecules in the surface region of the film led to the formation of a layer with trivalent ytterbium (with the [Xe]4f135d16s2 electron configuration). The minimum thickness of the ytterbium layer modified by adsorbed CO molecules is found to be composed of 16 single layers, corresponding to a thickness of 6.1 nm, which is anomalously higher than the values reported in publications.