E. Yu. Afanas’eva

Initial stages of the interaction of sodium and cesium with gold

The desorption of Cs and Na atoms from the corresponding layers applied to a gold film deposited on textured tungsten ribbon with a preferred orientation of the (100) surface is studied by thermal desorption spectroscopy with the products of thermal desorption scanned on a pulsed time-of-flight mass spectrometer. The Cs atoms evaporated at T = 300 K are desorbed by two phases, one of which can be identified with the filling of a monolayer and the other can be attributed to the formation of the CsAu compound. The Na atoms evaporated at T = 300 K are desorbed by three phases associated with the formation of a monolayer coating, a sodium compound of with gold, and a multilayer sodium film.

Thermodesorption of samarium from oxidized tungsten surface

Thermodesorption of samarium (Sm) atoms and samarium oxide (SmO) molecules from samarium films deposited in vacuum onto tungsten substrates covered with thin (<1 nm thick) layers of tungsten oxides has been studied. It is established that samarium reduces tungsten from its oxides. The parameters of Sm and SmO desorption from an oxidized tungsten surface are determined.

Oxidation kinetics of thin titanium films grown on tungsten

Growth of thin Ti films on (100)W and the kinetics of their oxidation are studied using thermal-desorption spectroscopy and Auger electron spectroscopy. Titanium films grow nearly layer by layer on the (100)W face at room temperature. The activation energy for desorption of Ti atoms decreases from 5.2 eV for coverage θ=0.1 to 4.9 eV in a multilayer film. Oxidation of a thin (θ=6) titanium film starts with dissolution of oxygen atoms in its bulk to the limiting concentration for a given temperature, after which the film oxidizes to TiO, with the TiO2 oxide starting to grow when exposure of the film to oxygen is prolonged. The thermal desorption of oxides follows zero-order kinetics and is characterized by desorption activation energies of 5.1 (TiO) and 5.9 eV (TiO2).

Europium adsorption on a tungsten surface with various degrees of oxidation

The kinetics of europium adsorption on a W(100) face with various degrees of oxidation were studied by thermal desorption and Auger electron spectroscopy. The spectrum of Eu atoms desorbed thermally from the W(100) face consists of three successively filling desorption phases whose desorption activation energy decreases from 3 to 2.1 eV with an increase in the surface coverage. The thermodesorption spectrum of Eu atoms from the W(100) face coated with a monatomic oxygen film contains five successively forming desorption phases, with the desorption activation energy increasing to 4 eV for the high-temperature phase. The oxidized W is reduced by europium, and the desorption of the W oxides is replaced by that of EuO. After a monolayer film has formed, the Eu film adsorbed on tungsten starts to grow in the form of three-dimensional crystallites. As the degree of W oxidation increases, the Eu film becomes less nonuniform, until a solid Eu film starts to grow on bulk W oxides and completely screens the tungsten Auger signal.

Intercalation of graphene on iridium with samarium atoms

It has been shown that sodium atoms deposited on the surface of graphene atop iridium at T ≤ 850 K diffuse under the graphene layer into an intercalated state and accumulate there in significant concentrations ∼(2–3) × 1014 atoms cm−2. The release of the atoms from under the graphene “carpet” takes place upon destruction of the layer at T ≥ 1800 K. The physical nature of the differences in the processes of release of atoms of different alkali metals from under graphene has been discussed.

Initial stages of the interaction with oxygen of samarium thin films grown on the iridium surface

The interaction of thin (<1 nm) samarium films deposited on a textured iridium ribbon has been investigated by thermal desorption spectrometry. Samarium atoms deposited at T = 300 K desorb in three phases associated with the formation of a submonolayer samarium coverage on iridium, a compound of samarium with iridium, and a multilayer samarium film. The interaction with oxygen leads to the appearance of a new desorption phase, which is associated with the formation of samarium oxide. Oxidation of samarium is observed during exposure in oxygen already at room temperature. An increase in temperature of the iridium ribbon, at which exposure in oxygen occurs, to T = 1100 K leads to the formation of the compound of samarium with iridium. Further, the film of the compound decomposes in the course of interaction with oxygen, and samarium oxide grows on the Ir surface.

Thermodesorption of silicon from textured tantalum ribbons

The interaction of silicon with tantalum is studied by the Auger spectroscopy and temperature-controlled desorption technique. It is shown that, at a monolayer coating, the adsorbed silicon atoms penetrate into the bulk of a substrate at temperature T≥1400 K. The spectral shape and the annealing curves are explained by the influence of the Si-Si lateral repulsion in an adsorbed layer on the desorption and diffusion of the Si atoms into the bulk. Some ratios between the kinetic parameters are determined from analysis of the experimental data. Their application in numerical calculations based on the model proposed earlier makes it possible to determine (from comparison of the calculated and experimental data) the kinetic parameters for all the processes of the interaction between silicon and the tantalum substrate during the temperature-controlled desorption (desorption, transfer into the bulk, diffusion, and migration of silicon onto the surface). An adequate description of the experiment is obtained only under the assumption that the diffusion at the final stages of temperature-controlled desorption after reaching a maximum occurs within a thin layer near the surface, so that the migration of the Si atoms to the surface and desorption proceed more rapidly than their diffusion into the bulk.

Kinetics of silicon interaction with textured tantalum ribbons

The kinetics of silicon interaction with textured tantalum ribbons having a predominantly (100)-oriented surface has been studied by Auger electron spectroscopy. For T<700 K, silicon builds up on the surface. Within the 900<T<1000-K interval, after the formation of a monolayer coating, the excess silicon enters into layer-by-layer growth of the silicide TaSi2. Within 1150<T<1320 K, this excess silicon reacts with tantalum to produce in a layer-by-layer manner the Ta5Si3 silicide; this compound is unstable and decomposes for T>1320 K to form Ta 4Si, with only one third of the original silicon monolayer being left on the surface. The activation energy of Ta5Si3 decomposition is 4.3±0.2 eV. The activation energy of Si thermal desorption at low coverages is 5.4±0.2 eV.

Intercalated samarium as an agent enabling the intercalation of oxygen under a monolayer graphene film on iridium

Using thermal desorption time-of-flight mass spectrometry and thermionic methods, it is shown that oxygen does not intercalate under a graphene monolayer grown correctly on iridium, at least at temperatures of T = 300–400 K and exposures below 12000 L. However, if the graphene film on iridium is preliminary intercalated with samarium atoms (up to coverage of θSm = 0.2–0.45), the penetration of oxygen atoms under the graphene film is observed. The oxygen atoms in the intercalated state are chemically bonded to samarium atoms and remain under graphene up to high temperatures (~2150 K).

Oxidation of a thin samarium film on iridium

Thermal desorption spectroscopy has been used to study the interaction of oxygen with a thin (<1 nm) samarium film deposited onto a textured iridium ribbon. Desorption of Sm atoms from Ir surface takes place from various states (chemisorbed, condensed, from compound with iridium, and oxide). The formation of samarium oxide is observed already at room temperature. As the temperature increases to T = 1100 K, a compound of samarium with iridium is formed at the first stage and then oxygen interacts with Sm atoms from this compound and “slow” (compared to the first process) growth of samarium oxide takes place.