Thermal ionization of methenamine (C6H12N4) on the surface of the NaAux intermetallic compound has been studied. It has been established that the processes of decomposition, desorption and ionization of adsorbed compounds, thermally stimulated on the surface, proceed due to the accumulation of energy at the degrees of freedom of the adsorption complex, including the adsorbed compound and a solid, by the mechanism of monomolecular decomposition reactions. In this case, the decomposition of the adsorption complex is accompanied by the desorption of ions that are not in thermal equilibrium with the solid. The uniformity of the temperature dependences of the ion current and their distribution over two groups allowed us to conclude that ions are desorbed from the surface, which correspond to the decays of individual adsorbed molecules, as well as the decays of dimers formed on the surface. The decay of methenamine molecules during thermal ionization occurs in the same way as their decay in vacuum during electron ionization, which indicates the preservation of the bulk structure of methenamine molecules during adsorption and a significant lifetime of the excited state of compounds on NaAux.

For the first time, the adsorption of barium atoms on the surface of the (0001) face of GaN was calculated using the density functional method. The 2D GaN layer was modeled using a GaN(0001) 2×2 supercell containing 10 GaN bilayers. The electron density of state and the adsorption energy of the Ba atom were calculated for five adsorption sites of the Ba atom: in the hollow position, in the bridge position between the surface Ga (N) atoms, and above the surface Ga (N) atom. There was one Ba atom per 4 surface Ga atoms in the first GaN bilayer. The adsorption of the barium atom above the surface N atom was most preferable. The adsorption energy was 2,96 eV. The adsorption of Ba atoms resulted in an insignificant reconstruction of the GaN surface: the maximum shift of the Ga (N) atoms did not exceed 0,11 Å. The adsorption of Ba resulted in the formation of a surface band below the Fermi level.

A mechanism is proposed for the decomposition of molecular clusters of diethylamine (C2H5)2NH on the surface of the NaAux intermetallic compound with the formation of decomposition products desorbed from the surface, including in the form of ions with m/z from 58 to 197, during heating of the intermetallic compound at a rate of 20 K/s. Exposure of the NaAux surface at a temperature of 320 K in diethylamine vapor leads to the formation of molecular clusters on it. Rapid heating of NaAux at a rate of 20 K/s leads to the decay of clusters, desorption, and ionization of the decay products due to the redistribution of internal energy over the degrees of freedom of the cluster. The study of thermal ionization processes during heating of NaAux at a rate of 20 K/s in the temperature range from 600 to 1000 K made it possible to establish that the surface stoichiometry during heating is quasi-stationary, dehydrogenation and ionization of individual diethylamine molecules occur under equilibrium conditions, while for compounds formed in the process of cluster decay, the conditions are not equilibrium.

The adsorption of gold atoms on the surface of the (100) tungsten face was calculated using the density functional method. A 2D layer of W atoms was used as a tungsten substrate. The 2D layer of W was modeled by a W (100) 2x2x2 supercell. The calculation was carried out for three sites of adsorption of the Au atom on the W (100) surface: in the hollow position, in the bridge position between the surface W atoms and on top the surface W atom. There was one Au atom per 8 surface W atoms. Adsorption of the Au atom in the bridge position is most preferable. The adsorption energy is 4,18 eV. Adsorption of Au atoms leads to the following reconstruction of the W surface: the shift of W atoms in the surface plane does not exceed 0,18 & Aring;, and the shift of the upper layer of W atoms is 0,022 & Aring; towards the volume of W . The valence band of the 2D W (100) layer is formed mainly W 5d electrons, with a minor contribution from W 6s electrons. Adsorption of gold leads to a change in the of the valence band of the surface

The effect of sodium adsorption on a gold film deposited on a tungsten substrate was studied. The deposition of Na atoms onto a thin film of gold on tungsten leads to a change in the spectra of the valence band and the core levels of gold and tungsten. An analysis of the spectra showed that the sodium atoms in the surface layer are in a neutral state, and the diffusion of sodium atoms deep into the gold film leads to the formation of the NaxAuy intermetallic compound. Heating a gold film with the formed NaxAuy intermetallic compound at a temperature 640 K leads to partial desorption of sodium and gold atoms from the surface layer of the NaxAuy intermetallic compound.

In a high-vacuum diode, the volt–ampere characteristic of the thermionic emission of Na+ with surface of NaxAu intermetallide. Its hysteresis was found, which is associated with changes in the surface NaxAu caused by the action of an external electric field. In accordance with the Schottky effect, analysis of the current–voltage characteristic and the value of the work function of the NaxAu surface was estimated. Suggested mechanism of thermionic emission of Na+ from the surface of NaxAu.

The processes electron-stimulated desorption (ESD) K atoms during the formation of 2D layers of the intermetallic compounds KxAuy on the gold surface at room temperature are investigated. The resonance dependence of the ESD yield of K atoms on the energy of exciting electrons is studied. The resonance dependence is due to the excitation of the core levels Au 5p3/2 и Au 5p1/2. It is shown that the processes of ESD excitation of K atoms occur at the K/KxAuy interface. Calculation of density of states 2D layers of intermetallic compound KAu showed that they can form semiconducting 2D layers, in contrast to crystals KAu which are metals. The band gap of intermetallic compounds KAu decreases with an increase in the thickness of the 2D layers of intermetallic compounds. The results obtained are explained by the formation of non-metallic islands, from which a 2D layer of the intermetallic compounds KxAuy on the gold surface is subsequently formed.

The effect of temperature on the electron-stimulated desorption of lithium atoms from the surface of 2D semiconductor LixAuy intermetallic compounds in the temperature range from 160 to 300 K was studied. LixAuy intermetallic compounds were formed during the deposition of lithium atoms on gold film 2 monolayers thick at room temperature. An island mechanism for the formation of LixAuy intermetallic compounds has been proposed. The decrease in the yield of electronically stimulated desorption of lithium atoms from the surface of LixAuy 2D semiconductor intermetallic compounds with decreasing temperature is associated with a decrease in the probability of capturing an excited electron into the conduction band into a local state near the bottom of the conduction band. The calculation by the density functional method showed that 2D LiAu layers form semiconductor compounds, the band width of which decreases with increasing thickness of the 2D LiAu layer.

lapushkin@ms.ioffe.ru Abstract. The electron-stimulated desorption of lithium and potassium atoms from LixAuy and KAu layers on the surface of gold adsorbed on W(100) has been studied. The yield of x y electron-stimulated desorption of Li and K atoms was measured by a direct method as a func-tion of the electron energy, the concentration of Li and K atoms, and the thickness of the Au film. The formation of semiconductor intermetallic compounds LixAuy and KxAuy is considered.

n situ photoelectron spectroscopy studies have been carried out in ultrahigh vacuum of the electronic structure of a 2D Au film deposited on a surface W with a natural oxide, before and after adsorption of Na atoms. The spectra of photoemission from the valence band and core levels of Au 4f, W 4f and Na 2p were studied under synchrotron excitation in the photon energy range of 120-300 eV. The investigated 2D Au film with a thickness of 0.83 nm has a valence band close to the valence band of the massive sample. The diffusion of Na atoms deep into the gold film was not detected, which indicates the layered growth of the 2D Au film. Two states have been found: Nadelta+ and Na+, which exist even with a 0.15 sodium coating of the monolayer, which indicates the formation of Na islands and single adsorption of Na atoms. The density functional method is used to calculate the electronic structure of a 2D Au layer without and with adsorbed Na. It is established that the adsorption of Na atoms in the pit or bridge position is preferable. It is found that the adsorption of Na leads to the reconstruction of the surface.

In a high-vacuum diode, the volt-ampere characteristic of the thermionic emission of Na+ with surface of NaxAu intermetallide. Its hysteresis was found, which is associated with changes in the surface NaxAu caused by the action of an external electric field. In accordance with the Schottky effect, analysis of the current–voltage characteristic and the value of the work function of the NaxAu surface was estimated. Suggested mechanism of thermionic emission of Na+ from the surface of NaxAu.

Проведен расчет плотности состояний различной толщины 2D-слоев интерметаллида RbAu. 2D-слои интерметаллида RbAu моделировались суперячейками RbAu (111) 2x2x2. Для монослойного 2D-слоя интерметаллида RbAu установлено наличие запрещенной зоны с шириной 2,70 эВ. Увеличение толщины 2D-слоев интерметаллида RbAu до трех монослоев показал уменьшение ширины запрещенной зоны до 0,8 эВ. Дальнейшее увеличение толщины 2D-слоев интерметаллида RbAu приводит к исчезновению запрещенной зоны, что указывает на переход полупроводник - металл для 2D-слоя интерметаллида RbAu толщиной четыре монослоя. Валентная зона 2D-слоя интерметаллида RbAu сформирована в основном Au 5d электронами, с незначительным вкладом Au 6s и Au 6p электронов. Зона проводимости RbAu образована в основном Au 6p электронами с незначительным вкладом электронов Rb 5s. The calculation of the density of states of various thicknesses of the 2D-layers of the intermetallic compound RbAu has been carried out. 2D-layers of intermetallic compound RbAu are simulated by supercells RbAu (111) 2x2x2. For a monolayer 2D-layer of an intermetallic compound RbAu the presence of a bandgap with a width of 2,70 eV has been established. An increase in the thickness of the 2D-layers of the intermetallic compound RbAu to three monolayers showed a decrease in the bandgap to 0,80 eV. A further increase in the thickness of the 2D-layers of the intermetallic compound RbAu leads to the disappearance of the band gap, which indicates a semiconductor-metal transition for the 2D-layer of the intermetallic compound RbAu with a thickness of four monolayers. The valence band of the 2D-layer of the intermetallic compound RbAu is formed mainly by Au 5d electrons, with an insignificant contribution from Au 6s and Au 6p electrons. The conduction band of RbAu is formed mainly by Au 6p electrons with an insignificant contribution of electrons Rb 5s.

Thermal ionization of methenamine (C6H12N4) on the surface of the NaAux intermetallic compound has been studied. It has been established that the processes of decomposition, desorption and ionization of adsorbed compounds, thermally stimulated on the surface, proceed due to the accumulation of energy at the degrees of freedom of the adsorption complex, including the adsorbed compound and a solid, by the mechanism of monomolecular decomposition reactions. In this case, the decomposition of the adsorption complex is accompanied by the desorption of ions that are not in thermal equilibrium with the solid. The uniformity of the temperature dependences of the ion current and their distribution over two groups allowed us to conclude that ions are desorbed from the surface, which correspond to the decays of individual adsorbed molecules, as well as the decays of dimers formed on the surface. The decay of methenamine molecules during thermal ionization occurs in the same way as their decay in vacuum during electron ionization, which indicates the preservation of the bulk structure of methenamine molecules during adsorption and a significant lifetime of the excited state of compounds on NaAux.

The formation of 2D LixAuy semiconductor layers on the surface of gold deposited on a tungsten substrate has been studied. The processes of electron-stimulated desorption of Li atoms in the Li/LixAuy/Au/W system are considered. The presence of two peaks in the kinetic energy distribution of desorbed lithium atoms is shown: a high energy peak at an energy of 0.3 eV and a low energy peak at an energy of 0.11 eV. The high energy peak is associated with the desorption of lithium atoms from the adsorbed lithium layers, and the low energy peak is associated with the LixAuy intermetallic compound. The influence of the number of deposited gold and lithium atoms on the process of formation of 2D semiconductor LixAuy layers is studied. It is shown that the processes of electron-stimulated desorption occur in the Li monolayer and the LixAuy layer closest to it. A model of electron-stimulated desorption of Li atoms in the Li/LixAuy/Au/W system is proposed. Keywords: electron-stimulated desorption, lithium, gold, semiconductor, intermetallic compound.

The electronic structure of a gold film deposited on W was studied during the adsorption of sodium atoms. An analysis of the photoemission spectra from the valence band and core levels of Au 4f and Na 2p upon synchrotron excitation in the photon energy range of 80–600 eV showed that Na adsorption leads to the formation of NaxAuy intermetallic compounds of various stoichiometry under the Na monolayer.

The formation of 2D LixAuy semiconductor layers on the surface of gold deposited on a tungsten substrate has been studied. The processes of electron-stimulated desorption of Li atoms in the Li/LixAuy/Au/W system are considered. The presence of two peaks in the kinetic energy distribution of desorbed lithium atoms is shown: a high energy peak at an energy of 0.3 eV and a low energy peak at an energy of 0.11 eV. The high energy peak is associated with the desorption of lithium atoms from the adsorbed lithium layers, and the low energy peak is associated with the LixAuy intermetallic compound. The influence of the number of deposited gold and lithium atoms on the process of formation of 2D semiconductor LixAuy layers is studied. It is shown that the processes of electron-stimulated desorption occur in the Li monolayer and the LixAuy layer closest to it. A model of electron-stimulated desorption of Li atoms in the Li/LixAuy/Au/W system is proposed.

Photoelectron spectroscopy was used to study the electronic structure in situ in an ultrahigh vacuum before and after the adsorption of sodium atoms on the surface of tungsten oxidized at an oxygen pressure of 1 Torr and a temperature of 950 K. The photoemission spectra from the valence band and the W 4f, O 2s, and Na 2p core states were studied under synchrotron excitation in the photon energy range 80-600 eV. It is found that a tungsten oxide film is formed containing various tungsten oxides with an oxidation state of 6+ to 4+. The deposition of a 1.1 monolayer of sodium atoms on the surface of oxidized tungsten leads to the reduction of the W6+ states to W4+ and the reaction with oxygen in the hydroxyl composition, which is reflected in the change in the spectrum of the W 4f and O 2s core states. It is shown that the cathodoluminescence spectrum is associated with the luminescence of tungsten oxide. Keywords: adsorption, sodium, tungsten oxides, photoelectron spectroscopy, cathodoluminescence.

A mechanism is proposed for the decomposition of molecular clusters of diethylamine (C2H5)2NН on the surface of the NaAux intermetallic compound with the formation of decomposition products desorbed from the surface, including in the form of ions with m/z from 58 to 197, during heating of the intermetallic compound at a rate of 20 K/s. Exposure of the NaAux surface at a temperature of 320 K in diethylamine vapor leads to the formation of molecular clusters on it. Rapid heating of NaAux at a rate of 20 K/s leads to the decomposition of clusters, desorption, and ionization of the decay products due to the redistribution of internal energy over the degrees of freedom of the cluster. The study of thermal ionization processes during heating of NaAux at a rate of 20 K/s in the temperature range from 600 to 1000 K made it possible to establish that the surface stoichiometry during heating is quasi-stationary, dehydrogenation and ionization of individual diethylamine molecules occur under equilibrium conditions, while for compounds formed in the process of cluster decay, the conditions are not equilibrium

Photoelectron spectroscopy was used to study the electronic structure in situ in an ultrahigh vacuum before and after the adsorption of sodium atoms on the surface of tungsten oxidized at an oxygen pressure of 1 Torr and a temperature of 950 K. The photoemission spectra from the valence band and the W 4f, O 2s, and Na 2p core states were studied under synchrotron excitation in the photon energy range 80–600 eV. It is found that a tungsten oxide film is formed which contains various tungsten oxides with an oxidation state of 6+ to 4+. The deposition of a 1.1 monolayer of sodium atoms on the surface of oxidized tungsten leads to the reduction of the W6+ states to W4+ and the reaction with oxygen in the hydroxyl composition, which is reflected in the change in the spectrum of the W 4f and O 2s core states. It is shown that the cathodoluminescence spectrum is associated with the luminescence of tungsten oxide.