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The results of a study of the unoccupied electronic states of ultrathin films of bis-carboxyphenyl-phthalide (DCA-DPP) and bis-methylphenyl-phthalide (DM-DPP) up to 8 nm thick are presented. The studies are carried out by total current spectroscopy (TCS) in the energy range from 5 to 20 eV above EF during thermal vacuum deposition of these organic films on the surface of highly ordered pyrolytic graphite (HOPG). The values of Evac relative to EF, i.e., the work function of electrons of the DM-DPP films at a film thickness of 5–8 nm are found to be 4.3 ± 0.1 eV. The values of the work function of electrons of the DCA‑DPP films are found to be 3.7 ± 0.1 eV. The structure of the maxima of unoccupied electronic states of DCA-DPP and DM-DPP films in the studied energy range is established. A comparison of the obtained properties of DCA-DPP and DM-DPP films with the properties of films of molecules of unsubstituted diphenylphthalide (DPP) is presented. Thus, the –CH3 substitution of the DPP molecule has almost no effect on the height of the potential barrier between the film and the HOPG surface, while –COOH substitution of the DPP molecule leads to an increase in the height of the potential barrier between the film and the HOPG substrate surface by 0.5–0.6 eV. Substitution of DPP molecules with –COOH functional groups and, thus, the formation of DCA-DPP molecules lead to a shift of two maxima of the fine structure of the total current spectra located at energies in the range from 5 to 8 eV above EF by about 1 eV towards the lower electron energies.

Unoccupied electronic states in the energy range from 5 to 20 eV above the Fermi level have been studied in ultrathin films of dimethyl-substituted thiophene–phenylene cooligomers CH3-phenylene–thiophene–thiophene–phenylene–CH3 (CH3–PTTP–CH3) on polycrystalline gold surfaces of two types: the ex situ Au layer thermally deposited in a special chamber and the in situ Au surface prepared inside an analytical chamber. The film structure is studied by the X-ray diffraction (XRD) method. The formation of a superposition of the amorphous phase and the crystalline phase with period 3.8 nm is discussed. The energy positions of the maxima of the unoccupied electronic states and the character of formation of the boundary potential barrier have been studied by the total current spectroscopy (TCS). The structures of the FSTCS maxima of the 5–7-nm-thick CH3–PTTP–CH3 films are not different when using various types of Au substrates and the ZnO semiconductor surface prepared by atomic layer deposition (ALD). As a CH3–PTTP–CH3 layer is deposited on the ex situ Au and in situ Au surfaces, the electron work function increases insignificantly (by ~0.1 eV) as the coating thickness increases to 5–7 nm. At such thicknesses of the CH3–PTTP–CH3 films, the electron work function is 4.7 ± 0.1 eV in the case of the ex situ Au substrate and 4.9 ± 0.1 eV in the case of the in situ Au substrate. A possible influence of the processes of physicochemical interaction at the boundary between the film and the substrate on the formation of the boundary potential barrier in the structures under study is discussed.

A comparative study has been performed for the structures of the maxima of the density of unoccupied electronic states (DOUS) in ultrathin films of the naphthalene-1,4,5,8-tetracarboxyl acid dianhydride (NTCDA) and naphthalene-1,8-dicarboxyl acid anhydride (NDCA) and two types of films based on phthalides: 3,3-diphenylphthalide (DPP) and 3,3-diphenylphthalide-4',4'-dicarboxyl acid (DPP–DCA). The structures of unoccupied electronic states of the 8–10-nm-thick films have been measured by total current spectroscopy (TCS) in the energy range from 5 to 20 eV above the Fermi level. The experimental results are analyzed by constructing the model total current spectra and the DOUS dependences using the results of calculation of the orbital energy of the molecules under study by the density functional theory (DFT) at the B3LYP/6-31G(d) level. The difference in the DOUS spectra of the NTCDA and NDCA films is the shift of the main DOUS maxima of the NTCDA film to lower energies approximately by 1 eV at energies lower than 12.5 eV; at higher energies, the DOUS maxima are shifted by 1.5–2 eV. The energy positions of the maxima of the total current spectra of the DPP–DCA and DPP films are changed only slightly as various substrates are used: highly ordered pyrolitic graphite (HOPG) and a CdS deposited layer-by-layer. The relative intensities of the maxima are different as various substrates are used. The characteristic shifts of the maxima of the total current spectra of the DPP–DCA films are approximately 1 eV at energies lower 12.5 eV above the Fermi level and 1.5–2 eV at higher energies, as compared to the positions of the corresponding maxima of the DPP films.

The formation of unoccupied electronic states and the boundary potential barrier during thermal deposition of tetracyanoquinodimethane (TCNQ) films to 7 nm in thickness on a (SiO2)n-Si surface has been studied. The electronic characteristics of the surface under study are measured by the total current spectroscopy (TCS) using a testing electron beam with energies from 5 to 20 eV above the Fermi level. The formation of a boundary potential barrier in the (SiO2)n-Si/TCNQ structure is accompanied by an increase in the work function of the surface from 4.2 ± 0.1 to 4.7 ± 0.1 eV. Using the results of the TCS experiments, the DOUS dependences of the TCNQ films have been built. To analyze the experimental DOUS dependences, the orbital energies of the TCNQ molecules are calculated by the density functional theory (DFT) at the B3LYP/6-31G(d) level with subsequent correction and the inclusion of the polarization energy of the condensed medium. In the energy range indicated above, DOUS of the TCNQ films has four main maxima. The DOUS maximum at energy 7.0 eV above EF is predominantly formed by π* orbitals. Three DOUS maxima in the energy range from 8.0 to 20 eV above EF are formed by approximately the same amount of the π* and σ* orbitals.

Colloidal nanocrystals of AgInS2 were synthesized in aqueous solution using L-glutathione as a ligand. Wider bandgap semiconductor ZnS shell was deposited on the nanocrystal cores in order to enhance luminescence properties and stability. Thus prepared nanocrystals generally had an asymmetric multiple band emission spectrum. Variation of cation ratio [Ag+] to [In3+] led to a variation in the spectrum so that raising indium content caused an intensity increase of longer wavelength emission band. Photoluminescence and absorption spectroscopies, transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy were used for the sample characterization.

The results of diagnostics of the atomic composition of a diphenylphthalide (DPP) film thermally precipitated in vacuum by the of X-ray photoelectric spectroscopy (XPS) method are presented. The results of examination of the unoccupied electronic states of the ultrathin DPP films with the thickness up to 10 nm on the surface of the highly oriented pyrolytic graphite (HOPG) by the total current spectroscopy (TCS) method in the energy range from 5 to 20 eV above EF are presented. In this range, the main maxima in the total current spectra are identified. The analysis of the TCS results with consideration of the theoretical calculation results has shown that the low-energy maxima observed at the energies from 6 to 7.5 eV are induced predominately by π* electron orbitals of DPP films. The values of the energy Evac in relation to EF, i.e., of the electron work function in the DPP films at the film thickness of 5–10 nm, are found experimentally at a level of 4.3 ± 0.1 eV. The negative charge transfer from an organic film to the substrate corresponds to the formation of the HOPG/DPP boundary potential barrier during the thermal deposition of the DPP film.

The atomic composition of films of a polyphenol antioxidant, namely, resveratrol (RVL), with a thickness of up to 50 nm thermally deposited on an oxidized silicon surface is studied by the method of X-ray photoelectron spectroscopy (XPS). It is found that the surface area of pores in the RVL film is about 15% of the total surface area. The results of studying the stability of the RVL films when their surface is treated with Ar+ ions of 3 keV under the electric current of 1 μA passing through the sample for 30 s are given. The treatment gives rise to an increase in the area of pores to 30–40%, while the ratio of the concentration of C atoms to the concentration of O atoms in the RVL film both before and after the treatment of the surface with ions does not correspond to the chemical formula of RVL molecules. Using the method of atomic force microscopy (AFM) in contact mode with a scanning area size of about 10 × 10 μm, RVL coatings deposited on the oxidized silicon and polycrystalline Au surfaces are studied. It is found that the RVL films produce grainy and porous coatings on the substrate surfaces. The typical size of grains in the sample surface plane is 150–300 nm, and the characteristic elevation reaches 30 nm.

The electronic properties of diphenylphthalide dicarboxylic acid are studied under gas-phase conditions using dissociative electron attachment spectroscopy and in the condensed environment by means of total current spectroscopy. The experimental features are assigned with the support of density functional theory calculations of the energies of the lowest-lying anion states to describe both the resonances responsible for low-energy (0-15 eV) electron attachment to the isolated molecule and the maxima in the density of unoccupied electronic states in the condensed ultrathin (up to 10 nm) films. Resonance electron attachment to diphenylphthalide dicarboxylic acid is found to be followed by opening of the -lactone ring in the molecular negative ions, an unusual mechanism leading to their stabilization. A similar mechanism is expected to be responsible for the unique properties of phthalide-based materials in the condensed state.

The unoccupied electron states and the boundary potential barrier during deposition of ultrathin films of dimethyl-substituted thiophene–phenylene coolygomers of the type of CH3–phenylene–thiophene–thiophene–phenylene–CH3 (CH3–PTTP–CH3) on an oxidized silicon surface have been studied. The electronic characteristics have been measured in the energy range from 5 to 20 eV above the Fermi level using total current spectroscopy (TCS). The structure of the CH3–PTTP–CH3 film surfaces has been studied by atomic force microscopy (AFM), and the atomic compositions of the films have been studied by X-ray photoelectron spectroscopy (XPS). The changes in the maximum intensities measured by the TCS method obtained from the deposited CH3–PTTP–CH3 film and from the substrate during increasing in the organic coating thickness to 6 nm is discussed. The formation of the boundary potential barrier in the n-Si/SiO2/CH3–PTTP–CH3 is accompanied by the decrease in the surface work function from 4.2 ± 0.1 to 4.0 ± 0.1 eV as the organic coating thickness increases to 3 nm. The ratio of atomic concentrations C: S in the CH3–PTTP–CH3 films well corresponds to the chemical formula of CH3–PTTP–CH3 molecules. The roughness of the CH3–PTTP–CH3 coating surface was not higher than 10 nm on the ~10 × 10 μm areas as the total CH3–PTTP–CH3-layer thickness was about 100 nm.

The results of examination of the electronic structure of the conduction band of naphthalenedicarboxylic anhydride (NDCA) films in the process of their deposition on the surface of oxidized silicon are presented. These results were obtained using total current spectroscopy (TCS) in the energy range from 5 to 20 eV above the Fermi level. The energy position of the primary maxima of the density of unoccupied states (DOUS) of an NDCA film was determined based on the experimental TCS data and calculated data and compared with the position of the DOUS maxima of a naphthalenetetracarboxylic dianhydride (NTCDA) film. The theoretical analysis involved calculating the energies and the spatial distribution of orbitals of the molecules under study at the B3LYP/6-31G(d) DFT (density functional theory) level and correcting the obtained energies in accordance with the procedure that was proven effective in earlier studies of the conduction band of films of small conjugated organic molecules. It was found that the DOUS maxima of the NTCDA film in the studied energy interval from 5 to 20 eV above the Fermi level are shifted toward lower electron energies by 1–2 eV relative to the corresponding DOUS maxima of the NDCA film Subdivision of the Ufa Federal Research Centre of the.

Atomic composition of monolayers based on siloxane dimer of quaterthiophene deposited by Langmuir–Blodgett technique on a silicon dioxide surface partially covered by gold film and the stability of these monolayers upon surface treatment by Ar+ ions bombardment have been studied. Experimental results for the chemical composition of a series of studied surfaces have been obtained by X-ray photoelectron spectroscopy (XPS) by recording XPS spectra of C 1s, O 1s, S 2p, and Au 4f core levels. The relative concentration of Au and Si substrate atoms and the composition of ex situ prepared surface under study were determined within 10–15%, which indicates that Langmuir–Blodgett monolayers based on siloxane dimer of quaterthiophene form continuous coating in a considerable extent. Prior to the treatment of the studied surface by Ar+ ions bombardment, carbon- and oxygen-containing surface adsorbates provided a considerable contribution to the results of XPS measurements. The surface cleaning by Ar+ ions with energy 3 keV at electric current through sample of ~1 μA in several 30-s steps has led to the etching of surface adsorbates and next Langmuir–Blodgett films of the siloxane dimer of quaterthiophene.

The results of the investigation of the density of unoccupied electronic states (DOUS) in the energy range from 5 to 20 eV above the Fermi level (E F) in dioctyl-substituted perylenedicarboximide (PTCDI-C8) and diphenyl-substituted perylenedicarboximide (PTCDI-Ph) ultrathin films have been presented. The experimental results have been obtained from measurements of the secondary low-energy electron current with the use of the total current spectroscopy (TCS) technique. A theoretical analysis has been performed, including the density functional theory calculation of the energies and spatial distribution of the orbitals of the molecules under investigation and the subsequent scaling of the calculated orbital energies according to the procedure well-proven previously in studies of small conjugated organic molecules. It has been found that, for each of the two types of the studied films, at energies below 8 eV above the Fermi level E F, there are two main maxima of the density of unoccupied electronic states predominantly formed by the π*-orbitals of the molecules. The higher-lying maxima have essentially a σ*-character. The influence of dioctyl- and diphenyl-substituent groups on the density of unoccupied electronic states has been analyzed in comparison with the results obtained for the studied types of films. In the case of the π*-maxima, the relative shift has been observed at an energy of approximately 1 eV. In the region of σ*-electronic states, there is a small transformation of the structure of the maxima.

The interface chemical reactions, the deoxygenation and the overall thermal stability of the ex situ deposited graphene oxide (GO) thick film on the polycrystalline tantalum surface were studied by means of x-ray photoelectron spectroscopy (XPS) at room temperature and after annealing up to 600 °С. The evolution of the Ta4f, C1s and O1s XPS core level spectra from the Ta/GO structure under study upon the increase of the annealing temperature was investigated with the reference to the uncovered Ta substrate surface. In the Ta/GO structure the Ta relative atomic concentration was about 1% at room temperature due to the low porosity of the GO layer while the thermal desorption of the overlayer at the elevated temperatures was accompanied by an increase of the Ta concentration up to 47% at 500 °С. The C atoms relative concentration started decreasing after the annealing at 250 °С accompanying the thermal desorption of the GO overlayer. The formation of the TaC compound starting from the 250 °С annealing temperatures was determined. The relative oxygen concentration in the GO thick film was decreased upon increasing the annealing temperature accompanying both the thermal desorption of the GO material and the thermal reduction of the GO film. Keywords: Graphene oxide, Tantalum oxide, Surfaces and interfaces, Thermal treatment, X-ray photoelectron spectroscopy

This study is aimed to point out the important role played by resonance electron attachment in reductive dehalogenation, in particular in phytoremediation of organic pollutants under conditions of excess negative charge. To model enzymatic reactions occurring in reductive conditions, low-energy electron capture by the halogenated herbicides atrazine and bromoxynil was studied in vacuo using electron transmission spectroscopy (ETS). A variety of decay channels of the temporary molecular negative ions was discovered by means of dissociative electron attachment spectroscopy (DEAS). The experimental results were interpreted with the support of quantum-chemical calculations. Dehalogenation of atrazine and bromoxynil was found to be the dominant decay of the molecular negative ions formed at thermal energies of the incident electrons. It is concluded that formation of negative ions by electron donation in enzymatic active centers followed by their dissociation along the * bond can be considered as the main mechanism of reductive dehalogenation.

The atomic composition and the electronic properties of ultrathin films of the four-conjugated rings thiophene/phenylene co-oligomers end-terminated by the −CH 3 and by the -CF 3 radicals vacuum deposited onto the oxidized silicon surface were studied using the X-ray photoelectron spectroscopy (XPS) and total current spectroscopy (TCS) techniques. The relative concentrations of the C, S and F atoms measured from the film deposits were evaluated and were found to correspond to the chemical formulae of the CH 3 -phenylene-thiophene-thiophene-phenylene−CH 3 (CH 3 -PTTP−CH 3 ) and CF 3 -phenylene-thiophene-thiophene-phenylene-CF 3 (CF 3 -PTTP-CF 3 ) molecules studied. The TCS measurements during the increase of the organic layer thickness up to 6 nm on a (SiO 2 )n-Si substrate were used to determine the conduction band peak structure related to the density of the unoccupied electronic states (DOUS) in the range from 5 eV to 22 eV above E F . DOUS of the films investigated was also obtained theoretically by means of ab initio calculations. According to the calculations, the energy position of the lowest unoccupied molecular orbital (LUMO) peak was found at 4.4 eV in the case of the CH 3 -PTTP−CH 3 film and at 3.9 eV in the case of the CF 3 -PTTP-CF 3 film. The effect of fluorine substitution on the DOUS was determined as approximately 2 eV peak shift towards low electron energies in the case of the CF 3 -PTTP-CF 3 film compared to the case of the CH 3 -PTTP−CH 3 film in the electron energy range from 10 eV to 22 eV above E F and as a more complex peak restructuring in the energy range from 5 eV to 10 eV above E F . The DOUS peaks of the two films studied were assigned to molecular orbitals with π* character in the 5–9.5 eV energy range and molecular orbitals with σ* character in the 9.5–22 eV energy range above E F .

The results of the investigation of the electronic structure of the conduction band and the interfacial potential barrier during the formation of interfaces of dioctyl-substituted perylenedicarboximide (PTCDI-C8) and diphenyl-substituted perylenedicarboximide (PTCDI-Ph) ultrathin films with the oxidized germanium surface have been presented. The experimental results have been obtained using the very low energy electron diffraction (VLEED) technique in the total current spectroscopy (TCS) mode at energies in the range from 5 to 20 eV above the Fermi level EF. The positions of the maxima of the fine structure of total current spectra (FSTCS) of the PTCDI-C8 and PTCDI-Ph films differ significantly in the energy range from 9 to 20 eV above the Fermi level EF, which can be associated with the difference between the substituents of the chosen molecules, dioctyl- and diphenyl-, respectively. At the same time, the positions of the lowenergy maxima in the FSTCS spectra at an energy 6–7 eV above the Fermi level EF for the PTCDI-C8 and PTCDI-Ph films almost coincide with each other. It has been suggested that these maxima are attributed to the electronic states of the perylene core of the molecules under investigation. The process of the formation of interfacial potential barriers of the PTCDI-C8 and PTCDI-Ph films with the oxidized germanium surface has been analyzed. It has been found that the work functions of the surface, Evac–EF, differ little from 4.6 ± 0.1 eV over the entire range of organic coating thicknesses from 0 to 6 nm.

The results of the investigation of the electronic structure of the conduction band in the energy range 5–25 eV above the Fermi level E F and the interfacial potential barrier upon deposition of aziridinylphenylpyrrolofullerene (APP-C60) and fullerene (C60) films on the surface of the real germanium oxide ((GeO2)Ge) have been presented. The content of the oxide on the (GeO2)Ge surface has been determined using X-ray photoelectron spectroscopy. The electronic properties have been measured using the very low energy electron diffraction (VLEED) technique in the total current spectroscopy (TCS) mode. The regularities of the change in the fine structure of total current spectra (FSTCS) with an increase in the thickness of the APP-C60 and C60 coatings to 7 nm have been investigated. A comparison of the structures of the FSTCS maxima for the C60 and APP-C60 films has made it possible to reveal the energy range (6–10 eV above the Fermi level E F) in which the energy states are determined by both the π* and σ* states and the FSTCS spectra have different structures of the maxima for the APP-C60 and unsubstituted C60 films. The formation of the interfacial potential barrier upon deposition of APP-C60 and C60 on the (GeO2)Ge surface is accompanied by an increase in the work function of the surface E vac–E F by the value of 0.2–0.3 eV, which corresponds to the transfer of the electron density from the substrate to the organic films under investigation. The largest changes occur with an increase in the coating thickness to 3 nm, and with further deposition of APP-C60 and C60, the work function of the surface changes only slightly.

Electron-accepting properties and, in particular, resonance dissociative electron attachment (DEA) to ascorbic acid (AA) are investigated by means of DEA spectroscopy in vacuo. The experimental features are assigned in silico and discussed in relation to expected dissociative electron transfer processes in vivo, with the support of density functional theory calculations and the polarizable continuum model. It is shown that formation of the two most abundant AA metabolites in living cells, namely monodehydroascorbic acid and dehydroascorbic acid, can be stimulated by cellular electron transfer to AA under reductive conditions. Prooxidant effects caused by AA are suggested to be mediated by hydroxyl radicals formation via the DEA mechanism. The involvement of excited electronic states under UV-irradiation in plants could open additional DEA channels leading to specific AA activity forbidden under dark state conditions.

This paper presents the results of the investigation of the interface potential barrier and vacant electronic states in the energy range of 5 to 20 eV above the Fermi level (EF) in the deposition of perylene tetracarboxylic dianhydride (PTCDA) films on the oxidized germanium surface ((GeO2)Ge). The concentration of oxide on the (GeO2)Ge surface was determined by X-ray photoelectron spectroscopy. In the experiments, we used the recording of the reflection of a test low-energy electron beam from the surface, implemented in the mode of total current spectroscopy. The theoretical analysis involves the calculation of the energy and spatial distribution of the orbitals of PTCDA molecules by the density functional theory (DFT) using B3LYP functional with the basis 6-31G(d), followed by the scaling of the calculated values of the orbital energy according to the procedure well-proven in the studies of small organic conjugated molecules. The pattern of changes in the fine structure of the total current spectra with increasing thickness of the PTCDA coating on the (GeO2)Ge surface to 6 nm was studied. At energies below 9 eV above EF, there is a maximum of the density of unoccupied electron states in the PTCDA film, formed mainly by π* molecular orbitals. The higher density maxima of unoccupied states are of σ* nature. The formation of the interface potential barrier in the deposition of PTCDA at the (GeO2)Ge surface is accompanied by an increase in the work function of the surface, Evac–EF, from 4.6 ± 0.1 to 4.9 ± 0.1 eV. This occurs when the PTCDA coating thickness increases to 3 nm, and upon further deposition of PTCDA, the work function of the surface does not change, which corresponds to the model of formation of a limited polarization layer in the deposited organic film.

This paper presents the results of the investigation into the electrical conductivity of thin films based on tin dioxide (SnO2) nanoparticles, a film consisting of copper phthalocyanine-3,4′,4″,4‴-tetrasulfonic acid tetrasodium salt (CuPc–4SO3Na) molecules, and a composite film based on a mixture of equal parts by volume of the two materials upon adsorption of ammonia. The adsorption experiments have been carried out in a vacuum at room temperature with an increase in the ammonia pressure to 3 × 103 Pa from the residual gas base pressure of 5 × 10–1 Pa. It has been found that, in the case of a single-component film based on SnO2 nanoparticles, an increase in the electrical conductivity reaches 100% and is not completely reversible at room temperature after evacuation of the gas. For the single-component CuPc–4SO3Na film and the composite CuPc–4SO3Na/SnO2 film, the electrical conductivities increase by a factor of 400 and 150, respectively. Upon evacuation of ammonia to the base pressure, the electrical conductivity decreases to the initial values for 1 s. The mechanism of the influence of adsorbed ammonia molecules on the electrical conductivity of the composite material under investigation has been discussed using the model of the formation of the composite sample, according to which the organic component is located in voids between the SnO2 nanoparticles.

The ultrathin films of aziridinylphenylpyrrol-C 60 (APP-C 60 ) and of the unsubstituted C 60 thermally deposited in UHV on an oxidized silicon substrate (SiO 2 )n-Si were studied experimentally using the very low energy electron diffraction (VLEED) method and the total current spectroscopy (TCS) measurement scheme. The density of the unoccupied electronic states (DOUS) located 2-20 eV above the Fermi level (E F ) of the films under study was determined using the TCS results and using the results of the density functional theory (DFT) calculations of the vacant electronic orbitals of the APP-C 60 and C 60 molecules. The DOUS peak structure obtained on the basis of the calculation results corresponds well to the structure of the major DOUS bands obtained from the TCS experiment. The comparison of the DOUS spectra of the APP-C 60 and C 60 films under study showed that the introduction of the APP substituent to the C 60 molecule was accompanied by the pronounced changes of the π* DOUS bands in the energy range from 2 eV to 5 eV above E F and of the DOUS band composed from both π* and σ* - type orbitals in the energy range from 5 eV to 9 eV above E F . The formation of the low-lying σ* DOUS band in the APP-C 60 film in the energy range from 8 eV to 13 eV above E F can be explained by the superposition of the relevant DOUS maxima from the C 60 film and from the APP fragment.

The results of the investigation of the conduction band electronic structure and the interfacial potential barrier during deposition of ultrathin dicarboximide-substituted perylene films (PTCBI-C8) on the oxidized silicon surface have been presented. The measurements have been performed using the very low energy electron diffraction (VLEED) technique implemented in the total current spectroscopy (TCS) mode with a variation in the incident electron energy from 0 to 25 eV. Changes in the intensities of the maxima from the deposited PTCBI-C8 film and from the substrate with an increase in the organic coating thickness to 7 nm have been analyzed using TCS measurements. A comparison of the structure of the maxima of PTCBI-C8 and perylene-tetracarboxylic-dianhydride (PTCDA) films has made it possible to distinguish the energy range (8–13 eV above EF) in which distinct differences in the structures of maxima for PTCDA and PTCBI-C8 films are observed. This energy range corresponds to low-lying σ*-states of the conduction band of the films studied. The formation of the interfacial region of the PTCBI-C8 film and (SiO2)n-Si substrate is accompanied by an increase in the surface work function by 0.6 eV, which corresponds to the electron density charge transfer from the (SiO2)n-Si substrate to the PTCBI-C8 film.

The antioxidant isoflavone retusin efficiently attaches low-energy electrons in vacuo, generating fragment species via dissociative electron attachment (DEA), as has been shown by DEA spectroscopy. According to in silico results obtained by means of density functional theory, retusin is able to attach solvated electrons and could be decomposed under reductive conditions in vivo, for instance, near the mitochondrial electron transport chain, analogous to gas-phase DEA. The most intense decay channels of retusin temporary negative ions were found to be associated with the elimination of H atoms and H2 molecules. Doubly dehydrogenated fragment anions were predicted to possess a quinone structure. It is thought that molecular hydrogen, known for its selective antioxidant properties, can be efficiently generated via electron attachment to retusin in mitochondria and may be responsible for its antioxidant activity. The second abundant species, i.e., quinone bearing an excess negative charge, can serve as an electron carrier and can return the captured electron back to the respiration cycle. The number of OH substituents and their relative positions are crucial for the present molecular mechanism, which can explain the radical scavenging activity of polyphenolic compounds.

The results of the investigation of the transmission of low-energy electrons through 8-nm-thick films of tin(IV) phthalocyanine oxide (SnOPc) on the surface of the oxidized silicon substrate are presented. The procedure of detecting the reflection of testing low-energy electron beam from the surface was implemented using the very low-energy electron diffraction (VLEED) technique in the total current spectroscopy (TCS) mode with a change in the incident electron beam energy from 0 to 25 eV. The structure of maxima in the total current spectra of SnOPc films was established and the variation in intensities of the maxima of total current spectra emitted from the deposited SnOPc film and (SiO2)n-Si substrate during an increase in the thickness of the organic coating to 8 nm was analyzed. With such an increase in the thickness of the organic coating, the work function of the surface increases by 0.7 eV, which corresponds to the transfer of the electron density from the (SiO2)n-Si substrate to the SnOPc film. Optical absorption spectra of SnOPc films were measured. The absorption spectra were compared with the spectra measured by the TCS method for the SnOPc films and the films of molecules of oxygen-free metal phthalocyanine.

The electron attaching properties and fragmentation of temporary negative ions of melatonin and its biosynthetic precursor tryptophan are studied in vacuo using dissociative electron attachment (DEA) spectroscopy. The experimental findings are interpreted in silico with the support of Hartree-Fock and density functional theory calculations of empty orbital energies and symmetries, and evaluation of the electron affinities of the indolic molecules under investigation. The only fragment anions formed by DEA to melatonin at incident electron energies below 2 eV are associated with the elimination of a hydrogen atom (energetically favored from the NH site of the pyrrole ring, keeping the ring intact) or a CH3• radical from the temporary molecular negative ion. Opening of the pyrrole ring of melatonin is not detected over the whole electron energy range of 0-14 eV. The DEA spectra of L- and D-tryptophan are almost identical under the present experimental conditions. The adiabatic electron affinity of melatonin is predicted to be -0.49 eV at the B3LYP/6-31+G(d) level, indicating that the DEA mechanism in melatonin is likely to be present in most life forms given the availability of low energy electrons in living systems in both plant and animal kingdoms. In particular, H atom donation usually associated with free-radical scavenging activity can be stimulated by electron attachment and N-H bond cleavage at electron energies around 1 eV.

The formation of an interface during the deposition of unsubstituted copper phthalocyanine (CuPc) films on the surface of hexadecafluoro copper phthalocyanine (F16-CuPc) films is studied. An incident low-energy electron beam with energies from 0 to 25 eV is used to test the surface under study according to the very-low-energy electron-diffraction technique (VLEED) in the mode of total current spectroscopy. For F16-CuPc films, the structure of the maxima in the total current spectra and its main differences from the structure of the maxima for the CuPc film are determined in the energy range from 5 to 15 eV above the Fermi level. The differences in the structure of vacant electron orbitals for CuPc and F16-CuPc are also revealed using density functional theory calculations. As a result of an analysis of variations in the intensities of the total current spectra of the CuPc and F16-CuPc films, it is assumed that an intermediate layer up to 1 nm thick appears during the formation of an interface between these films, which is characterized by a spread of the features in the total current spectrum. The height, width, and change in the work function are determined for the studied F16-CuPc/NuPc interface barrier. A decrease in the level of vacuum by 0.7 eV occurs in the boundary region, which corresponds to electron density transfer from the CuPc film toward the F16-CuPc substrate.

The photovoltaic effect has been detected and studied in thin-film structures based on thermally deposited 200-nm-thick copper phthalocyanine (CuPc) films on the surface of polycrystalline CdS. The structures under study demonstrate the linear current-voltage characteristics at external electric fields to 3.5 × 104 V/cm. Two components of the photovoltage of different signs have been revealed when the sample is illuminated in the wavelength range from 350 to 700 nm. The first component has the positive sign on the CuPc film side and is observed when using the radiation with a wavelength lesser than 500 nm, i.e., in conditions of predominant absorption of the radiation in the CdS layer. The second component has the negative sign on the CuPc film side and is observed when using the radiation with a wavelength in the range from 500 to 570 nm, corresponding to the spectral region of the absorption edge of the CuPc films. The dependences of the photovoltage on the radiation intensity studied in the range from 5 × 1012 to 1014 photons cm−2 s−1 are different in the cases of the two detected components. Mechanisms of generation of the photovoltage components associated with a change in the band bending during photogeneration of charge carriers in the region of space charge in CdS and a change in conditions of the charge transfer in the interfacial CuPc/CdS region during the radiation absorption in the CuPc film have been proposed.

Ultrathin films of trioligo(phenylene-vinylene) and of dinitro-substituted trioligo(phenylene-vinylene) end terminated by dibutyl-thiole were thermally deposited in an ultrahigh vacuum (UHV) on an oxidized silicon substrate (SiO2)n-Si. The surface work function and the density of the unoccupied electron states (DOUS) located 5–20 eV above the Fermi level (EF) were studied during the film deposition using the very low energy electron diffraction (VLEED) method and the total current spectroscopy (TCS) measurement scheme. The electronic structure typical for the organic films studied was formed, while the organic deposit thickness increased up to 5–6 nm. The DOUS peak structure of the organic films studied obtained from the TCS results showed good correspondence to the DOUS peaks obtained from the density functional theory (DFT) calculations. The calculations were made for the model oligo(phenylene-vinylene) films where the neighboring molecules had relatively weak interaction, which is also characteristic o...

Potential barrier formation during the deposition of ultrathin coatings of copper phthalocyanine (CuPc) and hexadecafluoro-copper-phthalocyanine (F16CuPc) on the surface of polycrystalline tin dioxide and during the deposition of F16CuPc coatings over a CuPc film is studied. A photoinduced change in the surface potential of the prepared structures upon exposure to light in the visible wavelength region is detected. The surface photovoltage of the studied organic films has a positive sign with respect to the substrate, its spectral dependences correspond to the absorption spectra of the organic materials CuPc and F16CuPc. Surface potential measurements are performed using a probe beam of low-energy electrons, based on the total current spectroscopy technique. A total decrease in the work function by 0.2 eV is detected during the deposition of a CuPc film up to 8 nm in thickness on a SnO2 substrate; in the case of the F16CuPc/SnO2 interface, an increase in the work function by 0.55 eV is detected. At the initial deposition stage, at organic film thicknesses of up to 1.5 nm, the interfacial potential barrier corresponded to electron density transfer from the organic film to the substrate in both cases of CuPc/SnO2 and F16CuPc/SnO2. It is assumed that the photoinduced change in the surface potential is caused by charge-carrier separation in a boundary region up to 1.5 nm thick.

The modification of the electronic structure during adsorption of ultrathin copper phthalocyanine (CuPc) and 3, 4, 9, 10 perylene-tetracarboxylic-dianhydride (PTCDA) coatings on the surface of polycrystalline tin dioxide is traced. Auger electron spectroscopy is employed to find changes in the atomic composition of the surface. It is found with the help of low-energy electron total current spectroscopy using a testing beam of electrons with energies up to 30 eV that the total current spectra typical of organic films are formed when the thickness of the coating being deposited is 2–7 nm. The formation of an interface layer 1.5–2.0 nm in thickness is detected, in which the intensity of the structure of the total current spectra decreases and the effect of interaction of PTCDA molecules with the SnO2 surface is manifested.

The systematic features of laser-induced desorption from an SnO2 surface exposed to 10-ns pulsed neodymium laser radiation are studied at the photon energy 2.34 eV, in the range of pulse energy densities 1 to 50 mJ/cm2. As the threshold pulse energy 28 mJ/cm2 is achieved, molecular oxygen O2 is detected in the desorption mass spectra from the SnO2 surface; as the threshold pulse energy 42 mJ/cm2 is reached, tin Sn, and SnO and (SnO)2 particle desorption is observed. The laser desorption mass spectra from the SnO2 surface coated with an organic copper phthalocyanine (CuPc) film 50 nm thick are measured. It is shown that laser irradiation causes the fragmentation of CuPc molecules and the desorption of molecular fragments in the laser pulse energy density range 6 to 10 mJ/cm2. Along with the desorption of molecular fragments, a weak desorption signal of the substrate components O2, Sn, SnO, and (SnO)2 is observed in the same energy range. Desorption energy thresholds of substrate atomic components from the organic film surface are approximately five times lower than thresholds of their desorption from the atomically clean SnO2 surface, which indicates the diffusion of atomic components of the SnO2 substrate to the bulk of the deposited organic film.

The results on the electronic structure of the unoccupied electronic states of the polycrystalline SnO2 in the energy range from 5 eV to 25 eV above the Fermi level are presented. The modification of the electronic structure and of the surface potential upon deposition of the ultrathin films of copper phthalocyanine (CuPc) and of perylene tetracarboxylic acid dianhydride (PTCDA) film onto the SnO2 surface were studied using the very low energy electron diffraction (VLEED) method and the total current spectroscopy (TCS) measurement scheme. A substantial attenuation of the TCS signal coming from the SnO2 surface was observed upon formation of a 1.5–2 nm thick organic deposit layer while no new spectral features from the deposit were distinguishable. It was observed that the electronic structure typical for the organic films was formed within the organic deposit thickness range from 2 nm to 7 nm. The interfacial charge transfer was characterized by the formation of the polarization layer up to 5 nm thick in the organic films. The PTCDA deposition on SnO2 was accompanied by the negative charge transfer onto the organic layer and to the 0.65 eV increase the surface work function. At the CuPc/SnO2 interface, the negative charge was transferred to the SnO2 surface and the overall surface work function decreased by 0.15 eV.

The photovoltaic effect has been detected and studied in structures based on ultrathin vacuum-deposited organic films of perylene-3,4,9,10-tetracarboxylic acid dianhydride on the titanium and tin dioxide surfaces. The interfacial potential barrier shape in these structures is studied by low-energy electron total current spectroscopy. Changes in the surface potential upon exposure to visible light are recorded in situ using an electron-beam probe with energies from 0 to 25 eV. The photovoltage is detected at incident photon energies of 1.5–2.5 eV, which corresponds to the organic film absorption range and simultaneously to the transmission band of titanium and tin dioxides. An analysis of the spectral distributions and transient responses shows that two components of the observed photovoltage can be distinguished. The relation of one of the components to the excitation of interband transitions in the organic film and another component to electronic transitions involving interfacial energy states are discussed.

Ultrathin conjugated layers of Pyronine B were thermally deposited in UHV on the surface of perylene tetracarboxylic acid dianhydride (PTCDA) film. The structure of unoccupied electron states located 5–20 eV above the Fermi level ( E F ) and the surface potential were monitored during the Pyronine B overlayer deposition, using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. Electronic work function of the PTCDA surface changed from 4.9 ± 0.1 eV, during the Pyronine B deposition due to the change of the contents of the surface layer, until it reached a stable value 4.6 ± 0.1 eV at the Pyronine B film thickness 8–10 nm. The interface dipole corresponds to electron transfer from the Pyronine B overlayer to the PTCDA surface and the polarization in the Pyronine B overlayer was found confined within approximately 1 nm near the interfaces. The edges of major bands of density of unoccupied electronic states (DOUS) of PTCDA substrate and of the Pyronine B overlayer were unaffected by the process of the interface formation. The major TCS spectral features of the Pyronine B film corresponding to the DOUS band edges were identified and the assignment of the π * , σ * (C–C) and σ * (C C) character was suggested.

This paper reports on the results of investigations of the electrophysical characteristics of films based on conjugated organic molecules of copper phthalocyanine (CuPc) and the perylene derivative 3,4,9,10-perylenetetracarboxylic acid dianhydride mixed with TiO2 microparticles and SnO2 nanoparticles. The electrical resistivity of the mixed films under investigation lies in the range from 5 × 108 to 5 × 109 GQ cm. The influence of adsorption on the surface of the films on the electrical conductivity is studied using vapors of water and volatile organic compounds, such as ethanol, ammonia, toluene, and acetone, at pressures in the range from 10−1 to 10 Pa. The adsorption of acetone and toluene vapors does not lead to considerable changes in the electrical conductivity of the films, whereas the exposure to vapors of water, ethanol, and ammonia results in a reversible multiple increase in the electrical conductivity of the studied films. In the case of mixed CuPc/TiO2 films, the electrical conductivity observed upon adsorption of ammonia vapors on the film surface exceeds the initial conductivity by a factor of approximately 2500. The mechanisms of the observed changes in the electrical conductivity are discussed with allowance made for the increase in the electron density of the films due to the electron exchange with adsorbed molecules of reducing gases.

The electrophysical parameters of polyhomoconjugated organosilicon polymer films are studied, and variation of their conductivity under the action of water, toluene, and ammonia vapors is measured. Films 1–2 μm thick are prepared by the casting method from a solution of poly[2,2-dimethyl-2-sila-1,3-propylene-(4, 4′-biphenylene)]a (polymer I) and poly[2-n -butyl-2-phenyl-2-sila-1,3-propylene-(4, 4′-biphenylene)]a (polymer II). In the course of conductivity measurement, organic volatiles and water are adsorbed due to a stepwise rise in the pressure over the sample from 10−3 to 10−1 Torr. The initial values of the resistivity of polymers I and II are estimated as 4 × 109 Θ cm. Exposure of the films to organic volatile vapors and water vapor causes a reversible change in the conductivity of the films. For polymer-I films, the conductivity upon adsorption of ammonia, toluene, and water vapors exceeds the initial value by 150, 10, and 600 times, respectively. The sensitivity of polymer-II films is lower by a factor of 1.5–2.0. The time of conductivity variation as the vapors are injected and evacuated is within 10 and 30 s, respectively. The mechanisms of organic volatile and water adsorption on the surface of polyhomoconjugated organosilicon polymer films are compared with adsorption mechanisms on the surface of π-polyconjugated organic films.

We have studied laser desorption mass spectra of copper phthalocyanine (CuPc) films deposited in vacuum onto single crystal silicon and cadmium sulfide substrates. The desorption was induced by 10-ns pulses of neodymium laser radiation (quantum energy, 2.34 eV) with an energy density E varied from 0.1 to 40 mJ/cm2. It is established that laser radiation produces fragmentation of CuPc molecules and desorption of the fragments. The main fragments observed in the mass spectra are identified. The intensity of the main desorbed species has been studied as a function of the laser pulse energy density. The components of CdS substrates penetrate into the volume of deposited CuPc films in the form of Cd atoms and S2 molecules.

A few nm thick 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA) and Cu-phthalocyanine (CuPc) overlayers were thermally deposited in situ in UHV onto TiO2 (1 1 0) surface. Atomic composition of the surfaces under study was monitored using Auger electron spectroscopy (AES). The formation of the interfacial potential barrier and the structure of the unoccupied electronic states located 5–25 eV above the Fermi level (EF) was monitored using a probing beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. The work function values upon the overlayer deposition changed from 4.6 to 4.9 eV at the PTCDA/TiO2 (1 1 0) interface and from 4.6 to 4.3 eV at the CuPc/TiO2 (1 1 0) interface. Band bending in the TiO2 substrate, molecular polarization in the organic film and changes in the work function due to the change in the surface composition were found to contribute to the formation of the interfacial potential barriers. Oxygen admixture related peaks were observed in the AES and in the TCS spectra of the CuPc overlayers. A mechanism of the transformations in the PTCDA and CuPc overlayers on the TiO2 (1 1 0) upon elevating temperature from 25 to 400 °C was suggested.

The interfacial structure made from the thermally deposited 5 – 7 nm thick layers of hexadecafluoro copper phthalocyanine (F

The process of interface formation between two organic films composed of donor (copper phthalocyanine, CuPc) and acceptor (perylene-3,4,9,10-tetracarboxylic dianhydride, PTCDA) molecules has been studied in situ using the total current spectroscopy technique. It is established that the donor-acceptor interaction between CuPc and PTCDA molecules do not distort the energy structure of the density of electron states. The main π*, σ*1, and σ*2 bands of antibonding (unoccupied) electron states are identified, which are determined both by C-C bonds in the aromatic rings and by additional C-N and C-O bonds. The width of the interface potential barrier is evaluated and its relation to the limiting polarizability of molecules is demonstrated. The interface potential barrier is formed in the course of negative charge transfer between donor (CuPc) and acceptor (PTCDA) molecules.

The photoelectronic properties of organic semiconductor-silicon heterostructures (such as PTCDA-Si, CuPc-Si, and OPV-Si) are investigated. The I-V characteristics, as well as the spectral dependences of photoconductivity and photoinduced potential, are measured. Photosensitivity is observed in the absorption bands of both silicon and the organic films. A maximum potential (up to 0.25 V) is observed for the PTCDA-Si heterojunctions. In the OPV-Si heterojunction, the photoinduced potential changes sign under illumination at different wavelengths in the optical range.

Thin films of Cu-phthalocyanine (CuPc), perylene and 3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA) were thermally deposited in situ in UHV on ZnO(0 0 0 −1) surface. The surface potential, the surface work function Φ and the structure of density of unoccupied electron states (DOUS) located 5–25 eV above the Fermi level ( E F ) were monitored during the film deposition, using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. Auger electron spectroscopy (AES) was used to monitor atomic composition of the surfaces under study. The deposition of the perylene and PTCDA films resulted in formation of the DOUS structure typical for these films while the deposition of CuPc films of less than 2 nm thickness resulted in formation of an intermediate DOUS structure which was replaced by a stable DOUS of CuPc along with a further increase of the deposit thickness. Migration of the substrate atoms into the intermediate layer was observed. The electronic work function Φ of the organic films changed during the film deposition until it reached stable values at a film thickness of 8–10 nm. Width of the interface dipole charge transfer layer and formation of intermediate TCS spectra during the film deposition are selected as relevant parameters for further comparison of the features of the interfaces studied.

Thin films of N , N ′-Bis(benzyl)-3,4,9,10-perylenetetracarboxylic diimide (BPTCDI, Fig. 1b) and N , N ′-Bis(benzyl)-1,4,5,8-naphthalenetetracarboxylic diimide (BNTCDI, Fig. 1d) were thermally deposited in UHV on 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA, Fig. 1a) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA, Fig. 1c) film surfaces, respectively, in order to form organic–organic interfaces so that molecules constituting the interfacing layers differ by the substituent group. The surface potential and the density of unoccupied electron states (DOUS) located 5–25 eV above the Fermi level (E F ) were measured during the film deposition using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. Analysis of the TCS data allowed us to assign the π( band located 5–7.5 eV above E F for all the four films under study and the higher located σ* 1 and σ* 2 bands and the splitting within them. In order to perform the analysis the molecules were hypothetically divided into benzene-like, conjugated and non-conjugated fragments that may individually contribute to the peaks in the DOUS bands. It was shown that a non-conjugated fragment would serve for decreasing of the energy corresponding to the σ* 1 and σ* 2 bands and the sub-bands within them while an addition of a benzene-like fragment would do the opposite. The BPTCDI/PTCDA and BNTCDI/NTCDA interfaces were found non-reacted and a 4.1±0.1 eV work function value for both BPTCDI and BNTCDI films was determined, which is about 0.25 eV lower than the work functions of the PTCDA and the NTCDA films.

Thin films of trioligo(phenylene–vinylene) end terminated by dibutylthiole (tOPV) were thermally deposited in UHV on highly ordered pyrolytic graphite (HOPG) and on Ge (1 1 1) substrates. The surface potential and the structure of unoccupied electron states (DOUS) located 1–25 eV above vacuum level were monitored during the film deposition, using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. The electronic work function of the tOPV films changed during the film deposition until it reached a stable value of 4.3±0.1 eV at the film thickness of 8–10 nm. Deposition of the tOPV under 3 nm led to formation of intermediate DOUS structures that were different for the cases of the two substrates used in the study. The intermediate structures got replaced by a DOUS structure of the tOPV films which was the same for the two substrates, along with the increase of the deposit thickness to 8–10 nm. A significant electron transfer from the tOPV film to Ge (1 1 1) surface was observed and the charge transfer layer in the film extended up to 10 nm. No significant charge transfer was observed at the interfaces between the tOPV film and the HOPG substrate. A substantial reconfiguration of the electronic structure of the tOPV films due to the interaction with the Ge(1 1 1) and also the HOPG surfaces was deduced and the charge transfer at the tOPV–Ge(1 1 1) interface was found to be consistent with the extended interface dipole model.

An evolution of an energy structure of the unoccupied electronic states and of a surface composition during the formation of a Pd/MgO/Cu (polycrystalline) thin layer system and NO 2 adsorption was studied using Auger electron spectroscopy, total current spectroscopy (TCS) and work function measurements. All investigations were performed in situ under UHV conditions. A 10nm thick MgO film was prepared via oxidation of a Mg overlayer on a clean polycrystalline Cu substrate. The MgO electronic structure was completely screened after deposition of a few monolayers of Pd and the Pd-related TCS fine structure appeared. We observed an irreversible NO 2 adsorption on the Pd layer. A negative charge transfer to adsorbed molecules and appearance of new adsorption-induced unoccupied bands were revealed. These new bands are considered as a result of hybridisation of palladium and unoccupied oxygen orbitals.

The effect of nitrogen-containing substituents such as phenyl imide and actyl imide on the character of fragmentation of perylene derivative molecules under laser irradiation has been studied by laser desorption (LD) mass spectrometry. Replacement of the central oxygen atom by a nitrogen atom in anhydride carboxy groups in perylene tetracarboxylic dianhydride (PTCDA) molecule results in the suppression of CO2 desorption and predominant desorption of CO. The LD mass spectrum exhibits peaks that correspond to fragments of the perylene nucleus and those of the aromatic and aliphatic substituents. Intact PTCDA molecules are present in the desorbed flux in insignificant amounts.

Resonance interaction of low energy (0-14 eV) electrons with gas-phase 7,7,8,8-tetracyanoquinodimethane (TCNQ) was investigated using dissociative electron attachment (DEA) spectroscopy. Spectral features associated with formation of long-lived TCNQ molecular negative ions are detected at incident electron energies of 0.3, 1.3, and 3.0 eV. A variety of negative fragments is observed around 4 eV, and slow (microseconds) dissociative decay channels are detected at about 3 eV, in competition with simple re-emission of the captured electron. The average electron detachment time from the TCNQ(-) negative ions formed at 3 eV was evaluated to be 250 μs. The experimental findings are interpreted with the support of density functional theory (DFT) calculations of the empty orbital energies, scaled with an empirical equation, and by comparison with earlier electron transmission spectroscopy (ETS) data. A possible mechanism for the unusual formation of long-lived molecular anions above zero energy (up to 3 eV) is briefly discussed. The present results on the interactions between electrons and isolated TCNQ molecules could give more insight into processes observed in TCNQ adsorbates under conditions of excess negative charge. In particular, electron-stimulated surface reactions are hypothesized, likely occurring when condensed TCNQ molecules are exposed to electron beam irradiation.

An unoccupied density of states (DOS) evolution under oxidation of ultrathin Mg, Zn and Cd layers on SrTiO 3 (1 0 0)-(2×2) substrates are investigated. The metal deposition and subsequent oxidation were studied in situ under UHV conditions by means of LEED, AES, TCS and work function measurements. An appearance of metal- and oxygen-derived bands of the unoccupied DOS was traced in the TC spectra. Metal oxidation was followed by the hybridization of metal and oxygen orbitals and by the appearance of the mainly O 2p oxygen-derived bands, which are characterized by a set of DOS maxima, located at the following energies (above the Fermi level): 8.0, 11.5, 14.3, 15.0 and 19.0 eV for MgO; 6.0, 8.1, 16.8 and 20.5 eV for ZnO and 7.5, 10.0 and 12.7 eV for CdO. The results obtained are discussed in comparison with previously published experimental and theoretical data on unoccupied DOS in metal oxides.