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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.

Electrical conductivity of film samples of a composite constituted by a perylene derivative (3,4,9,10-perylenetetracarboxylic-dianhydride) and SnO2 nanoparticles was studied in adsorption of vapors of ammonia, toluene, aqueous hydrogen peroxide, ethanol, and water. A model of formation of the composite sample under study and a mechanism by which adsorbed molecules affect its electrical conductivity are suggested.

The structure of electronic states at the interfaces between perylene tetracarboxyldianhydride films and ZnO, Cu, GaAs, and InAs substrates is studied by the method of total current spectroscopy. It is found that the physicochemical properties of the substrate have a strong effect on the electronic state configuration in the substrate and film. On the basis of the experimental data, potential diagrams of the interfaces are constructed, which illustrate the formation of sharp and extended dipole layers, change in the charge state of surface levels, and modification of the electronic structure of the film.

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 formation of interfaces between the single-crystalline InAs(001) surface and organic semiconductor molecules (PTCDA and NTCDA) is investigated. With the methods of total current spectroscopy and Auger electron spectroscopy, it is found that indium atoms diffuse from the substrate into the molecular film. Indium atoms present in the film change the structure of its π-electron states and decrease the energy of unoccupied molecular orbitals.

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.

The formation of the interface between the GaAs(100) single-crystal surface and PTCDA and NTCDA organic semiconductors is investigated. The method of total current spectroscopy makes it possible to trace the formation of the interfacial electronic structure. The two organic materials and the GaAs substrate are bonded together when the π electron cloud of an aromatic ring spreads toward the substrate. This modifies the electronic states of interfacial organic molecules and generates a dipole at the interface.

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.

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.

The vacuum-deposited films of corbatin (CRB) and perylene tetracarboxy dianhydride (PTCDA) were studied in situ by method of total electron-beam-induced current (EBIC) spectroscopy. The results are interpreted within the framework of the model of vacant electron states (VES) above the energy level of vacuum. For PTCDA samples, the VES density determined from the EBIC measurements shows a good agreement with the available NEXAFS data. For CRB films, the VES density above the vacuum level is reported for the first time.

The initial stage of formation of an organic coating of N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) on a crystalline (ZnO) surface in the course of thermal deposition in high vacuum has been studied using the low-energy total current spectroscopy technique. A change in the work function and the density of unoccupied electron states in an energy interval of 0–20 eV above the vacuum level was traced as the organic coating thickness increased up to 8 nm. The energy positions of the bands of unoccupied electron states in the TPD film have been determined, including π* band (7–9 eV above the Fermi level), σ1* band (10–12 eV), σ2* band (14–16 and 18–20 eV).

Unoccupied density of states (DOS) for the polar (0001) Zn, (000) O and non-polar (100) ZnO surfaces and for a MgO(001)-c(2 × 2) thin film were studied using total current spectroscopy (TCS). TC spectra of the ZnO surfaces reveal the Zn 4s-O 2p band (6.2 eV) and two DOS maxima in the Zn 4p-O 2p band which exhibited different energy positions on the Zn-terminated (8.1 eV) and O-terminated (11.0 eV) surfaces. In the TC spectra of the MgO thin film, the energy location of Mg-derived (8.0, 14.8 and 21.0 eV) and O-derived (11.6, 14.2 and 18.5 eV) maxima of DOS were determined. Previously reported data on DOS of these materials is discussed, and it is shown that additional detailed information on the energy structure of unoccupied DOS in ZnO and MgO in the 5-25 eV range above EF has been found.

A theoretical interpretation is given of the fine structure in the total-current spectra obtained from the (0001) plane of MoS2, ZrS2, and NbSe2 single crystals. The calculations took into account the energy dependences of band energy-level broadening and of the density of unfilled electronic states which become occupied by electrons entering a solid. The dominant contribution of the bulk band structure to the spectra is demonstrated.

Low energy electron diffraction, Auger electron spectroscopy, X-ray photoelectron spectroscopy and electron energy loss spectroscopy were used to study a process of electron beam evaporated deposition of magnesium oxide film on a strontium titanate substrate. An annealed substrate exhibited a SrTiO 3 (100)-(2×2) surface reconstruction and consisted of nearly equal areas of TiO 2 and SrO terminated planes (slightly rich TiO 2 ). A selective deposition of magnesium oxide onto TiO 2 terminated planes of strontium titanate substrate was carried out, and a formation of a MgO(100)-c(2×2) superstructure discovered. A plausible nature of the superstructure is discussed in terms of a non-stoichiometric MgO(100) plane with a 1/4 density of oxygen vacancies.

Thin copper oxide film formation on the polar ZnO(0001) and ZnO(0001) surfaces under ultra-high vacuum conditions was monitored by LEED, Auger, TCS and work-function measurements. The 2.5 nm thick discontinuous oxide films contained a mixture of CuO, Cu2O and ZnO. The effect of oxygen gas on the conductivity of the thin films has been measured, and a more pronounced increase of a relative resistance of the film is observed in the temperature range 400–500 K.

Laser-induced oxygen molecule desorption from crystalline (110) and compressed-powder rutile TiO 2 surfaces is investigated by time-of-flight distributions and desorption signal dependencies on laser fluence. A double-component distribution of desorbed O 2 molecules (a fast one and a slow one) justifies validity of both photoelectronic and thermo-activation mechanisms. The defected surfaces are characterized by the more intensive oxygen escape supporting the desorption flow formation via the surface defect sites.

Total current spectroscopy (TCS) was used to study an evolution of unoccupied states through the process of thin-layer copper deposition and its oxidation on polar ZnO(0001) and surfaces. Zn-derived and O-derived unoccupied bands were identified in the TC spectrum at 7.7 and 9.8 eV, respectively, from the clean and well ordered polar ZnO faces, while the spectra from a thin CuO layer reveal an intensive fine structure in the 6 - 25 eV energy range above the Fermi level, which is discussed in comparison with previously reported results of experimental and theoretical investigations. The obtained data provide additional information on the energy location of the edges of unoccupied bands in CuO in the 6 - 25 eV range relative to .

The process of lipid peroxidation (LPO) in biological membranes of cells is carried out by free radical mechanism, a feature of which is the interaction of radicals with other molecules. In this work we investigated the antioxidant activity of cationic whey protein isolate, obtained by the cation-exchange chromatography on KM-cellulose from raw cow's milk, in vitro and in vivo. In biological liquids, which are milk, blood serum, fetal fluids, contains a complex of biologically active substances with a unique multifunctional properties, and which are carrying out a protective, antimicrobial, regenerating, antioxidant, immunomodulatory, regulatory and others functions. Contents of the isolate were determined electrophoretically and by its biological activity. Cationic whey protein isolate included lactoperoxidase, lactoferrin, pancreatic RNase, lysozyme and angeogenin. The given isolate significantly has an antioxidant effect in model experimental systems in vitro and therefore may be considered as a factor that can adjust the intensity of lipid oxidation. In model solutions products of lipid oxidation were obtained by oxidation of phosphatidylcholine by hydrogen peroxide in the presence of a source of iron. The composition of the reaction mixture: 0,4 mM H2O2; 50 mcM of hemin; 2 mg/ml L-alpha-phosphatidylcholine from soybean (Sigma, German). Lipid peroxidation products were formed during the incubation of the reaction mixture for two hours at 37 degrees C. In our studies rats in the adaptation period immediately after isolation from the nest obtained from food given orally native cationic whey protein isolate at the concentration three times higher than in fresh cow's milk. On the manifestation of the antioxidant activity of cationic whey protein isolate in vivo evidence decrease of lipid peroxidation products concentration in the blood of rats from the experimental group receipt whey protein isolate in dos 0,6 mg/g for more than 20% (p0,05) with oral feeding. Thus, significantly cationic whey protein isolate has an antioxidant effect in model experimental systems, and so can be considered as a factor that can regulate the intensity of lipid oxidation.

An intensive triplet line is revealed in the total current spectrum (TCS) of a reconstructed surface. The nature of the observed structure in the TCS is discussed in comparison with previously reported data from photoemission, inverse photoemission and theoretical investigations. It is found to be a consequence of the electron transitions into an Fe 3d band of empty states. Energy locations of Fe 3d-band extrema ( and above the bottom of the conduction band) and its splitting are estimated from the proposed schemes of electron transitions.

The formation of thin organic films of copper phthalocyanine (CuPc) deposited onto the surface of gold-coated quartz crystal resonator was studied in situ under ultrahigh vacuum conditions by means of total electron-beam-induced current spectroscopy in combination with deposit thickness determination by piezocrystal microbalance technique. Variations in the fine structure of the total current spectra of CuPc layers of var-ious thicknesses in the 0–8 nm interval have been analyzed and the electron mean free path in thin CuPc films was determined as a function of the electron energy. For electron energies of 5.0, 7.2, 14.4, and 18.0 eV above the Fermi level, the mean free path is 6.4, 3.9, 2.6, and 2.3 nm.

Incidence angle dependent elastic electron reflection curves in the 0 to 30 eV range are measured on Cu(111) and Ni(111) using target current regime. They are compared with the calculated ones. Computations are made very fast using a simple approximation. The extrema of the reflection energy derivative are shown to correspond unambigiously to definite critical points of bands. These points are mapped when the energies of the experimental extrema are compared with the calculated ones. Varying the incidence angle, in this way bands in the variety of Brillouin zone directions may be investigated. [Russian Text Ignored.]

Studies are made of the characteristic energy losses of slow electrons during the formation of thin PTCDA films on a ZnO(0001) surface. It is shown that at low primary electron energies (

A combined analysis is made of the low-energy total current and secondary electron emission spectra at the initial stage of formation of a silver coating on a W(110) surface. It is shown that the features observed in the spectra are related to the energy structure of the density of empty states lying above the vacuum level. The dynamics of changes in these features in the total current spectra as the film thickness increases indicates that at the initial stage the silver coating is characterized by the Ag(111) orientation, but as the thickness increases, the Ag(110) orientation predominates.

A double-component time-of-flight distribution of laser-desorbed CO 2 molecules was observed for a system of CO adsorbed on ZnO(0001). A strong increase of amount and a lowering of the threshold for the CO 2 desorption was caused by a submonolayer deposition of Cu.

Recent results of surface electronic and geometrical properties of ultrathin copper layers on the crystalline metal-oxide substrates TiO2(110), α-Al2O3(0001), CaO(001), ZnO(1120) and ZnO(0001) are reviewed. The basic experimental data of interest have been obtained by using LEED, AES, PES and EELS. New experimental results on laser-induced desorption (LID) from the system C0/Cu/ZnO(0001) are presented.

The electron energy loss (EEL) spectra of thin NTCDA films on the ZnO(0001) surface were measured. In the low-energy range (

Experiments are described in which a new technique—total current spectroscopy (TCS)—has been used to investigate the energy dependence of the reflection of low-energy electrons from clean surfaces of the naturally occurring mineral molybdenite (2H-MoS2). A theory involving both elastic and inelastic scattering of electrons is applied to a band structure calculated for molybdenite by Mattheiss (1973 a, b). With relatively few approximations the results of numerical calculations for a TCS spectrum from molybdenite agree surprisingly well with experiment. It is suggested that TCS will prove to be a convenient and sensitive tool for the probing of energy structures in other solid surfaces. For the transition-metaldichalcogenide series it should be possible to observe systematic changes in TCS spectra associated with changes in band structure, and subsequently to predict details in the density-of-states distributions using iterative computer procedures.

In total current spectroscopy (TCS) a beam of low energy (0–15 eV) electrons is directed upon a solid sample and secondary electron emission investigated by monitoring the current to the target, rather than by direct energy analysis of emitted electrons. A TCS signal is the derivative of the direct current with respect to the incident energy E1 displayed as a function of that energy, and obtained experimentally in ultra high vacuum conditions using simple modulation and lock in amplification techniques. A typical experimental arrangement is described and factors influencing a typical spectrum outlined. A simple background theory is discussed and it is shown how TCS is a powerful tool for studying not only the surface and near surface regions, but also bulk physics. In particular the technique has already found application in studies of work function, chemi- and physisorption, epitaxy, interband transitions, densities of states, excitons, impurity atom excitation, plasmons, radiation damage and the measurement of thicknesses of very thin surface layers.

Total current spectroscopy (TCS) has been used to probe the {100} surface of a single crystal of vanadium. Primary electron energies were in the range 0–10 eV. Surface potential measurements are described for desorption of residual gas between room temperature and 1500°C. A value for the work function of vanadium is obtained from comparative measurements using evaporated layers of silver. Structure in the TCS curves is a consequence of both the reflection properties of the vanadium surface and excitation of interband transitions in the solid. Additional structure which appears after adsorption is due to resonances in the adsorbed layer. A method is described for the extraction of this component from the spectra and a simple analysis given in terms of multiple electron scattering. In this way estimates of the layer thickness d and the average potential V can be made.

Experiments are described in which thin layers of silver and gold, and of cadmium sulphide and cadmium selenide, have been grown on metal substrates in ultra-high vacuum. Total current spectroscopy (TCS) reveals details of the film formation processes until, finally, the spectrum obtained can be related to inelastic electron/electron scattering accompanied by interband transitions in the continuous overlayer. An analysis is presented which permits extraction of values for effective of values for effective mean free paths for different electron energies in the evaporated films.