Приведены результаты исследования топографии поверхности и плотности незаполненных электронных состояний при термическом осаждении сверхтонких пленок дибромо-биантрацена на поверхность ZnO. Измерения электронных характеристик незаполненных электронных состояний в процессе роста пленок дибромо-биантрацена до толщины 10 нм проводили методом спектроскопии полного тока с использованием тестирующего электронного пучка. Анализ экспериментальных зависимостей проводили с использованием теоретического расчета энергий орбиталей молекул дибромо-биантрацена методом теории функционала плотности.

The method of dissociative electron attachment (DEA) spectroscopy was used to study the attachment of electrons to 1-chloronaphthalene molecules. It has been established that the dominant channel for the decay of molecular ions is the formation of Clˉ ions in three resonances at 0.7, 1.5, and 3.0 eV. Ions [M-H]ˉ and [M-Cl]ˉ are observed at energies from 3.5 to 8.5 eV and have two to three orders of magnitude lower formation cross sections. Long-lived molecular ions were not registered. Calculations in the DFT CAM B3LYP/6-311+G(d,p) approximation predict the presence of six stable anionic structures in which the chlorine anion is coordinated to the neutral residue via noncovalent H–Clˉ–H bonds. The electron affinity of the most stable of these structures coincides with the experimentally measured value EAa=0.2771±0.003 eV. These results agree with the previously obtained data on the DEA of molecules of bromine-substituted biphenyls, naphthalenes, and anthracenes and confirm the existence of anionic structures with non-covalent H–Hal–H bonds. Such non-covalent anion structures should be extremely reactive, which makes them promising for the synthesis of self-assembling hydrocarbon nanomembranes.

The results of a study of the unoccupied electronic states of ultrathin films of phenolphthalein molecules on a ZnO surface formed by atomic layer deposition technique are presented. The atomic composition of the ZnO layer was determined by X-ray photoelectron spectroscopy (XPS) and its crystallinity was characterized using X-ray diffraction. The predominance of the content of O atoms by 5-10%, compared with the content of Zn atoms, was found. The electronic characteristics of the ZnO/phenolphthalein structure were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF during thermal vacuum deposition of phenolphthalein films up to 8 nm thick. Phenolphthalein molecules contain two hydroxyl functional groups. The TCS results on the phenolphthalein films are compared with the TCS results obtained from films of molecules that represent the backbone of phenolphthalein molecules without hydroxyl groups. The TCS fine structure maxima of phenolphthalein films located in the energy range from 5 eV to 8 eV above EF can be associated with the boundaries of the p* bands of electronic states. The work function of the ZnO surface formed by the ALD method were 4.2±0.1 eV. The deposition of a phenolphthalein film led to a decrease in the work function of the surface by 0.1 eV.

The results of studying the electronic states of the conduction band and interface potential barrier during the formation of ultrathin films of thiophene-phenylene co-oligomer CH3-phenylene-thiophene-thiophene-phenylene-CH3 (CH3-PTTP-CH3) on the surface of ZnO and films of biphenyl tetracarboxylic dianhydride (BPDA) on the ZnO surface are presented. A 100 nm thick ZnO layer was prepared by atomic layer deposition (ALD). Organic CH3-PTTP-CH3 films and BPDA films up to 8 nm thick were formed by thermal vacuum deposition. During film deposition, the electronic characteristics of the surface were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF. In this energy range, the structure of the maxima of the unoccupied electronic states of CH3-PTTP-CH3 and BPDA films was determined. As a result of the CH3-PTTP-CH3 film deposition, a decrease in the work function to 4.0 eV was found, compared with the value of the work function of 4.2 eV measured from the ALD ZnO substrate. This corresponds to the transfer of a negative charge from the СH3-PTTP-CH3 film to the substrate. The charge transfer at the interface between the BPDA film and the ALD ZnO substrate occurs in the opposite direction, since a 4.7 eV increase of the work function was registered during the formation of this interface. The СH3-PTTP-СH3 and BPDA films studied and the layer-by-layer grown ZnO film represent a continuous coating on sufficiently large surface areas of the order of 10 micrometers x 10 micrometers. The roughness of the ZnO surface does not exceed 4 nm, and the surface roughness of CH3-PTTP-CH3 and BPDA films was 10–15 nm.

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 were carried out by total current spectroscopy (TCS) technique in the energy range from 5 eV to 20 eV above EF during thermal vacuum deposition of these organic films on the surface of highly oriented pyrolytic graphite (HOPG). The energy Evac relative to EF, that is, the electronic work function of the DM-DPP films, at a film thickness of 5–8 nm was 4.3 ± 0.1 eV. The electronic work function of the DCA-DPP films was 3.7 ± 0.1 eV. The structure of the maxima of the unoccupied electronic states of DCA-DPP films and DM-DPP films in the studied energy range is determined. The properties determined of DCA-DPP and DM-DPP films are compared with the properties of films of unsubstituted diphenylphthalide (DPP). According to our analysis, –CH3 substitution of the DPP molecule practically did not affect the height of the potential barrier between the film and the HOPG surface, and –COOH substitution of the DPP molecule led 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 which represents formation of DCA-DPP molecules led to a shift of two peaks of the experimental total current spectra located at energies in the range from 5 eV to 8 eV above EF, by about 1 eV towards lower electron energies.

The results of a study of unoccupied electronic states and the formation of a boundary potential barrier during thermal vacuum deposition of ultrathin films of 4-quaterphenyl oligophenylene on the surface of CdS and on the surface of oxidized silicon are presented. Using X-ray photoelectron spectroscopy (XPS) it was determined, that the atomic concentrations of Cd and S were equal in the surface layer of a 75-nm-thick CdS film formed by atomic layer deposition (ALD). The electronic properties of 4-quaterphenyl films up to 8 nm thick were studied during their deposition on the surface of the CdS layer and on the surface of oxidized silicon using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF. The energetic position of the main maxima of the fine structure of the total current spectra (FSTCS) of 4-quaterphenyl films was determined. The location of the maxima was reproducible when two selected substrate materials were used. A minor decrease in the work function, from 4.2 eV to 4.1 eV, was registered during the thermal deposition of 4-quaterphenyl onto the CdS surface. During the deposition of a 4-quaterphenyl film on the oxidized silicon surface, an increase in the work function from 4.2 eV to 4.5 eV was found. Possible mechanisms of the physicochemical interaction between the 4-quaterphenyl film and the surface of the investigated substrates, which lead to a difference in the observed values of the work function of the films on these substrates, are discussed.

The results of studying unoccupied electronic states in the energy range from 5 eV to 20 eV above the Fermi level of ultrathin films of dimethyl-substituted thiophene-phenylene co-oligomers CH3-phenylene-thiophene-thiophene-phenylene-CH3 (CH3-PTTP-CH3) are presented. The films were deposited on two types of surface of polycrystalline Au: ex situ Au layer thermally deposited in a separate chamber, and on the in situ Au surface prepared inside the analytical chamber. The structure of the films was studied by X-ray diffraction (XRD). The formation of a superposition of the amorphous and crystalline phases with a period of 3.8 nm is discussed. Investigations of the energy positioning of the maxima of unoccupied electronic states and of the process of the formation of the potential boundary barrier were carried out by the method of total current spectroscopy (TCS). The maxima of the fine structure of the total current spectra (FSTCS) of the CH3-PTTP-CH3 film 5–7 nm thick did not differ when using different types of Au substrates and the surface of the ZnO semiconductor prepared by the atomic layer deposition (ALD) method. When the CH3-PTTP-CH3 layer was deposited both on the ex situ Au surface and on the in situ Au surface, a slight (about 0.1 eV) increase in the electronic work function was observed with an increase in the coating thickness to 5–7 nm. At such CH3-PTTP-CH3 film thicknesses, the electron work function was determined as 4.7 ± 0.1 eV for the ex situ Au substrate and 4.9 ± 0.1 eV for the in situ Au substrate. The possible influence of the processes of physicochemical interaction at the film – substrate interface on the formation of the potential boundary barrier in the structures under study is discussed.

The results on comparing the peak structure of the density of unoccupied electronic states (DOUS) of ultrathin films of naphthalene anhydride-1,4,5,8-teracabonic acid (NTCDA) and naphthalene-1,8-dicarboxylic acid anhydride (NDCA) and of two types of phthalide-based films: 3,3-bis (phenyl) phthalide (DPP) and 3,3-bis (phenyl) phthalide-4 ′, 4′-dicarboxylic acid (DPP-DCA) are presented. The measurements of the structure of the unoccupied electronic states in the energy range from 5 eV to 20 eV above the Fermi level of the films studied having thickness of 8–10 nm were conducted using the total current spectroscopy (TCS) technique. Analysis of the experimental results was conducted using the model total current spectra and DOUS dependences generated using the calculated orbital energies of the studied molecules by means of the density functional theory (DFT) method at the B3LYP/6-31G(d) level. The difference in the DOUS spectra of NTCDA and NDCA films is characterized by the shift of the main DOUS maxima of the NTCDA film to lower energies by about 1 eV at energies less than 12.5 eV, and 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 practically do not change when using various substrates: highly ordered pyrolytic graphite (HOPG) and layer-by-layer deposited CdS. The relative intensities of the maxima differ when using different substrates. The characteristic shift of the maxima of the total current spectra of DPP-DCA films is about 1 eV at energies less than 12.5 eV above the Fermi level and 1.5-2 eV and at higher energies, compared with the position of the corresponding maxima of the DPP films.

The results of the study of the formation of unoccupied electronic states and of the interface potential barrier during thermal deposition of tetracyanoquinodimethane (TCNQ) films, up to 7 nm thick, on the (SiO2)n-Si surface are presented. The electronic properties of the surface under study were determined using the total current spectroscopy (TCS) technique and as testing electron beam with energies in the range from 5 eV to 20 eV above the Fermi level. The formation of a potential barrier in the (SiO2)n-Si / TCNQ structure was accompanied by an increase in the surface work function from 4.2 ± 0.1 eV to 4.7 ± 0.1 eV. Based on the results of TCS experiments, the DOUS function of the studied TCNQ film is constructed. To analyze the experimental DOUS, the orbital energies of the studied TCNQ molecules were calculated using the density functional theory (DFT) method at the B3LYP/6-31G(d) level, which was followed by the correction procedure and by the allowance for the condensed phase polarization energy. DOUS of the TCNQ films has four main maxima in the energy range studied. The DOUS maximum at an energy of 7.0 eV above EF is mainly formed by pi* orbitals. Three DOUS maxima located in the energy range from 8.0 eV to 20 eV above EF are formed by approximately the same number of pi* and sigma* type orbitals.

AbstractThe 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 E _F 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 E _vac in relation to E _F, 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.

AbstractThe 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.

AbstractThe unoccupied electron states and the boundary potential barrier during deposition of ultrathin films of dimethyl-substituted thiophene–phenylene coolygomers of the type of CH_3–phenylene–thiophene–thiophene–phenylene–CH_3 (CH_3–PTTP–CH_3) 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 CH_3–PTTP–CH_3 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 CH_3–PTTP–CH_3 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/SiO_2/CH_3–PTTP–CH_3 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 CH_3–PTTP–CH_3 films well corresponds to the chemical formula of CH_3–PTTP–CH_3 molecules. The roughness of the CH_3–PTTP–CH_3 coating surface was not higher than 10 nm on the ~10 × 10 μm areas as the total CH_3–PTTP–CH_3-layer thickness was about 100 nm.

AbstractThe 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 .

Образование и распад отрицательных ионов производных фталида

Приведены результаты исследования плотности незаполненных электронных состояний в энергетическом диапазоне от 5 до 20 eV выше энергии Ферми (EF) в сверхтонких пленках диоктил-замещенного и дифенил-замещенного перилен-дикарбоксимида. Экспериментальные результаты получены путем регистрации тока вторичных низкоэнергетических электронов с использованием методики спектроскопии полного тока. Теоретический анализ включал в себя расчет энергий и пространственного распределения орбиталей исследованных молекул методом теории функционала плотности и последующее масштабирование рассчитанных значений энергий орбиталей согласно процедуре, хорошо зарекомендовавшей себя ранее при исследованиях малых сопряженных органических молекул. Обнаружено, что для обоих видов исследованных пленок при энергиях ниже 8 eV над EF расположены по два основных максимума плотности незаполненных электронных состояний, образованных преимущественно pi*-орбиталями молекул. Более высоколежащие максимумы имеют преимущественно sigma*характер. Проведен анализ влияния диоктил- и дифенил-замещающих групп на плотность незаполненных электронных состояний при сравнении результатов для исследованных видов пленок. В случае pi*-максимумов наблюдается относительный сдвиг, около 1 eV, по энергии. В области sigma*-электронных состояний наблюдается незначительная перестройка структуры максимумов. Работа выполнена при поддержке научного гранта СПбГУ 11.38.219.2014, РФФИ (14-03-00087 и 15-29-05786). DOI: 10.21883/FTT.2017.02.44068.142

Исследован атомный состав монослоев на основе силоксанового димера кватертиофена, нанесенных методом Ленгмюра-Блоджетт на поверхность диоксида кремния, частично покрытую пленкой золота, и стабильность этих монослоев при обработке поверхности путем бомбардировки ионами Ar+. Экспериментальные результаты по химическому составу серии исследованных поверхностей получены методом рентгеновской фотоэлектронной спектроскопии (XPS) путем регистрации XPS-спектров C1s, O1s, S2p и Au4f остовных уровней. Относительная концентрация атомов Au, Si и атомов подложки в составе приготовленной ex situ исследованной поверхности была определена в пределах 10-15%, что говорит о том, что монослои Ленгмюра-Блоджетт на основе силоксанового димера кватертиофена формируют в значительной степени сплошное покрытие. До проведения обработки исследованной поверхности путем бомбардировки ионами Ar+, углерод- и кислород-содержащие поверхностные адсорбаты вносили существенный вклад в результаты XPS измерений. Очистка поверхности ионами Ar+ с энергией 3 keV при значениях электрического тока через образец ~ 1 muA в несколько этапов по 30 s привела к стравливанию поверхностных адсорбатов, а затем и самих пленнок Ленгмюр-Блоджетт пленок силоксанового димера кватертиофена. Исследования по фотоэлектронной спектроскопии выполнены при финансовой поддержке РФФИ (16-33-50252-мол-нр, 15-29-05786). Исследования по нанесению монослоев Ленгмюра-Блоджетт и их характеризации выполнены за счет гранта Российского научного фонда (проект N 15-12-30031). В работе использовали оборудование научного парка СПбГУ "Физические методы исследования поверхности". DOI: 10.21883/FTT.2017.12.45249.132