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 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 .

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