Прохождение низкоэнергетических электронов и плотность незаполненных состояний сверхтонких слоев TCNQ на поверхности окисленного кремния

Abstract

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.