Unoccupied Electronic States and Potential Barrier in Films of Substituted Diphenylphthalides on the Surface of Highly Ordered Pyrolytic Graphite

• Published in: Physics of the solid state 2021-02, Vol.63 (2), p.362-367
• Main Authors: Komolov, A. S., Lazneva, E. F., Gerasimova, N. B., Sobolev, V. S., Pshenichnyuk, S. A., Asfandiarov, N. L., Kraikin, V. A., Handke, B.
• Format: Article
• Language: English
• Subjects: Analysis; Dielectric films; Electron states; Electrons; Film thickness; Fine structure; Functional groups; Graphite; Physics; Physics and Astronomy; Polymers; Potential barriers; Pyrolytic graphite; Solid State Physics; Spectrum analysis; Substitutes; Substrates; Thin films; Vacuum deposition; Work functions
• ISSN: 1063-7834; 1090-6460
• DOI: 10.1134/S1063783421020104

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 E F during thermal vacuum deposition of these organic films on the surface of highly ordered pyrolytic graphite (HOPG). The values of E vac relative to E F , 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 –CH 3 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 E F by about 1 eV towards the lower electron energies.