TY - JOUR

T1 - Unoccupied Electronic States and Potential Barrier in Films of Substituted Diphenylphthalides on the Surface of Highly Ordered Pyrolytic Graphite

AU - Komolov, A. S.

AU - Lazneva, E. F.

AU - Gerasimova, N. B.

AU - Sobolev, V. S.

AU - Pshenichnyuk, S. A.

AU - Asfandiarov, N. L.

AU - Kraikin, V. A.

AU - Handke, B.

N1 - Funding Information: TCS studies of phthalide films were carried out with the support of the Russian Science Foundation, grant no. 19-13-00021. HOPG diagnostics was performed with the support of the Russian Foundation for Basic Research (20-03-00026). The equipment of the Research park of Saint Petersburg State University “Physical methods of surface investigation” and “Diagnostics of functional materials for medicine, pharmacology and nanoelectronics” was used. Publisher Copyright: © 2021, Pleiades Publishing, Ltd. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

PY - 2021/2

Y1 - 2021/2

N2 - Abstract: 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 EF during thermal vacuum deposition of these organic films on the surface of highly ordered pyrolytic graphite (HOPG). The values of Evac relative to EF, 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 –CH3 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 EF by about 1 eV towards the lower electron energies.

AB - Abstract: 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 EF during thermal vacuum deposition of these organic films on the surface of highly ordered pyrolytic graphite (HOPG). The values of Evac relative to EF, 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 –CH3 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 EF by about 1 eV towards the lower electron energies.

KW - boundary potential barrier

KW - density of electronic states

KW - electronic properties

KW - highly ordered pyrolytic graphite

KW - low-energy electron spectroscopy

KW - phthalides

KW - ultra-thin films

UR - http://www.scopus.com/inward/record.url?scp=85101264218&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/b98c989c-36cf-3cbb-b0fc-10dee8e5c6fd/

U2 - 10.1134/s1063783421020104

DO - 10.1134/s1063783421020104

M3 - Article

AN - SCOPUS:85101264218

VL - 63

SP - 362

EP - 367

JO - Physics of the Solid State

JF - Physics of the Solid State

SN - 1063-7834

IS - 2

ER -