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.