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  • Similar results regarding film uniformity were obtained for

    2018-11-09

    Similar results regarding film uniformity were obtained for all other samples. Table 3 lists the data allowing to compare the calculated stoichiometric composition of elements with the averaged experimental results. The analysis of the data in Table 3 leads us to conclude that the CuTPP and ZnTPP samples exhibit an approximate agreement of the elemental contents in thin films with the calculated values. The copper content in the CuTPP sample turns out to be insignificantly (by about 1wt%) lower, and the zinc content in ZnTPP higher, compared with the calculated values. Substantially larger deviations have been observed in the content of nitrogen impurities, observed to be increased in comparison with stoichiometry only for CuTPP films. This may be associated with different content of the air adsorbed in the films, which substantially depends on the structure of the film and, respectively, on the surface area of the condensate. We are going to demonstrate below that a more developed surface is typical for CuTPP films, and, as a consequence, they can absorb a significantly larger amount of air. Differences in the structure and surface morphology of films of different tetraphenylporphyrins will be discussed further. Component analysis of thin film samples of the coordinated FeClTPP complex revealed two features distinguishing it from copper and zinc metalloporphyrins. Firstly, thin films of the complex are significantly (by about three times) chlorine-depleted. Secondly, a substantial amount of oxygen (up to 7wt%) is found in these films, which is much greater than the contents of adsorbed oxygen in copper and zinc tetraphenylporphyrin films. Quantum chemical calculations performed for the complex with FeCl showed that the Cl retinoid x receptor is weakly bound to the rest of the structure (the Mayer bond order of Fe–Cl in a coordinated complex has a value of 0.2). Ref. [9] established, for the MnIIICl porphyrin similar in structure, that a complete loss of chlorine atoms coordinated to the metal occurred for an adsorbed [SAc]P-MnIIICl monolayer on Ag(100) under heating up to 498K; however, there was no loss of metal atoms and no destruction of macrocycles. Thus, during the sublimation process and at temperatures of about 600K, atoms can partially break away from the metalloporphyrin, with the free radicals formed capable of effectively interacting with the residual oxygen and, potentially, with hydroxyl groups, establishing sufficiently strong chemical bonds. Fig. 2 shows possible scenarios of chlorine substitution by oxygen, the formation of complex structures with μ-bridged complexes [8] and of iron oxychloride, hydroxyl. However, all of these scenarios could explain an increase in the oxygen content in the films up to a maximum of 2.3% even in case of complete substitution of chlorine by oxygen complexes. The excess oxygen content cannot be associated with the air adsorbed on the surface, as it is not accompanied by a corresponding increase in its content in nitrogen films. However, a study of EPR spectra of cobalt porphyrins [10] noted that it is possible for CoIITPP to form a bond with an O2 molecular ligand coordinated to the metal atom. A similar presence of bound molecular oxygen in our samples could explain such high values of the oxygen content in FeClTPP films. Thus, accurate determination of the chemical structure of the films obtained by evaporation of the FeClTPP complex requires further study. It should be noted that the magnetic characteristics of these films would also substantially depend on the method by which they were fabricated.
    Surface morphology of metalloporphyrin films Surface morphology of 500nm-thick films prepared from the ZnTPP mixture (Fig. 3a) was investigated by electron microscopy, which revealed that the films have a smooth surface and are composed of large columnar crystals up to 2µm in length, closely packed and forming a thick film. It can be seen on the defect (cleavage) of the film that the crystallization is characterized by an elongated crystal axis and occurs mainly parallel to the substrate.