Polymerization of aromatic dinitroso derivatives initiated by nitroso-terminated monolayer on Au(111) surface: Insights from ellipsometry, AFM and nano-FTIR spectroscopy

L. Nuić, B. Panić, L.-K. Pereković, I. Š. Rakić, M. Kralj, A. Mihanović, H. Vančik and I. Biljan

Polymer 271, 125795 (2023)
The possibility of on-surface intermolecular interactions of aromatic C-nitroso derivatives and the formation of azodioxy polymer thin films were studied by ellipsometry, atomic force microscopy (AFM) and nanoscale Fourier transform infrared (nano-FTIR) spectroscopy. The nitroso terminal groups of monolayers of 3-thiocyanatopropyl-4-nitrosobenzoate on Au(111) surface were used as initiation sites for formation of azodioxy linkages by interactions with the six structurally different aromatic dinitroso derivatives prone to polymerization. Ellipsometry showed increased thicknesses of films formed by interactions of nitroso groups at the monolayer interface and aromatic dinitroso derivatives in solution suggesting the formation of azodioxy oligomer films. The obtained thickness values indicated that the films are composed of only a few monomeric subunits or that poorly organized surface structures are formed with possibly tilted and intertwined chains. Ellipsometry data were corroborated with AFM topography images which revealed the appearance of a high number of islands, attributed to domains of azodioxy oligomers, and increased local RMS roughness values. Both ellipsometry and AFM indicated a greater tendency towards the azodioxy oligomers on the Au(111) surface at longer adsorption times. Nano-FTIR spectroscopy enabled chemical identification of the films at the nanoscale. Bands attributed to the E-azodioxy groups were detected in nano-FTIR spectra, which strongly supported the conclusion that the islands in the AFM images represent azodioxy oligomers, the formation of which was initiated by interactions of nitroso groups at the monolayer interface with dinitroso derivatives in solution.