Synchrotron-based high-resolution photoelectron spectroscopy was applied to study the modification of the alkanethiol (AT) self-assembled monolayers on gold and silver substrates by nitrogen-oxygen downstream microwave plasma. Because of the low density and energy of the ionizing particles, the long-lived nitrogen and oxygen radicals provided the major impact of plasma treatment. The treatment resulted in massive damage and disordering of the initially well-ordered and chemically homogeneous AT films. The most pronounced processes are the complete (AT/Au) or partial (AT/Ag) oxidation of the pristine thiolate species, partial desorption of hydrogen and carbon-containing fragments with subsequent cross-linking within the residual hydrocarbon layer, and partial oxidation of this layer, and appearance of the nitrogen-containing entities. The plasma-treatment-induced changes in the alkyl matrix and at the S-substrate interface are only partly correlated. The rate and extent of the oxidation processes at this interface are noticeably larger for C18/Au than for C18/Ag, which suggests a stronger S-metal bond in the latter system. The results demonstrate that a smallest oxygen contamination should be avoided if one wants to perform a soft modification of thin organic layers or definite molecular entities attached to these layers through the exposure to plasma.

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High-resolution photoelectron spectroscopy was applied to study the modification of alkanethiolate (AT) self-assembled monolayers (SAMs) on gold and silver substrates by nitrogen-oxygen downstream microwave plasma. The dominating plasma-induced processes are the oxidation of the alkyl matrix and the thiolate headgroups and the desorption of the alkylsulfonate species. The rates and extent of these processes and the mechanism of film modification depend on the substrate and the length of the alkyl chain. The films on Ag were found to be much more resistant to degradation by the reactive plasma, which is related to stronger thiolate-metal and sulfonate-metal bonds as compared to those on Au and to a partial polymerization of the alkyl matrix in AT/Ag at the initial stages of the plasma treatment. On a given substrate, the length of the aliphatic chain noticeably affects the rates and extent of the oxidation and desorption processes. The major effect stems from a two-step character of the thiolate-sulfonate transformation process, which requires both the penetration of the reactive oxygen species to the headgroupsubstrate interface and the oxidation event itself. Whereas for short-chain SAMs the oxidation step is rate-determining, the process becomes diffusion-limited for the long-chain films.

Synchrotron-based high-resolution photoelectron spectroscopy was applied to study the modification of self-assembled monolayers (SAMs) of 4‘-methyl-1,1‘-biphenyl-4-thiols (BPT) on (111) gold and silver substrates by a nitrogen−oxygen downstream microwave plasma and the attachment of acrylic acid to the plasma-modified SAMs. The plasma treatment resulted in massive damage and disordering of the BPT films, with the extent and character being noticeably different for BPT/Au and BPT/Ag. Whereas for BPT/Au a profound desorption of the entire BPT moieties and a complete defragmentation of the residual hydrocarbon part occurred, only partial desorption and oxidation took place for BPT/Ag, where even a part of intact BPT moieties survived the plasma treatment. The differences in the response of BPT/Au and BPT/Ag to the plasma treatment are related to the stronger thiolate−substrate bonds for the latter system. Taking into account that an analogous difference was also observed in alkanethiolate films, one can consider it as a general property of thiol-derived SAMs. The extent of acrylic acid attachment to the plasma-treated BPT/Ag was found to be essentially larger than that to the hydrocarbon residues in the case of BPT/Au.

Glow discharge polymerization is not well understood due to the rapid/complex reaction at the plasma/gas precursor interface. Plasma reaction in a submerged condition allows post-plasma-polymerization, leading to further polymer growth and thus a stable structure. Electron collision with acetonitrile at the interface initiates the formation of radical monomers, which undergoes further rearrangement to form low-molecular (LM) nitrogen polymers (NPs). The radical-rich LM NPs go through further polymerization, forming stable high-molecular (HM) NPs (as determined using liquid chromatography/mass spectrometry). LM NPs absorb light at a wavelength of 270 nm (λ max) whereas HM NPs show absorption at 420 nm (λ max), as determined from ultraviolet-visible absorption spectra. The fluorescence spectra of HM NPs show characteristic emission at 430 nm, which indicates the presence of nitrogen functional groups with external conjugation. The proposed structure of HM NPs is verified with different analytical instruments.

Modification of octadecanethiolate self-assembled monolayers on Au by nitrogen-oxygen or argon-oxygen downstream microwave plasma with a low oxygen content (estimated below several percent) has been studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy and water contact angle measurements. For both types of plasma, the primary processes were found to be the loss of conformational and orientational order and the oxidation of the alkyl matrix and headgroup-substrate interface. At the same time, the film modification occurred much faster and with different intermediates for the nitrogen plasma than for the argon plasma. The reasons for these differences are considered in terms of the different reactivities and different efficiencies of the energy transfer between the plasma constituents in these two types of plasma.

In situ assessment of cell functions on N2/Ar micro‐plasma exposed fibroblast cells is examined to better understand the effect of atmospheric low‐dose plasma treatment. The cells number increased threefolds for plasma exposure time of 5 or 10 s, followed by cell culture for 48 h. The cell coverage rate rose 20% for the same plasma exposure time, followed by cell culture for 6 or 12 h. 0.5% N2/Ar micro‐plasma exposure can particularly be used to achieve the stimulated release of FGF7 and subsequent enhancement of cells proliferation and migration. This work thus provides a potential of using micro‐plasma system for cells related studies and the improvement of cutaneous wound healing.

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