Stability of oxygen-functionalized graphenic surfaces: Theoretical and experimental insights into electronic properties and wettability

Highlights: • Plasma treatment is an effective tool for tuning graphenic surface properties. • Oxygen functionalities result in dramatic changes in wettability and electronic properties. • Stability of surface oxygen groups was investigated by experiments and DFT modeling. • Plasma functionalization effect can be limited to several topmost atomic layers. • Strict timeframe for post-plasma processing of the carbon-based surfaces is pointed out. Introduction of polar oxygen functional groups into carbon surfaces by plasma treatment results in dramatic changes in their wettability and electronic properties. Herein, we propose the combined theoretical and experimental approach to explore the chemical nature and stability of these functionalities. The DFT calculations were performed to evaluate the value and direction of the formed surface dipoles of C_surf–OH, −CHO, –COOH, =O, C_surf-O-C_surf moieties, whereas the surface-sensitive techniques (XPS, SIMS), allow for their identification. The evolution of functionalization was monitored in time by the means of changes in wettability (water contact angle) and electrodonor properties (work function measured by Kelvin method). The results show that ~6 at.% of surface oxygen (−OH, −CHO, –COOH), led to dramatic changes in work function (increase by 1.15 eV) and water contact angle (decrease by 74°). The evolution of surface functionalization was systematically monitored over the period of 60 days after plasma treatment. Both, electronic properties and wettability tended to recover over time. SIMS depth profiling clearly illustrates the changes in surface composition of the aged graphenic surfaces, which were below the XPS sensitivity. Since plasma treatment is often used as the first step in the surface properties tuning of carbon materials, the practical importance of immediate functionalization after activation is highlighted.