Functionalization of graphenic surfaces by oxygen plasma toward enhanced wettability and cell adhesion: experiments corroborated by molecular modelling.

Graphenic materials attract huge attention because of their outstanding properties, and have a wide range of applications as, i.e., components of biomaterials. Due to their hydrophobic nature, however, the surfaces need to be functionalized to improve wettability and biocompatibility. In this study, we investigate the functionalization of graphenic surfaces by oxygen plasma treatment, introducing surface functional groups in a controlled way. The AFM images and LDI-MS results clearly show that the graphenic surface exposed to plasma is decorated with -OH groups, whereas the surface topography remains intact. The measured water contact angle decreases significantly after oxygen plasma treatment from 99° to ca. 5°, making the surface hydrophilic. It is also reflected in the surface free energy values which increase from 48.18 mJ m-2 to 74.53 mJ m-2 when the number of surface oxygen groups reaches 4 -OH/84 Å2. The DFT (VASP) molecular models of unmodified and oxygen-functionalized graphenic surfaces were constructed and used for molecular interpretation of water-graphenic surface interactions. The computational models were validated by comparison of the theoretically determined water contact angle (based on the Young-Dupré equation) to the experimentally determined values. Additionally, the VASPsol (implicit water environment) results were calibrated against the explicit water models that can be used in further research. Finally, the biological role of functional groups on the graphenic surface was examined in terms of cell adhesion with the use of mouse fibroblast cell line (NIH/3T3). The obtained results illustrate the correlation between surface oxygen groups, wettability, and biocompatibility providing the guidelines for the molecular level-driven design of carbon materials for various applications.

Towards the understanding of the gold interaction with AIII-BV semiconductors at the atomic level.

AIII-BV semiconductors have been considered to be a promising material for decades in overcoming the limitations of silicon semiconductor devices. One of the important aspects within the AIII-BV semiconductor technology is gold-semiconductor interactions on the nanoscale. We report on the investigations into the basic chemical interactions of Au atoms with AIII-BV semiconductor crystals by the investigation of the nanostructure formation in the process of thermally-induced Au self-assembly on various AIII-BV surfaces by means of atomically resolved High Angle Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM) measurements. We have found that the formation of nanostructures is a consequence of the surface diffusion and nucleation of adatoms produced by Au induced chemical reactions on AIII-BV semiconductor surfaces. Only for InSb crystals we have found that there is efficient diffusion of Au atoms into the bulk, which we experimentally studied by Machine Learning HAADF STEM image quantification and theoretically by Density Functional Theory (DFT) calculations with the inclusion of finite temperature effects. Furthermore, the effective number of Au atoms needed to release one AIII metal atom has been estimated. The experimental finding reveals a difference in the Au interactions with the In- and Ga-based groups of AIII-BV semiconductors. Our comprehensive and systematic studies uncover the details of the Au interactions with the AIII-BV surface at the atomic level with chemical sensitivity and shed new light on the fundamental Au/AIII-BV interactions at the atomic scale.