Stability of the surface termination of differently modified ultrananocrystalline diamond/amorphous carbon composite films

We have investigated the stability of the surface termination of ultrananocrystalline diamond/amorphous carbon (UNCD/a-C) composite films after their modification with UV/O3 treatments or NH3-containing plasmas. The films were prepared by microwave plasma chemical vapor deposition from CH4/N2 mixtures and possess the H-termination typical for all CVD grown diamond films. The treatment with UV/O3 or NH3/N2 plasma resulted in a change of the surface termination as revealed by contact angle measurements and X-ray photoelectron spectroscopy (XPS). Both processes rendered the as-grown hydrophobic UNCD surface hydrophilic; the influence of the treatment time as well as that of the carrier gas (N2 or Ar) for the plasma process were investigated. The main task of this investigation was to determine the stability of the surface termination with storage time and storage conditions and upon exposure to standard organic solvents, like acetone, ethanol and i-propanol. It was found that for the UV/O3 treated UNCD surfaces the storage in air, and after NH3/N2 plasma modification package under reduced pressure preserved to a great extent the achieved hydrophilic properties in a period up to three months. The changes that occur predominantly during the first days after the modification step were due mostly to interchange of surface groups with the ambient. Similar processes were observed after exposure of the UNCD surfaces to standard organic solvents.

► UNCD/a-C films were modified by UV/O3 treatments or NH3-containing plasmas.
► Stability of surface termination of UNCD/a-C films after the modifications was studied.
► Storage conditions preserving the achieved hydrophilic properties were established.
► Exposure to organic solvents influences the surface termination.