Structural characterization of ion-vapor deposited hydrogenated amorphous carbon coatings by solid state ~(13)C NMR

摘要

In the past three decades, hydrogenated amorphous carbon (a-C:H) coatings have attracted intensive interesting for their extraordinary mechanical and tribological performance [1, 2]. It has been argued that the wide range properties of a-C:H coatings are attributed to the relative amount of H and C atoms and the ratio of C hybridized in sp~2 and sp~3 phase [3,4]. Compared with the most frequently used techniques of chemical characterization such as X-ray photoelectron spectroscopy (XPS) [5], X-ray near edge absorption spectroscopy (XANES) [6], electron energy loss spectroscopy (EELS) [7], NMR is inherently quantitative and quantify the sp~3/(sp~3+sp~2) ratio at a molecular level since the intensity of macroscopic magnetization is proportional to the number of NMR-active spins. In a static magnetic field M0, nuclei with a magnetic moment μ may interact with radio frequency (r.f.) irradiation, thus reflect information of nuclear spin interactions and present the chemical structure of samples. In this paper, structural characterization of ion-vapor deposited a-C:H coating is studied by using solid state ~(13)C NMR (~(13)C MAS and ~1H-~(13)C CPMAS techniques) in order to classify the two distinct characteristics of sp~2 clusters, i.e., protonated and non-protonated sp~2 clusters. In addition, hydrogen behaviors in the a-C:H coating are discussed below.