Structure of carbon nitride films prepared by mass-separated low-energy ion beam deposition

Abstract

Carbon nitride films were prepared on Si(1 0 0) wafers by alternating irradiation with mass-separated ion beams of C + and N + at the ultra-high vacuum pressure 10 −7 Pa. The ion energy of both ion species was 50 eV. The Si substrate was kept at room temperature (rt), 460, 800 or 1130 K during deposition, and the effects of the substrate temperature on the film structure and chemical bonds formed were investigated. The films were characterized by transmission electron microscopy, X-ray diffraction, electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy. The CN film prepared at rt was amorphous. The nitrogen content decreased from 27 at.% in the film prepared at rt, to 20 at.% in the film prepared at 1130 K. The amorphous CN film prepared at rt consisted of sp 2 CN, sp 3 CN, sp 2 CC, and sp 3 CC bonds, whose bond angles were distorted. This distortion of the chemical bonds decreased, and the structure of the CN film changed to a graphite-like one on increasing the growth temperature. The graphite-like film has a highly preferential crystal orientation, and the c-axis of the graphite basal plane is parallel to the film growth surface. The basal plane is also curved and interlinked because of the presence of in-plane sp 2 CN and 3D sp 3 CN bonds.