Amorphous Carbon\nNitride Films: Surface and Subsurface\nComposition and Bonding

To obtain quantitative information about the composition\nand bonding\nof atoms located at and beyond the analyzed solid surface nondestructively,\nwe applied angle-resolved X-ray photoelectron spectroscopy aided by\nthe maximum entropy method to air-exposed amorphous carbon nitride\nfilms deposited by pulsed laser deposition of diamond-like carbon\nmodified by low-energy nitrogen ion bombardment during film growth.\nWe demonstrate that the composition, chemical bonding, and mass density\nvary significantly from the top surface to a shallow subsurface region.\nThe analyzed samples, in a shallow surface region of ∼1 nm,\nare composed of oxygen, nitrogen, hydrogen, and mostly carbon in sp<sup>2</sup> hybridization. In a deeper region, the C sp<sup>3</sup> content\nincreases substantially going to a maximum, whereas the nitrogen percentage\ndecreases to a minimum, then increases, and tends to saturate. Special\nattention has been paid to in-depth distributions of carbon atoms\nin trigonal and tetragonal arrangements because they specify numerous\nphysical and chemical properties of carbon-based materials. These\nresults indicate that the interaction of DLC:N surfaces with surroundings\ncan be influenced, barring oxygen and nitrogen, by sp<sup>2</sup>-bonded\ncarbon atoms located near the surface of the samples. The obtained\nresults can be useful for developing a deeper understanding of the\ninteraction between DLC:N layer surfaces and their surroundings and\nparticularly with living tissue.