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Hydrogen existence state of a hydrogenated amorphous carbon coating and its thermal stability

2019; Elsevier BV; Volume: 99; Linguagem: Inglês

10.1016/j.diamond.2019.107535

1879-0062

Jihua Peng, Manzhong Yang, Jun Bi, Ruida Sheng, Liejun Li,

Carbon Nanotubes in Composites

Hydrogenated amorphous carbon (a-C:H) coatings were deposited by plasma-enhanced chemical vapor deposition at a bias voltage of 740 V. The coated 316 L sample was annealed in 5 Pa argon media. The hydrogen content, chemical bond structure, and morphology of the coating and their evolution during annealing were characterised by elastic recoil detection analysis, mass spectrometry, Fourier transformation infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. It was found that the hydrogenated a-C:H coating had ~50 at. % hydrogen. However, a large part of the hydrogen probably exists in the form of hydrogen molecules, some of which was encapsulated in some “closed” voids. Obviously, this special structure is an effective way to improve the sp3 CC fraction in the a-C:H with high H content. The molecular hydrogen could stay in the “closed” voids stably during annealing below 490 °C. For these a-C:H coatings with specific structure, when annealed below 330 °C, the transformation of C sp3 to sp2 was controlled by the so-called active CH bond reaction in the a-C:H coating. Annealed above 330 °C, these active CH bonds were depleted out quickly, and carbon clusters started to grow. At annealing temperatures >490 °C, the rapid transformation of C sp3 to C sp2 was attributed to C sp3 bond breakage and atomic rearrangement induced by overcoming energy barrier.