Amorphous carbon is a carbon solid with no long-range crystalline order, in which the atoms are held in a mixture of threefold and fourfold coordination; the ratio of the two, usually written as sp2/sp3, sets nearly every property of the material. Determining that ratio is therefore the central characterisation problem, and X-ray photoelectron and X-ray excited Auger spectroscopy were among the first methods applied to it [1]. Near-edge X-ray absorption fine structure, interpreted with ab initio calculation of the spectra, gives a quantitative alternative [2]. At the extreme, a fully fourfold-coordinated form has been prepared and examined by transmission electron microscopy [3]. Because the two coordinations conduct differently, layered films that alternate sp3-rich and sp2-rich sublayers show electrical behaviour that neither component alone gives [4]. The ratio is not fixed once the film is made: thermal treatment converts the metastable network, and how far it goes depends on how much fourfold bonding was present to begin with [5].
- sp2/sp3 ratio
- tetrahedral amorphous carbon
- diamond-like carbon
- short-range order
- x-ray absorption
- hybridisation
- thin film
References
- Lascovich, J.; Giorgi, R.; Scaglione, S.; Evaluation of the sp2/sp3 ratio in amorphous carbon structure by XPS and XAES. Applied Surface Science 1991, 47, 17-21, 10.1016/0169-4332(91)90098-5.
- Titantah, J.; Lamoen, D.; Technique for the sp2∕sp3 characterization of carbon materials: Ab initio calculation of near-edge structure in electron-energy-loss spectra. Physical Review B 2004, 70, 075115, 10.1103/physrevb.70.075115.
- Wen, J.; Zeng, Z.; Yang, L.; Zeng, Q.; Lou, H.; Sheng, H.; Miller, D.J.; Yang, W.; Mao, H.k.; TEM Study of Amorphous Carbon with Fully sp3-Bonded Structure. Microscopy and Microanalysis 2017, 23, 2268-2269, 10.1017/s1431927617012004.
- Hastas, N.A.; Dimitriadis, C.A.; Tassis, D.H.; Panayiotatos, Y.; Logothetidis, S.; Papadimitriou, D.; Electrical properties of magnetron sputtered amorphous carbon films with sequential sp3-rich/sp2-rich layered structure. Applied Physics Letters 2001, 79, 3269-3271, 10.1063/1.1419044.
- Rouhani, M.; Chau-Nan Hong, F.; Jeng, Y.R.; In-situ thermal stability analysis of amorphous carbon films with different sp3 content. Carbon 2018, 130, 401-409, 10.1016/j.carbon.2018.01.034.