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
Diamond and Carbon-based Materials Research·Materials Chemistry·Materials Science·Physical Sciences
References
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