Electronic Properties of Carbyne Chains: Experiment and Theory

As the known allotropes of carbon have expanded, increasing interest has been shown in one-dimensional carbyne. One approach to studying carbyne has been to synthesize linear carbon chains (LCCs) within a crystal via ion-assisted plasma condensation. With this technique, although the interchain separation can be elucidated via diffraction data, much less is known about the intrachain structural properties. In this work, LCC samples deposited on substrates including intrinsic Si, n- and p-doped Si, Cu metal, and SiO2 were studied using X-ray absorption spectroscopy. The resulting spectra show broad features, which are incompatible with a highly ordered structure, and suggest that the sample is composed of LCC chains of varying lengths and orientations, yielding an overall amorphous X-ray absorption spectroscopy spectrum. No significant changes were observed by varying the film thickness or orientation. Density functional theory was used to model hydrogen-terminated and unterminated LCCs of various lengths. For pure carbon chains, the interatomic distance converges to an interatomic distance of 1.279 angstrom for non-negligible chain lengths. For hydrogen-terminated chains, the interatomic distances vary considerably with the chain length. There are conflicting reports regarding the interchain separation distance, but this work suggests the reported experimental value of 2.97 angstrom is most plausible.