Interfacial Interaction between Carbon Nanotube and Stoichio- and Nonstoichiometric Ceramic Surfaces by Ab-Initio Calculations

Abstract

This work deals with the interfacial interaction between single-walled carbon nanotubes (CNTs) and ceramic surfaces of SiC(0001) and ZrO₂(111) based on the density functional theory. The ab-initio calculations show that the adhesive energy per the projected contact area on the ceramic surfaces depends on not only the diameter of CNTs but also the stoichiometry of the surfaces. For stoichiometric surfaces, such as the O-terminated ZrO₂(111), the structures of the adsorbed CNTs do not drastically change from the original cylindrical shape and the interfacial interaction is relatively weak. In the case of nonstoichiometric surfaces, such as Si- and C-terminated SiC surfaces and Zr-terminated ZrO₂ surface, they have a strong interaction. Especially for the small-diameter CNTs, the structure was transformed into an arch-like shape. The strong interaction arises from the formation of the mixed covalent-ionic bonding and the subsequent opening of CNTs, which is catalytically induced by the nonstoichiometric surfaces. The covalent and ionic characteristics of the interfacial bonding states are discussed in terms of the integrated crystal orbital Hamilton populations calculation and the Bader charge transfer analysis. These properties of the interface might be related with how a crack propagates on the interface and how large fracture toughness the composite has. CNT-SiC, which has the lower adhesive energy and relatively large covalent strength, results in the slightly increased fracture toughness. And CNT-ZrO₂ with the same lower adhesive energy but the lower covalent strength does in the decreased, as seen in the experimental data.