TiCx–Ti2C nanocrystals and epitaxial graphene-based lamellae by pulsed laser ablation of bulk TiC in vacuum

Abstract

Nonstoichiometric δ-TiC_x, δ′/δ′′-Ti₂C and 2-D turbostratic graphene-based lamellae were co-synthesized by pulsed laser ablation of bulk δ-TiC in a vacuum and characterized using X-ray diffraction, electron microscopy and optical spectroscopy. The predominant δ-TiC_x occurred as submicron-sized particulates and nanocondensates with size dependent shapes (5 nm sphere vs. 10 and 15 nm cubo-octahedra), which tended to coalesce over well-developed (111) as a unit or impinged by the ~(001) vicinal surface to form a [10] tilt boundary. The minor Ti₂C nanocondensates occurred as cubo-octahedra for the cubic δ′-phase and triangular plates with well-developed (0001), {102} and {10} faces for the trigonal δ′′-phase, which tended to coalesce over (0001) as a unit. The turbostratic graphene-based lamellae occurred as nanoribbons or an artificial epitaxy shell on δ-TiC_x and δ′/δ′′-Ti₂C to facilitate carbon vacancy diffusion. The present TiC_x–Ti₂C-graphene phase assembly with characteristic Raman modes sheds light on their natural dynamic occurrence in presolar settings. The bimodal UV-visible absorbances of this phase assembly in the form of nanoparticles may have potential photocatalytic and abrasive/lubricant applications.