High pressure studies on core/shell amorphous carbon nanostructures

Abstract

High pressure behaviour of core/shell amorphous carbon (a-C) nanostructures was studied using synchrotron X-ray diffraction (XRD) and Raman spectroscopy up to ~25 GPa. These nanostructures having spherical a-C shells with γ-Fe₂O₃ nanoparticles at the core were synthesized by catalyst-assisted lamp black method. The typical size of core (γ-Fe₂O₃)/shell (a-C) is ~5 nm/20 nm. Comparative XRD of the core (γ-Fe₂O₃) in opened- and closed-shell (a-C) shows that the carbon shells do not fully transmit the applied high pressure inwards, under hydrostatic conditions. Raman spectroscopy shows that the graphitic G-mode blue shifts reversibly with applied pressure with a coefficient ~3.5 cm⁻¹ GPa⁻¹, which is ~25 to 40% less than that for graphite and carbon nanotubes. It is suggested that a rigid and crosslinked structure of the carbon shell might be lossy for the observed pressure drop.