Evidence of massless Dirac fermions in graphitic shells encapsulating hollow iron microparticles

Abstract

The electronic properties of graphite with rotational stacking faults are strongly modified with respect to Bernal-stacked graphite, with the recovery of the Dirac cones for sufficiently high misorientation angles. A particular case is represented by twisted bilayer graphene (TBLG), in which twist angles are univocally related to the frequency of rotation modes observed in Raman spectra. The electronic properties determined by Dirac fermions make highly desirable to develop simple routes to synthesize highly decoupled turbostratic graphite and TBLG, as an alternative to single-layer graphene (SLG) for graphene-based electronic devices. In this work, we present a synthesis of hollow iron microspheres wrapped by graphitic layers in water-submerged arc discharge experiments between graphite electrodes, with an iron wire inserted into the anode. The microspheres were studied by scanning electron microscopy, microprobe energy-dispersive X-ray spectroscopy and Raman spectroscopy. We observed domains showing rotation and combination Raman modes typical of TBLG with different rotation angles, together with domains made of turbostratic graphite. The twist angles found in TBLG domains are indicative of values of the Fermi velocity close to the value of SLG. Our results open a new road for the synthesis of robust graphitic materials with the electronic properties of SLG.