How functional groups change the electronic structure of graphdiyne: Theory and experiment

Graphdiyne's electrons have been verified to display near massless behavior, as was predicted by the Dirac cone-like shape of its band structure, and has thus resulted in an exceptionally promising semi-conducting material. We present a study of three graphdiyne samples with different thicknesses grown using a cross coupling reaction. Their electronic structures were examined using synchrotron soft X-ray absorption and emission spectroscopy, together with complementary full-potential, all-electron density functional theory calculations. Excellent agreement between the measured and calculated spectra was achieved, indicating strong evidence that the correct structural model was found. We show the existence of oxygen molecules and hydroxyl functional groups, as well as pyridinic nitrogen sites in each graphdiyne sample studied. Our study shows that the defect type varies with sample thickness, which in turn strongly depends on the synthesis conditions. The band gaps of three graphdiyne samples were measured to be 0.6 eV, 0.8 eV, and 0.9 eV in agreement with our calculated values. We propose that controlling the thickness of graphdiyne films may provide a novel method for tuning their band gaps. (C) 2017 Elsevier Ltd. All rights reserved.