Ni-Doped Epitaxial Graphene Monolayer on the Ni(111) Surface
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HYSICS OF 1D AND 2D MEDIA
Ni-Doped Epitaxial Graphene Monolayer on the Ni(111) Surface S. L. Kovalenkoa, T. V. Pavlovaa, B. V. Andryushechkina, *, G. M. Zhidomirova, †, and K. N. Eltsova a
Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected] Received December 15, 2019; revised December 15, 2019; accepted December 16, 2019
Abstract—Nickel-doped graphene has been synthesized from propylene on the Ni(111) surface and studied using scanning tunneling microscopy (STM) and density functional theory (DFT). It is established that nickel centers are formed during graphene synthesis on the Ni(111) surface by both chemical vapor deposition (CVD) and temperature-programmed growth (TPG); apparently, they are always present in graphene synthesized on Ni(111). The centers are observed in STM images as single defects or defect chains and identified by DFT calculations as Ni atoms in carbon bivacancies. These nickel atoms are positively charged and may be of interest for single-atom catalysis. The incorporated Ni atoms should remain in graphene after the detachment from the substrate since they bound more strongly with carbon atoms in graphene than with substrate nickel atoms. DOI: 10.3103/S1541308X20030115
1. INTRODUCTION Defects in graphene are known to affect significantly its properties. In particular, their presence may cause the shift of Fermi level, opening locally the energy gap. Moreover, defects can influence the carrier mobility, conductivity, magnetic and mechanical properties of graphene; and play the role of active centers in chemical reactions [1]. Doping graphene with nitrogen and boron also affects the Fermi level position (these processes can be considered as p-doping [2, 3] and n-doping [4, 5], respectively), leads to the energy gap opening (≈0.2 eV for nitrogen [4]), and changes the carrier mobility in graphene [6, 7]. Graphene doped with individual metal atoms has recently been studied for use as a single atom catalyst (SAC), in particular, in the hydrogen evolution reaction (HER) [8, 9] and oxygen reduction reactions (ORR) [9, 10]. Moreover, for single-atom catalysis, not only free graphene is interesting, but also graphene on a substrate (i.e. Ni (111) [10]), since the presence of a substrate allows one to change the activation barrier of reactions. The graphene/Ni(111) system attracts a lot of interest (see review [11]) due to the small (1.2%) lattices mismatch that potentially makes possible the fabrication of the large area graphene crystals of high quality. Many researchers [12–19] observed characteristic objects in scanning tunneling microscopy (STM) images of graphene synthesized on Ni(111), which looked much brighter than graphene structural defects. † Deceased.
The observation of such features (both individual objects and chains) was reported for graphene synthesized on Ni (111) by chemical vapor deposition (CVD) from toluene [12] or ethylene [13], although, their structure was not considered. Similar objects were observed in
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