Symmetry forbidden morphologies and domain boundaries in nanoscale graphene islands

Abstract

The synthesis of graphene nanoislands with tailored quantum properties requires an atomic control of the morphology and crystal structure. As one reduces their size down to the nanometer scale, domain boundary and edge energetics, as well as nucleation and growth mechanisms impose different stability and kinetic landscape from that at the microscale. This offers the possibility to synthesize structures that are exclusive to the nanoscale, but also calls for fundamental growth studies in order to control them. By employing high-resolution scanning tunneling microscopy we elucidate the atomic stacking configurations, domain boundaries, and edge structure of graphene nanoislands grown on Ni(111) by CVD and post-annealed at different temperatures. We find a non-conventional multistep mechanism that separates the thermal regimes for growth, edge reconstruction, and final stacking configuration, leading to nanoisland morphologies that are incompatible with their stacking symmetry. Whole islands shift their stacking configuration during cooling down, and others present continuous transitions at the edges. A statistical analysis of the domain structures obtained at different annealing temperatures reveals how polycrystalline, ill-defined structures heal into shape-selected islands of a single predominant stacking. The high crystallinity and the control on morphology and edge structure makes these graphene nanoislands ideal for their application in optoelectronics and spintronics.

Ni-doped epitaxial graphene monolayer on the Ni(111) surface

“…Note that similar bright objects were also observed on graphene islands synthesized by temperature programmed growth (TPG) on the Ni(111) surface from ethylene and propylene 17,18 . In our previous study 19 , we considered TPG synthesis of graphene on Ni(111) and assigned the bright features in STM images with nickel defects, i.e.…”

“…In the present work, graphene was synthesized from propylene on the Ni(111) surface by both CVD and TPG methods. In both cases, identical objects similar to the defects described in [12][13][14][15][16][17][18][19] were found in STM images. We performed a DFT simulation of the transition from one structure (nickel in monovacancies) to another structure (nickel in bivacancies) and found that the main nickel defect in graphene is the nickel atom in the carbon bivacancy.…”

“…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][13][14][15][16][17][18][19] observed characteristic objects in scanning tunneling microscopy (STM) images of graphene synthesized on Ni(111), which looked much brighter than graphene structural defects.…”

Unveiling the competitive role of etching in graphene growth during chemical vapor deposition

“…Luo et al [10] carried out a series of graphene growth on Cu (1 1 1) surfaces at the fixed CH 4 flow rate (0.5 standard cubic centimetres per minute (sccm)) and different H 2 flow rates (15,20,25,30,35,40,45, and 50 sccm, respectively). As shown in figures 2(a)-(h), the graphene morphology transforms from a fragmentary, to a fractal, and further to a compact domain with increasing H 2 flow rate.…”

“…Great theoretical efforts have been devoted to disclosing various mechanisms during CVD of graphene [21,22], such as initial nucleations [23][24][25], carbon sources [26], growth intermediates [27,28], edge structures [29][30][31][32], growth kinetics [33][34][35], vacancy kinetics [36][37][38], and domain morphologies [39][40][41][42][43][44]. Compared to ab initio calculations, kinetic Monte Carlo (kMC) simulations are able to provide atomistic level insights into the kinetics of the growth process with much larger time scale and length scale [27,32,34,43,44].…”