Selective Graphene Formation on Copper Twin Crystals

Abstract

Selective graphene growth on copper twin crystals by chemical vapor deposition has been achieved. Graphene ribbons can be formed only on narrow twin crystal regions with a (001) or high-index surface sandwiched between Cu crystals having (111) surfaces by tuning the growth conditions, especially by controlling the partial pressure of CH(4) in Ar/H(2) carrier gas. At a relatively low CH(4) pressure, graphene nucleation at steps on Cu (111) surfaces is suppressed, and graphene is preferentially nucleated and formed on twin crystal regions. Graphene ribbons as narrow as ~100 nm have been obtained in experiments. The preferential graphene nucleation and formation seem to be caused primarily by a difference in surface-dependent adsorption energies of reactants, which has been estimated by first principles calculations. Concentrations of reactants on a Cu surface have also been analyzed by solving a diffusion equation that qualitatively explains our experimental observations of the preferential graphene nucleation. Our findings may lead to self-organizing formation of graphene nanoribbons without reliance on top-down approaches in the future.

Graphene Nucleation Density on Copper: Fundamental Role of Background Pressure

“…Differences in the nucleation densities on various crystallographic orientations of copper have been reported previously [17,37,38] and they reflect an intricate interplay of various processes. Growth rates under LPCVD conditions were reported to have contradictory outcome.…”

“…[17,23] Reported calculations of the carbon atoms adsorption energies on a copper surface vary within 4.1 to 7.5 eV range, [17,[26][27][28][29][30] while the intermediate methane dehydrogenation products CH x have significantly smaller adsorption energies, decreasing roughly by ~1 eV per an additional hydrogen atom. [29] Except for a few reports, almost no attention has been given to the fact that copper itself has quite high evaporation rates in vacuum approaching 4 m/hour at 1000 C.…”

“…[17] Theoretical calculations suggest that complete methane dehydrogenation on (111) copper surface has ~ 1 eV higher energy barrier as compared to the (100) orientation. [26] The adsorption energies of both, copper adatoms [32] and carbon monomers, [17] are lower on (111) and consequently should have lower activation energies for surface diffusion. All these effects contribute to the variations of the nucleation densities on different surface orientations at lower growth temperatures [17] and require further elucidation.…”

“…[26] The adsorption energies of both, copper adatoms [32] and carbon monomers, [17] are lower on (111) and consequently should have lower activation energies for surface diffusion. All these effects contribute to the variations of the nucleation densities on different surface orientations at lower growth temperatures [17] and require further elucidation. At temperatures greater than 1000 C these differences seem to be minimal for both APCVD and LPCVD.…”

Structure of graphene and its disorders: a review

“…The approaches for synthesis of GNRs include epitaxial growth on templated silicon carbide (SiC) substrates [96], CVD growth on structured substrates (e.g. steps [97], twins [98], and trenches [99]), and directly partial growth on germanium(001) [100]. The lattice of GNR shows both zigzag and armchair edge orientations which can be observed by using AFM [101] and STM [79,100].…”