Graphene Nucleation Density on Copper: Fundamental Role of Background Pressure

Abstract

In this paper we discuss the effect of background pressure and synthesis temperature on the graphene crystal sizes in chemical vapor deposition (CVD) on copper catalyst. For the first time, we quantitatively demonstrate a fundamental role of the background pressure and provide the activation energy for graphene nucleation in atmospheric pressure CVD (9 eV), which is substantially higher than for low pressure CVD (4 eV). We attribute the difference to a greater importance of copper sublimation in low pressure CVD, where severe copper evaporation likely dictates the desorption rate of active carbon from the surface. At atmospheric pressure, where copper evaporation is suppressed, the activation energy is assigned to the desorption energy of carbon clusters instead. The highest possible temperature, close to the melting point of copper, should be used for large single crystal graphene synthesis. Using these conditions, we have synthesized graphene single crystals approaching 1 mm in size. Single crystal nature of synthesized graphene was confirmed by low energy electron diffraction. We also demonstrate that CVD of graphene at temperatures below 1000 oC shows higher nucleation density on (111) than on (100) and (101) copper surfaces but there is no identifiable preference at higher temperatures.

Oxygen-activated growth and bandgap tunability of large single-crystal bilayer graphene

“…The above results also observed that reducing the C flux can reduce the BLG nucleation density, similar to the case of SLG growth on Cu 20,22,23 . Indeed, by decreasing P CH4 (Figs.…”

A dilute Cu(Ni) alloy for synthesis of large-area Bernal stacked bilayer graphene using atmospheric pressure chemical vapour deposition

“…For instance, the effect of H 2 in CVD graphene growth was viewed as a co-catalyst in the formation of active surface bound carbon species required for graphene growth 32,35,36 and etches away the weak carbon-carbon bonds (graphene edges) for the growth of bilayer or multilayer graphene. 33,37 The effects of H 2 are expected to be the same for graphene films obtained on both Cu and Cu(0.46 at. % Ni) foils, since the two are synthesized simultaneously.…”

“…In fact, at higher pressures, the sublimation of Cu is suppressed. 33 Furthermore, under optimised AP-CVD graphene growth conditions, a bilayer graphene obtained on Cu foil showed larger-areas of incomplete bilayer graphene (i.e., small-areas of bilayer on a monolayer graphene background) as compared to large-area (or wafer-scale) bilayer graphene obtained on Cu(0.46 at. % Ni) foil and that could be due to graphene growth rate which is expected to be higher on Cu(0.46 at.…”

“…Though CVD graphene growth on Cu surface is a catalytic process which has simplicity view, the CVD growth mechanism is complicated and depends on growth background pressure. Generally, on the Cu surface where the decomposition of hydrocarbons and the surface diffusion induced graphene growth materialise, several processes are involved which includes: 4,33,38,39 Etching of the as-grown graphene, etc.…”

Radiation-mode optical microscopy on the growth of graphene

“…To date, the real-time observations of the growth of graphene have been performed in ultra-high vacuum or low-pressure (o20 Pa) conditions on various metal substrates by scanning tunnelling microscopy, scanning transmission electron microscopy, low-energy electron microscopy, in situ Raman spectroscopy, environmental scanning electron microscopy (SEM) and so on [13][14][15][16][17][18][19][20][21][22] . From the viewpoint of scalable production of graphene, however, the combination of CH 4 gas and Cu substrate is considered the most promising, which requires the source gases with relatively high pressure from several Pa to atmospheric pressure [23][24][25][26][27][28][29] . The above-mentioned techniques could not be used for the growth of graphene on Cu under the atmosphere of source gases.…”