Realizing controllable graphene nucleation by regulating the competition of hydrogen and oxygen during chemical vapor deposition heating

Abstract

Oxygen can passivate Cu surface active sites when graphene nucleates. Thus, the nucleation density is decreased. The CuO/Cu substrate was chosen for graphene domain synthesis in our study. The results indicate that the CuO/Cu substrate is beneficial for large-scale, single-crystal graphene domain synthesis. Graphene grown on the CuO/Cu substrate exhibits fewer nucleation sites than on Cu foils, suggesting that graphene follows an oxygen-dominating growth. Hydrogen treatment via a heating process could weaken the surface oxygen's role in limiting graphene nucleation under the competition of hydrogen and oxygen and could transfer the synthesis of graphene into a hydrogen-dominating growth. However, the competition only exists during the chemical vapor deposition heating process. For non-hydrogen heated samples, oxygen-dominating growth is experienced even though the samples are annealed in hydrogen for a long time after the heating process. With the temperature increases, the role of hydrogen gradually decreases. The balance of hydrogen and oxygen is adjusted by introducing hydrogen gas at a different heating temperatures. The oxygen concentration on the substrate surface is believed to determine the reactions mechanisms based on the secondary ion mass spectrometry test results. This study provides a new method for the controllable synthesis of graphene nucleation during a heating process.

Understanding the Reaction Kinetics to Optimize Graphene Growth on Cu by Chemical Vapor Deposition

“…It was shown that the flake nucleation suppression during CVD growth is observed if the Cu oxide still exists on the Cu foil during sample annealing until the temperature is reached where oxygen diffusion into the Cu bulk sets in. In this case the dissolved oxygen inside the Cu foil can act as an oxygen reservoir until the CVD process is started . It was also shown recently that stabilizing the Cu 2 O layer on the Cu foil up to the even higher temperature of 1050°C in oxygen followed by the sudden reduction in a hydrogen atmosphere leads to an irreversible conversion of the polycrystalline Cu towards a Cu(111) crystallized foil …”

“…the treatment also leads to a passivated surface during the initial stage of the CVD process, since Cu‐oxide is catalytically less active than the metallic Cu surface, although it has later been shown that graphene can be also grown on oxidized Cu in a pure CH 4 stream . Meanwhile, further studies proved that graphene flake nucleation during CVD can be effectively suppressed, when using Cu foils that have been oxidized before insertion into the reactor . It was shown that the flake nucleation suppression during CVD growth is observed if the Cu oxide still exists on the Cu foil during sample annealing until the temperature is reached where oxygen diffusion into the Cu bulk sets in.…”

Large-Area Synthesis and Growth Mechanism of Graphene by Chemical Vapor Deposition

“…And excess hydrogen could etch graphene to destroy the integrity of the lattice and make the quality of graphene worse [64]. It also affects the adsorption, stability, thickness [65][66][67], population of active species on the catalyst surface [68,69] and the morphology [70][71][72][73][74][75][76][77][78][79] of the grown graphene. Luo et al [72] determined the effect of hydrogen on the shape and orientation of graphene using DFT calculation (shown in Figure 7).…”

A critical review on the contributions of chemical and physical factors toward the nucleation and growth of large-area graphene

“…Suzuki et al [74] detailed a threefold atmospheric pressure CVD process that removes traces of Si impurities originating from the furnace and promotes the formation of wider terraces on Cu foils without having to change the CVD growth parameters. Zhang et al developed a method for controlling the nucleation process on a CuO substrate by regulating the hydrogen flow in the furnace [75]. It has also been reported that oxygen can form oxide nucleation sites for graphene growth under high hydrogen partial pressures to produce single-layer graphene [76,77].…”