How Low Nucleation Density of Graphene on CuNi Alloy is Achieved

Abstract

CuNi alloy foils are demonstrated to be one of the best substrates for synthesizing large area single‐crystalline graphene because a very fast growth rate and low nucleation density can be simultaneously achieved. The fast growth rate is understood to be due the abundance of carbon precursor supply, as a result of the high catalytic activity of Ni atoms. However, a theoretical understanding of the low nucleation density remains controversial because it is known that a high carbon precursor concentration on the surface normally leads to a high nucleation density. Here, the graphene nucleation on the CuNi alloy surfaces is systematically explored and it is revealed that: i) carbon atom dissolution into the CuNi alloy passivates the alloy surface, thereby drastically increasing the graphene nucleation barrier; ii) carbon atom diffusion on the CuNi alloy surface is greatly suppressed by the inhomogeneous atomic structure of the surface; and iii) a prominent increase in the rate of carbon diffusion into the bulk occurs when the Ni composition is higher than the percolation threshold. This study reveals the key mechanism for graphene nucleation on CuNi alloy surfaces and provides a guideline for the catalyst design for the synthesis of graphene and other 2D materials.

Vapor‐phase growth of high‐quality wafer‐scale two‐dimensional materials

“…CuNi alloy is demonstrated to be one of the best substrates for the growth of graphene because the very fast growth rate and low nucleation density can be simultaneously achieved. 10,15,48,77 As is shown in Figure 3D,E, from the growth of 1.5-in. single-crystal graphene from a single nucleus, we can observe that the nucleation density decreases monotonically when the Ni composition in the CuNi alloy increases from 0% to 30%.…”

“…CuNi alloy is demonstrated to be one of the best substrates for the growth of graphene because the very fast growth rate and low nucleation density can be simultaneously achieved . As is shown in Figure D,E, from the growth of 1.5‐in.…”

“…D‐F. Reproduced with permission . Copyright 2018, WILEY‐VCH Verlag GmbH & Co. LEED, low‐energy electron diffraction…”

“…On the one hand, carbon atoms dissolved into the CuNi alloy passivate the alloy surface, thereby leading to a drastically increased nucleation barrier. On the other hand, the Ni in the alloy increases surface diffusion barrier to suppress the diffusion of carbon atom on the surface and changes the diffusion behavior of carbon atoms from surface diffusion to bulk diffusion when the Ni composition is higher than the percolation threshold (19.9%) (Figure F) …”

“…On the other hand, the Ni in the alloy increases surface diffusion barrier to suppress the diffusion of carbon atom on the surface and changes the diffusion behavior of carbon atoms from surface diffusion to bulk diffusion when the Ni composition is higher than the percolation threshold (19.9%) ( Figure 3F). 77 Oxygen (O 2 ) or melamine pretreatment can play a role in passivating of the active sites. 30,33 According to recent reports, a small amount of oxygen has been demonstrated to suppress the nucleation of graphene and TMDs in CVD by rendering potential nucleation sites less active or by increasing the size of the critical nucleus.…”