Date Published: March 12, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Yifan Liu, Tianru Wu, Yuling Yin, Xuefu Zhang, Qingkai Yu, Debra J. Searles, Feng Ding, Qinghong Yuan, Xiaoming Xie.
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.
Experimental Details—Preparation of CuNi Binary Substrate: A 6 cm × 6 cm Cu foil (25 µm, 99.8%, Alfa‐Aesar) was first electrochemically polished with a current density of ≈0.3 A cm−2 for 90 s, then annealed at 1050 °C in a mixture of Ar/H2 (400/100 sccm) for 2 h followed by electroplated with a current density of ≈0.01 A cm−2. A Ni film with a certain thickness was deposited on the Cu foil at a rate of 200 nm min−1. The polishing solution was a mixture of 500 mL of water, 250 mL of ethanol, 250 mL of orthophosphoric acid, 50 mL of isopropyl alcohol, and 5 g of urea. The electrolytic solution consisted of 1 L of water, 280 g of NiSO4⋅6H2O, 8 g of NiCl2⋅6H2O, 4 g of NaF, and 30 g of H3BO3.
The authors declare no conflict of interest.