We developed a high-yield synthesis of highly crystalline bilayer graphene (BLG) with two preferential stacking modes using a Ni–Cu gradient alloy growth substrate. Previously reported approaches for BLG growth include flat growth substrates of Cu or Ni–Cu uniform alloys and “copper pocket” structures. Use of flat substrates has the advantage of being scalable, but the growth mechanism is either “surface limited” (for Cu) or carbon precipitation (for uniform Ni–Cu), which results in multicrystalline BLG grains. For copper pockets, growth proceeds through a carbon back-diffusion mechanism, which leads to the formation of highly crystalline BLG, but scaling of the copper pocket structure is expected to be difficult. Here we demonstrate a Ni–Cu gradient alloy that combines the advantages of these earlier methods: the substrate is flat, so easy to scale, while growth proceeds by a carbon back-diffusion mechanism leading to high-yield growth of BLG with high crystallinity. The BLG layer stacking was almost exclusively Bernal or twisted with an angle of 30°, consistent with first-principles calculations we conducted. Furthermore, we demonstrated scalable production of transistor arrays based crystalline Bernal-stacked BLG with a band gap that was tunable at room temperature.

中文翻译：

---

Ni-Cu梯度合金优先堆叠的结晶双层石墨烯

我们使用Ni-Cu梯度合金生长衬底开发了具有两种优先堆叠模式的高结晶性双层石墨烯（BLG）的高产率合成。先前报道的BLG生长方法包括平坦生长的Cu或Ni–Cu均匀衬底合金和“铜袋”结构。使用平坦的基板具有可扩展的优势，但是生长机理是“表面受限”（对于Cu）或碳沉淀（对于均匀的Ni-Cu），这导致了多晶BLG晶粒。对于铜袋，通过碳反向扩散机制进行生长，这导致形成高度结晶的BLG，但预计铜袋结构的结垢将很困难。在这里，我们展示了一种结合了这些早期方法优点的Ni-Cu梯度合金：基底平坦，易于结垢，同时通过碳反向扩散机制进行生长，从而导致高结晶度的BLG的高产率生长。BLG层堆叠几乎完全是Bernal或以30°的角度扭曲，与我们进行的第一性原理计算一致。此外，我们展示了基于晶体的伯纳尔堆叠BLG晶体管阵列的可规模化生产，其带隙在室温下可调节。