Highly Uniform Bilayer Graphene on Epitaxial Cu-Ni(111) Alloy
Highly Uniform Bilayer Graphene on Epitaxial Cu-Ni(111) Alloy
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DOI：
10.1021/acs.chemmater.6b01137
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发表时间：
2016-07-12
影响因子：
8.6
通讯作者：
Ago, Hiroki
中科院分区：
文献类型：
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作者：
Takesaki, Yuichiro;Kawahara, Kenji;Ago, Hiroki
垂直电场作用下双层石墨烯（BLG）的带隙打开是实现高性能石墨烯基半导体器件的重要条件，因此需要合成均匀且大面积的双层石墨烯。在这里，我们展示了化学气相沉积（CVD）在外延Cu-Ni（111）二元合金催化剂上合成高度均匀的BLG薄膜。Ni和Cu的相对浓度以及生长温度和冷却方式对BLG的均匀性有很大影响。特别是，关闭碳原料后的缓慢冷却过程对于获得均匀的第二层（覆盖总面积的90%以上）非常重要。此外，低能电子显微镜（LEEM）研究显示，第二层生长在第一层的下面。我们还通过拉曼光谱和LEEM研究了双层石墨烯的堆叠顺序，发现70-80%的双层石墨烯具有Bernal堆叠。在上层和下层也观察到亚稳的30度旋转取向。根据我们的实验观察，提出了一种新的生长模式；第一层在CH4供给Cu-Ni合金表面时生长，第二层在冷却过程中与本体合金分离。我们的工作突出了BLG的生长机制，为未来电子器件合成均匀、大面积的BLG提供了一条有希望的途径。
Band gap opening in bilayer graphene (BLG) under a vertical electric field is important for the realization of high performance graphene-based semiconductor devices, and thus, the synthesis of uniform and large-area BLG is required. Here we demonstrate the synthesis of a highly uniform BLG film by chemical vapor deposition (CVD) over epitaxial Cu-Ni (111) binary alloy catalysts. The relative concentration of Ni and Cu as well as the growth temperature and cooling profile was found to strongly influence the uniformity of the BLG. In particular, a slow cooling process after switching off the carbon feedstock is important for obtaining a uniform second layer, covering more than 90% of the total area. Moreover, low-energy electron microscopy (LEEM) study revealed the second layer grows underneath the first layer. We also investigated the stacking order by Raman spectroscopy and LEEM and found that 70-80% of bilayer graphene has Bernal stacking. The metastable 30 degrees-rotated orientations were also observed both in the upper and lower layers. From our experimental observations, a new growth mode is proposed; the first layer grows during the CH4 supply on Cu-Ni alloy surface, while the second layer is segregated from the bulk alloy during the cooling process. Our work highlights the growth mechanism of BLG and offers a promising route to synthesize uniform and large-area BLG for future electronic devices.