Department of Physics, Pohang University of Science and Technology, Pohang 37673, Korea.
Nanotechnology. 2017 May 19;28(20):205201. doi: 10.1088/1361-6528/aa6951. Epub 2017 Mar 27.
We report europium (Eu)-induced changes in the π-band of graphene (G) formed on the 6H-SiC(0001) surface by a combined study of photoemission measurements and density functional theory (DFT) calculations. Our photoemission data reveal that Eu intercalates upon annealing at 120 °C into the region between the graphene and the buffer layer (BL) to form a G/Eu/BL system, where a band gap of 0.29 eV opens at room temperature. This band gap is found to increase further to 0.48 eV upon cooling down to 60 K. Our DFT calculations suggest that the increased band gap originates from the enhanced hybridization of the graphene π-band with the Eu 4f band due to the increased magnetic ordering upon cooling. These Eu atoms continue to intercalate further down below the BL to produce bilayer graphene (G/BL/Eu) upon annealing at 300 °C. The π-band stemming from the BL then exhibits another band gap of 0.37 eV, which appears to be due to the strong hybridization between the π-band of the BL and the Eu 4f band. The Eu-intercalated graphene thus illustrates an example of versatile band gaps formed under different thermal treatments, which may play a critical role for future applications in graphene-based electronics.
我们通过光电子能谱测量和密度泛函理论（DFT）计算的联合研究，报告了在 6H-SiC(0001) 表面上形成的石墨烯（G）的π带在 Eu 诱导下的变化。我们的光电子能谱数据表明，Eu 在 120°C 退火时会嵌入到石墨烯和缓冲层（BL）之间的区域，形成 G/Eu/BL 体系，在室温下会打开 0.29 eV 的带隙。我们的 DFT 计算表明，冷却到 60 K 时，带隙进一步增加到 0.48 eV。我们的 DFT 计算表明，增加的带隙源于石墨烯 π 带与 Eu 4f 带的杂化增强，这是由于冷却导致的磁有序增强。这些 Eu 原子继续向下进一步嵌入 BL 中，在 300°C 退火时产生双层石墨烯（G/BL/Eu）。然后，来自 BL 的 π 带表现出另一个 0.37 eV 的带隙，这似乎是由于 BL 的 π 带和 Eu 4f 带之间的强烈杂化所致。因此，Eu 嵌入的石墨烯说明了在不同热处理下形成的多种带隙的一个例子，这可能对基于石墨烯的电子学的未来应用起着至关重要的作用。
