Quality of graphene on sapphire: long-range order from helium diffraction versus lattice defects from Raman spectroscopy
Quality of graphene on sapphire: long-range order from helium diffraction versus lattice defects from Raman spectroscopy
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DOI：
10.1039/c5ra27452d
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发表时间：
2016-01-01
期刊：
影响因子：
3.9
通讯作者：
Farias, Daniel
中科院分区：
文献类型：
--
作者：
Anemone, Gloria;Climent-Pascual, Esteban;Farias, Daniel
我们报告了一种新的方法来生产高品质，透明的石墨烯/蓝宝石样品，使用铜作为催化剂。起点是通过CVD在Cu（111）/Al 2 O3上制备的高质量石墨烯层。蓝宝石上的石墨烯是通过在超高真空中蒸发Cu膜原位获得的。氦衍射，原子力显微镜（AFM），拉曼光谱和光学传输已被用来评估在无金属区的石墨烯的质量。我们使用氦原子散射作为蓝宝石上石墨烯结晶度的灵敏探针。高反射率和清晰衍射峰的观察表明在微米的横向尺度上存在平坦且均匀的石墨烯域，与AFM结果一致。令人惊讶的是，将石墨烯放在蓝宝石上提高了He衍射光谱的质量。石墨烯形成具有（11 X 11）周期性的莫尔图案，与（1 X 1）蓝宝石单元格对齐。蓝宝石上石墨烯的晶格常数为a =（2.44 +/-0.02）埃。测量了石墨烯弯曲模的声子色散。这允许确定弯曲刚度k = 0.61 +/-0.15eV，以及石墨烯-蓝宝石耦合强度g =（5.8 +/-0.4）X 10（19）Nm（-3）。通过拉曼光谱研究了石墨烯的均匀性。通过2D峰与G峰的比率判断，石墨烯的质量不会因Cu去除而劣化。在可见光范围内测量的高透明度（80%）使该系统适用于许多需要通常与金属（导电性）和绝缘体（透明度）相关的混合特性的应用。我们的研究表明，氦衍射和拉曼提供了至关重要的信息，完全不同的，互补的方面相同的样品。
We report a new method to produce high-quality, transparent graphene/sapphire samples, using Cu as a catalyst. The starting point is a high-quality graphene layer prepared by CVD on Cu(111)/Al2O3. Graphene on sapphire is obtained in situ by evaporation of the Cu film in UHV. He-diffraction, atomic force microscopy (AFM), Raman spectroscopy and optical transmission have been used to assess the quality of graphene in a metal free area. We used helium atom scattering as a sensitive probe of the crystallinity of the graphene on sapphire. The observation of high reflectivity and clear diffraction peaks demonstrates the presence of flat and homogeneous graphene domains over lateral scales of microns, consistent with the AFM results. Surprisingly, putting graphene on sapphire improves the quality of the He-diffraction spectra. Graphene forms a moire pattern with a (11 x 11) periodicity, aligned with the (1 x 1) sapphire unit cell. The lattice constant of graphene on sapphire is a = (2.44 +/- 0.02) angstrom. The phonon dispersion of the graphene flexural mode has been measured. This allowed the determination of the bending rigidity k = 0.61 +/- 0.15 eV, and the graphene-sapphire coupling strength g = (5.8 +/- 0.4) x 10(19) N m(-3). The uniformity of the graphene has also been investigated by Raman mapping. Judging by the ratio of the 2D to G peaks, the quality of the graphene is not degraded by Cu removal. The high transparency (80%) measured in the visible range makes this system suitable for many applications that require hybrid properties commonly associated with metals (conductivity) and insulators (transparency). Our study shows that He-diffraction and Raman provide crucial information on quite different, complementary aspects of the same samples.