Direct Experimental Evidence of Metal-Mediated Etching of Suspended Graphene
Direct Experimental Evidence of Metal-Mediated Etching of Suspended Graphene
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DOI：
10.1021/nn300452y
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发表时间：
2012-05-01
期刊：
影响因子：
17.1
通讯作者：
Novoselov, Konstantin S.
中科院分区：
文献类型：
--
作者：
Ramasse, Quentin M.;Zan, Recep;Novoselov, Konstantin S.
在像差校正的扫描电子显微镜中，对沉积有铬、钛、钯、镍、铝和金原子的悬浮单层石墨烯进行了原子分辨率高角度环形暗场成像。结合用于识别单个杂质原子的电子能量损失谱，结果表明，在石墨烯中刻蚀了纳米级的孔洞，这些孔洞起始于除金以外的所有金属物种的单个原子与石墨烯发生剂量接触的位置。电子束扫描过程有助于将原始金属沉积过程中形成的团簇中的金属原子推进到Dine石墨烯表面，在那里它们启动空穴形成过程。我们的观察结果根据文献中的计算进行了讨论，预测当金属原子存在时，石墨烯中空位的形成要低得多。我们还讨论了氧原子在这一过程中的需求和重要性，尽管以前的计算没有预测到这一点，但在我们观察到原始石墨烯中存在硅杂质原子时形成空穴的情况下，我们也讨论了这一点，并得到了新的计算的支持，这些计算预测了当存在SiOx分子时，空位形成能会急剧下降。
Atomic resolution high angle annular dark field imaging of suspended, single-layer graphene, onto which the metals Cr, Ti, Pd, Ni, Al, and Au atoms had been deposited, was carried out in an aberration-corrected scanning transmission electron microscope. In combination with electron energy loss spectroscopy, employed to identify individual impurity atoms, it was shown that nanoscale holes were etched into graphene, initiated at sites where single atoms of all the metal species except for gold come into dose contact with the graphene. The e-beam scanning process is instrumental in promoting metal atoms from clusters formed during the original metal deposition process onto the dean graphene surface, where they initiate the hole-forming process. Our observations are discussed in the light of calculations in the literature, predicting a much lowered vacancy formation in graphene when metal ad-atoms are present. The requirement and Importance of oxygen atoms in this process, although not predicted by such previous calculations, is also discussed, following our observations of hole formation in pristine graphene in the presence of Si-Impurity atoms, supported by new calculations which predict a dramatic decrease of the vacancy formation energy, when SiOx molecules are present.