Highly Sensitive Detection of Surface and IntercalatedImpurities in Graphene by LEIS.

Low-energy ion scattering (LEIS)is known for its extreme surfacesensitivity, as it yields a quantitative analysis of the outermostsurface as well as highly resolved in-depth information for ultrathinsurface layers. Hence, it could have been generally considered tobe a suitable technique for the analysis of graphene samples. However,due to the low scattering cross section for light elements such ascarbon, LEIS has not become a common technique for the characterizationof graphene. In the present study we use a high-sensitivity LEIS instrumentwith parallel energy analysis for the characterization of CVD graphenetransferred to thermal silica/silicon substrates. Thanks to its highsensitivity and the exceptional depth resolution typical of LEIS,the graphene layer closure was verified, and different kinds of contaminantswere detected, quantified, and localized within the graphene structure.Utilizing the extraordinarily strong neutralization of helium by carbonatoms in graphene, LEIS experiments performed at several primary ionenergies permit us to distinguish carbon in graphene from that innongraphitic forms (e.g., the remains of a resist). Furthermore, metalimpurities such as Fe, Sn, and Na located at the graphene–silicainterface (intercalated) are detected, and the coverages of Fe andSn are determined. Hence, high-resolution LEIS is capable of bothchecking the purity of graphene surfaces and detecting impuritiesincorporated into graphene layers or their interfaces. Thus, it isa suitable method for monitoring the quality of the whole fabricationprocess of graphene, including its transfer on various substrates. [ABSTRACT FROM AUTHOR]