1 research outputs found
Highly Sensitive Detection of Surface and Intercalated Impurities in Graphene by LEIS
Low-energy ion scattering (LEIS)
is known for its extreme surface
sensitivity, as it yields a quantitative analysis of the outermost
surface as well as highly resolved in-depth information for ultrathin
surface layers. Hence, it could have been generally considered to
be a suitable technique for the analysis of graphene samples. However,
due to the low scattering cross section for light elements such as
carbon, LEIS has not become a common technique for the characterization
of graphene. In the present study we use a high-sensitivity LEIS instrument
with parallel energy analysis for the characterization of CVD graphene
transferred to thermal silica/silicon substrates. Thanks to its high
sensitivity and the exceptional depth resolution typical of LEIS,
the graphene layer closure was verified, and different kinds of contaminants
were detected, quantified, and localized within the graphene structure.
Utilizing the extraordinarily strong neutralization of helium by carbon
atoms in graphene, LEIS experiments performed at several primary ion
energies permit us to distinguish carbon in graphene from that in
nongraphitic forms (e.g., the remains of a resist). Furthermore, metal
impurities such as Fe, Sn, and Na located at the graphene–silica
interface (intercalated) are detected, and the coverages of Fe and
Sn are determined. Hence, high-resolution LEIS is capable of both
checking the purity of graphene surfaces and detecting impurities
incorporated into graphene layers or their interfaces. Thus, it is
a suitable method for monitoring the quality of the whole fabrication
process of graphene, including its transfer on various substrates