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In this report, we demonstrate a method for the enhancement of Raman active modes of hydrogen-intercalated quasi-free-standing epitaxial chemical vapor deposition graphene and the underlying semi-insulating 6H–SiC(0001) substrate through constructive signal interference within atomic-layer-deposited amorphous Al2O3 passivation. We find that an optimum Al2O3 thickness of 85 nm for the graphene 2D mode and one of 82 nm for the SiC longitudinal optical A1 mode at 964 cm–1 enable a 60% increase in their spectra intensities. We demonstrate the method's efficiency in Raman-based determination of the dielectric thickness and high-resolution topographic imaging of a graphene surface. [ABSTRACT FROM AUTHOR]

In this report, we present transfer-free p-type hydrogen-intercalated quasi-free-standing epitaxial Chemical Vapor Deposition graphene on 15-mm × 15-mm semi-insulating vanadium-compensated on-axis 6H SiC(0001), characterized in that its room-temperature direct-current Hall-effect-derived hole mobility μ p = 5019 cm2/Vs, and its statistical number of layers (N), as indicated by the relative intensity of the SiC-related Raman-active longitudinal optical A 1 mode at 964 cm−1, equals N = 1.05. The distribution of the ellipsometric angle Ψ measured at an angle of incidence of 50 ° and λ = 490 nm points out to N = 0.97. The close-to-unity value of N implies that the material under study is a close-to-perfect quasi-free-standing monolayer, which is further confirmed by High-Resolution Transmission Electron Microscopy. Therefore, its spectroscopic properties, which include the Si H peak at 2131 cm−1, the histograms of Ψ and Δ , and the Raman G and 2D band positions, widths, and the 2D-to-G band intensity ratios, constitute a valuable reference for this class of materials. • Quasi-free-standing single-layer graphene in an industrial technology • Direct observation of the hydrogen-related Si-H peak at 2131 cm-1 • Parameters for effective ellipsometric characterization of QFS graphene on SiC • Referential database of graphene spectroscopic properties • Novel approach to graphene certification [Display omitted] [ABSTRACT FROM AUTHOR]

In this report, we demonstrate an applied protocol for layer-resolved Raman imaging and analysis of undesirable ad-layers found in Chemical Vapor Deposition graphene grown on copper foil and transferred onto an oxidized silicon substrate. The method assumes that the intensity of the silicon-related Raman-active mode at 520 cm-1 is attenuated by 2.3 % each time the light passes through a single graphene layer. Upon normalization with respect to a reference graphene-free area, the 520 cm-1 mode relative intensity r-I Si measured in a back-scatter mode follows a univalent function of the number of the graphene layers N. Since N is treated as a continuous argument, it can be ascribed a fractional value and considered statistically. Importantly, the r-I Si offers higher layer differentiation capability and unambiguity than non-functional indicators, including the 2D band width or the 2D-to-G band intensity ratio, thus providing unequivocal evaluation. [Display omitted] • Method for high-resolution Raman imaging of CVD graphene. • Truly functional and univalent protocol for layer-resolved analysis. • Applicable to multilayer graphene. • Useful extension for the Graphene Flagship technical standard. [ABSTRACT FROM AUTHOR]

Kelvin Probe Force Microscopy is a method to assess the contact potential difference between a sample and the probe tip. It remains a relative tool unless a reference standard with a known work function is applied, typically bulk gold or cleaved highly oriented pyrolytic graphite. In this report, we suggest a verifiable, two-dimensional standard in the form of a photolithographically patterned, wire-bonded structure manufactured in the technology of transfer-free p-type hydrogen-intercalated quasi-free-standing epitaxial Chemical Vapor Deposition graphene on semi-insulating high-purity nominally on-axis 4H-SiC(0001). The particular structure has its hole density p S = 1.61 × 1013 cm−2 measured through a classical Hall effect, its number of the graphene layers N = 1.74 extracted from the distribution of the ellipsometric angle Ψ , measured at the angle of incidence AOI = 50 ° and the wavelength λ = 490 nm, and its work function ϕ G R = 4.79 eV postulated by a Density Functional Theory model for the specific p S and N. Following the algorithm, the contact potential difference between the structure and a silicon tip, verified at Δ V G R − Si = 0. 64 V , ought to be associated with ϕ G R = 4.79 eV and applied as a precise reference value to calculate the work function of an arbitrary material. [Display omitted] • QFS graphene on SiC as a KPFM reference standard. • Electrically verifiable and updatable. • A likely complement to HOPG and bulk gold. [ABSTRACT FROM AUTHOR]