The isolation of graphene supported on Si wafers (XG), 1 the synthesis of epitaxial graphene (EG), 2 and the fabrication of graphene nanoribbons 3,4 has now placed the graphene twodimensional π-electron system on the semiconductor industry roadmap for emerging logic devices. In principle, the availability of large-area graphene wafers offers the opportunity to fabricate the full complement of Si CMOS electronic devices and circuitry from carbon and additionally provides a route to new state variables for the semiconductor industry. Such an approach would require the atom-by-atom chemical functionalization of the whole graphene wafer and would therefore involve the practice of organic chemistry with a precision that is usually achieved only within natural systems. 5 Chemically modified graphene is expected to be broadly useful, and applications in catalysis and energy are already the subject of article highlights. 6,7 In the present Perspective, we discuss the use of Raman microscopy and spectroscopy, scanning tunneling microscopic channel semiconductors (band gap ≈ 1.1 eV). There are many important engineering characteristics for these latter two materials, which include the mobility (μ), which is typically μ = 43 cm 2 /V sec (copper) and μ(electron) = 280 cm 2 /V sec (doped silicon), and the carrier concentration (n), where n = 8.5 Â 10 22 cm À3 (copper) and n ≈ 10 20 cm À3 (dopant concentration) in transistors used today. 8

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Two-dimensional materials, such as graphene and MoS2, are films of a few atomic layers in thickness with strong in-plane bonds and weak interactions between the layers. The in-plane elasticity has been widely studied in bending experiments where a suspended film is deformed substantially; however, little is known about the films' elastic modulus perpendicular to the planes, as the measurement of the out-of-plane elasticity of supported 2D films requires indentation depths smaller than the films' interlayer distance. Here, we report on sub-ångström-resolution indentation measurements of the perpendicular-to-the-plane elasticity of 2D materials. Our indentation data, combined with semi-analytical models and density functional theory, are then used to study the perpendicular elasticity of few-layer-thick graphene and graphene oxide films. We find that the perpendicular Young's modulus of graphene oxide films reaches a maximum when one complete water layer is intercalated between the graphitic planes. This non-destructive methodology can map interlayer coupling and intercalation in 2D films.