A stoichiometric derivative of graphene with a fluorine atom attached to each carbon is reported. Raman, optical, structural, micromechanical, and transport studies show that the material is qualitatively different from the known graphene-based nonstoichiometric derivatives. Fluorographene is a high-quality insulator (resistivity >10(12) Ω) with an optical gap of 3 eV. It inherits the mechanical strength of graphene, exhibiting a Young's modulus of 100 N m(-1) and sustaining strains of 15%. Fluorographene is inert and stable up to 400 °C even in air, similar to Teflon.

We describe the identification of single-and few-layer boron nitride. Its optical contrast is much smaller than that of graphene but even monolayers are discernable by optimizing viewing conditions. Raman spectroscopy can be used to confirm BN monolayers. They exhibit an upshift in the fundamental Raman mode by up to 4 cm -1 . The number of layers in thicker crystals can be counted by exploiting an integer-step increase in the Raman intensity and optical contrast.Properties of few-nanometer-thick BN sheets (often referred to as few-layer BN) have been attracting steady interest over the last several years 1 . Although individual atomic planes of BN were also isolated 2 and investigated by transmission electron microscopy (TEM) 3-5 and atomic force microscopy (AFM) 6 , interest in BN monolayers has been rather limited, especially, if compared with the interest generated by its "sister" material, graphene 7 . This can be attributed to 1) the lack of hexagonal boron nitride (hBN) crystals suitable for the mechanical cleavage approach 7 and 2) difficulties in isolating and finding sufficiently large BN monolayers. The situation is now changing rapidly due to the availability of hBN single crystals, which allow the cleavage of relatively large (~100 μm) and relatively thin (several nm) BN samples with an atomically flat surface. 6,8,9 Such crystals have been used as a thin top dielectric to gate graphene 9 and as an inert substrate for graphene devices, which allowed a significant improvement of their electronic quality, 8 unlike the earlier attempts with highly-oriented pyrolytic boron nitride (HOPBN) 10 . Most recently, it has been demonstrated that BN films with 2 to 5 layer thickness can also be obtained by epitaxial growth on copper and subsequent transfer onto a chosen substrate. 11 Particularly motivating is the emerging possibility to use BN as an ultra-thin insulator separating graphene layers. The layers could then be isolated electrically but would remain coupled electronically via Coulomb interaction, similar to the case of narrow-spaced quantum well heterostructures. 12 Such atomically thin BN-graphene heterostructures may allow a variety of new interaction phenomena including, for example, exciton condensation 13 .In the case of graphene, its mono-, bi-and few-layers are often identified by their optical contrast 14 and Raman signatures 15 . Little is known about these characteristics for the case of BN and, in the previous AFM and TEM studies, 2,5,6 one had to rely on finding atomically thin BN regions either randomly or close to edges of thick BN flakes. In this Letter, we report optical and Raman properties of mono-and few-layer BN obtained by micromechanical cleavage of high-quality hBN. Because of its zero opacity (the band gap is larger than 5eV), 1 atomically-thin BN exhibits little optical contrast, even if the interference enhancement using oxidized Si wafers is employed. 14,16 For the standard oxide thickness of ~300 nm SiO 2 , 6,7 BN monolayers show white-light contrast of <1.5%, which makes ...

Graphene is one of the stiffest known materials, with a Young's modulus of 1 TPa, making it an ideal candidate for use as a reinforcement in high-performance composites. However, being a one-atom thick crystalline material, graphene poses several fundamental questions: (1) can decades of research on carbon-based composites be applied to such an ultimately-thin crystalline material? (2) is continuum mechanics used traditionally with composites still valid at the atomic level? (3) how does the matrix interact with the graphene crystals and what kind of theoretical description is appropriate? We have demonstrated unambiguously that stress transfer takes place from the polymer matrix to monolayer graphene, showing that the graphene acts as a reinforcing phase. We have also modeled the behavior using shear-lag theory, showing that graphene monolayer nanocomposites can be analyzed using continuum mechanics. Additionally, we have been able to monitor stress transfer efficiency and breakdown of the graphene/polymer interface

Central to most applications involving monolayer graphenes is its mechanical response under various stress states. To date most of the work reported is of theoretical nature and refers to tension and compression loading of model graphenes. Most of the experimental work is indeed limited to the bending of single flakes in air and the stretching of flakes up to typically approximately 1% using plastic substrates. Recently we have shown that by employing a cantilever beam we can subject single graphenes to various degrees of axial compression. Here we extend this work much further by measuring in detail both stress uptake and compression buckling strain in single flakes of different geometries. In all cases the mechanical response is monitored by simultaneous Raman measurements through the shift of either the G or 2D phonons of graphene. Despite the infinitely small thickness of the monolayers, the results show that graphenes embedded in plastic beams exhibit remarkable compression buckling strains. For large length (l)-to-width (w) ratios (> or =0.2) the buckling strain is of the order of -0.5% to -0.6%. However, for l/w < 0.2 no failure is observed for strains even higher than -1%. Calculations based on classical Euler analysis show that the buckling strain enhancement provided by the polymer lateral support is more than 6 orders of magnitude compared to that of suspended graphene in air.

We present a systematic experimental and theoretical study of the two-phonon (2D) Raman scattering in graphene under uniaxial tension. The external perturbation unveils that the 2D mode excited with 785 nm has a complex line-shape mainly due to the contribution of two distinct double resonance scattering processes (inner and outer) in the Raman signal. The splitting depends on the direction of the applied strain and the polarization of the incident light. The results give new insight into the nature of the 2D band and have significant implications for the use of graphene as reinforcement in composites since the 2D mode is crucial to assess how effectively graphene uptakes an applied stress or strain.