Understanding biological interaction with graphene and hexagonal-boron nitride (h-BN) membranes has become essential for the incorporation of these unique materials in contact with living organisms. Previous reports show contradictions regarding the bacterial interaction with graphene sheets on metals. Here, we present a comprehensive study of the interaction of bacteria with copper substrates coated with single-layer graphene and h-BN. Our results demonstrate that such graphitic coatings substantially suppress interaction between bacteria and underlying Cu substrates, acting as an effective barrier to prevent physical contact. Bacteria do not "feel" the strong antibacterial effect of Cu, and the substrate does not suffer biocorrosion due to bacteria contact. Effectiveness of these systems as barriers can be understood in terms of graphene and h-BN impermeability to transfer Cu(2+) ions, even when graphene and h-BN domain boundary defects are present. Our results seem to indicate that as-grown graphene and h-BN films could successfully protect metals, preventing their corrosion in biological and medical applications.
We report a chemically specific x-ray photoelectron diffraction (XPD) investigation using synchrotron radiation of the thermally induced growth of epitaxial graphene on the 6H -SiC(0001). The XPD results show that the buffer layer on the SiC(0001) surface is formed by two domain regions rotated by 60 • with respect to each other. The experimental data supported by a comprehensive multiple scattering calculation approach indicates the existence of a long-range ripple due the (6 √ 3 × 6 √ 3)R30 • reconstruction, in addition to a local range buckling in the (0001) direction of the two sublattices that form the honeycomb structure of the buffer layer. This displacement supports the existence of an sp 2 -to-sp 3 rehybridization in this layer. For the subsequent graphene layer this displacement is absent, which can explain several differences between the electronic structures of graphene and the buffer layer.
Collective surface excitations in alkali-metal overlayers are observed using photoyield spectroscopy. Spectra for Na and K on Al͑111͒ reveal a multipole surface plasmon and bulklike overlayer plasmon. In contrast, Li on Al exhibits only the multipole mode. In the submonolayer regime, all three alkali metals provide evidence for the threshold excitation. Time-dependent density-functional calculations for realistic alkali-metal overlayers agree well with these observations. ͓S0163-1829͑98͒07408-6͔
Using angle-and energy-resolved photoyield spectroscopy, we investigate the properties of the multipole plasmon excitation. At higher energies, a systematic dependence of the photoyield on the photon angle of incidence is observed and explained on the basis of classical Fresnel theory, indicating the possibility of obtaining information about optical constants from such measurements. A feature above the multipole plasmon is assigned to the excitation of a bulk plasmon by the photon field. ͓S0163-1829͑98͒51132-0͔
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