3 research outputs found

    Two-Dimensional Nitrogen-Enriched Carbon Nanosheets with Surface-Enhanced Raman Scattering

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    We have fabricated two-dimensional nitrogen-enriched carbon nanosheets (2D-NECNs) through the pyrolysis of cross-linked poly­(4-vinylpyridine) homopolymers as a platform for detecting physically absorbed dye molecules using Raman-scattering spectra. Upon pyrolysis, a polymeric layer consisting of pyridinic rings was converted into a carbonized nanosheet enriched with pyridinic nitrogen (N<sub>6</sub>), pyrrolic nitrogen (N<sub>5</sub>), graphitic nitrogen (GN), and nitrogen oxide (NO) groups, the fractions of which were finely controlled through pyrolysis at temperatures selected in the range of 430–550 °C. The effects of temperature on the formation of nitrogen- and carbon-containing species in 2D-NECN were examined by XPS, which showed that N<sub>6</sub> and N<sub>5</sub> were the dominant species over GN and NO at 430 °C. Increasing the temperature of pyrolysis produced carbonized nanosheets containing more GN and NO generated at the expense of pyridinic groups. Using rhodamine 6G (R6G) and crystal violet (CV) molecules as probes for Raman measurements, we found that the Raman enhancement on 2D-NECN is due to a chemical mechanism (CM) and that the observed enhancement of the Raman intensity of molecules adsorbed on 2D-NECN hence shows a clear dependence on the nitrogen configuration of the four types. Among the nitrogen species, GN dominates the large enhancement. The chemical Raman enhancement is ascribed to the ability of GN to improve the π-conjugated domains and narrow the energy gap in 2D-NECN

    Tailoring Carbon Nanostructure with Diverse and Tunable Morphology by the Pyrolysis of Self-Assembled Lamellar Nanodomains of a Block Copolymer

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    The pyrolysis of a block copolymer thin film, the free surface of which was in contact with air or a capping layer of SiO<sub>2</sub>, produced four carbon nanostructures. Thin films of a diblock copolymer having perpendicularly oriented lamellar nanodomains served as carbon and nitrogen precursors. Before pyrolysis, the lamellar nanodomains were cross-linked with UV irradiation under nitrogen gas (UVIN). Without a capping layer, pyrolysis caused a structural transformation from lamellar nanodomains to short carbon nanowires or to dropletlike nanocarbons in a row via Rayleigh instability, depending on the duration of pyrolysis. When capped with a layer of SiO<sub>2</sub> followed by pyrolysis, the lamellar nanodomains were converted to pod-like, spaghetti-like, or long worm-like carbon nanostructures. These carbon nanostructures were driven by controlling the surface or interface tension and the residual yield of solid carbonaceous species
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