41 research outputs found

    Characterization of Growth Patterns of Nanoscale Organic Films on Carbon Electrodes by Surface Enhanced Raman Spectroscopy

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    Electrochemical deposition of aromatic organic molecules by reduction of diazonium reagents enables formation of molecular layers with sufficient integrity for use in molecular electronic junctions of interest to microelectronics. Characterization of organic films with thicknesses in the 1–10 nm range is difficult with Raman spectroscopy, since most molecular structures of electronic interest have Raman cross sections which are too small to observe as either thin films on solid electrodes or within intact molecular junctions. Layer formation on a 10 nm thick Ag island film on a flat carbon surface (eC/Ag) permitted acquisition of structural information using surface enhanced Raman spectroscopy (SERS), in many cases for molecules with weak Raman scattering. Raman spectra obtained on eC/Ag surfaces were indistinguishable from those on carbon without Ag present, and the spectra of oligomeric molecular layers were completely consistent with those of the monomers. Layer growth was predominantly linear for cases where such growth was sterically allowed, and linear growth correlated strongly with the line width and splitting of the CC phenyl ring stretches. Molecular bilayers made by successive reduction of different diazonium reagents were also observable and will be valuable for applications of 1–20 nm organic films in molecular electronics

    Hybrid Graphene Ribbon/Carbon Electrodes for High‐Performance Energy Storage

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    The utility of supercapacitors for both fixed and portable energy storage would be greatly enhanced if their energy density could be increased while maintaining their high power density, fast charging time, and low cost. This study describes a simple, solution\u2010phase, scalable modification of carbon materials by a covalently bonded \u201cbrush\u201d of hydrogen\u2010terminated graphene ribbons (GRs) with layer thicknesses of 2\u201320 nm, resulting in a 20\u2013100 times increase in the areal capacitance of the unmodified electrode surface. On a flat sp2 carbon surface modified by GRs, the capacitance exceeds 1200 \ub5F cm 122 in 0.1 m H2SO4 due to a distinct type of pseudocapacitance during constant current charge/discharge cycling. Modification of high surface area carbon black electrodes with GRs yields capacitances of 950\u20131890 F g 121, power densities >40 W g 121, and minimal change in capacitance during 1500 charge/discharge cycles at 20 A g 121. A capacitance of 1890 F g 121 affords an energy density of 318 Wh kg 121 operating at 1.1 V and 590 Wh kg 121 at 1.5 V. The projected energy density of a hybrid GR/carbon supercapacitor greatly exceeds the current 10 Wh kg 121 for commercial supercapacitors and approaches that of lithium ion batteries.Peer reviewed: YesNRC publication: Ye
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