41 research outputs found
Characterization of Growth Patterns of Nanoscale Organic Films on Carbon Electrodes by Surface Enhanced Raman Spectroscopy
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 CC 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
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