Browsing by Author "Choudhury, MH"

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    The detailed characterization of electrochemically switchable molecular assemblies on silicon electrodes
    (Royal Society of Chemistry, 2013-01-01) Ciampi, S; James, M; Choudhury, MH; Darwish, N; Gooding, JJ
    In this paper we explore a multi-step synthetic strategy toward fabrication of monolayer-modified Si(100) electrodes that can be electrochemically switched. The synthetic scheme is modular and benefits from an established intramolecular lactonization scheme of benzoquinone analogs. A redox-tagged pendant group can be released from the surface such as to allow for in situ monitoring of the switch process. We show that this model system can be used to elucidate chemical and structural events for a surface dynamic system that is rapidly gaining popularity. The influence of polarization times, overpotentials and semiconductor doping type on the kinetic of the switch event is also investigated. In both basic and acidic aqueous electrolytes the release of suitable redox-active markers is found to require unexpectedly large cathodic overpotentials. The release event is accompanied by minor oxidation of the electrode surface and the switched constructs can be regenerated by chemical means with no appreciable deterioration of surface quality.© 2013, Royal Society of Chemistry
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    The impact of surface coverage on the kinetics of electron transfer through redox monolayers on a silicon electrode surface
    (Elsevier, 2015-12-20) Ciampi, S; Choudhury, MH; Ahmad, SABA; Darwish, N; Le Brun, AP; Gooding, JJ
    The impact of the coverage of ferrocene moieties, attached to a silicon electrode modified via hydrosilylation of a dialkyne, on the kinetics of electron transfer between the redox species and the electrode is explored. The coverage of ferrocene is controlled by varying the coupling time between azidomethylferrocene and the distal alkyne of the monolayer via the copper assisted azide-alkyne cycloaddition reaction. All other variables in the surface preparation are maintained identical. What is observed is that the higher the surface coverage of the ferrocene moieties the faster the apparent rates of electron transfer. This surface coverage-dependent kinetic effect is attributed to electrons hopping between ferrocene moieties across the redox film toward hotspots for the electron transfer event. The origin of these hotspots is tentatively suggested to result from minor amounts of oxide on the underlying silicon surface that reduce the barrier for the electron transfer. © 2015 Elsevier Ltd.