Browsing by Author "Darwish, N"

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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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    Electro-polymerization rates of diazonium salts are dependent on the crystal orientation of the surface
    (Elsevier, 2022-11-15) Rahpeima, S; Le Brun, AP; Raston, CL; Darwish, N
    Electro-polymerization of diazonium salts is widely used for modifying surfaces with thin organic films. Initially this method was primarily applied to carbon, then to metals, and more recently to semiconducting Si. Unlike on other surfaces, electrochemical reduction of diazonium salts on Si, which is one of the most industrially dominant material, is not well understood. Here, we report the electrochemical reduction of diazonium salts on a range of silicon electrodes of different crystal orientations (111, 211, 311, 411, and 100). We show that the kinetics of surface reaction and the reduction potential is Si crystal-facet dependent and is more favorable in the hierarchical order (1 1 1) > (2 1 1) > (3 1 1) > (4 1 1) > (1 0 0), a finding that offers control over the surface chemistry of diazonium salts on Si. The dependence of the surface reaction kinetics on the crystal orientation was found to be directly related to differences in the potential of zero charge (PZC) of each crystal orientation, which in turn controls the adsorption of the diazonium cations prior to reduction. Another consequence of the effect of PZC on the adsorption of diazonium cations, is that molecules terminated by distal diazonium moieties form a compact film in less time and requires less reduction potentials compared to that formed from diazonium molecules terminated by only one diazo moiety. In addition, at higher concentrations of diazonium cations, the mechanism of electrochemical polymerization on the surface becomes PZC-controlled adsorption-dominated inner-sphere electron transfer while at lower concentrations, diffusion-based outer-sphere electron transfer dominates. These findings help understanding the electro-polymerization reaction of diazonium salts on Si en route towards an integrated molecular and Si electronics technology. © 2022 Elsevier Inc
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    Multi-responsive photo- and chemo-electrical single-molecule switches
    (ACS Publications, 2014-11-24) Darwish, N; Aragonès, AC; Darwish, TA; Ciampi, S; Díez-Pérez, I
    Incorporating molecular switches as the active components in nanoscale electrical devices represents a current challenge in molecular electronics. It demands key requirements that need to be simultaneously addressed including fast responses to external stimuli and stable attachment of the molecules to the electrodes while mimicking the operation of conventional electronic components. Here, we report a single-molecule switching device that responds electrically to optical and chemical stimuli. A light pointer or a chemical signal can rapidly and reversibly induce the isomerization of bifunctional spiropyran derivatives in the bulk reservoir and, consequently, switch the electrical conductivity of the single-molecule device between a low and a high level. The spiropyran derivatives employed are chemically functionalized such that they can respond in fast but practical time scales. The unique multistimuli response and the synthetic versatility to control the switching schemes of this single-molecule device suggest spiropyran derivatives as key candidates for molecular circuitry. © 2014, American Chemical Society.
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    Oxidative acetylenic coupling reactions as a surface chemistry tool
    (2011-09-14) Ciampi, S; James, M; Darwish, N; Luais, E; Guan, B; Harper, JB; Gooding, JJ
    A novel method to prepare redox monolayers on silicon electrodes has been developed that employs CuI-catalyzed oxidative acetylenic coupling reactions for molecular electronic type applications. As the first case study, ethynylferrocene was covalently immobilized onto an acetylene-terminated monolayer on a Si(100) surface to give a 1,3-diyne (C[triple bond, length as m-dash]C-C[triple bond, length as m-dash]C-) linked redox assembly. The derivatization process requires no protection/de-protection steps, nor activation procedures. The effect of the conjugated diyne linkage on the rate of electron transfer between tethered ferrocenyl units and the silicon electrode is benchmarked against well-established "click" products (i.e. 1,2,3-triazole linkage). The surfaces, after each step, are characterized thoroughly using X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The coupling chemistry provides a useful strategy for functionalizing silicon surfaces and contributes to an expanding repertoire of wet chemistry routes for the functionalization of solid substrates.© 2011, Royal Society of Chemistry
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    Sliding silicon-based Schottky diodes: maximizing triboelectricity with surface chemistry
    (Elsevier, 2022-03) Ferrie, S; Le Brun, AP; Krishnan, G; Andersson, GG; Darwish, N; Ciampi, S
    Triboelectric nanogenerators are an emerging energy technology which harvests electricity from mechanical energy. Within this technology there are sliding metal–semiconductor contacts, which can be miniaturized, and having a direct current (DC) output are suitable as autonomous power sources for electronic devices. Herein we explore the scope of engineering the surface chemistry of silicon towards maximizing the output of a Pt–Si Schottky diode-based triboelectric nanogenerator. Through the attachment of covalent Si–C-bound organic monolayers we have engineered silicon surface chemistry to systematically tune friction, wettability and surface work function, with the overall aim of clarifying the interplay between mechanical and electronic properties defining the DC output of a zero-bias sliding Schottky diode. Current outputs increase two-fold in amine- and alcohol-terminated monolayers compared to shorter and carbon-terminated films. This trend parallels the change in friction measured in response to surface functionalization. A pronounced effect of silicon doping on friction and current was revealed by atomic force microscopy, indicating a link between doping and friction, even at zero applied bias. This work reveals an electrical component of friction by demonstrating a friction excess in response to the flow of current, and it opens up novel avenues into the use of silicon, and its surface chemistry, as platform for triboelectric nanogenerators. © 2021 Elsevier Ltd.