Browsing by Author "Ciampi, S"

Now showing 1 - 12 of 12
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    Comparing the reactivity of alkynes and alkenes on silicon (100) surfaces
    (American Chemical Society, 2009-12-15) Ng, A; Ciampi, S; James, M; Harper, JB; Gooding, JJ
    The relative reactivities of alkynes to alkenes on hydrogen-terminated silicon (100) surfaces, under conditions where a monolayer will be produced via hydrosilylation, were measured using two different approaches. The first approach was to form monolayers from a series of solutions containing different mole fractions of an alkyne, with a trifluorothioacetate distal moiety and an alkene with a terminal carboxylic acid functional. X-ray photoelectron spectroscopic analysis of the resultant surfaces showed that the mole fraction of alkyne on the surface was larger than that in the respective alkyne/alkene mixture. By filling the XPS data, we estimated that the reactivity ratio of alkynec to alkene was approximately 1.7 +/- 0.2 when monolayers were formed at 120 degrees C. The second approach was using a molecule containing both an alkyne at one end and an alkene at the other, non-1-yne-8-ene, as the hydrosilylation reagent such that either end Could attach to the silicon surface. The relative orientation of this molecule, once reacted with it hydrogen-terminated Si(100) surface, was determined by coupling ail additional reagent to the distal end of the monolayer. The reagent used was azidoferrocene, which could attach onto free alkyne moieties on the surface only via the 1,3-Huisgen cycloaddition "click" reaction. Electrochemical analysis was then used to determine how many ferrocene moieties were attached to the SAM surface. In this way, it was shown that the alkyne end reacted preferentially with the silicon surface compared with the alkene end. The reactivity ratio of the alkyne end to the alkene end was increased front 2.0 +/- 0.2 to 9 +/- 1 when the temperature was decreased from 120 to 65 degrees C. © 2009, American Chemical Society
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    Depth-resolved chemical modification of porous silicon by wavelength-tuned irradiation
    (American Chemical Society, 2012-11-06) Guan, B; Ciampi, S; Luais, E; James, M; Reece, PJ; Gooding, JJ
    The ability to impart discrete surface chemistry to the inside and outside of mesoporous silicon is of great importance for a range of biomedical applications, from selective (bio)sensing to tissue-specific drug delivery. Here we present a generic strategy toward achieving depth-resolved functionalization of the external and internal porous surfaces by a simple change in the wavelength of the light being used to promote surface chemical reactions. UV-assisted hydrosilylation, limited by the penetration depth of UV light, is used to decorate the outside of the mesoporous structure with carboxylic acid molecules, and white light illumination triggers the attachment of dialkyne molecules to the inner porous matrix. © 2012, American Chemical Society.
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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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    Functionalization of acetylene-terminated monolayers on Si(100) surfaces: a click chemistry approach
    (American Chemical Society, 2007-08-28) Ciampi, S; Bocking, T; Kilian, KA; James, M; Harper, JB; Gooding, JJ
    In this article, we report the functionalization of alkyne-terminated alkyl monolayers on Si(100) using "click" chemistry, specifically, the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction of azides with surface-bound alkynes. Covalently immobilized, structurally well-defined acetylene-terminated organic monolayers were prepared from a commercially available terminal diyne species using a one-step hydrosilylation procedure. Subsequent derivatization of the alkyne-terminated monolayers in aqueous environments with representative azide species via a selective, reliable, robust cycloaddition process afforded disubstituted surface-bound [1,2,3]-triazole species. Neither activation procedures nor protection/deprotection steps were required, as is the case with more established grafting approaches for silicon surfaces. Detailed characterization using X-ray photoelectron spectroscopy and X-ray reflectometry demonstrated that the surface acetylenes had reacted in moderate to high yield to give surfaces exposing alkyl chains, oligoether anti-fouling moieties, and functionalized aromatic structures. These results demonstrate that click immobilization offers a versatile, experimentally simple, chemically unambiguous modular approach to producing modified silicon surfaces with organic functionality for applications as diverse as biosensors and molecular electronics. © 2007, American Chemical Society
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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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    Nanoscale condensation of water on self-assembled monolayers
    (Royal Society of Chemistry, 2011-06-07) James, M; Darwish, TA; Ciampi, S; Sylvester, SO; Zhang, Z; Ng, A; Gooding, JJ; Hanley, TL
    We demonstrate that water is almost universally present on apparently dry self-assembled monolayers, even on those considered almost hydrophobic by conventional methods such as water contact goniometry. The structure and kinetics of nanoscale water adsorption onto these surfaces were investigated using X-ray and neutron reflectometry, as well as atomic force microscopy. Condensation of water on hydrophilic surfaces under ambient conditions formed a dense sub-nanometre surface layer; the thickness of which increased with exponentially limiting kinetics. Tapping mode AFM measurements show the presence of nanosized droplets that covered a small percentage ([similar]2%) of the total surface area, and which became fewer in number and larger in size with time. While low vacuum pressures ([similar]10-8 bar) at room temperature did nothing to remove the adsorbed water from these monolayers, heating to temperatures above 65 [degree]C under atmospheric conditions did lead to evaporation from the surface. We demonstrate that water contact angle measurements are not necessarily sensitive to the presence of nanoscale adsorbed water and do not vary with time. For the most part they are a poor indicator of the kinetics and the amount of water condensation onto these surfaces at the molecular level. In summary, this study reveals the need to exclude air containing even trace amounts of water vapor from such surfaces when characterizing using techniques such as X-ray reflectometry.© 2011, Royal Society of Chemistry
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    Nanoscale water condensation on click-functionalized self-assembled monolayers
    (American Chemical Society, 2011-09-06) James, M; Ciampi, S; Darwish, TA; Hanley, TL; Sylvester, SO; Gooding, JJ
    We have examined the nanoscale adsorption of molecular water under ambient conditions onto a series of well-characterized functionalized surfaces produced by Cu(I)-catalyzed alkyne–azide cycloaddition (CuAAC or “click†) reactions on alkyne-terminated self-assembled monolayers on silicon. Water contact angle (CA) measurements reveal a range of macroscopic hydrophilicity that does not correlate with the tendency of these surfaces to adsorb water at the molecular level. X-ray reflectometry has been used to follow the kinetics of water adsorption on these “click†-functionalized surfaces, and also shows that dense continuous molecular water layers are formed over 30 h. For example, a highly hydrophilic surface, functionalized by an oligo(ethylene glycol) moiety (with a CA = 34°) showed 2.9 Ã… of adsorbed water after 30 h, while the almost hydrophobic underlying alkyne-terminated monolayer (CA = 84°) showed 5.6 Ã… of adsorbed water over the same period. While this study highlights the capacity of X-ray reflectometry to study the structure of adsorbed water on these surfaces, it should also serve as a warning for those intending to characterize self-assembled monolayers and functionalized surfaces to avoid contamination by even trace amounts of water vapor. Moreover, contact angle measurements alone cannot be relied upon to predict the likely degree of moisture uptake on such surfaces.© 2011, American Chemical Society
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    Organic monolayers on Si(211) for triboelectricity generation: etching optimization and relationship between the electrochemistry and current output
    (American Chemical Society, 2022-09-28) Hurtado, C; Lyu, X; Ferrie, S; Le Brun, AP; MacGregor, M; Ciampi, S
    Triboelectric nanogenerators (TENGs) based on sliding silicon-organic monolayer-metal Schottky diodes are an emerging autonomous direct-current (DC) current supply technology. Herein, using conductive atomic force microscopy and electrochemical techniques, we explore the optimal etching conditions toward the preparation of DC TENGs on Si(211), a readily available, highly conductive, and underexplored silicon crystallographic cut. We report optimized conditions for the chemical etching of Si(211) surfaces with subnanometer root-mean-square roughness, explore Si(211) chemical passivation, and unveil a relationship between the electrochemical charge-transfer behavior at the silicon-liquid interface and the zero-applied bias current output from the corresponding dynamic silicon-organic monolayer-platinum system. The overall aim is to optimize the etching and functionalization of the relatively underexplored Si(211) facet, toward its application in out-of-equilibrium Schottky diodes as autonomous power supplies. We also propose the electrochemical behavior of surface-confined redox couples as a diagnostic tool to anticipate whether or not a given surface will perform satisfactorily when used in a TENG design. © 2022 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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    Silicon (100) electrodes resistant to oxidation in aqueous solutions: an unexpected benefit of surface acetylene moieties
    (American Chemical Society, 2009-02-17) Ciampi, S; Eggers, PK; Le Saux, G; James, M; Harper, JB; Gooding, JJ
    Here we report on the functionalization of alkyne-terminated alkyl monolayers on highly doped Si(100) using click" reactions to immobilize ferrocene derivatives. The reaction of hydrogen-terminated silicon surfaces with a diyne species was shown to afford very robust functional surfaces where the oxidation of the underlying substrate was negligible. Detailed characterization using X-ray photoelectron spectroscopy, X-ray reflectometry, and cyclic voltammetry demonstrated that the surface acetylenes had reacted in moderate yield to give surfaces exposing ferrocene moieties. Upon extensive exposure of the redox-active architecture to oxidative environments during preparative and characterization steps, no evidence of SiOx contaminants was shown for derivatized SAMs prepared from single-component 1,8-nonadiyne, fully acetylenylated, monolayers. An analysis of the redox behavior of the prepared Si(100) electrodes based on relevant parameters such as peak splitting and position and shape of the reduction/oxidation waves depicted a well-behaved redox architecture whose spectroscopic and electrochemical properties were not significantly altered even after prolonged cycling in aqueous media between -100 and 800 mV versus AglAgCl. The reported strategy represents an experimentally simple approach for the preparation of silicon-based electrodes where, in addition to close-to-ideal redox behavior, remarkable electrode stability can be achieved. Both the presence of a distal alkyne moiety and temperatures of formation above 100 degrees C were required to achieve this surface stabilization. © 2009, American Chemical Society
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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.
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    Tandem “click” reactions at acetylene-terminated Si(100) monolayers
    (American Chemical Society, 2011-06-07) Ciampi, S; James, M; Michaels, P; Gooding, JJ
    We demonstrate a simple method for coupling alkynes to alkynes. The method involves tandem azide-alkyne cycloaddition reactions ("click" chemistry) for the immobilization of 1-alkyne species onto an alkyne modified surface in a one-pot procedure. In the case presented, these reactions take place on a nonoxidized Si(100) surface although the approach is general for linking alkynes to alkynes. The applicability of the method in the preparation of electrically well-behaved functionalized surfaces is demonstrated by coupling an alkyne-tagged ferrocene species onto alkyne-terminated Si(100) surfaces. The utility of the approach in biotechnology is shown by constructing a DNA sensing interface by derivatization of the acetylenyl surface with commercially available alkyne-tagged oligonucleotides. Cyclic voltametry, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and X-ray reflectometry are used to characterize the coupling reactions and performance of the final modified surfaces. These data show that this synthetic protocol gives chemically well-defined, electronically well-behaved, and robust (bio)functionalized monolayers on silicon semiconducting surfaces. © 2010, American Chemical Society