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Serge G Lemay

Publications and source records attributed to Serge G Lemay.

9 recordsLinked to original sources
PubMed2006

Electrochemistry at single-walled carbon nanotubes: the role of band structure and quantum capacitance.

We present a theoretical description of the kinetics of electrochemical charge transfer at single-walled carbon nanotube (SWNT) electrodes, explicitly taking into account the SWNT electronic band structure. SWNTs have a distinct and low density of electronic states (DOS), as expressed by a small value of the quantum capacitance. We show that this greatly affects the alignment and occupation of electronic states in voltammetric experiments and thus the electrode kinetics. We model electrochemistry at metallic and semiconducting SWNTs as well as at graphene by applying the Gerischer-Marcus model of electron transfer kinetics. We predict that the semiconducting or metallic SWNT band structure and its distinct van Hove singularities can be resolved in voltammetry, in a manner analogous to scanning tunneling spectroscopy. Consequently, SWNTs of different atomic structure yield different rate constants due to structure-dependent variations in the DOS. Interestingly, the rate of charge transfer does not necessarily vanish in the band gap of a semiconducting SWNT, due to significant contributions from states which are a few k(B)T away from the Fermi level. The combination of a nanometer critical dimension and the distinct band structure makes SWNTs a model system for studying the effect of the electronic structure of the electrode on electrochemical charge transfer.

Journal Article↗
PubMed2006

Charge inversion at high ionic strength studied by streaming currents.

We report charge inversion, the sign reversal of the effective surface charge in the presence of multivalent counterions, for the biologically relevant regimes of divalent ions and mixtures of monovalent and multivalent ions. Using streaming currents, the pressure-driven transport of countercharges in the diffuse layer, we find that charge inversion occurs in rectangular silica nanochannels at high concentrations of divalent ions. Strong monovalent screening is found to cancel charge inversion, restoring the original surface charge polarity. An analytical model based on ion correlations successfully describes our observations.

Ion Channels↗
PubMed2006

Fabrication and characterization of nanopore-based electrodes with radii down to 2 nm.

We report on the fabrication and characterization of gold nanoelectrodes with carefully controlled nanometer dimensions in a matrix of insulating silicon nitride. A focused electron beam was employed to drill nanopores in a thin silicon nitride membrane. The size and shape of the nanopores were studied with high-resolution transmission electron microscopy and electron-energy-loss two-dimensional maps. The pores were subsequently filled with gold, yielding conically shaped nanoelectrodes. The nanoelectrodes were examined by atomic and electrostatic force microscopy. Their applicability in electrochemistry was demonstrated by steady-state cyclic voltammetry. Pores with a radii down to 0.4 nm and electrodes with radii down to 2 nm are demonstrated.

Journal Article↗
PubMed2006

Experimental observation of nonlinear ionic transport at the nanometer scale.

Nanometer-sized electrodes are used to probe the transport of ions in liquid by monitoring heterogeneous electrochemical reactions. We observe pronounced nonlinearities of ion flux versus concentration when transport is localized within a region smaller than 10 nm. We show that these observations cannot be explained using conventional continuum, mean-field descriptions of ionic transport. The data indicate that these deviations are caused by the high flux of charged species that is achieved at nanometer-sized electrodes.

Electrochemistry↗
PubMed2005

Lithographically fabricated nanopore-based electrodes for electrochemistry.

We report a new technique for fabricating electrodes for electrochemical applications with lateral dimensions in the range 15-200 nm and a reproducible, well-defined geometry. This technique allows determining the electrode size by electron microscopy prior to electrochemical measurements and without contamination of the metal electrode. We measured the diffusion-limited current with stepped-current voltammetry and showed that its dependence on electrode size can be quantitatively understood if the known geometry of the electrodes is explicitly taken into account.

Journal Article↗
PubMed2005

Individual single-walled carbon nanotubes as nanoelectrodes for electrochemistry.

We demonstrate the use of individual single-walled carbon nanotubes (SWNTs) as nanoelectrodes for electrochemistry. SWNTs were contacted by nanolithography, and cyclic voltammetry was performed in aqueous solutions. Interestingly, metallic and semiconducting SWNTs yielded similar steady-state voltammetric curves. We clarify this behavior through a model that considers the electronic structure of the SWNTs. Interfacial electron transfer to the SWNTs is observed to be very fast but can nonetheless be resolved due to the nanometer critical dimension of SWNTs. These studies demonstrate the potential of using a SWNT as a model carbon nanoelectrode for electrochemistry.

Journal Article↗
PubMed2005

Electrical docking of microtubules for kinesin-driven motility in nanostructures.

We demonstrate localized electrical control of the docking of microtubules onto engineered kinesin-coated structures. After applying a voltage to a gold electrode, we observe an enhanced transport of microtubules from solution toward the surface and a subsequent increase of the amount of moving microtubule shuttles. Switching off the voltage leads to a partial detachment of microtubules from the surface. The surface coverage of microtubules, during both the docking and undocking events, follows an exponential time dependence. We provide a simple kinetic model, incorporating the equilibrium between free and surface-bound microtubules, that explains these data.

Binding Sites↗