arXiv subjects

François Lapointe

Publications and source records attributed to François Lapointe.

3 recordsLinked to original sources

arXiv2017

Experimentally Probing 'Hydrophobic' Water at the Gold Electrode/Aqueous Interface

Quantitative description of reaction mechanisms in aqueous phase electrochemistry requires experimental characterization of local water structure at the electrode/aqueous interface and its evolution with changing potential. Gaining such insight experimentally under electrochemical conditions is a formidable task. Here we characterize the potential dependent structure of a sub-population of interfacial water that have one OH group pointing towards a gold working electrode using interface specific vibrational spectroscopy in a thin film electrochemical cell. Such 'free-OH' groups are the molecular level observable of an extended hydrophobic interface. This 'free-OH' interacts only weakly with the Au surface at all potentials, has an orientational distribution that narrows as one approaches the potential of zero charge and disappears on the oxidation of the gold electrode.

physics.chem-ph↗

arXiv2015

Phonon-Induced Transparency in Functionalized Single Layer Graphene

Herein, intervalley scattering is exploited to account for anomalous antiresonances in the infrared spectra of doped and disordered single layer graphene. We present infrared spectroscopy measurements of graphene grafted with iodophenyl moieties in both reflection microscopy and transmission configurations. Asymmetric transparency windows at energies corresponding to phonon modes near the Γ and K points are observed, in contrast to the featureless spectrum of pristine graphene. These asymmetric antiresonances are demonstrated to vary as a function of the chemical potential. We propose a model which involves coherent intraband scattering with defects and phonons, thus relaxing the optical selection rule forbidding access to ${\bf q} \neq$ Γ phonons. This interpretation of the new phenomenon is supported by our numerical simulations that reproduce the experimental features.

cond-mat.mes-hall↗

arXiv2012

Fano Resonances in Mid-Infrared Spectra of Single-Walled Carbon Nanotubes

This work revisits the physics giving rise to the carbon nanotubes phonon bands in the mid- infrared. Our measurements of doped and undoped samples of single-walled carbon nanotubes in Fourier transform infrared spectroscopy show that the phonon bands exhibit an asymmetric lineshape and that their effective cross-section is enhanced upon doping. We relate these observations to electron-phonon coupling or, more specifically, to a Fano resonance phenomenon. We note that only the dopant-induced intraband continuum couples to the phonon modes and that defects induced in the sidewall increase the resonance probabilities.

cond-mat.mtrl-sci↗