Random sequential adsorption of spheres on a cylinder

Inspired by observations of beads packed on a thin string in such systems as sea-grapes and dental plaque, we study the random sequential adsorption of spheres on a cylinder. We determine the asymptotic fractional coverage of the cylinder as a function of the sole parameter in the problem, the ratio of the sphere radius to the cylinder radius (for a very long cylinder) using a combination of analysis and numerical simulations. Examining the asymptotic structures, we find weak chiral ordering on sufficiently small spatial scales. Experiments involving colloidal microspheres that can attach irreversibly to a silica wire via electrostatic forces or DNA hybridization allow us to verify our predictions for the asymptotic coverage

Ferroelectric gating of narrow band-gap nanocrystal arrays with enhanced light-matter coupling

International audienceAs narrow band gap nanocrystals become a viable building block for the design of infrared sensors, device design needs to match with their actual operating conditions. While in the near IR and shortwave infrared room temperature operation have been demonstrated, longer wavelengths still require low temperature operation requiring specific design. Here, we discuss how field-effect transistors (FETs) can be compatible with low temperature detection. To reach this goal two key developments are proposed. First, we report gating of nanocrystal films from SrTiO3 used as a ferroelectric material leading to high gate capacitance with leakage and breakdown free operation in the 4-100 K range. Secondly, we demonstrate that this FET is compatible with a plasmonic resonator which role is to achieve strong light absorption from a thin film used as the channel of the FET. Combining three resonances, broad band absorption from 1.5 to 3 µm reaching 30% is demonstrated. Finally combining gate and enhanced light matter coupling, we show that detectivity can be as high as 10 12 jones for a device presenting a 3 µm cutoff wavelength and 30 K operation

The Strong Confinement Regime in HgTe Two-Dimensional Nanoplatelets

International audienceThe confinement in colloidal HgTe nanocrystals enables this material to be promising for colloidal optoelectronics over a wide range of energies, from the THz spectral range up to the visible region. Herein, by using a combination of high energy absorption HgTe nanoplatelets and low energy absorption HgTe nanocrystals, we probe optical transmission of HgTe nanoparticles over the 0.26-1.8 eV range, from 0 K to 300 K temperatures and under simultaneous pressure, up to 4 GPa. While the pressure dependence of nanoplatelets follows the one observed for bulk and nanocrystals, the temperature dependence dramatically differs for nanoplatelets. The modeling of the electronic energy dispersion using up to 14-band k.p formalism suggests that the second conduction band and higher bands of HgTe play a vital role to describe and explain the HgTe nanoparticle spectroscopies