Role of Manganese in Lithium- and Manganese-Rich Layered Oxides Cathodes.

Lithium-rich transition-metal-oxide cathodes are among the most promising materials for next generation lithium-ion-batteries because they operate at high voltages and deliver high capacities. However, their cycle-life remains limited, and individual roles of the transition-metals are still not fully understood. Using bulk-sensitive X-ray absorption and emission spectroscopy on Li[Li0.2Ni0.16Mn0.56Co0.08]O2, we inspect the behavior of Mn, generally considered inert upon the electrochemical process. During the first charge Mn appears to be redox-active showing a partial transformation from high-spin Mn4+ to Mn3+ in both high and low spin configurations, where the latter is expected to favor reversible cycling. The Mn redox-state with cycling continues changing in opposition to the expected charge compensation and is correlated with Ni oxidation/reduction, also spatially. The findings suggest that strain induced on the Mn-O sublattice by Ni oxidation triggers Mn reduction. These results unravel the Mn role in controlling the electrochemistry of Li-rich cathodes.

Deflectometry encoding the measured angle in a time-dependent intensity signal.

We propose a new concept of a deflectometer, aimed to provide high accuracy measurements with high sampling rate and low noise, as required by state-of-the-art slope-measuring profilometers, like Long Trace Profilometers or Nanometer Optics Measuring instruments. For this purpose, we introduce certain modifications to the usual working principle of autocollimators so that the measured angle is not given by the displacement of the pattern captured by a CCD, but by the harmonic contents of the time-modulated intensity signal acquired by a photodiode. By doing this, the signal can be sampled not by just a few thousand pixels but by millions of samples/s.

The single molecule probe: nanoscale vectorial mapping of photonic mode density in a metal nanocavity.

We use superresolution single-molecule polarization and lifetime imaging to probe the local density of states (LDOS) in a metal nanocavity. Determination of the orientation of the molecular transition dipole allows us to retrieve the different LDOS behavior for parallel and perpendicular orientations with respect to the metal interfaces. For the perpendicular orientation, a strong lifetime reduction is observed for distances up to 150 nm from the cavity edge due to coupling to surface plasmon polariton modes in the metal. Contrarily, for the parallel orientation we observe lifetime variations resulting from coupling to characteristic lambda/2 cavity modes. Our results are in good agreement with calculations of the nanoscale variations of the projected LDOS, which demonstrates the potential of single molecules as nonperturbative, nanoscale vectorial point probes in photonic and biological nanostructures.

Local observation of plasmon focusingin Talbot carpets.

We present a detailed experimental and theoretical study of plasmon Talbot effect. A theoretical model based on simple scattering theory is developed to describe the Talbot self-imaging pattern generated by a linear arrangement of cylindrical nanostructures forming a periodic array. We first show the experimental observation of plasmon Talbot carpets created by propagating surface plasmon polaritons (SPP) interacting with cylindrical nanostructures positioned on a thin Au film using leakage radiation microscopy. Such images provide information on the distribution of the plasmon intensity close to the nanostructures. Next, heterodyne interferometer based near-field imaging is carried out to extract information on the plasmonic modes forming the Talbot carpet deployment. We report the experimental observation of Talbot focal spots with dimensions down to lambda/4.

Feedback-induced voltage change of a Vertical-Cavity Surface-Emitting Laser as an active detection system for miniature optical scanning probe microscopes.

We propose a novel detection technique for scanning probe microscopy based on the measuring of the feedback-induced voltage change of 780-nm VCSEL operating at constant current in far-field regime when we modulate mechanically the length of a coupled-cavity generating the feedback conditions. The voltage change of the VCSEL is produced by light back reflected from the sample to the laser cavity. Two-dimensional image probing is successfully demonstrated with high temporal resolution, offering a viable solution for miniature parallel scanning probe optical microscopes, such as confocal microscope, where the use of a photodetector is avoided. This approach opens the possibility to perform imaging tasks in a low cost and hand-held miniature device with much improved effective-space.