A parabolic approach to the control of opinion spreading

We analyze the problem of controlling to consensus a nonlinear system modeling opinion spreading. We derive explicit exponential estimates on the cost of approximately controlling these systems to consensus, as a function of the number of agents N and the control time-horizon T. Our strategy makes use of known results on the controllability of spatially discretized semilinear parabolic equations. Both systems can be linked through time-rescalin

First proof-of-principle of inorganic lead halide perovskites deposition by magnetron-sputtering

The present work reports the application of RF-magnetron sputtering technique to realize CsPbBr 3 70 nm thick films on glass substrate by means of a one-step procedure. The obtained films show highly uniform surface morphology and homogeneous thickness as evidenced by AFM and SEM investigations. XRD measurements demonstrate the presence of two phases: a dominant orthorhombic CsPbBr 3 and a subordinate CsPb 2 Br 5 . Finally, XPS data reveals surface bromine depletion respect to the stoichiometrical CsPbBr 3 composition, nevertheless photoluminescence spectroscopy results confirm the formation of a highly luminescent film. These preliminary results demonstrate that our approach could be of great relevance for easy fabrication of large area perovskite thin films. Future developments, based on this approach, may include the realization of multijunction solar cells and multicolor light emitting devices

Superlinear emission in bare perovskite: amplified spontaneous emission in disordered film versus single crystal lasing

Abstract We present an experimental study concerning the superlinear emission in organic-inorganic halide perovskites. Microphotoluminescence experiments under CW and picosecond excitation condition at low temperature and near field optical photoluminescence spectra at room temperature provide clear evidence of the very different origin of the superlinear regime in disordered films and microplates/microwires. Insights on the origin of modal structures of the emission spectra in the high excitation regime will be given by polarization-resolved photoluminescence experiments

Near-field imaging of single walled carbon nanotubes emitting in the telecom wavelength range

International audienceHybrid systems based on carbon nanotubes emitting in the telecom wavelength range and Si-photonic platforms are promising candidates for developing integrated photonic circuits. Here, we consider semiconducting single walled carbon nanotubes (s-SWNTs) emitting around 1300 nm or 1550 nm wavelength. The nanotubes are deposited on quartz substrate for mapping their photoluminescence in hyperspectral near-field microscopy. This method allows for a sub-wavelength resolution in detecting the spatial distribution of the emission of single s-SWNTs at room temperature. Optical signature delocalized over several micrometers is observed, thus denoting the high quality of the produced carbon nanotubes on a wide range of tube diameters. Noteworthy, the presence of both nanotube bundles and distinct s-SWNT chiralities is uncovered

Near-field speckle imaging of light localization in disordered photonic

Optical localization in strongly disordered photonic media is an attractive topic for proposing novel cavity-like structures. Light interference can produce random modes confined within small volumes, whose spatial distribution in the near-field is predicted to show hot spots at the nanoscale. However, these near-field speckles have not yet been experimentally investigated due to the lack of a high spatial resolution imaging techniques. Here, we study a system where the disorder is induced by random drilling air holes in a GaAs suspended membrane with internal InAs quantum dots. We perform deep-subwavelength near-field experiments in the telecom window to directly image the spatial distribution of the electric field intensity of disordered-induced localized optical modes. We retrieve the near-field speckle patterns that extend over few micrometers and show several single speckles of the order of λ/10 size. The results are compared with the numerical calculations and with the recent findings in the literature of disordered media. Notably, the hot spots of random modes are found in proximity of the air holes of the disordered system

N-nH complexes in GaAs studied at the atomic scale by cross-sectional scanning tunneling microscopy

Hydrogenation of nitrogen (N) doped GaAs allows for reversible tuning of the bandgap and the creation of site controlled quantum dots through the manipulation of N-nH complexes, N-nH complexes, wherein a nitrogen atom is surrounded by n hydrogen (H) atoms. Here we employ cross-sectional scanning tunneling microscopy (X-STM) to study these complexes in the GaAs (110) surface at the atomic scale. In addition to that we performed density functional theory (DFT) calculations to determine the atomic properties of the N-nH complexes. We argue that at or near the (110) GaAs surface two H atoms from N-nH complexes dissociate as an H$_2$ molecule. We observe multiple features related to the hydrogenation process, of which a subset is classified as N-1H complexes. These N-1H related features show an apparent reduction of the local density of states (LDOS), characteristic to N atoms in the GaAs (110) surface with an additional apparent localized enhancement of the LDOS located in one of three crystal directions. N-nH features can be manipulated with the STM tip. Showing in one case a switching behavior between two mirror-symmetric states and in another case a removal of the localized enhancement of the LDOS. The disappearance of the bright contrast is most likely a signature of the removal of an H atom from the N-nH complex.Comment: 11 pages, 12 figure

Shallow radar (SHARAD) sounding observations of the Medusae Fossae Formation, Mars

The SHARAD (shallow radar) sounding radar on the Mars Reconnaissance Orbiter detects subsurface reflections in the eastern and western parts of the Medusae Fossae Formation (MFF). The radar waves penetrate up to 580 m of the MFF and detect clear subsurface interfaces in two locations: west MFF between 150 and 155◦ E and east MFF between 209 and 213◦ E. Analysis of SHARAD radargrams suggests that the real part of the permittivity is ∼3.0, which falls within the range of permittivity values inferred from MARSIS data for thicker parts of the MFF. The SHARAD data cannot uniquely determine the composition of the MFF material, but the low permittivity implies that the upper few hundred meters of the MFF material has a high porosity. One possibility is that the MFF is comprised of low-density welded or interlocked pyroclastic deposits that are capable of sustaining the steep-sided yardangs and ridges seen in imagery. The SHARAD surface echo power across the MFF is low relative to typical martian plains, and completely disappears in parts of the east MFF that correspond to the radar-dark Stealth region. These areas are extremely rough at centimeter to meter scales, and the lack of echo power is most likely due to a combination of surface roughness and a low near-surface permittivity that reduces the echo strength from any locally flat regions. There is also no radar evidence for internal layering in any of the SHARAD data for the MFF, despite the fact that tens-of-meters scale layering is apparent in infrared and visible wavelength images of nearby areas. These interfaces may not be detected in SHARAD data if their permittivity contrasts are low, or if the layers are discontinuous. The lack of closely spaced internal radar reflectors suggests that the MFF is not an equatorial analog to the current martian polar deposits, which show clear evidence of multiple internal layers in SHARAD dat

A lithographic approach for quantum dot-photonic crystal nanocavity coupling in dilute nitrides

We report on a novel lithographic approach for the fabrication of integrated quantum dot (QD)-photonic crystal (PhC) nanocavity systems. We exploit unique hydrogen's ability to tailor the band gap energy of dilute nitride semiconductors to fabricate isolated site-controlled QDs via a spatially selective hydrogenation at the nanometer-scale. A deterministic integration of the realized site-controlled QDs with PhC nanocavities is provided by the inherent realignment precision (~ 20 nm) of the electron beam lithography system used for the fabrication of both QDs and PhC cavities. A detailed description of the fabrication steps leading to the realization of integrated QD-PhC cavity systems is provided, together with the experimental evidence of a weak coupling effect between the single-photon emitter and the PhC cavity