Room temperature magneto-optic effect in silicon light-emitting diodes

In weakly spin-orbit coupled materials, the spin-selective nature of recombination can give rise to large magnetic-field effects, for example on electro-luminescence from molecular semiconductors. While silicon has weak spin-orbit coupling, observing spin-dependent recombination through magneto-electroluminescence is challenging due to the inefficiency of emission due to silicon's indirect band-gap, and to the difficulty in separating spin-dependent phenomena from classical magneto-resistance effects. Here we overcome these challenges to measure magneto-electroluminescence in silicon light-emitting diodes fabricated via gas immersion laser doping. These devices allow us to achieve efficient emission while retaining a well-defined geometry thus suppressing classical magnetoresistance effects to a few percent. We find that electroluminescence can be enhanced by up to 300\% near room temperature in a seven Tesla magnetic field showing that the control of the spin degree of freedom can have a strong impact on the efficiency of silicon LEDs

Silicon Superconducting Quantum Interference Device

We have studied a Superconducting Quantum Interference SQUID device made from a single layer thin film of superconducting silicon. The superconducting layer is obtained by heavily doping a silicon wafer with boron atoms using the Gas Immersion Laser Doping (GILD) technique. The SQUID device is composed of two nano-bridges (Dayem bridges) in a loop and shows magnetic flux modulation at low temperature and low magnetic field. The overall behavior shows very good agreement with numerical simulations based on the Ginzburg-Landau equations.Comment: Published in Applied Physics Letters (August 2015

Subkelvin tunneling spectroscopy showing Bardeen-Cooper-Schrieffer superconductivity in heavily boron-doped silicon epilayers

Scanning tunneling spectroscopies in the subKelvin temperature range were performed on superconducting Silicon epilayers doped with Boron in the atomic percent range. The resulting local differential conductance behaved as expected for a homogeneous superconductor, with an energy gap dispersion below +/- 10%. The spectral shape, the amplitude and temperature dependence of the superconductivity gap follow the BCS model, bringing further support to the hypothesis of a hole pairing mechanism mediated by phonons in the weak coupling limit.Comment: 4 pages, 3 figure

Thickness dependence of the superconducting critical temperature in heavily doped Si:B epilayers

International audienceWe report on the superconducting properties of a series of heavily doped Si:B epilayers grown by gas immersion laser doping with boron content (nB) ranging from ∼3 × 1020 cm−3 to ∼6 × 1021cm−3 and thickness (d) varying between ∼20 nm and ∼210 nm. We show that superconductivity is only observed for nB values exceeding a threshold value (nc,S ) which scales as nc,S ∝ 1/d. The critical temperature (Tc) then rapidly increases with nB, largely exceeding the theoretical values which can be estimated by introducing the electron-phonon coupling constant (λe-ph) deduced from ab initio calculations into the McMillan equation. Surprisingly Tc(nB,d) is fully determined by the boron dose (nB × d) and can be well approximated by a simple Tc(nB,d) ≈ Tc,0[1 − A/(nB.d)] law, with Tc,0 ∼ 750 mK and A ∼ 8(±1) × 1015 cm−2

Carbon nanotubes adhesion and nanomechanical behavior from peeling force spectroscopy

Applications based on Single Walled Carbon Nanotube (SWNT) are good example of the great need to continuously develop metrology methods in the field of nanotechnology. Contact and interface properties are key parameters that determine the efficiency of SWNT functionalized nanomaterials and nanodevices. In this work we have taken advantage of a good control of the SWNT growth processes at an atomic force microscope (AFM) tip apex and the use of a low noise (1E-13 m/rtHz) AFM to investigate the mechanical behavior of a SWNT touching a surface. By simultaneously recording static and dynamic properties of SWNT, we show that the contact corresponds to a peeling geometry, and extract quantities such as adhesion energy per unit length, curvature and bending rigidity of the nanotube. A complete picture of the local shape of the SWNT and its mechanical behavior is provided

STEM analysis of deformation and B distribution in nanosecond laser ultra-doped Si1−x_{1-x} Bx_x

We report on the structural properties of highly B-doped silicon (> 2 at. %) realised by nanosecond laser doping. We investigate the crystalline quality, deformation and B distribution profile of the doped layer by STEM analysis followed by HAADF contrast studies and GPA, and compare the results to SIMS analyses and Hall measurements. When increasing the active B concentration above 4.3 at.%, the fully strained, perfectly crystalline, Si:B layer starts showing dislocations and stacking faults. These only disappear around 8 at.% when the Si:B layer is well accommodated to the substrate. When increasing B incorporation, we increasingly observe small precipitates, filaments with higher active B concentration and stacking faults. At the highest concentrations studied, large precipitates form, related to the decrease of active B concentration. The structural deformation, defect type and concentration, and active B distribution are connected to the initial increase and subsequent gradual loss of superconductivity

Active PSF shaping and adaptive optics enable volumetric localization microscopy through brain sections

Application of single-molecule switching nanoscopy (SMSN) beyond the coverslip surface poses substantial challenges due to sample-induced aberrations that distort and blur single-molecule emission patterns. We combined active shaping of point spread functions and efficient adaptive optics to enable robust 3D-SMSN imaging within tissues. This development allowed us to image through 30-μm-thick brain sections to visualize and reconstruct the morphology and the nanoscale details of amyloid-β filaments in a mouse model of Alzheimer's disease

Nanosecond Laser Annealing: impact on superconducting Silicon on Insulator epilayers

We present superconducting monocrystalline Silicon On Insulator thin 33 nm epilayers. They are obtained by nanosecond laser annealing under ultra-high vacuum on 300 mm wafers heavily pre-implantated with boron ($2.5\times \,10^{16}\, at/cm^2$, 3 keV). Superconductivity is discussed in relation to the structural, electrical and material properties, a step towards the integration of ultra-doped superconducting Si at large scale. In particular, we highlight the effect of the nanosecond laser annealing energy and the impact of multiple laser anneals. Increasing the energy leads to a linear increase of the layer thickness, and to the increase of the superconducting critical temperature $T_c$ from zero ($<35\, mK$) to $0.5\,K$. This value is comparable to superconducting Si layers realised by Gas Immersion Laser Doping where the dopants are incorporated without introducing the deep defects associated to implantation. Superconductivity only appears when the annealed depth is larger than the initial amorphous layer induced by the boron implantation. The number of subsequent anneals results in a more homogeneous doping with reduced amount of structural defects and increased conductivity. The quantitative analysis of $T_c$ concludes on a superconducting/ non superconducting bilayer, with an extremely low resistance interface. This highlights the possibility to couple efficiently superconducting Si to Si channels

Population-Wide Emergence of Antiviral Resistance during Pandemic Influenza

Background: The emergence of neuraminidase inhibitor resistance has raised concerns about the prudent use of antiviral drugs in response to the next influenza pandemic. While resistant strains may initially emerge with compromised viral fitness, mutations that largely compensate for this impaired fitness can arise. Understanding the extent to which these mutations affect the spread of disease in the population can have important implications for developing pandemic plans. Methodology/Principal Findings: By employing a deterministic mathematical model, we investigate possible scenarios for the emergence of population-wide resistance in the presence of antiviral drugs. The results show that if the treatment level (the fraction of clinical infections which receives treatment) is maintained constant during the course of the outbreak, there is an optimal level that minimizes the final size of the pandemic. However, aggressive treatment above the optimal level can substantially promote the spread of highly transmissible resistant mutants and increase the total number of infections. We demonstrate that resistant outbreaks can occur more readily when the spread of disease is further delayed by applying other curtailing measures, even if treatment levels are kept modest. However, by changing treatment levels over the course of the pandemic, it is possible to reduce the final size of the pandemic below the minimum achieved at the optimal constant level. This reduction can occur with low treatment levels during the early stages of the pandemic, followed by a sharp increase in drug-use before the virus becomes widely spread. Conclusions/Significance: Our findings suggest that an adaptive antiviral strategy with conservative initial treatment levels, followed by a timely increase in the scale of drug-use, can minimize the final size of a pandemic while preventing large outbreaks of resistant infections

Strong Neutral Spatial Effects Shape Tree Species Distributions across Life Stages at Multiple Scales

Traditionally, ecologists use lattice (regional summary) count data to simulate tree species distributions to explore species coexistence. However, no previous study has explicitly compared the difference between using lattice count and basal area data and analyzed species distributions at both individual species and community levels while simultaneously considering the combined scenarios of life stage and scale. In this study, we hypothesized that basal area data are more closely related to environmental variables than are count data because of strong environmental filtering effects. We also address the contribution of niche and the neutral (i.e., solely dependent on distance) factors to species distributions. Specifically, we separately modeled count data and basal area data while considering life stage and scale effects at the two levels with simultaneous autoregressive models and variation partitioning. A principal coordinates of neighbor matrix (PCNM) was used to model neutral spatial effects at the community level. The explained variations of species distribution data did not differ significantly between the two types of data at either the individual species level or the community level, indicating that the two types of data can be used nearly identically to model species distributions. Neutral spatial effects represented by spatial autoregressive parameters and the PCNM eigenfunctions drove species distributions on multiple scales, different life stages and individual species and community levels in this plot. We concluded that strong neutral spatial effects are the principal mechanisms underlying the species distributions and thus shape biodiversity spatial patterns