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International audience; Midinfrared spectroscopy is a universal way to identify chemical and biological substances. Indeed, when interacting with a light beam, most molecules are responsible for absorption at specific wavelengths in the mid-IR spectrum, allowing to detect and quantify small traces of substances. On-chip broadband light sources in the midinfrared are thus of significant interest for compact sensing devices. In that regard, supercontinuum generation offers a mean to efficiently perform coherent light conversion over an ultrawide spectral range, in a single and compact device. This work reports the experimental demonstration of onchip two-octave supercontinuum generation in the mid-infrared wavelength, ranging from 3 to 13 μm (that is larger than 2500 cm −1) and covering almost the full transparency window of germanium. Such an ultrawide spectrum is achieved thanks to the unique features of Ge-rich graded SiGe waveguides, which allow second-order dispersion tailoring and low propagation losses over a wide wavelength range. The influence of the pump wavelength and power on the supercontinuum spectra has been studied. A good agreement between the numerical simulations and the experimental results is reported. Furthermore, a very high coherence is predicted in the entire spectrum. These results pave the way for wideband, coherent, and compact mid-infrared light sources by using a single device and compatible with large-scale fabrication processes.

International audience; Visible nanocrystal-based light-emitting diodes (LEDs) are about to become commercially available. However, their infrared counterparts suffer from two key limitations. First, III–V semiconductor technologies are strong competitors. Second, their potential for operation beyond 1.7 µm remains unexplored. The range from 1.5 to 4 µm corresponds to a technological gap in which the efficiency of interband quantum-well-based devices vanishes and quantum cascade lasers are not efficient enough. Powerful infrared LEDs in this range are needed for applications such as active imaging, organic molecule sensing and airfield lighting. Here we report the design of a HgTe nanocrystal-based LED with luminescence between 2 and 2.3 µm. With an external quantum efficiency of 0.3% and radiance up to 3 W Sr−1 m−2, these HgTe LEDs already present a competitive performance for emission above 2 µm.

GeSn alloys are promising materials for CMOS-compatible mid-infrared lasers manufacturing. Indeed, Sn alloying and tensile strain can transform them into direct bandgap semiconductors. This growing laser technology however suffers from a number of limitations, such as poor optical confinement, lack of strain, thermal, and defects management, all of which are poorly discussed in the literature. Herein, a specific GeSn-on-insulator (GeSnOI) stack using stressor layers as dielectric optical claddings is demonstrated to be suitable for a monolithically integration of planar Group-IV semiconductor lasers on a versatile photonic platform for the near- and mid-infrared spectral range. Microdisk-shape resonators on mesa structures were fabricated from GeSnOI, after bonding a Ge0.9Sn0.1 alloy layer grown on a Ge strain-relaxed-buffer, itself on a Si(001) substrate. The GeSnOI microdisk mesas exhibited significantly improved optical gain as compared to that of conventional suspended microdisk resonators formed from the as-grown layer. We further show enhanced vertical out-coupling of the disk whispering gallery mode in-plane radiation, with up to 30% vertical out-coupling efficiency. As a result, the GeSnOI approach can be a valuable asset in the development of silicon-based mid-infrared photonics that combine integrated sources in a photonic platform with complex lightwave engineering.

The mechanical stability of commercial GaP/Si templates during thermal an-nealing and subsequent MOCVD growth of GaP and AlGaP is investigated.Although the GaP layer of the template originally presents an excellent surfacemorphology, annealing at high enough temperatures to remove the native oxideprior to growth leads to plastic relaxation, accompanied by a variety of defects,including a dense grid of micro-twins. These micro-twins detrimentally affectGaP and AlGaP layers grown subsequently on the template., Comment: 6 figures

Millimeter wave (mmWave) generation using photonic techniques has so far been limited to the use of near-infrared lasers that are down-converted to the mmWave region. However, such methodologies do not currently benefit from a monolithic architecture and suffer from the quantum defect i.e. the difference in photon energies between the near-infrared and mmWave region, which can ultimately limit the conversion efficiency. Miniaturized terahertz (THz) quantum cascade lasers (QCLs) have inherent advantages in this respect: their low energy photons, ultrafast gain relaxation and high nonlinearities open up the possibility of innovatively integrating both laser action and mmWave generation in a single device. Here, we demonstrate intracavity mmWave generation within THz QCLs over the unprecedented range of 25 GHz to 500 GHz. Through ultrafast time resolved techniques, we highlight the importance of modal phases and that the process is a result of a giant second-order nonlinearity combined with a phase matched process between the THz and mmWave emission. Importantly, this work opens up the possibility of compact, low noise mmWave generation using modelocked THz frequency combs., Photonic solutions for generating free space millimeter radiation is a fast developing field that combines optoelectronics and RF domains but has many challenges. Here the authors present a quantum cascade laser (QCL) based solution for THz laser emission and millimeter wave generation in a single device.

Zinc oxide (ZnO) is a II–VI group semiconductor with a wide direct bandgap and is an important material for various fields of industry and high-technological applications. The effects of thickness, annealing process in N2 and air, optical properties, and morphology of ZnO thin-films are studied. A low-cost sol–gel spin-coating technique is used in this study for the simple synthesis of eco-friendly ZnO multilayer films deposited on (100)-oriented silicon substrates ranging from 150 to 600 nm by adjusting the spin coating rate. The ZnO sol–gel thin-films using precursor solutions of molarity 0.75 M exhibit an average optical transparency above 98%, with an optical band gap energy of 3.42 eV. The c-axis (002) orientation of the ZnO thin-films annealed at 400 °C were mainly influenced by the thickness of the multilayer, which is of interest for piezoelectric applications. These results demonstrate that a low-temperature method can be used to produce an eco-friendly, cost-effective ZnO sol–gel that is compatible with a complementary metal-oxide-semiconductor (CMOS) and integrated-circuits (IC).

In atomically thin transition metal dichalcogenide semiconductors, there is a crossover from indirect to direct band gap as the thickness drops to one monolayer, which comes with a fast increase of the photoluminescence signal. Here, we show that for different alloy compositions of WS2(1−x)Se2x this trend may be significantly affected by the alloy content and we demonstrate that the sample with the highest Se ratio presents a strongly reduced effect. The highest micro-PL intensity is found for bilayer WS2(1−x)Se2x (x = 0.8) with a decrease of its maximum value by only a factor of 2 when passing from mono-layer to bi-layer. To better understand this factor and explore the layer-dependent band structure evolution of WS2(1−x)Se2x, we performed a nano-angle-resolved photoemission spectroscopy study coupled with first-principles calculations. We find that the high micro-PL value for bilayer WS2(1−x)Se2x (x = 0.8) is due to the overlay of direct and indirect optical transitions. This peculiar high PL intensity in WS2(1−x)Se2x opens the way for spectrally tunable light-emitting devices.

Electron states in semiconductor materials can be modified by quantum confinement. Adding to semiconductor heterostructures the concept of lateral geometry offers the possibility to further tailor the electronic band structure with the creation of unique flat bands. Using block copolymer lithography, we describe the design, fabrication, and characterization of multiorbital bands in a honeycomb In0.53Ga0.47As/InP heterostructure quantum well with a lattice constant of 21 nm. Thanks to an optimized surface quality, scanning tunnelling spectroscopy reveals the existence of a strong resonance localized between the lattice sites, signature of a p-orbital flat band. Together with theoretical computations, the impact of the nanopatterning imperfections on the band structure is examined. We show that the flat band is protected against the lateral and vertical disorder, making this industry-standard system particularly attractive for the study of exotic phases of matter.

International audience; Hexagonal boron nitride (h-BN) can be used as a p-doped material in wide-bandgap optoelectronic heterostructures or as a release layer to allow lift-off of grown three-dimensional (3D) GaN-based devices. To date, there have been no studies of factors that lead to or prevent lift-off and/or spontaneous delamination of layers. Here, we report a unique approach of controlling the adhesion of this layered material, which can result in both desired lift-off layered h-BN and mechanically inseparable robust h-BN layers. This is accomplished by controlling the diffusion of Al atoms into h-BN from AlN buffers grown on h-BN/sapphire. We present evidence of Al diffusion into h-BN for AlN buffers grown at high temperatures compared to conventional-temperature AlN buffers. Further evidence that the Al content in BN controls lift-off is provided by comparison of two alloys, Al 0.03 B 0.97 N/sapphire and Al 0.17 B 0.83 N/sapphire. Moreover, we tested that management of Al diffusion controls the mechanical adhesion of high-electron-mobility transistor (HEMT) devices grown on AlN/h-BN/sapphire. The results extend the control of two-dimensional (2D)/3D hetero-epitaxy and bring h-BN closer to industrial application in optoelectronics.

International audience; Single section quantum dash (QDash) mode locked lasers (MLL) can provide a flat and broadband optical frequency comb with low energy consumption, operational simplicity and large-scale low-cost production possibilities. MLL longitudinal modes can be employed as single carriers with a regular spectral spacing in a dense wavelength division multiplexing (DWDM) link, making them promising components for next generation DWDM transceivers. However, individual modes of a MLL suffer from relatively high phase noise while high capacity coherent transmission requires carriers with low phase noise. Optical feedback, which is a well-known method to reduce the linewidth of a single mode laser, can be used to stabilize comb lasers. This paper reports on the investigation of phase noise properties of comb lines delivered from a single section QDash MLL under optical feedback and shows that each MLL longitudinal mode optical linewidth can be drastically narrowed. It enables coherent transmission with extended link budget over 50 km at Tbit/s line rates.

GeSn alloys are nowadays considered as the most promising materials to build Group IV laser sources on silicon (Si) in a full complementary metal oxide semiconductor-compatible approach. Recent GeSn laser developments rely on increasing the band structure directness, by increasing the Sn content in thick GeSn layers grown on germanium (Ge) virtual substrates (VS) on Si. These lasers nonetheless suffer from a lack of defect management and from high threshold densities. In this work we examine the lasing characteristics of GeSn alloys with Sn contents ranging from 7 \% to 10.5 \%. The GeSn layers were patterned into suspended microdisk cavities with different diameters in the 4-\SI{8 }{\micro\meter} range. We evidence direct band gap in GeSn with 7 \% of Sn and lasing at 2-\SI{2.3 }{\micro\meter} wavelength under optical injection with reproducible lasing thresholds around \SI{10 }{\kilo\watt\per\square\centi\meter}, lower by one order of magnitude as compared to the literature. These results were obtained after the removal of the dense array of misfit dislocations in the active region of the GeSn microdisk cavities. The results offer new perspectives for future designs of GeSn-based laser sources., 30 pages, 9 figures

International audience; This paper presents the effect of BCB sealing ring flatness on BCB bonding for wafer-scale BCB cap transfer packaging. BCB sealing ring has shown partial bonding or full bonding depending on its flatness. It is found that the principal cause of the partial bonding is due to non-flat BCB sealing ring caused by multilayer BCB coating process. As a solution, BCB dry etching has been proposed to improve the flatness of the BCB sealing ring for full BCB bonding. Besides, partial bonding of BCB ring has been analyzed through FEM modeling of BCB cap with a non-flat sealing ring. The FEM model consists of Si carrier wafer, BCB cap, and Si target substrate. Unique load is applying pressure on top of Si carrier wafer like wafer-scale bonding. The role of applying pressure is to get BCB sealing ring to be contacted and expand bondable area with target Si substrate. As BCB sealing ring is bonded through BCB polymerization by holding the pressure for 1 hour at 250 °C, mechanical properties of virgin BCB sealing ring has been changed during bonding. Thus, it has been chosen as variable for parametric analysis. Also, BCB cap dimension has been used as another parameter for the parametric analysis.

Gain-dissipative systems of various physical origin have recently shown the ability to act as analogue minimisers of hard combinatorial optimisation problems. Whether or not these proposals will lead to any advantage in performance over the classical computations depends on the ability to establish controllable couplings for sufficiently dense short- and long-range interactions between the spins. Here, we propose a polaritonic XY-Ising machine based on a network of geometrically isolated polariton condensates capable of minimising discrete and continuous spin Hamiltonians. We elucidate the performance of the proposed computing platform for two types of couplings: relative and absolute. The interactions between the network nodes might be controlled by redirecting the emission between the condensates or by sending the phase information between nodes using resonant excitation. We discuss the conditions under which the proposed machine leads to a pure polariton simulator with pre-programmed couplings or results in a hybrid classical polariton simulator. We argue that the proposed architecture for the remote coupling control offers an improvement over geometrically coupled condensates in both accuracy and stability as well as increases versatility, range and connectivity of spin Hamiltonians that can be simulated with polariton networks., 23 pages, 3 figures, invited submission

The fruitful association of quantum and integrated photonics holds the promise to produce, manipulate, and detect quantum states of light using compact and scalable systems. Integrating all the building blocks necessary to produce high-quality photonic entanglement in the telecom-wavelength range out of a single chip remains a major challenge, mainly due to the limited performance of on-chip light rejection filters. We report a stand-alone, telecom-compliant device that integrates, on a single substrate, a nonlinear photon-pair generator and a passive pump-rejection filter. Using standard channel-grid fiber demultiplexers, we demonstrate the first entanglement qualification of such an integrated circuit, showing the highest raw quantum interference visibility for time-energy entangled photons over two telecom-wavelength bands. Genuinely pure, maximally entangled states can therefore be generated thanks to the high-level of noise suppression obtained with the pump filter. These results will certainly further promote the development of more advanced and scalable photonic-integrated quantum systems compliant with telecommunication standards.

We demonstrate multimode optomechanical sensing of individual nanoparticles with radius of a hundred of nanometers. A semiconductor optomechanical disk resonator is optically driven and detected under ambient conditions, as nebulized nanoparticles land on it. Multiple mechanical and optical resonant signals of the disk are tracked simultaneously, providing access to several physical informations about the landing analyte in real-time. Thanks to a fast camera registering the time and position of landing, these signals can be employed to weight each nanoparticle with precision. Sources of error and deviation are discussed and modeled, indicating a path to evaluate the elasticity of the nanoparticles on top of their mere mass. The device is optimized for future investigation of biological particles in the high megadalton range, such as large viruses.; Nous démontrons la détection optomécanique multimode de nanoparticules individuelles d'un rayon de quelques centaines de nanomètres. Un résonateur semi-conducteur en disque optomécanique est actionné et détecté optiquement en conditions ambiantes, pendant que des nanoparticules nébulisées se déposent sur lui. Les multiples signaux de résonances mécaniques et optiques du disque sont suivis simultanément, donnant accès en temps réel à plusieurs informations physiques sur l'analyte qui se dépose. Grâce à une caméra rapide enregistrant l'instant et la position du dépôt, ces signaux sont utilisés pour peser chaque nanoparticule avec précision. Les sources d'erreur et de déviation sont discutées et modélisées, indiquant une manière d'évaluer l'élasticité des nanoparticules en plus de leur simple masse. Le dispositif est optimisé pour l'étude de particules biologiques de l'ordre de plusieurs megadaltons, tels que certains grands virus.

III-V semiconductor lasers integrated on Si-based photonic platforms are eagerly awaited by the industry for mass-scale applications, from interconnect to on-chip sensing. The current understanding is that only quantum dot lasers can reasonably operate at the high dislocation densities generated by the III-V-on-Si heteroepitaxy, which induces high non-radiative carrier recombination rates. Here we propose a strategy based on a type-II band alignment to fabricate quantum well lasers highly tolerant to dislocations. A mid-IR GaInSb/InAs interband cascade laser grown on Si exhibits performances similar to those of its counterpart grown on the native GaSb substrate, in spite of a dislocation density in the 10 8 c m − 2 range. Over 3800 h of continuous-wave operation data have been collected, giving an extrapolated mean time to failure exceeding 312,000 h. This validates the proposed strategy and opens the way to new integrated laser development.

A new transistor architecture is developed by reusing already existing fabrication process bricks in an embedded non-volatile memory (eNVM) sub-40 nm CMOS technology, resulting in a middle-voltage zero-cost transistor, ideal for low-cost products. TCAD simulations are undertaken to confirm the feasibility of the process optimization and predict the transistor performance and reliability. The new transistor is fabricated then electrically characterized. The new device shows good analogue performances for no cost added. A hot-carrier injection (HCI) degradation evaluation is performed and confirms the reliability of the device.

International audience; We report on experiments with Möbius strip microlasers, which were fabricated with high optical quality by direct laser writing. A Möbius strip, i.e., a band with a half twist, exhibits the fascinating property that it has a single nonorientable surface and a single boundary. We provide evidence that, in contrast to conventional ring or disk resonators, a Möbius strip cavity cannot sustain whispering gallery modes (WGM). Comparison between experiments and 3D finite difference time domain (FDTD) simulations reveals that the resonances are localized on periodic geodesics.

The strain in hybrid van der Waals heterostructures, made of two distinct two-dimensional van der Waals materials, offers an interesting handle on their corresponding electronic band structure. Such strain can be engineered by changing the relative crystallographic orientation between the constitutive monolayers, notably, the angular misorientation, also known as the “twist angle”. By combining angle-resolved photoemission spectroscopy with density functional theory calculations, we investigate here the band structure of the WS2/graphene heterobilayer for various twist angles. Despite the relatively weak coupling between WS2 and graphene, we demonstrate that the resulting strain quantitatively affects many electronic features of the WS2 monolayers, including the spin-orbit coupling strength. In particular, we show that the WS2 spin-orbit splitting of the valence band maximum at K can be tuned from 430 to 460 meV. Our findings open perspectives in controlling the band dispersion of van der Waals materials.

We propose a unified description of intersubband absorption saturation for quantum wells inserted in a resonator, both in the weak and strong light-matter coupling regimes. We demonstrate how absorption saturation can be engineered. In particular, we show that the saturation intensity increases linearly with the doping in the strong coupling regime, while it remains doping independent in weak coupling. Hence, countering intuition, the most suitable region to exploit low saturation intensities is not the ultrastrong coupling regime, but is instead at the onset of the strong light-matter coupling. We further derive explicit conditions for the emergence of bistability. This Letter sets the path toward, as yet, nonexistent ultrafast midinfrared semiconductor saturable absorption mirrors (SESAMs) and bistable systems. As an example, we show how to design a midinfrared SESAM with a 3 orders of magnitude reduction in saturation intensity, down to ≈5 kW cm^{-2}.

In this work, we measure and tune simultaneously the vibration of a 1-nm thick MoS2 suspended monolayer with standard electrical excitation and optical techniques. At ambient temperature, we first investigate the strong parametric coupling between two different mechanical modes (ω1 and ω2). We demonstrate a high and quasi-linear tunability of the mode frequencies with the parametric pump voltage. Then, we couple the highly tunable main vibration (ω1) to a parametric pump frequency (ωp) to obtain a high number of sidebands at frequencies ω1 ± m ωp, driving the mechanical mode with a large external electrical force. This oscillating force, applied via the gate voltage, acts as a stress onto the MoS2 sheet. The obtained frequency comb has a large spectral band and contains up to 100 harmonics, with potential applications in quantum information processing and heat or sound transport.

Nanowire (NW)-based opto-electronic devices require certain engineering in the NW geometry to realize polarized-dependent light sources and photodetectors. We present a growth procedure to produce InAs/InP quantum dot-nanowires (QD-NWs) with an elongated top-view cross-section relying on the vapor-liquid-solid method using molecular beam epitaxy. By interrupting the rotation of the sample during the radial growth sequence of the InP shell, hexagonal asymmetric (HA) NWs with long/short cross-section axes were obtained instead of the usual symmetrical shape. Polarization-resolved photoluminescence measurements have revealed a significant influence of the asymmetric shaped NWs on the InAs QD emission polarization with the photons being mainly polarized parallel to the NW long cross-section axis. A degree of linear polarization (DLP) up to 91% is obtained, being at the state of the art for the reported DLP values from QD-NWs. More importantly, the growth protocol herein is fully compatible with the current applications of HA NWs covering a wide range of devices such as polarized light emitting diodes and photodetectors., 20 pages, 7 figures

We study the low frequency admittance of a quantum Hall bar of size much larger than the electronic coherence length. We find that this macroscopic conductor behaves as an ideal quantum conductor with vanishing longitudinal resistance and purely inductive behavior up to f, 4 pages article with 4 figures, submitted to Physical Review B Letters, concatenated with 12 pages supplementary information (having 15 figures) in a 17 pages article with concantenated bibliography

Single Photon Avalanche Diodes (SPAD) are key optoelectronic detectors for medical imaging, camera ranging and automotive laser imaging detection and ranging (LiDAR) applications. Today, most of SPADs in the Time Of Flight (TOF) market are composed of a micrometric Silicon PN junction associated to a proximity CMOS electronics biasing the system above the breakdown voltage. These devices present low noise, high pixel-matrix integration capabilities, but their Photon Detection Efficiency (PDE) is relatively modest in the near infrared operating region (achieving typically only few percent at a wavelength of 940 nm). A considerable optimisation of the SPAD design is currently on going at an industrial level with a view of increasing the PDE without compromising the timing statistic response to avalanche (Jitter) and its quench probability. Within these perspectives, standard commercial Technology-Computer-Assisted-Design (TCAD) simulations can only provide a limited guidance for technological and design splits optimisation since they are based on deterministic solvers that are unable to capture these stochastic figures of merit. Since the seminal work from Spinelli [1] clearly showing that Monte Carlo simulations predictions can compare favourably with experimental measurements of PDE and timing resolution, the Monte Carlo method can be considered to be a useful one for the design of improved structures. It has been recently applied to optimize the PDE and Jitter of Silicon [3] and InGaAs SPADs [4],[5]. In this abstract we report a rigorous comparison between Monte Carlo predictions and measurements of PDE and Jitter. We also discuss in detail, the quench probability of these diodes once in avalanche. This latter point has rarely been discussed in literature and to the best of our knowledge never addressed within a Monte Carlo perspective.

International audience; Polymer materials attract more and more interests for a biocompatible package of novel implantable medical devices. Medical implants need to be packaged in a biocompatible way to minimize FBR (Foreign Body Reaction) of the implant. One of the most advanced implantable devices is neural prosthesis device, which consists of polymeric neural electrode and silicon neural signal processing integrated circuit (IC). The overall neural interface system should be packaged in a biocompatible way to be implanted in a patient. The biocompatible packaging is being mainly achieved in two approaches; (1) polymer encapsulation of conventional package based on die attach, wire bond, solder bump, etc. (2) chip-level integrated interconnect, which integrates Si chip with metal thin film deposition through sacrificial release technique. The polymer encapsulation must cover different materials, creating a multitude of interface, which is of much importance in long-term reliability of the implanted biocompatible package. Another failure mode is bio-fluid penetration through the polymer encapsulation layer. To prevent bio-fluid leakage, a diffusion barrier is frequently added to the polymer packaging layer. Such a diffusion barrier is also used in polymer-based neural electrodes. This review paper presents the summary of biocompatible packaging techniques, packaging materials focusing on encapsulation polymer materials and diffusion barrier, and a FEM-based modeling and simulation to study the biocompatible package reliability.

International audience; Slot-die coating is a promising technique paving the way for large-area perovskite deposition and commercially relevant solar devices fabrication with sharp control over the thickness and material composition. However, before transferring perovskite solar cells technology to commercial applications, it is required to develop ink formulations guaranteeing

International audience; We report on AlGaAs-based heterojunction solar cells grown by solid source molecu- lar beam epitaxy (MBE). We investigate InGaP and AlGaAs material quality and we demonstrate significant efficiency improvements by combining the best of each alloy: a thick p-AlGaAs base with tunable bandgap, and a thin 50 nm n-InGaP emitter separated by a thin intrinsic AlGaAs layer. We report a certified solar cell conversion efficiency of 18.7% with a 2-μm-thick AlGaAs layer and a bandgap of 1.73 eV, suit- able for high efficiency Si-based tandem devices.

Waveguide integrated optical modulators in the mid-infrared wavelength range are of significant interest for molecular spectroscopy. This is because on-chip synchronous detection can improve the performance of detection systems and can also be used for free-space communications where optical modulators working in atmospheric transparency windows are needed. Here we report optical modulation in a mid-infrared photonic circuit, reaching wavelengths larger than 8 µm. Optical modulation in the wavelength range from 5.5 to 11 µm is shown, relying on a broadband Ge-rich graded-SiGe platform. This demonstration experimentally confirms the free-carrier absorption effect modeling. These results pave the way towards efficient high-performance electrically-driven integrated optical modulators in the mid-infrared wavelength range. Mid-infrared optical modulators are important for detecting compounds in a wide range of applications, but are typically limited to short wavelengths. Now, a SiGe waveguide is used to fabricate an optical modulator that can reach wavelengths spanning 5.5 µm to 11 µm.

International audience; We report on the development of highly reflective back contacts (RBCs) made of multilayer stacks for ultrathin CIGS solar cells. Two architectures are compared: they are made of a silver mirror coated either with a single layer of In2O3:Sn (ITO) or with a bilayer of ZnO:Al/ITO. Due to the improvement of CIGS rear reflectance, both back contacts result in a significant external quantum efficiency enhancement, in agreement with optical simulations. However, solar cells fabricated with Ag/ITO back contacts exhibit a strong shunting behavior. The key role of the ZnO:Al layer to control the morphology of the top ITO layer and to avoid silver diffusion through the back contact is highlighted. For a 500-nm-thick CIGS layer, this optimized RBC leads to a best cell with a short-circuit current of 27.8 mA/cm2 (+2.2 mA/cm2 as compared to a Mo back contact) and a 12.2%-efficiency (+2.5% absolute).

International audience; We report the first investigation of indium (In) as the vapor-liquid-solid catalyst of GaP and GaAs nanowires by molecular beam epitaxy. A strong asymmetry in the Ga distribution between the liquid and solid phases allows one to obtain pure GaP and In 0.2 Ga 0.8 As nanowires while the liquid catalyst remains nearly pure In. This uncommon In catalyst presents several advantages. First, the nanowire morphology can be tuned by changing the In flux alone, independently of the Ga and group V fluxes. Second, the nanowire crystal structure always remains cubic during steady state growth and catalyst crystallization, despite the low contact angle of the liquid droplet measured after growth (95 •). Third, the vertical yield of In-catalyzed GaP and (InGa)As nanowires arrays on patterned silicon substrates increases dramatically. Combining straight sidewalls, controllable morphologies and a high vertical yield, In-catalysts provide an alternative to the standard Au or Ga alloys for the bottom-up growth of large scale homogeneous arrays of (InGa)As or GaP nanowires. We note that the SET and NT curves nearly coincide over all 78 the explored composition range. This typical of NW growth and 79 was already observed by Glas on [Ga]-(AlGa)As NWs 34. It relates 80 to the low concentration of group V in the liquid catalyst, as com-81 puted using SET (see Supplementary Information †) or deduced 82 from other experiments 36. 83 From both NT and SET, we find that the Ga distribution is 84 strongly asymmetric. This particular Ga distribution is not unique 85 to our system and similar curves were calculated for ternary 86 [Au]-(InGa)As NWs using NT 25. These fast changes in the solid 87 (x) at near constant liquid composition (y) are often hindering 88 the fabrication of NW with uniform composition. Yet, away from 89 these abrupt changes, the solid composition varies slowly over 90 large ranges of liquid composition. Most relevant to the present 91 work, Ga contents (x) in solid In 1−x Ga x P and In 1−x Ga x As reach 92 near unity while the Ga fractions (y) in the liquid remain below 93 a few atomic percents. Hence the VLS growth of nearly pure GaP 94 and GaAs NWs from nearly pure In catalyst seems achievable. 95 3 Steady state growth 96 In light of the above calculations, we have proceeded to grow 97 [In]-(InGa)P and [In]-(InGa)As NWs on patterned Si(111) sub-98 strates using MBE (see experimental). Both In and Ga atoms are 99 supplied continuously to sustain the NW growth so that In evap-100 oration is compensated and the catalyst composition remains In-101 rich. Compared to [Ga]-GaAs or [Ga]-GaP NWs, typically grown 102 at 600 • C 15,36 , the substrate temperature is reduced to 520 • C to 103 limit the evaporation of In adatoms. Identical Si(111) wafers with 104 hexagonal arrays (300 nm pitch) of 50 nm diameter holes in a 105 14 nm thick silica mask are used to grow selectively the GaAs and 106 GaP NWs. The details of the growth and patterning procedures 107 can be found in the experimental section.

International audience; Helical microrobots with dimensions below 100 mm could serve many applications for manipulation and sensing in small, closed environments such as blood vessels or inside microfluidic chips. However, environmental conditions such as surface stiction from the channel wall or local flow can quickly result in the loss of control of the microrobot, especially for untrained users. Therefore, to automatically adapt to changing conditions, we propose an algorithm that switches between a surfacebased motion of the microrobot and a 3D swimming motion depending on the local flow value. Indeed swimming is better for avoiding obstacles and difficult surface stiction areas but it is more sensitive to the flow than surface motion such as rolling or spintop motion. First, we prove the flow sensing ability of helical microrobots based on the difference between the tracked and theoretical speed. For this, a 50 mm long and 5 mm diameter helical microrobot measures the flow profile shape in two different microchannels. These measurements are then compared with simulation results. Then, we demonstrate both swimming and surface-based motion using closed-loop control. Finally, we test our algorithm by following a 2D path using closedloop control, and adapting the type of motion depending on the flow speed measured by the microrobot. Such results could enable simple high-level control that could expand the development of microrobots toward applications in complex microfluidic environments.

International audience; Power consumption, thermal management, and wiring challenge of the binary serial architecture drive the search for alternative paradigms to computing. Of special interest is neuromorphic computing, in which materials and device structures are designed to mimic neuronal functionalities with energy-efficient non-linear responses and both short- and long-term plasticities. In this work, we explore and report on the enabling potential of single-electron tunneling (SET) in PbS nanoplatelets epitaxially grown in the liquid phase on InP, which present these key features. By extrapolating the experimental data in the SET regime, we predict and model synaptic operations. The low-energy (

4 pags., 5 figs., Integrated microspectrometers implemented in silicon photonic chips have gathered a great interest for diverse applications such as biological analysis, environmental monitoring, and remote sensing. These applications often demand high spectral resolution, broad operational bandwidth, and large optical throughput. Spatial heterodyne Fourier-transform (SHFT) spectrometers have been proposed to overcome the limited optical throughput of dispersive and speckle-based on-chip spectrometers. However, state-of-the-art SHFT spectrometers in near-infrared achieve large optical throughput only within a narrow operational bandwidth. Here we demonstrate for the first time, to the best of our knowledge, a broadband silicon nitride SHFT spectrometer with the largest light collecting multiaperture input (320 × 410 µm) ever implemented in an SHFT on-chip spectrometer. The device was fabricated using 248 nm deep-ultraviolet lithography, exhibiting over 13 dB of optical throughput improvement compared to a single-aperture device. The measured resolution varies between 29 and 49 pm within the 1260-1600 nm wavelength range., Spanish Ministry of Science and Innovation (MICINN) (RED2018-102768-T, RTI2018-097957-B-C33, TEC2015-71127-C2-1-R (FPI Scholarship BES-2016-077798)); Community of Madrid-FEDER funds (S2018/NMT-4326); Horizon 2020 Research and Innovation Program (Marie Sklodowska-Curie 734331); H2020 European Research Council (ERC POPSTAR 647342); European Commission (H2020- ICT-26127-2017 COSMICC 688516); French Industry Ministry (Nano2022 project under IPCEI program); Agence Nationale de la Recherche (ANR-MIRSPEC-17-CE09-0041

International audience; We report on the microscopic behavior of residual hydrogen on nanometric field emitters. By using homogeneous or heterostructured semiconductor specimens analyzed in a laser-assisted atom probe, it is possible to study how the relative abundances of the ionic species H+, H2+, and H3+ depend on the microscopic electric field, estimated through post-ionization statistics. In the case of Ga-containing semiconductors, the relative abundances of H+, H2+, and H3+ follow a common trend, independent of the nonmetallic component of the matrix. The dependence of the total H flux on the electric field exhibits a more complex behavior, which depends also on the spatial direction of the variation of the field (in-depth or on-surface). The analysis of multiple detection events provides further insights into surface chemistry. Noticeably, H+–H3+ ion pairs are both correlated in number and separated by very small distances on the detector space, suggesting a possible reaction 2H2 → H3++H++2e– taking place on the field emitter surface.

Depositions of the dielectric thin-films at low temperatures without greenhouse gas, nitrous oxide (N $$_{2}$$ O) is one of the most critical challenges in modern technologies for microelectronics, optoelectronics, and nanoelectronics. The present study demonstrates that thin dielectric layers deposit by inductively-coupled plasma-enhanced chemical vapor deposition (ICPECVD) technology at lower temperatures ( $$< 300\,^{\circ }$$ C) can be successfully optimized and has the potential to reduce the environmental impact significantly. A particular focus is made on the improvement of the optical properties that are strongly correlated to the physicochemical bonds film properties. Typical deposition rates range from 10 to 20 nm/min, depending mainly on power, pressure, and gas flows. This study opens up large scale applications that require lower hydrogen content and a stable process. The presented results emphasize green manufacturing technologies and can be valuable for a wide range of applications using a complementary metal-oxide-semiconductor (CMOS)-compatible technology.

International audience; In recent years, neural network models [1] have demonstrated human-level competency in multiple tasks, such as pattern recognition, [2] game playing, [3] and strategy development. [4] This progress has led to the promise that a new generation of intelligent computing systems could be applied to such high-complexity tasks at the edge. [5] However, the current generation of edge computing hardware cannot support the energetic demands nor the data volume required to train and adapt such neural network models locally at the edge. [6,7] One solution is ex situ training: a software model is trained on a cloud computing platform and then subsequently transferred onto a hardware system that acts only to perform inference. [8,9] The engine room of such inference hardware is the dot-product (multiply-and-accumulate) operation that is ubiquitous in machine learning. Non-von Neumann dot-product implementations based on nonvolatile resistive random access memory (RRAM) [10-13] technologies, otherwise known as memristors, are a particularly promising path toward reducing the energy required during inference. Here, the dot product between an input voltage vector and an array of RRAM conductance states, storing the parameters of the model, can be evaluated in-memory through the physics of Ohm's and Kirchhoff m's laws-obviating the need to transfer information on-chip. [14,15] In these systems, however, intrinsic cycle-to-cycle and device-to-device conductance variability constitute a considerable challenge. This random variability constrains the number of separable multilevel conductance states that can be achieved, preventing the high-precision transfer of the model parameters in a single programming step. To mitigate against this variability, iterative closed-loop programming schemes (also referred to as program-verify schemes) are often used, whereby devices are repeatedly programmed until their conductance falls within a discretized window of tolerated error. However, such approaches entail costly circuit overheads as well as energy and time during model transfer. [16-18] Other approaches propose to use multiple one-transistor-one-resistor (1T1R) structures in parallel at each array cross-point, [19-21] which, although allow for a higher precision in the transferred weight, entail additional costs in area and transfer energy. Other approaches propose to sidestep intrinsic randomness altogether through the quantization of conductance levels into one of either a low-conductance state (LCS) or a highconductance state (HCS) in binarized neural networks. [22] However, such models require a significantly higher number of neuron elements and model parameters to approach the performance of conventional neural networks. [23] The reality is that the programming of resistive memory is an inherently random process, and the devices, therefore, are not well suited to being treated as deterministic quantities.

International audience; In this contribution, we propose an experimentally-validated systemlevel model of a magnetoelectric transducer and a general methodology for future characterization of similar transducers. This methodology provides insights into the main origin of power losses. An analogy with piezoelectric generators leads to a system-level figure of merit which is strongly impacted by the nonlinear behavior of the transducer. Considering the complexity of the observed nonlinear behavior, we opt for a grey-box model of the dependencies between the transducer characteristics and the operating point. Applying our methodology to an optimized sample shows that nonlinear mechanical losses are the main origin of power dissipation. The maximum transferable power is proven to be up to 61% lower than the power one would expect from a linear characterization.

International audience; We have developed and tested a novel microfluidic device for blood oxygenation, which exhibits a large surface area of gas exchange and can support long-term sustainable endothelialization of blood microcapillaries, enhancing its hemocompatibility for clinical applications. The architecture of the parallel stacking of the trilayers is based on a central injection for blood and a lateral injection/output for gas which allows significant reduction in shear stress, promoting sustainable endothelialization since cells can be maintained viable for up to 2 weeks after initial seeding in the blood microchannel network. The circular design of curved blood capillaries allows covering a maximal surface area at 4 inch wafer scale, producing high oxygen uptake and carbon dioxide release in each single unit. Since the conventional bonding process based on oxygen plasma cannot be used for surface areas larger than several cm2, a new “wet bonding” process based on soft microprinting has been developed and patented. Using this new protocol, each 4 inch trilayer unit can be sealed without a collapsed membrane even at reduced 15 μm thickness and can support a high blood flow rate. The height of the blood channels has been optimized to reduce pressure drop and enhance gas exchange at a high volumetric blood flow rate up to 15 ml min−1. The simplicity of connecting different units in the stacked architecture is demonstrated for 3- or 5-unit stacked devices that exhibit remarkable performance with low primary volume, high oxygen uptake and carbon dioxide release and high flow rate of up to 80 ml min−1.

International audience; The low sensitivity of photons to external magnetic fields is one of the major challenges for the engineering of photonic lattices with broken time-reversal symmetry. Here we show that time-reversal symmetry can be broken for microcavity polaritons in the absence of any external magnetic field thanks to polarization dependent polariton interactions. Circularly polarized excitation of carriers in a micropillar induces a Zeeman-like energy splitting between polaritons of opposite polarizations. In combination with optical spin-orbit coupling inherent to semiconductor microstructures, the interaction induced Zeeman splitting results in emission of vortical beams with a well-defined chirality. Our experimental findings can be extended to lattices of coupled micropillars opening the possibility of controling optically the topological properties of polariton Chern insulators.

International audience; We study experimentally and theoretically the consumption of the apical gallium droplet that mediates the self-catalyzed vapor-liquid-solid growth of GaP nanowires. Consumption is achieved after growth by providing only phosphorous and its progress is monitored ex situ in nanowire arrays fabricated by molecular beam epitaxy. We develop detailed calculations of the process, taking into account four channels of liquid gallium consumption. These include the formation of GaP using phosphorous delivered to the droplet by direct impingement or after re-emission from the substrate. We show that two other channels contribute significantly, namely the diffusion of phosphorous along the sidewalls and gallium back diffusion from the droplet. All currents are calculated analytically as a function of droplet geometry. Complementary experiments are performed to extract the two model parameters governing the diffusion currents. We then compute numerically the dynamics of the system exposed to a constant external phosphorous flux. Our quantitative model allows one to predict how droplet contact angle and radius change while operating blindly in a standard epitaxy chamber. Controlling these parameters is crucial for tailoring the crystal phase of III-V nanowires and fabricating quantum size structures.

International audience; The giant negative magnetoresistance (GNMR), observed in two-dimensional electron gases of high mobility, is studied by controlled definition of additional short-range scatterers in form of two-dimensional Lorentz arrays of varying obstacle density, as well as in the presence of edge scattering. The results support models, which ascribe the temperature-independent regime of the GNMR to strong, classical scattering and the temperaturedependent regime to electron-electron interactions under the influence of mixed disorder. The threshold magnetic field, which separates the two regimes, is in rough agreement with the lower percolation transition of the Lorentz array. At large obstacle densities, interaction corrections are suppressed and memory effects become more relevant. Shape, amplitude, and width of the GNMR depend sensitively on the time scales of the contributing scattering mechanisms. This can lead to qualitatively similar shapes for quite different parameter values.

International audience; Radiofrequency (RF) coils fashioned from high-temperature superconductor (HTS) have the potential to increase the sensitivity of the magnetic resonance imaging (MRI) experiment by more than a dozen times compared to conventional copper coils. Progress, however, has been slow due to a series of technological hurdles. In this article, we present the developments that recently led to new perspectives for HTS coil in MRI, and challenges that still need to be solved. First, we recall the motivations for the implementations of HTS coils in MRI by presenting the limits of cooled copper coil technology, such as the anomalous skin effect limiting the decrease of the electric resistance of normal conductors at low temperature. Then, we address the progress made in the development of MRI compatible cryostats. New commercially available low-noise pulsed-tube cryocoolers and new materials removed the need for liquid nitrogen-based systems, allowing the design of cryogen-free and more user-friendly cryostats. Another recent advance was the understanding of how to mitigate the imaging artifacts induced by HTS diamagnetism through field cooling or temperature control of the HTS coil. Furthermore, artifacts can also originate from the RF field coupling between the transmission coil and the HTS reception coil. Here, we present the results of an experiment implementing a decoupling strategy exploiting nonlinearities in the electric response of HTS materials. Finally, we discuss the potential applications of HTS coils in bio-imaging and its prospects for further improvements. These include making the technology more user-friendly, implementing the HTS coils as coil arrays, and proposing solutions for the ongoing issue of decoupling. HTS coil still faces several challenges ahead, but the significant increase in sensitivity it offers lends it the prospect of being ultimately disruptive.

The manipulation of fast domain wall motion in magnetic nanostructures could form the basis of novel magnetic memory and logic devices. However, current approaches for reading and writing domain walls require external magnetic fields, or are based on conventional magnetic tunnel junctions (MTJs) that are not compatible with high-speed domain wall motion. Here we report domain wall devices based on perpendicular MTJs that offer electrical read and write, and fast domain wall motion via spin-orbit torque. The devices have a hybrid free layer design that consists of platinum/cobalt (Pt/Co) or a synthetic antiferromagnet (Pt/Co/Ru/Co) into the free layer of conventional MTJs. We show that our devices can achieve good tunnelling magnetoresistance readout and efficient spin-transfer torque writing that is comparable to current magnetic random-access memory technology, as well as domain wall depinning efficiency that is similar to stand-alone materials. We also show that a domain wall conduit based on a synthetic antiferromagnet offers the potential for reliable domain wall motion and faster write speed compared with a device based on Pt/Co. Domain wall devices based on perpendicular magnetic tunnel junctions with a hybrid free layer design can offer electrical read and write, and fast domain wall motion driven via spin-orbit torque.

We present an experimental study of vortex dynamics in magnetic nanocontacts based on pseudo spin valves comprising the ${\mathrm{Co}}_{2}\mathrm{MnGe}$ Heusler compound. The films were grown by molecular beam epitaxy, where precise stoichiometry control and tailored stacking order allowed us to define the bottom ferromagnetic layer as the reference layer, with minimal coupling between the free and reference layers. 20-nm diameter nanocontacts were fabricated using a nanoindentation technique, leading to self-sustained gyration of the vortex generated by spin-transfer torques above a certain current threshold. By combining frequency- and time-domain measurements, we show that different types of spin-transfer induced dynamics related to different modes associated to the magnetic vortex configuration can be observed, such as mode hopping, mode coexistence, and mode extinction appearing in addition to the usual gyration mode.

The nitrogen-vacancy (NV) defect in diamond is an efficient quantum sensor of randomly fluctuating signals via relaxometry measurements. In particular, the longitudinal spin relaxation of the NV defect accelerates in the presence of magnetic noise with a spectral component at its electron spin resonance frequency. We look into this effect quantitatively by applying a calibrated and tunable magnetic noise on a single NV defect. We show that an increase of the longitudinal spin relaxation rate translates into a reduction of the photoluminescence (PL) signal emitted under continuous optical illumination, which can be explained using a simplified three-level model of the NV defect. This PL quenching mechanism offers a simple, all-optical method to detect magnetic noise sources at the nanoscale., 5 pages, 3 figures

Funding Information: The authors J.E., C.D. and A.K. would like to thank Jean Dussaud for his work on the MOVPE setup. V.N. would like to thank Maria Baeva for her assistance with the stretchable LED transparency measurements.J.E., C.D. and A.K. thank French National Labex GaNeX (ANR-11-LABX-0014) for MW synthesis and CL measurements. V.N. thanks the Russian Foundation for Basic Research (RFBR project no. 19-32-60040) for PDMS/MW membrane fabrication and optical measurements. I.S.M., V.N., F.M.K. thank the support from the Russian Science Foundation (grant 20-19-00256) for PDMS synthesis and electrical measurements. D.K. and A.G.N. thank Russian Foundation of Basic Research project no. 20-03-00804 for the synthesis of carbon nanotubes. F.E.K. thanks the support from the Russian Science Foundation (grant 19-79-00313) for the LED array encapsulation and membrane transfer. I.S.M., F.M.K., V.N., V.A.M., S.M., A.A.V., A.V.U., and D.A.M. thank the Ministry of Science and Higher Education of the Russian Federation (FSRM-2020-0005) for the general support. N.A. and M.T. acknowledge the financial support from the ITN Marie Curie project INDEED (grant no. 722176), by the Indo-French Centre for the Promotion of Advanced Research (IFCPAR/CEFIPRA project no. 6008-1) for MW/PDMS membrane processing and characterization. Funding Information: Funding: J.E., C.D. and A.K. thank French National Labex GaNeX (ANR-11-LABX-0014) for MW synthesis and CL measurements. V.N. thanks the Russian Foundation for Basic Research (RFBR project no. 19-32-60040) for PDMS/MW membrane fabrication and optical measurements. I.S.M., V.N., F.M.K. thank the support from the Russian Science Foundation (grant 20-19-00256) for PDMS synthesis and electrical measurements. D.K. and A.G.N. thank Russian Foundation of Basic Research project no. 20-03-00804 for the synthesis of carbon nanotubes. F.E.K. thanks the support from the Russian Science Foundation (grant 19-79-00313) for the LED array encapsulation and membrane transfer. I.S.M., F.M.K., V.N., V.A.M., S.M., A.A.V., A.V.U., and D.A.M. thank the Ministry of Science and Higher Education of the Russian Federation (FSRM-2020-0005) for the general support. N.A. and M.T. acknowledge the financial support from the ITN Marie Curie project INDEED (grant no. 722176), by the Indo-French Centre for the Promotion of Advanced Research (IFCPAR/CEFIPRA project no. 6008-1) for MW/PDMS membrane processing and characterization. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. We propose and demonstrate both flexible and stretchable blue light-emitting diodes based on core/shell InGaN/GaN quantum well microwires embedded in polydimethylsiloxane membranes with strain-insensitive transparent electrodes involving single-walled carbon nanotubes. InGaN/GaN core-shell microwires were grown by metal-organic vapor phase epitaxy, encapsulated into a polydimethylsiloxane film, and then released from the growth substrate. The fabricated free-standing membrane of light-emitting diodes with contacts of single-walled carbon nanotube films can stand up to 20% stretching while maintaining efficient operation. Membrane-based LEDs show less than 15% degradation of electroluminescence intensity after 20 cycles of stretching thus opening an avenue for highly deformable inorganic devices.

Polycrystalline thin-film solar cells are attractive for low-cost photovoltaics, but their efficiencies are hindered by material quality issues. State-of-the-art CdTe solar cells use ${\mathrm{CdCl}}_{2}$ annealing treatments whose effects are still being discovered at a fundamental level. Here, a series of CdTe samples with different annealing temperatures is investigated with high-resolution hyperspectral cathodoluminescence mapping measured at both room temperature and low temperature on the same microscopic areas. A statistical analysis over a large number of grains is combined with a local analysis at grain boundaries. The results elucidate the dynamic interplay between grain boundary and intragrain defect passivation and formation, in the midst of grain growth. The ${\mathrm{CdCl}}_{2}$ annealing initially contributes to an increase of the grain size and the passivation of both grain boundaries and grain interiors, increasing the overall luminescence and diffusion length. For higher annealing temperatures, a further increase of grain size is counterbalanced by the rise of bulk defects. The results illustrate the tradeoffs that lead to an optimal annealing temperature, as well as new methods for understanding defect passivation and creation in thin film solar cells.

Two-dimensional (2D) semiconductors are promising channel materials for next-generation field-effect transistors (FETs) thanks to their unique mechanical properties and enhanced electrostatic control. However, the performance of these devices can be strongly limited by the scattering processes between carriers and phonons, usually occurring at high rates in 2D materials. Here, we use quantum transport simulations calibrated on first-principle computations to report on dissipative transport in antimonene and arsenene n-type FETs at the scaling limit. We show that the widely-used approximations of either ballistic transport or simple acoustic deformation potential scattering result in large overestimation of the ON current, due to neglecting the dominant intervalley and optical phonon scattering processes. We additionally investigate a recently proposed valley engineering strategy to improve the device performance by removing the valley degeneracy and suppressing most of the intervalley scattering channels via an uniaxial strain along the zigzag direction. The method is applicable to other similar 2D semiconductors characterized by multivalley transport., npj 2D Materials and Applications, 5 (1), ISSN:2397-7132

We use time-resolved measurement and modeling to study the spin-torque induced motion of a domain wall in perpendicular anisotropy magnets. In disc of diameters between 70 and 100 nm, the wall drifts across the disc with pronounced back-and-forth oscillations that arise because the wall moves in the Walker regime. Several switching paths occur stochastically and lead to distinct switching durations. The wall can cross the disc center either in a ballistic manner or with variably marked oscillations before and after the crossing. The crossing of the center can even occur multiple times if a vertical Bloch line nucleates within the wall. The wall motion is analyzed using a collective coordinate model parametrized by the wall position $q$ and the tilt $\phi$ of its in-plane magnetization projection. The dynamics results from the stretch field, which describes the affinity of the wall to reduce its length and the wall stiffness field describing the wall tendency to reduce dipolar energy by rotating its tilt. The wall oscillations result from the continuous exchange of energy between to the two degrees of freedom $q$ and $\phi$. The stochasticity of the wall dynamics can be understood from the concept of the retention pond: a region in the $q-\phi$ space in which walls are transiently bound to the disc center. Walls having trajectories close to the pond must circumvent it and therefore have longer propagation times. The retention pond disappears for a disc diameter of typically 40 nm: the wall then moves in a ballistic manner irrespective of the dynamics of its tilt. The propagation time is then robust against fluctuations hence reproducible., Comment: submitted to Phys. Rev. B

The ultraconfined light of plasmonic modes put their effective wavelength close to the mean free path of electrons inside the metal electron gas. The Drude model, which can not take the repulsive interactions of electrons into account, then clearly begins to show its limits. In an intermediate length scale where a full quantum treatment is computationally prohibitive, the semiclassical hydrodynamic model, instrinsically non-local, has proven successful. Here we generalize the expression for the absorption volume density and the reciprocity theorem in the framework of this hydrodynamic model. We validate numerically these generalized theorems and show that using classical expressions instead leads to large discrepancies., 10 pages, 8 figures