In the search for novel technology platforms supporting the transition towards ”beyond 6G” telecommunications, magnonics is emerging as a viable route, primarily due to its intrinsic compatibility with the UWB-FR3 bands and its easy tunability. In this paper, we present a proof-of-concept device based on a CoFeB magnonic waveguide, fully integrated on silicon, which demonstrates all the key features of our integration approach, based on co-integrated hard magnetic micromagnets, magnonic conduits, reconfigurable soft magnetic elements and MEMS. The bias field enabling operation up to about 12 GHz is provided by SmCo micromagnets embedded in the silicon substrate. Real-time tunability is implemented in two ways. First, current-driven control is achieved via an integrated current line that generates an additional localized magnetic field, enabling continuous tuning of Backward Volume spin-wave propagation. Second, we achieve voltage-controlled tunability by integrating a NiFeMo soft magnetic element onto a piezoelectric MEMS cantilever and flip-chipping it onto the magnonic device. Upon actuation, the cantilever brings the NiFeMo into proximity with the permanent micromagnets, where it captures the stray field. The resulting voltage-controlled displacement modulates the coupling between the hard and soft magnetic components, effectively reducing the local bias field on the CoFeB waveguide and enabling fine control of Damon–Eshbach spin waves.

Our multifunctional bonding layer for III-V//Si tandem solar cells uses an innovative architecture boasting high transparency, conductivity, and Si surface roughness accommodation, eliminating costly polishing requirements. An optical loss analysis demonstrated the feasibility of current-matching.

Nanowires (NWs) offer unique possibilities to control semiconductor heterostructures and polytypes at the nanometer scale. The crystal structure of GaAs can be switched from bulk cubic zinc blende (ZB) to the hexagonal wurtzite (WZ) phase, but the properties and doping of WZ GaAs are still poorly known. Here, we grow high-quality GaAs NWs containing large segments of pure ZB and WZ phases using self-catalyzed, vapor-liquid-solid molecular beam epitaxy. Undoped, Be-doped and Si-doped WZ GaAs are investigated by high-resolution cathodoluminescence (CL) at low temperature (10 K). The luminescence originating from the WZ region is unambiguously distinguished by its strong anisotropy, evidenced by polarimetry. In undoped GaAs, the WZ CL peak is found ∼1 meV higher than the free exciton energy in ZB. The recombination dynamics is probed by time-resolved CL and features a lifetime of 0.6 ns for exciton recombination and 1.65 ns for the free-electron-to-acceptor transition. From Be-doped NWs, we infer an ionization energy of ∼30 meV for the Be acceptor in GaAs WZ. The CL spectra broaden and redshift with increasing Be concentration due to the bandgap narrowing, following a trend similar to GaAs ZB. Si-doped WZ GaAs exhibits a low-energy CL peak (1.47 eV) attributed to the donor-acceptor pair recombination involving Si impurities. The degree of polarization of WZ luminescence decreases with increasing doping levels for both p-type and n-type. These results shed light on the properties and doping of WZ GaAs and show that time-resolved CL and CL polarimetry constitutes a powerful tool to characterize the crystal phase, local defect, transport and recombination mechanism at the nanoscale.

Nanowires (NWs) offer unique possibilities to control semiconductor heterostructures and polytypes at the nanometer scale. The crystal structure of GaAs can be switched from bulk cubic zinc blende (ZB) to the hexagonal wurtzite (WZ) phase, but the properties and doping of WZ GaAs are still poorly known. Here, we grow high-quality GaAs NWs containing large segments of pure ZB and WZ phases using self-catalyzed, vapor-liquid-solid molecular beam epitaxy. Undoped, Be-doped and Si-doped WZ GaAs are investigated by high-resolution cathodoluminescence (CL) at low temperature (10 K). The luminescence originating from the WZ region is unambiguously distinguished by its strong anisotropy, evidenced by polarimetry. In undoped GaAs, the WZ CL peak is found ∼1 meV higher than the free exciton energy in ZB. The recombination dynamics is probed by time-resolved CL and features a lifetime of 0.6 ns for exciton recombination and 1.65 ns for the free-electron-to-acceptor transition. From Be-doped NWs, we infer an ionization energy of ∼30 meV for the Be acceptor in GaAs WZ. The CL spectra broaden and redshift with increasing Be concentration due to the bandgap narrowing, following a trend similar to GaAs ZB. Si-doped WZ GaAs exhibits a low-energy CL peak (1.47 eV) attributed to the donor-acceptor pair recombination involving Si impurities. The degree of polarization of WZ luminescence decreases with increasing doping levels for both p-type and n-type. These results shed light on the properties and doping of WZ GaAs and show that time-resolved CL and CL polarimetry constitutes a powerful tool to characterize the crystal phase, local defect, transport and recombination mechanism at the nanoscale.

In the race towards "beyond 6G" telecommunication platforms, magnonics emerges as a promising solution due to its wide tunability within the FR3 band (7-24 GHz). So far, however, the need for an external magnetic bias field to allow the coherent excitation of spin waves has been a major bottleneck. Conventional bulky electromagnets are power-intensive and challenging to integrate on-chip, restricting magnonic applications largely to academic research. Here, we present the first demonstration of a standalone, tunable magnonic device featuring all-electric input and output, fully integrated on a silicon substrate with a compact footprint of 100 x 150 μm. The device consists of a CoFeB waveguide equipped with two radio frequency antennas, flanked by a symmetric configuration of T-shaped magnetic flux concentrators and rectangular SmCo permanent micromagnets. By varying the distance D between the flux concentrators and the permanent magnets from 0 to 12 μm, the transverse bias field can be tuned from 20.5 mT to 11 mT, respectively. This variation directly modulates the dispersion relation of Damon-Eshbach spin wave modes in the CoFeB waveguide. In these proof-of-concept devices, the spin wave frequency band ranges from 3 to 8 GHz, with precise phase shift tuning of up to 120 degrees at 6 GHz achieved by varying D within the 0-8 μm range. The operational frequency band could even be pushed to higher frequencies through optimized micromagnet engineering.

Metal-organic frameworks (MOFs) offer remarkable chemical versatility, structural diversity, and, in some cases, stimuli-responsiveness. In the latter case, they typically rely on external inputs to trigger these changes. In contrast, living systems possess the ability to internally self-regulate and autonomously adapt their properties without external intervention, utilizing internal feedback mechanisms. To fill this gap, we develop a MOF-based metasurface that exhibits autonomous optical self-regulation, dynamically adjusting light absorption in response to varying incident light intensity. This device integrates colloidal MOFs with a plasmonic metasurface to create a thermo-optical negative feedback mechanism based on vapor sorption in and out of the colloidal MOF device. The self-regulation process is dynamic, leading each MOF/antenna unit to exhibit self-oscillatory behavior in the presence of a constant external energy input, analogous to a light-fueled nanoscale steam engine. This proof-of-concept highlights the potential of harnessing MOFs and sorption processes for designing metasurfaces for adaptable optical applications. It also represents a first step toward the design of materials integrating feedback mechanisms and internal clocks paving the way for a new generation of porous materials with life-like autonomy.

Nowadays, Si is the main technology deployed on terrestrial applications. However, it is limited to applications in flexible applications, such as for electric vehicles, and space applications. Furthermore, the efficiency limitation on single junctions below 30% is fundamental in these applications as they are naturally limited in area. Thinner Si cells (

Large surface transfer is a long-standing challenge for applications that require stacking 2D and 3D materials with only a limited number of combinations and techniques currently found in the literature. We report a systematic study of CVD graphene transfer to GaAs surfaces by mechanical exfoliation from Ge(110) substrates using highly stressed Ni layers. A uniform contact at the 2D-3D interface, achieved by aircushion pressing, enables a high yield of the transfer process to GaAs and other substrates exceeding 95% of the initial surface over cm-scales. Raman spectroscopy verifies that the crystalline quality of the transferred graphene is similar to that of the as-grown graphene, with its initially high compressive strain partially relaxed and no unintentional doping. After a two-step selective etching of the Ni layer in H2SO4: Sodium-n nitrobenzene sulfonate: thiourea (Transene etchant TFG) and HCl, we studied the surface chemistry of the resulting graphene/GaAs surfaces by X-ray photoelectron spectroscopy (XPS). Undoped GaAs remains unoxidized during the transfer process with an increase of the As-As related peaks due to preferential Ga dissolution during the acid-based deoxidation and etching processes, whereas p-type GaAs in contact with graphene showed corrosion damage attributed to a galvanic process with graphene acting as the cathode. This work provides new insights on the potential and processing constraints of dry-transferred graphene/GaAs heterostructures.

Selective area growth by hydride vapor phase epitaxy of GaN nanostructures with different shapes was investigated versus the deposition conditions including temperature and ammonia flux. Growth experiments were carried out on templates of GaN on sapphire masked with SiNx. We discuss two occurrences related to axial and radial growth of GaN nanowires. A growth suppression phenomenon was observed under certain conditions, which was circumvented by applying the cyclic growth mode. A theoretical model involving inhibiting species was developed to understand the growth suppression phenomenon on the masked substrates. Various morphologies of GaN nanocrystals were obtained by controlling the competition between the growth and blocking mechanisms as a function of the temperature and vapor phase composition. The optimal growth conditions were revealed for obtaining regular arrays of ∼5μm long GaN nanowires.

Temperature-induced sorption in porous materials is a well-known process. What is more challenging is to determine how the rate at which temperature is varied affects these processes. To address this question, we introduce a methodology called "cyclic thermo-ellipsometry" to explore the thermo-kinetics of vapor physisorption in metal-organic framework films.

A spin wave (SW) filter, consisting of a magnonic waveguide, a spacing layer, and an reconfigurable soft magnetic structure, is introduced. Micromagnetic simulations, along with preliminary experimental results, demonstrate the potential for a reconfigurable filtering action mediated by the dipolar coupling between the waveguide and the reconfigureble layer. This proof of concept lays the groundwork for a future device capable of serving as both a dedicated filter in radiofrequency signal processing and a tunable unit in computing applications.

Surface Plasmon Polaritons (SPPs) in Au thin films are nowadays intensively exploited for sensing applications that leverage the strong optical field confinement at the metal/dielectric interface and the easy functionalization of the Au surface. Moreover, Au thin films represent one of the common starting points for the top-down nanofabrication of plasmonic nanostructures supporting localized resonances. In this framework, strategies for the growth of high-quality Au films on transparent substrates are crucial and not yet fully established. In this study, we exploit MgO(001) substrates for the growth of thin (about 45 nm) Au films, also including an additional buffer layer of Fe. We successfully demonstrate Au samples with reduced roughness and presenting Low-Energy Electron Diffraction (LEED) features, indicating a high degree of crystalline ordering. This is supported by the experimental evidence of an increased (by almost a factor of 3) propagation length compared to a reference Au sample grown on standard glass slides, which is however still significantly lower than the one expected from first principles.

One of the most appealing features of magnonics is the easy tunability of spin-wave propagation via external magnetic fields. Typically, this requires bulky and power-hungry electromagnets, which are not compatible with device miniaturization. Here, we propose a different approach, exploiting the stray field from permanent micromagnets integrated on the same chip of a magnonic waveguide. In our monolithic device, we employ two SmCo square micromagnets (10 x 10 mu m2) flanking a CoFeB conduit at different distances from its axis, which produces a tunable transverse bias field between 7.5 and 3.0 mT in the conduit region between the magnets. This field is large enough to significantly affect the spin-wave propagation, when an external transverse bias field of 60 mT is applied to stabilize the Damon-Eshbach configuration. Spin waves excited by an antenna just outside the region between the magnets, indeed, enter a region with a variable higher (or lower) effective field depending on the parallel (or antiparallel) alignment between the external and micromagnets fields. Consequently, the attenuation length and phase shift of Damon-Eshbach spin waves can be tuned in a wide range by changing the parallel-antiparallel configuration of the external bias and the distance between SmCo micromagnets and the CoFeB conduit. This work demonstrates the potential of permanent micromagnets for the realization of low-power, integrated magnonic devices with tunable functionalities.

Hot carrier solar cells are a concept of photovoltaic devices, which offers the opportunity to harvest solar energy beyond the Shockley-Queisser limit. Unlike conventional photovoltaic devices, hot carrier solar cells convert excess kinetic energy into useful electrical power rather than losing it through thermalisation mechanisms. To extract the carriers while they are still "hot", efficient energy-selective contacts must be developed. In previous studies, the presence of the hot carrier population in a p-i-n solar cell based on a single InGaAsP quantum well on InP substrate at room temperature has been demonstrated by means of complementary optical and electrical measurements, leading to an operating condition for this device beyond the limit for classical device operation. This result allows to design a new generation of devices to increase the hot carrier conversion contribution. In this work, we study InGaAs/AlInAs type II heterojunction as a selective contact for a future hot carrier solar cell device epitaxially grown on (001) oriented InP substrate. Two p-i-n solar cells have been grown by molecular beam epitaxy on InP. The absorber is a 50 nm-thick InGaAs layer surrounded by AlInAs barriers, all lattice-matched to InP. Two architectures are compared, the first with two symmetrical AlInAs barriers and the second with a single InGaAs quantum well in the center of the n-side barrier to allow electron tunneling across the barrier. Electrical characteristics under laser illumination with two different wavelengths have been measured to investigate the effect of the selective contact compared to the barrier. This preliminary study of InGaAs/AlInAs-based selective contacts show that such III-V combination is adapted for a future hot carrier solar cell in the InP technology.

Spin waves represent the collective excitations of the magnetization field within a magnetic material, providing dispersion curves that can be manipulated by material design and external stimuli. Bulk and surface spin waves can be excited in a thin film with positive or negative group velocities and, by incorporating a symmetry-breaking mechanism, magnetochiral features arise. Here we study the band diagram of a chiral magnonic crystal consisting of a ferromagnetic film incorporating a periodic Dzyaloshinskii-Moriya coupling via interfacial contact with an array of heavy-metal nanowires. We provide experimental evidence for a strong asymmetry of the spin wave amplitude induced by the modulated interfacial Dzyaloshinskii-Moriya interaction, which generates a nonreciprocal propagation. Moreover, we observe the formation of flat spin-wave bands at low frequencies in the band diagram. Calculations reveal that depending on the perpendicular anisotropy, the spin-wave localization associated with the flat modes occurs in the zones with or without Dzyaloshinskii-Moriya interaction.

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Probing the formation of sol–gel mesoporous films and characterizing them under environmental/in-operando conditions represents an important challenge to optimize their performances. Obtaining a complete picture of the system usually requires a combination of multiple techniques. In this work, we introduce in situ infrared (IR) ellipsometry equipped with an environmental chamber as a tool to follow simultaneously the evolution of structural, optical and chemical properties during the formation of sol–gel derived mesoporous films. As a case study, we investigate the formation of mesoporous TiO2 by comparing a conventional thermal treatment and a low-temperature annealing by UV irradiation. In both cases, the structural optical and chemical evolution could be monitored during the IR ellipsometric experiment. Interestingly, UV-annealing allows the fabrication of mesoporous TiO2 films at low temperatures enabling the formation of plasmonic mesoporous composites. At last, we critically discuss the advantages and drawbacks of IR ellipsometry for in situ investigations compared to conventional UV–visible ellipsometry by providing additional insights for future developments.

Cathodoluminescence mapping is used as a contactless method to probe the electron concentration gradient of Te-doped GaAs nanowires. The room temperature and low temperature (10 K) cathodoluminescence analysis method previously developed for GaAs:Si is first validated on five GaAs:Te thin film samples, before extending it to the two GaAs:Te NW samples. We evidence an electron concentration gradient ranging from below 1 × 1018cm-3to 3.3 ×1018cm-3along the axis of a GaAs:Te nanowire grown at 640 °C, and a homogeneous electron concentration of around 6-8 × 1017cm-3along the axis of a GaAs:Te nanowire grown at 620 °C. The differences in the electron concentration levels and gradients between the two nanowires is attributed to different Te incorporation efficiencies by vapor-solid and vapor-liquid-solid processes.

Noble metal coordination xerogel films (mesostructured with block-copolymers) exhibit solubility switching with increasing X-ray irradiation. Different from other sol-gel systems, these are attributed to film deconstruction under irradiation. These materials can be used as recyclable negative tone resists for deep X-ray lithography that can be further converted into metallic nanoarchitectured films.