Magneto-transport properties in hybrid magnetic tunnel junctions (MTJs) integrating Self-Assembled Monolayers (SAMs) as tunnel barriers are critically influenced by spinterface effects, which arise from the electronic properties at ferromagnet (FM)/SAM interfaces. Understanding the mechanisms governing spinterface formation in well-controlled model systems is essential for the rational design of efficient molecular spintronic devices. However, the fabrication of FM/SAM/FM systems remains a significant challenge due to the difficulty in preventing electrical shorts through the SAM tunnel barrier during top FM electrode deposition. In this study, we address these challenges by developing model hybrid MTJs incorporating alkanethiol SAM tunnel barriers grafted under ultrahigh vacuum conditions onto single-crystalline Fe(001) bottom electrodes. A soft-landing deposition method is used for the deposition of a top Co FM electrode. The deposition process and the electronic properties of the formed FM/SAM interfaces are first studied by spatially integrated X-ray Photoelectron Spectroscopy (XPS). Furthermore, Ballistic Electron Emission Microscopy (BEEM) and spectroscopy are used to investigate the lateral homogeneity of the organic barrier. Optimal soft-landing deposition conditions allow the preparation of homogeneous Co/SAM interfaces with no evidence of metal diffusion through the SAM at the nanoscale. These observations are further confirmed at the micron scale by the high-yield patterning of large-area (5 & times; 5 mu m2) MTJs presenting fingerprints of electron tunneling through the SAM. These findings provide critical insights into the fabrication and optimization of molecular spintronic devices, paving the way for advancements in hybrid MTJ technology.

Direct orientation contrast imaging of zinc-blende III-V materials is studied using scanning electron microscopy. A quantitative approach is taken using a 3 μm thick orientation-patterned GaP grown on GaAs sample, studying the anti-phase domain contrast with respect to the electron beam energy and the tilt angle. A qualitative approach is taken for III-V grown on non-polar materials with and without chemical mechanical polishing. Finally, a processing of the acquired image for GaP on Si reveals in plane preferential anti-phase boundaries.

This article exposes an in-depth analysis of the chemical interaction between Cu(In,Ga)S2 thin-film and GaP/Si(001) pseudo-substrate, in the framework of the development of high-efficiency tandem solar cells on Si. A rich Cu-Ga-P-S chemistry at the Cu(In,Ga)S2/GaP interface is uncovered, in the case of Cu(In,Ga)S2 films grown in Cu-excess conditions. The involved chemical reactions are studied and modeled by breaking the system down to its binary constituents, such as Cu2-xS and GaP and by characterizing the reaction products. A chemical model is proposed to explain the chemical fluctuations observed at Cu(In,Ga)S2/GaP interface. It is found that Cu-rich Cu(In,Ga)S2 decomposes the underlying GaP film. This knowledge of Cu(In,Ga)S2/GaP interface chemical reactions can benefit the future development of two-terminal monolithic Cu(In,Ga)S2/Si tandem solar cells.

Green hydrogen (H2) can play a pivotal role in reducing global carbon emissions. This renewable fuel can be produced by water-splitting photoelectrochemical (PEC) devices that require a photoanode and a photocathode to serve as solar light absorbers and energy converters. So far, the use of III-V semiconductor materials as photoelectrodes has resulted in the best performance for PEC water splitting. However, the cost of these materials still prohibits their spread. Instead of employing bulk III-V wafers as photoelectrode substrates, using III-V thin film layers on inexpensive substrates to manufacture photoelectrodes appears to be, thus, a promising solution to solve this problem. Herein, we present the preparation and the study of photocathodes consisting of a thin film of GaAs grown by molecular beam epitaxy (MBE) on a p-doped Si (Si:p) substrate, which are subsequently modified by photoelectrodeposition of Ni catalyst. These Ni/GaAs/Si:p photocathodes are used for the solar-driven H2 evolution reaction (HER) in alkaline medium. We show that these photocathodes are stable in operation for several hours under illumination with a 100% Faradaic efficiency for H2. This constitutes the first example of the use of Ni as a catalyst on GaAs photocathodes. While these results support the fact that MBE-grown III-V thin films can afford HER in alkaline media when modified with an inexpensive catalyst, the effect of the GaAs thickness on incident-photon-to-electron conversion efficiency (IPCE) data shows that the III-V layer hinders the overall HER activity of the photoelectrode. Therefore, further material engineering strategies are required to improve the HER performance of these promising photocathodes.

GaAs is an excellent candidate for high‐performance photoelectrochemical water splitting due to its appropriate band‐edge and bandgap energies, as well as its excellent transport properties. The most significant limitations of GaAs for photoelectrochemical applications are its instability against corrosion, the high substrate cost, and the huge overpotentials required for triggering water electrolysis. The monolithic epitaxial integration of GaAs thin films directly on the Earth‐abundant Si fundamentally limits the costs associated with the substrate fabrication. Herein, photocathodes made of 1 µm thick GaAs layers epitaxially grown on p‐doped Si substrates are developed and their performances are compared to those of bare p‐doped GaAs electrodes. Sulfur passivation and standard interfacing with Pt catalyst are applied and analyzed for both series of photocathodes. A massive onset potential shift of 0.63 V is demonstrated for GaAs/Si photocathodes after electroless Pt deposition and sulfur passivation, reaching an onset potential of 0.4 V versus the reversible hydrogen electrode. The stability of the Pt/GaAs/Si photocathode is finally assessed over more than 112 h. These findings are essential for further development toward the fabrication of cost‐efficient and stable unassisted photoelectrochemical cells for green hydrogen production.

Solar photoelectrochemical (PEC) H 2 production has the potential to solve one of the biggest issues confronting humanity nowadays: producing inexpensive, clean and renewable energy. Among various semiconductor materials, GaAs is an excellent candidate for the development of photoelectrodes within PEC cells for unassisted solar water splitting thanks to its appropriate band gap, good transport and optical properties and high quantum yield. However, the main limitations of GaAs photoelectrodes are related to the high substrate cost, their huge overpotentials and the short lifetime under operation. To address these issues, in this work, we report on the photocathode performance of 1 µm-thick GaAs layers grown on a low-cost Si p-doped substrate by MBE (Molecular Beam Epitaxy) and compare them to those of GaAs:p doped wafers . The photocathodes were investigated in 0.2 M H 2 SO 4 (aq) electrolyte under 1 sun (100 mW/cm 2 ) illumination. The onset potential (V onset ) of bare GaAs/Si and bare GaAs:p wafer is quite comparable, at around -0.2 V vs reversible hydrogen electrode (RHE). The significant reduction of surface states density with a sulfur passivation (S-passivation) by immersing samples in (NH 4 ) 2 S solution is demonstrated but with very limited changes on the V onset value, for both GaAs:p wafer and GaAs/Si photocathodes. In contrast, the deposition of thin Pt catalyst layers on both photocathodes by electroless deposition technique leads to a large positive shift V onset . The V onset of GaAs/Si and GaAs:p wafer photocathodes are increased up to 0.34 and 0.15 V vs RHE respectively. We show that the V onset of GaAs/Si can be even improved by combining the Pt catalyst and the S-passivation process, reaching 0.4 V vs RHE (Fig. 1), a record value for GaAs-based Schottky-like photocathodes. STEM-EDX analysis was performed to investigate further the difference between Pt/GaAs/Si and Pt/GaAs:p wafer photocathodes. The EDX-line scans show that after the Pt electroless deposition, the Pt layer on GaAs:p wafer is homogeneous and shows an As 0 -rich Pt surface that can explain the weaker catalytic activity in comparison with GaAs/Si. Indeed, for the latter, Pt is deposited inhomogenously in the form of clusters leaving some bare surface. Here, As 0 is expected to be more easily removed from the surface during the electroless deposition, resulting in more efficient catalyst properties of Pt. The morphology differences between the two Pt-coated electrodes are confirmed by XPS measurements. Since the process of electroless deposition strongly depends on the doping concentration of the materials deposited, the difference between GaAs:p wafer and GaAs/Si photocathodes is attributed to variations in their doping concentrations. Furthermore, the inhomogeneity of the Pt coating on GaAs/Si can also benefit to the passivation process by allowing the (NH 4 ) 2 S solution to reduce more efficiently the surface defects at the oxide/semiconductor interface. Finally, the stability of Pt/GaAs/Si photocathodes was evaluated, and a lifetime larger than 112 h was established. These findings provide guidance for further studies towards the fabrication of scalable, cost-efficient and stable unassisted PEC cells for green hydrogen production. This research is supported by the “France 2030” French National Research Agency NAUTILUS Project (Grant no. ANR-22-PEHY-0013). Figure 1

A transmission electron microscopy study of epitaxial Cu(In,Ga)S 2 (CIGS) films coevaporated on GaP/Si(001), in either Cu‐rich or Cu‐poor conditions, is presented. The spatial distribution and the orientation of the different phases by means of electron diffraction are unveiled. From atomically resolved imaging of the CIGS film's atomic structure, it is concluded that different chalcopyrite domains, sharing cation antiphase symmetries of the cation sublattice, coexist in the films. At least three types of cation antiphase boundaries (CAPBs), which do or do not lead to a violation of the octet rule, depending on the propagation direction, are conceptualized. Even though it is observed that epitaxial CIGS is highly prone to cation antiphase disorder (CAPD), and it is found that the growth of CIGS in Cu‐rich conditions leads to a lower density of CAPBs, as compared to Cu‐poor growth conditions. This opens the question of the influence of CAPBs on CIGS electronic properties.

III-V semiconductor whispering gallery mode (WGM) microdisks have many assets for second order nonlinear optics. Their large nonlinear susceptibility combined with their high refractive index allows us to consider low power optical function based on nonlinear effects in a broad spectral range. In this paper, we will review our recent results on WGM GaP microdisks. We will present our experimental results on Q-factor characterization and second harmonic generation measurements under modal 4 phase matching. We will also review some phase-matching schemes propositions based on antiphase boundary engineering. Finally, we will discuss other device configurations based on coupled microdisks.

The best solar conversion efficiencies have been reached thanks to multijunction solar based on III-V semiconductors on GaAs or Ge substrates. While displaying high conversion efficiencies, these solar cells suffer from the high cost of such substrates. To benefit from both the low cost and technological maturity of silicon cells, III-V tandem cells on silicon seem a good compromise to overpass the theoretical efficiency limit of the Si single cells. To study the GaP/Si interface effect on the solar cell characteristic, a GaP n-i-p solar cell has been grown on silicon substrate. Two types of electrical contacts configurations have been processed: a top-top configuration in which the current does not see the GaP/Si interface and the top-bottom configuration where the electric current crosses the interface. A comparison of dark I-V, I-V under solar illumination, and EQE measurements on both configurations is performed. The top-bottom contacts configuration shows an EQE a little bit lower than the top-top contact one, likely due to lower carrier diffusion length or recombination at the lower interface. However, the result on the EQE of the top-bottom configuration is encouraging for the future development of the GaP-based/Si tandem solar cells, and any other tandem cell on silicon using GaP as an intermediate selective contact.

This study examines the growth condition to obtain a single-phase Cu(In,Ga)S2 (CIGS) chalcopyrite film epitaxially grown by coevaporation on a GaP/Si(001) pseudo-substrate. In particular, we report the structural differences between KCN-etched Cu-rich and Cu-poor CIGS films coevaporated on GaP/Si(001) by 1-stage process. The Cu-poor CIGS film consists of at least three phases; the main crystal is found to be chalcopyrite-ordered, coexisting with In-rich CuIn5S8, and CuAu-ordered CuInS2, all sharing epitaxial relationships with each other and the GaP/Si(001) pseudo-substrate. On the other hand, the Cu-rich CIGS film is single-phase chalcopyrite and displays sharper X-ray diffraction peaks and a lower density of microtwin defects. The elimination of the secondary CuAu-ordered phase with Cu excess is demonstrated. In both films, the chalcopyrite crystal exclusively grows with its c-axis aligned with the out-of-plane direction of Si[001]. This study confirms prior findings on the thermodynamics of Cu–In-Ga-S and the stability of secondary phases.

Lately, lead-free flexible piezoelectric nanogenerators (PENGs) have drawn much attention because of the threat posed by lead (Pb)-based piezoelectric materials to the environment. Here, we reported an organic-inorganic hybrid perovskites (OIHP) PENG, which is a combination of lead-free formamidinium tin (Sn) halide perovskite (CH(NH2)(2)SnBr3 (FASnBr(3))) nanoparticles (NPs) and polydimethylsiloxane (PDMS) polymer matrix. By using piezoelectric force microscopy (PFM) measurements, we unveil the excellent piezoelectric properties of the FASnBr(3) NPs with a high piezoelectric charge coefficient (d(33)) of similar to 50 pm/V. Due to the outstanding flexibility and uniform distribution properties, the device demonstrated a maximum piezoelectric peak to peak output voltage of 94.5 Vp-p, peak to peak current of 19.1 mu Ap-p, and output power density of 18.95 mu W/cm(2) with a tiny force of 4.2 N; these characteristics substantially outperform a number of the state-of-the-art halide perovskite based PENGs (Table S1). Given their high electromechanical energy conversion efficiency, the electrical energy produced from the PENGs was used to power a Bluetooth-capable system on chip (SoC) to build an entirely self-powered radio frequency (RF) communication system. For the first time, we established a self-powered RF wireless communication between nanogenerator and smart electronic devices which is solely based on a lead-free PENG. It is anticipated that the fabricated FASnBr(3)@PDMS nanocomposite PENG not only possesses outstanding performance and reliability but also serves as a stepping-stone towards achieving self-powered Internet of Things (IoT) devices built using environment-friendly perovskite piezoelectric materials.

Here, the structural, electronic and optical properties of the GaP1-xSbx/Si tandem materials association are determined in view of its use for solar water splitting applications. The GaPSb crystalline layer is grown on Si by Molecular Beam Epitaxy with different Sb contents. The bandgap value and bandgap type of GaPSb alloy are determined on the whole Sb range, by combining experimental absorption measurements with tight binding (TB) theoretical calculations. The indirect (X-band) to direct ({\Gamma}-band) cross-over is found to occur at 30% Sb content. Especially, at a Sb content of 32%, the GaP1-xSbx alloy reaches the desired 1.7eV direct bandgap, enabling efficient sunlight absorption, that can be ideally combined with the Si 1.1 eV bandgap. Moreover, the band alignment of GaP1-xSbx alloys and Si with respect to water redox potential levels has been analyzed, which shows the GaPSb/Si association is an interesting combination both for the hydrogen evolution and oxygen evolution reactions. These results open new routes for the development of III-V/Si low-cost high-efficiency photoelectrochemical cells.

Hybrid materials taking advantage of the different physical properties of materials are highly attractive for numerous applications in today's science and technology. Here, it is demonstrated that epitaxial bi‐domain III–V/Si are hybrid structures, composed of bulk photo‐active semiconductors with 2D topological semi‐metallic vertical inclusions, endowed with ambipolar properties. By combining structural, transport, and photoelectrochemical characterizations with first‐principle calculations, it is shown that the bi‐domain III–V/Si materials are able within the same layer to absorb light efficiently, separate laterally the photo‐generated carriers, transfer them to semimetal singularities, and ease extraction of both electrons and holes vertically, leading to efficient carrier collection. Besides, the original topological properties of the 2D semi‐metallic inclusions are also discussed. This comb‐like heterostructure not only merges the superior optical properties of semiconductors with good transport properties of metallic materials, but also combines the high efficiency and tunability afforded by III–V inorganic bulk materials with the flexible management of nano‐scale charge carriers usually offered by blends of organic materials. Physical properties of these novel hybrid heterostructures can be of great interest for energy harvesting, photonic, electronic or computing devices.

III-V semiconductors grown on silicon recently appeared as a promising platform to decrease the cost of photonic components and circuits. For nonlinear optics, specific features of the III-V crystal arising from the growth on the nonpolar Si substrate and called antiphase domains (APDs) offer a unique way to engineer the second-order properties of the semiconductor compound. Here we demonstrate the fabrication of microdisk resonators at the interface between a gallium-phosphide layer and its silicon substrate. The analysis of the whispering gallery mode quality factors in the devices allows the quantitative assessment of losses induced by a controlled distribution of APDs in the GaP layer and demonstrates the relevance of such a platform for the development of polarity-engineered III-V nonlinear photonic devices on silicon.