Insulator‐to‐metal transitions in (V 1‐ x Cr x ) 2 O 3 Mott materials can be triggered by adjusting temperature, pressure, and Cr content. Beyond these conventional routes, the insulating phases of these compounds also display an out‐of‐equilibrium insulator‐to‐metal transition under electric pulses, associated with the formation of a percolating metallic pathway within an insulating matrix. This resistive‐switching property holds promise for emerging devices, such as nonvolatile memories and artificial synapses or neurons. However, understanding the microscopic nature of the electrically induced metallic state remains a key challenge. Electron energy‐loss spectroscopy (EELS) in a transmission electron microscope (TEM) is demonstrated here as a sensitive and spatially resolved technique for distinguishing metallic and insulating domains in (V 1‐ x Cr x ) 2 O 3 Mott systems at the nanoscale. Studies on single crystals reveal the existence of a 0.25 eV shift in volume plasmon energy between the paramagnetic metal (PM) and the insulating phases—paramagnetic insulator (PI) and antiferromagnetic insulator (AFI). This shift arises from the unit cell volume expansion occurring at the metal‐to‐insulator transition, which decreases the density of valence electrons. It is further demonstrated that this nanoscale characterization approach can be effectively extended to polycrystalline V 2 O 3 thin films and to memory devices based on (V 1‐ x Cr x ) 2 O 3 .

Insulator-to-metal transitions in (V1-xCrx)2O3 Mott materials can be triggered by adjusting temperature, pressure, and Cr content. Beyond these conventional routes, the insulating phases of these compounds also display an out-of-equilibrium insulator-to-metal transition under electric pulses, associated with the formation of a percolating metallic pathway within an insulating matrix. This resistive-switching property holds promise for emerging devices, such as nonvolatile memories and artificial synapses or neurons. However, understanding the microscopic nature of the electrically induced metallic state remains a key challenge. Electron energy-loss spectroscopy (EELS) in a transmission electron microscope (TEM) is demonstrated here as a sensitive and spatially resolved technique for distinguishing metallic and insulating domains in (V1-xCrx)2O3 Mott systems at the nanoscale. Studies on single crystals reveal the existence of a 0.25 eV shift in volume plasmon energy between the paramagnetic metal (PM) and the insulating phases-paramagnetic insulator (PI) and antiferromagnetic insulator (AFI). This shift arises from the unit cell volume expansion occurring at the metal-to-insulator transition, which decreases the density of valence electrons. It is further demonstrated that this nanoscale characterization approach can be effectively extended to polycrystalline V2O3 thin films and to memory devices based on (V1-xCrx)2O3.

Single-phase lamellar CIGS5 (Cu0.65In1.75Ga1.4S5, nominal composition) thin films were synthesized using co-evaporation. Structural, morphological and optoelectronic properties of these films have been investigated. The optical bandgap was calculated at approximately 2.1 eV, but extended band tails hinder an accurate determination. Such behavior may be related to the high density of point defects inherent in the crystal structure of CIGS5, which exhibits intrinsic cationic vacancies and mixed site occupancy. This results in compensated semiconducting behavior, with no clearly identified charge carriers. Nevertheless, photoelectrochemical measurements suggest an extremely weak excess of electrons. Diverse solar cell architectures with CIGS5 as absorber were fabricated. All exhibit very low efficiency. These poor performances are discussed and are attributed to the intrinsic optoelectronic properties of CIGS5 material in ambient conditions due to a charge compensating effect.

The ban on the use of hexavalent chromium in the protection process for food-grade tinplate has led to the development of a new passivation process called CFPA (Chromium-Free Passivation Alternative). Nevertheless, its corrosion performance is lower than that of the original process. The objective of this work is to thoroughly characterize the 555-CFPA layer in order to identify the origin of the adhesion and corrosion weaknesses observed. To achieve this, XPS spectroscopy in conventional and image mode and STEM HAADF imaging combined with EELS spectroscopy were used. A "ridge-valley" nano-roughness following the rolling patterns was observed. The thickness of the passivation layer is dependent upon its location and varies from single (similar to 8 nm) to double (similar to 18 nm). In the valleys, the passivation consists of a gradient of transition metal oxides or even (oxy)fluorides and a polymer on the surface, arranged on a protective layer of tin oxides. On the ridges, the thinner passivation layer consists of a single nano-layer of oxides. Its lateral distribution is very heterogeneous, even leading to the formation of nano-clusters at the extreme surface. Indeed, the chemical heterogeneity in passivated tinplate leads to variations in chemical potential at the surface, which could lead to different responses to corrosion and weakened steel protection.

Functional organic nanoparticles, largely praised for optoelectronics and bioimaging applications, are usually manufactured through the mere self-assembly of molecular dyes. Undesirable dissociation due to noncovalent interactions between the molecular constituents can be prevented by further photo-cross-linking. In order to study the reactivity within nanoparticles and the impact of photo-cross-linking on their mechanical properties of nanoparticles, we elaborate nanoparticles and films based on a photoactivatable network derived from reacting bis-acrylate-functionalized azo photochromic units and bis(dithiolane) cross-linkers of variable flexibility. Photochromic studies, recording azo relaxation dynamics after photoisomerization, are combined with force spectroscopy investigations using atomic force microscopy, following a nanocompression method, to give access to the elastic modulus at the single nanoparticle level. We find that the average thermal relaxation of the azo units in cross-linked nanoparticles is largely enhanced in comparison to that in cross-linked films, whereas similar values are obtained for both the more flexible and stiffer networks. While the elastic modulus slightly increases for thin films incorporating stiffer cross-linkers, the difference is amplified 10-fold in nanoparticles. These results first demonstrate that high structural confinement in nanoparticles upon nanoprecipitation favors large reactivity and thereby a large incorporation of the cross-linkers in the final three-dimensional networks. Second, they point out that nanoparticle elasticity is mainly ruled by the stiffness of the cross-linkers. The enhanced discrepancy in elasticity at the nanoparticle level is thus tentatively interpreted as nanoconfinement effects, impacting the free volume distribution and chain mobility.

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.

Design of tailored materials using innovative approaches that allow faster charging/discharging processes could be the key for improvement of electric mobility. In this work, a strategy is developed to modify KNbO3 perovskite structure by partially substituting K+ with La3+ at the A-site of the structure, creating two cation vacancies per substitution in the lattice. Materials with the general formula K1-3x La x square 2x NbO3 (with 0 <= x <= 0.15; square is an A-site vacancy) have been synthesized by the sol-gel method. With La substitution and creation of artificial vacancies in the structure, KNbO3 became activated for Li+ insertion. The highly substituted K0.55La0.15 square 0.30NbO3 (30% atomic A-site vacancies) exhibited 164 mAh g-1 at 0.02 A g-1 in the 0.05-3.0 V vs Li+/Li potential window. Ex situ 7Li and 93Nb MAS NMR confirmed an increased Li+ insertion in relation to vacancies and corresponding changes in Nb5+ local environment, respectively. In situ X-ray diffraction (XRD) analysis revealed a solid-solution-type storage mechanism with a maximum volume change of only 1.3% upon Li+ insertion for highly substituted material. This accounts for the remarkable capacity retention obtained after 900 cycles at 0.1 Ag-1. Diverged from the classical design of insertion materials, this study presents an alternative approach of creating vacancies without sacrificing the pristine phase, with a possibility to use the not so common class of ABO3-type perovskites as the battery electrode.

2D transition metal chalcogenides have been examined as versatile platforms for exotic quantum phenomena, optoelectronic and photocatalytic applications. La2O2S2, a layered oxysulfide built of [La2O2](2+) slabs and 2D arrays of [S-2](2-) dimers, was recently found to be a promising precursor to fabricate such 2D materials. Redox reactions with external zerovalent metals cleaved its S-S bonds, triggering intercalation of those metal guests. This process serves as a novel approach to construct 2D metal sulfides between rigid [La2O2](2+) slabs, but so far demonstrated only for Cu (+) cations. We herein report that the same intercalation process takes place also when Ni and Fe were used as reagents. While XRD indicated that the reactions with Ni and Fe converted La2O2S2 into the sulfur-deficient La2O2S1.5-x (0 <= x <= 0.38) phase, our TEM analyses evidenced diffusion of those metals in between [La2O2](2+) slabs at the local scale. This finding suggested the formation of 2D nickel and iron sulfides intergrown with [La2O2](2+) slabs, either as the unprecedented La-O-M-S (M = Ni, Fe) phase, or a biphasic heterostructure. In addition, our computational structure prediction also supported stability of such intergrowth [La2O2][MxS2-y] structures, encouraging future attempts to isolate those elusive 2D materials.

MXenes are a large family of two-dimensional transition metal carbides and/or nitrides combining hydrophilicity with metallic conductivity, thereby leading to a plethora of potential applications. This study expands the current possibilities for the structural engineering of MXenes by demonstrating medium energy range ion irradiation as a controllable and flexible strategy to deeply modify Ti3C2Tz thin films. By adjusting the fluence of a 180 kV He+ ion beam, we evidence the gradual modification of the different structural elements of typical MXene multilayers, inducing well-defined impacts on properties. Low fluences allow modifying the interlayer spacing, inhibiting the long-term rehydration capacity of the thin films with expected major benefits on MXene aging issues. In addition to this, irradiation allows affecting the layers functionalization with major impact on the normalized optical transmission profile, suppressing the absorption valley at IR-visible limit and expanding their transparency in the UV. These effects, combined with improved electrical contact between the Ti3C2Tz layers, are highly desirable for transparent conductive electrodes applications. Finally, higher fluence irradiations induce preferential sputtering of titanium atoms. Transition metal vacancies being known to be highly relevant to deeply modify properties beyond those investigated here, these results show the large benefits of ion irradiation for MXene design.

Quantum dots (QDs) have gained significant attention as efficient photosensitizers for light-harnessing applications. While quantum dots are extensively employed in dye-sensitized solar cells (DSSCs), their exploration as sensitizers on metal oxide nanoparticles, such as TiO2, for dye sensitized photocatalytic systems (DSPs) remains relatively unexplored. The successive ionic layer adsorption and reaction (SILAR) method offers a promising solution to prepare QDs on metal oxide nanoparticles, since it is a simple, mild, and cost-effective approach. In this study, we present the first successful utilization of the SILAR methodology for growing cadmium sulfide (CdS) QDs on TiO2 nanoparticles (NPs). The structural characterization of CdS-TiO2 hybrids was conducted using Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS). The photocatalytic performances of CdS-TiO2 NPs were thoroughly examined for light driven simultaneous benzyl-alcohol oxidation into aldehydes and H2 evolution. Remarkably, the CdS-TiO2 nanoparticles operate without any catalyst or sacrificial electron donor. Furthermore, these composite species demonstrate excellent stability, retaining over 95% of their initial efficiency after three recycling cycles.

In this work, we have designed an all-organic and all-solid-state lithium metal battery based on 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as the organic electroactive material and a COF (Covalent Organic Framework)/PEO (PolyEthylene Oxide) composite as solid electrolyte. The use of a solid electrolyte allows fixing the solubility problem of organic electroactive materials in classical liquid electrolytes. This is the first time an all-solid-state organic battery based on TCNQ versus lithium metal is reported, since no liquid additive was included in the formulation of the electrolyte. We obtained a reversible capacity of 88 mAh g-1 at the second discharge, and still 58 mAh g-1 at the tenth discharge. The redox processes were investigated by X-ray Photoelectron Spectroscopy (XPS). We could evidence the involvement of the two lithiation steps of TCNQ (LiTCNQ and Li2TCNQ) in the reversible capacity. Optimization of the electrode manufacturing and formulation, and replacing the salt (LiI) by alternative ones opens the door to future improvements in the electrochemical performances. This study demonstrates the interest of COF-type organic structures in the formulation of organic solid electrolytes.

We report the observation of the high-pressure B2 phase in CdO nanoparticles obtained by temperature induced phase transition from the CdO B1 phase in CdxZn1-xO films grown on a Si substrate. The structural transformation occurs upon annealing the film from 700 to 900 °C and is monitored by X-ray diffraction and Raman spectroscopy. Concomitantly, willemite Zn2SiO4 nanoparticles form at the CdxZn1-xO/Si interface and are evidenced using scanning transmission electron microscopy, X-ray absorption and photoelectron spectroscopies. The presence of Zn2SiO4 at the film-substrate interface is assumed to exert locally a high pressure on the CdO crystallites. The B1 to B2 phase transition in CdO was previously only reported under hydrostatic pressure conditions. By varying the Cd content and adjusting the growth conditions, we have succeeded in stabilizing the metastable B2 phase under ambient conditions, which holds significant potential for applications in energy storage and stress sensing.

LAS glass-ceramics stimulate considerable attention in academic and industrial fields due to exceptional properties, such as low thermal expansion coefficient, transparency or superior mechanical strength. We report here an experimental investigation of LAS structure and microstructure using conventional techniques as XRD or S/TEM, but also an innovative technique based on electron diffraction mapping. The later gives a topography of the sample and a clear picture of the distribution between the glass and the spodumene particles. All the data converge towards a model of hard spheres where 75% of the volume is composed of spheroid particles and 25% of the remaining volume is composed of glass, which is present in the inter-particle interstices. These findings provide a new knowledge about the LAS system and may offer useful guidance for other researchers in ceramic community.

In this study, a model AgNbO3 perovskite is prepared via polyacrylamide synthesis technique, and the underlying unique Li+ storage mechanism is studied. This structure is projected to provide low Li+ storage capacity due to all occupied crystallographic sites. It delivered a specific capacity of 17 mAh.g(-1) at 0.1A.g(-1) within the potential range of 1.2-3.0 V vs. Li+/Li. However, at lower potentials, the material undergoes activation for Li+ storage by a multistep structural transition that included in-situ Ag-exsolution from the A-site of the lattice and an electrochemically induced crystalline-to-amorphous transition. At low potential the materials delivers high specific capacity (226 mAh.g(-1) at 0.1 A.g(-1) in 0.01-3 V vs. Li+/Li potential range) due to the contribution of improved Nb-redox activity and nanoscale Ag-Li (de)alloying mechanisms that were comprehensively examined utilizing advanced characterization tools. In addition, good capacity retention of 72 mAh.g(-1) at high current density of 2A.g(-1) and an excellent cyclic stability with coulombic efficiencies above 99.9 % are obtained for 2500 cycles at 1 A.g(-1) underlining the performance and the stability of AgNbO3. This study introduces an alternative approach for tailoring electrode material using an electrochemically driven in-situ activation process. It also serves as a paradigm for the use of exsolved materials as negative electrodes in fast-charging batteries, paving the way for a better understanding of charge storage mechanisms in perovskites.