This study focuses on the challenge of converting ZnO films into uniform zeolitic imidazolate framework-8 (ZIF-8) layers or membranes, an essential key step in shaping metal-organic frameworks (MOFs). It compares two ZnO deposition techniques: atomic layer deposition (ALD) and physical vapor deposition (PVD), examining how each method affects the surface chemistry of ZnO and its subsequent conversion into ZIF-8. The investigation includes contact angle measurements using methanol and water to assess surface wettability as well as X-ray diffraction (XRD) analysis combined with electronic microscopy to characterize the resulting ZIF-8 layers. The study indicates that ALD ZnO films are more hydrophilic, with a water contact angle of ∼75°, compared to the more hydrophobic PVD films, which exhibit a contact angle of ∼98°. XRD analysis reveals that PVD films display a pronounced (002) crystal orientation, while ALD films consist of randomly oriented nanocrystals. To optimize the conversion of ZnO to ZIF-8, the methanol-to-water ratio was adjusted, with a 3:1 mixture yielding the most uniform ZIF-8 layers. Additionally, thermal treatment of PVD films at 600 °C significantly altered their surface reactivity and conversion behavior, leading to distinct ZIF-8 morphologies. In contrast, ALD films exhibited a higher conversion efficiency, producing continuous, well-crystallized ZIF-8 layers with minimal defects. This improved performance is attributed to their superior surface wettability and reactivity. These findings underscore the critical role of ZnO surface chemistry in ZIF-8 formation and emphasize the importance of optimizing both deposition methods and conversion conditions to achieve high-quality MOF layers.

In this paper, the sensitivity to sub-ppm NO2 concentration of 50 nm thick Ga-doped ZnO (GZO) films grown by RF magnetron sputtering is studied. The films were annealed under dry air for 4 h at either 500 °C, 600 °C, or 700 °C. The increase in the annealing temperature leads to an improvement of the crystallinity while no significant evolution of the surface grain size is observed. The electrical resistance of the thin films was measured at 250 °C under neutral argon atmosphere, humid air reference atmosphere, and reference atmosphere polluted by 100 ppb of NO2. An increase in sensitivity to NO2 is noted for samples annealed at 600 °C, leading to a response RNO2/Rair of ~10 for 100 ppb of NO2. Finally, photoluminescence spectra are compared with their electrical resistance at 250 °C under the various atmospheres to understand this phenomenon. It is proposed that the origin of the NO2 maximum sensitivity for films annealed at 600 °C is the consequence of a specific annihilation of point defects resulting in an increase in the relative concentration of oxygen vacancies, which improves selectivity toward NO2.

This work aims to explore the impact of factors influencing ZnO : Ga to ZIF-8 conversion for the formation of a continuous MOF layer.

In this work, gallium-doped zinc oxide was deposited with a Radio Frequency Magnetron sputtering method on test platforms. The NO2 sensing properties of the resulting devices were studied. The sensing properties of ZnO:Ga thin films were successfully stabilized through annealing in dry air, and then improved by either a thinning of the layer or an increase in the roughness of the substrate. The sensing response with an Rgas/Rair of 15 for 100 ppb of NO2 under 50% humidity was obtained, with a response time below 10 min.

The paper reports the synthesis and characterization of a copper ferrospinel thin layer. The thin layer (25 nm) was synthesized by RF sputtering of a pure CuFe2O4 target. The material structure and microstructure were characterized using X-ray diffraction and transmission electron microscopy. Simplified test substrates were microfabricated with interdigitated Pt electrodes to investigate electrical properties in a controlled atmosphere. The sensitive layer was stabilized by annealing at 550 °C under air. NO2 responses at a low concentration (<1 ppm) and 50% relative humidity were measured between 100 and 500 °C. The optimal response was obtained at 250 °C.

The demand for high-performance energy storage devices to power Internet of Things applications has driven intensive research on micro-supercapacitors (MSCs). In this study, RuN films made by magnetron sputtering as an efficient electrode material for MSCs are investigated. The sputtering parameters are carefully studied in order to maximize film porosity while maintaining high electrical conductivity, enabling a fast charging process. Using a combination of advanced techniques, the relationships among the morphology, structure, and electrochemical properties of the RuN films are investigated. The films are shown to have a complex structure containing a mixture of crystallized Ru and RuN phases with an amorphous oxide layer. The combination of high electrical conductivity and pseudocapacitive charge storage properties enabled a 16 mu m-thick RuN film to achieve a capacitance value of 0.8 F cm(-2) in 1 m KOH with ultra-high rate capability.

Fast charging is a critical concern for the next generation of electrochemical energy storage devices, driving extensive research on new electrode materials for electrochemical capacitors and micro-supercapacitors. Here we introduce a significant advance in producing thick ruthenium nitride pseudocapacitive films fabricated using a sputter deposition method. These films deliver over 0.8 F cm–2 (~500 F cm–3) with a time constant below 6 s. By utilizing an original electrochemical oxidation process, the volumetric capacitance doubles (1,200 F cm–3) without sacrificing cycling stability. This enables an extended operating potential window up to 0.85 V versus Hg/HgO, resulting in a boost to 3.2 F cm–2 (3,200 F cm–3). Operando X-ray absorption spectroscopy and transmission electron microscopy analyses reveal novel insights into the electrochemical oxidation process. The charge storage mechanism takes advantage of the high electrical conductivity and the morphology of cubic ruthenium nitride and Ru phases in the feather-like core, leading to high electrical conductivity in combination with high capacity. Accordingly, we have developed an analysis that relates capacity to time constant as a means of identifying materials capable of retaining high capacity at high charge/discharge rates. Fast charging is driving extensive research on enhanced electrodes for high-performance electrochemical capacitors and micro-supercapacitors. Thick ruthenium nitride pseudocapacitive films are shown to exhibit enhanced capacitance with a time constant of less than 6 s.

In this article, we investigate the performance of 950 nm thick p-type gamma-CuI uni-track thin film thermoelectric modules. A model was first developed to optimize a module's geometry, focusing on the length and the number of the gamma-CuI tracks. Based on the maximum power achieved and the open circuit voltage (above 225 mV), the simulation optimized module consists of three tracks of gamma-CuI, each with a length of 13 mm. Using these simulation results, modules were elaborated through solid iodination process of Cu thin tracks. These gamma-CuI tracks were then connected with Pt electrodes. After characterizing the structure and electrical properties of the gamma-CuI material, the module's performance was measured at various applied temperatures in a free gradient mode. The results were in agreement with the simulation. Experimental and simulated performances highlight the significant impact of contact resistance as the temperature increases limiting module performances. A maximum power of 61nW was achieved at an applied temperature of 190 degrees C. This suggests that higher values could be attained through optimized contacts, with the goal of enabling some commercial applications for easily manufactured modules. Due to the optoelectrical properties of gamma-CuI, this even paves the way for the development of new transparent thermoelectric generators.

With the objective to achieve high-performance photoactive 2D films, a variety of large-surface-area, nanostructured films composed of 2D transition metal dichalcogenides (TMDCs) building blocks was successfully self-assembled using a customized, surface-functionalized, metallic sulfide template. Since 2D/2D contacts in these nanostructured films were anticipated to play a crucial role in charge carrier transport properties, control of 2D/2D contact properties was explored by varying 2D building block sizes and film-forming processes. High-resolution trans-mission electron microscopy (HRTEM) deep characterization of morpho-logical properties of 2D/2D contacts using focused ion beam (FIB) cross-sections reveals a variety of contact configurations mainly depending on the 2D building block thickness. Particularly, the effects of nanostructuration on 2D/2D contact characteristics such as the contact density, plane/plane vs edge/plane contact ratio, and contact boundary angles are clearly demonstrated on a large range of MoS2, WS2 and WSe2 building blocks varying from monolayers to nanoflakes, displaying various thicknesses. Correlations with electrical and photoelectrochemical properties demonstrate that the 2D/2D contact surface area, 2D/2D contact density, and contact boundary angles are key parameters controlling the recombination of photogenerated carriers. These findings are validated both on p-WSe2 and p-WS2 nanostructured films with photocurrents up to 4.5 mA cm-2 for the photoelectrochemical decomposition of H2O.

This work focuses on the recovery of rare earth elements (REEs = La, Ce, Nd, Pr) from spent nickel–metal hydride batteries by hydrometallurgical processing. The REEs were precipitated in the form of sodium-lanthanide double sulfate salts by adding Na2SO4 to a leach liquor prepared from industrially processed spent batteries. The objectives were to better understand the parameters driving the purity of the product and to identify the phases involved, as well as their crystallographic structure. The methodology included experiments performed in a 2 L reactor, thermodynamic calculations and product characterization. We confirmed that high REE precipitation yields (>95%) can be achieved under a wide range of hydrodynamic conditions. Furthermore, we demonstrated and quantified how appropriately washing the product allows for a significant reduction in nickel losses while maintaining control over REE product purity. Finally, using X-ray Diffraction analyses, it was established that REEs form a solid solution with a chemical formula (Na0.9K0.1)(La0.65Ce0.24Pr0.04Nd0.07)(SO4)2·H2O, which has not been reported so far.

Due to its transparency and its thermoelectric performances that imply significant temperature variations, stabilized γ-CuI presents a real interest as a transparent thermoelectric thin film.

Large scale development of the 2D transition metal di-chalcogenides (TMDC) relies on landmark improvement in performance, which could emerge from nanostructuration. Using p-WS2 nanoflakes with different degrees of exfoliation and fracturing, perspectives were provided to develop high-surface-area 2D p-WS2 films for the photocatalytic hydrogen generation. The critical role of inter-nanoflakes contacts within high-surface-area 2D films was demonstrated, highlighting the benefit of plane/plane versus edge/plane contacts. Evidence of the high density of surface states displayed by these 2D films was provided through electrochemical measurements. In addition to operating as recombination centers, the surface states were shown to give rise to deleterious Fermi-level pinning (FLP), which dramatically decreased the efficiency of charge carrier separation. Lastly, promising strategies yielding FLP suppression via surface states modification were proposed. In particular, use of a multifunctional ultrathin film displaying healing, catalytic, and n-type semiconduction properties was shown to greatly enhance charge carrier separation and transport to the photo-electrode/electrolyte interface. When the 2D photoelectrodes were fabricated with the above prerequisites (i. e., a high proportion of plane/plane contacts and a successful surface states chemical modification), a photocurrent up to 4.5 mA cm-2 was achieved for the first time on 2D p-WS2 photocathodes for hydrogen generation.

Films deposited on glass substrate by RF sputtering, were heat treated in air by a low power laser spot thanks to conventional photolithography machine, to obtain pure CuCr0.97Mg0.03O2 delafossite with an optical transmittance of 0.58 and a conductivity of 5.8S.cm(-1). The Haacke's figure of merit is improved to reach 2.07 x 10(7)Omega(-1). Laser annealing by a photolithography machine is thus very interesting for enhancing the p-type transparent conductor properties of such delafossite phases. A local annealing according to selected patterns could also be envisaged, opening up exciting prospects for fast and low cost making the most of these transparent ptype semiconductors.

This work considers the equilibria between the stable phases of the Cr-Cu-0 ternary chemical system at atmospheric pressure and in a large temperature range that includes the high-temperature liquid phase. Based on a thorough evaluation of literature data, we performed complementary experimental investigations of solid-phase properties (especially the mixed oxides) by implementation of spark plasma sintering and microanalysis, high-temperature X-ray diffraction combined with Rietveld analysis, differential thermal analysis, and thermogravimetry. We show that neither the spinel CuCr2O4 nor the delafossite CuCrO2 phases exhibit significant cationic nonstoichiometry. We provide an assessment of the thermodynamic functions of the spinel up to 1200 K, taking into account the alpha/beta phase transition. We propose, for the first time, a consistent thermodynamic description of the Cr-Cu-O system based on the Calphad method, allowing the computation of reactions and phase equilibria, including the high-temperature liquid phase described by the modified quasichemical model.

2D photoactive materials may offer interesting opportunities in photocatalytic devices since they combine strong light absorption and shortening of charge carriers' diffusion path. Because of their high surface defect concentration and the formation of a majority of edge/plane vs plane/plane contacts between the anisotropic building blocks, surface defect passivation and improvement of charge carrier transport are critical for the large development of high surface area, 2D photo-catalysts. Here, we propose a hetero-structure nanoporous network with a patch-like coating as high performance 2D photo-catalysts. The hetero-structured building blocks are composed of a photo-active WSe2 nanoflake in direct contact with both a conducting rGO nanosheet and an ultrathin layer of healing catalyst. The resulting nanoporous film achieves a H-2 evolution photocurrent density up to 5 mA cm(-2) demonstrating that the patch-like hetero-structures represent an effective strategy to simultaneously improve hole collection, defect passivation and charge transfer. These hetero-structures made of an ultrathin healing catalyst layer represent promising building blocks for the bottom-up fabrication of high surface area photocathodes particularly for 2D photo-catalysts displaying high defect concentration.

2D semiconducting nanosheets of Transition Metal Dichalcogenides are attractive materials for solar energy conversion because of their unique absorption properties. Here, we show that Mo thio- and oxo-thio-complexes anchored on 2D p-WSe2 nanosheets considerably boost water splitting under visible light irradiation with photocurrent density up to 2.0 mA cm(-2) at -0.2 V/NHE. Besides developing high electro-catalytic activity, the Mo-complexes film is also shown to be capable of healing surface defects. We propose that the observed healing of surface defects arises from the strong adsorption on point defects of the 2D WSe2 substrate of Mo complexes such as (MoS4)(2-), (MoOS3)(2-), (Mo2S6O2)(2-) as supported by DFT calculations. In addition, the thio-, oxo-thio Mo complexes films are shown to enhance charge carrier separation and migration favouring the hydrogen evolution reaction, putting forward the use of thio-, oxo-thio-Mo complexes as a multicomponent passivation layer exhibiting multiple properties.

Delafossite type Mg doped CuFeO2 thin films have been deposited on fused silica by radio-frequency magnetron sputtering. As-deposited 300 nm thick films have been obtained and post-annealed between 350 and 750 degrees C under primary vacuum. The delafossite structure appears for the samples annealed above 550 degrees C. The microstructural analysis showed the presence of cracks and an inhomogeneous distribution of the dopant in the thickness. Only the sample annealed at 700 degrees C showed CuFeO2 stable phases, lower impurities amount, a high and constant Seebeck coefficient (+416 +/- 3 mu V K-1) and good electrical conductivity (1.08 S cm(-1) at 25 degrees C). High accuracy temperature sensors based on the Seebeck effect not only need high Seebeck coefficient without any drift with the temperature, but also a sufficient electrical conductivity and high phase stability. Thanks to its properties and also its low thermal conductivity (4.8 +/- 0.6 W m(-1)K(-1) at 25 degrees C) due to the thin film configuration and the polaronic transport, the Mg doped CuFeO2 thin film annealed at 700 degrees C was found to be a very good p-type material for high accuracy miniaturized temperature measurement sensors based on the Seebeck effect in the medium temperature range. (C) 2020 Elsevier B.V. All rights reserved.

Copper bismuth oxide (CuBi2O4 or Bi2CuO4) thin films have been elaborated for the first time by radio-frequency magnetron sputtering using a homemade CuBi2O4 ceramic target. X-ray diffraction characterizations revealed an amourphous phase for as-deposited films. After air annealing at 450 degrees C for 12 h, a pure polycristalline CuBi2O4 phase can been obtained. Raman spectroscopy confirmed the film phase purity. The influence of the thickness on the structural properties of the films has been studied and we observed that all films treated above 450 degrees C are crystallized. The thinner films show preferred orientation while there are less crystal defects for the thickest films (similar to 700 nm). Atomic force microscopy shows a homogeneous polycristalline microstructure at the surface of the film. Optical measurements performed by UV-vis-IR spectrophotometry indicate that these films have one of their optical band gaps in the visible region (E-g similar to 1.5 eV) which makes them suitable as thin films solar absorption materials.

CuFeO2, the structure prototype of the delafossite family, has received renewed interest in recent years. Thermodynamic modeling and several experimental Cu-Fe-O system investigations did not focus specifically on the possible nonstoichiometry of this compound, which is, nevertheless, a very important optimization factor for its physicochemical properties. In this work, through a complete set of analytical and thermostructural techniques from 50 to 1100 °C, a fine reinvestigation of some specific regions of the Cu-Fe-O phase diagram under air was carried out to clarify discrepancies concerning the delafossite CuFeO2 stability region as well as the eutectic composition and temperature for the reaction L = CuFeO2 + Cu2O. Differential thermal analysis and Tammann's triangle method were used to measure the liquidus temperature at 1050 ± 2 °C with a eutectic composition at Fe/(Cu + Fe) = 0.105 mol %. The quantification of all of the present phases during heating and cooling using Rietveld refinement of the high-temperature X-ray diffraction patterns coupled with thermogravimetric and differential thermal analyses revealed the mechanism of formation of delafossite CuFeO2 from stable CuO and spinel phases at 1022 ± 2 °C and its incongruent decomposition into liquid and spinel phases at 1070 ± 2 °C. For the first time, a cationic off-stoichiometry of cuprous ferrite CuFe1- yO2-δ was unambiguous, as evidenced by two independent sets of experiments: (1) Electron probe microanalysis evidenced homogeneous micronic CuFe1- yO2-δ areas with a maximum y value of 0.12 [i.e., Fe/(Cu + Fe) = 0.47] on Cu/Fe gradient generated by diffusion from a perfect spark plasma sintering pristine interface. Micro-Raman provided structural proof of the existence of the delafossite structure in these areas. (2) Standard Cu additions from the stoichiometric compound CuFeO2 coupled with high-temperature X-ray diffraction corroborated the possibility of obtaining a pure Cu-excess delafossite phase with y = 0.12. No evidence of an Fe-rich delafossite was found, and complementary analysis under a neutral atmosphere shows narrow lattice parameter variation with an increase of Cu in the delafossite structure. The consistent new data set is summarized in an updated experimental Cu-Fe-O phase diagram. These results provide an improved understanding of the stability region and possible nonstoichiometry value of the CuFe1- yO2-δ delafossite in the Cu-Fe-O phase diagram, enabling its optimization for specific applications.