We investigate the mechanical and electrical properties of cuprous oxide (Cu2O) thin films processed by low-temperature oxidation of bulk annealed copper. These oxide layers were characterized using advanced techniques unveiling a microstructure composed of nanocrystalline grains. Mechanical and electrical properties were assessed through the combination of electrical-nanoindentation experiments and multiphysics numerical simulation by the Finite Element Method. Regarding the mechanical aspect, the oxide film elastic modulus was determined at 22 ± 5 GPa and its plastic behavior was successfully modeled with a Drucker-Prager yield criterion. In addition, the oxide layer was found to act as a non-penetrable barrier against dislocation gliding in the copper substrate near-surface, significantly enhancing size effects. Regarding the electrical aspect, Poole–Frenkel conduction was identified as the driving conduction mechanism in Cu2O, with a dielectric permittivity of 7 and a trap level of 320 meV, the latter result suggesting an electrical transport through hole-trapping copper vacancies.

The mechanical properties of materials at the nanoscale are still poorly understood, despite intensive research efforts, in particular because mechanical tests are blind to the detailed microstructure of the samples. The latter is however crucial at small scales, when stochastic response dominates the initial elasto-plastic transition. To extract a comprehensive mechanical behavior at this scale, and despite this stochastic aspect, studying a large population of nano-objects is necessary. Additionally, investigating the early stage of the plasticity, correlated with the initial microstructure of the nano-objects, is essential. In this regard, we use a statistical approach to extract deterministic laws from various techniques such as nano-compression or nanoindentation, and we discuss the results in light with Bragg coherent diffraction imaging (BCDI) which provides the detailed crystalline state of the sample before and after mechanical testing. This ex situ approach is able to provide a more complete description of plastic behavior at small and large strains.

Zn x Cu4-x (OH)6Cl2 single crystals were grown under varying experimental conditions such as dissolution and growth temperatures, pH, and initial ZnCl2 concentration of the solution. The crystals were characterized to determine their crystallographic phase purity and lattice parameters, chemical composition, and surface morphology. Two spatially resolved mapping techniques, laser-induced breakdown spectroscopy (LIBS) and micro-X-ray fluorescence spectroscopy (mu-XRF), were used to firmly establish the Cu and Zn concentrations of the crystals obtained in different growth conditions. Once correctly calibrated, LIBS allowed for mapping of Cu and Zn contents with very good statistics and at various depths from the crystal surface. An interesting correlation between the c-lattice parameter and the x-value was observed in the range of x = 0.75-1.04. Using the microdiffraction multimodal station (mu-Laue, mu-XRF) at the BM32 beamline of the European Synchrotron Radiation Facility (ESRF), we were able to orient the most salient features of the (101) facets' morphology, including the ubiquitous macrosteps. Combining these data with an exhaustive thermochemical investigation of the growth solutions, aimed at identifying the most concentrated Cu- and Zn-based species as a function of the growth conditions (T, pH, Zn, Cu, Cl, and O concentrations), we proposed plausible growth and point defect disorder formation reactions. This analysis was partially supported for Zn-based species by in situ Raman spectroscopy. Further, through a systematic analysis of the height-difference correlation function obtained by atomic force microscopy (AFM) images of large terraces and macrosteps, we concluded that surface diffusion and related thermal noise are the kinetically limiting mechanisms in the growth process.

Nanoindentation has now become the key technique for measuring the mechanical properties of materials at small scales. However, the quantitative and accurate processing of nanoindentation data relies on a physical quantity that is not directly available: the contact area (Ac) between the indenter tip and the sample under test. In complex systems, determining Ac is challenging due to the limitations of standard methods: analytical models have restricted validity domains (sample homogeneity and rheology), and post-mortem observations of residual imprints are time-consuming, do not appraise property gradients and cannot be applied to materials with significant elastic recovery. In this paper, a comprehensive methodology is proposed to continuously measure contact area during indentation. The proposed methodology, referred to as electrical-nanoindentation (ENI), is based on real-time monitoring of the electrical contact resistance (ECR). The protocol only requires mechanical and electrical calibrations of the indenter tip on reference materials, leading to one-to-one relationship between ECR and contact area. An original approach is also proposed to deal with the presence of surface passivating layers that generally disturb ECR measurements. As an illustration, the methodology is applied to the characterization of a multiphase alloy (MPA) composed of silver, copper and palladium. This alloy raises the same challenges as those usually faced by nanoindentation in advanced metallurgy: heterogenous distribution of individual phases at the micro-scale, composite response of a complex mixture of hard/stiff and ductile/soft phases, ... In addition, the ohmicity of contact is disturbed by surface passivating layers. Despite these numerous hindrances, the proposed methodology is successfully applied to this material. The evolution of contact area is compared with standard methods: an impressive accuracy of <2% standard-deviation is achieved when compared to post-mortem observations. The elastic moduli and hardnesses of individual phases are then accurately extracted. In addition, in order to gain in spatial definition, the ENI set-up is integrated into a scanning electron microscope (SEM), enabling indent positioning with a precision close to 100 nm. Two challenges are successfully met with the ENI methodology. On a mechanical point of view, the response of individual phases can be identified despite the complex rheology of heterogeneous materials, proving the approach applies to all mechanical behaviors (sink-in or pile-up rheologies, homogeneous or heterogeneous materials, with or without elastic recovery, ...). On an electrical point of view, even if contact ohmicity is the only requirement of the methodology, it is possible to identify and overcome deviations from contact ohmicity induced by surface passivation. In particular, the non-linear resistive contribution of insulating layers fades during indentation thanks to its dependence as the reciprocal of the square of contact radius. The present work provides the keys to monitoring the contact area on any metallic sample, whether oxide-free or oxidized, making this methodology a promising alternative to standard methods.

The influence of devitrification on microstructure, corrosion, and mechanical properties of two new FeCrMoNbB and FeCrMoNiB pseudo-high entropy (PHE) amorphous alloys have been investigated to be used as coatings. Amorphous ribbons produced by melt spinning were heat-treated to simulate crystallization. Amounts of amorphous phases were kept at high temperatures and crystallized in multi-principal element bcc or FCC phases and borides. A 500 mu m thick physically simulated coating of commercial-grade precursors using spray forming was produced to infer their viability. The Nb-PHE alloy's coating was nearly amorphous. Ribbons' hardness and elastic modulus evaluated by nanoindentation depended on annealing temperatures and were remarkably high. Potentiodynamic polarization curves in chlorine-rich solution at different pHs showed outstanding corrosion resistance in amorphous conditions. After devitrification, both compositions preserved excellent corrosion behavior up to similar to 700 degrees C. Pitting corrosion was absent. Resistance to corrosion and wear indicates that these materials are promising for coating applications.

Current societal challenges, such as climate change and resource depletion, highlight an unprecedented need for disruptive innovation in materials science. Significant breakthroughs are expected in multinary materials whose efficient exploration necessitates dedicated strategies. The exploration of a refractory high entropy alloy Nb-Ti-Zr-Cr-Mo is proposed here as test case for a new strategy. Based on the proven methodology of mixture design and on combinatorial thin film metallurgy, the composition space is explored by a limited number of chosen gradients to build an alloy library comprising hardness and ductility, two antagonistic properties. The workflow is showcased here by studying the properties of the as-grown graded film, which presents wide amorphous domains and contrasted mechanical properties. This experimental dataset then trains machine learning models to provide continuous predictions of the alloy properties over the entire composition space. We show that optimal alloy properties are expected close to the binary edges of the quinary.

The Ni-Mn-based shape memory alloys as a promising candidate of elastocaloric material has been reported in many literatures, especially on bulk samples. The as-spun ribbon, which has a larger surface area and is more efficient for heat transfer, is rarely studied and hence of importance. In the present work, we succeeded in producing very long as-spun Ni-Fe-Mn-(Al, In) ribbons, with around 300 mm in length. The microstructure and mechanical properties of these as-spun ribbons were thoroughly investigated by scanning electron microscopy / electron backscattered diffraction (SEM/EBSD), nanoindentation and 3-points bending experiments. Through SEM/EBSD analyses, the microstructure and texture of the as-spun ribbons were studied. A gradient in microstructure exists along the thickness direction (TD) of the ribbon, which is induced by the temperature gradient during fast rate solidification, resulting in fine equiaxed grains along the surface contacted with the rotating wheel in melt spinning process and elongated grains, respectively. Both equiaxed and elongated grains possess a strong {001} fiber texture (<001>//TD). Nanoindentation analyses show little variation of hardness between the two different microstructures. The ductility index of both Ni-Fe-Mn-Al and Ni-Fe-Mn-In ribbons are within the range of intermetallic materials. The substitution of In by Al allows to increase very slightly the ductility index, which can reach 0.75. The fine equiaxed grains show better tensile resistance than the elongated grains in 3-points bending test. The substitution of In by Al improves the maximum bending strain by a factor of 3. The maximum strain for Ni-Fe-Mn-Al as-spun ribbons can reach 3 % before fracture. Fractography shows that the intergranular fracture is the main damage mechanism in these as-spun ribbons.

Functional devices such as microelectronic systems, solar cells and power devices are composed of complex stacks of various materials, including semiconductors, ceramics and metallic alloys. The knowledge of the mechanical response of those stacks is a key point, as they are submitted to harsh stresses during the fabrication process (induced by thermal treatments, mechanical polishing, packaging processes, ...) as well as during the device lifetime.& nbsp;We report the mechanical study of a microelectronic-dedicated stack where a silicon nitride (Si3N4) layer was deposited on top of a thick metallic alloy (AlSiCu) layer. In microelectronic chips, Si3N4 is widely used as a passivation layer, while AlSiCu is the electrical connection layer. The structure has been tested experimentally by nanoindentation. Multiple pop-in events were observed on the loading curves, indicating multiple cracking, with cracks initiated at various loading stages. The high reproducibility of the loading curves then allowed their full analysis by numerical modeling.& nbsp;The complete damage process of the multilayer during indentation is analyzed using modeling by the Finite Element Method (FEM), accounting for plasticity in AlSiCu, crack propagation in the Si3N4 layer and possible delamination at the interface between the two layers. The various stages of the damage process occurring in the Si3N4 are elucidated, showing in particular the occurrence of a first crack in the region underneath the indenter (hence not visible by a surface observation), followed by a second crack forming further away from the indenter, on the top surface of the layer. Moreover, a novel procedure for the identification of the Si3N4 layer tensile strength is presented, using an inverse method based on FEM simulations and experimental data. The results of the simulations (cracking patterns and cracks locations) are also further validated by the observation of structure cross-sections with a Scanning Electron Microscope (SEM) after Focused Ion Beam (FIB) milling of the sample. In addition, the proposed identification procedure is quite generic and can be adapted to other systems showing similar multiple-cracking patterns under indentation.

The influence of thermally induced devitrification on microstructure, corrosion, and mechanical properties of two novel Fe-based amorphous alloys has been investigated in this work (FeCrMoXB, where X=Nb, Ni). Hence, providing an overview of the perspectives for using these new alloys as coatings. Ribbons were produced by melt spinning. Samples were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM), accompanied by chemical analysis via energy dispersive spectroscopy (EDS). As-cast ribbons were amorphous. Considering DSC data of such ribbons, they were heat-treated under an Ar protective atmosphere to simulate crystallization that may occur during coating processing. The mechanical behavior was evaluated by nanoindentation. High hardness (around 14 GPa) and elastic modulus (>220 GPa) were identified for both compositions. Corrosion properties were analyzed by potentiodynamic polarization in seawater at three different pHs. Both compositions in the amorphous state exhibited outstanding corrosion resistance, forming a broad passivation plateau in the various media analyzed. After devitrification, the Nb-containing alloy preserved excellent corrosion behavior, with a slight decrease in corrosivity up to 720°C, better than the Ni-containing alloy that exhibited lower corrosion resistance with good corrosivity kept only up to 690°C. Results indicate outstanding corrosion behavior and wear resistance, indicating that these materials are promising for coating application through different techniques.

On one hand, coherent diffraction imaging (CDI) in Bragg geometry has emerged as a unique 3D microscopy of nanocrystals thanks to 3rd generation synchrotron sources.Away from absorption edges and at space-group allowed reflections, it provides not only the electronic density, but also, encoded in the phase, the atomic displacement field with respect to the mean lattice, which in turn reveals crystal strain, defects and domains [1][2][3].On the other hand, some crystal structures have crystallographic reflections which are forbidden by the spacegroup symmetry but can nevertheless be observed at a suitable X-ray absorption edge, due to the anisotropy of the tensor of scattering (ATS) [4].They are several orders of magnitude weaker than allowed reflections, but the absence of Thomson scattering allows the observation of various electronic phenomena related to electronic orders (magnetic, charge, orbital), as well as static and dynamic atomic displacements.The new generation of synchrotron sources, such as the ESRF "Extremely Bright Source", opens opportunities to perform CDI on such weak reflections.Here we report on the measurement of the ( 115) forbidden reflection of a GaN nanopillar at the Ga K edge (Figure 1).Sufficient statistics could be obtained in a total accumulation time of ~30 minutes for an entire rocking curve to retrieve the phase of the scattering function (Figure 2).Such measurement at high temperature would provide an image of the inhomogeneity of thermal motion in the crystal [5], which would be particularly interesting close to surfaces, inversion domain boundaries [3] and crystal defects.This proof-of-principle experiment demonstrates that forbidden reflections are a new opportunity for CDI with the new synchrotron sources.

Advanced devices (for microelectronics, energy storage, power sourcing) are complex architectures of metals and dielectrics subjected to harsh mechanical stresses. The functional reliability of the embedded dielectrics is driven by their ability to preserve their electrical properties (such as leakage and breakdown). Accordingly, understanding the interplay between the mechanical and electrical behaviors of dielectric films is critical to predict the lifetime of functional devices. In this study, the effect of plastic deformation on the electrical conduction of an ultra‐low‐k dielectric film is elucidated by combining in situ advanced experiments and finite element modeling. Experimentally, “electrical‐nanoindentation” tests emphasize the strong correlation between electrical and mechanical failures (leakage degradation, breakdown, plasticity, cracking). These experiments also reveal a counterintuitive electrical conduction drop under high mechanical stresses. This phenomenon is reproduced numerically by correcting the Poole–Frenkel conduction law with a strain‐dependent factor, and described analytically in terms of space‐charge build‐up induced by the trapping of holes at the mechanically generated defects. A threshold strain is identified as the keystone relating this strain‐dependent conduction to the current line distribution within the dielectric. This study provides a new understanding of the mechanical/electrical couplings in dielectrics, which opens promising insights into reliability issues for advanced devices.

This paper reports the experimental, analytical, and numerical study of resistive-nanoindentation tests performed on gold samples (bulk and thin film). First, the relevant contributions to electrical contact resistance are discussed and analytically described. A brief comparison of tests performed on gold and on natively oxidized metals highlights the high reproducibility and the voltage-independence of experiments on gold (thanks to its oxide-free surface). Then, the evolution of contact resistance during nanoindentation is fully explained in terms of electronic transport regimes: starting from tunneling, electronic transport is then driven by ballistic conduction before ending with pure diffusive conduction. The corresponding analytical expressions, as well as their validity domains, are determined and compared with experimental data, showing excellent agreement. From there, focus is made on the diffusive regime. Resistive-nanoindentation outputs are fully described by analytical and finite-element modeling. The developed numerical framework allows a better understanding of the main parameters: it first assesses the technique capabilities (validity domains, sensitivity to tip defect, sensitivity to rheology, effect of an oxide layer, and so on), but it also validates the different assumptions made on current line distribution. Finally, it is shown that a simple calibration procedure allows a well-resolved monitoring of the contact area during resistive-nanoindentation performed on samples with complex rheologies (ductile thin film on an elastic substrate). Comparison to analytical and numerical approaches highlights the strength of resistive-nanoindentation for continuous area monitoring.

The rising complexity of multi-material structures integrated into multi-functional devices requires the development of dedicated characterization tools capable of simultaneously monitoring different physical magnitudes with a relevant spatial resolution. This paper reports the development and the application of an original instrument based on a nanoindenter coupled with fine electrical measurements and integrated in-situ a Scanning Electron Microscope (SEM). The performances and capabilities of this home-developed instrument are illustrated through two different case studies. First, a micrometer-scale piezoelectric structure made up of wurtzite-single crystalline AlN islands grown on top of conductive Si pillars is tested. In-situ SEM imaging is used to precisely position the indenting probe on these individual islands, while the instrument sensitivity and repeatability are used to monitor their low-signal piezoresponse. Effective piezoelectric coefficients are also extracted for different loading/unloading conditions. Secondly a Si3N4/AlSiCu/SiO2 stack, which is standardly integrated as a passivation structure on top of microelectronic chips, is electrically and mechanically stressed and monitored up to its failure. The mechanical failure mechanisms (buried or emerging cracks) are discriminated thanks to the real-time SEM imaging of the indentation test. The instrument high sensitivity is used to monitor early current leakages that are attributed to conduction paths induced by mechanical failures. Combining high electro-mechanical sensitivity and precise probe positioning appears as an efficient way to monitor and analyze low-level electrical responses of small-scale structures. This approach paves the way to the fine characterization of micro/nano-systems displaying mechanically-driven electrical properties (conduction mechanism, leakage, breakdown,) like 2D-materials, dielectrics in microelectronic devices, strain-sensors, enamelled Litz wires,...

The design of the dissimilar metal weld investigated here is aimed at applications in the steam generator of a sodium-cooled nuclear reactor, with a multi-decade lifespan in demanding operational conditions. It consists in a narrow-gap joint between 2.25Cr-1Mo low-alloy steel and an austenitic alloy using a nickel-based alloy 82 as filler material. This study focuses on understanding the microstructural and micromechanical evolution in the near fusion boundary region between the low-alloy steel and the nickel alloy filler metal during post-weld heat treatment, using notably electron probe micro-analysis and nano-indentation. The difference in matrix phase and chemical composition between the two alloys leads to a large difference in chemical potential for carbon, which is mobile at the post-weld heat treatment temperature. A number of fine-scale characterization techniques were used to assess the gradient of composition, hardness, and microstructures across the fusion boundary, both as-welded and after post-weld heat treatment. This complete analysis permits to highlight and understand the main microstructural and micromechanical changes occurring during post-weld heat treatment and opens the way to their long term study in service conditions.

The near-surface properties of maraging steels are key to controlling their mechanical properties. They can be tailored by surface treatments such as shot peening and can also be influenced by prior machining. This study aims at determining the respective roles of grinding and shot peening processes on the near-surface microstructure of Custom 465 maraging stainless steel. A combination of experimental techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), and atom probe tomography (APT) provides an in-depth characterization of the initial microstructure and its modifications. The results show that grinding results in a very shallow nano-crystalline region less than 1 mu m thick, which contains a high fraction of retained austenite and where most Ni3Ti precipitates initially present, have been dissolved. Shot peening, on the other hand, results in a moderate localized strain close to the surface, and in a deeper destabilization of the retained austenite initially present, which decreases from similar to 5% to similar to 2% in the first 100 mu m below the surface. It has no visible effect on the precipitate microstructures. The different mechanisms that may cause these modifications are discussed.

Only achievable with two photons' polymerization, 3D printing at the micrometer scale is essential for the fabrication of complex objects such as photonic components, deformable microstructures, or microscaffolds for biological cells. Integrating magnetic materials inside those structures has made their remote actuation with an external magnetic field possible. However, the nature of the magnetic material, its volume, and precise position in the structure are keys for the efficiency, dexterity, and compatibility with optical or biological functions. Herein, an original approach consisting in the bonding of discrete and fully magnetic microbeads to unaffected 3D-microprinted structures is presented. Implemented in combination with the fine control of optical and mechanical properties allowed by the careful design of the 3D architecture, it is applied to the fabrication of the first remotely tunable biconvex microlens (focal length of 18 mu m). Combined with the additional precise positioning and magnetic orientation of multiple microbeads, the presented technique enables the fabrication of complex actuators such as a 100 mu m microtweezer that can be translated, rotated, and opened with a single variable external magnetic field. The dexterity of this untethered micromanipulator is demonstrated through a pick-and-place operation of 40 mu m objects in a confined environment.

Gallium nitride (GaN) is of technological importance for a wide variety of optoelectronic applications. Defects in GaN, like inversion domain boundaries (IDBs), significantly affect the electrical and optical properties of the material. We report, here, on the structural configurations of planar inversion domain boundaries inside n-doped GaN wires measured by Bragg coherent X-ray diffraction imaging. Different complex domain configurations are revealed along the wires with a 9 nm in-plane spatial resolution. We demonstrate that the IDBs change their direction of propagation along the wires, promoting Ga-terminated domains and stabilizing into {11̅00}, that is, m-planes. The atomic phase shift between the Ga- and N-terminated domains was extracted using phase-retrieval algorithms, revealing an evolution of the out-of-plane displacement (∼5 pm, at maximum) between inversion domains along the wires. This work provides an accurate inner view of planar defects inside small crystals.

Detailed characterization of the near fusion-boundary region of 18MND5/Alloy 52 dissimilar metal weld joints was performed to investigate the effect of thermal aging on the microstructure and mechanical properties and to quantify the diffusion of carbon into the weld metal. It was shown that the microstructural features of dissimilar metal welds, such as the size of the partially mixed zone in the weld and the adjacency to micro-segregations in the low-alloy steel have an effect on the peak carbon concentration in the enriched region of the weld. Aging conditions (time and temperature) influence the position of this concentration peak in the weld. Those trends were supported by thermodynamic calculations.

Magnetic shape memory alloys (MSMAs) and in particular Ni-Mn based Heusler materials are a new class of functional materials capable of magnetic-field-induced actuation, mechanical sensing, magnetocaloric and elastocaloric refrigeration as well as energy harvesting. However innovative ideas are needed to overcome many obstacles such as mechanical brittleness and materials shaping while having interesting functional properties. In the present work, flexible Ni45Co5Mn50-xInx ribbons with different x compositions have been developed by melt-spinning process. Good magnetic properties and bending strain up to 1% are very interesting for the use of these ribbons as actuators, sensors or in the field of magnetocaloric cooling. Entropy variations of about 15 J/kg K under 5 T and a cooling recovery RCeff of 144 J/kg can be obtained at around 300 K. Long ribbon lengths close to 20 cm with a two-way shape memory effect have been processed. We present a complete set of properties (magnetic, crystallographic, mechanical, actuating) for the optimal composition x = 12.5.

Fundamental understanding and quantitative characterization of electron transport mechanisms between two solids brought into mechanical contact require the development of a dedicated multifunctional device. In this study, we report original measurements and analysis based on a nanoindenter coupled with fine electrical measurements in-situ a Scanning Electron Microscope (SEM). After a description of the experimental set-up, we report quantitative results on resistive-nanoindentation on metallic systems with increasing complexity. Starting from a model case (Au single crystal), a procedure is developed and further applied to a complex rheology structure (200 nm Au thin film plastically deformed against an elastic substrate) to demonstrate the quantitative monitoring of contact area. Then a two-phase AgPdCu alloy is used to illustrate the resolution of spatial mapping of both mechanical properties and electrical resistance. Finally, we present our experimental results on natively-oxidized Al single crystal. The resistance evolutions during indentation are discussed in terms on dielectric breakdown and electrochemical processes.