Advanced small-scale mechanical characterization: strength, plasticity, fracture and fatigue

Resume : Small scale mechanical measurements did not only lead to new insights on size scaling effects in single crystal metals, but also opened new insights on fundamentals of plasticity, fatigue and fracture of bulk materials. In steels, for example, the different phases like ferrite, martensite, and/or cementite have a complex interaction, but often little is known about the performance of the individual phases. Small scale mechanical testing can be used to determine critical resolved shear stresses of different glide systems, study brittle-to-ductile transitions, deformation mechanisms and fracture toughness of brittle phases like cementite or Laves phases. Similarly, understanding environmental impact on mechanical properties of engineering alloys, like hydrogen embrittlement, where numerous phenomena are reported in literature, could benefit from small scale mechanical testing by focusing on different microstructure components. In that case it is important to ensure hydrogen charging of the small samples and avoiding surface roughening by chemical attack during electro-chemical exposure. In this presentation, recent advances on small scale testing of phases, grain boundaries and hydrogen embrittlement will be presented. Acknowledgement Major contributions by H. Tsybenko, C. Tian, F. Stein, J. Rao, N. Malyar, W. Luo, C. Kirchlechner, M. Kini, J. Duarte, S. Brinckmann are gratefully acknowledged. Part of this project was funded by the DFG within the project KI-1889/1-1. GD acknowledges financial support from the European Research Council (ERC) through Grant No. 787446 — GB-CORRELATE

Resume : Theoretical investigations of the mechanical properties of nanoparticles are essentially conducted by performing classical molecular dynamics simulations. A legitimate question is the reliability of classical interatomic potentials in these studies, due to conditions of large deformations and the need to accurately describe nanoparticles surfaces where plasticity is usually initiated. To overcome this limitation, I have recently developed an original approach allowing for the numerical simulation of nanoparticles compression at finite temperature with a first principles accuracy [1]. A moving flat punch indenter, modeled by a repulsive force field, was first implemented in a Car-Parrinello molecular dynamics code. The parameters were optimized to make the simulation feasible. Two main obstacles were encoutered during the tests. First, the high compression speed could result in an increasing unwelcome electron-ion coupling during the simulation. This issue was resolved by thermostating the electrons. Second, the nanoparticle was observed to start spinning during the simulation. Friction forces were added to largely mitigate this phenomenon. The pros and cons of the method will be discussed, followed by an example of successful application: the compression of buckminsterfullerene C60 at room temperature. It is shown that the C60 shell breaks at much lower strains than previously predicted with classical interatomic potentials, with a maximum contact force of 30 nN. It is also found that the huge elastic energy that can be stored in the molecule could lead to a complete recovery after release, even if a few carbon bonds were broken during compression. These results confirm the extraordinary resilience of the C60 fullerene. Our calculations also suggest that the molecule stiffness depends on the initial orientation, confirming the results of AFM experiments. Finally, I will discuss the potential application of this method to other systems, as for instance small crystalline nanoparticles. [1] L. Pizzagalli, Phys. Rev. B 102, 094102 (2020)

Resume : The mechanical properties of olivine (Mg,Fe)2SiO4 control the rheology of the upper mantle which ensures the mechanical coupling between the ductile asthenospheric mantle (which is involved in mantle convection) and the lithospheric plates. The subject is therefore of primary importance in geodynamics. Despite years of research, the viscoplastic behaviour of olivine is still insufficiently understood. It has been recently shown that amorphization of the grain boundary layer can occur under particular pressure and temperature conditions [1]. Amorphous grain boundaries might play a major role in governing the resistance to deformation of the polycrystal by high temperature grain boundary sliding (GBS), close to the glass transition. In this study, the rheology of amorphous olivine (a-olivine) films deposited by pulsed laser deposition has been explored by nanoindentation, at ambient temperature, in order to shed light on the mechanical behaviour that can be expected in such an amorphous layer. More precisely, a stress relaxation method via nanoindentation is used in order to extract the room temperature rheology. The contact stiffness is controlled in order to keep a constant contact area between the Berkovich?s tip and the material?s surface [2]. During this step, the load decreases and therefore, the mean contact pressure decreases as well. With this method, the strain rate sensitivity and activation volume can be accurately determined, as important characteristics of the atomistic mechanisms controlling the viscoplastic deformation. The major advantage of the stress relaxation method coupled to standard nanoindentation measurement is to access to strain rates from 10-7 to 10-1 s-1. Results highlight that a-olivine is five times more rate sensitive than crystalline olivine. When extrapolating this result to tectonic strain rates (between 10-16 to 10-14 s-1), the yield stress of a-olivine is shown to be almost five times lower than the crystal strength. This result is of primary importance for geophysics since it supports the hypothesis of plastic deformation mediated by grain boundary sliding within olivine polycrystals. The trend is already present at ambient temperature and should be enhanced when temperature increases to a significant portion of the a-olivine glass transition. As a perspective, more work will be performed with a high temperature nanoindentation set-up in order to characterize the limit temperature where GBS can be triggered. [1] K. Kranjc, A.S. Thind, A.Y. Borisevich, R. Mishra, K.M. Flores, P. Skemer, Amorphization and Plasticity of Olivine During Low-Temperature Micropillar Deformation Experiments, J. Geophys. Res. Solid Earth. 125 (2020) 0?3. [2] P. Baral, G. Guillonneau, G. Kermouche, J.-M. Bergheau, J.-L. Loubet, A new long-term indentation relaxation method to measure creep properties at the micro-scale with application to fused silica and PMMA, Mech. Mater. 137 (2019).

Resume : As the backbone material of the information age, Si is extensively used as a functional semiconductor and structural material in microelectronics and microsystems. At ambient temperature, the extreme brittleness of Si handicaps its manufacturing and performance in devices and systems. Here, we demonstrate Si processed by modern lithography procedures exhibits an ultrahigh elastic strain limit, near ideal strength (shear strength ~4 GPa) and plastic deformation at the micron-scale, one magnitude larger than previous observations, due to superior surface quality. This extended elastic regime enables enhanced functional properties by allowing higher elastic strains to modify the band structure. Further, the micron-scale plasticity of Si allowed us to investigate the intrinsic size effects and dislocation behavior in diamond-structured materials. This revealed a transition in deformation mechanisms from full to partial dislocations upon increasing specimen size at ambient temperature. This study demonstrates a surface engineering pathway for the fabrication of more robust Si-based structures and microdevices with enhanced semiconductor functionality.

Resume : Oxide glasses are an integral part of the modern world, but their usefulness can be limited by their characteristic brittleness at room temperature. Using in situ TEM and numerical simulations, we show that amorphous aluminum oxide can permanently deform without fracture at room temperature and high strain rate by a viscous creep mechanism [1]. These thin-films can reach flow stress at room temperature and can flow plastically up to a total elongation of 100%, provided that the material is dense and free of geometrical flaws coupled with an effective activation energy that allows sufficient bond-switching activity in the atom network. Our study demonstrates a much higher ductility for an amorphous oxide at low temperature than previous observations and we formulate a criterion that can help to find other oxides with similar behavior. This discovery may facilitate the realization of damage-tolerant glass materials that contribute in new ways, with the potential to improve the mechanical resistance and reliability of applications such as electronic devices and batteries. Moreover, the results indicate that amorphous oxides have potential to be used as high-strength, damage-tolerant engineering materials. The results reveal new aspects of glass thermodynamics below glass transition temperature and could lead to a new paradigm on how glass materials can be used in engineering. [1] Frankberg et al. Science Vol. 366, Issue 6467, pp. 864-869 (2019)

Resume : Friction and wear in mechanical systems cause a substantial contribution to global energy consumption. Studying fundamental mechanisms governing dislocation mediated plasticity as well as friction at metal sliding interfaces may greatly help advance the development of materials tailored for low friction and little wear. As the stress state in ball-on-flat contacts is notoriously complex and makes quantitative analysis difficult, deformation mechanisms in such systems warrant further investigation. This work therefore analyzes microstructural changes occurring on the micron scale as a result of sliding a sapphire sphere over high-purity copper in the vicinity of a twin boundary. Two characteristic horizontal line features (dislocation trace lines, DTL) are observed parallel to the sliding interface. Their interaction with the twin boundary is studied using automated crystal orientation mapping (ACOM). Making use of the twin boundary as a marker, three complementary fundamental deformation mechanisms are identified: A simple shear process affecting the immediate subsurface area and a localized plastic shear process occurring at the lower DTL as well as a crystal rotation of the areas between the sliding interface and both DTLs. Analysis reveals that the three processes are physically compatible. They can be considered decisive for guiding future experiments as well as computational modeling efforts.

Resume : Ductile fracture, the slow dissipation-controlled propagation of cracks, remains a key unsolved challenge in the mechanics of amorphous materials, currently limiting their strength and lifetime. Structural weakening within the highly focused strain field preceding the crack tip is thought to play the central role during ductile fracture. However, no consensus exists on the magnitude and nature of this dissipation as its dynamics remain elusive as atomic-scale observations continue to be prohibitively difficult. Colloidal glasses allow direct particle-scale insight into the structure and dynamics of deformation and fracture. Here, by direct particle-scale observation of a cohesive colloidal glass during slow fracture, we reveal remarkable spatio-temporal organization in the structural weakening process. Direct local measurement of the strain at the crack tip during crack propagation shows the intriguing interplay between elastic energy and dissipation behind these complex spatio-temporal correlations. We also use colloidal glasses to elucidate the mechanism behind plastic deformation of an amorphous solid, and find intriguing signs of criticality: local plastic regions grow until they percolate across the sample and the material yields. These results shed new light on the small-scale mechanical behaviour and dynamics.

Resume : High-throughput materials characterization is an emerging area in materials science. Starting from cheap raw materials, annealing of diffusion couples or multiples at elevated temperature allows the fabrication of specimens with a wide range of chemical compositions at small scales. This way, a single specimen can provide an enormous amount of data for database construction of novel alloys, including properties such as lattice parameters, phase stability and other physical properties. Considering the length scale of the composition profiles generated by interdiffusion, the determination of mechanical properties requires the use of advanced nanomechanical testing techniques. In this study, Mg/Mg-Zn and Mg/Mg-Al diffusion couples were produced with the aim of fast screening the composition-microstructure-mechanical properties relationships, for Mg-Al-Zn magnesium alloys. A range of techniques, like nanoindentation and micropillar compression, were used to determined the local mechanical properties, including strength and creep behavior at elevated temperature, over the available composition and grain orientation spectra in the diffusion zone, while the deformation mechanisms were determined by focused ion beam (FIB) and transmission electron microscopy (TEM). The outcome of this study and the feasibility of the approach to construct a quantitative composition-microstructure-property relationship for Mg-Al-Zn alloys will be discussed.

Resume : When a multilayer system is thermally cycled it undergoes a corresponding stress/strain cycle due to the different coefficients of thermal expansion of the respective materials. For thin metal films on silicon substrates it is known that the heating rate used for such a thermo-mechanical treatment has a significant influence on the system?s mechanical response. For microelectronic applications, it is indispensable to replicate application-typical heating conditions, which are characteristic pulses of sub-millisecond duration. In this study, the thermo-mechanical fatigue behavior of copper on silicon is investigated under repetitive thermal pulsing. In order to achieve extreme thermal conditions, special polysilicon-based actively heated devices, with a copper metallization on top, are used. Due to the low thermal mass, the heating devices allow quasi-adiabatic heating with heating rates in the order of 10^6 K/s reaching peak temperatures above 450°C. This corresponds to relative strain rates >10 s^(-1) in the Cu films. A novel in-situ setup is used to actuate the devices inside a scanning electron microscope to allow one to study the gradual deformation of the metallization on a microscopic scale, while applying several thousands of thermal pulses. In-situ electrical resistance monitoring and roughness measurements serve as additional means for characterizing degradation and deformation. For a more comprehensive understanding of the deformation behavior, tests have been performed at different base temperatures and at different heating rates.

Resume : Metallic glasses (MGs) have been intensively studied since the 60’s, due to their amorphous structure, intrinsic chemical homogeneity and lack of crystallographic defects, resulting in unique characteristics in comparison with conventional polycrystalline materials. Their mechanical behavior is characterized by an outstandingly high elastic domain and maximal strength. Although they are macroscopically weak at room temperature, they are highly ductile under high temperature [1], with a so-called “superplastic” deformation behavior. Thin film metallic glasses (TFMGs) deposited by magnetron sputtering show particular interest in terms of wide range of accessible chemical composition and enhanced ductility [2]. Zr-Cu based TFMGs are of particular interest for their good antibacterial and corrosion properties [3]. In this work, the mechanical behavior of Zr-Cu based TFMGs at high temperature is studied. Thanks to high temperature nanoindentation, the superplastic behavior of TFMGs is studied from hardness response during isothermal as well as temperature ramp experiments. Based on the work of Baral et al. [4], high temperature nanoindentation is also used as an original technique to evaluate the crystallization kinetic of metallic glasses. Results are correlated to high temperature X-Ray Diffraction measurements and microstructure imaging. [1] Spaepen, Acta Mater. 1977 [2] Chu et al., JOM 2010 [3] Nkou Bouala et al., Surf Coat Tech. 2018 [4] Baral et al., Mater. Des. 2018

Resume : High temperature materials depend on formation of a protective oxide scale for corrosion prevention. Variation of mechanical and thermal loads during operation causes scale cracking and can initiate damage in the material. It is therefore imperative to study oxide scale fracture and evaluate their mechanical properties. Despite chromia being the protective oxide for many materials, limited number of fracture studies have been performed. Our recent study on microscale fracture of chromia scales using at room temperature and 600 °C revealed the presence of transgranular fracture, though stress concentrations were present at grain boundaries, which implies that grain orientation also plays a role in fracture. However, the complex microstructure makes cleavage plane determination difficult. Microcantilever experiments were designed on single crystal wafers of known orientation, such that tensile direction was perpendicular to known cleavage planes for corundum structure. Fracture testing followed by SEM imaging of fracture surface was used to identify the cleavage plane, which showed pyramidal and rhombohedral fracture, though surface energy studies show only the latter. There was, however, a preference for rhombohedral fracture over pyramidal, which was seen both from microcantilevers and micropillar splitting experiments. Thus, it can be said that such an approach is beneficial to experimentally determine preferred cleavage planes.

Resume : High performance materials, from natural bone over ancient damascene steel to modern superalloys, typically possess a complex structure at the microscale. Their properties exceed those of the individual components and their knowledge-based improvement therefore requires understanding beyond that of the components? individual behaviour. Electron microscopy has been instrumental in unravelling the most important mechanisms of co-deformation and in-situ deformation experiments have emerged as a popular and accessible technique. However, a challenge remains: to achieve high spatial resolution and statistical relevance in combination. Here, we overcome this limitation by using panoramic imaging and machine learning to study damage in dual phase steels. This high-throughput approach now gives us strain and microstructure dependent insights into the prevalent damage mechanisms across a large area of this heterogeneous material. Aiming for the first time at automated classification of the majority of damage sites rather than only the most distinct, the new method also encourages us to expand current research past interpretation of exemplary cases of distinct damage sites towards the less clear-cut reality. A transfer to other materials, such as dual phase magnesium or high stiffness steels, has also been begun, as has the exploration of the third dimension of these complex microstructures to further expand the physical interpretation of the large datasets of electron micrographs now available.

Resume : The acceleration of product development while maintaining reliability is achievable through systematic digitalization of materials and sophisticated material models. However, the sparsity of materials data raises the demand for automated acquisition and generalizable processing of experimental data to account for the vast material space. In this work we address two fundamental tasks in materials science. Namely, automated and quantitative analyses of fatigue-induced surface damage and the microstructure inference from light optical or scanning electron microscopy micrographs. We apply deep learning (DL) methods since they can achieve generalizability across processing and material domains, when trained appropriately. Compared to conventional computer vision algorithms, DL not only alleviates the need for elaborate tuning of image processing pipelines to be applicable for other materials, surface treatments and imaging conditions but also achieves substantially higher accuracies in challenging tasks. Therefore, a U-Net network is utilized for semantic segmentation (multi-class pixel-wise classification) of slip traces and micro cracks in various materials as well as lath-bainite regions in complex phase steels. A comparison of both tasks is conducted and characteristics of both are highlighted. Thereby, this presentation aims to supply an intuition for DL methodology and necessary quantity and quality of data.

Resume : This research explores the viability of fabricating tailored micro-metallic membranes suitable for mechanical testing by using Focused Ion Beam (FIB) micromachining, or combining Differential Sputtering (DS) and subsequent FIB milling. The DS technique is currently widely applied in the silicon industry, but it has not been deeply developed for metallic alloys. In this work, the use of DS as a first step of the fabrication, allows simultaneous milling of a great number of micro-membranes, giving a high throughput in comparison to the typical serial manufacturing associated with FIB, and reducing the time devoted to sample preparation. A posterior precise milling by FIB is able to tailor the final shape and dimensions of the micro-membranes being tested. The assessment of the mechanical properties of these thin membranes is successfully carried out by micro-punch tests developed in this research inside a SEM microscope. This novel fabrication path followed by in-situ microtesting represents a breakthrough in the assessment of the mechanical behaviour of metals. It is of particular interest to cases in which the volume of material is small, the region of interest is micrometric (coatings or ion irradiated materials), or when samples are activated, avoiding in this latter case the need for hot cells infrastructures.

Resume : At small scales, materials often exhibit unique behavior. These size effects, often summarized as ?smaller is stronger?, have been extensively studied during the last two decades using various methods such as nano-indentation, synchrotron based x-ray diffraction, wafer-curvature, micropillar compression, bulge testing, cantilever bending, nanowire tensile experiments, and recently also by reflectance anisotropy spectroscopy (RAS). Most of these methods have issues with the characterization of ultra-thin polycrystalline films with thicknesses below 50 nm. Nevertheless, these ultra-thin films are widely used in industry as reflection- or diffusion-barriers. Therefore, the importance of understanding their mechanical properties, to avoid failures in service, is expected to increase with the rise of flexible electronics. RAS operates by probing the dielectric function in two orthogonal directions, and this makes it highly sensitive small changes in lattice spacing or elastic strain. Unlike Raman spectroscopy, RAS is not limited to any particular materials class, so nearly any continuous film can be investigated if the material has an electronic transition within the detection range: 1.5 - 5.5 eV. In this work, we demonstrate how to qualitatively and reliably test ultra-thin films on flexible substrates in uniaxial tension in-situ with RAS on film thicknesses below 50 nm. This allowed a new size effect study on Gold polycrystalline films with sizes down to 20 nm.

Resume : Organic materials are key candidates for the development of future technologies. In particular, polymer-based systems present outstanding mechanical properties, allowing the preparation of flexible and resistant components. They are of utmost interest in the fabrication of micro and nanodevices as a result of ease of processing down to nanoscales. A current challenge consists in studying the nanometric features of these materials using laterally-resolved techniques. In this work, we present a nanomechanical study of nanostructured polyesters films, using Atomic Force Microscopy (AFM). The nanostructures were formed by pulsed laser irradiation (Laser Induced Periodic Surface Structures, LIPSS). The nanomechanical properties were studied using a combination of techniques. We mapped the surface mechanical contrast using PeakForce Quantative Nanomechanical Mapping. Then, on selected areas of the films we performed force spectroscopy measurements. A detailed analysis of the force-distance curves allowed extracting quantitative values of the Young’s modulus, stiffness, indentation depth, and adhesion force. It was possible to determine that laser irradiated polymer surfaces presented enhanced properties, for example higher Young’s modulus, compared to their non-irradiated counterparts. Finally, on selected samples we performed Lateral Force Microscopy (LFM) measurements to study the impact of laser structuring on surface friction.

Resume : The present study deals with effect of welding speed on transient temperature distribution and its correlation with microstructure and mechanical properties during bead-on-plate experiment of electron beam welded Zircaloy-4 plate. Experimentally temperature was measured by K-type thermocouple at some selected location. Numerical analysis was investigated using finite element model (FEM) and found good correlation between experiment and simulated temperature data. Joint prepared with high welding speed (lower heat input) demonstrated lower peak temperature and faster cooling rate that resulted in decrease in the size of fusion and heat affected zone. Also the grain size of fusion zone and HAZ decreased with increase in welding speed. Widmanstätten type structure developed in fusion zone and randomly oriented acicular type structure developed in HAZ. Hardness of fusion zone and heat affected zone was found to be higher than base metal and it varied linearly with welding speed.

Resume : Recently, the metal nanoparticle formation technology has attracted a vast amount of interest due to its simplicity and practicality. Specifically, the metal nanoparticle networks are extremely useful in wearable electronics because they can maintain electrical properties under strong external deformation. Previously, we have developed a novel method to form Ag nanoparticles inside polymer based textiles using chemical reduction process. The Ag nanoparticle networks provoke change in the resistance of textile due to external mechanical stimulus, and this property allows the textiles embedded with Ag nanoparticle to be applied onto wearable electronics as a sensor. To improve the performance of this sensor, nano-/micro-scale architectures inspired by nature have been proposed. In our study, hierarchical microsized hairy architectures was developed to exhibit remarkable stretchability (<200%) and sensitivity of textile based sensor. The regularly ordered microhairy structures constructed with polyurethane-carbon black-silver nanowire (PU/CB/AgNW) composite mixtures are layered onto the Ag nanoparticle embedded textiles using imprinting technique. We analyzed the correlation between the aspect ratio and electrical conductivity of the microsized hairy architectures, and proposed a fabrication method of the optimized condition. Additionally, finite element method (FEM) simulation was modeled to understand the linear resistance changes by the microsized hairy architectures in pressure/strain condition. Consequently, the Ag nanoparticle embedded textiles with hierarchical microsized hairy architecture was applied to wearable electronics, which can monitor human movements.

Resume : Among micromechanical tests, bending of micro-cantilever specimens milled with FIB is particularly attractive as it offers several advantages. Specimens can be prepared directly from the surface of the bulk material, tests can be carried out using a nanoindenter, and the analysis can be relatively straightforward. This study investigates the use of this method to evaluate the fracture properties of different ceramic materials: zirconium dioxide ZrO2, uranium dioxide UO2, UO2 irradiated in commercial nuclear reactors, and nacre-like alumina Al2O3. Each of these oxide ceramics has different microstructures and mechanical properties. For example, UO2 shows bubbles of fission gas after use in a nuclear reactor, while nacre-like Al2O3 has platelet shaped grains and a weaker secondary phase at grain boundaries. The application of the micro-bending method to these ceramics has not only enabled to bring mechanical data on each material, but also to study the different parameters related to their microstructure: ‐ The influence of elastic anisotropy on mechanical properties at the grain scale ‐ The influence of defects on the measured fracture properties ‐ The local strength of an individual grain boundary ‐ The tensile and shear strength of an individual interface The analysis of these experimental data provides answers on the size effect observed on the fracture strength measured at a local scale, which is of the order of several GPa, i.e. an order of magnitude above macroscopic values.

Resume : Due to increasing problem of infectious diseases, there is a need to introduce solutions that limit the development of microorganisms in food industry, medical facilities and public places. Some products used in these areas are made of austenitic stainless steel, which is corrosion resistant and has aesthetic metallic surface, however it is not antimicrobial and scratch resistant, which results in the creation of sites favouring the development of biofilm. In order to overcome these limitations the deposition of hard S-phase coatings with copper is proposed. S-phase commonly considered as supersaturated nitrogen solution in austenite are characterized by high hardness and wear resistance. Coatings with different copper content in the S phase structure were obtained by reactive magnetron sputtering method by simultaneous sputtering of austenitic steel and copper targets in a nitrogen atmosphere with varying copper target current. The coatings were tested for microstructure, chemical and phase composition as well as for mechanical properties and antimicrobial activity. The presence of S-phase was evaluated using X-ray diffraction. Copper has been found to have about 44% threshold of solubility in S-phase, and within this range it has limited influence on high mechanical properties of S-phase coatings as studied by nanoindentation method. The coatings with the addition of copper were characterized by good antimicrobial properties: 100% bactericidal, high biostaticity and good antimicrobial activity against Staphylococcus aureus.

Resume : GaP nanowires (NWs) are promising materials for flexible devices. Bulk GaP has the zinc blende (ZB) structure, GaP NWs may have a wurtzite structure (WZ) with a direct band gap. During the growth planar defects (stacking faults and twinning) may occur. Mechanical properties of the WZ GaP NWs and an impact of the planar defects on the Young’s modulus almost have not been studied. Here, we studying these features by atomic force microscopy (AFM). Pure WZ GaP NWs were grown by MBE on a graphene/SiC substrate. NWs with high density of the planar defects were grown by MOVPE on Si substrate. We investigated inclined NWs with diameters of 60 to 100 nm and with the length up to 3 microns. Previously, we have developed an AFM method based on the PeakForce technique (Bruker) for determining the Young's modulus of single NWs obliquely grown on substrate [1]. This technique allows measuring the force-distance curves at each point of the scan, as well as the deformation of the object by the probe with a well-controlled force. By analyzing the deformation profiles along the axis of a NW one can determine its stiffness and Young's modulus. The Young's modulus of the NWs with a pure WZ structure was 160±20 GPa which is close to the theoretical value (167 GPa). Planar defects did not impact on the Young's modulus. Theoretical explanation of the experimental findings is also presented. [1] M. Dunaevskiy et al.// Nano Lett., 17, 3441 (2017) This work is supported by Russian Presidential Grant МК-1543.2020.2

Resume : Microstructure strongly influences the mechanical properties of thin films. Consequently, the characterization of mechanical behavior at small length scales is fundamental. In particular, stress mapping is of great interest since it allows the study of fracture mechanics, e.g. visualizing the stress distribution around a crack tip. Conventional lab scale stress mapping techniques are based on electron microscopy (EM) and Raman spectroscopy (RS). Common drawbacks are the required high vacuum for EM and the need of Raman active materials for RS, hindering the range of materials that can be analyzed. Here, we present an advanced reflectance anisotropy spectroscopy (RAS) microscope based on a super continuum laser source as a non-destructive stress mapping technique for a wide range of materials. Our microscope enables insight into the electronic band structure, phase and crystal orientation. We demonstrate strain mapping in sputtered thin films on flexible substrates and outline the potential of the technique for mapping grain orientation using polycrystalline copper. The simultaneous stress and grain orientation mapping will enable future studies on the fracture mechanics of thin films and novel materials with different microstructure and environmental conditions.

Resume : One-dimensional electrodes and devices using nanomaterials and nanostructures have been developed due to a lot of advantages, such as highly flexible, low cost and light weight. Precious studies, however, presented limited structure of certain metals and could only sense one property like mechanical stress. Herein, we fabricated Palladium (Pd) nanoparticles on polyurethane (PU) based fiber using a novel method that immersed elastomeric fibers into metal precursor chemical solutions. Pd nanoparticle shells were fabricated on the PU fiber, which acts as a conducting path and lowers electrical resistance of polymer. When the fiber was stretched, nano-cracks of Pd nanoparticle shells were formed on the fiber surface. The formation of Pd nano-cracks can be controlled by the number of chemical solution processes. Depending on the stretching rate (10 ~ 110%), the connection between Pd nanoparticle shells was changed which determine conductivity of fiber. In addition, exposure to hydrogen (H2) gas changes the conducting network of Pd nano-cracks since Pd reacts with H2 gas to form PdHx. We could also detect very small amounts of H2 gas (5 ppm) by analyzing variation in Pd nano-cracks. To conclude, an unprecedented process was used to fabricate the Pd nanostructures on fiber and simultaneously detect H2 gas concentration and mechanical strains through crack network analysis between Pd nanoparticles.

Resume : Microscale experiments enable to isolate microstructural contributions to the global mechanical deformation behavior of a sample. By structuring micropillars at specific regions of interest of a sample, the quasi-static and fatigue behavior of these microstructural features can be analyzed independently. Local fatigue tests were carried out on a bimodal copper sample containing alternating layers of ultrafine and coarse grainsize. Micropillars are fabricated in the plain coarse domain, ultrafine domain and in the interface region. In quasi-static compression, the bimodal micropillars show a 12 % increased strength (at 1 % plastic strain) compared to the ultrafine grained micropillars, revealing the pronounced hardening effect of the bimodal interface. In fatigue testing, the bimodal micropillars show a reduced lifetime compared to the ultrafine grained micropillars. This reduced fatigue lifetime likely originates from extrusions forming in the coarse grained area of the micropillar. In addition, the ultrafine grained part experiences cyclic softening by microstructural coarsening. The cyclic deformation mechanisms will be discussed based on Focused Ion Beam (FIB) cross-sections of the tested micropillars.

Resume : The aggregation and structure formation of PEGylated gold nanoparticles have been investigated by in-situ time resolved UV-Vis spectroscopy and small angle X-ray scattering (SAXS) upon triggering the conformational change of the surface grafted PEG chains at high temperature and ionic strength. We found that during the aggregation procedure the particles accommodate an effective equilibrium particle-particle distance of 2 nm. The results are in qualitative agreement with the data obtained from colloidal interaction energy calculations. Additionally, the aggregation process is reversible to some extent based on both the spectroscopy and SAXS data, pointing towards a rather moderate attraction between the particles in the clusters. The work received support from the bilateral French-Hungarian S&T Cooperation (2018-2.1.13-TÉT-FR-2018-00002). We acknowledge beamtime allocation by the SOLEIL synchrotron (project number 20181790)

Resume : Colloidal crystals (CCs)[1] made of self-assembled polymer nanoparticles can be used as photonic[2] and phononic crystals[3], smart coatings, and masks for nanolithography. However, their fragility remains a critical limitation in device fabrication. Recently, we reported the mechanical reinforcement of CCs utilizing gas hydrostatic pressure[4]. Here, we discuss the size dependence of nanoscale soldering of polystyrene (PS) particles in various gaseous environments. We used N2, Ar, and He gases to have a comparative study of the effect of plasticization on the soldering of nanoparticles. We utilized in-situ Brillouin light scattering to measure the acoustic vibrations of the particles, allowing us to determine the optimal gas pressure for achieving mechanical reinforcement at room temperature. We also identified the trend in the relative contact area change as a function of particle size in the presence of the gas plasticizers. Acknowledgments: The work was support by the Foundation for Polish Science (POIR.04.04.00-00-5D1B/18). References: [1] Hailin Cong, B. Yu, J. Tang, Z. Li, X. Liu, Chem. Soc. Rev. 2013, 42, 7774. [2] J. Hou, M. Li, Y. Song, Nano Today 2018, 22, 132. [3] E. Alonso-Redondo, M. Schmitt, Z. Urbach, C. M. Hui, R. Sainidou, P. Rembert, K. Matyjaszewski, M. R. Bockstaller, G. Fytas, Nat. Commun. 2015, 6. [4] V. Babacic, J. Varghese, E. Coy, E. Kang, M. Pochylski, J. Gapinski, G. Fytas, B. Graczykowski, J. Colloid Interface Sci. 2020, 579, 786.

Resume : There is a significant interest in using piezo-ceramics in emerging technologies that combine flexible electronics with energy-scavenging from ambient mechanical vibrations. However, these novel applications require the piezoelectric materials to demonstrate high flexibility and to have lightweight while maintaining moderate/high stiffness as well as high piezoelectric and dielectric coefficients. One promising approach to meet these requirements of material-properties is to use smart polymer nanocomposite films where piezo-ceramics are embedded in a polymer matrix. The nanoceramics because of their small size have a high surface-to-volume ratio resulting in high interfacial energy. This gives rise to the formation of an interphase layer between matrix and filler with distinct material properties, which often becomes a dominating factor in developing the properties of the nanocomposites. Several researchers have experimentally worked and developed computational models to determine the effect of interphase on the effective properties of nanocomposites. Most of the computational models address the effect of interphase only on the mechanical properties of the nanocomposite and a very few results are available in the literature on the effect of interphase on the effective electroelastic properties of nanocomposites. Thus, in an attempt to study the effect of interphase on the effective electroelastic properties of smart nanocomposites, Finite Element Method (FEM), which is one of the popular predictive computational tools, has been used in this work to determine the effect of interphase on the effective electroelastic properties of Polydimethylsiloxane (PDMS) / PMN-30%PT polymer nanocomposite. PDMS/PMN-PT combines the light weight and flexibility of PDMS as the matrix with excellent piezoelectric charge constant and high electromechanical coupling factor, is one the popular nanocomposites for vibration-based piezoelectric energy harvesting device. Periodic Boundary Conditions (PBCs) have been used in the finite element analysis to ensure periodicity in the nanocomposite. Different representative volume elements (RVEs) with different interphase properties as well as with different interphase thickness are also proposed. Finite element software ABAQUS is used for the finite element analysis. A cubic RVE having dimensions 100×100×100 with unidirectional spherical type reinforcements is considered. Different representative volume elements (RVEs) based on the distribution of reinforcement are generated. The interphase is modeled as a continuum material having continuous and homogeneous material properties and can be considered as a third phase in the matrix/reinforcement system. A perfect bonding is assumed between the phases. The interphase properties are assumed to be weaker than matrix, stiffer than matrix, as well as Voigt average of matrix and reinforcement. The thickness of the interphase is varied from 1 nm, 2 nm, and 3 nm. Four-noded tetrahedral element ‘C3D4E’ is used for meshing the geometry. PBCs in the form of displacement and electric potential was applied to determine five elastic constants, three piezoelectric stress coefficients, and two dielectric coefficients of the nanocomposite system. The results establish a high dependence of the effective nanocomposite properties on the properties and thickness of the interphase.

Resume : Numerous applications require comprehensive understanding of tribological processes on the micro- and nanoscales. We propose pin-on-disk microtribological test for investigation of wear behavior of materials and coatings in contact with a sliding motion. For this purpose, precision rotational stage was developed and integrated to the multifunctional “Micron-gamma” indentation tester. Friction force and indenter penetration depth are recorded continuously through rotational motion of the sample. Surface morphology of the tracks is measured by “Micron-alpha” optical profilometer. We studied thin films with a thickness of up to 100 nm consisted of several layers of Cr, Cu, Ni, obtained by different deposition techniques on a single-crystal Si (100) substrate. Tribological measurements were performed for the films in as-deposited state, after low-energy (1000 eV) Ar+ ion irradiation, after annealing at ~500 oC in vacuum, and complex treatment with ion pre-irradiation and post-annealing in vacuum. Samples were explored using conical diamond indenter with tip radius 50 µm and maximum normal load 500 mN. Indenter load increased gradually during rotation along the circle with the diameter of 200 µm. The highest wear resistance is revealed for the film after complex ion and heat treatment, no film failure or delamination occur, and track depth is 20 nm. All other films start to fail at different indenter loads with a various failure mechanisms and track depth ranging from 60 to 80 nm. It is shown, that proposed method using “Micron-gamma” indentation tester can be successfully applied for characterization of tribological behavior of thin films to optimize the deposition process as well as to investigate the effects of ion and heat treatment.

Resume : Composite materials attract a huge scientific interest as materials with a wide spectrum of controlled properties. In particular, organically-linked Fe3O4 nanocomposites based supercrystals demonstrate unique combination of strength and stiffness [1]. Nevertheless it is not fully clear if the "smaller is stronger" trend is also relevant for such new materials. Better understanding of the mechanical properties requires in-situ deformation experiments with nano- and micro-specimens. Such kind of studies can only be performed using nanoprobes with high spatial resolution and sensitive to small structural changes, such as nanofocused, high energy X-ray beams. The P03 Nanofocus Endstation at PETRA III at DESY (Hamburg, Germany) is operated by Helmholtz Zentrum Geesthacht and offers unique conditions for mechanical tests coupled with X-ray nanodiffraction [2]. The highly stabile experimental setup is dedicated to structural analysis with sub-micron precision. The X-ray beam is focused down to a size of only 250 x 250 nm^2 by means of KB-mirrors with focal distance of ~10cm which provides space for extended, in-situ sample environment implementation. The strong focus on materials science at P03 is demonstrated by the wide range of in-situ experiments already performed, such as mechanical testing with strain resolution of 10^-5 [3]. In this presentation the applicability of P03 instrumentation for in-situ mechanical tests will be presented. Combining scanning X-ray nanodiffraction with a self-developed nanoindenter we have performed unique experiments separating the influence of organic and non-organic components to the mechanical properties of a microsized supercrystal. Detailed technical specification of the beamline will be shown as well as results obtained during the experiment. References: [1] Dreyer A., Feld A., Kornowski A.,Yilmaz E., Noei H., Meyer A., Krekeler T., Jiao C., Stierle A., Abetz V., Weller H. Schneider G., Nature Materials 15 5 (2016); [2] Krywka C., Neubauer H., Priebe M., Salditt T., Keckes J., Buffet A., Stephan Volkher Roth S., Döhrmann R., Müller M., J.Appl.Cryst.45, 85 (2012); [3] Zeilinger A., Todt J., Krywka C., Müller M., Ecker W., Sartory B., Meindlhumer M., Stefenelli M., Daniel R., Mitterer C. Keckes J., Sci. Rep. 6,22670 (2016).

Resume : Since the discovery of picosecond ultrasonics by H. J. Maris and his team in 1984, this nondestructive technique continuously expanded and found numerous applications. Where the first application concerned thin film thickness measurement in the semiconductor industries with a complex setup, the picosecond ultrasonics technique is now much more efficient, user-friendly and widespread. Indeed, thickness measurement is now easily reachable and this technique also allows the elastic properties measurement of thin films, multilayers and nanostructures, adhesion properties evaluation, etc. Thus, among all the fields that are potentially interested in this new technique are mainly surface engineering, microelectronics, and biology. We will see how the photo-generation and the photo-detection of ultra-high frequency ultrasounds (of the order of THz) can accurately and rapidly measure the thickness of a TiN hard coating on a Ti substrate. This measurement can be performed either locally with a high spatial resolution or by scanning the sample, hence giving a mapping of the thickness measurement on the whole surface. Up to now, the shape of the samples had to be very flat; in this presentation, we will demonstrate that we can also analyze even highly curved samples. Compared to concurrent techniques such as ellipsometry or the Calo tester, picosecond ultrasonics presents the unique advantages to be contactless, nondestructive, and able to evaluate the properties of a complex shape sample. To illustrate this last point, results will be presented showing outstanding features such as an advanced 3D mapping of a hard coating thickness on a cylinder or a sphere.

Resume : Sodium borosilicate (SBN) glasses concern an important research topic as the three components (SiO2, Na2O, and B2O3) corresponding to the three principal oxides of many industrial glasses. For certain chemical compositions, an important feature includes amorphous phase separation (APS) which has industrial relevance for crush resistant glasses, porous glasses and glass ceramics. Moreover, theory, simulations, and experiments evidenced two-phase APS glasses; however, there is the possibility of three-phase APS for some compositions. APS inside the glasses induces complex heterogeneous structures at the nano-scale, which alters the glasses' physical and mechanical properties (including stress corrosion cracking (SCC) behavior). However, the connection between the structure of APS glasses and their properties remains poorly understood, especially the SCC behavior. In this presentation, we will look at a SBN sample with compositions falling in the hypothesized three-phase APS zone. I will present results on how annealing the sample aids the growth of the phase separation as seen by an AFM. Besides, TEM provides some clues to the APS structure. Additionally, NMR spectrums aid in understanding the short-range structure of the APS glasses. Nano-mechanical (PF-Tapping) AFM techniques were used to characterize the local mechanical properties of different phases. Moreover, stress corrosion cracking tests along with post-mortem studies of fracture surfaces were performed to understand the failure mechanisms in these phases separated systems. These results will also be discussed. This study will aid in capturing holistic viewpoint of how glasses fail.

Resume : Recently it has been demonstrated [1] that electrical devices based on Silicon Carbide can be used as transparent mode detectors for the real-time in line beam position monitors and intensity monitors of hard X-ray radiation. This material is also promising for quantum sensing [2] and MEMS applications [3]. One of the important steps for the production of such devices is a partial or total removal of thick substrate material (>350 μm) in order to form micro- and nanoscale membranes confining the active regions of fabricated devices to the high quality, doped controlled, epitaxies. Therefore, the development of doping selective electrochemical processes for the local etching of SiC layers is crucial for design and realization of advanced nanoscale devices. In this work, we present extensive experimental results on the electrochemical etching (ECE) of n-type highly doped (1·1018 cm-3) 365 μm thick SiC layers in Hydrogen Fluoride (HF) based electrolytes using galvanostatic (constant current density, J) and potentiostatic (constant voltage, V) modes. The process control is performed following the corresponding V(t) and J(t) curves, while the membrane thickness is adjusted via the implementation of low doped stopping layers. The structural modifications of etched SiC films at different ECE stages assigned by in-situ electrical measurements are investigated as a function of HF concentration, current density and electrolyte composition. The optimized recipes allow to reach high etching rates, >2.5 µm/min, with roughnesses lower than 50 nm. The obtained nanoscale SiC membranes are applicable for the fabrication of in-situ X-ray sensors, in line beam position/ intensity monitors and quantum sensing devices. [1] S. Nida et al. J. Synchrotron Rad. (2019) 26, 28. [2] S. Castelleto et al. Nature Materials (2014) 13, 151. [3] F. Zhao et al. Microsyst. Technol. (2017) 23, 5631.

Resume : One of the most common methods to measure the elastic modulus and hardness of thin films is to use nanoindentation. In order to remove the influence of a substrate the well-known “10% rule of thumb” is utilized. This “rule” states that the elastic modulus and hardness can be taken at 10% of the film thickness with no or little influence from the substrate. While this guideline may hold true for some film-substrate systems (hard-on-soft or soft-on-hard) and film thicknesses (greater than 100 nm), it cannot and should not, be applied universally. It will be shown on single crystalline copper films on sapphire, grown by thermal evaporation (50, 100, and 300 nm thick) that the hardness can be evaluated but the elastic modulus cannot be properly measured when compared to bulk single crystal copper. It will be demonstrated that the elastic modulus is a long range property that is substantially influenced by the substrate even at indentations of 10% of the thickness. For example, using the initial Hertzian elastic portion of the load-displacement curve before a pop-in occurs does not allow for the elastic modulus of copper to be measured. The findings reveal that the 10% rule should not be applied to evaluating the elastic modulus of thin films.

Resume : Colloidal crystals realized by self-assembled polymer nanoparticles are volumetric and low-effort materials that found various applications, from assembling photonic and phononic crystals to coating applications. However, the fragility of these systems limits their application horizon. This work reports the uniform mechanical reinforcement and tunability of 3D polystyrene colloidal crystals employing a new concept termed “cold soldering”. The structural strengthening is achieved by supercritical gas (N2 or Ar) plasticization at temperatures well below the glass transition. This method is a synergistic combination of nanoscale plasticization of particles’ surface and compressive hydrostatic pressure. It results in permanent physical bonds forming between the particles while maintaining their shape and periodic arrangement. We employed Brillouin light scattering to monitor in-situ the mechanical vibrations of the crystal and thereby determine preferential pressure, temperature, and time ranges for soldering, i.e., the formation of physical bonding among the nanoparticles. This low-cost method offers a chemical-free and efficient solution for the fabrication and tuning of durable devices. It is also a potential remedy for the release of micro/nano contaminants into the environment. Moreover, the fundamental idea of our approach, plasticization of polymeric nanostructures by means of supercritical gasses, remains an uncharted territory offering new effects and opportunities. Acknowledgements The work was supported by the Foundation for Polish Science (POIR.04.04.00-00-5D1B/18) and ERC AdG SmartPhon (Grant No. 694977).

Resume : Chemical disorder represents a major component of multicomponent high-entropy alloys (HEA), materials that appear to have favorable thermo-mechanical properties and numerous industrial applications in extreme environments. The roles that chemical disorder plays in controlling mechanical properties of HEAs, may be clarified through high-throughput nanoindentation studies. Here, we compare mechanical nanoindentation responses of single-crystalline HEA and single-component metals as a function of temperature, and investigate the related microscopic dislocation defect behaviors. We carry out Molecular Dynamics (MD) simulations of the effects of temperature on mechanical properties and nanoscale deformation of crystalline Mo, Fe and FeCoCrMnNi under spherical nanoindentation at constant-displacement rate of 20 m/s. MD simulations are performed by considering [100], [110], and [111] crystal orientations, a sample temperature range of 30-1000 K, and an indentation depth of 10 nm. We find that the formation, shape and ensemble of surface-nucleated dislocation loops are drastically influenced by increasing temperature and chemical disorder. Results point towards both qualitative and quantitative differences in the response of HEAs, compared to single-component metals, that can be tracked by the material hardness, Young modulus, and surface displacement images, and classified through the use of statistical means and machine learning.

Resume : Chalcogenide glasses are attractive optical materials due to their high transmittance and low losses in the near infrared spectrum. Many applications of these glasses require patterning with micro/nano- structures, e.g. diffraction gratings, antireflection morphologies, or waveguides. These patterns can be imprinted due to the low glass transition temperature (Tg) of those glasses. However, high imprint pressure and temperature deforms the imprinted substrate. Here, we demonstrate a novel approach for the direct imprint of chalcogenide glasses, by which the glass solution is spin coated on the glass substrate, and baked to produce a plasticized film whose glass transition point is below that of the bulk chalcogenide glass. The film is then imprinted with soft mold at the temperature below that of the Tg of the bulk chalcogenide glass, thereby maintaining the original substrate shape. We demonstrated this approach by imprinting As2Se3. First, we characterized Tg of the solution-deposited As2Se3 films using nano-indentation, to optimize the conditions for the film formation. We then fully characterized the chemical composition and optical properties of the frim and imprinted structures, and verified that they are similar to that of bulk As2Se3. Finally, we patterned As2Se3 surface with diffraction grating and moth-eye antireflective coating. Our approach opens a novel route for facile micro-processing of chalcogenide glasses and enables their numerous future applications

Resume : Few-layer van der Waals (vdW) materials have been extensively investigated in terms of their exceptional electronic, optoelectronic, optical, and thermal properties. However, the impact of nanoconfinement on their mechanical properties remains controversial in the scientific community. Due to the small lateral sizes of samples, and the limitations of experimental approaches, a complete evaluation of their mechanical properties is an undeniable challenge. In particular, there is no systematic experimental study on whether the elastic constants change when reducing the material thickness, with respect to the bulk, and to which extent. In this work, we employ micro-Brillouin light scattering to investigate the anisotropic elastic properties of single-crystal free-standing 2H-MoSe2 as a function of thickness, down to the two molecular layers. We report the so-called elastic size effect, i.e., significant and systematic elastic softening of the material with decreasing numbers of layers. Besides, we show that our approach allows for a complete mechanical examination of few-layer membranes, i.e., their elasticity, residual stress, and thickness. In perspective, this method can be applied to other few-layer vdW materials for their mechanical evaluation. Our findings are highly relevant for related research fields such as nanoscale thermal transport, electronics, or resonators employing vdW materials. Furthermore, the reported nanoscale softening has profound implications in designing and developing nanodevices, where mechanical properties are essential for their durability and robust performance. Acknowledgments: The work was supported by the Foundation for Polish Science (POIR.04.04.00-00-5D1B/18). ICN2 was supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706). K.-J.T. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 804349 (ERC StG CUHL), RyC fellowship No. RYC-2017-22330 and IAE project PID2019-111673GB-I00. E.C. acknowledges the partial financial support from the National Science Centre (NCN) of Poland by the OPUS grant 2019/35/B/ST5/00248.

Resume : Understanding of mechanisms of phase transitions under electric field is very important from practical point of view. Possibility of control a phase transition in ferroic material such as lead zirconate-titanate (PZT) opens door to electric field domain engineering. As a result, we have new possibility in developing new electronic memory devices, based in charge domain walls, energy harvesters, and so on. In this work we studied sequence of phase transitions of in Zr-rich PZT single crystal under weak electric field using X-Ray diffraction. Sample was prepared from 101 crystalographically orientated piece of PZT single crystal with 4% of Ti content (PZT2.4). Sample was cutted with diamond disc with consequent polishing and etching in sulfuric acid. Finally, sample had a needle form 50*50*1000 um. Sample was mounted in special device (electric field cell). Measurements were carried-out at single crystal diffractometer in field-cool regime: heating sample up to 750 K, application of electric field of 5kV/cm in 101 crystalographical direction and acquiring diffraction datasets on cooling with 3 degree per step. PZT2.4 has two phase transitions on cooling: from paraelectric (PE) to intermediate ferroelectric (FE), and then from (FE) to Antiferroelectric (AFE). We founded that phase transition from FE to AFE in presence of electric field is splinted into two stages. In present time we have explanation of this mechanism. And now we study dependence of this effect on magnitude of electric field.

Resume : In the electronics industry achieving a strong bonding between dissimilar materials such as metal and polymer composites is one of the most challenging issues. Improvement of the interfacial adhesion strength between copper foil and dielectric material is essential to enhance the performance of the printed circuit boards (PCBs). Adhesion is generally enhanced by treating copper surface mechanically to increase the surface roughness. However, increasing roughness on the copper surface significantly deteriorates signal transmission in high frequency applications due to the skin effect. Herein, we present an adhesion promoter layer which is coated onto a very low profile (smooth) copper foil via solventless techniques such as vapor deposition and initiated vapor deposition (iCVD). As an adhesion promoter 3-[2-(2-Amino-ethylamino)ethyl-amino]propyl-trimethoxysilane (APTMS) and 4-Vinylpyridine (4VP) are applied to copper surface and dielectric resin, respectively. Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), variable angle spectroscopic ellipsometry (VASE), and contact angle goniometer are used to characterize thin film properties. Adhesion strength of copper foil to dielectric material is determined by using universal testing machine (UTM). The results show that thin film coatings enhanced the peel strength of the laminated copper/dielectric composite at least 20% without compromising the smoothness of the low profile copper foil. The increased adhesion obtained in this study plays a critical role to avoid delamination during multilayer PCB construction processes.

Resume : Several studies have recently reported the formation of stacking faults in silicon compressed at low temperatures and high stresses. This observation contradicts the generally accepted framework for the plastic deformation of silicon. We propose here an original plasticity mechanism that could potentially explain stacking fault formation in these conditions: the nucleation and migration of a partial edge dislocation with a Burgers vector equal to 1/3<112>. These results were obtained thanks to a multiscale approach combining three computational methods. Dislocation nucleation is modeled using molecular dynamics in both a nanowire and a 2D slab. Results are next used as inputs for hybrid MD/DFT “learn on the fly” calculations, allowing for studying the dynamical propagation of the dislocation. Selected configurations at different steps are next used for initiating nudged elastic band density functional theory calculations. These calculations revealed that the dislocation displacement mechanism depends on the compression strain. For low values, a dangling bond is temporarily created in the core, resulting in high activation energies. For compression strains larger than about 8%, the reduction of the interlayer distance allows for a more complex displacement mechanism with no dangling bonds in the dislocation core and a significant decrease of the activation energy.

Resume : The nature of the interface in contact with living species is the prime interest in the field of biomaterials, prostheses, biosensors, implants… This interface can be easily modified through PVD processes in terms of chemistry, structure, microstructure… In the past decade, intense research activity was devoted to Ti-Ag coatings for biosensors, titanium being strongly biocompatible, while silver brought its good electrical response. Even though some papers are focused on optimizing the films’ chemical composition and phases, no data are available, to the best of our knowledge, on the wear resistance of these films. Such a requirement is crucial for biosensors, if we consider rubbing against the body, skin, clothes… To better understand the tribological behaviour of this metallic ductile thin system, an original approach is required. It consists of using a laboratory-made reciprocating ball-on-disc mini tribometer specifically-designed to be introduced into an SEM chamber [1], allowing a small-scale in situ characterisation of the damaging surface. Besides, the device can also be coupled with a Raman spectrometer to give further dynamic information on the wear track's chemical evolution. The study’s objective is to link the tribological behaviour of films with their mechanical properties, chemical composition and microstructure. Titanium-based films were deposited by PVD magnetron sputtering, silver content was controlled by the relative Ag/Ti areas ratio of targets. Considering a previous study on both flexibility and electrical conductivity of films [2], 4 compositions were identified (Ag-free, low-, moderate and high-Ag contents). Films characteristics were determined by RBS spectroscopy, TEM, XRD and high-temperature XRD. Even if mechanical properties are not really influenced by the silver content of films, their microstructure is drastically changed with presence of Ag-rich submicrometric particles for moderate and high silver enrichments. The presence of this further phase appears to change the rubbing dynamics strongly. [1] Masters’ internship reports in LaMCoS & MATEIS on Tribometry and In-situ Instrumentation in E-SEM and under Raman spectrometry : A. KRID in 2018, L. JIN in 2019 [2] Etiemble, A., Lopes, C., Bouala, G. I., Borges, J., Malchère, A., Langlois, C., Vaz, F., & Steyer, P. (2019). Fracture resistance of Ti-Ag thin films deposited on polymeric substrates for biosignal acquisition applications. Surface and Coatings Technology, 358, 646-653. doi:10.1016/j.surfcoat.2018.11.078

Resume : Abstract Olivine, is a silicate with (Mg, Fe)2SiO4 composition and orthorhombic symmetry and which is present in the Earth’s mantle down to 410 km depth. There is evidence that in the convective mantle, olivine deformation involves dislocation glide and climb. However, due to its low symmetry, this mineral does not possess enough slip systems to satisfy the Von Mises criterion [1,2]. Several recent studies have focused on the possible contribution of grain boundaries (GBs) (sliding, migration) to the deformation of olivine aggregates, but so far, the mechanisms at play are not yet clarified. Recently, high resolution TEM microstructural investigation of olivine aggregates deformed at ca. 1100°C revealed a ductile behavior involving amorphization of GBs. Here we use in situ TEM nanomechanical testing on olivine aggregate samples (without amorphous layer at the GB) to gain information on the underlying deformation mechanisms. We use the PI-95 TEM Pico-indenter holder and the Push-to-Pull (PTP) device (Bruker. Inc) to perform quantitative in situ TEM tensile tests at room temperature. Bi- and tri-crystal olivine samples were prepared by focused ion beam (FIB). We show that the specimens deform exclusively by grain boundary sliding while observing evidence of stress-induced amorphization in the sliding GBs. The elementary mechanisms involved are discussed and compared to the literature. Reference: [1] R. E. Bernard, W. M. Behr, T. W. Becker, and D. J. Young, “Relationships Between Olivine CPO and Deformation Parameters in Naturally Deformed Rocks and Implications for Mantle Seismic Anisotropy,” Geochemistry, Geophys. Geosystems, vol. 20, no. 7, pp. 3469–3494, 2019, doi: 10.1029/2019GC008289. [2] M. Thieme, S. Demouchy, D. Mainprice, F. Barou, and P. Cordier, “Stress evolution and associated microstructure during transient creep of olivine at 1000–1200 °C,” Phys. Earth Planet. Inter., vol. 278, no. February, pp. 34–46, 2018, doi: 10.1016/j.pepi.2018.03.002.

Resume : The precise characterization of micro- and nanomechanical material properties is up to now a field of material scientists with fundamental knowledge of contact mechanics. Failure to follow the device-related preparations for the actual measurement can have a major impact on the measurement results and make a quantitative statement often impossible. As digitalization progresses, the need for micro and nanomechanical sensors and actuators increases. This means that the need for quality-assuring analysis technology is growing in order to ensure that such components are of sufficient quality. This also increases the need to adapt the measurement method to the industrial environment. The expertise for the measuring process must pass from the user to the machine. Therefore, the entire chain of effects of the measuring process - the preparation of the measuring device, the sample preparation, the implementation of the measurement and the processing of the measured values ​​must be designed to be variable and error-free. SURFACE has taken with its sm@rt system the first step in this direction. Thanks to its modularity, the new sensor concept can be adapted to the application area - wide load range, large linearity range, high resolution, high measurement quality. All this is paired with very small sensor dimensions. Microcontroller systems with the latest signal processors and scalable software / hardware architecture are also used on the control side. The operating mode of the system is adapted to the operator's know-how by means of variable user levels and the measurement processing and preparation is carried out accordingly, so that the measurement process is finally carried out as a “one button action”. The evaluation of the current measurement results can then be compared and checked using stored material data. The deviations of the current data from the stored material data can then serve as a correction or evaluation of the local measurement. We will show examples to demonstrate the functionality of the system.

Resume : Atomic force microscopy (AFM) membrane deflection is probably the most commonly used tool to characterize the mechanical properties of 2D materials. Associated with different imaging modes that provide high quality micrographs of the studied systems, it provides accurate force/displacement data. In the present study, the mechanical properties of graphene have been investigated experimentally and with finite element simulations to consolidate the data reduction schemes. Differences between the experimental results and simulations can not only be attributed to the intrinsic structural defects such as grain boundaries, dislocations and graphene edges induced by the synthesis and transferring processes but also to instrumentation and testing sources of uncertainties. These last factors are associated to the imaging and me-chanical testing limitations of AFM such as the degradation of the tip, the uncertainty on the measured displacement, on the membrane radius, on the location of the application of the load. The stiffness is for instance significantly overestimated when the tip is not well centered and an approach is proposed to circumvent this difficulty. All these parameters have been carefully investigated and quantified. The methodology was then applied to the extraction of the Young’s modulus and the fracture strength of single- and bi-layer graphene to highlight the differences between both systems. The procedure was also applied to 2D hexagonal boron nitride (hBN).

Resume : Nanoindentation enables testing mechanical properties on a very small length scale. Consequently it is usually combined with a high resolution imaging system, to correlate mechanical properties to the structure of the object. These imaging techniques are mostly based on optical microscopy, scanning probe techniques and scanning electron microscopy. They only provide a detailed image of the sample surface, while a high voltage SEM beam can penetrate the surface by 1-3 µm. Here we present the advantages of the modular approach of the sm@rt 500 nanoindenter. The conventional large-range nanoindentation head can be combined with a high frequency ultrasound transducer. This transducer enables us to create a 3-D map of the sample prior to the mechanical testing. This offers new possibilities for material testing: Since the elastic field of deformation is long ranging -even with sharp tips-, quantitative testing requires homogeneous samples. With the analysis of elastic ultrasonic waves, sample heterogeneities can be detected, avoided or addressed.

Resume : Bulk Metallic glasses (BMGs) are metallic alloys characterized by an amorphous atomic structure reporting superior mechanical properties with large strength and elastic deformability. Despite of these interesting properties, BMGs suffer of a macroscopically brittle behaviour with the formation of shear banding phenomena. Recent studies have shown that this behavior can be mitigated by reducing their intrinsic size developing thin film metallic glasses (TFMGs, thickness < 1 m) reporting the suppression of shear banding process together with the mutual combination of large plastic deformation (> 10%) and superior yield strength (~3500 MPa, close to the theoretical limit). Nevertheless, several scientific challenges involving their mechanical properties and thermal stability are still open, specially focusing on the role of the composition, addressing key questions involving the effect of local order, bond strength and free volume. In this context, we studied a large variety of binary ZrxCu100-x TFMG compositions (24 < at.% < 61), while investigating the mechanical and thermal behavior. Firstly, we achieved fine control of film composition by accurate regulating of synthesis parameters by magnetron sputtering. Then, using X-Ray diffraction (XRD) we analyzed the amorphous structure as well as its behavior as a function of temperature (with in-situ XRD heating) and we show that different crystallization temperatures (up to ~380°C) are found, depending on the composition. The mechanical characterization involving surface Brillouin light scattering enabled us to extract the elastic constants and we show that both Young’s, shear and bulk modulus increased with content of Cu (at. %), while Poisson ratio remained constant. These results were consolidated by nanoindentation showing that the hardness increases with Cu content (at.%) from 5.5 up to 7.7 GPa. In addition, we investigated the dependency of loading rate and we found a different behaviour, in terms of pop-in’s appearance and size, with lager pop-in’s appearing at low Cu percentage and slower indentation rates. Finally, tensile tests were performed on films deposited on flexible polymeric substrates to study crack evolution. Both crack and buckling density displayed relevant differences as a function of the composition with large onset for crack nucleation appearing for Cu-rich samples. Overall, the presented research clearly highlights the role of film composition in affecting both ZrCu TFMGs mechanical properties and thermal stability making them very attractive for applications such as hard coatings, MEMS (Micro Electro Mechanical Systems), biomedical tools or flexible electronics.

Resume : This work describes a novel methodology of data documentation in materials characterisation, which has as starting point the creation and usage of any Data Management Plan (DMP) for scientific data in the field of materials science and engineering, followed by the development and exploitation of ontologies for the harnessing of data created through experimental techniques. The case study that is discussed here is nanoindentation, a widely used method for the experimental assessment of mechanical properties on a small scale. Except for technology development and synthesis of new materials and hybrid composite structures, the need of developing new evaluation methodologies is highlighted to assist and accelerate developments. Artificial Intelligence (AI) is a promising candidate to bridge the gap between Research and Development (R&D) and industry by establishing unbiased relations between microstructure and properties. This is majorly appreciated in case of Safe-by-Design requirements regarding mechanical performance, and real-time characterisation. Being representative, k-means, Random Forrest (RF), Support Vector Machines (SVM), k-Nearest Neighbors (KNN) are common Machine Learning (ML) algorithms used in multiclass classification problems for automated classification of microstructures. This work contributes to nanocomposites design and quality control associated with identifying the optimum inclusion in nanomaterials reinforcement by microstructure assessment. In this direction, Artificial Intelligence can provide a module for enabling fast, in-line, and real-time metrological characterisation of nanoindentation data. This work has been partially supported by the EU Horizon 2020 Programmes: MODCOMP (GA No 685844), SMARTFAN (GA No 760779), OYSTER (GA No 760827) and REPAIR3D (GA No 814588).

Resume : The general objective of the work is to contribute to the understanding of processes occurring in austenitic stainless steels at very early stages under irradiation and under Stress Corrosion Cracking (SCC) testing, leading to crack initiation by Irradiation Assisted Stress Corrosion Cracking (IASCC) phenomena. In this work, the material under study is the AISI-316L because it is a recurrent material in the construction of internal components of nuclear plants. Our approach is to perform interrupted slow strain rate tests as well as in-situ straining experiments, at the interior of a Transmission Electron Microscope (TEM). The latter type of experiments provides direct information of the microstructural processes occurring while the sample is strained, such as nucleation, propagation, and interaction of dislocations and defects. The 316L has been implanted with He and both, the as-received and implanted material, are being tested and the resulting deformed microstructure is being characterized by means of scanning and transmission electron microscopy. In particular, specific qualitative and quantitative information is expected to be obtained from dislocation-defect interaction or early stages of defect free channels formation. The outlook of the work to be performed, as well as preliminary obtained results, will be presented and discussed

Resume : Deformation twinning and dislocation slip are two competing deformation modes in crystalline solids. The twinning mechanism and size-dependent dislocation-twin competition have been well documented in face-centered cubic nanoscale crystals. However, it remains largely unclear in body-centered cubic (BCC) metals. By using in situ nanomechanical testing and ex situ characterizations, we systematically investigate the twinning mechanism and size-dependent dislocation-to-twin transition in BCC metallic nanowires and single crystals. We found that deformation twinning can dominate over the ordinary dislocation slip and become a competing deformation mechanism with the reduction of crystal size and this competition can be controlled by the loading orientation and loading mode. Moreover, we observe the nucleation and growth of anti-twins in BCC metallic nanowires with diameters less than about 20 nm, which previously thought impossible in BCC metals. The anti-twinning produces a shear displacement of 1/3<111> on every successive {112} plane, in contrast to an opposite 1/6<-1-1-1> shear by ordinary twinning. However, anti-twinning becomes active in nano-sized BCC crystals that have limited plastic shear carriers and thus develop ultra-high stresses. Finally, the deformation twinning in BCC single crystals will be briefly discussed. Based on our experimental observations, a full twinning map is established.

Resume : Sodium borosilicate, SiO2-B2O3-Na2O, or simply SBN, glasses are commonly used as model industrial glasses. The oxides in these glasses have two different roles. SiO2 and B2O3 are network formers, they can form glass by themselves. The network modifier Na2O is traditionally added to improve the glass‘ properties. Experiments evidence phase separation in the SBN glass system with the possibility two or more phases. Such phase separations are expected to have profound effects on thermodynamical and mechanical properties. However, despite their importance, these phase separations are rarely investigated at the atomic scale. Molecular dynamics (MD) simulations provide an excellent technique to probe complex materials like oxide glasses. They provide an in-depth viewpoint to the glass structure unreachable by other techniques. Furthermore, they aid in understanding how the structure is linked to other physical, thermodynamical, and mechanical properties of glasses such as density, enthalpy of mixing, heat capacity, fracture toughness, Young's, bulk and shear modulus. In this presentation, I will concentrate on the thermodynamical viewpoint and show some results from MD simulations on SBN glasses and compare them to theories and experiments. These results will help in understanding the mechanisms of phase separation in SBN glass.

Resume : Single crystals, sSelf-assembled assemblies from of crystallographicly aligned nanoparticles, also known as Mesocrystalsmesocrystals, have raised considerable interest due to the possibility to tailor their physical , e.g. optical, mechanical or magnetic properties (e.g. optical, mechanical or magnetic) by changing the size of the nanocrystals, their packing and orientational order s or connectivity. However, due to the currently limited crystal sizes of assembled mesocrystals usually in the sub-100µm range and currently approaching the mm size, advanced characterization tools are sought after that can handle small sample sizes and yield spatially resolved information in a non-destructive way. For the first test experiments we performed athe study onf 3D faceted mesocrystals assembled from the magnetite nanocubes (c.a. 10 nm) stabilized by oleic acid. We Hereby, we want to present an approach based on picosecond ultrasonics where acoustic pulses in the GHz frequency range are excited and detected inside the crystals and can potentially yield information about their mechanical and optical properties with an axial resolution in the nanometer regime and lateral resolution given by the optical spotsize. The technique is based on the laser induced excitation of acoustic pulses by fs-optical pulses and subsequent detection of the changes in the optical properties of the crystals. These changes are caused by the propagating acoustic pulses and are mediated by the photoelastic effect. For transparent or semi-transparent samplessamples, the technique can be thought of as a time-domain counterpart to the well- known Brillouin scattering method. First measurements on magnetite-based mesocrystals will be presented and discussed and finally further perspectives of the application of picosecond ultrasonics in nanoparticle based crystals will be given.

Resume : Complex loading scenarios like torsion produce special dislocation structures. Analyzing these can help understand plasticity the micron scale. Formation mechanisms are often only indirectly accessible in experiments due to lack of resolution. Or it is just impossible to look into the sample during testing and obtain three dimensional information. The combination of experiments with tailored simulations can provide insight into the formation mechanisms. But while experiments and simulations produce similar data they are often not directly comparable. By combining results from small scale experiments with discrete dislocation dynamics in the common language of “misorientations” we show successful data fusion and explain dislocation structures and their behavior during torsion loading. This successful example shows that the key to fusing data is to find a common language between the two data sets. A new term for this common language in machine learning applications in materials science is ‘descriptor’. We will subsequently discuss the role of suitable descriptors in data fusion from experiments and simulations in small scale plasticity.