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A series of Al and Al/Al$_{2}$O$_{3}$ thin-film multilayer structures on flexible polymer substrates are fabricated with a unique deposition chamber combining magnetron sputtering (Al) and atomic layer deposition (ALD, Al$_{2}$O$_{3}$, nominal thickness 2.4–9.4 nm) without breaking vacuum and thoroughly characterized using transmission electron microscopy (TEM). The electromechanical behavior of the multilayers and Al reference films is investigated in tension with in situ X-ray diffraction (XRD) and four-point probe resistance measurements. All films exhibit excellent interfacial adhesion, with no delamination in the investigated strain range (12%). For the first time, an adhesion-promoting naturally forming amorphous interlayer is confirmed for thin films sputter deposited onto polymers under laboratory conditions. The evolution of Al film stresses and electrical resistance reveal changes in the deformation behavior as a function of oxide thickness. Strengthening of Al is observed with increasing oxide thickness. Significant embrittlement can be avoided for oxide layer thicknesses ≤2.4 nm.

Many different methods, such as screen printing, gravure, flexography, inkjet etc., have been employed to print electronic devices. Depending on the type and performance of the devices, processing is done at low or high temperature using precursor- or particle-based inks. As a result of the processing details, devices can be fabricated on flexible or non-flexible substrates, depending on their temperature stability. Furthermore, in order to reduce the operating voltage, printed devices rely on high-capacitance electrolytes rather than on dielectrics. The printing resolution and speed are two of the major challenging parameters for printed electronics. High-resolution printing produces small-size printed devices and high-integration densities with minimum materials consumption. However, most printing methods have resolutions between 20 and 50 μm. Printing resolutions close to 1 μm have also been achieved with optimized process conditions and better printing technology.

With progressing miniaturization of modern electronic devices, interconnects become increasingly smaller. Additionally, as electronic devices move away from rigid substrates toward flexible ones, understanding their mechanical and structural stability is becoming crucial. In this work, a thorough mechanical characterization of copper thin films deposited on flexible substrates was performed with two techniques, namely well-established synchrotron X-ray diffraction (sXRD) and the rather new usage of reflectance anisotropy spectroscopy (RAS) for mechanical characterization of thin films. The comparison of these two techniques shows that RAS can be reliably used for the accurate and prompt yield stress measurements. The acquisition time of RAS is much faster than that of sXRD: 1 second per data point compared to several seconds per data point for sXRD experiments. Moreover, the signal-to-noise ratio of the RAS data is much higher than that of the sXRD. Our results show that yield stress of Cu films increases with the decrease in the film thickness, going from 352 MPa for a 500 nm films to 793 MPa for a 50 nm thick film. Microstructure analyses of the films by electron microscopy allowed correlation of the mechanical behavior of the films to their grain morphologies. We have shown that RAS can supplement sXRD measurements due to a faster acquisition rate which allowed us to analyze the creep behavior of our copper thin film at different strain rates.

Printed and flexible metal‐oxide transistor technology has recently demonstrated great promise due to its high performance and robust mechanical stability. Herein, fully printed inverter structures using electrolyte‐gated oxide transistors on a flexible polyimide (PI) substrate are discussed in detail. Conductive graphene ink is printed as the passive structures and interconnects. The additive printed transistors on PI substrates show an 𝐼$_{on}$/𝐼$_{off}$ ratio of 10$^{6}$ and show mobilities similar to the state‐of‐the‐art printed transistors on rigid substrates. Printed meander structures of graphene are used as pull‐up resistances in a transistor–resistor logic to create fully printed inverters. The printed and flexible inverters show a signal gain of 3.5 and a propagation delay of 30 ms. These printed inverters are able to withstand a tensile strain of 1.5% following more than 200 cycles of mechanical bending. The stability of the electrical direct current (DC) properties has been observed over a period of 5 weeks. These oxide transistor‐based fully printed inverters are relevant for digital printing methods which could be implemented into roll‐to‐roll processes.

In order to investigate an almost pure extrinsic size effect we propose an experimental approach to investigate the deformation structure within single crystalline cross-sections of twisted bamboo-structured Au microwires. The cross-sections of individual 〈1 0 0〉 oriented grains of 25 μm thick Au microwires have been characterized by Laue microdiffraction. The diffraction data were used to calculate the misorientation of each data point with respect to the neutral fiber in the center of the cross-section as well as the kernel average misorientation to map the global and local deformation structure as function of the imposed maximum plastic shear strain. The study is accompanied by crystal plasticity simulations which yield the equivalent plastic strain distributions in the cross-section of the wire. The global deformation structures are directly related to the activated slip systems, resulting from the real orientations of the investigated grains. When averaging the degree of deformation along ring segments, an almost continuous but non-linear increase of misorientation from the center toward the surface is observed, reflecting the overall strain gradient imposed by torsion. For the local deformation structure, pronounced and graded deformation traces are observed which often pass over the neutral fiber of the twisted wire and which are obviously reflecting domains of high geometrically necessary dislocations content.

The thickness dependence of the electrical stability under monotonic and cyclic tensile loading is investigated for Cu films on polymer substrates. As for monotonic tensile deformation, thicker films show better stability than thinner films due to their higher ductility and the larger capability of strain accommodation. For the fatigue resistance, however, a more complex behavior was observed depending on the amount of the applied strain. For low strain amplitude in the high cycle fatigue (HCF) regime, thinner films exhibit longer fatigue life because the larger strength of thinner films suppresses dislocation movement and damage nucleation. However, for high strain amplitudes in the low cycle fatigue (LCF) regime, the fatigue life for thinner films is drastically reduced compared to thicker films. It is shown that fatigue coefficients in the LCF regime can be obtained when applying the Coffin–Manson relationship.

We present all-solution processed, indium tin oxide-free organic solar cells on mechanically flexible polyethylene terephthalate (PET) substrates with power conversion efficiencies up to 4.8%. The mechanical properties of the devices are dictated by the electrodes from either metal-organic silver inks or a combination of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) and silver nanowires. Both electrodes can sustain high tensile strains. The influence of mechanical strain on the solar cell performance was experimentally studied in situ by measuring the J–V curves of elongated samples under illumination. At a strain of 14%, we still observed 90% of the initial device power output. At higher strain, crack formation within the electrodes was identified as the origin for device failure.

Fatigue behavior of 100 nm and 1.0 µm thick Cu films with 10 nm Ta passivation layers has been studied using cyclic tensile testing. The results show that Ta capping-layer has influences on fatigue damage by suppression of extrusion formation and, thereby, improved the fatigue life dramatically in the 1.0 µm thick Cu film, but does not change the fatigue life of 100 nm thick Cu film for which crack formation is the dominant damage mechanism.

Nanocrystalline thin films on compliant substrates become increasingly important for the development of flexible electronic devices. In this study, nanocrystalline AuCu thin films on polyimide substrate were tested in tension while using a synchrotron-based in situ testing technique. Analysis of X-ray diffraction profiles allowed identifying the underlying deformation mechanisms. Initially, elastic and microplastic deformation is observed, followed by dislocation-mediated shear band formation, and eventually macroscopic crack formation. Particularly the influence of alloy composition, heat-treatment, and test temperature were investigated. Generally, a highly ductile behavior is observed. However, high Cu concentrations, annealing, and/or large plastic strains lead to localized deformation and hence reduced ductility. On the other hand, enhanced test temperature allows for a delocalized deformation and extended ductility.

Nanocrystalline (nc) materials possess unique mechanical properties, such as very high strength. However, an understanding of the deformation mechanisms and the succession of related microscopic processes that occur during deformation is still incomplete. We used synchrotron-based in situ compression testing to investigate the sequence of deformation mechanisms emerging in bulk nc nickel with a grain size of 30 nm. The study was accompanied by high-resolution grain size analysis and crystal orientation mapping using transmission electron microscopy. Regardless of the initial microstructure, the deformation behavior of electrodeposited nc Ni is initiated by inhomogeneous elastic lattice straining and its accommodation within the grain boundary network, followed by the onset of dislocation plasticity, which was inferred from texture evolution, and stress-driven grain growth. This observation indicates that deformation in nc metals is governed by a succession of different, partly overlapping mechanisms. It is estimated that intragranular dislocation plasticity contributes only about 40% to the overall deformation.

The deformation behavior of nanocrystalline Pd films on compliant polyimide substrates is investigated using a synchrotron-based in situ tensile testing technique. The combination of analytical and physical modeling of the evolution of peak shape during deformation allows to subdivide the deformation behavior into elastic, microplastic and macroplastic deformation. The results confirm that the deformation behavior of nanocrystalline Pd in the grain size regime of 50 nm is still governed by dislocation plasticity, however, in addition, thermally activated grain boundary mediated deformation mechanisms are active. The deformation behavior of the nanocrystalline Pd films is thus given by a specific sequence of a highly heterogeneous elastic response of the nanocrystalline aggregate, its accommodation by grain boundary mediated deformation and upcoming dislocation activity within individual grains.

Understanding the deformation behavior of nanocrystalline (nc) materials is important because of their possible application as structural materials. The investigation of macroscopic nc samples during in situ mechanical tests can shed light on operating deformation mechanisms. For example, observations during a compression test in a scanning electron microscope (SEM) or results obtained by more localized methods like transmission electron microscopy can extend our knowledge on this subject. In this study, we present the results of in situ SEM compression tests on nc Pd–10 at.% Au alloy with a mean grain size of 23 nm produced using the combination of inert gas condensation with subsequent high-pressure torsion. We show that plastic flow in this material is very inhomogeneous on both the macro and the mesoscale as it is localized in one area of the compression sample and within shear bands. The formation of shear bands is accompanied by strain softening. We propose that such behavior can be explained by the activation of grain boundary mediated deformation mechanisms instead of dislocation-based plasticity. This conclusion was supported by in situ synchrotron XRD measurements which revealed that no preferential grain orientation is forming during the compression of identically prepared samples of the same material.

Micro-compression tests were performed on pre-strained nickel (Ni) single crystals in order to investigate the influence of the initial dislocation arrangement on the size dependence of small-scale metal structures. A bulk Ni sample was grown using the Czochralski method and sectioned into four compression samples, which were then pre-strained to nominal strains of 5, 10, 15 and 20%. Bulk samples were then characterized using transmission electron microscopy (TEM), micro-Laue diffraction, and electron backscatter diffraction. TEM results show that a dislocation cell structure was present for all deformed samples, and Laue diffraction demonstrated that the internal strain increased with increased amount of pre-straining. Small-scale pillars with diameters from 200 nm to 5 μm were focused ion beam (FIB) machined from each of the four deformed bulk samples and further compressed via a nanoindenter equipped with a flat diamond punch. Results demonstrate that bulk pre-straining inhibits the sample size effect. For heavily pre-strained bulk samples, the deformation history does not affect the stress–strain behavior, as the pillars demonstrated elevated strength and rather low strain hardening over the whole investigated size range. In situ TEM and micro-Laue diffraction measurements of pillars confirmed little change in dislocation density during pillar compression. Thus, the dislocation cell walls created by heavy bulk pre-straining become the relevant internal material structure controlling the mechanical properties, dominating the sample size effect observed in the low dislocation density regime.

The abnormal growth of individual (1 0 0) oriented grains is monitored by the in situ electron backscatter diffraction technique for more than 24 h at three different annealing temperatures (90 °C, 104 °C and 118 °C) in 1–5 μm thick Cu films on polyimide substrates. The (1 0 0) grain growth velocity increases with higher film thickness and annealing temperature, as suggested by an earlier model by Thompson and Carel. As a result, the final (1 0 0) texture fraction becomes more dominant for higher annealing temperatures and larger film thicknesses. The Thompson–Carel model, however, predicts that the (1 1 1) grains will preferably grow at temperatures up to 118 °C. Our calculations of the driving forces revealed that in addition to minimization of the strain energy (due to the thermal mismatch between film and substrate) and of the surface energy, the energy stored in the dislocations plays a decisive role in grain growth. Our observations can be understood by the notion that initially available (1 0 0) grain nuclei start to grow very rapidly, due to dislocation annihilation, and thus “overrun” the (1 1 1) grains in size.

Despite much technological interest, a standardized test method for the quantification of the cohesive properties of thin films has not yet been established. In addition, for thin brittle coatings on compliant substrates, which are of great interest for flexible electronic devices, conventional techniques cannot be applied. In this work we use a synchrotron-based technique to determine biaxial stress–strain curves of Ta coatings on polyimide substrates in a uniaxial tensile test geometry and apply a two-dimensional shear lag model to derive the fracture strength and the fracture toughness of the coatings. The combined approach of fragment size analysis by in situ microscopy and stress measurement is used to establish a correlation between the modeled and the measured coating stress, which directly illustrates the range of applicability for our model. This technique is used to elucidate the influence of the crystallographic phase of Ta on its cohesive properties. The fracture strength and fracture toughness are greater for body-centered cubic α-Ta compared to tetragonal β-Ta, and plasticity may play a role in reducing stress concentrations at crack tips in α-Ta films. In addition, this study highlights the roles of film thickness, defect density and residual stress in the ability of brittle coatings to withstand considerably high strains without cracking.

The material behavior of nano-shaped and -scaled materials is a key issue for their system integration in modern micro electro-mechanical systems (MEMS). In this article, the thermo mechanical properties of (i) homogeneous gold thin films with a thickness of 20 nm on polyimide substrate and (ii) gold nanoline ensembles with 40 nm width, 20 nm height and 1 mm length on polyimide substrate were measured using the synchrotron based sin 2 ( φ )-tensile testing technique. Both, passivated and unpassivated samples were tested in a temperature range of 173–393 K. As main findings: (i) homogeneous thin films are remarkably stronger than the nanolines, (ii) the yield strength shows a strong temperature dependence, and (iii) the yield strength of passivated samples is significantly increased compared to their unpassivated counterparts. The activation energy also shows a pronounced temperature dependency and indicates plastic deformation controlled by (i) dislocation motion for temperatures below 223 K, (ii) diffusion along (1 1 1) surfaces in the temperature range of 223–343 K and (iii) diffusion along the remaining surfaces (others than (1 1 1)) in the temperature range of 334–393 K.

The size effect in body-centered cubic metals is comprehensively investigated through micro/nano-compression tests performed on focused ion beam machined tungsten (W), molybdenum (Mo) and niobium (Nb) pillars, with single slip [2 3 5] and multiple slip [0 0 1] orientations. The results demonstrate that the stress–strain response is unaffected by the number of activated slip systems, indicating that dislocation–dislocation interaction is not a dominant mechanism for the observed diameter dependent yield strength and strain hardening. Furthermore, the limited mobility of screw dislocations, which is different for each material at ambient temperature, acts as an additional strengthening mechanism leading to a material dependent size effect. Nominal values and diameter dependence of the flow stress significantly deviate from studies on face-centered cubic metals. This is demonstrated by the correlation of size dependence with the material specific critical temperature. Activation volumes were found to decrease with decreasing pillar diameter further indicating that the influence of the screw dislocations decreases with smaller pillar diameter.

The effect of prior deformation on mechanical behavior as a function of size is investigated for body-centered cubic (bcc) molybdenum (Mo) pillars. Experiments were performed using focused ion beam (FIB) manufactured [0 0 1] and [2 3 5] Mo micro/nanopillars, which were compressed, re-FIB machined, and compressed again. Unlike in bulk materials, pre-straining has a negligible effect on stress–strain behavior of the pillars, suggesting that dislocation storage does not occur in small-scale bcc specimens. The prevailing mechanism behind the size effect is attributed to dislocation nucleation mechanisms.

This review examines the size effects observed in the mechanical strength of thin metal films and small samples such as single-crystalline pillars, whiskers, and wires. Experimental results from mechanical testing and electron microscopy studies, as well as recent insights from discrete dislocation dynamics simulations, are presented. The size dependency of deformation may be separated into three regimes: the nanometer regime of roughly 100 nm and below, an intermediate regime between 100 nm and approximately 1 μm, and a bulk-like regime. We argue that there is no scaling law with one universal power-law exponent encompassing the entire range. Instead, there are a number of different mechanisms and underlying effects, e.g., the initial dislocation microstructure or loading conditions. The complex interaction of these mechanisms leads to the typically observed scaling behavior.

The current report covers the establishment of an in situ X-ray diffraction tensile experiment at the synchrotron ANKA located at Forschungszentrum Karlsruhe for probing diffraction signals from nanocrystalline thin films during tensile deformation. Measurements on nanocrystalline palladium films verify the capabilities of the setup.

Recently, much work has focused on the size effect in face centered cubic (fcc) structures, however few pillar studies have focused on body centered cubic (bcc) metals. This paper explores the role of bcc crystal structure on the size effect, through compression testing of [001] and [235] Molybdenum (Mo) small-scale pillars manufactured by focused ion beam (FIB). The pillar diameters ranged from 200 nm to 5 μm. Results show that the relationship between yield stress and diameter exhibits an inverse relationship ( σ y ∝ d −0.22 for [001] Mo and σ y ∝ d −0.34 for [235] Mo) weaker than that observed for face centered cubic (fcc) metals ( σ y ∝ d −0.6 to −1.0 ). Additional tests at various loading rates revealed that small-scale Mo pillars exhibit a strain rate sensitivity similar to bulk Mo.

Diffusion-controlled deformation mechanisms may become relevant for nanocrystalline and nanostructured materials at room temperature. In this paper, the stress–strain behavior of gold nanowires 40 nm wide, 20 nm high and 1 mm long on a flexible substrate was investigated in the temperature range of 173–393 K. For decreasing temperatures, the yield strength and the fracture resistance increase. Both can be qualitatively explained by diffusion-driven deformation. The activation energy at room temperature indicates diffusion on (1 1 1) surfaces.

Plastic deformation of micron and sub-micron scale specimens is characterized by intermittent sequences of large strain bursts (dislocation avalanches) which are separated by regions of near-elastic loading. In the present investigation we perform a statistical characterization of strain bursts observed in stress-controlled compressive deformation of monocrystalline Molybdenum micropillars. We characterize the bursts in terms of the associated elongation increments and peak deformation rates, and demonstrate that these quantities follow power-law distributions that do not depend on specimen orientation or stress rate. We also investigate the statistics of stress increments in between the bursts, which are found to be Weibull distributed and exhibit a characteristic size effect. We discuss our findings in view of observations of deformation bursts in other materials, such as face-centered cubic and hexagonal metals., Comment: 14 pages, 8 figures, submitted to Phil Mag

Temperature and film thickness are expected to have an influence on the mechanical properties of thin films. However, mechanical testing of ultrathin metallic films at elevated temperatures is difficult, and few experiments have been conducted to date. Here, we present a systematic study of the mechanical properties of 80–500-nm-thick polycrystalline Au films with and without SiNx passivation layers in the temperature range from 123 to 473 K. The films were tested by a novel synchrotron-based tensile testing technique. Pure Au films showed strong temperature dependence above 373 K, which may be explained by diffusional creep. In contrast, passivated samples appeared to deform by thermally activated dislocation glide. The observed activation energies for both mechanisms are considerably lower than those for the bulk material, indicating that concomitant stress relaxation mechanisms are more pronounced in the thin film geometry.

We present a systematic study of the mechanical properties of different Cu, Ta/Cu and Ta/Cu/Ta films systems. By using a novel synchrotron-based tensile testing technique isothermal stress–strain curves for films as thin as 20 nm were obtained for the first time. In addition, freestanding Cu films with a minimum thickness of 80 nm were tested by a bulge testing technique. The effects of different surface and interface conditions, film thickness and grain size were investigated over a range of film thickness up to 1 μm. It is found that the plastic response scales strongly with film thickness but the effect of the interfacial structure is smaller than expected. By considering the complete grain size distribution and a change in deformation mechanism from full to partial dislocations in the smallest grains, the scaling behavior of all film systems can be described correctly by a modified dislocation source model. The nucleation of dissociated dislocations at the grain boundaries also explains the strongly reduced strain hardening for these films.

Although it is well known that thin films exhibit mechanical properties very different from those of their bulk counterparts, knowledge of the underlying mechanisms is incomplete. Single-crystalline films have a favorable microstructure for investigating the scaling behavior of mechanical properties. We present a novel experimental route for preparing single-crystalline Au films on a compliant polyimide substrate. For such single-crystals, we have developed a synchrotron-based tensile testing technique to measure the isothermal stress–strain curves and average peak widths. The analysis of Laue diffraction patterns as well as a parallel transmission electron microscopy study give new insight in the initial and evolving microstructure of the films. Complex novel deformation mechanisms are found, including a transition of the dominant deformation mechanism from full to partial dislocations in films thinner than 160 nm. The scaling behavior is described in view of the coexistence of different deformation mechanisms where the nucleation stress for single dislocations very likely governs the behavior.

Metallic conductors on polymeric substrates are frequently used for printed circuit boards or flexible displays. Optimization of these devices is mostly associated with the miniaturization of the conductors which changes their electrical and mechanical properties. We focus on crack formation in gold nano-interconnects about 20 nm high, 40 nm wide and 1 mm long on flexible substrates. The fracture toughness of the gold nanolines is decreased significantly compared to bulk gold.

When Chen et al. (2015, Acta Mater. 87, 78-85) investigated the deformation behavior of oligocrystalline gold microwires with varying diameters in both uniaxial tension and torsion, contrary size effects were observed for the different load cases. In accompanying microstructural studies it was found, that the microwires of different thickness reveal distinctive differences in grain size and texture, respectively. As a consequence, a significant influence of these microstructural variations on the determined size effects was assumed. However, within the frame of their work, a direct confirmation could only be presented for the effect of the grain size. In the present work, the size-dependent mechanical response of the microwires is modeled with a gradient plasticity theory. By finite element simulations of simplified grain aggregates, the influence of the texture on the size effects is investigated under both loading conditions. It is shown that the experimentally observed contrary size effects can only be reproduced when taking into account the individual textures of the microwires of different thickness within the modeling., in Journal of Materials Science, 2016

Epitaxial Au thin films with thicknesses of 40–160 nm were grown on (1 0 0)-oriented single-crystal NaCl substrates at 300 °C by magnetron sputtering. Microstructural analyses revealed that all films possess orthogonal twin networks along the 〈0 1 1〉 directions. The experimentally observed relationship of an increase in twin density with decreasing film thickness is explained by kinematical and thermodynamical modeling. The developed twin model predicts a nanometer-sized width of the twins, in agreement with the experiment.

Gold is an ideal material for wires and electrodes on the nanoscale because of its corrosion resistance and biocompatibility. For system integration the mechanical properties of gold nanowires are highly important. In this paper, a study on the deformation behavior of parallel line arrays of gold on polyimide substrates is presented. Arrays of 45–60 nm nanolines were produced by extreme ultraviolet interference lithography, evaporation of gold and a subsequent lift-off process. Tensile testing of these samples was performed by using an in situ synchrotron-based technique, which allows for the fast acquisition of diffraction peaks. The samples show yield stresses of about 400 MPa. This is comparable to thin films of similar thickness, but significantly lower than previously reported results on single electrodeposited wires deformed in bending. The differences are explained in terms of strain gradient plasticity theory.

In situ transmission electron microscopy straining experiments were performed on 40, 60, 80 and 160 nm thick single crystalline Au films on polyimide substrates. A transition in deformation mechanisms was observed with decreasing film thickness: the 160 nm thick film deforms predominantly by perfect dislocations while thinner films deform mainly by partial dislocations separated by stacking faults. In contrast to the 160 nm thick film, interfacial dislocation segments are rarely laid down by threading dislocations for the thinner films. At the late stages of deformation in the thicker Au films prior to fracture, dislocations start to glide on the (0 0 1) planes (cube-glide) near the interface with the polymer substrate. The impact of size-dependent dislocation mechanisms on thin film plasticity is addressed.

Common failure mechanisms in microelectronics such as electromigration, creep and fatigue can be positively influenced by microstructure optimization. In this paper a new mechanism of microstructure optimization in thin metal films is proposed. Post-deposition ion bombardment can produce an in-plane texture in originally highly fiber textured thin metal films by a selective grain growth process. In extreme cases the in-plane texture becomes as sharp as the out-of-plane fiber texture. A subset of grains oriented for ion channeling was found to grow significantly at the expense of the remaining grain fraction. We studied the selective grain growth as a function of ion species (N+, Ne+, Ar+), ion energy (1–3.5 MeV) and target temperature (liquid nitrogen to 400 °C). In a textured thin film the degree of preferred in-plane orientation can be strongly influenced by ion bombardment, and therefore this technique has the potential to become a powerful tool for the enhancement of reliability in micro- and nanosystems.

The microtexture of 0.5–10 μm thick Cu films on polyimide substrates was characterized by automated electron backscatter diffraction (EBSD). The transition from a dominant (1 1 1) to a (1 0 0) fibre texture with increasing film thickness is clearly evident and is in agreement with X-ray diffraction measurements. For interpretation of the texture evolution, a driving force map is constructed which displays the energy balance for interfacial and elastic driving forces using experimental yield stress values. The observations follow the predictions of the texture evolution model of Thompson and Carel [Thompson CV, Carel R. MSF 1996;204–206:83; Thompson CV, Carel R. J Mech Phys Solids 1996;44:657] but add new elements: the texture does not switch abruptly as predicted by energetic considerations, but a broad transition is found. Furthermore, access to the microtexture as well as grain size statistics is given by the EBSD technique, allowing new insight into the details of texture evolution.

Nanoparticles are essential building blocks for nanotechnology. In this paper we demonstrate a novel method to create nanoplatelets by thin film cracking. The thickness of the resulting platelets is determined by the film thickness, and their aspect ratio is controlled by the total strain and the elastic mismatch between substrate and thin film. Platelets can be created from any brittle film independently of microstructure and materials class. The feasibility of this method is substantiated by a statistical analysis of the fracture process.

The mechanical properties of metallic thin films on the nanoscale acquire increasingly more importance as applications in microelectromechanical systems/NEMS as well as microelectronics have reached this size scale. Here, we present a synchrotron x-ray diffraction technique by which it is possible to characterize the evolution of mechanical stress in a metallic film thinner than 100 nm at measurement times shorter than 60 s per data point. This high data acquisition rate is achieved because no relative motions or tilting of specimen, x-ray source and detector (a large-area charge coupled device camera) are required. The technique comprises an initial “sin2 ψ” measurement to establish the absolute stress values followed by periodic “sin2 φ” measurements during straining to determine stress increments. We describe an experimental setup established at the synchrotron radiation source ANKA (Karlsruhe, Germany) which is specifically suited for monitoring the stress evolution during in situ tensile tests on thi...

In their comment (M. Lagos et al., Scripta Mater. (2012), http://dx.doi.org/10.1016/j.scriptamat.2012.04.018 ), Lagos et al. propose a two-dimensional plasticity model based on grain boundary sliding to explain the deformation behavior of ultrathin Cu and Ta/Cu film systems on polyimide substrates. Here, we critically discuss their comments and include new results obtained by peak profile analysis of the original in situ diffraction data; they strongly suggest that the deformation behavior of the different film systems is very likely not self-similar as claimed by Lagos et al.

We utilized synchrotron-based in-situ diffraction and dominant shear deformation to identify, dissect, and quantify the relevant deformation mechanisms in nanocrystalline $\mathrm{Pd}_{90}\mathrm{Au}_{10}$ in the limiting case of grain sizes at or below 10 nm. We could identify lattice and grain boundary elasticity, shear shuffling operating in the core region of grain boundaries, stress driven grain boundary migration, and dislocation shear along lattice planes to contribute, however, with significantly different and nontrivial stress-dependent shares to overall deformation. Regarding lattice elasticity, we find that Hookean linear elasticity prevailed up to the maximal stress value of $\approx$ 1.6 GPa. Shear shuffling that propagates strain at/along grain boundaries increases progressively with increasing load to carry about two thirds of the overall strain in the regime of macroplasticity. Stress driven grain boundary migration requires overcoming a threshold stress slightly below the yield stress of $\approx$ 1.4 GPa and contributes a share of $\approx$ 10% to overall strain. Appreciable dislocation activity begins at a stress value of $\approx$ 0.9 GPa to then increase and eventually propagate a maximal share of $\approx$ 15% to overall strain. In the stress regime below 0.9 GPa, which is characterized by a markedly decreasing tangent modulus, shear shuffling and lattice- and grain boundary elasticity operate exclusively. The material response in this regime seems indicative of nonlinear viscous behavior rather than being correlated with work- or strain hardening as observed in conventional fcc metals., 22 pages, 11 figures, published in Mechanics of Materials, text revisions due to changing from IJP to MechMat

The development of highly conductive metallic electrodes with long-term reliability is in great demand for real industrialization of flexible electronics, which undergo repeated mechanical deformation during service. In the case of vacuum-deposited metallic electrodes, adequate conductivity is provided, but it degrades gradually during cyclic mechanical deformation. Here, we demonstrate a long-term reliable Ag electrode by inkjet printing. The electrical conductivity and the mechanical reliability during cyclic bending are investigated with respect to the nanoporous microstructure caused by post heat treatment, and are compared to those of evaporated Ag films of the same thickness. It is shown that there is an optimized nanoporous microstructure for inkjet-printed Ag films, which provides a high conductivity and improved reliability. It is argued that the nanoporous microstructure ensures connectivity within the particle network and at the same time reduces plastic deformation and the formation of fatigue damage. This concept provides a new guideline to develop an efficient method for highly conductive and reliable metallic electrodes for flexible electronics.

The microstructure and mechanical properties of nanocrystalline Pd films prepared by magnetron sputtering have been investigated as a function of strain. The films were deposited onto polyimide substrates and tested in tensile mode. In order to follow the deformation processes in the material, several samples were strained to defined straining states, up to a maximum engineering strain of 10%, and prepared for post-mortem analysis. The nanocrystalline structure was investigated by quantitative automated crystal orientation mapping (ACOM) in a transmission electron microscope (TEM), identifying grain growth and twinning/detwinning resulting from dislocation activity as two of the mechanisms contributing to the macroscopic deformation. Depending on the initial twin density, the samples behaved differently. For low initial twin densities, an increasing twin density was found during straining. On the other hand, starting from a higher twin density, the twins were depleted with increasing strain. The findings from ACOM-TEM were confirmed by results from molecular dynamics (MD) simulations and from conventional and in-situ synchrotron X-ray diffraction (CXRD, SXRD) experiments.

Synchrotron-based in situ tensile testing was used to study the dominant deformation mechanisms of nanocrystalline Pd thin films on a compliant substrate. An x-ray diffraction peak profile analysis reveals an (hkl) independent deformation induced peak asymmetry. It is argued that the asymmetry is caused by a broad distribution of elastic strains among individual grains and the complexity of accommodation processes. The reversal of peak asymmetry manifests the transition from heterogeneous microplasticity to dislocation-based macroplasticity. Independently, stress-driven grain boundary migration is active.

The chemical and electrochemical insertion of lithium into the spinel structure of CuCr(2)Se(4) was studied and the chemical reaction pathway was followed by ex situ X-ray diffraction on samples with different Li contents. The electrochemical reaction was investigated by in situ X-ray diffraction and in situ scanning electron microscopy. In the early steps of chemical intercalation, two phases with a different Li content coexist and Cu is extruded from the host material. After 4 days of Li intercalation, a conversion reaction is observed. The overall Li uptake is 8 Li ions per formula unit. The structural behaviour of the two intercalated phases at the early stages of intercalation is totally different. For one phase a strong expansion of the a-axis is observed while for the other phase it is only slightly affected by Li uptake. A three-step mechanism was found consisting of reduction of Se(-) followed by a Cu-Li exchange and finally a complete reduction of Cr(3+) to the metallic state accompanied by the formation of Li(2)Se. The discharge capacity of the first cycle amounts to 530 mAh g(-1) and drops to about 380 mAh g(-1) in the fifth cycle. In in situ SEM images the occurrence of Cu whiskers that partially grow out of the crystallites can be observed.

Microcompression tests were performed on focused-ion-beam-machined micropillars of several body-centered-cubic metals (W, Mo, Ta, and Nb) at room temperature. The relationship between yield strength and pillar diameter as well as the deformation morphologies were found to correlate with a parameter specific for bcc metals, i.e., the critical temperature T(c). This finding sheds new light on the phenomenon of small-scale plasticity in largely unexplored non-fcc metals.

Journal of Materials Research, 24 (6), ISSN:0884-2914, ISSN:2044-5326

The texture, microstructure and mechanical behavior of bulk ultrafine-grained (ufg) Zr fabricated by accumulative roll bonding (ARB) is investigated by electron backscatter diffraction, transmission electron microscopy and mechanical testing. A reasonably homogeneous and equiaxed ufg structure, with a large fraction of high angle boundaries (HABs, ∼70%), can be obtained in Zr after only two ARB cycles. The average grain size, counting only HABs (θ > 15°), is 400 nm. (Sub)grain size is equal to 320 nm. The yield stress and UTS values are nearly double those from conventionally processed Zr with only a slight loss of ductility. Optimum processing conditions include large thickness reductions per pass (ε ∼ 75%), which enhance grain refinement, and a rolling temperature (T ∼ 0.3Tm) at which a sufficient number of slip modes are activated, with an absence of significant grain growth. Grain refinement takes place by geometrical thinning and grain subdivision by the formation of geometrically necessary boundaries. The formation of equiaxed grains by geometric dynamic recrystallization is facilitated by enhanced diffusion due to adiabatic heating.

Grain growth in thin films is usually accompanied by texture evolution due to the crystallographic dependencies of surface, interface and strain energies. In this work the driving forces for grain growth for a 1 and 5 μm thick Cu thin film on a polyimide substrate are calculated assuming biaxial and uniaxial stress. While the results for the biaxial stress state are used to explain observed textures, for the case of uniaxial stress predictions suggest new ways to control the texture of thin films.

A novel synchrotron-based X-ray diffraction technique is presented by which it is possible to characterize the evolution of stresses in polycrystalline metallic films thinner than 100 nm. The film under investigation is deposited on a flexible polyimide substrate which is subjected to a uniaxial tensile test. The evolutions of longitudinal and transverse elastic strains in the film are monitored simultaneously by means of a high-resolution area detector. The strain resolution is better than 10−4. The samples are typically subjected to 6 % total strain and subsequently unloaded. First experiments carried out on Au films in the thickness range between 20 nm and 1000 nm show the usefulness and the power of this new technique.

Layered structures of Cu and Ta thin films on silicon are well established for many technological applications in microelectronics. Electronic circuits used for flexible displays or wearable electronics are becoming increasingly popular. For such applications, the Cu/Ta system must be transferred to flexible substrates, incorporating a design rule for several percent of total strain. We have investigated the deformation behaviour of different Cu/Ta and Ta/Cu/Ta thin film systems on a flexible polyimide substrate subjected to total strains of more than 5%. A novel synchrotron X-ray diffraction technique allowed us to characterize the evolution of mechanical stress in very thin metallic films during isothermal tensile tests. We found that samples with a Cu film thickness below 300 nm showed a sudden stress decrease at a total strain of about 2.5%. This stress drop was attributed to fracture of the entire film system, initiated by cracks in the Ta layers.

Petra Sonnweber-Ribic , Patric Gruber , Gerhard Dehm , Eduard Arzt a,b,* a Max Planck Institute for Metals Research, Heisenbergstrase 3, 70569 Stuttgart, Germany b Institute for Physical Metallurgy, University of Stuttgart, Heisenbergstrase 3, 70569 Stuttgart, Germany c Department of Material Physics, University of Leoben and Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstrase 12, 8700 Leoben, Austria