Search

As the microelectronics field pushes to increase device density through downscaling component dimensions, various novel micro- and nano-scale additive manufacturing technologies have emerged to expand the small scale design space. These techniques offer unprecedented freedom in designing 3D circuitry but have not yet delivered device-grade materials. To highlight the complex role of processing on the quality and microstructure of AM metals, we report the electrical properties of micrometer-scale copper interconnects fabricated by Fluid Force Microscopy (FluidFM) and Electrohydrodynamic-Redox Printing (EHD-RP). Using a thin film-based 4-terminal testing chip developed for the scope of this study, the electrical resistance of as-printed metals is directly related to print strategies and the specific morphological and microstructural features. Notably, the chip requires direct synthesis of conductive structures on an insulating substrate, which is shown for the first time in the case of FluidFM. Finally, we demonstrate the unique ability of EHD-RP to tune the materials resistivity by one order of magnitude solely through printing voltage. Through its novel electrical characterization approach, this study offers unique insight into the electrical properties of micro- and submicrometer-sized copper interconnects and steps towards a deeper understanding of micro AM metal properties for advanced electronics applications., RSC Advances, 13 (20), ISSN:2046-2069

The combination of conventional physical vapor deposition and a gas aggregation nanoparticle source enabled the study of model systems of unique material combinations and dimensions. Zr50Cu45Ag5 thin film metallic glasses with varying contents of single-crystalline 5 nm tungsten nanoparticles were synthesized using this technique. This approach provides precise control over nanoparticle shape, size, distribution, and concentration. The films were later annealed at 150 °C, 250 °C, 350 °C, and 450 °C. At room temperature inclusion of 0.01 vol% tungsten nanoparticles caused a 15% increase in the nanoindentation hardness of a thin film metallic glass, while having no significant effect on pop-in length or frequency, as seen in the loading curves. Even more remarkably, at 450 °C a control film containing no nanoparticles experienced significant segregation and subsequent crystallization, whereas this effect was repressed in the tungsten nanoparticle composite thin film metallic glass. Unobstructed by nanoparticles, at high temperatures zirconium diffused to the surface of the film, forming a crystalline layer of up to 80 nm. In contrast, this layer is kept to below 30 nm when the nanoparticles are present. The stabilization of the microstructure is also clear from indentation results, while the hardness of the reference sample changes significantly due to the undesired crystallization, the hardness of the composite remains constant., Thin Solid Films, 773, ISSN:0040-6090, ISSN:1879-2731

The control of materials’ microstructure is both a necessity and an opportunity for micro/nanometer-scale additive manufacturing technologies. On the one hand, optimization of purity and defect density of printed metals is a prerequisite for their application in microfabrication. On the other hand, the additive approach to materials deposition with highest spatial resolution offers unique opportunities for the fabrication of materials with complex, 3D graded composition or microstructure. As a first step toward both ‒ optimization of properties and site-specific tuning of microstructure ‒ an overview of the wide range of microstructure accessed in pure copper (up to >99.9 at.%) by electrohydrodynamic redox 3D printing is presented, and on-the-fly modulation of grain size in copper with smallest segments ≈400 nm in length is shown. Control of microstructure and materials properties by in situ adjustment of the printing voltage is demonstrated by variation of grain size by one order of magnitude and corresponding compression strength by a factor of two. Based on transmission electron microscopy and atom probe tomography, it is suggested that the small grain size is a direct consequence of intermittent solvent drying at the growth interface at low printing voltages, while larger grains are enabled by the permanent presence of solvent at higher potentials., Small, 18 (51), ISSN:1613-6810, ISSN:1613-6829

Electrohydrodynamic redox 3D printing (EHD-RP) is an additive manufacturing (AM) technique with submicron resolution and multi-metal capabilities, offering the possibility to switch chemistry during deposition “on-the-fly”. Despite the potential for synthesizing a large range of metals by electrochemical small-scale AM techniques, to date, only Cu and Ag have been reproducibly deposited by EHD-RP. Here, we extend the materials palette available to EHD-RP by using aqueous solvents instead of organic solvents, as used previously. We demonstrate deposition of Cu and Zn from sacrificial anodes immersed in acidic aqueous solvents. Mass spectrometry indicates that the choice of the solvent is important to the deposition of pure Zn. Additionally, we show that the deposited Zn structures, 250 nm in width, can be partially converted into semiconducting ZnO structures by oxidation at 325 °C in air., Nanoscale, 14 (46), ISSN:2040-3364, ISSN:2040-3372

The design and fabrication of large-area metamaterials is an ongoing challenge. In the present work, we propose a scalable design route and low-footprint strategy for the production of large-area, frequency-selective Cu-Sn disordered network metamaterials with quasi-perfect absorption. The nanoscale networks combine the robustness of disordered systems with the broad-band optical response known from connected wire-mesh metamaterials. Using experiments and simulations, we show how frequency-selective absorption in the networks can be designed and controlled. We observe a linear dependence of the optical response as a function of Sn content ranging from the near-infrared to the visible region. The absorbing state exhibits strong sensitivity to both changes in the global network topology and the chemistry of the network. We probe the plasmonic response of these nanometric networks by electron energy loss spectroscopy (EELS), where we resolve extremely confined gap surface-plasmon (GSP) modes.

To explore a minimal feature size of, Nanoscale, 14 (14), ISSN:2040-3364, ISSN:2040-3372

With high resistance against interdiffusion, electromigration, creep and fatigue, single-crystal films of refractory metals are highly desired for applications in opto- and micro-electronic devices. Their fabrication is nevertheless very challenging, primarily due to their high melting points. Requiring no external thermal input, ion-irradiation presents an alternative route for single-crystal films by converting from their polycrystalline counterparts through irradiation-induced selective grain growth. The incomplete poly- to single-crystal conversion is however a common problem which limits the application of this method. Here we use refractory W thin films, the element with the highest melting point, as a model system. We systematically investigate the influences of film microstructure (texture and grain size) and irradiation temperature (77 K and room temperature) on the evolution of selective grain growth under 4.5 MeV Au+ ion-irradiation. We find that the driving force for selective grain growth can be increased by narrowing the texture spread of the films, refining the grain size and decreasing the irradiation temperature. Following this guidance, a complete conversion of a polycrystalline W film into a single crystal is achieved. This study therefore provides insights into the mechanism of selective grain growth and proves that it is an effective technique for microstructure engineering in thin film materials. The concepts can be applied to all crystalline metal films.

Microfabrication of synthetic single crystal diamond using accelerated helium ions beams has significant potential for functional applications, such as high precision optical devices, through tailoring of the optical properties via diamond graphitization. The use of helium ion microscopes (HIM) with nano-scaled focused ion beam spot sizes also allows for precision nano-patterning of the diamond surface through post-exposure selective etching of the generated graphitic phase. Here, single-crystalline diamonds with ⟨100⟩, ⟨110⟩, ⟨111⟩ and ⟨123⟩ orientations are exposed to He ion radiation from a HIM at a range of acceleration voltages and fluences. It is observed that ⟨123⟩ orientation was notably more sensitive to ion irradiation as sp3 bonds transition to sp2 bonds at lower fluence (1015 ions/cm2) compared to other orientations. In situ uniaxial compression of SC diamond micro-pillars revealed the strength of ⟨123⟩-oriented pillars is strongly dependent on the ion fluence, and thus is tunable by ion irradiation. Notably, ⟨100⟩-oriented pillars exhibit a better damage resistance as a small strength degradation due to its higher ion channeling efficiency. The irradiation damage of energetic helium ions on the structure and strength of diamond is therefore highly orientation-dependent. Such results provide the critical knowledge for precise patterning and designing of diamond-based functional structures in nano-fabrication.

Additive manufacturing of metals by 3D printing of polymeric filaments containing high loading of metal powder, subsequent debinding, and sintering offers a potent alternative to the widespread beam-based processes. The polymeric binder is the decisive component for a successful fabrication process. This study presents the development of a multi-component binder system for filament-based 3D printing of 316 L stainless steel in various optimization steps. The binder contains a polyethylene (PE) backbone, which ensures the structural integrity during solvent debinding. A soluble binder component consisting of a thermoplastic elastomer (TPE) and a second PE is used, to reduce the polymer content via solvent extraction prior to thermal debinding. The TPE grants flexibility to the filaments, while the PE allows reduction of the viscosity and increase in stiffness and strength. This enables precise tuning of the rheological and mechanical properties of the filaments. The capabilities of the binder system developed, are demonstrated by the fabrication of 3D plate-lattices. The structures are printed, subjected to a two-step solvent – thermal debinding procedure, and finally sintered. In the compression tests the structures are able to undergo large plastic deformations without fracture, highlighting their potential for energy absorption applications. The main contribution of this work is the development and disclosure of a binder system with two types of soluble polymers. This allows the precise control of the mechanical and rheological properties, as well as the backbone fraction of the binder. Based on the characterization performed, the binder system can be easily modified to adapt for other solid loading materials and fractions, as parameters like stiffness, viscosity, or backbone content can be adjusted precisely., Additive Manufacturing, 49, ISSN:2214-8604

Correlated high-speed nanoindentation and energy-dispersive spectroscopy are applied in a combinatorial investigation of the Ni-Ta system. All seven phases in the system are clearly resolved in the resulting maps, and the mechanical properties and composition ranges for each phase are determined. Good agreement with ab initio calculations is generally observed with some exceptions, most notably NiTa2. This is achieved using a simple correlation method utilizing directly overlaid data matrices to allow compositional labeling of mechanical data. This allows easy data segmentation without requiring complicated statistical deconvolution methods. Without this correlative method, phase deconvolution of the Ni-Ta system would be challenging due to several phases possessing adjacent compositions and mechanical properties. This demonstrates the potential of this new correlative approach for future investigations, particularly those involving complex microstructures and/or compositional variation., Small Methods, 6 (2), ISSN:2366-9608

Hyperbolic metamaterials show exceptional optical properties, such as near-perfect broadband absorption, due to their geometrically-engineered optical anisotropy. Many of their proposed applications, such as thermophotovoltaics or radiative cooling, require high-temperature stability. In this work, Ag/a-Si multilayers are examined as a model system for the thermal stability of hyperbolic metamaterials. Using a combination of nanotomography, finite element simulations, and optical spectroscopy, the thermal and optical instability of the metamaterials is mapped. Although the thermal instability initiates at 300 degrees C, the hyperbolic dispersion persists up to 500 degrees C. Direct finite element simulations on tomographical data provide a route to decouple and evaluate interfacial and elastic strain energy contributions to the instability. Depending on stacking order the instability's driving force is either dominated by changes in anisotropic elastic strain energy due thermal expansion mismatch or by minimization of interfacial energy. These findings open new avenues to understand multilayer instability and pave the way to design hyperbolic metamaterials able to withstand high temperatures., Advanced Optical Materials, 10 (24), ISSN:2195-1071

Thermal management is conventionally the design of microelectronics circuitry to maximize heat extraction and minimize local heating. In this work, we investigate a reverse thermal management problem related to understanding and preventing heat dissipation during the propagation of a self-sustained reaction in Ni/Al reactive multilayers, metastable nanostructures that can release heat through a self-sustained propagating exothermic reaction. While it was recently demonstrated that reactive multilayers can serve as on-chip heat sources for on-demand healing of metal films, they still face challenges of device integration due to conductive heat losses to the substrate or adjacent on-chip components, which act as heat sinks and consequently quench the reaction. Here, we study the impact of different heat sink materials, such as gold, copper, and silicon, on the propagation velocity and temperature of the self-sustained heat wave and show that the propagation can be controlled and even stopped by varying the heat sink thickness. Further, we demonstrate that the introduction of a multilayered Al

Nanocrystalline NbMoTaW high entropy alloys (HEAs) have attracted significant attention due to their superior mechanical properties at elevated temperatures. However, the fracture behavior of nanocrystalline HEAs is still unknown. In this study, the fracture behavior of thin HEA films was investigated using micro-cantilever bending. The nanocrystalline films demonstrated critical stress intensities of ~3 MPa√m, which is significantly higher than previous single- and bi-crystalline values. This work demonstrates the capability of ion beam assisted deposition to strengthen nanocrystalline thin films with only minor losses in toughness.

The mechanical properties of multilayer films consisting of alternating layers of magnesium and niobium are investigated through micropillar compression experiments across a broad range of temperatures. The data collected from the variable temperature micropillar compression tests and strain rate jump tests are used to gain insight into the operative deformation mechanisms within the material. At higher temperatures, diffusion-based deformation mechanisms are shown to determine the plastic behavior of the multilayers. Diffusion occurs more readily along the magnesium–niobium interface than within the bulk, acting as pathway for magnesium diffusion. When individual layer thicknesses are sufficiently small, diffusion can remain the dominant deformation mechanism down to room temperature. Multilayer strengthening models historically rely solely on dislocation-based arguments; therefore, consideration of diffusion-based deformation in nanolaminates with low melting temperature components offers improved understanding of multilayer behavior. acceptedVersion

To cover the wide range of applications of reactive multilayers, it is necessary to have the ability to vary and control their front propagation velocities as well as their maximum reaction temperatures. In this paper, Molecular Dynamics simulations are used to study the influence of Al alloying, Ni alloying, and Co alloying on Al–Ni multilayers. In the case of alloying with Al and Ni, the iso-stoichiometric case where both the Al and the Ni layers are alloyed is first studied. In the second step, the stoichiometry is varied by alloying only one of the two layers with the other element. This allows for achieving very small front propagation velocities. Furthermore, the Ni layer is alloyed with Co and the whole range from a binary Al–Ni to the binary Al–Co system is studied. The front propagation velocity does not change linearly with the alloying fraction and reaches a minimum where the Ni/Co alloy changes from a face centered cubic to a hexagonal close packed lattice., Journal of Applied Physics, 132 (6), ISSN:0021-8979, ISSN:1089-7550

Combining the unprecedented design freedom in microscale additive manufacturing (AM) with the ability to control the chemical nature of each printed voxel could unlock unique possibilities for tailoring mechanical, chemical, electrical, optical and magnetic properties of metal microstructures. A variety of techniques for micro- and nanoscale AM has been proposed for the fabrication of device-grade metals and alloys [1]. Electrochemical approaches to small-scale AM generally lead to superior microstructures (in terms of porosity and contamination) compared with techniques that transfer pre-synthesized materials [2]. The deposition of alloys with controlled composition, however, remains a challenge with electrochemical small scale AM techniques. In this talk, we will present our work on additive manufacturing of alloyed structures using electrohydrodynamic redox (EHD-RP) 3D printing [3]. EHD-RP is based on the deposition of solvent droplets containing metal ions onto a conductive substrate, where the solvent evaporates and the ions are reduced. In general, this technique allows the direct deposition of polycrystalline 3D metal structures with a resolution of approx. 250 nm and a feature size down to 100 nm. We will present our work in expanding the materials range of EHD-RP from the limited range reported previously to a wide range of metals and subsequently discuss in detail the direct deposition of alloys. As it will be shown, the approach of spatially confining electrodeposition enables the fabrication of multi-metal and alloyed structures with a chemical voxel size In summary, we present a novel approach to the bottom-up manufacturing of locally alloyed microstructures, adding an additional parameter in the design of novel nano- and microstructured inorganic materials. [1] L. Hirt, A. Reiser, R. Spolenak & T. Zambelli. Additive Manufacturing of Metal Structures at the Micrometer Scale. Adv. Mater., 29(17), 2017. [2] A. Reiser, R. Spolenak et al. Metals by Micro-scale Additive Manufacturing: Comparison of Microstructure and Mechanical Properties. Adv. Funct. Mater., 30, 1910491, 2020 [3] A. Reiser, M. Lindén, P. Rohner, A. Marchand, H. Galinski, A. S. Sologubenko, J. M. Wheeler, R. Zenobi, D. Poulikakos & R. Spolenak. Multi-metal electrohydrodynamic redox 3D printing at the submicron scale. Nat. Comm., 10(1):1-8, 2019. Figure 1

The effect of the specimen size on the mechanical characteristics of material, a phenomenon commonly referred to as the “size effect”, becomes increasingly important at micron and sub-micron dimensions of the specimen. However, the majority of size effect studies on face-centered cubic (fcc) metals have focused on pure elements, where deformation is accomplished by dislocation glide. In this work, single crystalline Ni – x at. % Co (with x = 0, 30, 50) solid solution micropillars were studied by mechanical testing and transmission electron microscopy (TEM) to elucidate the role of stacking fault energy on the size effect in Ni as a function of Co-addition. In situ strain rate jump (SRJ) microcompression testing allowed the evaluation of strain rate sensitivity and activation volumes for all pillar sizes at different strain rates, spanning over three orders of magnitude. TEM analysis showed that for an increase in Co content up to 50%, the SFE decreased from ~85 to ~28 mJ/m2. We observed all Ni – x at. % Co micropillars to exhibit consistent size effect trends (n=~−0.7), independent of composition and yield criterion, and similar trends between activation volume and different sizes: activation volume increases with grain size/pillar size., Materials Science and Engineering: A, 800, ISSN:0921-5093, ISSN:1873-4936

Many emerging applications in microscale engineering rely on the fabrication of three-dimensional architectures in inorganic materials. Small-scale additive manufacturing (AM) aspires to provide flexible and facile access to these geometries. Yet, the synthesis of device-grade inorganic materials is still a key challenge towards the implementation of AM in microfabrication. Here, we present a comprehensive overview of the microstructural and mechanical properties of metals fabricated by most state-of-the-art AM methods that offer a spatial resolution $\leq$10$\mu$m. Standardized sets of samples were studied by cross-sectional electron microscopy, nanoindentation and microcompression. We show that current microscale AM techniques synthesize metals with a wide range of microstructures and elastic and plastic properties, including materials of dense and crystalline microstructure with excellent mechanical properties that compare well to those of thin-film nanocrystalline materials. The large variation in materials performance can be related to the individual microstructure, which in turn is coupled to the various physico-chemical principles exploited by the different printing methods. The study provides practical guidelines for users of small-scale additive methods and establishes a baseline for the future optimization of the properties of printed metallic objects $-$ a significant step towards the potential establishment of AM techniques in microfabrication.

The existence of a premixed interlayer has a direct influence on the reaction kinetics in reactive multilayers. In this study, molecular dynamics simulations are used as a tool to study the influence of premixed interlayers on the front propagation and diffusion in Al-Ni multilayers. For this, premixed interlayers with different, namely, homogeneous, gradient, and s-shaped profiles are studied. Comparison with existing experimental results further increases the understanding of the nature and importance of the premixed interlayer. Moreover, this study shows how this premixed interlayer can be used as a reaction barrier to decrease and thus control the front propagation velocity. Diffusion of Al and Ni atoms through the interlayer takes place, even if the interlayer has partially crystallized, which means the front propagation is driven by a combination of diffusion and crystallization of the interlayer. Furthermore, it is shown that the heat of crystallization of amorphous AlNi to B2-AlNi alone is high enough for a self-propagating reaction to occur., Journal of Applied Physics, 131 (7), ISSN:0021-8979, ISSN:1089-7550

The development of non-noble nano-porous metal materials is hindered by surface oxidation reactions and from the difficulty to generate long range order pore arrays. Dealloying is a promising route to generate such materials by selective chemical etching of metal alloy materials. This process can generate nano-metal materials with superior plasmonic, catalytic and adsorptive surface properties. Here, the impact of properties of the etching solution on the dealloying process to generate nano-pores across thin film alloys was investigated by in-situ SAXS dealloying experiments. Single phase CuZn alloys were used as model materials to evaluate the influence of the solution temperature on the pore formation kinetics. This novel analysis allowed to visualize the change in surface properties of the materials over time, including their surface area as well as their pore and ligament sizes. The dealloying kinetics at the very early stage of the process were found to be critical to both stable pore formation and stabilization. SAXS in-situ data were correlated to the morphological properties of the materials obtained from ex-situ samples by Rutherford back scattering and scanning electron microscopy., Scientific Reports, 8, ISSN:2045-2322

Intentional breaking of the lattice symmetry in solids is a key concept to alter the properties of materials by modifying their electronic band structure. However, the correlation of strain-induced effects and breaking of the lattice symmetry is often indirect, resorting to vibrational spectroscopic techniques such as Raman scattering. Here, we demonstrate that reflectance anisotropy spectroscopy (RAS), which directly depends on the complex dielectric function, enables the direct observation of electronic band structure modulation. Studying the strain-induced symmetry breaking in copper, we show how uniaxial strain lifts the degeneracy of states in the proximity of the both L and X symmetry points, thus altering the matrix element for interband optical transitions, directly observable in RAS. We corroborate our experimental results by analysing the strain-induced changes in the electronic structure based on ab-initio density functional theory calculations. The versatility to study breaking of the lattice symmetry by simple reflectance measurements opens up the possibility to gain a direct insight on the band-structure of other strain-engineered materials, such as graphene and two-dimensional (2D) transition metal dichalcogenides (TMDCs)., 6 pages, 3 figures, 11 panels, 33 references

Reactive multilayers can be used for energy storage as well as releasing large amounts of heat in a short time. Molecular Dynamics (MD) simulations are used to study the influence of the crystal structure on the reaction front propagation in Al–Ni multilayers. Different microstructures, namely, amorphous, single crystal, columnar grains, and randomly oriented grains of varying size, are investigated. The effect of the microstructure on the propagation speed is studied and compared to existing experimental results. Furthermore, MD simulations allow to study the inter-diffusion of the Al and Ni layers. It is found that crystallinity has a significant impact on the front propagation speed, which is likely related to different diffusion mechanisms. The more disordered the individual layers become, e.g., by increasing the grain boundary density, the higher is the resulting propagation speed.

The fabrication of 3D ink-printed and sintered porous Si scaffolds as electrode material for lithium-ion batteries is explored. A hierarchically-porous architecture consisting of channels (~220 μm in diameter) between microporous Si struts is created to accommodate the large volume change from Si (de)lithiation during electrochemical (dis)charging. The influence of sintering parameters on Si strut porosity and the resulting mechanical and electrochemical properties of the scaffolds are studied experimentally and computationally. Varying sintering temperatures (1150–1300 °C) and sintering times (1–16 h) the open porosity within the Si filaments can be tailored between 46 and 60%. Pore size (3–6 μm) and wall thickness (3–8 μm) can be adjusted to tailor the surface-to-volume ratio. Computational results show that maximum capacity is expected at ~50% Si strut porosity, balancing short diffusion lengths and sufficient volume of active material. Stress concentrations are reduced at higher filament porosities albeit at the cost of energy density. For a filament porosity of 46%, hierarchically porous Si microlattice electrodes display gravimetric and volumetric capacities as high as 2,990 mA h g−1 and 2,860 mA h cm−3, respectively. The simple 3D printing + sintering approach provides further opportunities for optimization of Si electrodes by geometrical freedom.

This paper presents the proof-of-concept for a 4D printed active compliant hinge with a selectively variable stiffness for the deployment and reorientation of satellite appendages. We use 4D printing to create an active compliant hinge capable of bending to a given angular position, holding the position without consuming energy and reorienting itself multiple times in a slow and controlled manner without using rigid mechanisms and, therefore, requiring no lubrication. The deployment and the reorientation of the hinge are achieved by exploiting thermally induced stiffness modulation of one of the constituting materials and two antagonistic shape memory alloy actuators. The hinge is specifically designed for the case study of a 6U CubeSat with two orientable solar panels. In this work, we first explain the working principle of the hinge and propose three different actuation strategies to increase the energy collection of the considered CubeSat. Second, we describe the specific functional and geometric requirements of the hinge, the resulting design and the fabricated functional prototype. The latter is tested in a standard laboratory environment to measure the range of motion, the energy consumption and the actuation time. Finally, the feasibility of the three proposed actuation strategies is evaluated considering the corresponding net increase in collected energy. The results show that the hinge is compatible with the stowing requirements and capable of achieving maximum angular positions larger than 90° in both directions and holding any intermediate position with an accuracy of less than 3°. The three actuation strategies considered lead, in a standard laboratory environment, to an increase in energy generation between 54% and 72%., Smart Materials and Structures, 30 (8), ISSN:1361-665X, ISSN:0964-1726

A combinatorial science approach is utilized to study the microstructural and mechanical properties of metastable copper‑tungsten solid solutions. Lateral compositional gradient (also called composition-spread) samples were deposited by simultaneously sputtering copper and tungsten targets positioned obliquely at opposite ends of a silicon substrate. The chemical composition of the film varies continuously along its length from 12 to 45 atomic % copper and has a nominal thickness of 1 μm. Nanoindentation was performed to measure the hardness and elastic modulus of the film. Grain size and solid solution strengthening models are applied to interpret the hardness of the film, though a simple rule of mixtures is found to give a more satisfactory fit to the data. The elastic modulus of the film is consistently below that predicted by the rule of mixtures. X-ray diffraction revealed plane spacing less than that predicted by Vegard's law as well as three chemical compositions exhibiting enhanced long-range order. Transmission electron microscopy analysis confirms that the film consists of a single metastable body centred cubic solid solution where the lattice spacing and grain size depend on chemical composition.

In this work, the onset strains of fragmentation, the fracture strength, and fracture toughness of amorphous and crystalline Ge2Sb2Te5 (GST) films are determined. Using in situ methods, such as resistance measurements, reflectance anisotropy spectroscopy (RAS), and light microscopy during uniaxial tensile loading, we demonstrate that onset strain of fragmentation and delamination depend on both, crystallographic state of the GST film and the film thickness. We observe that amorphous GST fractures at larger strains than crystalline GST. However, due to its small Young's modulus the fracture toughness KIC of amorphous GST is lower than that of crystalline GST (amorphous: K I C = 0.4 ± 0.2 MPa m0.5; crystalline: K I C = 0.8 ± 0.2 MPa m0.5). The results presented are critically discussed with respect to the potential application of GST films in flexible displays.

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.

Elastic strain is an effective and thus widely used parameter to control and modify the electrical, optical, and magnetic properties of crystalline solid-state materials. It has a large impact on device performance and enables adjusting the materials functionality. Here, we promote a micromechanical strain enhancement technology to achieve ultra-high strain in semiconductors. The here presented suspended membranes enable the accurate control of the strain on a wafer-scale by standard top-down fabrication methods making it attractive for both device applications and also, thanks to the simplicity of the method, for fundamental research. This review aims at discussing the process of strain enhancement and its usage as an investigation platform for strain-related physical properties. Furthermore, we present design rules and a detailed analysis of fracture effects limiting the strain enhancement.

Metals with nanometer-scale grains or nanocrystalline metals exhibit high strengths at ambient conditions, yet their strengths substantially decrease with increasing temperature, rendering them unsuitable for usage at high temperatures. Here, we show that a nanocrystalline high-entropy alloy (HEA) retains an extraordinarily high yield strength over 5 GPa up to 600 °C, 1 order of magnitude higher than that of its coarse-grained form and 5 times higher than that of its single-crystalline equivalent. As a result, such nanostructured HEAs reveal strengthening figures of merit-normalized strength by the shear modulus above 1/50 and strength-to-density ratios above 0.4 MJ/kg, which are substantially higher than any previously reported values for nanocrystalline metals in the same homologous temperature range, as well as low strain-rate sensitivity of ∼0.005. Nanocrystalline HEAs with these properties represent a new class of nanomaterials for high-stress and high-temperature applications in aerospace, civilian infrastructure, and energy sectors.

Most refractory high-entropy alloys (HEAs) are brittle and suffer from limited formability at ambient temperature. Previous studies imply that grain boundaries affect their fracture behavior, but quantitative studies on the fracture properties of body-centered-cubic HEAs are scarce. Here, using in situ micro-cantilever tests, we show that the fracture toughness of a bi-crystal HEA, Nb 25 Mo 25 Ta 25 W 25 , is one order of magnitude lower than that of single crystalline ones. Atom probe tomography of the bi-crystal HEA reveals element segregation and formation of oxides and nitrides at grain boundaries, suggesting that minimizing grain boundary segregation is critical to improving fracture properties in refractory HEAs.

Sample geometries for micro-mechanical testing, e.g. micro-pillars and micro-cantilevers are primarily produced using gallium focused ion beam technology. However, the effects of the gallium ions on the mechanical properties of metals which are embrittled by liquid metal gallium are still unknown. In this work, micro-compression samples from single crystalline and ultrafine-grained aluminum are fabricated using both xenon and/or gallium ions. The different ions have little effect on the yield strength of single crystalline aluminum. However, for the ultrafine-grained aluminum, the strength is reduced with increasing Ga dose, and considerable differences in the deformation morphology and resulting microstructures are observed.

Controlling the grain boundary network of small-scale materials—such as coatings and thin films—is an ambitious goal that would ultimately enable the production of components with tailored properties and improved reliability. In this work we present a new technique—which we term ion-induced grain boundary engineering (iGBE)—to engineer the character distribution and connectivity of grain boundaries in gold films in situ, as they are being deposited. iGBE consists of a repeated sequence of ion-induced material removal and material deposition which results in the selection and growth of crystal grains in twinned relationship. This phenomenon yields a substantial increase in the density and connectivity of Σ3 twin boundaries, which have renowned beneficial effects on the material's resistance to intergranular degradation. We confirm the improved reliability of iGBE microstructures by assessing their resistance to electromigration—one of the most common causes of failure in integrated circuit interconnects. We find that, through iGBE, interconnect lifetime increases by three orders of magnitude at standard operating conditions. Since iGBE is material-insensitive and compatible with standard microfabrication technology, we expect it to have significant impact on microelectronics industry.

Many biological systems consisting of mechanically graded composites can be used to join mechanically different materials like bone, cartilage and mussel. Synthetic routes have so far been unable to achieve both the 3-D nature and the property tuning at micrometer length scales to replicate such systems. Deliberate strengthening of the mismatched surfaces and weak regions could be beneficial for a wide range of applications such as flexible electronics with locally stiff constituents, NEMS and MEMS systems, dental prosthesis having heterogeneous particle distributions resembling to natural tooth and joining mechanically different biological materials such as bone, cartilage and mussel. Dip Pen Nanolithography (DPN) can be a strategy to achieve this goal. In this study, DPN is utilized to locally deposit graded polymer-based composite materials at the micron scale. Spatial resolutions of 3–20 μm are obtained on entire pattern profiles with 6–70 μm width and up to 2 μm height. Colloidal probe microscopy and nanoindentation are used for mechanical characterization. Results show that the hardness and modulus of the gradient nanocomposite patterns can be tuned locally by changing the concentration of the ceramic nanoparticles.

Micro-compression testing of focused ion beam fabricated pillars is a popular technique for mechanical characterization at small scales. However, there are concerns associated with these ion-prepared samples, including irradiation damage from Ga ions and Ga segregation at grain boundaries resulting in liquid metal embrittlement. In this work, this is investigated using strain rate jump nanoindentation and micro-compression of single crystalline and ultrafine-grained aluminum with different grain boundary conditions. The extracted strain rate sensitivity and activation volume are used to study the effects of Ga and Xe ion species from fabrication and testing methods on deformation behavior of aluminum samples. Results show that the measured strain-rate sensitivity of non-equilibrium, ultrafine-grained aluminum is significantly affected by the dosage of Ga. Activation volumes suggest that the dominant deformation mechanism remains consistent despite Ga at the boundaries. Atom probe tomography reveals that Ga was observed to segregate to aluminum grain boundaries up to 2.2 at.% in the FIB prepared sample., Materials & Design, 181, ISSN:0264-1275, ISSN:1873-4197

Zero-index (ZI) materials are synthetic optical materials with vanishing effective permittivity and/or permeability at a given design frequency. Recently, it has been shown that the permeability of a zero-index host material can be deterministically tuned by adding photonic dopants. Here, we apply metal-induced crystallization (MIC) in quasi-random metal-semiconductor composites to fabricate large-area zero-index materials. Using Ag-Si as a model systems, we demonstrate that the localized crystallization of the semiconductor at the metal/semiconductor interface can be used as design parameter to control light interaction in such a disordered system. The induced crystallization generates new zero-index states corresponding to a hybridized plasmonic mode emerging from selective coupling of light to the \r{a}ngstr\"om-sized crystalline shell of the semiconductor. Photonic doping can be used to enhance the transmission in these disordered metamaterials as is shown by simulation. Our results break ground for novel large-area zero-index materials for wafer scale applications and beyond., Comment: 23 pages, 4 figures

An extensive range of metals can be dissolved and re-deposited in liquid solvents using electrochemistry. We harness this concept for additive manufacturing, demonstrating the focused electrohydrodynamic ejection of metal ions dissolved from sacrificial anodes and their subsequent reduction to elemental metals on the substrate. This technique, termed electrohydrodynamic redox printing (EHD-RP), enables the direct, ink-free fabrication of polycrystalline multi-metal 3D structures without the need for post-print processing. On-the-fly switching and mixing of two metals printed from a single multichannel nozzle facilitates a chemical feature size of, Nature Communications, 10 (1), ISSN:2041-1723

Controlling anisotropy in self-assembled structures enables engineering of materials with highly directional response. Here, we harness the anisotropic growth of ice walls in a thermal gradient to assemble an anisotropic refractory metal structure, which is then infiltrated with Cu to make a composite. Using experiments and simulations, we demonstrate on the specific example of tungsten-copper composites the effect of anisotropy on the electrical and mechanical properties. The measured strength and resistivity are compared to isotropic tungsten-copper composites fabricated by standard powder metallurgical methods. Our results have the potential to fuel the development of more efficient materials, used in electrical power grids and solar-thermal energy conversion systems. The method presented here can be used with a variety of refractory metals and ceramics, which fosters the opportunity to design and functionalize a vast class of new anisotropic load-bearing hybrid metal composites with highly directional properties., Scientific Reports, 9 (1), ISSN:2045-2322