Interfaces, inclusions, and impurities in nanolaminate metallic structures

The use of thin metal structures to add strength to metallic systems due to dislocation interactions with interfaces has been well documented in laminate blanket bilayer composites such as Cu–Nb or Cu–Ni thin films. Adding a third layer, such as Cu–Ni–Nb, alters the landscape for dislocation motion and results in added strain hardening which is not possible in bimetallic systems. This study extends the impact of heterogeneities into three different systems of reduced dimension: one of adding impurities and solid solution elements to the systems, and two where the defects of hard second-phase structures are deposited and precipitated within a softer FCC layers. Cu–Ni alloying is used in the Cu–Ni–Nb system to examine solid solution strengthening, whereas Cr in a bilayer of Cr–CuCr is used to examine precipitate effects on strengthening. A third system, ZnO in Au is used to compare the combined effects of solute Zn and precipitated ZnO to separate the effects of the impurities from the interfacially dominated behavior of the multilayer systems. A combination of nanoindentation and microcompression testing are used to demonstrate hardening effects as a function of layer thickness, and the strength enhancement beyond what would be expected using a classical Hall–Petch model is described in terms of the confined layer slip model. Testing has been carried out at room temperature and elevated temperatures (up to 600K) to examine any changes in mechanisms which may occur in these cases. The ability to strain harden in the trilayer structures is well beyond that of the bilayer films both with and without additional impurities that increase strength. The addition of harder precipitates of Cr in the FCC layers, adding an additional obstacle to dislocation motion, is shown both through simulation and experiment to add significant strength to these new structures. The size of the defects also controls the behavior at elevated temperatures and after extended annealing, leading to films which strengthen after annealing. Finally, solute Zn and precipitated ZnO demonstrates how these strengthening methods, used in conventional bulk systems, need to be balanced versus grain size strengthening if composition, rather than only structural features, is to become a parameter to open new design windows in metallic thin films for electronic and MEMS applications

Core-Shell Copper and Nickel Nanofoam: Uniform Electroplating and Properties

Characterizing materials on the nanoscale is a key factor to enhance nanotechnology in diverse applications, ranging from electronics to energy fields. However, controlling the structure of the material at the nanoscale or mimicking the nanoscale features of a structure that already exists requires linking processing conditions to the nanostructure. This work focuses on solids that show porous patterns at the nano-micro scale; these are often called cellular solids and classified into two categories: honeycombs and foams. This study focuses on nanofoams; with ligament dimensions in the sub-micron scale. Electrospinning has been developed to produce nanofoam structures of polymers with controlled ligament sizes. In this current research, a copper nanofoam was produced by electrospinning a polymer which contained a Cu component. This was followed by heat treatments that formed an oxide, and then subsequently reduced to form the pure metal foam. The obtained copper nanofoam was then electroplated with nickel by putting it in a nickel bath and applying current. It was found, after taking images using scanning electron microscopy, that the electroplated nickel takes a uniform shape along with the existing foam of copper, it was observed also that the nickel is depositing over the ligaments of the copper nanofoam structure. Obtaining core-shell metallic nanofoams such as copper and nickel appears to be possible through electrospinning, thermal treatments, and subsequent electroplating, but controlling the thickness of the shell of nickel over the copper ligaments of the nanofoam requires further experimentation and can be done on different types of metals

Statistical analysis of nanoindentation hardness and pop-in behavior: variation as a characterization tool

Accurate determination of nanomechanical materials properties is required for successful nanoscale materials characterization and subsequent design. Advancements in indentation science have been made in recent decades; however, widely varying nanoindentation hardness and elastic moduli are still currently reported in the literature on nominally similar samples, particularly at small depths or when only a few tests can be carried out in a limited sample volume. The study explores changes in the variation of hardness of platinum tested at five different depths between 50 and 300 nm for three different dislocation densities. Analysis of nearly 1500 indents showed that the coefficient of variation in hardness increases with decreasing dislocation density and sampling volume. Dislocation density plays a critical role in the variation, beyond solely instrumentation uncertainty, and supports a defect-based explanation for the stochastic behavior. The elasto-plastic transition has also been studied from a statistical standpoint. There is substantial research on the first so-called pop-in, however there has been little research concerning muliple pop-in events. Software has been developed for detecting first and subsequent pop-ins from indentation load-depth curves. The analysis of many indentation tests, combined with well-accepted models of deformation evolution allows nanoindentation to be used as a tool for characterizing dislocation density in crystalline materials. Heavily worked materials containing many preexisting dislocations exhibit little or no initial pop-in and no subsequent pop-ins. Alternatively, after annealing to reduce the dislocation content, larger and later pop-ins are exhibited. Other microstructural features such as impurities may be detected. This study additionally explores the transition from staircase yielding to bulk plasticity

Predicting Flock Vigilance from Simple Passerine Interactions: Modelling with Cellular Automata

Vigilance in flocks can be described and modelled as a plausible set of local interactions between neighbouring birds. Each bird in the modelled flock chooses to feed or to scan based solely on whether or not its neighbours are feeding or scanning. This simple model has the ability both to reproduce observations that have not been previously explained and to predict flock behaviours that might be confirmed with future field studies. Examples include simulations showing decreased vigilance with increased flock size (as observed in the field), greater time spent scanning when obstacles such as trees are present (as observed) and a coordinated feed/scan pattern (that is predicted to become increasingly coordinated when the birds look up from feeding more frequently). The numerical model also predicts that flock geometry influences vigilance. If two flocks are the same size, individuals in the one with the larger perimeter will spend more time scanning. This prediction could be tested with field studies and already has been observed empirically for two limiting cases: birds arranged in a line (high perimeters, high scan times) and birds in a circle (lower perimeters, lower scan times). As demonstrated by its multiple successes, cellular models of this type are a powerful new approach to understanding bird flock behaviours

Characterization of Hardness and Elastic Modulus of a Pharmaceutical Material for Multiple Crystal Orientations

Nanoindentation has made it possible to test material properties of extremely brittle molecular crystals, which include many pharmaceuticals. An antifungal, griseofulvin, is tested to determine differences in hardness and elastic modulus for different crystal orientations. Hardness and elastic modulus are determined by nanoindentation on single crystals that are rotated in 15° intervals. There are differences in hardness at rotation degrees of 45°, 60°, and 75° from the 0° orientation and differences in elastic modulus at rotation degrees of 15°, 60°, and 75° from the 0° orientation. It is also found that the elastic modulus and hardness values of the 75° rotation are only similar to the 60° rotation. Griseofulvin displays anisotropy in hardness and elastic modulus, which implies that different crystal rotations activate different slip systems. Further work is needed to correlate rotation angle with the crystal structure as well as confirm these findings on another crystal

Wireless event-recording device with identification codes

A wireless recording device can be interrogated to determine its identity and its state. The state indicates whether a particular physical or chemical event has taken place. In effect, the physical or chemical event is recorded by the device. The identity of the device allows it to be distinguished from a number of similar devices. Thus the sensor device may be used in an array of devices that can be probed by a wireless interrogation unit. The device tells the interrogator who it is and what state it is in. The interrogator can thus easily identify particular items in an array that have reached a particular condition

Addressing the impact of fracture during indentation of molecular crystals

There are inherent challenges in mechanical testing of anisotropic molecular crystals, one of which being their propensity for brittle fracture, which can limit the usage conditions of the material as well as the range of conditions in which mechanical testing results are valid. Molecular crystals, which contain the families of many energetic materials and pharmaceutical materials (in addition to ice), are commonly considered to be both compliant and brittle, and in most common forms the materials are used as small crystalline powders suspended in binders rather than in pure polycrystalline aggregates. Indentation testing on molecular crystals has previously been shown to be able to quantify modulus, hardness, and yield points in materials ranging from sucrose [1] to energetics and pharmaceuticals [2], [3]. To quantify the fracture response in materials that cannot be subjected to traditional toughness tests due to limited particle size and morphology, a technique is used in which nanoindentation tests are performed on a material with probes of varying acuity, and analysis of the unloading portion of the resulting load-depth curve indicates presence or lack thereof of radial cracking [4]. This technique has been used to define a radial cracking threshold for the secondary explosives HMX (cyclotetramethylenetetranitramine) and PETN (pentaerythritol tetranitrate) of 4 mN as well as a cracking threshold beginning at 100 mN for the pharmaceutical idoxuridine. The low indentation fracture toughness in the explosives may be the reason for difficulty that has been seen previously in accurately obtaining mechanical property measurements over a wide range of depths in these materials. Please click Additional Files below to see the full abstract

Running primordial perturbations: Inflationary Dynamics and Observational Constraints

Inflationary cosmology proposes that the early Universe undergoes accelerated expansion, driven, in simple scenarios, by a single scalar field, or inflaton. The form of the inflaton potential determines the initial spectra of density perturbations and gravitational waves. We show that constraints on the duration of inflation together with the BICEP3/Keck bounds on the gravitational wave background imply that higher derivatives of the potential are nontrivial with a confidence of 99%. Such terms contribute to the scale-dependence, or running, of the density perturbation spectrum. We clarify the ``universality classes'' of inflation in this limit showing that a very small gravitational wave background can be correlated with a larger running. If pending experiments do not observe a gravitational wave background the running will be at the threshold of detectability if inflation is well-described at third-order in the slow roll expansion.Comment: 5 pages; 5 figures; as published in PRD -- change of title, minor clarification

Measurement of the matter-radiation equality scale using the extended Baryon Oscillation Spectroscopic Survey Quasar Sample

The position of the peak of the matter power spectrum, the so-called turnover scale, is set by the horizon size at the epoch of matter-radiation equality. It can easily be predicted in terms of the physics of the Universe in the relativistic era, and so can be used as a standard ruler, independent of other features present in the matter power spectrum, such as baryon acoustic oscillations (BAO). We use the distribution of quasars measured by the extended Baryon Oscillation Spectroscopic Survey (eBOSS) to determine the turnover scale in a model-independent fashion statistically. We avoid modelling the BAO by down-weighting affected scales in the covariance matrix using the mode deprojection technique. We measure the wavenumber of the peak to be $k_\mathrm{TO} = \left( 17.7^{+1.9}_{-1.7} \right) \times 10^{-3}h/\mathrm{Mpc}$, corresponding to a dilation scale of $D_\mathrm{V}(z_\mathrm{eff} = 1.48) = \left(31.5^{+3.0}_{-3.4}\right)r_\mathrm{H}$. This is not competitive with current BAO distance measures in terms of determining the expansion history but does provide a useful cross-check. We combine this measurement with low-redshift distance measurements from type-Ia supernova data from Pantheon and BAO data from eBOSS to make a sound-horizon free estimate of the Hubble-Lema\^itre parameter and find it to be $H_0=64.8^{+8.4}_{-7.8} \ \mathrm{km/s/Mpc}$with Pantheon, and$H_0=63.3^{+8.2}_{-6.9} \ \mathrm{km/s/Mpc}$ with eBOSS BAO. We make predictions for the measurement of the turnover scale by the Dark Energy Spectroscopic Instrument (DESI) survey, the Maunakea Spectroscopic Explorer (MSE) and MegaMapper, which will make more precise and accurate distance determinations.Comment: 11 pages, 9 figure

Structure and mechanical response of metallized electrospun polymeric mats and foams for filter applications

Polymeric non-woven structures for filters are often formed from wet-laid melt blown or spun-bounded fibers, where the polymeric fibers are on the order of microns in diameter. Ultra-filtration applications use finer diameter fibers (100s to 1000 nm) which can be formed via electrospinning. In these cases, composite filter structures have been shown to enhance flow rates of fluids by tailoring multiple polymeric structures of mixed spacing, diameters, and hydrophobicity [1]. Adding anti-microbial functionality to these filters has been achieved through the addition of metallic nanoparticles, such as silver. The particles have been introduced by a variety of methods, ranging from incorporating silver nitrate and subsequently precipitating silver nanoparticles during electrospinning [2] to simple immersion. Silver is not the only metal that exhibits antimicrobial properties; copper has also been shown to exhibit antimicrobial applications when present in nanoparticle form [3]. Please click Additional Files below to see the full abstract