Hierarchical Surface Pattern on Ni-Free Ti-Based Bulk Metallic Glass to Control Cell Interactions.

Ni-free Ti-based bulk metallic glasses (BMGs) are exciting materials for biomedical applications because of their outstanding biocompatibility and advantageous mechanical properties. The glassy nature of BMGs allows them to be shaped and patterned via thermoplastic forming (TPF). This work demonstrates the versatility of the TPF technique to create micro- and nano-patterns and hierarchical structures on TiZrCuPdSn BMG.

Size-dependent deformation behavior in nanosized amorphous metals suggesting transition from collective to individual atomic transport.

The underlying atomistic mechanism of deformation is a central problem in mechanics and materials science. Whereas deformation of crystalline metals is fundamentally understood, the understanding of deformation of amorphous metals lacks behind, particularly identifying the involved temporal and spatial scales. Here, we reveal that at small scales the size-dependent deformation behavior of amorphous metals significantly deviates from homogeneous flow, exhibiting increasing deformation rate with reducing size and gradually shifted composition.

Size-dependent vitrification in metallic glasses.

Reducing the sample size can profoundly impact properties of bulk metallic glasses. Here, we systematically reduce the length scale of Au and Pt-based metallic glasses and study their vitrification behavior and atomic mobility. For this purpose, we exploit fast scanning calorimetry (FSC) allowing to study glassy dynamics in an exceptionally wide range of cooling rates and frequencies.

Compositional dependence of the fragility in metallic glass forming liquids.

The viscosity and its temperature dependence, the fragility, are key properties of a liquid. A low fragility is believed to promote the formation of metallic glasses. Yet, the fragility remains poorly understood, since experimental data of its compositional dependence are scarce.

Nonaffine Strains Control Ductility of Metallic Glasses.

The origin of limited plasticity in metallic glasses is elusive, with no apparent link to their atomic structure. We propose that the response of the glassy structure to applied stress, not the original structure itself, provides a gauge to predict the degree of plasticity. We carried out high-energy x-ray diffraction on various bulk metallic glasses (BMGs) under uniaxial compression within the elastic limit and evaluated the anisotropic pair distribution function.

Single-Crystal Nanostructure Arrays Forming Epitaxially through Thermomechanical Nanomolding.

For nanostructures in advanced electronic and plasmonic systems, a single-crystal structure with controlled orientation is essential. However, the fabrication of such devices has remained challenging, as current nanofabrication methods often suffer from either polycrystalline growth or the difficulty of integrating single crystals with substrates in desired orientations and locations to create functional devices. Here we report a thermomechanical method for the controlled growth of single-crystal nanowire arrays, which enables the simultaneous synthesis, alignment, and patterning of nanowires.

Unleashing nanofabrication through thermomechanical nanomolding.

Advancements in nanotechnology require the development of nanofabrication methods for a wide range of materials, length scales, and elemental distributions. Today’s nanofabrication methods are typically missing at least one demanded characteristic. Hence, a general method enabling versatile nanofabrication remains elusive.

Data-driven discovery of a universal indicator for metallic glass forming ability.

Despite the importance of glass forming ability as a major alloy characteristic, it is poorly understood and its quantification has been experimentally laborious and computationally challenging. Here, we uncover that the glass forming ability of an alloy is represented in its amorphous structure far away from equilibrium, which can be exposed by conventional X-ray diffraction. Specifically, we fabricated roughly 5,700 alloys from 12 alloy systems and characterized the full-width at half-maximum, Δq, of the first diffraction peak in the X-ray diffraction pattern.

Correlation symmetry analysis of electron nanodiffraction from amorphous materials.

Angular symmetry in diffraction reflects rotational symmetry in the sample. We introduce the angular symmetry coefficient as a method to extract local symmetry information from electron nanodiffraction patterns of amorphous materials. Symmetry coefficients are the average of the angular autocorrelation function at the characteristic angles of a particular rotational symmetry.

Nanomolding of Gold and Gold-Silicon Heterostructures at Room Temperature.

Nanofabrication techniques are limited by at least one of the required characteristics such as choice of material, control over geometry, fabrication requirements, yield, cost, and scalability. Our previously developed method of thermomechanical nanomolding fulfills these requirements, although it requires high processing temperatures. Here, we demonstrate low-temperature molding where we utilize the enhanced diffusivity on "eutectic interfaces".

Fast Surface Dynamics on a Metallic Glass Nanowire.

The dynamics near the surface of glasses can be much faster than in the bulk. We studied the surface dynamics of a Pt-based metallic glass using electron correlation microscopy with sub-nanometer resolution. Our studies show an ∼20 K suppression of the glass transition temperature at the surface.

Static-state particle fabrication via rapid vitrification of a thixotropic medium.

Functional particles that respond to external stimuli are spurring technological evolution across various disciplines. While large-scale production of functional particles is needed for their use in real-life applications, precise control over particle shapes and directional properties has remained elusive for high-throughput processes. We developed a high-throughput emulsion-based process that exploits rapid vitrification of a thixotropic medium to manufacture diverse functional particles in large quantities.

Biocompatibility of platinum-based bulk metallic glass in orthopedic applications.

Bulk metallic glasses (BMGs) are a class of amorphous metals that exhibit high strength, ductility paired with wear and corrosion resistance. These properties suggest that they could serve as an alternative to conventional metallic implants that suffer wear and failure. In the present study, we investigated Platinum (Pt)-BMG biocompatibility in bone applications.

Combinatorial measurement of critical cooling rates in aluminum-base metallic glass forming alloys.

Direct measurement of critical cooling rates has been challenging and only determined for a minute fraction of the reported metallic glass forming alloys. Here, we report a method that directly measures critical cooling rate of thin film metallic glass forming alloys in a combinatorial fashion. Based on a universal heating architecture using indirect laser heating and a microstructure analysis this method offers itself as a rapid screening technique to quantify glass forming ability.

Atomic-Scale Imprinting by Sputter Deposition of Amorphous Metallic Films.

With its ease of implementation, low cost, high throughput, and excellent feature replication accuracy, nanoimprinting is used to fabricate structures for electrical, optical, and biological applications or to modify surface properties. If ultraprecise and/or subnanometer-sized patterns are desired, nanoimprinting has shown only limited success with polymers, silica glasses, or crystalline materials. In contrast, the absence of an intrinsic length scale that would interfere with imprinting resolution enables bulk metallic glasses (BMGs) to replicate structures down to the atomic scale through thermoplastic forming (TPF).

Semiconductor-to-conductor transition in 2D copper(ii) oxide nanosheets through surface sulfur-functionalization.

Functionalization is a widely-used strategy to modulate and optimize the properties of materials towards various applications, including sensing, catalysis, and energy generation. While the influence of sulfur-functionalization of carbon materials and oxides like ZnO and TiO has been studied, far less research has been devoted to analyzing sulfur-functionalization of CuO and other transition metal oxide nanomaterials. Here, we report sulfur-functionalization of copper(ii) oxide nanosheets synthesized by using a soft-templating procedure, with sulfur-addition based on hydrogen sulfide gas as a source.

General Nanomolding of Ordered Phases.

Large-scale, controlled fabrication of ordered phases is challenging at the nanoscale, yet highly demanded as their well-ordered structure and chemistry is the key for advanced functionality. Here, we demonstrate a general nanomolding process of ordered phases based on atomic diffusion. Resulting nanowires are single crystals and maintain their composition and structure throughout their length, which we explain by a self-ordering process originating from their narrow Gibbs free energy.

Intrinsic dissipation mechanisms in metallic glass resonators.

Micro- and nanoresonators have important applications including sensing, navigation, and biochemical detection. Their performance is quantified using the quality factor Q, which gives the ratio of the energy stored to the energy dissipated per cycle. Metallic glasses are a promising material class for micro- and nanoscale resonators since they are amorphous and can be fabricated precisely into complex shapes on these length scales.

Fast Screening of Corrosion Trends in Metallic Glasses.

Corrosion trends in the bulk metallic glass forming alloy system Zr-Cu-Al are studied through a fast screening visual characterization method of thin film alloy libraries prepared by magnetron co-sputtering. Significant distinct brightness changes are present within the Zr-Cu-Al system when the thin film library is immersed in 3.5 wt % NaCl.

Accelerated discovery and mechanical property characterization of bioresorbable amorphous alloys in the Mg-Zn-Ca and the Fe-Mg-Zn systems using high-throughput methods.

Ternary amorphous alloys in the magnesium (Mg)-zinc (Zn)-calcium (Ca) and the iron (Fe)-Mg-Zn systems are promising candidates for use in bioresorbable implants and devices. The optimal alloy compositions for biomedical applications should be chosen from a large variety of available alloys with best combination of mechanical properties (modulus, strength, hardness) and biological response (in situ degradation rates, cell adhesion and proliferation). As a first step towards establishing a database designed to enable such targeted material selection, amorphous alloy composition libraries were fabricated employing a combinatorial magnetron sputtering approach where Mg, Zn, and Ca/Fe are co-deposited from separate sources onto a silicon wafer substrate.

Formation and stability of complex metallic phases including quasicrystals explored through combinatorial methods.

Aluminum-based quasicrystals typically form across narrow composition ranges within binary to quaternary alloys, which makes their fabrication and characterization challenging. Here, we use combinatorial approaches together with fast characterization techniques to study a wide compositional range including known quasicrystal forming compositions. Specifically, we use magnetron co-sputtering to fabricate libraries of ~140 Al-Cu-Fe and ~300 Al-Cu-Fe-Cr alloys.

High-temperature bulk metallic glasses developed by combinatorial methods.

Since their discovery in 1960, metallic glasses based on a wide range of elements have been developed. However, the theoretical prediction of glass-forming compositions is challenging and the discovery of alloys with specific properties has so far largely been the result of trial and error. Bulk metallic glasses can exhibit strength and elasticity surpassing those of conventional structural alloys, but the mechanical properties of these glasses are critically dependent on the glass transition temperature.

Supercluster-coupled crystal growth in metallic glass forming liquids.

While common growth models assume a structure-less liquid composed of atomic flow units, structural ordering has been shown in liquid metals. Here, we conduct in situ transmission electron microscopy crystallization experiments on metallic glass nanorods, and show that structural ordering strongly affects crystal growth and is controlled by nanorod thermal history. Direct visualization reveals structural ordering as densely populated small clusters in a nanorod heated from the glass state, and similar behavior is found in molecular dynamics simulations of model metallic glasses.

Nanomolding of Crystalline Metals: The Smaller the Easier.

We report on a thermomechanical nanomolding method for crystalline metals. Quantified by the aspect ratio, this process becomes easier with decreasing mold diameter. As the responsible underlying diffusion mechanism is present in all metals and alloys, the discovered nanomolding process provides a toolbox to shape essentially any metal and alloy into a nanofeature.

Author Correction: Determination of critical cooling rates in metallic glass forming alloy libraries through laser spike annealing.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.