Additively manufactured hierarchical stainless steels with high strength and ductility.

Many traditional approaches for strengthening steels typically come at the expense of useful ductility, a dilemma known as strength-ductility trade-off. New metallurgical processing might offer the possibility of overcoming this. Here we report that austenitic 316L stainless steels additively manufactured via a laser powder-bed-fusion technique exhibit a combination of yield strength and tensile ductility that surpasses that of conventional 316L steels.

Synthesis of Nanostructured/Macroscopic Low-Density Copper Foams Based on Metal-Coated Polymer Core-Shell Particles.

A robust, millimeter-sized low-density Cu foam with ∼90% (v/v) porosity, ∼30 nm thick walls, and ∼1 μm diameter spherical pores is prepared by the slip-casting of metal-coated polymer core-shell particles followed by a thermal removal of the polymer. In this paper, we report our key findings that enable the development of the low-density Cu foams. First, we need to synthesize polystyrene (PS) particles coated with a very thin Cu layer (in the range of tens of nanometers).

In Situ Real-Time Radiographic Study of Thin Film Formation Inside Rotating Hollow Spheres.

Hollow spheres with uniform coatings on the inner surface have applications in optical devices, time- or site-controlled drug release, heat storage devices, and target fabrication for inertial confinement fusion experiments. The fabrication of uniform coatings, which is often critical for the application performance, requires precise understanding and control over the coating process and its parameters. Here, we report on in situ real-time radiography experiments that provide critical spatiotemporal information about the distribution of fluids inside hollow spheres during uniaxial rotation.

Ultra-strong and low-density nanotubular bulk materials with tunable feature sizes.

The synthesis of ultralow-density (>5 mg/cm(3) ) bulk materials with interconnected nanotubular morphology and deterministic, fully tunable feature size, composition, and density is presented. A thin-walled nanotubular design realized by employing templating based on atomic layer deposition makes the material about 10 times stronger and stiffer than aerogels of the same density.

Atomic layer deposition-derived ultra-low-density composite bulk materials with deterministic density and composition.

A universal approach for on-demand development of monolithic metal oxide composite bulk materials with air-like densities (<5 mg/cm(3)) is reported. The materials are fabricated by atomic layer deposition of titania (TiO2) or zinc oxide (ZnO) using the nanoscale architecture of 1 mg/cm(3) SiO2 aerogels formed by self-organization as a blueprint. This approach provides deterministic control over density and composition without affecting the nanoscale architecture of the composite material that is otherwise very difficult to achieve.

Deterministic control over high-Z doping of polydicyclopentadiene-based aerogel coatings.

We report on simple and efficient routes to dope polydicyclopentadiene (PDCPD)-based aerogels and their coatings with high-Z tracer elements. Initially, direct halogenation of PDCPD wet gels and aerogels with elemental iodine or bromine was studied. Although several pathways were identified that allowed doping of PDCPD aerogels by direct addition of bromine or iodine to the unsaturated polymer backbone, they all provided limited control over the amount and uniformity of doping, especially at very low dopant concentrations.

Defective twin boundaries in nanotwinned metals.

Coherent twin boundaries (CTBs) are widely described, both theoretically and experimentally, as perfect interfaces that play a significant role in a variety of materials. Although the ability of CTBs in strengthening, maintaining the ductility and minimizing the electron scattering is well documented, most of our understanding of the origin of these properties relies on perfect-interface assumptions. Here we report experiments and simulations demonstrating that as-grown CTBs in nanotwinned copper are inherently defective with kink-like steps and curvature, and that these imperfections consist of incoherent segments and partial dislocations.

ALD functionalized nanoporous gold: thermal stability, mechanical properties, and catalytic activity.

Nanoporous metals have many technologically promising applications, but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au).

Matrix-assisted energy conversion in nanostructured piezoelectric arrays.

We demonstrate an organic/inorganic hybrid energy-harvesting platform, based on nanostructured piezolelectric arrays embedded in an environmental-responsive polymer matrix, which can self-generate electrical power by scavenging energy from the environment. A proof of principle device is designed, fabricated, and tested using vertically aligned ZnO nanowires and heat as the local energy source. The device layout takes advantage of the collective stretching motion of piezoelectric ZnO NWs, induced by the shape-change of the matrix polymer, to convert the thermal energy into direct current with output power densities of ∼20 nW/cm(2) at a heating temperature of ∼65 °C.

Effect of surface chemistry on the stability of gold nanostructures.

Understanding the role of surface chemistry in the stability of nanostructured noble-metal materials is important for many technological applications but experimentally difficult to access and thus little understood. To develop a fundamental understanding of the effect of surface chemistry on both the formation and stabilization of self-organized gold nanostructures, we performed a series of controlled-environment annealing experiments on nanoporous gold (np-Au) and ion-bombarded Au(111) single-crystal surfaces. The annealing experiments on np-Au in ambient ozone were carried out to study the effect of adsorbed oxygen under dynamic conditions, whereas the ion-bombarded Au single-crystal surfaces were used as a model system to obtain atomic-scale information.

Electrocapillary maximum and potential of zero charge of carbon aerogel.

We present an electrochemical study of carbon aerogel (CA) in aqueous sodium fluoride solutions, focusing on the comparison of two quantities that are related to the potential of zero charge (pzc): the capacitance minimum and the 'electrocapillary maximum' of the surface forces. Capacitance minima are well resolved in our samples. Their potential emerges reproducibly as around 90 mV (vs.

Three-dimensional nanofabrication with elastomeric phase masks.

This Feature Article reviews recent work on an optical technique for fabricating, in a single exposure step, three-dimensional (3D) nanostructures with diverse structural layouts. The approach, which we refer to as proximity field nanopatterning, uses conformable, elastomeric phase masks to pattern thick layers of transparent, photosensitive materials in a conformal contact mode geometry. Aspects of the optics, the materials, and the physical chemistry associated with this method are outlined.

Ductile crystalline-amorphous nanolaminates.

It is known that the room-temperature plastic deformation of bulk metallic glasses is compromised by strain softening and shear localization, resulting in near-zero tensile ductility. The incorporation of metallic glasses into engineering materials, therefore, is often accompanied by complete brittleness or an apparent loss of useful tensile ductility. Here we report the observation of an exceptional tensile ductility in crystalline copper/copper-zirconium glass nanolaminates.

Structure of low-density nanoporous dielectrics revealed by low-vacuum electron microscopy and small-angle X-ray scattering.

Aerogels (AGs) are ultralow-density nanoporous solids that have numerous potential applications. However, as most AGs are strong insulators with poor mechanical properties, direct studies of the complex nanoporous structure of AGs by methods such as atomic force and conventional scanning electron microscopy (SEM) have not proven feasible. Here, we use low-vacuum SEM to image directly the ligament and pore size and shape distributions of representative AGs over a wide range of length scales (approximately 100-105 nm).

Size effects on the mechanical behavior of nanoporous Au.

Recent nanomechanical tests on submicron metal columns and wires have revealed a dramatic increase in yield strength with decreasing sample size. Here, we demonstrate that nanoporous metal foams can be envisioned as a three-dimensional network of ultrahigh-strength nanowires, thus bringing together two seemingly conflicting properties: high strength and high porosity. Specifically, we characterized the size-dependent mechanical properties of nanoporous gold using a combination of nanoindentation, column microcompression, and molecular dynamics simulations.