Julia R. Greer

Julia R. Greer
California Institute of Technology | CIT · Department of Applied Physics & Materials Science

About

195
Publications
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13,615
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Publications

Publications (195)
Preprint
Additive manufacturing (AM) of metals can enable rapid development of advanced parts with complex geometries, opening potential applications in the aerospace, automotive, and biomedical fields. Most existing metal AM techniques rely on costly thermally initiated melting or sintering processes, limiting the fabrication of materials with high thermal...
Article
Full-text available
Architected materials with nanoscale features have enabled extreme combinations of properties by exploiting the ultralightweight structural design space together with size-induced mechanical enhancement at small scales. Apart from linear waves in metamaterials, this principle has been restricted to quasi-static properties or to low-speed phenomena,...
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Solar steam water purification and fog collection are two independent processes that could enable abundant fresh water generation. We developed a hydrogel membrane that contains hierarchical three-dimensional microstructures with high surface area that combines both functions and serves as an all-day fresh water harvester. At night, the hydrogel me...
Article
Lithium–sulfur batteries are poised to outcompete lithium-ion batteries in key sectors such as transportation and grid storage due to the low cost and high theoretical energy density of sulfur as a cathode material. Widespread implementation of this technology is hindered by significant degradation during cycling, including mechanical failure via c...
Article
In article number 2002637, Kai Narita and co‐workers report a simple method using digital light processing 3D printing and pyrolysis to fabricate 3D architected carbon anodes for energy storage, with independently controlled micrometer‐to‐centimeter form factors and mechanical robustness. The 3D architected carbon anodes provide a potential path to...
Article
In article number 2000791, Daryl W. Yee and co‐workers report a facile approach for the additive manufacturing of architected multicomponent metal oxides via calcination of metal‐ion containing 3D printed hydrogels. Architected lithium cobalt oxide lattices were fabricated with this technique and used as 3D lithium‐ion battery cathodes. As highligh...
Article
Natural hard composites like human bone possess a combination of strength and toughness that exceeds that of their constituents and of many engineered composites. This augmentation is attributed to their complex hierarchical structure, spanning multiple length scales; in bone, characteristic dimensions range from nanoscale fibrils to microscale lam...
Article
Vat photopolymerization (VP) is one of the most remarkable additive manufacturing techniques today, and has been used for a variety of applications, from materials research to product manufacturing. The main challenge with VP is the limited choice of compatible materials, which motivates significant interest in VP material development. We provide a...
Article
3D multicomponent metal oxides with complex architectures can enable previously impossible energy storage devices, particularly lithium‐ion battery (LIB) electrodes with fully controllable form factors. Existing additive manufacturing approaches for fabricating 3D multicomponent metal oxides rely on particle‐based or organic–inorganic binders, whic...
Article
The ability to design a particular geometry of porous electrodes at multiple length scales in a lithium‐ion battery can significantly and positively influence battery performance because it enables control over distribution of current and potential and can enhance ion and electron transport. 3D architecturally designed carbon electrodes are develop...
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Hierarchy in natural and synthetic materials has been shown to grant these architected materials properties unattainable independently by their constituent materials. While exceptional mechanical properties such as extreme resilience and high deformability have been realized in many human‐made three‐dimensional (3D) architected materials using beam...
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In article number 2001271, Carlos M. Portela and co‐workers present an architected material design in which fibers are interwoven to construct effective beams. Mechanical characterization of additively manufactured samples and numerical analysis reveal the superior ability of woven architectures to achieve high tensile and compressive strains while...
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Sub-wavelength periodic arrays exhibit narrow near-unity reflection bands that arise from guided mode resonances. These resonances have extremely high quality factor (i.e., narrow band features) and are ideal for filtering applications. A high quality factor requires many periods, causing large lateral footprints that limit an imaging system's spat...
Preprint
Natural hard composites like human bone possess a combination of strength and toughness that exceeds that of their constituents and of many engineered composites. This augmentation is attributed to their complex hierarchical structure, spanning multiple length scales; in bone, characteristic dimensions range from nanoscale fibrils to microscale lam...
Article
Development of high energy density solid-state batteries with Li metal anodes has been limited by uncontrollable growth of Li dendrites in liquid and solid electrolytes (SEs). This, in part, may be caused by a dearth of information about mechanical properties of Li, especially at the nano- and microlength scales and microstructures relevant to Li b...
Article
Additive manufacturing at small scales enables advances in micro- and nano-electromechanical systems, micro-optics, and medical devices. Materials that lend themselves to AM at the nano-scale, especially for optical applications, are limited. State-of-the-art AM processes for high refractive index materials typically suffer from high porosity, poor...
Article
Low-density materials with tailorable properties have attracted attention for decades, yet stiff materials that can resiliently tolerate extreme forces and deformation while being manufactured at large scales have remained a rare find. Designs inspired by nature, such as hierarchical composites and atomic lattice-mimicking architectures, have achie...
Conference Paper
Development for refreshable braille devices has recently shifted to electroactive polymers (EAP). This paradigm benefits from greater precision, smaller size, and lower cost assocd. with modern electronics, opening the door for higher resoln. and less expensive devices. Displays with resoln. finer than required to display braille characters will en...
Conference Paper
Since the discovery of chemotherapy, researchers around the world have been actively developing new and more effective chemotherapeutic agents to better treat cancer. Traditionally, chemotherapeutic agents work by interfering with cell division. However, by virtue of their mechanism of action, healthy normal cells can also be targeted and destroyed...
Conference Paper
Additive manufg. has been at the forefront of manufg. in the past decade, due to its ability to overcome geometric limitations inherent with traditional manufg. processes. Photolithog. 3D printing processes, in particular, have been of significant interest due to the resoln. of features that can be achieved using these techniques. However, a large...
Conference Paper
The development of 3D printing or additive manufg. has grown rapidly in the past decade, which calls for more sustainable photoresins to accommodate the increasing demand of the future 3D printed products. In particular, stereolithog. (SLA) 3D printing have been demonstrated as an efficient method to produce high-accuracy and isotropic parts using...
Conference Paper
Additive manufg. is one of the most powerful manufg. tools available today, due to its potential in fabricating a wide variety of materials at resolns. ranging from nanometers to meters. In particular, significant advances have been made in polymeric 3D printing, with recent work showing the fabrication of polymers with unique properties, such as s...
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Full-text available
High-entropy alloys (HEAs) represent an important class of structural materials because of their high strength, ductility, and thermal stability. Understanding the mechanical response of isolated phases of a FCC/BCC dual-phase HEA is integral to understanding the mechanical properties of these alloys in the bulk. We investigate the compressive resp...
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Next-generation lithium-battery cathodes often involve the growth of lithium-rich phases, which enable specific capacities that are 2−3 times higher than insertion cathode materials, such as lithium cobalt oxide. Here, we investigated battery chemistry previously deemed irreversible in which lithium oxide, a lithium-rich phase, grows through the re...
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Full-text available
The coloration of some butterflies, Pachyrhynchus weevils, and many chameleons are notable examples of natural organisms employing photonic crystals to produce colorful patterns. Despite advances in nanotechnology, we still lack the ability to print arbitrary colors and shapes in all three dimensions at this microscopic length scale. Here, we intro...
Article
The extraordinary ability of shape-memory alloys to recover after large imposed deformation motivates efforts to transpose these properties onto ceramics, which would enable practical shape-memory properties at high temperatures and in harsh environments. The theory of mechanical compatibility was utilized to predict promising ceramic candidates in...
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Architected materials can actively respond to external stimuli—such as mechanical forces, hydration and magnetic fields—by changing their geometries and thereby achieve novel functionalities. Such transformations are usually binary and volatile because they toggle between ‘on’ and ‘off’ states and require persistent external stimuli. Here we develo...
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Full-text available
Additive manufacturing (AM) of complex three‐dimensional (3D) metal oxides at the micro‐ and nanoscales has attracted considerable attention in recent years. State‐of‐the‐art techniques that use slurry‐based or organic–inorganic photoresins are often hampered by challenges in resin preparation and synthesis, and/or by the limited resolution of patt...
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Full-text available
The creation of materials with a combination of high strength, substantial deformability and ductility, large elastic limit and low density represents a long-standing challenge, because these properties are, in general, mutually exclusive. Using a combination of two-photon lithography and high-temperature pyrolysis, we have created micro-sized pyro...
Article
The dielectric reliability of low k materials during mechanical deformation attracts tremendous attention owing to the increasing demand for thin electronics to meet the ever-shrinking form factor of consumer products. However, the strong coupling between dielectric/electric and mechanical properties limits the use of low-k dielectrics in industria...
Article
The rings, spots and stripes found on some butterflies, Pachyrhynchus weevils, and many chameleons are notable examples of natural organisms employing photonic crystals to produce colorful patterns. Despite advances in nanotechnology, we still lack the ability to print arbitrary colors and shapes in all three dimensions at this microscopic length s...
Preprint
The rings, spots and stripes found on some butterflies, Pachyrhynchus weevils, and many chameleons are notable examples of natural organisms employing photonic crystals to produce colorful patterns. Despite advances in nanotechnology, we still lack the ability to print arbitrary colors and shapes in all three dimensions at this microscopic length s...
Article
Full-text available
It has been a long-standing challenge in modern material design to create low-density, lightweight materials that are simultaneously robust against defects and can withstand extreme thermomechanical environments, as these properties are often mutually exclusive: The lower the density, the weaker and more fragile the material. Here, we develop a pro...
Conference Paper
Fabrication of 3D dielectric photonic crystals in the visible and in the infrared range typically requires sub-micron structural features and high-refractive index materials. We developed a template-free additive manufacturing (AM) process based on direct laser writing (DLW) that can create complex 3D architectures out of titania (TiO_2) with ~100...
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Full-text available
3D nano‐ and micro‐architected materials are resilient under compression; their susceptibility to flaws and fracture remain unexplored. This work reports the fabrication and tensile‐to‐failure response of hollow alumina nanolattices arranged into 5 µm octet‐truss unit cells. Some specimens contained through‐thickness center notches oriented at diff...
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Designing mechanical metamaterials is overwhelming for most computational approaches because of the staggering number and complexity of flexible elements that constitute their architecture—particularly if these elements don’t repeat in periodic patterns or collectively occupy irregular bulk shapes. We introduce an approach, inspired by the freedom...
Article
We report the optical properties obtained through experiments, simulation, and theory, of ultra-thin (<0.1λ), amorphous Si nanopillar arrays embedded in a thin film of SiO2 designed for narrow band filtering for multi- and hyper-spectral imaging in the near-infrared. The fabricated nanopillar arrays are square-packed with subwavelength periodicity,...
Article
Creating materials that simultaneously possess ultralow thermal conductivity, high stiffness, and damage tolerance is challenging because thermal and mechanical properties are coupled in most fully dense and porous solids. Nanolattices can fill this void in the property space because of their hierarchical design and nanoscale features. We report th...
Article
Three-dimensional (3D), lattice-based micro- and nano-architected materials can possess desirable mechanical properties that are unattainable by homogeneous materials. Manufacturing these so-called structural metamaterials at the nano- and microscales typically results in non-slender architectures (e.g., struts with a high radius-to-length ratio r∕...
Article
The authors create life‐sized synthetic replicas of marine diatom coscinodiscus sp frustules out of cyclohexyl polyhedral oligomeric silsesquioxanes (POSS). The authors demonstrate that these synthetic structures have biosilica‐like amorphous atomic‐level microstructure and mechanical attributes similar to those of a natural diatom. In situ beam be...
Conference Paper
Interest in negative refraction has been motivated by the possibility of creating a “superlens” as proposed by Pendry (Phys. Rev. Lett. 85, 3966 (2000)). This theoretical work showed that a material capable of negative refraction amplifies evanescent waves and allows this material to act as a lens with a resolution not limited by working wavelength...
Article
Solar disinfection of drinking water (SODIS) is an approach for water purification widely used in households with limited access to fresh water. SODIS relies on microorganism inactivation triggered by sunlight energy in the UV spectrum and requires processing times of up to 48 h. Water treatment rate is drastically increased by using photocatalytic...
Article
The quest for radiation-damage tolerant materials has found good candidates in nanoporous metals, whose abundance of free surfaces provides ample sinks for radiation-induced defects, as well as in metallic glasses, whose characteristic failure via shear banding can be alleviated by irradiation. This type of catastrophic failure in metallic glass ca...
Conference Paper
Sub-wavelength arrays have garnered significant interest for many potential optoelectronics applications. We fabricated sub-wavelength silicon nanopillar arrays with a ratio of radius, r and a center-to-center distance, a, of r/a ≈ 0.2 that were fully embedded in SiO_2 for narrow stopband filters that are compact and straightforward to fabricate co...
Article
The transition from elastic to plastic deformation in crystalline metals shares history dependence and scale-invariant avalanche signature with other non-equilibrium systems under external loading: dilute colloidal suspensions, plastically-deformed amorphous solids, granular materials, and dislocation-based simulations of crystals. These other syst...
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Full-text available
Most existing methods for additive manufacturing (AM) of metals are inherently limited to ~20–50 μm resolution, which makes them untenable for generating complex 3D-printed metallic structures with smaller features. We developed a lithography-based process to create complex 3D nano-architected metals with ~100 nm resolution. We first synthesize hyb...
Article
Statement of significance: Creating prostheses that lead to optimal bone remodeling has been a challenge for more than two decades because of a lack of thorough knowledge of cell behavior in three-dimensional (3D) environments. Literature has shown that 2D substrate stiffness plays a significant role in determining cell behavior, however, limitati...
Article
Lightweight materials that are simultaneously strong and stiff are desirable for a range of applications from transportation to energy storage to defense. Micro- and nanolattices represent some of the lightest fabricated materials to date, but studies of their mechanical properties have produced inconsistent results that are not well captured by ex...
Article
We investigate the mechanical behavior of 3D periodically architected metallic glass nanolattices, constructed from hollow beams of sputtered Zr-Ni-Al metallic glass. Nanolattices composed of beams with different wall thicknesses are fabricated by varying the sputter deposition time, resulting in nanolattices with median wall thicknesses of ∼88 nm,...
Conference Paper
We use a plane wave expansion method to define parameters for the fabrication of 3-dimensional (3D) core-shell photonic crystals (PhCs) with lattice geometries that are capable of all-angle negative refraction (AANR) in the midinfrared centered around 8.0 μm. We discuss the dependence of the AANR frequency range on the volume fraction of solid with...
Article
The atomic-level structures of liquids and glasses are amorphous, lacking long-range order. We characterize the atomic structures by integrating radial distribution functions (RDF) from molecular dynamics (MD) simulations for several metallic liquids and glasses: Cu_(46)Zr_(54), Ni_(80)Al_(20), Ni_(33.3)Zr_(66.7), and Pd_(82)Si_(18). Resulting cumu...
Article
An investigation was conducted to examine the mechanical behavior and microstructure evolution during deformation of ultrafine-grained pure magnesium at low temperatures within the temperature range of 296–373 K. Discs were processed by high-pressure torsion until saturation in grain refinement. Dynamic hardness testing revealed a gradual increase...
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Full-text available
In small-scale metallic systems, collective dislocation activity has been correlated with size effects in strength and with a step-like plastic response under uniaxial compression and tension. Yielding and plastic flow in these samples is often accompanied by the emergence of multiple dislocation avalanches. Dislocations might be active pre-yield,...
Article
Shape memory alloys that produce and recover from large deformation driven by martensitic transformation are widely exploited in biomedical devices and micro-actuators. Generally their actuation work degrades significantly within first a few cycles, and is reduced at smaller dimensions. Further, alloys exhibiting unprecedented reversibility have re...
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Full-text available
We investigate the mechanical behavior and atomic-level structure of glassy Zr-Ni-Al nano-tensile specimens with widths between 75 and 215 nm. We focus our studies on two different energy states: (1) as-sputtered and (2) sputtered then annealed below the glass transition temperature (Tg). In-situ tensile experiments conducted inside a scanning elec...
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Full-text available
We give a bird's-eye view of the plastic deformation of crystals aimed at the statistical physics community, and a broad introduction into the statistical theories of forced rigid systems aimed at the plasticity community. Memory effects in magnets, spin glasses, charge density waves, and dilute colloidal suspensions are discussed in relation to th...
Article
Nanoarchitected Cu–Si core–shell lattices were fabricated via two-photon lithography and tested as mechanically robust Li-ion battery electrodes which accommodate ∼250% Si volume expansion during lithiation. The superior mechanical performance of the nanolattice electrodes is directly observed using an in situ scanning electron microscope, which al...