Julia R. Greer's research while affiliated with California Institute of Technology and other places

Publications (46)

Article
The ubiquitous nature of atmospheric moisture makes it a significant water resource available at any geographical location. Atmospheric water harvesting (AWH) technology, which extracts moisture from ambient air to generate clean water, is a promising strategy to realize decentralized water production. The high water uptake exhibited by salt‐based...
Article
Rationally designed architected materials have attained previously untapped territories in materials property space. The properties and behaviours of architected materials need not be stagnant after fabrication; they can be encoded with a temporal degree of freedom such that they evolve over time. In this Review, we describe the variety of material...
Article
Full-text available
Shape memory polymers (SMPs) respond to heat by generating programmable movement in devices that require substantial deformation and operate at transient temperatures, including stents and embolization coils. To enable their use in small‐scale applications like retinal vasculature stenting, shape transformations must occur in SMPs with complex 3D g...
Article
Full-text available
Thin metal films deposited on patterned or rough substrates play an increasing role in microelectronics, sensing, catalysis, and other areas of nanotechnology. However, the thermal stability and solid state dewetting of thin metal films with complex three-dimensional architecture is still poorly understood. In this work we employed a model system o...
Article
Thin metal films deposited on patterned or rough substrates play an increasing role in microelectronics, sensing, catalysis, and other areas of nanotechnology. However, the thermal stability and solid state dewetting of thin metal films with complex three-dimensional architecture is still poorly understood. In this work we employed a model system o...
Article
Full-text available
3D architectured materials with features at the micro-/nano-scale can attain extreme mechanical properties, overcoming the tradeoff between lightness, strength and damage tolerance. The combination of the material size effect and the geometry (architecture) gives rise to peculiar mechanical behaviors, often found in biological systems. Despite stif...
Article
This disclosure is directed to structured compositions, including DNA-functionalized scaffolds, for drug capture, and methods and devices for sequestering chemotherapeutics from physiological fluids using the functionalized scaffolds.
Article
The integration of materials and architectural features at multiple length scales into structural mechanics has shifted the paradigm of structural design toward optimally engineered structures, which resulted in, for example, the Eiffel Tower. This structural revolution paved the way for the development of computational design approaches used in mo...
Conference Paper
In recent years, 3D printing of ceramics has become a significant area of interest as it has the potential to remove the geometrical limitations assocd. with the current state of the art of ceramic processing. In particular, processes involving photolithog. are esp. promising due to the high resoln. and small feature sizes achievable.These photolit...
Conference Paper
Since the discovery of chemotherapy in the beginning of the 20th century, 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 cel...
Article
Creating materials with a suite of designed properties is one of key challenges in our society. Solving this grand challenge will open pathways to create entirely new classes of materials, whose properties are determined a priori and are attained through a multiscale physically informed approach. These new material classes will offer breakthrough a...
Conference Paper
Since the discovery of nitrogen mustard as an effective anti-cancer agent in the 1940s, and consequently, the concept 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. Howeve...
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Full-text available
Light-weight aluminum (Al) alloys have widespread applications. However, most Al alloys have inherently low mechanical strength. Nanotwins can induce high strength and ductility in metallic materials. Yet, introducing high-density growth twins into Al remains difficult due to its ultrahigh stacking-fault energy. In this study, it is shown that inco...
Article
Low dielectric constant (low-k) materials have gained increasing popularity because of their critical role in developing faster, smaller, and higher performance devices. Their practical use has been limited by the strong coupling between mechanical, thermal, and electrical properties of materials and their dielectric constant; low-k is usually atta...
Conference Paper
The systemic, off-target toxicity of chemotherapy is a well-known problem in oncol. In an effort to overcome this challenge, many approaches have been developed to deliver chemotherapy directly and exclusively the tumor. One of these approaches is transarterial chemoembolization (TACE), a procedure in which chemotherapy is introduced via catheter d...
Conference Paper
Two photon lithog. has recently emerged as one of the most powerful tools for fabricating structures with virtually any geometry. This architectural versatility renders these 3D polymer structures useful for many technol. applications, including drug delivery and tissue engineering. While significant headway has been made in understanding the physi...
Conference Paper
Intra-arterial chemotherapy delivery (IAC) for treating cancer can lead to significant cardiac toxicity due to the drainage of excess drug to the systemic circulation. A catheter-based Chemofilter device temporarily inserted into the veins downstream of the tumor can remove chemotherapy drugs out of the blood stream right after these drugs have had...
Article
Fabrication of functionalized 3D architected materials is achieved by a facile method using functionalized acrylates synthesized via thiol-Michael addition, which are then polymerized using two-photon lithography. A wide variety of functional groups can be attached, from Boc-protected amines to fluoroalkanes. Modification of surface wetting propert...
Article
Creating implants 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 Limitations in traditional fabrication techniques and difficulties in characterizing cell-scaffold interactions have limited our understanding of how fa...
Article
Full-text available
Most next-generation Li ion battery chemistries require a functioning lithium metal (Li) anode. However, its application in secondary batteries has been inhibited because of uncontrollable dendrite growth during cycling. Mechanical suppression of dendrite growth through solid polymer electrolytes (SPEs) or through robust separators has shown the mo...
Article
In human bone, an amorphous mineral serves as a precursor to the formation of a highly substituted nanocrystalline apatite. However, the precise role of this amorphous mineral remains unknown. Here, we show by using transmission electron microscopy that 100-300 nm amorphous calcium phosphate regions are present in the disordered phase of trabecular...
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Full-text available
Cellular solids are instrumental in creating lightweight, strong, and damage-tolerant engineering materials. By extending feature size down to the nanoscale, we simultaneously exploit the architecture and material size effects to substantially enhance structural integrity of architected meta-materials. We discovered that hollow-tube alumina nanolat...
Article
Fibrotic encapsulation limits the efficacy and lifetime of implantable biomedical devices. Microtopography has shown promise in the regulation of myofibroblast differentiation, a key driver of fibrotic encapsulation. However, existing studies have not systematically isolated the requisite geometric parameters for suppression of myofibroblast differ...
Article
Ordered cellular solids have higher compressive yield strength and stiffness compared to stochastic foams. The mechanical properties of cellular solids depend on their relative density and follow structural scaling laws. These scaling laws assume the mechanical properties of the constituent materials, like modulus and yield strength, to be constant...
Conference Paper
Despite common characterizations of modern wind energy technology as mature, there remains a persistent disconnect between the vast global wind energy resource—which is 20 times greater than total global power consumption—and the limited penetration of existing wind energy technologies as a means for electricity generation worldwide. We describe an...
Article
The catalytic properties of materials depend strongly on their microscopic structure, with the atomic-level chemistry and structure directly influencing the activity and durability of the catalyst. However, these microscopic properties can be difficult to understand and control. Furthermore, most efficient catalysts contain substantial amounts of p...
Article
The yield strengths of nanomaterials are highly sensitive to their internal and surface structures. However, it is difficult to identify a priori which structural feature will govern plastic yield. We employ very large scale molecular dynamics simulations to explicitly identify the relevant yield mechanisms for Cu nanowires with four distinct, expe...
Article
The emergence of a substantial body of literature focusing on uniaxial compression experiments of micro- and nano-sized single-crystalline cylindrical papers has unambiguously demonstrated that, at these scales, the sample dimensions dramatically affect crystalline strength (for reviews, see [1-3]). In most of these experimental studies, cylindrica...
Article
Full-text available
We report the synthesis, mechanical properties and deformation mechanisms of polycrystalline, platinum nanocylinders of grain size d=12nm. The number of grains across the diameter, D/d, was varied from 5 to 80 and 1.5 to 5 in the experiments and molecular dynamics simulations, respectively. An abrupt weakening is observed at a small D/d, while the...
Article
Arrays of vertically aligned Si microwires embedded in polydimethylsiloxane (PDMS) have emerged as a promising candidate for use in solar energy conversion devices. Such structures are lightweight and concurrently demonstrate competitive efficiency and mechanical flexibility. To ensure reliable functioning under bending and flexing, strong interfac...
Article
Our current understanding of size-dependent strength in nano- and microscale crystals is centered around the idea that the overall strength is determined by the stress required to propagate dislocation sources. The nature and type of these dislocation sources is the subject of extensive debate, however, one commonality amongst these theories is tha...
Article
A material strength depends on its microstructure, which in turn, is controlled by an engineering process. Strengthening mechanisms like work hardening, precipitate, and grain boundary strengthening can alter the strength of a material in a predictive, quantitative manner and are readily linked to the deformation mechanism. This quantification stro...
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Full-text available
We report that single-layer graphene on a SiO_2/Si substrate withstands ion bombardment up to ~7 times longer than expected when exposed to focused Ga^+ ion beam. The exposure is performed in a dual beam scanning electron microscope/focused ion beam system at 30 kV accelerating voltage and 41 pA current. Ga^+ ion flux is determined by sputtering a...
Article
Full-text available
We provide an overview of our work where carbon-based nanostructures have been applied to two-dimensional (2D) planar and three-dimensional (3D) vertically-oriented nano-electro-mechanical (NEM) switches. In the first configuration, laterally oriented single-walled nanotubes (SWNTs) synthesized using thermal chemical vapor deposition (CVD) were imp...
Conference Paper
We provide an overview of our work where carbon-based nanostructures have been applied to twodimensional (2D) planar and three-dimensional (3D) vertically-oriented nano-electro-mechanical (NEM) switches. In the first configuration, laterally oriented single-walled nanotubes (SWNTs) synthesized using thermal chemical vapor deposition (CVD) were impl...
Article
We provide an overview of our work where carbon-based nanostructures have been applied to twodimensional (2D) planar and three-dimensional (3D) vertically-oriented nano-electro-mechanical (NEM) switches. In the first configuration, laterally oriented single-walled nanotubes (SWNTs) synthesized using thermal chemical vapor deposition (CVD) were impl...
Conference Paper
We have developed manufacturable approaches to form single, vertically aligned carbon nanotubes, where the tubes are centered precisely, and placed within a few hundred nm of 1-1.5 μm deep trenches. These wafer-scale approaches were enabled by chemically amplified resists and inductively coupled Cryo-etchers to form the 3D nanoscale architectures....
Article
We have developed manufacturable approaches to form single, vertically aligned carbon nanotubes, where the tubes are centered precisely, and placed within a few hundred nm of 1-1.5 μm deep trenches. These wafer-scale approaches were enabled by chemically amplified resists and inductively coupled Cryo-etchers to form the 3D nanoscale architectures....
Article
The strain rate effects on the mechanical properties of carbon nanotube forests were studied by anchoring dense vertically aligned foam-like forests of carbon nanotubes on a thin, flexible polymer layer to provide structural stability. The nanotubes are found to be vertically aligned throughout the entire thickness of the sample and possess a compl...
Article
We have demonstrated electrostatic switching in vertically oriented nanotubes or nanofibers where a nanoprobe was used as the actuating electrode inside an SEM. When the nanoprobe was manipulated to be in close proximity to a single tube, switching voltages between 10 V-40 V were observed, depending on the geometrical parameters used. The turn-on t...
Article
Uniaxial compression of micro- and nanopillars is frequently used to elicit plastic size effects in single crystals. Uniaxial tensile experiments on nanoscale materials have the potential to enhance the understanding of the experimentally widely observed strength increase. Furthermore, these experiments allow for investigations into the in-strength...
Article
Full-text available
While this article provides insight into differences in mechanics between Ga+-irradiated and “pure” surfaces of molybdenum, there are several statements that are either inaccurate or poorly stated. It is clear that when a surface is directly irradiated by orthogonal ion beam (0.07–0.21 mW), a focused ion beam (FIB) damage layer will likely form and...

Citations

... Thermotropic shape memory polymers (SMPs) are a kind of active materials that can sense external temperature changes and produce an autonomous deformation response, which are characterized by large deformability, variable stiffness and shape memory effects (Biswas et al., 2021;Elliott et al., 2020;King et al., 2021;Zeng et al., 2021). To facilitate the application of SMPs in practical engineering, systematic theoretical frameworks have been established to predict the thermomechanical behavior and shape memory effects of SMPs (Yu et al., 2012(Yu et al., , 2014aFang et al., 2018;Gu et al., 2017Gu et al., , 2020Liu et al., 2006;Nguyen et al., 2008;Qi et al., 2008;Zhao et al., 2020). ...
... Through the emergence of additive and other advanced manufacturing technologies, there has been an increasing interest in the design and fabrication of architected and microstructured materials in recent years [1]. In particular, open-cell foams and metamaterials with truss-or beam-like struts have been extensively investigated, covering aspects such as stretchability and compressibility [2,3], resilience, damage-tolerance 5 and failure [4][5][6], uncertainties, instabilities and rate-dependence [7][8][9][10][11][12], or energy absorption and dissipation [13,14]. ...
... The procedure can be limited to the electron-beam and ionic processing of the sample according to the standard protocol using ESEM (on the living samples [108,109]) or LVEM [110,111] (which is also suitable for the samples that maintain biochemical functions during exposure) or FIB-SEM [112][113][114][115]. Polymer melting can be carried out either in a microdischarge (including corona discharge or a stray / traveling over the dielectric surface discharge) directly in the SEM / ESEM chamber [116][117][118] or, if microdischarge technique is not available, on a heated microscope table [119]. To overcome the limitations of scaling, it is necessary during extrusion to move from the nanolevel, considered as a record one, aimed at registration of transport of the the single nucleic acid molecules through nanopores [120][121][122][123][124][125][126][127], which is used in DNA research, especially aimed at developing methods of nanopore sequencing [128][129][130][131][132] (including epigenetically modified genetic material, in particular, methylated DNA [133][134][135][136]), to the level of standard nozzles -extruders, 3D printers, etc., adapted for some operations with DNA [137][138][139][140],including thermal cycling. In the case of XNA, the last part of the comment is not obligatory. ...
... The procedure can be limited to the electron-beam and ionic processing of the sample according to the standard protocol using ESEM (on the living samples [108,109]) or LVEM [110,111] (which is also suitable for the samples that maintain biochemical functions during exposure) or FIB-SEM [112][113][114][115]. Polymer melting can be carried out either in a microdischarge (including corona discharge or a stray / traveling over the dielectric surface discharge) directly in the SEM / ESEM chamber [116][117][118] or, if microdischarge technique is not available, on a heated microscope table [119]. To overcome the limitations of scaling, it is necessary during extrusion to move from the nanolevel, considered as a record one, aimed at registration of transport of the the single nucleic acid molecules through nanopores [120][121][122][123][124][125][126][127], which is used in DNA research, especially aimed at developing methods of nanopore sequencing [128][129][130][131][132] (including epigenetically modified genetic material, in particular, methylated DNA [133][134][135][136]), to the level of standard nozzles -extruders, 3D printers, etc., adapted for some operations with DNA [137][138][139][140],including thermal cycling. In the case of XNA, the last part of the comment is not obligatory. ...
... With resolution as high as B400 nm, TPL can endow some entirely new functionalities to metal oxides beyond those achievable with planar geometries, such as ultralight weight and damage-tolerant mechanical and optical properties. 7 Nevertheless, all material feedstocks of TPL are mainly composed of targeted metal ions and acrylic monomers. Therefore, a high-temperature calcination process is required to achieve organic-to-inorganic transformation, which undesirably results in incompatibility with other electronic components on the same substrates. ...
... X. H. Zhang et al. [111] obtained an Al-Fe alloy with high-density nanotwins and 9R phase using DC magnetic sputtering. The mechanical properties of the alloy were examined via unidirectional compression and nanoindentation. ...
... Recent studies demonstrate that mechanical metamaterials with optimized microstructure architectures can yield unconventional thermal expansion behaviors, such as near-zero thermal expansion, [1][2][3][4][5] negative thermal expansion, [6][7][8][9][10][11] and thermally induced shear. [12] These mechanical metamaterials are of increasing interest, because of their potential for use in applications such as high-precision space optical systems, [13,14] adaptive connecting components in satellites, [15,16] flexible MEMS that require excellent thermal stability, [17][18][19][20][21][22][23][24] battery electrodes with Advanced mechanical metamaterials with unusual thermal expansion properties represent an area of growing interest, due to their promising potential for use in a broad range of areas. In spite of previous work on metamaterials with large or ultralow coefficient of thermal expansion (CTE), achieving a broad range of CTE values with access to large thermally induced dimensional changes in structures with high filling ratios remains a key challenge. ...
... Manufacturability of the designed cellular architectures are demonstrated here using digital light processing (DLP) 3D printing, in which a sample is printed layer by layer by exposing a photopolymer resin to UV light. [95] Figure 8a-e showcases some of the 3D printed parts using this method. While some imperfections, such as rough surface finish, small distortions, holes/bubbles, and partial strut connectivity are present in 3D printed samples, exploring possible methods to reduce these imperfections are beyond the scope of this article. ...
... In addition, the thickness of the constituent beams are taken to be t = 20 μm for both classic and MCST dispersion curves. Further, the relative density of the lattice material, defined as the ratio of the volume of the structural material to the volume of the unit cell [63] , is assumed constant equaling to 50. Each band of the micro-lattice is seen to form at higher frequencies in comparison to its counterpart in the classic lattice structure. ...