Novel phase diagram behavior and materials design in heterostructural semiconductor alloys
AuthorHolder, Aaron M.
Ndione, Paul F.
Deml, Ann M.
Matthews, Bethany E.
Schelhas, Laura T.
Toney, Michael F.
Gordon, Roy G.
Perkins, John D.
Ginley, David S.
Gorman, Brian P.
Computational materials science
Permanent link to this recordhttp://hdl.handle.net/20.500.12613/8749
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AbstractStructure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.
Citation to related workAmerican Association for the Advancement of Science
Has partScience Advances, Vol. 3, No. 6
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METAL NANOMATERIALS: SYNTHESIS, DESIGN, AND APPLICATIONSSun, Yugang; Wunder, Stephanie L.; Quan, Zewei; Borguet, Eric; Zhang, Yuanzhu (Temple University. Libraries, 2022)As an important part of the periodic table, metal elements have attracted widespread attention due to their special physical and chemical properties, as well as effective functionalities. Many metals at the nanoscale level exhibit a wide array of applications, ranging from catalysis to photonics, electronics, energy conversion/storage, and medicine. To obtain a more effective functionality in application, it is indispensable to synthesize uniform metal nanoparticles with well-defined size, morphology, composition, and crystal structures. In this dissertation, we will demonstrate high-boiling point solvent method for synthesizing metal nanocrystals, ranging from single metal nanocrystals (e.g., iridium (Ir), ruthenium (Ru), germanium (Ge), bismuth (Bi)) to binary metal nanocrystals (e.g., Sn-Ge), and ternary intermetallic compounds (e.g., Pt1-xPdxBi). By varying different halogen ions, we can get different morphologies of metal nanocrystals. We will further study the catalytic effect of Pd metal nanocrystals supported on silicon spheres and realize the hydrodeoxygenation reaction of vanillin under mild conditions.First, we used bismuth as an example to study the shape-controlled synthesis of metal nanocrystals by adjusting the injection temperature and the added halide ions (e.g., Cl-, Br-). Our findings indicated that due to the different electronegativities, halide ions are selectively adsorbed on specific crystal planes during the growth of Bi NCs, leading to different morphologies. Then we proposed a tungsten hexacarbonyl (W(CO)6)-assisted reduction strategy for obtaining uniform metal nanoparticles (e.g., Ir, Ru, Ge, Bi) of different metal salts. This strategy was extended to the synthesis of uniform binary metal (e.g., Sn-Ge) nanoparticles, which we can get tunable bandgap (0.51 eV to 0.72 eV) based on the controlled reaction of Ge2+ precursor solution with uniform tin (Sn) nanocrystals (NCs) as the template. Next, we realized the synthesis of intermetallic Pt1-xPdxBi nanoplates with controllable compositions, including Pt0.5Pb0.5Bi, Pt0.25Pd0.75Bi, and Pt0.75Pd0.25Bi via the sequential complexation-reduction-sorting method. Furthermore, we used palladium (Pd) metal nanoparticles (NPs) as a photocatalyst to trigger the hydrodeoxygenation reaction of vanillin. We demonstrated a model to disperse free-standing Pd NP on dielectric silica nanospheres (SiOx NSs). The spherical shape of SiOx can cause scattering resonance, thereby enhancing the local electric field on or near the surface to enhance light absorption of Pd NPs, further realizing a more effective catalyze on chemical reactions. We found that the adsorption of H2 on Pd is too strong to support the reaction effectively, but light absorption can reduce the "poisoning effect" by weakening the adsorption of hydrogen on Pd surface. Overall, we use innovative strategies to effectively synthesize a variety of high-quality metal nanomaterials. Our work shows that the Pd-NP/SiOx-NS composite nanostructure using dielectric SiOx as an optical nanoantenna is a promising photocatalyst that can drive photonic chemical conversion with high efficiency.
Magnesium diboride coated bulk niobium: a new approach to higher acceleration gradientTan, Teng; Wolak, Matthäus A.; Xi, X. X.; Tajima, T.; Civale, L. (2016-10-24)Bulk niobium Superconducting Radio-Frequency cavities are a leading accelerator technology. Their performance is limited by the cavity loss and maximum acceleration gradient, which are negatively affected by vortex penetration into the superconductor when the peak magnetic field at the cavity wall surface exceeds the vortex penetration field (Hvp). It has been proposed that coating the inner wall of an SRF cavity with superconducting thin films increases Hvp. In this work, we utilized Nb ellipsoid to simulate an inverse SRF cavity and investigate the effect of coating it with magnesium diboride layer on the vortex penetration field. A significant enhancement of Hvp was observed. At 2.8K, Hvp increased from 2100Oe for an uncoated Nb ellipsoid to 2700Oe for a Nb ellipsoid coated with ~200nm thick MgB2 thin film. This finding creates a new route towards achieving higher acceleration gradient in SRF cavity accelerator beyond the theoretical limit of bulk Nb.
Smart Surgical Needle Actuated by Shape Memory Alloys for Percutaneous ProceduresHutapea, Parsaoran; Yin, Jie; Sadeghipour, Keya; Elahinia, Mohammad H.; Ochia, Ruth Shada (Temple University. Libraries, 2016)Background: Majority of cancer interventions today are performed percutaneously using needle-based procedures, i.e. through the skin and soft tissue. Needle insertion is known as one of the recent needle-based techniques that is used in several diagnostic and therapeutic medical procedures such as brachytherapy, thermal ablations and breast biopsy. The difficulty in most of these procedures is to attain a precise navigation through tissue reaching target locations. Insufficient accuracy using conventional surgical needles motivated researchers to provide actuation forces to the needle’s body for compensating the possible errors of surgeons/physicians. 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Rigorous experiments with SMA wires were performed to determine the material properties as well as to show the capability of the code to predict a stabilized SMA transformation behavior with sufficient accuracy. The isothermal stress-strain curves of SMAs were simulated and defined as a material model for the Finite Element Analysis of the active needle. In the second part of this work, a three-dimensional finite element (FE) model of the active steerable needle was developed to demonstrate the feasibility of using SMA wires as actuators to bend the surgical needle. In the FE model, birth and death method of defining boundary conditions, available in ANSYS, was used to achieve the pre-strain condition on SMA wire prior to actuation. This numerical model was validated with needle deflection experiments with developed prototypes of the active needle. The third part of this work describes the design optimization of the active using genetic algorithm aiming for its maximum flexibility. Design parameters influencing the steerability include the needle’s diameter, wire diameter, pre-strain, and its offset from the needle. A simplified model was developed to decrease the computation time in iterative analyses of the optimization algorithm. In the fourth part of this work a design of an active needling system was proposed where actuation forces of SMAs as well as shape memory polymers (SMPs) were incorporated. SMP elements provide two major additional advantages to the design: (i) recovery of the SMP’s plastic deformation by heating the element above its glass transition temperature, and (ii) achieving a higher needle deflection by having a softer stage of SMP at higher temperatures with less amount of actuation force. Finally, in the fifth and last part of this study, an Arbitrary-Lagrangian-Eulerian formulation in LS-DYNA software was used to model the solid-fluid interactions between the needle and tissue. A 150mm long needle was considered to bend within the tissue due to the interacting forces on its asymmetric bevel tip. Some additional assumptions were made to maintain a reasonable computational time, with no need of parallel processing, while having practical accuracies. Three experimental tests of needle steering in a soft phantom were performed to validate the simulation. Results: The finite element model of the active needle was first validated experimentally with developed prototypes. Several design parameters affecting the needle’s deflection such as the needle’s Young’s modulus, the SMA’s pre-strain and its offset from the neutral axis of the cannula were studied using the FE model. Then by the integration of the SMA characteristics with the automated optimization schemes an improved design of the active needle was obtained. Real-time experiments with different prototypes showed that the quickest response and the maximum deflection were achieved by the needle with two sections of actuation compared to a single section of actuation. Also the feasibility of providing actuation forces using both SMAs and SMPs for the surgical needle was demonstrated in this study. The needle insertion simulation was validated while observing less than 10% deviation between the estimated amount of needle deflection by the simulation and by the experiments. Using this model the effect of needle diameter and its bevel tip angle on the final shape of the needle was investigated. Conclusion: The numerical and experimental studies of this work showed that a highly maneuverable active needle can be made using the actuation of multiple SMA wires in series. To maneuver around the anatomical obstacles of the human body and reach the target location, thin sharp needles are recommended as they would create a smaller radius of curvature. The insertion model presented in this work is intended to be used as a base structure for path planning and training purposes for future studies.