Publications by authors named "Mingyuan Ge"

40 Publications

Formation of three-dimensional bicontinuous structures via molten salt dealloying studied in real-time by in situ synchrotron X-ray nano-tomography.

Nat Commun 2021 Jun 9;12(1):3441. Epub 2021 Jun 9.

Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY, USA.

Three-dimensional bicontinuous porous materials formed by dealloying contribute significantly to various applications including catalysis, sensor development and energy storage. This work studies a method of molten salt dealloying via real-time in situ synchrotron three-dimensional X-ray nano-tomography. Quantification of morphological parameters determined that long-range diffusion is the rate-determining step for the dealloying process. The subsequent coarsening rate was primarily surface diffusion controlled, with Rayleigh instability leading to ligament pinch-off and creating isolated bubbles in ligaments, while bulk diffusion leads to a slight densification. Chemical environments characterized by X-ray absorption near edge structure spectroscopic imaging show that molten salt dealloying prevents surface oxidation of the metal. In this work, gaining a fundamental mechanistic understanding of the molten salt dealloying process in forming porous structures provides a nontoxic, tunable dealloying technique and has important implications for molten salt corrosion processes, which is one of the major challenges in molten salt reactors and concentrated solar power plants.
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http://dx.doi.org/10.1038/s41467-021-23598-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8190292PMC
June 2021

Hierarchical nickel valence gradient stabilizes high-nickel content layered cathode materials.

Nat Commun 2021 Apr 20;12(1):2350. Epub 2021 Apr 20.

Chemistry Division, Brookhaven National Laboratory, Upton, NY, USA.

High-nickel content cathode materials offer high energy density. However, the structural and surface instability may cause poor capacity retention and thermal stability of them. To circumvent this problem, nickel concentration-gradient materials have been developed to enhance high-nickel content cathode materials' thermal and cycling stability. Even though promising, the fundamental mechanism of the nickel concentration gradient's stabilization effect remains elusive because it is inseparable from nickel's valence gradient effect. To isolate nickel's valence gradient effect and understand its fundamental stabilization mechanism, we design and synthesize a LiNiMnCoO material that is compositionally uniform and has a hierarchical valence gradient. The nickel valence gradient material shows superior cycling and thermal stability than the conventional one. The result suggests creating an oxidation state gradient that hides the more capacitive but less stable Ni away from the secondary particle surfaces is a viable principle towards the optimization of high-nickel content cathode materials.
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http://dx.doi.org/10.1038/s41467-021-22635-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8058063PMC
April 2021

Kinetic Limitations in Single-Crystal High-Nickel Cathodes.

Angew Chem Int Ed Engl 2021 Aug 11;60(32):17350-17355. Epub 2021 Mar 11.

Energy and Photon Sciences Directorate, Brookhaven National Laboratory, Upton, NY, 11973, USA.

High-nickel cathodes attract immense interest for use in lithium-ion batteries to boost Li-storage capacity while reducing cost. For overcoming the intergranular-cracking issue in polycrystals, single-crystals are considered an appealing alternative, but aggravating concerns on compromising the ionic transport and kinetic properties. We report here a quantitative assessment of redox reaction in single-crystal LiNi Mn Co O using operando hard X-ray microscopy/spectroscopy, revealing a strong dependence of redox kinetics on the state of charge (SOC). Specifically, the redox is sluggish at low SOC but increases rapidly as SOC increases, both in bulk electrodes and individual particles. The observation is corroborated by transport measurements and finite-element simulation, indicating that the sluggish kinetics in single-crystals is governed by ionic transport at low SOC and may be alleviated through synergistic interaction with polycrystals integrated into a same electrode.
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http://dx.doi.org/10.1002/anie.202012773DOI Listing
August 2021

Insights into interfacial effect and local lithium-ion transport in polycrystalline cathodes of solid-state batteries.

Nat Commun 2020 Nov 11;11(1):5700. Epub 2020 Nov 11.

MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150001, China.

Interfacial issues commonly exist in solid-state batteries, and the microstructural complexity combines with the chemical heterogeneity to govern the local interfacial chemistry. The conventional wisdom suggests that "point-to-point" ion diffusion at the interface determines the ion transport kinetics. Here, we show that solid-solid ion transport kinetics are not only impacted by the physical interfacial contact but are also closely associated with the interior local environments within polycrystalline particles. In spite of the initial discrete interfacial contact, solid-state batteries may still display homogeneous lithium-ion transportation owing to the chemical potential force to achieve an ionic-electronic equilibrium. Nevertheless, once the interior local environment within secondary particle is disrupted upon cycling, it triggers charge distribution from homogeneity to heterogeneity and leads to fast capacity fading. Our work highlights the importance of interior local environment within polycrystalline particles for electrochemical reactions in solid-state batteries and provides crucial insights into underlying mechanism in interfacial transport.
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http://dx.doi.org/10.1038/s41467-020-19528-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7658997PMC
November 2020

Fast Heat Transport Inside Lithium-Sulfur Batteries Promotes Their Safety and Electrochemical Performance.

iScience 2020 Oct 18;23(10):101576. Epub 2020 Sep 18.

State Key Lab for Modification of Chemical Fibers & Polymer Materials, College of Materials Science & Engineering, Donghua University, Shanghai 201620, China.

Lithium-sulfur batteries are paid much attention owing to their high specific capacity and energy density. However, their practical applications are impeded by poor electrochemical performance due to the dissolved polysulfides. The concentration of soluble polysulfides has a linear relationship with the internal heat generation. The issue of heat transport inside lithium-sulfur batteries is often overlooked. Here, we designed a functional separator that not only had a high thermal conductivity of 0.65 W m K but also alleviated the diffusion of dissolved active materials to the lithium anode, improving the electrochemical performance and safety issue. Lithium-sulfur batteries with the functional separator have a specific capacity of 1,126.4 mAh g at 0.2 C, and the specific capacity can be remained up to 893.5 mAh g after 100 cycles. Pouch Cells with high sulfur loading also showed a good electrochemical performance under a lean electrolyte condition of electrolyte/sulfur (E/S) = 3 μL mg.
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http://dx.doi.org/10.1016/j.isci.2020.101576DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7549117PMC
October 2020

Surface regulation enables high stability of single-crystal lithium-ion cathodes at high voltage.

Nat Commun 2020 Jun 16;11(1):3050. Epub 2020 Jun 16.

MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, 150001, Harbin, China.

Single-crystal cathode materials for lithium-ion batteries have attracted increasing interest in providing greater capacity retention than their polycrystalline counterparts. However, after being cycled at high voltages, these single-crystal materials exhibit severe structural instability and capacity fade. Understanding how the surface structural changes determine the performance degradation over cycling is crucial, but remains elusive. Here, we investigate the correlation of the surface structure, internal strain, and capacity deterioration by using operando X-ray spectroscopy imaging and nano-tomography. We directly observe a close correlation between surface chemistry and phase distribution from homogeneity to heterogeneity, which induces heterogeneous internal strain within the particle and the resulting structural/performance degradation during cycling. We also discover that surface chemistry can significantly enhance the cyclic performance. Our modified process effectively regulates the performance fade issue of single-crystal cathode and provides new insights for improved design of high-capacity battery materials.
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http://dx.doi.org/10.1038/s41467-020-16824-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7298058PMC
June 2020

Origin of Plasticity in Nanostructured Silicon.

Phys Rev Lett 2020 May;124(18):185701

Department of Geological Sciences, Stanford University, Stanford, California 94305, USA.

The mechanism of plasticity in nanostructured Si has been intensively studied over the past decade but still remains elusive. Here, we used in situ high-pressure radial x-ray diffraction to simultaneously monitor the deformation and structural evolution of a large number of randomly oriented Si nanoparticles (SiNPs). In contrast to the high-pressure β-Sn phase dominated plasticity observed in large SiNPs (∼100  nm), small SiNPs (∼9  nm) display a high-pressure simple hexagonal phase dominated plasticity. Meanwhile, dislocation activity exists in all of the phases, but significantly weakens as the particle size decreases and only leads to subtle plasticity in the initial diamond cubic phase. Furthermore, texture simulations identify major active slip systems in all of the phases. These findings elucidate the origin of plasticity in nanostructured Si under stress and provide key guidance for the application of nanostructured Si.
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http://dx.doi.org/10.1103/PhysRevLett.124.185701DOI Listing
May 2020

Perovskite neural trees.

Nat Commun 2020 05 7;11(1):2245. Epub 2020 May 7.

School of Materials Engineering, Purdue University, West Lafayette, IN, 47907, USA.

Trees are used by animals, humans and machines to classify information and make decisions. Natural tree structures displayed by synapses of the brain involves potentiation and depression capable of branching and is essential for survival and learning. Demonstration of such features in synthetic matter is challenging due to the need to host a complex energy landscape capable of learning, memory and electrical interrogation. We report experimental realization of tree-like conductance states at room temperature in strongly correlated perovskite nickelates by modulating proton distribution under high speed electric pulses. This demonstration represents physical realization of ultrametric trees, a concept from number theory applied to the study of spin glasses in physics that inspired early neural network theory dating almost forty years ago. We apply the tree-like memory features in spiking neural networks to demonstrate high fidelity object recognition, and in future can open new directions for neuromorphic computing and artificial intelligence.
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http://dx.doi.org/10.1038/s41467-020-16105-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7206050PMC
May 2020

Versatile compact heater design for in situ nano-tomography by transmission X-ray microscopy.

J Synchrotron Radiat 2020 May 16;27(Pt 3):746-752. Epub 2020 Apr 16.

National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973, USA.

A versatile, compact heater designed at National Synchrotron Light Source-II for in situ X-ray nano-imaging in a full-field transmission X-ray microscope is presented. Heater design for nano-imaging is challenging, combining tight spatial constraints with stringent design requirements for the temperature range and stability. Finite-element modeling and analytical calculations were used to determine the heater design parameters. Performance tests demonstrated reliable and stable performance, including maintaining the exterior casing close to room temperature while the heater is operating at above 1100°C, a homogenous heating zone and small temperature fluctuations. Two scientific experiments are presented to demonstrate the heater capabilities: (i) in situ 3D nano-tomography including a study of metal dealloying in a liquid molten salt extreme environment, and (ii) a study of pore formation in icosahedral quasicrystals. The progression of structural changes in both studies were clearly resolved in 3D, showing that the new heater enables powerful capabilities to directly visualize and quantify 3D morphological evolution of materials under real conditions by X-ray nano-imaging at elevated temperature during synthesis, fabrication and operation processes. This heater design concept can be applied to other applications where a precise, compact heater design is required.
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http://dx.doi.org/10.1107/S1600577520004567DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7285687PMC
May 2020

Revealing 3D Morphological and Chemical Evolution Mechanisms of Metals in Molten Salt by Multimodal Microscopy.

ACS Appl Mater Interfaces 2020 Apr 3;12(15):17321-17333. Epub 2020 Apr 3.

Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, New York 11794, United States.

Growing interest in molten salts as effective high-temperature heat-transfer fluids for sustainable energy systems drives a critical need to fundamentally understand the interactions between metals and molten salts. This work utilizes the multimodal microscopy methods of synchrotron X-ray nanotomography and electron microscopy to investigate the 3D morphological and chemical evolution of two-model systems, pure nickel metal and Ni-20Cr binary alloy, in a representative molten salt (KCl-MgCl 50-50 mol %, 800 °C). In both systems, unexpected shell-like structures formed because of the presence of more noble tungsten, suggesting a potential route of using Ni-W alloys for enhanced molten-salt corrosion resistance. The binary alloy Ni-20Cr developed a bicontinuous porous structure, reassembling functional porous metals manufactured by dealloying. This work elucidates better mechanistic understanding of corrosion in molten salts, which can contribute to the design of more reliable alloys for molten salt applications including next-generation nuclear and solar power plants and opens the possibility of using molten salts to fabricate functional porous materials.
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http://dx.doi.org/10.1021/acsami.9b19099DOI Listing
April 2020

Systems-level investigation of aqueous batteries for understanding the benefit of water-in-salt electrolyte by synchrotron nanoimaging.

Sci Adv 2020 Mar 6;6(10):eaay7129. Epub 2020 Mar 6.

Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY 11794, USA.

Water-in-salt (WIS) electrolytes provide a promising path toward aqueous battery systems with enlarged operating voltage windows for better safety and environmental sustainability. In this work, a new electrode couple, LiVO-LiMnO, for aqueous Li-ion batteries is investigated to understand the mechanism by which the WIS electrolyte improves the cycling stability at an extended voltage window. Operando synchrotron transmission x-ray microscopy on the LiMnO cathode reveals that the WIS electrolyte suppresses the mechanical damage to the electrode network and dissolution of the electrode particles, in addition to delaying the water decomposition process. Because the viscosity of WIS is notably higher, the reaction heterogeneity of the electrodes is quantified with x-ray absorption spectroscopic imaging, visualizing the kinetic limitations of the WIS electrolyte. This work furthers the mechanistic understanding of electrode-WIS electrolyte interactions and paves the way to explore the strategy to mitigate their possible kinetic limitations in three-dimensional architectures.
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http://dx.doi.org/10.1126/sciadv.aay7129DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7060054PMC
March 2020

PyXAS - an open-source package for 2D X-ray near-edge spectroscopy analysis.

J Synchrotron Radiat 2020 Mar 20;27(Pt 2):567-575. Epub 2020 Feb 20.

National Synchrotron Light Source II (NSLS-II), Upton, NY 11973, USA.

In the synchrotron X-ray community, X-ray absorption near-edge spectroscopy (XANES) is a widely used technique to probe the local coordination environment and the oxidation states of specific elements within a sample. Although this technique is usually applied to bulk samples, the advent of new synchrotron sources has enabled spatially resolved versions of this technique (2D XANES). This development has been extremely powerful for the study of heterogeneous systems, which is the case for nearly all real applications. However, associated with the development of 2D XANES comes the challenge of analyzing very large volumes of data. As an example, a single 2D XANES measurement at a synchrotron can easily produce ∼10 spatially resolved XANES spectra. Conventional manual analysis of an individual XANES spectrum is no longer feasible. Here, a software package is described that has been developed for high-throughput 2D XANES analysis. A detailed description of the software as well as example applications are provided.
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http://dx.doi.org/10.1107/S1600577520001071DOI Listing
March 2020

Lanthanide-Binding Tags for 3D X-ray Imaging of Proteins in Cells at Nanoscale Resolution.

J Am Chem Soc 2020 02 21;142(5):2145-2149. Epub 2020 Jan 21.

National Synchrotron Light Source II , Brookhaven National Laboratory , Upton , New York 11973 , United States.

We report the application of lanthanide-binding tags (LBTs) for two- and three-dimensional X-ray imaging of individual proteins in cells with a sub-15 nm beam. The method combines encoded LBTs, which are tags of minimal size (ca. 15-20 amino acids) affording high-affinity lanthanide ion binding, and X-ray fluorescence microscopy (XFM). This approach enables visualization of LBT-tagged proteins while simultaneously measuring the elemental distribution in cells at a spatial resolution necessary for visualizing cell membranes and eukaryotic subcellular organelles.
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http://dx.doi.org/10.1021/jacs.9b11571DOI Listing
February 2020

Designing Multiscale Porous Metal by Simple Dealloying with 3D Morphological Evolution Mechanism Revealed via X-ray Nano-tomography.

ACS Appl Mater Interfaces 2020 Jan 2;12(2):2793-2804. Epub 2020 Jan 2.

Department of Materials Science and Chemical Engineering , Stony Brook University , Stony Brook , New York 11794 , United States.

Designing materials with multiscale, hierarchical structure is critical to drive the advancement of new technology. Specifically, porous metals with multiscale porosity from nanometer to micrometer sizes would lead to enhanced physical and chemical properties-the micron-sized pores can increase the effective diffusivity of ion transport within the porous media, and the nano-sized pores provide high specific surface area, enabling functionalities that are unique to nanoporous metals. A new ternary precursor alloy selection concept utilizing the different mixing enthalpies is demonstrated in this work for the design of multiscale, bimodal porous copper from a simple, one-step dealloying of Cu-Fe-Al ternary alloy. The nanoporosity in the bimodal porous structure is formed from dealloying of the Cu-rich phase, whereas the microporosity is controlled by dissolving the Fe-rich phase, determined by both the initial Fe particle size and sintering profile. In addition to advancing the materials design method, the multiscale pore formation during dealloying was directly visualized and quantified via an interrupted in situ synchrotron X-ray nano-tomography. The 3D morphological analysis on tortuosity showed that the presence of the microporosity can compensate the increase of the diffusion path length due to nanoporosity, which facilitates diffusion within the porous structure. Overall the focus of the work is to introduce a new strategy to design multiscale porous metals with enhanced transport properties, and sheds light on the fundamental mechanisms on the 3D morphological evolution of the system using advanced synchrotron X-ray nano-tomography for future materials development and applications.
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http://dx.doi.org/10.1021/acsami.9b16392DOI Listing
January 2020

Anisotropically Electrochemical-Mechanical Evolution in Solid-State Batteries and Interfacial Tailored Strategy.

Angew Chem Int Ed Engl 2019 Dec 6;58(51):18647-18653. Epub 2019 Nov 6.

Department of Mechanical and Materials Engineering, University of Western Ontario, 1151 Richmond St, London, Ontario, N6A 3K7, Canada.

All-solid-state batteries have attracted attention owing to the potential high energy density and safety; however, little success has been made on practical applications of solid-state batteries, which is largely attributed to the solid-solid interface issues. A fundamental elucidation of electrode-electrolyte interface behaviors is of crucial significance but has proven difficult. The interfacial resistance and capacity fading issues in a solid-state battery were probed, revealing a heterogeneous phase transition evolution at solid-solid interfaces. The strain-induced interfacial change and the contact loss, as well as a dense metallic surface phase, deteriorate the electrochemical reaction in solid-state batteries. Furthermore, the in situ growth of electrolytes on secondary particles is proposed to fabricate robust solid-solid interface. Our study enlightens new insights into the mechanism behind solid-solid interfacial reaction for optimizing advanced solid-state batteries.
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http://dx.doi.org/10.1002/anie.201910993DOI Listing
December 2019

Design, characterization, and performance of a hard x-ray transmission microscope at the National Synchrotron Light Source II 18-ID beamline.

Rev Sci Instrum 2019 May;90(5):053701

National Synchrotron Light Source-II, Brookhaven National Laboratory, Upton, New York 11973, USA.

A transmission X-ray microscope has been designed and commissioned at the 18-ID Full-field X-ray Imaging beamline at the National Synchrotron Light Source II. This instrument operates in the 5-11 keV range, and, with the current set of optics, is capable of 30 nm spatial resolution imaging, with a field of view of about 40 μm. For absorption contrast, the minimum exposure time for a single projection image is about 20 ms and an entire 3D tomography data set can be acquired in under 1 min. The system enables tomographic reconstructions with sub-50 nm spatial resolution without the use of markers on the sample or corrections for rotation run-outs.
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http://dx.doi.org/10.1063/1.5088124DOI Listing
May 2019

Resolving 500 nm axial separation by multi-slice X-ray ptychography.

Acta Crystallogr A Found Adv 2019 Mar 12;75(Pt 2):336-341. Epub 2019 Feb 12.

National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, USA.

Multi-slice X-ray ptychography offers an approach to achieve images with a nanometre-scale resolution from samples with thicknesses larger than the depth of field of the imaging system by modeling a thick sample as a set of thin slices and accounting for the wavefront propagation effects within the specimen. Here, we present an experimental demonstration that resolves two layers of nanostructures separated by 500 nm along the axial direction, with sub-10 nm and sub-20 nm resolutions on two layers, respectively. Fluorescence maps are simultaneously measured in the multi-modality imaging scheme to assist in decoupling the mixture of low-spatial-frequency features across different slices. The enhanced axial sectioning capability using correlative signals obtained from multi-modality measurements demonstrates the great potential of the multi-slice ptychography method for investigating specimens with extended dimensions in 3D with high resolution.
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http://dx.doi.org/10.1107/S2053273318017229DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6396394PMC
March 2019

Deconvolution of octahedral PtNi nanoparticle growth pathway from in situ characterizations.

Nat Commun 2018 10 26;9(1):4485. Epub 2018 Oct 26.

Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH, 44325, USA.

Understanding the growth pathway of faceted alloy nanoparticles at the atomic level is crucial to morphology control and property tuning. Yet, it remains a challenge due to complexity of the growth process and technical limits of modern characterization tools. We report a combinational use of multiple cutting-edge in situ techniques to study the growth process of octahedral PtNi nanoparticles, which reveal the particle growth and facet formation mechanisms. Our studies confirm the formation of octahedral PtNi initiates from Pt nuclei generation, which is followed by continuous Pt reduction that simultaneously catalyzes Ni reduction, resulting in mixed alloy formation with moderate elemental segregation. Carbon monoxide molecules serve as a facet formation modulator and induce Ni segregation to the surface, which inhibits the (111) facet growth and causes the particle shape to evolve from a spherical cluster to an octahedron as the (001) facet continues to grow.
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http://dx.doi.org/10.1038/s41467-018-06900-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6203767PMC
October 2018

X-ray Fluorescence Nanotomography of Single Bacteria with a Sub-15 nm Beam.

Sci Rep 2018 09 7;8(1):13415. Epub 2018 Sep 7.

Department of Chemistry, Stony Brook University, Stony Brook, NY, 11794, USA.

X-ray Fluorescence (XRF) microscopy is a growing approach for imaging the trace element concentration, distribution, and speciation in biological cells at the nanoscale. Moreover, three-dimensional nanotomography provides the added advantage of imaging subcellular structure and chemical identity in three dimensions without the need for staining or sectioning of cells. To date, technical challenges in X-ray optics, sample preparation, and detection sensitivity have limited the use of XRF nanotomography in this area. Here, XRF nanotomography was used to image the elemental distribution in individual E. coli bacterial cells using a sub-15 nm beam at the Hard X-ray Nanoprobe beamline (HXN, 3-ID) at NSLS-II. These measurements were simultaneously combined with ptychography to image structural components of the cells. The cells were embedded in small (3-20 µm) sodium chloride crystals, which provided a non-aqueous matrix to retain the three-dimensional structure of the E. coli while collecting data at room temperature. Results showed a generally uniform distribution of calcium in the cells, but an inhomogeneous zinc distribution, most notably with concentrated regions of zinc at the polar ends of the cells. This work demonstrates that simultaneous two-dimensional ptychography and XRF nanotomography can be performed with a sub-15 nm beam size on unfrozen biological cells to co-localize elemental distribution and nanostructure simultaneously.
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http://dx.doi.org/10.1038/s41598-018-31461-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6128931PMC
September 2018

Hierarchical Carbon-Coated Ball-Milled Silicon: Synthesis and Applications in Free-Standing Electrodes and High-Voltage Full Lithium-Ion Batteries.

ACS Nano 2018 Jun 8;12(6):6280-6291. Epub 2018 Jun 8.

Mork Family Department of Chemical Engineering and Materials Science , University of Southern California , Los Angeles , California 90089 , United States.

Lithium-ion batteries have been regarded as one of the most promising energy storage devices, and development of low-cost batteries with high energy density is highly desired so that the cost per watt-hour ($/Wh) can be minimized. In this work, we report using ball-milled low-cost silicon (Si) as the starting material and subsequent carbon coating to produce low-cost hierarchical carbon-coated (HCC) Si. The obtained particles prepared from different Si sources all show excellent cycling performance of over 1000 mAh/g after 1000 cycles. Interestingly, we observed in situ formation of porous Si, and it is well confined in the carbon shell based on postcycling characterization of the hierarchical carbon-coated metallurgical Si (HCC-M-Si) particles. In addition, lightweight and free-standing electrodes consisting of the HCC-M-Si particles and carbon nanofibers were fabricated, which achieved 1015 mAh/g after 100 cycles based on the total mass of the electrodes. Compared with conventional electrodes, the lightweight and free-standing electrodes significantly improve the energy density by 745%. Furthermore, LiCoO and LiNiMnO cathodes were used to pair up with the HCC-M-Si anode to fabricate full cells. With LiNiMnO as cathode, an energy density up to 547 Wh/kg was achieved by the high-voltage full cell. After 100 cycles, the full cell with a LiNiMnO cathode delivers 46% more energy density than that of the full cell with a LiCoO cathode. The systematic investigation on low-cost Si anodes together with their applications in lightweight free-standing electrodes and high-voltage full cells will shed light on the development of high-energy Si-based lithium-ion batteries for real applications.
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http://dx.doi.org/10.1021/acsnano.8b03312DOI Listing
June 2018

Seasonal differences in trace element concentrations and distribution in Spartina alterniflora root tissue.

Chemosphere 2018 Aug 13;204:359-370. Epub 2018 Apr 13.

Biological Sciences Department, Brookhaven National Laboratory, Upton, NY 11973, USA.

The present study uses nanometer-scale synchrotron X-ray nanofluorescence to investigate season differences in concentrations and distributions of major (Ca, K, S and P) and trace elements (As, Cr, Cu, Fe and Zn) in the root system of Spartina alterniflora collected from Jamaica Bay, New York, in April and September 2015. The root samples were cross-sectioned at a thickness of 10 μm. Selected areas in the root epidermis and endodermis were mapped with a sampling resolution of 100 and 200 nm, varying with the mapping areas. The results indicate that trace element concentrations in the epidermis and endodermis vary among the elements measured, possibly because of their different chemical properties or their ability to act as micronutrients for the plants. Elemental concentrations (As, Ca, Cr, Cu, Fe, K, P, S and Zn) within each individual root sample and between the root samples collected during two different seasons are both significantly different (p < 0.01). Furthermore, this study indicates that the nonessential elements (As and Cr) are significantly correlated (p < 0.01) with Fe, with high concentrations in the root epidermis, while others are not, implying that Fe may be a barrier to nonessential element transport in the root system. Hierarchy cluster analysis shows two distinct groups, one including As, Cr and Fe and the other the rest of the elements measured. Factor analysis also indicates that the processes and mechanisms controlling element transport in the root system can be different between the nutrient and nonessential elements.
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http://dx.doi.org/10.1016/j.chemosphere.2018.04.058DOI Listing
August 2018

High-Capacity Cathode Material with High Voltage for Li-Ion Batteries.

Adv Mater 2018 Mar 15;30(9). Epub 2018 Jan 15.

CAS Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Sciences (CAS), Beijing, 100190, P. R. China.

Electrochemical energy storage devices with a high energy density are an important technology in modern society, especially for electric vehicles. The most effective approach to improve the energy density of batteries is to search for high-capacity electrode materials. According to the concept of energy quality, a high-voltage battery delivers a highly useful energy, thus providing a new insight to improve energy density. Based on this concept, a novel and successful strategy to increase the energy density and energy quality by increasing the discharge voltage of cathode materials and preserving high capacity is proposed. The proposal is realized in high-capacity Li-rich cathode materials. The average discharge voltage is increased from 3.5 to 3.8 V by increasing the nickel content and applying a simple after-treatment, and the specific energy is improved from 912 to 1033 Wh kg . The current work provides an insightful universal principle for developing, designing, and screening electrode materials for high energy density and energy quality.
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http://dx.doi.org/10.1002/adma.201705575DOI Listing
March 2018

Anomalous Growth Rate of Ag Nanocrystals Revealed by in situ STEM.

Sci Rep 2017 11 27;7(1):16420. Epub 2017 Nov 27.

Center for Functional Nanomaterials (CFN), Brookhaven National Laboratory, Upton, NY, 11973, USA.

In situ microscopy of colloidal nanocrystal growth offers a unique opportunity to acquire direct and straightforward data for assessing classical growth models. Here, we observe the growth trajectories of individual Ag nanoparticles in solution using in situ scanning transmission electron microscopy. For the first time, we provide experimental evidence of growth rates of Ag nanoparticles in the presence of Pt in solution that are significantly faster than predicted by Lifshitz-Slyozov-Wagner theory. We attribute these observed anomalous growth rates to the synergistic effects of the catalytic properties of Pt and the electron beam itself. Transiently reduced Pt atoms serve as active sites for Ag ions to grow, thereby playing a key role in controlling the growth kinetics. Electron beam illumination greatly increases the local concentration of free radicals, thereby strongly influencing particle growth rate and the resulting particle morphology. Through a systematic investigation, we demonstrate the feasibility of utilizing these synergistic effects for controlling the growth rates and particle morphologies at the nanoscale. Our findings not only expand the current scope of crystal growth theory, but may also lead to a broader scientific application of nanocrystal synthesis.
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http://dx.doi.org/10.1038/s41598-017-15140-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5703889PMC
November 2017

Rapid alignment of nanotomography data using joint iterative reconstruction and reprojection.

Sci Rep 2017 09 18;7(1):11818. Epub 2017 Sep 18.

Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL, 60439, USA.

As x-ray and electron tomography is pushed further into the nanoscale, the limitations of rotation stages become more apparent, leading to challenges in the alignment of the acquired projection images. Here we present an approach for rapid post-acquisition alignment of these projections to obtain high quality three-dimensional images. Our approach is based on a joint estimation of alignment errors, and the object, using an iterative refinement procedure. With simulated data where we know the alignment error of each projection image, our approach shows a residual alignment error that is a factor of a thousand smaller, and it reaches the same error level in the reconstructed image in less than half the number of iterations. We then show its application to experimental data in x-ray and electron nanotomography.
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http://dx.doi.org/10.1038/s41598-017-12141-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5603591PMC
September 2017

Electrochemical (de)lithiation of silver ferrite and composites: mechanistic insights from ex situ, in situ, and operando X-ray techniques.

Phys Chem Chem Phys 2017 Aug;19(33):22329-22343

Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, USA.

The structure of pristine AgFeO and phase makeup of AgFeO (a one-pot composite comprised of nanocrystalline stoichiometric AgFeO and amorphous γ-FeO phases) was investigated using synchrotron X-ray diffraction. A new stacking-fault model was proposed for AgFeO powder synthesized using the co-precipitation method. The lithiation/de-lithiation mechanisms of silver ferrite, AgFeO and AgFeO were investigated using ex situ, in situ, and operando characterization techniques. An amorphous γ-FeO component in the AgFeO sample is quantified. Operando XRD of electrochemically reduced AgFeO and AgFeO composites demonstrated differences in the structural evolution of the nanocrystalline AgFeO component. As complimentary techniques to XRD, ex situ X-ray Absorption Spectroscopy (XAS) provided insight into the short-range structure of the (de)lithiated nanocrystalline electrodes, and a novel in situ high energy X-ray fluorescence nanoprobe (HXN) mapping measurement was applied to spatially resolve the progression of discharge. Based on the results, a redox mechanism is proposed where the full reduction of Ag to Ag and partial reduction of Fe to Fe occur on reduction to 1.0 V, resulting in a LiFeFeO phase. The LiFeFeO phase can then reversibly cycle between Fe and Fe oxidation states, permitting good capacity retention over 50 cycles. In the AgFeO composite, a substantial amorphous γ-FeO component is observed which discharges to rock salt LiFeO and Fe metal phase in the 3.5-1.0 V voltage range (in parallel with the AgFeO mechanism), and reversibly reoxidizes to a nanocrystalline iron oxide phase.
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http://dx.doi.org/10.1039/c7cp04012aDOI Listing
August 2017

In Situ and Ex Situ TEM Study of Lithiation Behaviours of Porous Silicon Nanostructures.

Sci Rep 2016 08 30;6:31334. Epub 2016 Aug 30.

Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States.

In this work, we study the lithiation behaviours of both porous silicon (Si) nanoparticles and porous Si nanowires by in situ and ex situ transmission electron microscopy (TEM) and compare them with solid Si nanoparticles and nanowires. The in situ TEM observation reveals that the critical fracture diameter of porous Si particles reaches up to 1.52 μm, which is much larger than the previously reported 150 nm for crystalline Si nanoparticles and 870 nm for amorphous Si nanoparticles. After full lithiation, solid Si nanoparticles and nanowires transform to crystalline Li15Si4 phase while porous Si nanoparticles and nanowires transform to amorphous LixSi phase, which is due to the effect of domain size on the stability of Li15Si4 as revealed by the first-principle molecular dynamic simulation. Ex situ TEM characterization is conducted to further investigate the structural evolution of porous and solid Si nanoparticles during the cycling process, which confirms that the porous Si nanoparticles exhibit better capability to suppress pore evolution than solid Si nanoparticles. The investigation of structural evolution and phase transition of porous Si nanoparticles and nanowires during the lithiation process reveal that they are more desirable as lithium-ion battery anode materials than solid Si nanoparticles and nanowires.
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http://dx.doi.org/10.1038/srep31334DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5004143PMC
August 2016

Facile Five-Step Heteroepitaxial Growth of GaAs Nanowires on Silicon Substrates and the Twin Formation Mechanism.

ACS Nano 2016 Feb 8;10(2):2424-35. Epub 2016 Feb 8.

Ming Hsieh Department of Electrical Engineering, ‡Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, and Department of Chemical Engineering and Materials Science, §Mork Family Department of Chemical Engineering and Materials Science, and ∥Center for Energy Nanoscience, University of Southern California , Los Angeles, California 90089, United States.

Monolithic integration of III-V semiconductors with Si has been pursued for some time in the semiconductor industry. However, the mismatch of lattice constants and thermal expansion coefficients represents a large technological challenge for the heteroepitaxial growth. Nanowires, due to their small lateral dimension, can relieve strain and mitigate dislocation formation to allow single-crystal III-V materials to be grown on Si. Here, we report a facile five-step heteroepitaxial growth of GaAs nanowires on Si using selective area growth (SAG) in metalorganic chemical vapor deposition, and we further report an in-depth study on the twin formation mechanism. Rotational twin defects were observed in the nanowire structures and showed strong dependence on the growth condition and nanowire size. We adopt a model of faceted growth to demonstrate the formation of twins during growth, which is well supported by both a transmission electron microscopy study and simulation based on nucleation energetics. Our study has led to twin-free segments in the length up to 80 nm, a significant improvement compared to previous work using SAG. The achievements may open up opportunities for future functional III-V-on-Si heterostructure devices.
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http://dx.doi.org/10.1021/acsnano.5b07232DOI Listing
February 2016

Artificial Photosynthesis on TiO2-Passivated InP Nanopillars.

Nano Lett 2015 Sep 14;15(9):6177-81. Epub 2015 Aug 14.

Material Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.

Here, we report photocatalytic CO2 reduction with water to produce methanol using TiO2-passivated InP nanopillar photocathodes under 532 nm wavelength illumination. In addition to providing a stable photocatalytic surface, the TiO2-passivation layer provides substantial enhancement in the photoconversion efficiency through the introduction of O vacancies associated with the nonstoichiometric growth of TiO2 by atomic layer deposition. Plane wave-density functional theory (PW-DFT) calculations confirm the role of oxygen vacancies in the TiO2 surface, which serve as catalytically active sites in the CO2 reduction process. PW-DFT shows that CO2 binds stably to these oxygen vacancies and CO2 gains an electron (-0.897e) spontaneously from the TiO2 support. This calculation indicates that the O vacancies provide active sites for CO2 absorption, and no overpotential is required to form the CO2(-) intermediate. The TiO2 film increases the Faraday efficiency of methanol production by 5.7× to 4.79% under an applied potential of -0.6 V vs NHE, which is 1.3 V below the E(o)(CO2/CO2(-)) = -1.9 eV standard redox potential. Copper nanoparticles deposited on the TiO2 act as a cocatalyst and further improve the selectivity and yield of methanol production by up to 8-fold with a Faraday efficiency of 8.7%.
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http://dx.doi.org/10.1021/acs.nanolett.5b02511DOI Listing
September 2015

Step-Edge-Guided Nucleation and Growth of Aligned WSe2 on Sapphire via a Layer-over-Layer Growth Mode.

ACS Nano 2015 Aug 29;9(8):8368-75. Epub 2015 Jul 29.

Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States.

Two-dimensional (2D) materials beyond graphene have drawn a lot of attention recently. Among the large family of 2D materials, transitional metal dichalcogenides (TMDCs), for example, molybdenum disulfides (MoS2) and tungsten diselenides (WSe2), have been demonstrated to be good candidates for advanced electronics, optoelectronics, and other applications. Growth of large single-crystalline domains and continuous films of monolayer TMDCs has been achieved recently. Usually, these TMDC flakes nucleate randomly on substrates, and their orientation cannot be controlled. Nucleation control and orientation control are important steps in 2D material growth, because randomly nucleated and orientated flakes will form grain boundaries when adjacent flakes merge together, and the formation of grain boundaries may degrade mechanical and electrical properties of as-grown materials. The use of single crystalline substrates enables the alignment of as-grown TMDC flakes via a substrate-flake epitaxial interaction, as demonstrated recently. Here we report a step-edge-guided nucleation and growth approach for the aligned growth of 2D WSe2 by a chemical vapor deposition method using C-plane sapphire as substrates. We found that at temperatures above 950 °C the growth is strongly guided by the atomic steps on the sapphire surface, which leads to the aligned growth of WSe2 along the step edges on the sapphire substrate. In addition, such atomic steps facilitate a layer-over-layer overlapping process to form few-layer WSe2 structures, which is different from the classical layer-by-layer mode for thin-film growth. This work introduces an efficient way to achieve oriented growth of 2D WSe2 and adds fresh knowledge on the growth mechanism of WSe2 and potentially other 2D materials.
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http://dx.doi.org/10.1021/acsnano.5b03043DOI Listing
August 2015
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