Publications by authors named "Ilke Arslan"

36 Publications

Visualization of Plasmonic Couplings Using Ultrafast Electron Microscopy.

Nano Lett 2021 07 21;21(13):5842-5849. Epub 2021 Jun 21.

Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States.

Hybrids of graphene and metal plasmonic nanostructures are promising building blocks for applications in optoelectronics, surface-enhanced scattering, biosensing, and quantum information. An understanding of the coupling mechanism in these hybrid systems is of vital importance to its applications. Previous efforts in this field mainly focused on spectroscopic studies of strong coupling within the hybrids with no spatial resolution. Here we report direct imaging of the local plasmonic coupling between single Au nanocapsules and graphene step edges at the nanometer scale by photon-induced near-field electron microscopy in an ultrafast electron microscope for the first time. The proximity of a step in the graphene to the nanocapsule causes asymmetric surface charge density at the ends of the nanocapsules. Computational electromagnetic simulations confirm the experimental observations. The results reported here indicate that this hybrid system could be used to manipulate the localized electromagnetic field on the nanoscale, enabling promising future plasmonic devices.
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http://dx.doi.org/10.1021/acs.nanolett.1c01824DOI Listing
July 2021

Nanoporous Dielectric Resistive Memories Using Sequential Infiltration Synthesis.

ACS Nano 2021 Mar 1;15(3):4155-4164. Epub 2021 Mar 1.

Institute for Molecular Engineering, Eckhardt Research Center, University of Chicago, 5640 S. Ellis Avenue, Chicago, Illinois 60637, United States.

Resistance switching in metal-insulator-metal structures has been extensively studied in recent years for use as synaptic elements for neuromorphic computing and as nonvolatile memory elements. However, high switching power requirements, device variabilities, and considerable trade-offs between low operating voltages, high on/off ratios, and low leakage have limited their utility. In this work, we have addressed these issues by demonstrating the use of ultraporous dielectrics as a pathway for high-performance resistive memory devices. Using a modified atomic layer deposition based technique known as sequential infiltration synthesis, which was developed originally for improving polymer properties such as enhanced etch resistance of electron-beam resists and for the creation of films for filtration and oleophilic applications, we are able to create ∼15 nm thick ultraporous (pore size ∼5 nm) oxide dielectrics with up to 73% porosity as the medium for filament formation. We show, using the Ag/AlO system, that the ultraporous films result in ultrahigh on/off ratio (>10) at ultralow switching voltages (∼±600 mV) that are 10× smaller than those for the bulk case. In addition, the devices demonstrate fast switching, pulsed endurance up to 1 million cycles. and high temperature (125 °C) retention up to 10 s, making this approach highly promising for large-scale neuromorphic and memory applications. Additionally, this synthesis methodology provides a compatible, inexpensive route that is scalable and compatible with existing semiconductor nanofabrication methods and materials.
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http://dx.doi.org/10.1021/acsnano.0c03201DOI Listing
March 2021

Glutamate Sensing inside the Mouse Brain with Perovskite Nickelate-Nafion Heterostructures.

ACS Appl Mater Interfaces 2020 Jun 20;12(22):24564-24574. Epub 2020 May 20.

Department of Biological Sciences, Purdue Institute for Integrative Neuroscience, Purdue University, West Lafayette, Indiana 47907, United States.

Glutamate, one of the main neurotransmitters in the brain, plays a critical role in communication between neurons, neuronal development, and various neurological disorders. Extracellular measurement of neurotransmitters such as glutamate in the brain is important for understanding these processes and developing a new generation of brain-machine interfaces. Here, we demonstrate the use of a perovskite nickelate-Nafion heterostructure as a promising glutamate sensor with a low detection limit of 16 nM and a response time of 1.2 s amperometric sensing. We have designed and successfully tested novel perovskite nickelate-Nafion electrodes for recording of glutamate release in electrically stimulated brain slices and from the primary visual cortex (V1) of awake mice exposed to visual stimuli. These results demonstrate the potential of perovskite nickelates as sensing media for brain-machine interfaces.
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http://dx.doi.org/10.1021/acsami.0c02826DOI Listing
June 2020

Perfect Strain Relaxation in Metamorphic Epitaxial Aluminum on Silicon through Primary and Secondary Interface Misfit Dislocation Arrays.

ACS Nano 2018 Jul 28;12(7):6843-6850. Epub 2018 Jun 28.

Laboratory for Physical Sciences , University of Maryland , College Park , Maryland 20740 , United States.

Understanding the atomically precise arrangement of atoms at epitaxial interfaces is important for emerging technologies such as quantum materials that have function and performance dictated by bonds and defects that are energetically active on the micro-electronvolt scale. A combination of atomistic modeling and dislocation theory analysis describes both primary and secondary dislocation networks at the metamorphic Al/Si (111) interface, which is experimentally validated by atomic resolution scanning transmission electron microscopy. The electron microscopy images show primary misfit dislocations for the majority of the strain relief and evidence of a secondary structure allowing for complete relaxation of the Al-Si misfit strain. This study demonstrates the equilibrium interface that represents the lowest energy structure of a highly mismatched and semicoherent single-crystal interface with complete strain relief in an atomically abrupt structure.
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http://dx.doi.org/10.1021/acsnano.8b02065DOI Listing
July 2018

Improved Three-Dimensional (3D) Resolution of Electron Tomograms Using Robust Mathematical Data-Processing Techniques.

Microsc Microanal 2017 12 16;23(6):1121-1129. Epub 2017 Nov 16.

2Physical Sciences Division,Pacific Northwest National Laboratory,Richland,WA 99352,USA.

Electron tomography has become an essential tool for three-dimensional (3D) characterization of nanomaterials. In recent years, advances have been made in specimen preparation and mounting, acquisition geometries, and reconstruction algorithms. All of these components work together to optimize the resolution and clarity of an electron tomogram. However, one important component of the data-processing has received less attention: the 2D tilt series alignment. This is challenging for a number of reasons, namely because the nature of the data sets and the need to be coherently aligned over the full range of angles. An inaccurate alignment may be difficult to identify, yet can significantly limit the final 3D resolution. In this work, we present an improved center-of-mass alignment model that allows us to overcome discrepancies from unwanted objects that enter the imaging area throughout the tilt series. In particular, we develop an approach to overcome changes in the total mass upon rotation of the imaging area. We apply our approach to accurately recover small Pt nanoparticles embedded in a zeolite that may otherwise go undetected both in the 2D microscopy images and the 3D reconstruction. In addition to this, we highlight the particular effectiveness of the compressed sensing methods with this data set.
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http://dx.doi.org/10.1017/S1431927617012636DOI Listing
December 2017

Electron tomography and fractal aspects of MoS and MoS/Co spheres.

Sci Rep 2017 09 26;7(1):12322. Epub 2017 Sep 26.

Instituto Mexicano del Petróleo (IMP), Eje Central Lázaro Cárdenas Norte 152 Col. San Bartolo Atepehuacan, México, D.F., C.P 07730, USA.

A study was made by a combination of 3D electron tomography reconstruction methods and N adsorption for determining the fractal dimension for nanometric MoS and MoS/Co catalyst particles. DFT methods including Neimarke-Kiselev's method allowed to determine the particle porosity and fractal arrays at the atomic scale for the S-Mo-S(Co) 2D- layers that conform the spherically shaped catalyst particles. A structural and textural correlation was sought by further characterization performed by x-ray Rietveld refinement and Radial Distribution Function (RDF) methods, electron density maps, computational density functional theory methods and nitrogen adsorption methods altogether, for studying the structural and textural features of spherical MoS and MoS/Co particles. Neimark-Kiselev's equations afforded the evaluation of a pore volume variation from 10 to 110 cm/g by cobalt insertion in the MoS crystallographic lattice, which induces the formation of cavities and throats in between of less than 29 nm, with a curvature radius r  < 14.4 nm; typical large needle-like arrays having 20 2D layers units correspond to a model consisting of smooth surfaces within these cavities. Decreasing D , D , D and D values occur when Co atoms are present in the MoS laminates, which promote the formation of smoother edges and denser surfaces that have an influence on the catalytic properties of the S-Mo-S(Co) system.
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http://dx.doi.org/10.1038/s41598-017-12029-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5615070PMC
September 2017

Recovering fine details from under-resolved electron tomography data using higher order total variation ℓ regularization.

Ultramicroscopy 2017 03 3;174:97-105. Epub 2017 Jan 3.

Department of Chemistry, Lehigh University, United States.

Over the last decade or so, reconstruction methods using ℓ regularization, often categorized as compressed sensing (CS) algorithms, have significantly improved the capabilities of high fidelity imaging in electron tomography. The most popular ℓ regularization approach within electron tomography has been total variation (TV) regularization. In addition to reducing unwanted noise, TV regularization encourages a piecewise constant solution with sparse boundary regions. In this paper we propose an alternative ℓ regularization approach for electron tomography based on higher order total variation (HOTV). Like TV, the HOTV approach promotes solutions with sparse boundary regions. In smooth regions however, the solution is not limited to piecewise constant behavior. We demonstrate that this allows for more accurate reconstruction of a broader class of images - even those for which TV was designed for - particularly when dealing with pragmatic tomographic sampling patterns and very fine image features. We develop results for an electron tomography data set as well as a phantom example, and we also make comparisons with discrete tomography approaches.
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http://dx.doi.org/10.1016/j.ultramic.2016.12.020DOI Listing
March 2017

Current status and future directions for in situ transmission electron microscopy.

Ultramicroscopy 2016 11 6;170:86-95. Epub 2016 Aug 6.

Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, MD 20899-6203, USA. Electronic address:

This review article discusses the current and future possibilities for the application of in situ transmission electron microscopy to reveal synthesis pathways and functional mechanisms in complex and nanoscale materials. The findings of a group of scientists, representing academia, government labs and private sector entities (predominantly commercial vendors) during a workshop, held at the Center for Nanoscale Science and Technology- National Institute of Science and Technology (CNST-NIST), are discussed. We provide a comprehensive review of the scientific needs and future instrument and technique developments required to meet them.
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http://dx.doi.org/10.1016/j.ultramic.2016.08.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5100813PMC
November 2016

Improving Stability of Zeolites in Aqueous Phase via Selective Removal of Structural Defects.

J Am Chem Soc 2016 Apr 24;138(13):4408-15. Epub 2016 Mar 24.

Institute for Integrated Catalysis, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99352, United States.

Missing silicon-oxygen bonds in zeolites are shown to be the cause for structural instability of zeolites in hot liquid water. Their selective removal drastically improved their structural stability as demonstrated using zeolite beta as example. The defects in the siloxy bonds were capped by reaction with trimethylchlorosilane, and Si-O-Si bonds were eventually formed. Hydrolysis of Si-O-Si bonds of the parent materials and dissolution of silica-oxygen tetrahedra in water causing a decrease in sorption capacity by reprecipitation of dissolved silica and pore blocking was largely mitigated by the treatment. The stability of the modified molecular sieves was monitored by (29)Si-MAS NMR, transmission electron micrographs, X-ray diffraction, and adsorption isotherms. The microporosity, sorption capacity, and long-range order of the stabilized material were fully retained even after prolonged exposure to hot liquid water.
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http://dx.doi.org/10.1021/jacs.5b12785DOI Listing
April 2016

Gaining Control over Radiolytic Synthesis of Uniform Sub-3-nanometer Palladium Nanoparticles: Use of Aromatic Liquids in the Electron Microscope.

Langmuir 2016 Feb 1;32(6):1468-77. Epub 2016 Feb 1.

Department of Chemical Engineering, Virginia Polytechnic Institute and State University , Blacksburg, Virginia 24061, United States.

Synthesizing nanomaterials of uniform shape and size is of critical importance to access and manipulate the novel structure-property relationships arising at the nanoscale, such as catalytic activity. In this work, we synthesize Pd nanoparticles with well-controlled size in the sub-3 nm range using scanning transmission electron microscopy (STEM) in combination with an in situ liquid stage. We use an aromatic hydrocarbon (toluene) as a solvent that is very resistant to high-energy electron irradiation, which creates a net reducing environment without the need for additives to scavenge oxidizing radicals. The primary reducing species is molecular hydrogen, which is a widely used reductant in the synthesis of supported metal catalysts. We propose a mechanism of particle formation based on the effect of tri-n-octylphosphine (TOP) on size stabilization, relatively low production of radicals, and autocatalytic reduction of Pd(II) compounds. We combine in situ STEM results with insights from in situ small-angle X-ray scattering (SAXS) from alcohol-based synthesis, having similar reduction potential, in a customized microfluidic device as well as ex situ bulk experiments. This has allowed us to develop a fundamental growth model for the synthesis of size-stabilized Pd nanoparticles and demonstrate the utility of correlating different in situ and ex situ characterization techniques to understand, and ultimately control, metal nanostructure synthesis.
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http://dx.doi.org/10.1021/acs.langmuir.5b04200DOI Listing
February 2016

Genesis of Delaminated-Zeolite Morphology: 3-D Characterization of Changes by STEM Tomography.

J Phys Chem Lett 2015 Jul 22;6(13):2598-602. Epub 2015 Jun 22.

§Department of Chemical and Biomolecular Engineering, University of California-Berkeley, Berkeley, California 94720, United States.

Zeolite delamination increases the external surface area available for catalyzing the conversion of bulky molecules, but a fundamental understanding of the delamination process remains unknown. Here we report morphological changes accompanying delamination on the length scale of individual zeolite clusters determined by 3-D imaging in scanning transmission electron microscopy. The results are tomograms that demonstrate delamination as it proceeds on the nanoscale through two distinct key steps: a chemical treatment that leads to a swelled material and a subsequent calcination that leads to curling and peeling off of delaminated zeolite sheets over hundreds of nanometers. These results characterize the direct, local, 3-D morphological changes accompanying delaminated materials synthesis and, with corroboration by mercury porosimetry, provide unique insight into the morphology of these materials, which is difficult to obtain with any other technique.
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http://dx.doi.org/10.1021/acs.jpclett.5b01004DOI Listing
July 2015

Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography.

Nat Commun 2015 Jul 2;6:7589. Epub 2015 Jul 2.

Faculty of Science, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, Utrecht 3584 CG, The Netherlands.

Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Using a nearest-neighbour statistical analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al-Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming.
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http://dx.doi.org/10.1038/ncomms8589DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4506508PMC
July 2015

In-situ electrochemical transmission electron microscopy for battery research.

Microsc Microanal 2014 Apr;20(2):484-92

1 Fundamental and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA.

The recent development of in-situ liquid stages for (scanning) transmission electron microscopes now makes it possible for us to study the details of electrochemical processes under operando conditions. As electrochemical processes are complex, care must be taken to calibrate the system before any in-situ/operando observations. In addition, as the electron beam can cause effects that look similar to electrochemical processes at the electrolyte/electrode interface, an understanding of the role of the electron beam in modifying the operando observations must also be understood. In this paper we describe the design, assembly, and operation of an in-situ electrochemical cell, paying particular attention to the method for controlling and quantifying the experimental parameters. The use of this system is then demonstrated for the lithiation/delithiation of silicon nanowires.
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http://dx.doi.org/10.1017/S1431927614000488DOI Listing
April 2014

Probing the degradation mechanisms in electrolyte solutions for Li-ion batteries by in situ transmission electron microscopy.

Nano Lett 2014 Mar 27;14(3):1293-9. Epub 2014 Feb 27.

Fundamental and Computational Sciences Directorate and ‡Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States.

Development of novel electrolytes with increased electrochemical stability is critical for the next generation battery technologies. In situ electrochemical fluid cells provide the ability to rapidly and directly characterize electrode/electrolyte interfacial reactions under conditions directly relevant to the operation of practical batteries. In this paper, we have studied the breakdown of a range of inorganic/salt complexes relevant to state-of-the-art Li-ion battery systems by in situ (scanning) transmission electron microscopy ((S)TEM). In these experiments, the electron beam itself caused the localized electrochemical reaction that allowed us to observe electrolyte breakdown in real-time. The results of the in situ (S)TEM experiments matches with previous stability tests performed during battery operation and the breakdown products and mechanisms are also consistent with known mechanisms. This analysis indicates that in situ liquid stage (S)TEM observations could be used to directly test new electrolyte designs and identify a smaller library of candidate solutions deserving of more detailed characterization. A systematic study of electrolyte degradation is also a necessary first step for any future controlled in operando liquid (S)TEM experiments intent on visualizing working batteries at the nanoscale.
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http://dx.doi.org/10.1021/nl404271kDOI Listing
March 2014

Direct visualization of initial SEI morphology and growth kinetics during lithium deposition by in situ electrochemical transmission electron microscopy.

Chem Commun (Camb) 2014 Feb 13;50(17):2104-7. Epub 2014 Jan 13.

Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.

Deposition of Li is a major safety concern existing in Li-ion secondary batteries. Here we perform the first in situ high spatial resolution measurement coupled with real-time quantitative electrochemistry to characterize SEI formation on gold using a standard battery electrolyte. We demonstrate that a dendritic SEI forms prior to Li deposition and that it remains on the surface after Li electrodissolution.
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http://dx.doi.org/10.1039/c3cc49029gDOI Listing
February 2014

Direct observation of aggregative nanoparticle growth: kinetic modeling of the size distribution and growth rate.

Nano Lett 2014 Jan 12;14(1):373-8. Epub 2013 Dec 12.

Department of Chemical Engineering and Materials Science, University of California , Davis, Davis, California 95616, United States.

Direct observations of solution-phase nanoparticle growth using in situ liquid transmission electron microscopy (TEM) have demonstrated the importance of "non-classical" growth mechanisms, such as aggregation and coalescence, on the growth and final morphology of nanocrystals at the atomic and single nanoparticle scales. To date, groups have quantitatively interpreted the mean growth rate of nanoparticles in terms of the Lifshitz-Slyozov-Wagner (LSW) model for Ostwald ripening, but less attention has been paid to modeling the corresponding particle size distribution. Here we use in situ fluid stage scanning TEM to demonstrate that silver nanoparticles grow by a length-scale dependent mechanism, where individual nanoparticles grow by monomer attachment but ensemble-scale growth is dominated by aggregation. Although our observed mean nanoparticle growth rate is consistent with the LSW model, we show that the corresponding particle size distribution is broader and more symmetric than predicted by LSW. Following direct observations of aggregation, we interpret the ensemble-scale growth using Smoluchowski kinetics and demonstrate that the Smoluchowski model quantitatively captures the mean growth rate and particle size distribution.
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http://dx.doi.org/10.1021/nl4043328DOI Listing
January 2014

Demonstration of an electrochemical liquid cell for operando transmission electron microscopy observation of the lithiation/delithiation behavior of Si nanowire battery anodes.

Nano Lett 2013 15;13(12):6106-12. Epub 2013 Nov 15.

Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.

Over the past few years, in situ transmission electron microscopy (TEM) studies of lithium ion batteries using an open-cell configuration have helped us to gain fundamental insights into the structural and chemical evolution of the electrode materials in real time. In the standard open-cell configuration, the electrolyte is either solid lithium oxide or an ionic liquid, which is point-contacted with the electrode. This cell design is inherently different from a real battery, where liquid electrolyte forms conformal contact with electrode materials. The knowledge learnt from open cells can deviate significantly from the real battery, calling for operando TEM technique with conformal liquid electrolyte contact. In this paper, we developed an operando TEM electrochemical liquid cell to meet this need, providing the configuration of a real battery and in a relevant liquid electrolyte. To demonstrate this novel technique, we studied the lithiation/delithiation behavior of single Si nanowires. Some of lithiation/delithation behaviors of Si obtained using the liquid cell are consistent with the results from the open-cell studies. However, we also discovered new insights different from the open cell configuration-the dynamics of the electrolyte and, potentially, a future quantitative characterization of the solid electrolyte interphase layer formation and structural and chemical evolution.
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http://dx.doi.org/10.1021/nl403402qDOI Listing
September 2014

The potential for Bayesian compressive sensing to significantly reduce electron dose in high-resolution STEM images.

Microscopy (Oxf) 2014 Feb 22;63(1):41-51. Epub 2013 Oct 22.

National Security Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA.

The use of high-resolution imaging methods in scanning transmission electron microscopy (STEM) is limited in many cases by the sensitivity of the sample to the beam and the onset of electron beam damage (for example, in the study of organic systems, in tomography and during in situ experiments). To demonstrate that alternative strategies for image acquisition can help alleviate this beam damage issue, here we apply compressive sensing via Bayesian dictionary learning to high-resolution STEM images. These computational algorithms have been applied to a set of images with a reduced number of sampled pixels in the image. For a reduction in the number of pixels down to 5% of the original image, the algorithms can recover the original image from the reduced data set. We show that this approach is valid for both atomic-resolution images and nanometer-resolution studies, such as those that might be used in tomography datasets, by applying the method to images of strontium titanate and zeolites. As STEM images are acquired pixel by pixel while the beam is scanned over the surface of the sample, these postacquisition manipulations of the images can, in principle, be directly implemented as a low-dose acquisition method with no change in the electron optics or the alignment of the microscope itself.
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http://dx.doi.org/10.1093/jmicro/dft042DOI Listing
February 2014

Electron tomography: seeing atoms in three dimensions.

Nat Mater 2012 Nov;11(11):911-2

Pacific Northwest National Laboratory, Richland, Washington 993352, USA.

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http://dx.doi.org/10.1038/nmat3472DOI Listing
November 2012

Direct in situ determination of the mechanisms controlling nanoparticle nucleation and growth.

ACS Nano 2012 Oct 13;6(10):8599-610. Epub 2012 Sep 13.

Department of Chemical Engineering and Materials Science, University of California, Davis, Davis, California 95616, USA.

Although nanocrystal morphology is controllable using conventional colloidal synthesis, multiple characterization techniques are typically needed to determine key properties like the nucleation rate, induction time, growth rate, and the resulting morphology. Recently, researchers have demonstrated growth of nanocrystals by in situ electron beam reduction, offering direct observations of single nanocrystals and eliminating the need for multiple characterization techniques; however, they found nanocrystal morphologies consistent with two different growth mechanisms for the same electron beam parameters. Here we show that the electron beam current plays a role analogous to the concentration of reducing agent in conventional synthesis, by controlling the growth mechanism and final morphology of silver nanocrystals grown via in situ electron beam reduction. We demonstrate that low beam currents encourage reaction limited growth that yield nanocrystals with faceted structures, while higher beam currents encourage diffusion limited growth that yield spherical nanocrystals. By isolating these two growth regimes, we demonstrate a new level of control over nanocrystal morphology, regulated by the fundamental growth mechanism. We find that the induction threshold dose for nucleation is independent of the beam current, pixel dwell time, and magnification being used. Our results indicate that in situ electron microscopy data can be interpreted by classical models and that systematic dose experiments should be performed for all future in situ liquid studies to confirm the exact mechanisms underlying observations of nucleation and growth.
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http://dx.doi.org/10.1021/nn303371yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3482139PMC
October 2012

Experimental procedures to mitigate electron beam induced artifacts during in situ fluid imaging of nanomaterials.

Ultramicroscopy 2013 Apr 27;127:53-63. Epub 2012 Jul 27.

Department of Chemical Engineering and Materials Science, University of California, Davis, Davis, CA 95616, USA.

Scanning transmission electron microscopy of various fluid and hydrated nanomaterial samples has revealed multiple imaging artifacts and electron beam-fluid interactions. These phenomena include growth of crystals on the fluid stage windows, repulsion of particles from the irradiated area, bubble formation, and the loss of atomic information during prolonged imaging of individual nanoparticles. Here we provide a comprehensive review of these fluid stage artifacts, and we present new experimental evidence that sheds light on their origins in terms of experimental apparatus issues and indirect electron beam sample interactions with the fluid layer. A key finding is that many artifacts are a result of indirect electron beam interactions, such as production of reactive radicals in the water by radiolysis, and the associated crystal growth. The results presented here will provide a methodology for minimizing fluid stage imaging artifacts and acquiring quantitative in situ observations of nanomaterial behavior in a liquid environment.
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http://dx.doi.org/10.1016/j.ultramic.2012.07.018DOI Listing
April 2013

Atomic-scale imaging and spectroscopy for in situ liquid scanning transmission electron microscopy.

Microsc Microanal 2012 Jun;18(3):621-7

Department of Chemical Engineering and Materials Science, University of California, Davis, One Shields Ave, Davis, CA 95616, USA.

Observation of growth, synthesis, dynamics, and electrochemical reactions in the liquid state is an important yet largely unstudied aspect of nanotechnology. The only techniques that can potentially provide the insights necessary to advance our understanding of these mechanisms is simultaneous atomic-scale imaging and quantitative chemical analysis (through spectroscopy) under environmental conditions in the transmission electron microscope. In this study we describe the experimental and technical conditions necessary to obtain electron energy loss (EEL) spectra from a nanoparticle in colloidal suspension using aberration-corrected scanning transmission electron microscopy (STEM) combined with the environmental liquid stage. At a fluid path length below 400 nm, atomic resolution images can be obtained and simultaneous compositional analysis can be achieved. We show that EEL spectroscopy can be used to quantify the total fluid path length around the nanoparticle and demonstrate that characteristic core-loss signals from the suspended nanoparticles can be resolved and analyzed to provide information on the local interfacial chemistry with the surrounding environment. The combined approach using aberration-corrected STEM and EEL spectra with the in situ fluid stage demonstrates a plenary platform for detailed investigations of solution-based catalysis.
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http://dx.doi.org/10.1017/S1431927612000104DOI Listing
June 2012

Direct in situ observation of nanoparticle synthesis in a liquid crystal surfactant template.

ACS Nano 2012 Apr 2;6(4):3589-96. Epub 2012 Apr 2.

Department of Chemical Engineering and Materials Science, University of California-Davis, One Shields Avenue, Davis, California 95616, United States.

Controlled and reproducible synthesis of tailored materials is essential in many fields of nanoscience. In order to control synthesis, there must be a fundamental understanding of nanostructure evolution on the length scale of its features. Growth mechanisms are usually inferred from methods such as (scanning) transmission electron microscopy ((S)TEM), where nanostructures are characterized after growth is complete. Such post mortem analysis techniques cannot provide the information essential to optimize the synthesis process, because they cannot measure nanostructure development as it proceeds in real time. This is especially true in the complex rheological fluids used in preparation of nanoporous materials. Here we show direct in situ observations of synthesis in a highly viscous lyotropic liquid crystal template on the nanoscale using a fluid stage in the STEM. The nanoparticles nucleate and grow to ∼5 nm particles, at which point growth continues through the formation of connections with other nanoparticles around the micelles to form clusters. Upon reaching a critical size (>10-15 nm), the clusters become highly mobile in the template, displacing and trapping micelles within the growing structure to form spherical, porous nanoparticles. The final products match those synthesized in the lab ex situ. This ability to directly observe synthesis on the nanoscale in rheological fluids, such as concentrated aqueous surfactants, provides an unprecedented understanding of the fundamental steps of nanomaterial synthesis. This in turn allows for the synthesis of next-generation materials that can strongly impact important technologies such as organic photovoltaics, energy storage devices, catalysis, and biomedical devices.
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http://dx.doi.org/10.1021/nn300671gDOI Listing
April 2012

Visualizing macromolecular complexes with in situ liquid scanning transmission electron microscopy.

Micron 2012 Nov 15;43(11):1085-90. Epub 2012 Feb 15.

Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, United States.

A central focus of biological research is understanding the structure/function relationship of macromolecular protein complexes. Yet conventional transmission electron microscopy techniques are limited to static observations. Here we present the first direct images of purified macromolecular protein complexes using in situ liquid scanning transmission electron microscopy. Our results establish the capability of this technique for visualizing the interface between biology and nanotechnology with high fidelity while also probing the interactions of biomolecules within solution. This method represents an important advancement towards allowing future high-resolution observations of biological processes and conformational dynamics in real-time.
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http://dx.doi.org/10.1016/j.micron.2012.01.018DOI Listing
November 2012

Controlled growth of nanoparticles from solution with in situ liquid transmission electron microscopy.

Nano Lett 2011 Jul 27;11(7):2809-13. Epub 2011 May 27.

Department of Molecular and Cellular Biology, University of California, Davis, Davis, California 95616, United States.

Direct visualization of lead sulfide nanoparticle growth is demonstrated by selectively decomposing a chemical precursor from a multicomponent solution using in situ liquid transmission electron microscopy. We demonstrate reproducible control over growth mechanisms that dictate the final morphology of nanostructures while observing growth in real-time with subnanometer spatial resolution. Furthermore, while an intense electron beam can initiate nanoparticle growth, it is also shown that a laser can trigger the reaction independently of the imaging electrons.
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http://dx.doi.org/10.1021/nl201166kDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3162246PMC
July 2011

Three-dimensional pore evolution of nanoporous metal particles for energy storage.

J Am Chem Soc 2011 Jun 31;133(24):9144-7. Epub 2011 May 31.

Department of Mechanical & Aeronautical Engineering, University of California-Davis, Davis, California 95616, USA.

A well characterized and predictable aging pattern is necessary for practical energy storage applications of nanoporous particles that facilitate rapid transport of ions or redox species. Here we use STEM tomography with segmentation to show that surface diffusion and grain boundary diffusion are responsible for pore evolution at intermediate and higher temperatures, respectively. This unprecedented three dimensional understanding of pore behavior as a function of temperature suggests routes for optimizing pore stability in future energy storage materials.
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http://dx.doi.org/10.1021/ja200561wDOI Listing
June 2011

Direct formation of mesoporous coesite single crystals from periodic mesoporous silica at extreme pressure.

Angew Chem Int Ed Engl 2010 Jun;49(25):4301-5

Department of Chemistry, Lehigh University, Bethlehem, PA 18015, USA.

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http://dx.doi.org/10.1002/anie.201001114DOI Listing
June 2010

Using electrons as a high-resolution probe of optical modes in individual nanowires.

Nano Lett 2009 Dec;9(12):4073-7

Sandia National Laboratories, 7011 East Avenue, Livermore, California 94550, USA.

While nanowires show increasing promise for optoelectronic applications, probing the subwavelength details of their optical modes has been a challenge with light-based techniques. Here we report the excitation of dielectric optical waveguide modes in a single GaN nanowire using transition radiation generated by a 1 nm diameter electron beam. This spatially resolved study opens important gateways to probing the optical modes of more complex nanostructures, fundamental for optimization of optoelectronic device performance.
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http://dx.doi.org/10.1021/nl902266nDOI Listing
December 2009

Towards better 3-D reconstructions by combining electron tomography and atom-probe tomography.

Ultramicroscopy 2008 Nov 1;108(12):1579-85. Epub 2008 Jun 1.

Sandia National Laboratories, Livermore, CA 94550, USA.

Scanning transmission electron microscope tomography and atom-probe tomography are both three-dimensional techniques on the nanoscale. We demonstrate here the combination of the techniques by analyzing the very same volume of an Al-Ag alloy specimen. This comparison allows us to directly visualize the theoretically known artifacts of each technique experimentally, providing insight into the optimal parameters to use for reconstructions and assessing the quality of each reconstruction. The combination of the techniques for accurate morphology and compositional information in three dimensions at the nanoscale provides a route for a new level of materials characterization and understanding.
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http://dx.doi.org/10.1016/j.ultramic.2008.05.008DOI Listing
November 2008

Toward three-dimensional nanoengineering of heterogeneous catalysts.

J Am Chem Soc 2008 Apr 5;130(17):5716-9. Epub 2008 Apr 5.

Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ UK.

Cobalt-based Fischer-Tropsch systems are widely used to convert synthesis gas to clean hydrocarbon fuel. However, surprisingly little is known about the morphology of the catalysts on the nanoscale. Here we show that scanning transmission electron tomography reveals their true 3-D morphology and provides direct evidence that the support controls the final morphology of the catalyst. Such direct local three-dimensional measurements provide unprecedented insight into catalysis, and can henceforth transform our understanding of these complex materials.
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http://dx.doi.org/10.1021/ja710299hDOI Listing
April 2008