PMCx62: Practical Challenges and Opportunities for

In Situ/Operando Microscopy in Liquids and Gases Sunday, August 5, 2018

Room 345 – 346

Welcome

7:30 – 8:30 am Registration, Coffee, & Breakfast

8:30 – 8:45 am Opening Remarks

Technical Session I

Developments in Gas Cells & Integration with Multi-Modal Techniques

8:45 – 9:15 am Xiaoqing Pan, University of California Irvine

9:15 – 9:45 am Renu Sharma, NIST

9:45 – 10:15 am Eric Stach, University of Pennsylvania

Poster Session I & Morning Break

10:15 – 11:00 am Poster Session I & Refreshments

Technical Session II Nanofabrication for In Situ TEM & Ultra-Fast Microscopy

11:00 – 11:30 am Bryan Reed, Integrated Dynamic Electron Solutions Inc.

11:30 – 12:00 pm Alex Liddle, NIST

Lunch 12:00 – 1:10 pm Lunch served

Technical Session III

Challenges and Opportunities for Data Management and Analytics

1:10 – 1:40 pm Alex Belianinov, Oak Ridge National Laboratory

1:40 – 2:10 pm Stephen Mick, Gatan

Poster Session II & Afternoon Break

2:10 pm – 2:40 pm Poster Session II & Refreshments

Technical Session IV

Low-Dose, Liquid Cell, and Cryo-Electron Microscopy

2:40 – 3:10 pm Katherine Jungjohann, Sandia National Laboratory

3:10 – 3:40 pm Lena Kourkoutis, Cornell University

3:40 – 4:10 pm See-Wee Chee, University of Singapore

Discussion Session

4:10 – 4:45 pm Open Discussion on Practical Challenges and Opportunities

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Platform Presentations

Xiaoqing Pan, University of California Irvine

In Situ Electron Microscopy of Catalysts with Atomic Resolution under Atmospheric Pressure

Renu Sharma, NIST

Multi-modal Methods for In Situ Microscopy

Eric Stach, University of Pennsylvania

Operando and Multi-modal Studies of Speciation and Activity of Pt Catalysts During the Hydrogenation

of Ethylene

Bryan Reed, Integrated Dynamic Electron Solutions, Inc.

The Full Spectrum of Time Resolution in TEM

Alex Liddle, NIST

Nanofluidic Liquid Cell with Integrated Electrokinetic Pump for In Situ TEM

Alex Belianinov, Oak Ridge National Laboratory

Big Data Analytics Applied to In Situ Microscopy

Stephen Mick, Gatan

Addressing Data Challenges for In Situ Electron Microscopy

Katherine Jungjohann, Sandia National Laboratory

Environmental Control and Complete Sample Characterization for Investigating Solid-Liquid Interfaces

In Situ

Lena Kourkoutis, Cornell University

Cryo-STEM Mapping of Processes at Solid-Liquid Interfaces in Devices for Energy Applications

See-Wee Chee, University of Singapore

Following Nanoparticle Dynamics in Liquids with High Frame-Rate CMOS Cameras

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Poster Presentations

Matthew Hauwiller and Justin Ondry, University of California, Berkeley

Towards Reproducible Chemical Reactions in Graphene Liquid Cell TEM Experiments

Meng Li, University of Pittsburgh

Quantification of Gas Cooling Effect on In Situ Heating Devices Used in Environmental TEM

Meng Li, University of Pittsburgh

Probing Dynamic Processes of the Initial Stages of Cu(100) Surface Oxidation by Correlated In Situ

Environmental TEM and Multiscale Simulations

Ethan Lawrence, Arizona State University

Surface Dynamics on CeO2 Nanoparticles using Time-Resolved High-Resolution TEM

Shinya Nagashima, Toyota Motor Corporation

Atomic-level Observation of Platinum Dissolution and Re-deposition Using Liquid Electrochemical TEM

Joshua Vincent, Arizona State University

Atomic-Resolution Operando TEM of Pt/CeO2 Catalysts Performing CO Oxidation

Tanya Prozorov, US DOE Ames Laboratory

Mapping the Fields in Liquid Phase: Opportunities and Challenges

Stephen House, University of Pittsburgh

In situ Insights into the Uncorking and Oxidative Decomposition Dynamics of Gold Nanoparticle Corked

Carbon Nanotube Cups for Drug Delivery

PMCx62 Organized by the Electron Microscopy in Liquids and Gas Focused Interest Group

Become a member of the EMLG FIG!

Come to our meeting on Tuesday at 12:15 PM, Room 331.

M&M 2018 PMCx62 Co-Organizers:

Raymond R. Unocic, Oak Ridge National Laboratory

Patricia J. Kooyman, University of Cape Town, South Africa

Ethan L. Lawrence, Arizona State University

Houlin L. Xin, Brookhaven National Laboratory

Joshua L. Vincent, Arizona State University

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Thank you to our sponsors!

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Thank you to our sponsors!

In situ Electron Microscopy of Catalysts with Atomic Resolution under Atmospheric

Pressure

Xiaoqing Pan1,2, Sheng Dai1, Wenpei Gao1, Shuyi Zhang1, and George. W. Graham1

1. Department of Chemical Engineering and Materials Science, University of California – Irvine, Irvine,

CA 92697, USA 2. Department of Physics and Astronomy, University of California – Irvine, Irvine, CA 92697, USA

In situ transmission electron microscopy (TEM) under gaseous environment has attracted attention not

only for basic scientific research but also for important industrial applications of materials and catalysts.

Although differential pumped environmental TEM (ETEM) is a well-established platform to investigate

the dynamic gas-solid interaction, some constraints still exist at the current stage: (1) The maximum gas

pressure allowed in ETEM is no more than 1/100 of the atmospheric pressure, which is not favorable for

building a bridge between the in situ results and real applications; (2) It is difficult to obtain atomic-

resolution high angle annular dark-field (HAADF) images in scanning transmission electron microscopy

(STEM) mode since no probe corrector is available in commercialized ETEMs while normal annular dark

field (ADF) imaging is limited to the low-angle regime due to the post-specimen differential pumping

apertures. Recently, it has become possible to overcome these limitations through the use of a MEMS-

based, electron-transparent windowed gas cell. Using this instrumentation, the gaseous environment is

normally sealed between two silicon nitride windows, reaching the pressure of 760 Torr (1.0 atm) under

static gas conditions or with low flow rates[1-4]. The gas cell holder can be safely inserted in any state of

art TEMs without any modification to the column and vacuum system, thus removing the limitation of

HAADF-STEM imaging encountered in differentially pumped ETEMs. In this talk, we illustrate the

advantages of the windowed gas cell as applied to our in situ study of two important systems: (1) CO-

induced Pt nanoparticle surface reconstruction at saturation coverage (2) Facet-dependent oxidation of

Pt3Co fuel cell catalysts.

It is well-known that different geometric configurations of surface atoms on supported metal nanoparticles

have different catalytic reactivity and that the adsorption of reactive species can cause reconstruction of

metal surfaces. Thus, characterizing metallic surface structures under reaction conditions at atomic scale

is critical for understanding reactivity. Here, we observed the truncated octahedron shape adopted by bare

Pt nanoparticles undergoes a reversible, facet-specific reconstruction due to CO adsorption, where flat

(100) facets roughen into vicinal stepped high Miller index facets, while flat (111) facets remain intact[1].

It is noticeable that high partial pressure of CO (> 20 Torr) allowed in the gas cell, ensuring the saturation

CO coverage, triggered the surface reconstruction of Pt nanoparticles. The in situ electron microscopy

evidence shows excellent agreement quantitatively with the result of density functional theory (DFT)-

based calculation, providing a clear insight for CO-induced reconstruction of (100) sites.

By taking advantage of the Z-contrast STEM imaging, we studied of surface composition and the

dynamics involved in facet-dependent oxidation of equilibrium-shaped Pt3Co fuel cell catalysts in an

initially disordered state[2]. Using our in situ gas cell technique, evolution of the surface of the Pt3Co

nanoparticles was monitored at the atomic scale during their exposure to an oxygen atmosphere at elevated

temperature, and it was found that Co segregation and oxidation take place on {111} surfaces but not on

{100} surfaces. These results may prove useful for a better understanding of the catalyst durability and

possible further attempts at surface engineering of Pt-metal fuel cell catalysts.

References:

[1] T. Avanesian, S. Dai, et al. J. Am. Chem. Soc. 139 (2017), p.4551-4558.

[2] S. Dai, Y. Hou, et al. Nano Lett. 17 (2017), p.4683-4688.

[3] S. Dai, Y. You, et al, Nat. Commun. 8 (2017), 204.

[4] S. Dai, S. Zhang, et al. ACS Catal. 7 (2017) p.1579-1582.

Multimodal Methods for In Situ Transmission Electron Microscopy

Renu Sharma1

1. Center for Nanoscale Science and Technology, National Institute of Standards and Technology,

Gaithersburg, MD, USA 20899

Recently, the applications of transmission electron microscopy (TEM) related techniques have extended

from ex situ nanoscale characterization of structure and chemistry of reaction products to dynamic

measurements of nanostructures during reaction processes. Commercially-available modified TEM

specimen holders and TEM columns (environmental scanning-transmission electron microscope or

ESTEM are being routinely employed to follow the structural and chemical changes at elevated

temperatures and even under controlled atmospheres. The combination of atomic-resolution images and

high spatial and energy resolution has successfully revealed the functioning of catalyst nanoparticles.

However, quantitative measurements of reaction rates and chemical changes are limited by (a) the

nanoscale regions needed for atomic-resolution imaging, (b) uncertainty in the temperature of the imaged

region and (c) difficulty in analyzing the large quantities of data generated. We present various technical

and analytical techniques that have been developed to address these issues.

We have incorporated a free-standing, broad-band, light focusing system in the ESTEM to excite and

collect vibrational and optical spectroscopies under reactive environments. This bimodal data collection

enables not only the acquisition of vibrational spectroscopy data concurrently with other electron

microscopy data, such as imaging, diffraction and electron energy-loss spectroscopy, under identical

chemical environment, it expands the spatial resolution from nanoscale to microscale. For example, we

have collected Raman signals from ≈ 80 μm2 areas, while collecting atomic-resolution videos from 200

nm2 area, during in situ growth of single-walled carbon nanotubes (SWCNT) at 625 °C in 0.005 Pa of

C2H2. The Raman peak shifts are also used to measure the sample temperature under gaseous

environments. Selected-area diffraction patterns from Au or Ag thin films can also be used for temperature

calibration. Plasmon peak shifts, as measured using EELS, can also be used to measure temperature under

reactive environments.

In order to obtain quantitative information from the large image data sets generated during in situ

measurements, we have developed a scheme that utilizes a combination of home-built and publicly

available algorithms for image drift correction, noise reduction, and peak location to accurately and

automatically determine the position of atomic columns. A Delaunay triangulation connects each point to

its nearest neighbors and the average nearest neighbor distance for each point is calculated to identify

phases and thus phase transformations at the atomic-scale. The effect of gaseous environment on local

surface plasmon resonance energies and the application of plasmonic nanoparticles to initiate room

temperature reactions will also be presented.

Operando and Multimodal Studies of Speciation and Activity of Pt Catalysts During

the Hydrogenation of Ethylene

Eric A. Stach1*, Yuanyuan Li,3 Deyu Liu,5 Shen Zhao,2,5 Jing Liu,3 Yao-Min Liu,5 Dmitri N. Zakharov,2

Qiyuan Wu,4 Alexander Orlov,4 Andrew A. Gewirth,5 Ralph G. Nuzzo,5 Anatoly I. Frenkel3,4

1. Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA

19104 3. Department of Chemistry, Brookhaven National Laboratory, Upton, NY 11793 4. Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook,

NY 11794 5. Department of Chemistry, University of Illinois, Urbana, IL 61801

*stach@seas.upenn.edu

The creation of fuels and large volume chemicals (such as olefins) from crude oil feedstocks involves the

hydrogenation of unsaturated hydrocarbons. These processes involve numerous catalytic reforming and

hydrogenation/dehydrogenation processes, and are generally mediated by supported metal nanoparticle

catalysts. These catalysts are generally chosen for their high activity, long term stability and the ease with

which they can be regenerated and recovered. However, despite the extensive use of these materials, there

are many questions that remain about how specific attributes of the structure and composition of the

catalysts are affected by the gases with which they interact. Furthermore, it is critically important to

understand how these structural changes affect selectivity, as well as how deactivation occurs because of

the conversion process.

In this work, we will describe how we use a multi-modal, operando experimental approach to understand

the subtle changes that occur to both the atomic structure and the chemical state of palladium nanoparticle

catalysts supported on SiO2 during the hydrogenation of ethylene. The core of this approach is the use of

a closed-cell microreactor [1] that allows sequential experimental investigation via scanning transmission

electron microscopy (STEM), x-ray absorption spectroscopy (XAS) and microbeam infrared spectroscopy

(µ-IR), and gas-chromotography/mass spectroscopy (GC-MS), with all measurements being made in the

same operando reaction conditions.[2]

We will describe how this approach allows us to directly correlate the measurements in a robust fashion,

leading to novel insights regarding several aspects of ethylene conversion. In specific, we will describe

how the specifics of reactive gas composition lead to interconversion of both hydride and carbide phases

of the Pd clusters, which processes affect the stability of the particles against coarsening, the reversibility

of structural and compositional transformations and the role that surface oligomers that form under

hydrogen limited reactant conditions, leading to deactivation.[3-5]

References:

[1] Li, Y., D. Zakharov, S. Zhao, R. Tappero, U. Jung, A. Elsen, Ph Baumann, Ralph G. Nuzzo, E. A.

Stach, and A. I. Frenkel. “Complex structural dynamics of nanocatalysts revealed in Operando

conditions by correlated imaging and spectroscopy probes”, Nature Comm. 6, 7583, 2015.

[2] Zhao, S., Li, Y., Stavitski, E., Tappero, R., Crowley, S., Castaldi, M.J., Zakharov, D.N., Nuzzo,

R.G., Frenkel, A.I. and Stach, E.A., “Operando Characterization of Catalysts through use of a Portable

Microreactor”, ChemCatChem, 7(22), pp.3683-3691, 2015.

[3] S. Zhao, Y. Li, D. Liu, J. Liu, Y.-M. Liu, D. N. Zakharov, Q. Wu, A. Orlov, A. A. Gewirth, E. A.

Stach, R. G. Nuzzo, A. I. Frenkel, J. Phys. Chem. C., 121, 18962-18972, 2017.

[4] D. Liu, Y. Li, M. Kottwitz, B. Yan, S. Yao, A. Gamalski, D. Grolimund, O. V. Safonova, M.

Nachtegaal, J. G. Chen, E. A. Stach, R. G. Nuzzo, A. I. Frenkel, ACS Catalysis 8, 4120-4131 (2018).

[5] The authors gratefully acknowledge support for this by the US Department of Energy, Office of

Basic Energy Sciences under Grant No. DE-FG02-03ER15476. The development of the micro-cell was

supported, in part, by an LDRD grant at Brookhaven National Laboratory. We acknowledge the

facilities support provided at the Centre for Functional Nanomaterials, the National Synchrotron Light

Source at the Brookhaven National Laboratory (US Department of Energy, Office of Basic Energy

Sciences, Contract No. DE-SC0012704) and the Synchrotron Catalysis Consortium (US Department of

Energy, Office of Basic Energy Sciences, Grant No. DE-SC0012335).

Figure 1. Schematic of the portable microreactor utilized for operando and multimodal studies

which shows both the probes that we have demonstrated and the information that we can obtain

from each technique.

The Full Spectrum of Time Resolution in Transmission Electron Microscopy

B. W. Reed1, N. Moghadam1, R. S. Bloom1, S. T. Park1, and D. J. Masiel1

1. Integrated Dynamic Electron Solutions, Inc., Pleasanton, CA, USA.

Time-resolved transmission electron microscopy has been growing for decades, with new techniques,

approaches, and instruments appearing at an accelerating rate. Far from converging onto a single approach,

instrument design, or short list of research topics, the field is quickly diversifying on all fronts. A critical

mass of capabilities and community has appeared, and people are trying out some of the vast number of

crazy ideas that burst onto the scene in the field’s early, highly-speculative days—and quite a few of those

crazy ideas actually work. These capabilities are enabled by modern lasers, control systems, electronics,

and data analysis combined with ongoing developments in conventional TEM.

This presentation will survey the field over a spectrum of time scales covering 15 orders of magnitude. At

one end, ultrafast TEM provides a unique platform for the study of materials physics including electron

phase transitions and plasmonics. At the other end, conventional in situ experimentation is being enhanced

with new camera and compressive sensing systems, pushing experiments into the millisecond regime. In

the middle, dynamic TEM covers many nanosecond-scale irreversible processes of interest to materials

science, including the emergence of mesoscale order in systems driven far from equilibrium. The

combination of all of these methods transforms transmission electron microscopy into an incredibly broad

and powerful tool for studying material dynamics.

In particular, this presentation will focus on how compressive sensing and related techniques can help

make the best use of the information and instrument bandwidth we already have. We will show how

compressive sensing using electrostatic subframing can allow a conventional TEM camera to capture kHz-

scale video, while related mathematical techniques can greatly improve the signal-to-noise ratio even

without making any use of compressive sensing or time resolution.

References:

[1] This material is based in part upon work supported by the U.S. Department of Energy, Office of

Science, Office of Basic Energy Sciences, under Award Number DE-SC0013104.

Nanofluidic Liquid Cell with Integrated Electrokinetic Pump for In Situ TEM

Alokik Kanwal, Christopher H. Ray, B. Robert Ilic, Renu Sharma, Glenn Holland, Vladimir Aksyuk,

Samuel M. Stavis, J. Alexander Liddle*

Center for Nanoscale Science and Technology, National Institute of Standards and Technology, 100

Bureau Drive, Gaithersburg, MD 20899

*liddle@nist.gov

Breakthroughs in the science of material growth and dissolution, electrochemistry, nanofluidics,

biomineralization, and soft materials [1] are being enabled by closed cells for the measurement of

materials and processes in liquid environments by the transmission electron microscope (TEM). Cell

design, and the types of fluidic interface they employ determine the functionality of such liquid cells.

Liquid thicknesses ~ 1 µm permit flow [2], while thicknesses of ~ 100 nm, allow for high-resolution

imaging, but, if flow is possible, have limited flow control. We have developed a monolithic liquid cell

that maintains a liquid layer of constant thickness (≈ 100 nm) across a viewing area of 200 µm × 200 µm

[3] to address some of these limitations. The addition of precise flow control would dramatically expand

the range and quality of experiments that could be conducted using such a cell, enabling reactions to be

initiated at specific instants, or to mitigate the perturbing effects of reactive radiolysis products on the

observed system.

Currently, fluid flow through liquid cells is pressure-driven, typically by macroscopic equipment such as

syringe pumps and capillaries external to the TEM. Nanofluidic liquid cells would require prohibitively

high pressure to pump in this way, and, because of the concomitant low flow rates, would suffer from very

slow exchange of fluids through macroscopic capillaries. We are developing an integrated electrokinetic

pump to solve these problems and enable future integration of lab-on-a-chip analysis within the TEM.

Here, we describe some of the critical design and process considerations involved in making such a

system.

The critical steps in the fabrication process that enable the wafer-scale integration of the nanofluidic

viewing area, fluid reservoirs, fluidic channels, and pump electrodes depend on the use of a sacrificial

layer of Cr2O3 that solves a number of challenging material and process compatibility issues. Further

integration is enabled by the use of 3D-printed parts to create a custom chip-holder interface that allows

for up to eleven separate electrical contacts to the nanofluidic chip. We will explain the rationale behind

the device design, and provide details of the chip fabrication process flow, holder interface, and imaging

performance.

References:

[1] Ross FM Opportunities and challenges in liquid cell electron microscopy. Science, 350, 9886-1, (2015)

[2] Ring, EA, de Jonge N. Microfluidic System for Transmission Electron Microscopy. Microsc.

Microanal. 16, 622–629, (2010)

[3] Tanase M, Winterstein J, Sharma R, Aksyuk V, Holland G, Liddle JA, High-Resolution Imaging and

Spectroscopy at High Pressure: A Novel Liquid Cell for the Transmission Electron Microscope. Microsc.

Microanal. 21, 1629–1638, (2015)

Big-Data Analytics Applied to In Situ Microscopy

Alex Belianinov,1,2 Stephen Jesse, 1,2 Gabriel Veith,3 Erik Endeve,4 Yawei Hui,4 Ganesh

Panchapakesan,1 Raymond Unocic1,2

1 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, TN 37831 2 Institute for Functional Imaging of Materials, Oak Ridge National Laboratory, Oak Ridge, TN 37831 3 Materials Science and Technology, Oak Ridge National Laboratory, Oak Ridge, TN 37831 4 Computer Science and Mathematics, Oak Ridge National Laboratory, Oak Ridge, TN 37831

Scanning (transmission) electron and associated focused ion beam microscopies spectroscopies have

proved to be powerful tools for visualization of structure and functionality of materials with atomic

resolution. Improvements in instrument hardware has allowed the determination of atomic positions with

sub-10 pm precision enabling visualization of chemical and mechanical strains as well as order parameter

fields. Today, growing interest in imaging processes in-situ: in gas or liquid environments has renewed

efforts in specialized instrument hardware. Relatedly, this resulted in a a wealth of extracted information

necessitating a drastic improvement in capability to transfer, store and analyze multidimensional data sets.

Current data volumes are already approaching the capacity for analysis on a local compute resource – like

a workstation computer. Soon computational clusters will be necessary in order to handle even the simplest

of operations in data visualization. These data generation volumes extend beyond issues in processing and

storage, but also in data transfer – particularly in experiments that rely on real time feedback to the tool

operator. This problem is complicated even further by the fact that many of the experiments summarized

may happen concurrently with parallel data flows coming from independent detectors.

In this talk, data from STEM and FIB in working with liquids and gas will be presented and discussed

considering data challenges faced by imaging communities. Practical approaches to big-data analytics to

extract real-space atomic information, automated image analysis, event detection, and compressed sensing

to track atomic scale changes and directly visualize molecular scaled interactions at well-defined model

interfaces, will be presented and discussed.

References:

[1] A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is a

DOE Office of Science User Facility. This research was funded by and by the Laboratory Directed

Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC,

for the U. S. Department of Energy.

Addressing Data Challenges for In-Situ Electron Microscopy

Stephen Mick1 and Benjamin K. Miller1

1. Gatan Inc., Pleasanton, CA, USA 94588

Advances in instrumentation and camera technology have led to a rapid increase in the amount and quality

of digital data captured during electron microscopy experiments. In particular, the recent transition to

high-speed, large field of view detectors makes possible the collection of hundreds of Gigabytes of high-

quality data from a single electron microscopy session.

This advent of large, fast cameras allows dynamic changes to be captured during in-situ experiments, but

the vast amount of captured data creates several challenges. New approaches to data handling, reduction,

and analysis are required. Moreover, workflows are needed to provide near-real-time analysis and

feedback at the microscope during data collection to enhance decision making during data collection. This

talk will discuss both the data challenges and strategies for working with fast detectors to maximize the

quality of collected data.

Environmental Control and Complete Sample Characterization for Investigating

Solid-Liquid Interfaces In Situ

Katherine L. Jungjohann1, Claire Chisholm1, Subrahmanyam Goriparti1, Katharine Harrison2, Andrew

Leenheer3, and Kevin Zavadil2

1. Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, USA. 2. Material, Physical & Chemical Sciences, Sandia National Laboratories, Albuquerque, USA. 3. Microsystems Science & Technology, Sandia National Laboratories, Albuquerque, USA.

We have found new research opportunities in liquid phase S/TEM through a combinatorial experimental

approach that includes exhaustive characterization of real-world-relevant materials prior to in-situ

experimentation, and increasing environmental control over the sample. In the 15 years since Williamson

et al. demonstrated the stability and electron transparency of SiN membrane windows for imaging liquid

phases within the TEM [1], there has been a gradual progression in this field towards increasing the control

over the specimen’s environment, control over the electron beam, and utilizing spectroscopy and different

imaging modes to increase the quality of data obtained [2-4]. The greatest obstacle in this field is the

acquisition of unperturbed images and spectra, as the high-energy electron beam can rapidly degrade the

material structure or reaction mechanism when capturing materials’ processes at the nanoscale in situ [5-

6]. Our approach has been to limit the number of electrons used, by imaging in STEM mode at 300 kV.

As fewer electrons produce more image noise for dynamic processes, it is important to fully understand

the sample structure and composition prior to the in-situ experiment. Additionally, it is necessary to have

precise control over the environmental conditions to properly interpret the reaction mechanism at solid-

liquid interfaces. Our approach will be detailed, including its implementation for corrosion and energy

storage applications, where future experimental design is directed towards a multimodal technique [7].

References:

[1] M. J. Williamson et al, Nat. Mater. 2 (2003), p. 532.

[2] F. M. Ross, Science 350 (2015), p. 1490.

[3] R. R. Unocic et al, Nanoscale 8 (2016), p. 15581.

[4] A. J. Leenheer et al, Microsc. Microanal. 21 (S3) (2015), p. 1293.

[5] K. Jungjohann et al, Microsc. Microanal. 18 (2012), p. 621.

[4] P. Abellan et al, Chem. Commun. 50 (2014), p. 4873.

[5] T. J. Woehl and P. Abellan, J. Microsc. 265 (2016), p. 135.

[7] This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science

User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National

Laboratories is a multi-mission laboratory managed and operated by National Technology and

Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for

the U.S. DOE’s National Nuclear Security Administration under contract DE-NA-0003525. The views

expressed in the article do not necessarily represent the views of the U.S. DOE or the United States

Government.

Cryo-STEM Mapping of Processes at Solid-Liquid Interfaces in Devices for Energy

Applications

Lena F. Kourkoutis1,2

1. School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853, USA 2. Kavli Institute for Nanoscale Science, Cornell University, Ithaca, NY 14853, USA

Solid-liquid interfaces play a key role in a range of processes, including electrochemical energy generation

and storage, but often lack characterization at sufficiently high spatial resolution. Here, I will discuss our

approach of using analytical cryo-STEM to understand processes at solid-liquid interfaces. Inspired by

electron microscopy of biological systems, these complex interfaces are stabilized by rapid freezing which

enables structural and spectroscopic studies by cryo-STEM/EELS. To gain access to internal interfaces of

samples and devices too thick to image directly, we have developed cryo-focused ion beam lift-out to

prepare thin lamellas for subsequent analysis by cryo-STEM. Using this technique, we demonstrate

structural and chemical mapping of internal solid-liquid interfaces in lithium-metal batteries. We identify

distinct dendrites and solid–electrolyte interphase layers, not previously observed. The insights into the

formation of lithium dendrites that our work provides demonstrate the potential of cryogenic electron

microscopy for probing nanoscale processes at intact solid–liquid interfaces in functional devices for

energy applications.

Following Nanoparticle Dynamics in Liquids with High Frame Rate CMOS

Cameras

See Wee Chee1,2, Utkarsh Anand1,2,3, Abhik Datta1,2, Duane Loh1,2, Utkur Mirsaidov1,2,3,4

1. Centre for Bioimaging Sciences and Department of Biological Sciences, National University of

Singapore, 14 Science Drive 4, Singapore 117543 2. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117551 3. NUSNNI-Nanocore, National University of Singapore, 5A Engineering Drive 1, Singapore, 117576 4. Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore,

6 Science Drive 2, Singapore 117546

The development of new CMOS electron cameras has provided with us with the ability to follow material

dynamics at the millisecond timescale. Furthermore, CMOS cameras with direct electron detection have

been shown to be powerful tools for the low dose imaging of beam sensitive specimens, such as biological

macromolecules. Here, I will first discuss experiments where we use a direct electron detection camera to

track the motion of Au nanorods at 300 frames per second and at electron fluxes of 20-80 electrons/(Å2•s).

The movies show that both rotation and translation of the nanorods consist of intermittent motion with

timescale of a few milliseconds and exhibit characteristics of anomalous diffusion. We also find that at

the lowest electron flux of 20 electrons/(Å2•s), the nanorods no longer move due to beam induced motion.

Next, I will talk about the lessons that we had learnt about optimizing the imaging conditions for in situ

experiments with these high frame rate cameras. Since liquid cell experiments are generally sensitive to

electron beam artefacts, it is often necessary to be as close to low dose imaging conditions as possible.

Under such conditions, there is an inherent tradeoff between spatial and temporal resolution because the

images get increasingly noisy with decreasing electron flux on the camera. Here, I will discuss results

where we look at the change in localization error as we decrease the electron flux at the camera. Lastly, I

will briefly describe the work we are doing at the Center of BioImaging Sciences to reduce the size of the

large, noisy datasets comes with using these cameras for in situ experiments at the very low electron fluxes

used for cryo-TEM imaging.

Towards Reproducible Chemical Reactions in Graphene Liquid Cell TEM

Experiments

Matthew R. Hauwiller1, Justin Ondry1 and A. Paul Alivisatos 1,2,3,4

1. Department of Chemistry, University of California Berkeley, Berkeley, California, United States. 2. Department of Materials Science and Engineering, University of California Berkeley, Berkeley,

California, United States. 3. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United

States 4. Kavli Energy NanoScience Institute, University of California Berkeley and Lawrence Berkeley

National Laboratory, Berkeley, California, United States

The development of liquid cell electron microscopy technologies has provided an opportunity to view

previously unseen nanoscale processes, but a more rigorous understanding and control of the reaction

environment, especially electron beam sample interactions, is necessary to systematically study

nanomaterials. We have recently developed strategies to control many aspects of the liquid cell

environment using a model system of metallic nanocrystal etching. We are able reproducibly fabricate

graphene liquid cell pockets, control the concentration of reagents, and automate our control of the

electron beam dose rate and data acquisition, which allows us to further understand the chemistry in the

liquid pocket. The first step is to reproducibly fabricate graphene liquid cell samples, allowing for many

comparable experiments and reliable tuning of pocket contents. This has been achieved through

refinement of the original graphene liquid cell technique [1] which we recently reported in a methods

publication. [2]

In many of the experiments where reactions are initiated by electron beam radiolysis products, fast and

accurate tuning of the dose rate is important for studying kinetic reactions. This is difficult to achieve by

manually controlling electron beam dose rate. To get around this problem, we have developed a custom

script which calibrates the condenser system of the TEM to the dose rate measured by the camera. Further,

this calibration is integrated with our movie acquisition allowing quick, reproducible dose rate changes

from searching at low dose rates to data acquisition.

Using the etching of gold nanocrystals, we have learned that the concentration of FeCl3 etchant controls

which atoms are removed by modulating the chemical potential, and the electron beam dose rate controls

the rate at which atoms are removed from the gold nanocrystal. By deepening our understanding of the

liquid environment for in-situ experiments, this technique can become valuable to a of materials scientists

studying nanocrystal growth and transformation mechanisms. In this poster, we will share the techniques

we use to reproducibly fabricate graphene liquid cell pockets, the computational tools to automate the data

collection, and the insights we have made regarding beam-initiated chemistry in the graphene liquid cell.

We have shown the graphene liquid cell technique can be reproducible and comes with added benefits of

low start-up costs and the ability to work with traditional TEM holders in any instrument. Further, the

strategies we have employed to realize reproducibility in graphene liquid cell experiments should translate

to traditional silicon nitride liquid cell holders, gas cells, and environmental TEM experiments.

References:

[1] J. M. Yuk et al., Science. 336, 61–64 (2012).

[2] M. R. Hauwiller, J. C. Ondry, A. P. Alivisatos, J. Vis. Exp. 135, 1–9 (2018).

Figure 1. When etching cubes in the graphene liquid cell, the modulating the potential by adjusting the

initial concentration of FeCl3 control the facets on the tetrahexahedra intermediate.

Quantification of Gas Cooling Effect on in situ Heating Devices Used in Environmental TEM

Meng Li1,3, Degang Xie1, Xixiang Zhang2, Judith C. Yang3, Zhiwei Shan1

1. Center for Advancing Materials Performance from the Nanoscale (CAMP-Nano), State Key

Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China. 2. King Abdullah University of Science & Technology (KAUST), Division of Physical Science and

Engineering, Thuwal 23955-6900, Saudi Arabia 3. Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA (USA)

In situ heating experiment in TEM is a very powerful tool in understanding dynamic process of

temperature related material behaviors, such as phase transformations, catalytic reactions, growth of

nanostructures etc. An ideal stage for in situ TEM heating requires low spatial drift and accurate

temperature measurement and control during the experiment process. Current commercial heating stages

can be divided into three categories: conventional furnace heating, direct filament heating and MEMS

based heating chips. In recent years, although the spatial resolution of current heating stages has been

improved to atomic scale using MEMS heater, accurate temperature control lags far behind, especially in

case of gaseous environments. With the development of the environmental TEM in the past few years,

increasing numbers of heating experiments are carried out in gas environments, especially in the field of

catalysts. The introduction of gas usually cools down the heated parts, and fluctuation of gas pressure and

flow state also dynamically change the sample temperature. Therefore, accurate temperature measurement

is critical to achieve precise temperature control in environmental TEM. However, most of the current in

situ heating stages are designed without real-time temperature sensing, the temperature is only calculated

from calibrations in vacuum.

In this work, a home-made MEMS based in situ heating stage with real-time temperature sensing and

feed-back temperature control will be shown. With exquisite structural optimization, we also achieved so

far the lowest thermal drift rate for in situ TEM imaging during temperature ramping1. Using this new

device, the dynamic change of temperature with gas pressure is quantified systematically with several

conventional gas species like O2, N2, H2 and Air. Our presentation will introduce this new heating device

and would provide a general reference for estimation of the actual sample temperature for device without

temperature sensing in gas environments.

References:

[1] Li, M. et al. Effect of hydrogen on the integrity of aluminium-oxide interface at elevated temperatures.

Nat. Commun. 8, 1–7 (2017).

[2] The authors acknowledge funding from Natural Science Foundation of China (NSFC) (51231005,

11132006 and 51321003). The authors thank Dr. Longqing Chen from Nanofabrication Core Lab, King

Abdullah University of Science and Technology (KAUST) for the help in the MEMS fabrication.

Figure 1. (a) Schematic illustration of the experimental setup inside the environmental TEM. The MEMS

heating chip is installed on the heating holder. The gas is injected into the specimen chamber using a gas

injection nozzle, the gas pressure is measured by the vacuum gauge. (b) Illustration of functioning part of

the home-made MEMS heater with both heating and temperature sensing availability. (c) Schematic model

of the gas cooling experiment.

Probing Dynamic Processes of the Initial Stages of Cu(100) Surface Oxidation by correlated in situ

Environmental TEM and Multiscale Simulations

Meng Li1, Matthew T. Curnan1, Xinyu Li2, Graeme Henkelman2, Wissam A. Saidi3 , Judith C. Yang1,4 1Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA (USA) 2Department of Chemistry and the Institute for Computational and Engineering Sciences,

University of Texas at Austin, Austin, TA (USA) 3Department of Mechanical Engineering & Materials Science, University of Pittsburgh, Pittsburgh, PA

(USA) 4Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA (USA)

Corrosion is one of the biggest challenges facing the safe and reliable use of metals and alloys, especially

under elevated temperatures. Understanding the microscopic mechanisms for surface oxidation is critical

to unveil the mysteries of corrosion, and will also facilitate research in fields such as environmental

stability, high-temperature corrosion, and catalytic reactions. The process of surface oxidation can be

divided into three stages, namely oxygen chemisorption, oxide nucleation and growth, and bulk oxide

growth. Despite numerous studies focusing on the initial stage of oxidation that commences with oxygen

chemisorption on clean metal surfaces and ends with oxide nucleation and growth, this stage remains

poorly understood due to the lack of experimental methods available for studying this stage. For example,

surface science techniques such as Scanning Tunneling Microscopy (STM) and atomistic simulations have

shown that after oxygen chemisorption, clean Cu(100) surfaces will undergo several surface

reconstructions, demonstrating c(2×2) reconstruction and missing row reconstruction (MRR) structures[1].

However, characterization of the atomic mechanisms forming reconstructions, as well as determination of

whether reconstruction is necessary for oxide nucleation, have not been conclusively investigated, given

the lack of direct experimental observation.

In this work, using state-of-the-art Environmental TEM (ETEM) (Hitachi H-9500 operating at 300 keV)

and multiscale atomistic simulation, we explore the dynamic processes of the initial stages of Cu(100)

oxidation. By in situ annealing and reducing Cu(100) thin films inside the ETEM with flowing H2 gas

injection, pristine Cu films with faceted holes were created, enabling observation of surface

reconstructions as well as oxide nucleation and growth processes on the facets from the cross-sectional

view. Oxidation experiments were carried out at various temperatures with flowing O2 gas to study the

initial stages of oxidation. As is shown in Figure 1, surface reconstruction was observed prior to oxide

nucleation and the dynamic process of oxide growth was observed, delimiting the initial oxidation stage

threshold at which ETEM can effectively discern dynamic processes.

In order to understand what contributes to these differences in oxidation behavior, computational study

was carried out to investigate the initial stage of oxidation up to the experimental threshold between

surface reconstruction and oxide nucleation [2-4]. Single initial oxidation stage events from oxygen

chemisorption to surface reconstruction are first assessed using the Nudged Elastic Band (NEB) method

on systems modeled with Reactive Force Field (RFF) potentials (Figure 2). Oxide nucleation and growth

is then affordably modeled at size scales consistent with ETEM results. This simulation methodology

forms a feedback loop with ETEM results, allowing computational and experimental results to validate

one other. Ultimately, these results can be used to improve current understanding of how surface structure

impacts the initial stage of oxidation on an atomistic scale, as well as how surface reconstruction enables

oxide nucleation to conclude initial stage oxidation [5].

References:

[1] Zhu, Q., Zou, L., Zhou, G., Saidi, W. A. & Yang, J. C. Surf. Sci. 652, 98–113 (2016).

[2] Saidi, W. A., Lee, M. Y., Li, L., Zhou, G. W. & McGaughey, A. J. H. Phys. Rev. B 86, 245429-245421-

245428 (2012).

[3] Zhu, Q., Saidi, W. A. & Yang, J. C. J. Phys. Chem. C 119, 251-261(2015).

[4] Zhu, Q., Saidi, W. A. & Yang, J. C. J Phys. Chem. Lett 7, 2530-2536 (2016).

[5] The authors acknowledge funding from National Science Foundation (NSF) grants DMR-1410055,

NSF DMR-1508417, and DMR-1410335, as well as support from Hitachi-High-Tech and technical

assistance from the Nanoscale Fabrication and Characterization Facility (NFCF) in the Petersen Institute

of Nano Science and Engineering (PINSE) at the University of Pittsburgh.

Figure 1. (a) HRTEM image of the MRR Cu(100) surface, the inset shows the atomic model for MRR;

(b) HRTEM image showing the layer-by-layer growth of Cu2O island on Cu(100) surface.

Figure 2. MD simulation depicting widespread Cu ejection, O subsurface diffusion, and surface reconstruction adjacent to the Cu(001){110} facet.

Determination of Surface Dynamics on CeO2 Nanoparticles using Time-Resolved

High-Resolution TEM

Ethan L. Lawrence1, Barnaby D.A. Levin1, Benjamin K. Miller2, & Peter A. Crozier1

1. School for the Engineering of Matter, Transport and Energy, Arizona State University, Tempe Arizona

85287-6106. 2. Gatan, Inc., Pleasanton, CA 94588, USA.

Characterizing the structural evolution of catalyst nanoparticle surfaces can provide insights into the active

motifs responsible for catalysis. High-resolution transmission electron microscopy (HRTEM) has been

used extensively to study surface dynamics on nanoparticles using in situ imaging techniques [1]. Recent

advances in imaging detector technology, namely direct detection cameras with fast acquisition modes,

have enabled many new materials phenomena to be investigated, such as the imaging of each sequential

step of the synthesis of Ni silicide nanostructures within Si nanowires [2]. With the advent of fast image

acquisition, large datasets, otherwise known as “big data”, are becoming increasingly common and new

developments in data storage, data mining, and processing methods are necessary [3]. Thus, batch

processing techniques are essential for reducing processing time and extracting useful information from

large, often noisy image datasets. By combining advanced acquisition and processing techniques, time-

resolved HRTEM will enable new insights into the structural evolution of nanoparticle surfaces. In this

work, we use time-resolved HRTEM to achieve high spatial and temporal resolution of surface atom

migration on CeO2 nanoparticles, a material that is used extensively in catalysis applications due to its

oxygen exchange properties [4].

An aberration-corrected FEI Titan ETEM equipped with a Gatan K2 IS direct detection camera (with high

detection quantum efficiency) was used to image CeO2 nanoparticles at 400 frames/second and 104 e-

/(Å2s) in vacuum. A single frame of 1/400 second exposure is shown in Figure 1a), and due to the fast

acquisition rate, the signal-to-noise ratio of the image was low. To reduce noise in each individual frame,

a Kalman filter was applied to an image stack of ~9000 frames and Figure 1b) shows the resulting filtered

image from Figure 1a). For each pixel in the image, the Kalman filter uses a prediction step to produce an

estimate of the pixel intensity and its uncertainty. The prediction is then averaged with the measured value

from the image through a weighted average, with more weight given to estimates with higher certainty,

producing a “filtered” value. The “filtered” value is then used to update the prediction for the next image

frame. Thus, the Kalman filter is a computationally light, recursive filtering technique which adapts at

each time step to significantly reduce noise in each frame. MIPAR, a commercially available software

with a recipe-based image processing method, was used to identify atomic column positions and quantify

column intensities [5]. Using MIPAR’s batch processing feature, each image from the ~9000 image stack

was analyzed with the same recipe. Figure 2a) shows the resulting mask of atomic columns (shown in red)

that was detected from a single frame during processing. The mask was then used to generate

measurements, including the position, area, intensity mean, and integrated intensity of each atomic

column, from the unfiltered image frames. The integrated intensity quantization of each atomic column is

overlaid on the image in Figure 2b) and was used to estimate the number of atoms within each column.

With this approach, atoms within the small CeO2 nanoparticle were tracked with 1/400 second temporal

resolution for ~30 seconds. Additional details outlining the batch processing workflow and relating the

atomic movement on the CeO2 nanoparticle surface to oxygen exchange processes will be presented [6].

References:

[1] Jinschek, J.R., Chemical Communications 50 (2014), p. 2696-2706.

[2] Panciera, F., et al, Nature Materials 14 (2015), p. 820-825.

[3] Taheri, M.L., et al, Ultramicroscopy 170 (2016), p. 86-95.

[4] Trovarelli, A., and Llorca, J., ACS Catalysis 7 (2017), p. 4716-4735.

[5] Sosa, J.M., et al, Integrating Materials and Manufacturing Innovation 3 (2014), p. 10.

[6] We gratefully acknowledge support of NSF grant DMR-1308085, the use of ASU’s John M. Cowley

Center for High Resolution Electron Microscopy and use of the K2 IS camera courtesy of Gatan.

Figure 2. a) Atomic column detection mask (red) determined through image batch processing in

MIPAR b) Atomic column integrated intensity overlaid on image.

Figure 1. HRTEM images of a CeO2 nanoparticle in (111) projection. a) 1/400 second-exposure

raw image b) Kalman-filtered image of raw image from a).

a) b)

Inte

gra

ted

In

ten

sity (

co

un

ts)

(x1

04)

a) 5

4.5

4

3.5

3

2.5

2

1.5

b)

Atomic-level Observation of Platinum Dissolution and Re-deposition Using Liquid

Electrochemical TEM

Shinya Nagashima1, 2, Toshihiro Ikai3, Yuki Sasaki4, Tadahiro Kawasaki4, Tatsuya Hatanaka5, Hisao

Kato6, Keisuke Kishita1, 2

1. Material Creation & Analysis Department, Toyota Motor Corporation, Toyota, Japan 2. Advanced Technology, Toyota Motor Europe, Zaventem, Belgium 3. Catalyst Design Department, Toyota Motor Corporation, Toyota, Japan 4. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, Japan 5. Sustainable Energy & Environment Department, Toyota Central R&D Labs., Inc., Nagakute, Japan 6. MEGA Development Department, Toyota Motor Corporation, Toyota, Japan

A polymer electrolyte fuel cell (PEFC) is a promising energy source for fuel cell vehicles. Platinum

nanoparticles are typical electrocatalysts used in PEFCs. While reduction of Pt usage and improvement in

their durability are important subjects for developing advanced PEFCs, catalytic performance of Pt

nanoparticles is degraded as repetitious operation of PEFC. Pt nanoparticles’ surface area is decreased

with a redox process promoting dissolution and re-deposition [1, 2]. To optimize material design and

operating conditions of PTFCs, it is essential to understand the Pt dissolution and re-deposition

mechanisms in real space.

To clarify the Pt dissolution and re-deposition behaviors relating with electrochemical potentials, we have

developed an electrochemical TEM observation technique using a liquid flow cell TEM holder with

electrical biasing capabilities (Poseidon, Protochips Inc.) and an environmental TEM with the Cs corrector

(Titan ETEM, FEI Company)[3]. An electrochemical cell for simulating an activated PEFC environment

was comprised of in-house developed MEMS chips and flowing electrolyte of 0.1 M aqueous solution of

HClO4. Pt polycrystalline thin film was deposited onto the MEMS chip as a model catalyst. We performed

electrochemical measurements and dynamic TEM observations simultaneously.

Figure 1 shows configurations of the developed MEMS chip. The MEMS chip has a Pt electrode with a

hole array pattern on a SiN viewing window which enables to observe an interface between Pt electrode

and liquid at corners of SiN viewing windows. Figure 2 shows a low magnification TEM image of the

viewing windows (Fig. 2(a)) and EELS spectra for cell thickness estimation (Fig. 2(b)). The MEMS chip

enables to avoid bowing effect of SiN windows into a vacuum and achieve a cell thickness of ~110 nm

which dramatically improved spatial resolution of a TEM image. Furthermore, we have employed the

energy filter (GIF Tridiem, Gatan, Inc.) to eliminate innelastically scattered electrons blurring a TEM

image. Figures 3 show a series of in situ energy filtered TEM images at an interface of polycrystalline Pt

thin film electrode and 0.1 M HClO4 electrolyte during a potential step voltammetry. Elevating the

potential from 0.1 VRHE to 1.2 VRHE (Figs. 3(a), (b)), some part of Pt dissolved from its surface. On the

other hand, putting the potential back to 0.1 VRHE (Fig. 3(c)), Pt was re-deposited at a surface of Pt

electrode. Thus, we have achieved an atomic-scale observation of electrochemical behaviour of a Pt

catalyst in a liquid electrolyte for the first time. In conclusion, we believe that in situ liquid electrochemical

TEM is a powerful tool to understand electrochemical behaviors of solid-liquid interfaces in atomic scale.

References:

[1] Y. Shao-Horn et al., Top catal, 46, (2007), p. 285-305.

[2] J. C. Meier et al., ACS Catal 2, (2012), p. 832-843.

[3] S. Nagashima et al., Microsc. Micro anal., 21(suppl 3), (2015), p.1295-1296.

Figure 1. (a-c) Optical microscope images of a developed MEMS chip. (b), (c) Enlarged images

correspond to the red rectangles in (a), (b), respectively. (d) A schematic cross section diagram of an

electrochemical cell in a TEM chamber.

Figure 2. (a) A low magnification TEM image of the SiN viewing windows. The cell was filed with

electrolyte. (b) EELS spectra obtained from a corner and a center of the viewing windows with

electrolyte, and the viewing windows with no liquid, respectively. Each cell thickness was estimated as

SiN thickness.

Figure 3. In situ energy filtered TEM images of Pt polycrystalline thin film electrode during a potential

step voltammetry. The energy filter was set to zero loss with 30 eV slit width. The sequence of the

applied potential was 0.1 V, 0.8 V, 1.0 V, 1.2 V and 0.1 V vs. RHE. Each potential was kept for 3 min.

(a) Initial state at 0.1 VRHE. (b) Oxidation state at 1.2 VRHE. (c) Reduction state at 0.1 VRHE.

Atomic-Resolution Operando Observations of Nanostructured Pt/CeO2 Catalysts

Performing CO Oxidation

Joshua L. Vincent and Peter A. Crozier

School for the Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona

85287-6106

Heterogeneous catalysts accelerate reactions by reducing the activation energy for the rate limiting step.

The specific locations on the catalyst at which the activation energy is lowest – the so-called active sites

– are poorly understood, as catalytically relevant atomic structures only emerge under reaction conditions.

Even with in situ TEM, atomic-level structure-activity relationships are difficult to determine due to the

large number of surface structures that form dynamically during catalysis. Discerning catalytically

relevant structures may be facilitated by studying supported metal systems in which the active sites are

localized to the metal-support interface. The rate of CO oxidation (CO + 0.5O2 CO2) over Pt/CeO2 has

been shown to depend strongly on the perimeter length of the metal-support interface [1]. However, at

present there is no experimental data on the atomic structures that comprise the Pt/CeO2 interface during

catalysis. Here, we use operando techniques in an image-corrected environmental TEM (AC-ETEM) to

visualize the atomic structures forming at and near the Pt/CeO2 interface during CO oxidation.

Nanostructured CeO2 cubes were loaded with 2 wt. % Pt by a photodeposition technique, and their activity

for CO oxidation was confirmed [2]. An aqueous dispersion of the catalyst powder was wet-impregnated

onto an inert borosilicate glass microfiber pellet, leading to a loading of ~1 mg Pt/CeO2 [3]. A drop of the

dispersion was placed onto a 200 mesh Ta grid pre-reduced in H2 at 400 °C for 2 hours. The Ta mesh and

pellet were loaded into an Inconel Gatan furnace-style heating holder. The Inconel holder was determined

to be unreactive at the temperatures of interest in this study. An FEI Titan AC-ETEM tuned to a negative

Cs condition was used for operando imaging. Approximately 1 Torr of CO and 0.5 Torr of O2 was admitted

into the cell. The pressure stabilized over an hour and then the sample was heated to 350 °C. Images were

acquired at 300 kV with an incident electron flux of ~1,000 e-/Å2/s. A residual gas analyzer (RGA)

measured the gas composition within the cell, allowing for changes in activity to be tracked. Estimates of

the in situ conversion, XCO, can be made with the below equation, where ij is the RGA current reported for

species j, ij[0] is the current reported at zero conversion, and σj is the standard ionization cross section [3].

𝑋𝐶𝑂 =𝐶𝑂𝑟𝑒𝑎𝑐𝑡𝑒𝑑𝐶𝑂𝑖𝑛

=𝐶𝑂2𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑

𝐶𝑂𝑖𝑛~(

𝑖𝐶𝑂2 − 𝑖𝐶𝑂2[0]

𝜎𝐶𝑂2)/𝑖𝐶𝑂[0]𝜎𝐶𝑂

Figure 1a) shows the RGA current reported for CO, O2, and CO2. When the sample temperature increases

to 350 °C (at approximately 4 minutes), the CO2 signal is seen to increase while the CO and O2 signals

simultaneously decrease – demonstrating the in situ conversion of CO and O2 to CO2. Figure 1b) plots the

in situ conversion obtained at this temperature as a function of time. After 20 minutes, the conversion

approaches a value of ~16%. Interestingly, our work with this catalyst showed that it achieves conversions

approaching 100% at 200 °C [2]. The lack of in situ conversion below 350 °C suggests that too little

catalyst was loaded onto the operando pellet. However, since the catalyst is known to be active at 200 °C,

interfacial atomic behavior observed at this temperature can be inferred to correspond to the processes of

catalysis. Figure 2 shows a series of AC-ETEM images acquired 1 second apart at 200 °C in 1 Torr of CO

and 0.5 Torr of O2. A Pt nanoparticle is seen to restructure dynamically, suggesting that the bonding with

the underlying CeO2 is constantly changing. The inset FFTs in (b) and (c) reveal that the Pt nanoparticle

rotates into (on the left side) and away from (on the right side) the CeO2 support, through an angle of 6.8°.

In the FFTs, spots corresponding to CeO2 do not move, indicating that the change in angle is due to Pt

restricting and not image drift. The interfacial instability driving the nanoparticle’s restructuring may be

caused by the rapid creation and annihilation of oxygen vacancies during the Mars van Krevelen oxidation

process, which is the hypothesized mechanism for CO oxidation over Pt/CeO2 catalysts [1, 4].

References:

[1] Cargnello, M., et al; Science 341 (2013), p. 771-773.

[2] Vincent, J. L., O’Keefe, V., and Crozier, P. A., ibid.

[3] Miller, B. K., Barker, T. M., and Crozier, P. A.; Ultramicroscopy 156 (2015), p. 18-22.

[4] We gratefully acknowledge the support of NSF grant CBET-1604971 and ASU’s John M. Cowley

Center for High Resolution Electron Microscopy.

Figure 1. In situ mass spectrometry detects conversion of CO and O2 to CO2 when the sample is

heated to 350 °C, at t = 4 minutes (a). The conversion can be estimated from the RGA current, and

approaches ~16% (b). Signals were measured every 10 seconds; symbols shown every 35 data points.

0 4 8 12 16 20

0

200

400

600

800

1000

Ion

Cu

rre

nt / n

A

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CO

O2

CO2

0 4 8 12 16 20

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n / %

Time / minutes

(a) (b)

Figure 2. AC-ETEM images of a Pt nanoparticle attached to the edge of a CeO2 cube, taken in 1.5

Torr of stoichiometric CO and O2 at 200 °C (a). The inset FFTs show that the particle rotates through

an angle of 6.8°, with the rotation directed as a rocking along the plane of the metal-support interface.

(a) (b) (c)

Mapping the fields in liquid phase: opportunities and challenges

Tanya Prozorov1, Trevor P. Almeida 2, András Kovács 3 and Rafal E. Dunin-Borkowski3

1 US DOE Ames Laboratory, Division of Materials Science and Engineering, Ames, IA 50011, USA. 2 †Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK 3 Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute,

Forschungszentrum Jülich, 52425 Jülich, Germany

The mapping of electrostatic potentials and magnetic fields in liquids using electron holography has

been considered to be unrealistic. However, it was recently demonstrated that the advanced transmission

electron microscopy (TEM) technique of off-axis electron holography can be carried out using a

specially-designed fluid cell TEM sample holder. Specifically, we studied both intact and fragmented

cells of magnetotactic bacterial strain Magnetospirillum magneticum AMB-1 in a 800-nm-thick layer of

liquid using electron holography. Although the holographic object and reference wave both pass through

liquid, the recorded electron holograms show sufficient interference fringe contrast to allow

reconstruction of the electron phase shift and mapping of the magnetic induction of the bacterial

magnetite nanocrystals. Magnetotactic bacteria biomineralize ordered chains of magnetite or greigite

nanocrystals with nearly perfect crystal structures and strain-specific morphologies. These

microorganisms have been established as one of the best model systems for investigating the

mechanisms of biomineralization. The biogenic magnetite crystals that they form have crystal habits and

properties that have been studied in great detail. Furthermore, the magnetic fields that are associated

with ferrimagnetic nanocrystal chains biomineralized by magnetotactic bacteria have been visualized

using off-axis electron holography. We selected this specimen based on extensive reports of the

characterization of the chemistry and magnetism of magnetotactic bacteria by a variety of methods, as

well as on our own report on imaging viable bacterial cells in liquid using an in situ fluid cell TEM

specimen holder. We began by measuring the magnetic fields of magnetite nanoparticles located both

within and outside hydrated bacterial cells. We also estimated the MIP of the liquid in the fluid cell

holder.

Off-axis electron holography in liquid offers great promise for studying interactions between magnetic

nanoparticles, as well as for the visualization of nanoparticle response to external magnetic stimuli with

nanometer spatial resolution. Prospects for other applications of in situ off-axis electron holography in a

liquid cell include research into magnetic resonance imaging, tissue repair and targeted drug delivery.

The method also promises to be applicable to other interfacial phenomena in liquids, including the direct

imaging of electrochemical double layers at solid-liquid interfaces, which is of relevance to colloidal

suspensions, catalysis, nanofluidic devices, batteries and tribology. Other potential applications include

studies of biomineralization and the mapping of electrostatic potentials associated with protein

aggregation and folding. The technique promises to open a new era in the physics of liquids by revealing

what role magnetostatic and electrostatic interactions play in phase transformations, the physics of

coalescence, the effects of confinement and other complex phenomena.

The poster describes some of the challenges of performing in situ magnetization reversal experiments

using a fluid cell specimen holder, discusses approaches for improving spatial resolution and specimen

stability, and outlines future perspectives for studying scientific phenomena, ranging from interparticle

interactions in liquids and electrical double layers at solid-liquid interfaces to biomineralization and the

mapping of electrostatic potentials associated with protein aggregation and folding.

References:

[1] T. Prozorov, T.P. Almeida, A. Kovács, R.E. Dunin-Borkowski “Off-axis electron holography of

bacterial cells and magnetic nanoparticles in liquid”, Journal of the Royal Society Interface, Interface 14

20170464 (2017). http://dx.doi.org/10.1098/rsif.2017.0464

[2]. This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic

Energy Sciences, Research, Materials Sciences and Engineering Division . The research was performed

at the Ames Laboratory, which is operated for the U.S. Department of Energy by Iowa State University

under Contract No. DE-AC02-07CH11358.

Figure 1 shows schematic diagrams of the experimental setup for TEM imaging using a fluid cell

(Fig. 1A) and off-axis electron holography (Fig. 1B). Upon assembly of the fluid cell, a small amount of

liquid is sandwiched between two electron-transparent SiN membranes. When examining bacterial cells,

the microorganisms and surrounding growth medium are trapped by the windows, resulting in a

mechanical stress on the bacterial cell walls. In the present study, the holographic reference wave was

usually obtained through a layer of liquid, in addition to passing through two 50-nm-thick layers of SiN.

In situ Insights into the Uncorking and Oxidative Decomposition Dynamics of Gold Nanoparticle Corked Carbon Nanotube Cups for Drug Delivery Stephen D. House1, Christopher M. Andolina1, Seth C. Burkert2, Alexander Star2 and Judith C. Yang1 1. Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA (USA). 2. Department of Chemistry, University of Pittsburgh, Pittsburgh, PA (USA). Nitrogen-doped carbon nanotube cups (NCNCs) are an intriguing material for drug-delivery applications due to their cup-shaped morphology and their propensity for chemical modification. NCNCs can readily uptake small molecules, which can be effectively sealed within the inner cavity through the formation of nanoparticles (NP) on the open end of the cup. The resulting nanocapsules can then undergo oxidative biodegradation through biologically available peroxidase enzymes, [1] effectively releasing their loaded cargo. This mechanism has been applied for Au NP-corked NCNCs loaded with chemotherapeutic molecules for immunotherapy in melanoma models.[2] However, a better understanding of the mechanisms of cargo release – through uncorking and/or nanotube degradation – is crucial for improving their effectiveness as drug delivery platforms. The environmental transmission electron microscope (ETEM) is a powerful tool to directly investigate these questions, combining sub-nanoscale spatial resolution with the ability to image Au NP-NCNCs under similar gas, thermal, and liquid environments as their intended applications. In this work, we present our in situ ETEM study of the dynamic oxidation-dependent uncorking and degradation of Au NP-NCNCs. NCNCs were synthesized using a liquid (a mixture of xylenes, acetonitrile, and ferrocene) injection chemical vapor deposition method. The resulting stacked NCNCs were separated into short stacked segments [3,4] and corked with Au NPs through a sodium citrate reduction of hydrogen tetrachloroauric acid. TEM specimens were prepared from aqueous solutions of the NCNCs. We used a Hitachi H9500 ETEM equipped a homebuilt multi-species gas injection system and specialized sample heating holders to study the structure of the Au NP-capped NCNCs and the dynamics of their uncorking and subsequent degradation in situ. Structural examination of the NP-capped NCNCs revealed a multilayered tube structure, typically with multiple internal compartments. The Au NP morphology consisted of either a cap (interacting only with the uppermost lip of the NCNC) or plug (extending deeper into the tube). Under vacuum, the corked NCNCs exhibited remarkable tolerance to temperatures of up to 800 °C, though the internal structures of the carbon tubes exhibited restructuring at around 500 °C. The segmented cavities transformed from truncated cones in shape to round-capped cylindrical or ovoid cavities, resulting in pressurization of the cavities. The Au NP caps were slowly "pulled" into the tubes at high temperatures (700-750 °C) while the Au plugs showed no meaningful change. Upon exposure to ~10-2 Pa of O2, however, the ingrown Au plugs were ejected from the tubes at a temperature-dependent rate that increased 2-3 orders of magnitude from 400 °C to 800 °C. This uncorking was of a stepwise, punctuated nature, rather than continuous. Importantly, the onset of uncorking occurred prior to any observed oxidative degradation of the NCNCs, significant decomposition of which required temperatures of ~500 °C. The exterior walls and any interior walls of cavities that were exposed (e.g., from a breach) exhibited the same manner of attack. The oxidation primarily initiated at the rims (exterior wall) and cup bottoms (interior wall) of each of the NCNCs,

progressing along the cup walls. Oxidation of the exterior walls typically proceeded at a slower rate and after a period of delay, attributed to the presence of an amorphous carbon layer on the outside of the tube, which could act as a sacrificial barrier hindering oxidation. In all cases, once oxidation began, it occurred along the entire length of the tube, with no preference for the ends. In contrast, interior cavities without an obvious breach exhibited an isotropic thinning of their walls, indicating a different mechanism was involved. This behavior is currently under investigation. It is important to note that the oxidative degradation of the NCNCs in aqueous solution may not necessarily proceed by the same mechanisms as these solid-gas reactions. For this reason, ETEM experiments are underway using an in situ liquid cell holder to study the uncorking and degradation reactions in the enzymatic solution environments. Surface chemistry changes are being explored by in situ X-ray photoelectron spectroscopy experiments to correlate with the gas-based ETEM structural changes. The knowledge gained from these studies will enhance the tailoring of the Au NP-corked NCNCs properties for a more effective therapeutic delivery. [5] [1] I Vlasova, et al., Toxicology Applied Pharmacology 299 (2016), p. 58. [2] Y Zhao, et al., Journal of the American Chemical Society 137 (2015), p. 675. [3] Y Tang, et al., Journal of Physical Chemistry C 117 (2013), p. 25213. [4] Y Zhao, et al., ACS Nano 6 (2012), p. 6912. [5] This work was supported by NSF DMR grants #1508417 and 1410055, NSF DMREF #CHE-1534630, NSF career award #0954345, NIH R01ES019304, and the ETEM Catalysis Consortium (ECC, funded through U. Pitt and Hitachi High Technologies). The microscopy work was performed at the Peterson Institute for NanoScience and Engineering (PINSE) Nanoscale Fabrication and Characterization Facility (NFCF) at U. Pitt. The authors would like to acknowledge Mr. Matt France and Dr. Susheng Tan for their assistance with the experimental setup.

Figure 1. Selected stills from in situ ETEM videos showing examples of (a) uncorking of an Au NP plug (scalebar = 100 nm) and (b) oxidation of an NCNC (scalebar = 50 nm). The triangle indicates the bottom of an exposed stacked nano-cup, one of the initiation sites.