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Publication list for Themis ETEM for Materials Science

Title: Stable amorphous georgeite as a precursor to a high-activity catalyst
Authors: Simon A. Kondrat, Paul J. Smith, Peter P. Wells, Philip A. Chater, James H. Carter, David J. Morgan, Elisabetta M. Fiordaliso, Jakob B. Wagner, Thomas E. Davies, Li Lu, Jonathan K. Bartley, Stuart H. Taylor, Michael S. Spencer, Christopher J. Kiely, Gordon J. Kelly, Colin W. Park, Matthew J. Rosseinsky, Graham J. Hutchings
References: Nature (2016)  
Date: February 2016
Abstract
Title: Stable amorphous georgeite as a precursor to a high-activity catalyst
Authors: Simon A. Kondrat, Paul J. Smith, Peter P. Wells, Philip A. Chater, James H. Carter, David J. Morgan, Elisabetta M. Fiordaliso, Jakob B. Wagner, Thomas E. Davies, Li Lu, Jonathan K. Bartley, Stuart H. Taylor, Michael S. Spencer, Christopher J. Kiely, Gordon J. Kelly, Colin W. Park, Matthew J. Rosseinsky, Graham J. Hutchings
References: Nature (2016)  
Date: February 2016
Abstract: Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable-and hence little known and largely ignored-georgeite. The first three of these minerals are widely used as catalyst precursors for the industrially important methanol-synthesis and low-temperature water-gas shift (LTS) reactions, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite; with few exceptions it uses sodium carbonate as the carbonate source, but this also introduces sodium ions-a potential catalyst poison. Here we show that supercritical antisolvent (SAS) precipitation using carbon dioxide , a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts.
Title: Oxidation of Carbon Nanotubes in an Ionizing Environment
Authors: Ai Leen Koh, Emily Gidcumb, Otto Zhou, and Robert Sinclair
References: Nano Lett. 16 (2), 856-863 (2016)
Date: January 2016
Abstract
Title: Oxidation of Carbon Nanotubes in an Ionizing Environment
Authors: Ai Leen Koh, Emily Gidcumb, Otto Zhou, and Robert Sinclair
References: Nano Lett. 16 (2), 856-863 (2016)
Date: January 2016
Abstract: In this work, we present systematic studies on how an illuminating electron beam which ionizes molecular gas species can influence the mechanism of carbon nanotube oxidation in an environmental transmission electron microscope (ETEM). We found that preferential attack of the nanotube tips is much more prevalent than for oxidation in a molecular gas environment. We establish the cumulative electron doses required to damage carbon nanotubes from 80 keV electron beam irradiation in gas versus in high vacuum. Our results provide guidelines for the electron doses required to study carbon nanotubes within or without a gas environment, to determine or ameliorate the influence of the imaging electron beam. This work has important implications for in situ studies as well as for the oxidation of carbon nanotubes in an ionizing environment such as that occurring during field emission.
Title: Influence on nickel particle size on the hydrodeoxygenation of phenol over Ni/SiO2
Authors: Peter M. Mortensen, Jan-Dierk Grunwaldt, Peter A. Jensen, Anker D. Jensen
References: Catalysis Today 259, 277-284 (2016)  
Date: January 2016
Abstract
Title: Influence on nickel particle size on the hydrodeoxygenation of phenol over Ni/SiO2
Authors: Peter M. Mortensen, Jan-Dierk Grunwaldt, Peter A. Jensen, Anker D. Jensen
References: Catalysis Today 259, 277-284 (2016)  
Date: January 2016
Abstract: Hydrodeoxygenation (HDO) of phenol over nickel nano-particles of different size (5-22 nm) supported on SiO 2  has been investigated in a batch reactor at 275 °C and 100 bar. Deoxygenation was only observed as a consecutive step of initial hydrogenation of phenol at the given conditions. Both the hydrogenation and deoxygenation reaction were found to be Ni-particle size dependent. Rapid hydrogenation of phenol to cyclohexanol was achieved over the catalysts with large particles, while the rate of deoxygenation of cyclohexanol was slow. For the catalysts with small Ni particles, the opposite behavior was observed Specifically, the turn over frequency (TOF) of hydrogenation was 85 times slower for 5 nm particles than for 22 nm particles. On the contrary, the TOF of cyclohexanol deoxygenation increased by a factor of 20 when decreasing the particle size from 20 nm to 5 nm. A simple kinetic model showed that the rate limiting step for phenol HDO shifted from deoxygenation to hydrogenation when the particle size was below 9-10 nm. Surface site population theory evidenced that the deoxygenation reactions were favored on step/corner sites, giving higher deoxygenation rates at small particles. For hydrogenation, the influence of particle size on the rate could be related to the size of the Ni facets with larger facets thus being better.
Title: In-situ transmission electron microscopy study of surface oxidation for Ni–10Cr and Ni–20Cr alloys
Authors: Langli Luo, Lianfeng Zou, Daniel K. Schreiber, Donald R. Baer, Stephen M. Bruemmer, Guangwen Zhou, Chong-Min Wang
References: Scripta Materialia 114, 129-132 (2016)
Date: December 2015
Abstract
Title: In-situ transmission electron microscopy study of surface oxidation for Ni–10Cr and Ni–20Cr alloys
Authors: Langli Luo, Lianfeng Zou, Daniel K. Schreiber, Donald R. Baer, Stephen M. Bruemmer, Guangwen Zhou, Chong-Min Wang
References: Scripta Materialia 114, 129-132 (2016)
Date: December 2015
Abstract: The early-stage oxidation of Ni (001) thin films alloyed with 10 or 20 at.% Cr at 700 °C has been directly visualized using  in-situ  TEM. Independent of Cr concentration, the oxidation initiates  via  nucleation of surface NiO islands and subsurface Cr 2 O 3 . The NiO grows and transitions into a continuous film, followed by the nucleation and growth of NiCr 2 O 4  islands. For Ni-20 at.% Cr, a continuous Cr 2 O 3  was developed, but not for Ni-10 at.% Cr. NiO whiskers are observed to preferentially nucleate/grow from the NiCr 2 O 4 islands through a short-circuit diffusion of Ni along the NiCr 2 O 4  interfaces in Ni-10 at.% Cr.
Title: Chemical and Phase Evolution of Amorphous Molybdenum Sulfide Catalysts for Electrochemical Hydrogen Production
Authors: Sang Chul Lee, Jesse D Benck, Charlie Tsai, Joonsuk Park, Ai Leen Koh, Frank Abild-Pedersen, Thomas F. Jaramillo, and Robert Sinclair
References: ACS Nano , 10, 624-632 (2016) 
Date: December 2015
Abstract
Title: Chemical and Phase Evolution of Amorphous Molybdenum Sulfide Catalysts for Electrochemical Hydrogen Production
Authors: Sang Chul Lee, Jesse D Benck, Charlie Tsai, Joonsuk Park, Ai Leen Koh, Frank Abild-Pedersen, Thomas F. Jaramillo, and Robert Sinclair
References: ACS Nano , 10, 624-632 (2016) 
Date: December 2015
Abstract: Amorphous MoS x  is a highly active, earth-abundant catalyst for the electrochemical hydrogen evolution reaction. Previous studies have revealed that this material initially has a composition of MoS3, but after electrochemical activation, the surface is reduced to form an active phase resembling MoS2 in composition and chemical state. However, structural changes in the MoS x catalyst and the mechanism of the activation process remain poorly understood. In this study, we employ transmission electron microscopy (TEM) to image amorphous MoS x  catalysts activated under two hydrogen-rich conditions:  ex situ  in an electrochemical cell and  in situ  in an environmental TEM. For the first time, we directly observe the formation of crystalline domains in the MoS x  catalyst after both activation procedures as well as spatially localized changes in the chemical state detected  via  electron energy loss spectroscopy. Using density functional theory calculations, we investigate the mechanisms for this phase transformation and find that the presence of hydrogen is critical for enabling the restructuring process. Our results suggest that the surface of the amorphous MoS x  catalyst is dynamic: while the initial catalyst activation forms the primary active surface of amorphous MoS2, continued transformation to the crystalline phase during electrochemical operation could contribute to catalyst deactivation. These results have important implications for the application of this highly active electrocatalyst for sustainable H2 generation.
Title: Coarsening of Pd nanoparticles in an oxidizing atmosphere studied by in situ TEM
Authors: Søren Bredmose Simonsen, Ib Chorkendorff, Søren Dahl, Magnus Skoglundh, Stig Helveg
References: Surface Science , in press (2015)
Date: November 2015
Abstract
Title: Coarsening of Pd nanoparticles in an oxidizing atmosphere studied by in situ TEM
Authors: Søren Bredmose Simonsen, Ib Chorkendorff, Søren Dahl, Magnus Skoglundh, Stig Helveg
References: Surface Science , in press (2015)
Date: November 2015
Abstract: The coarsening of supported palladium nanoparticles in an oxidizing atmosphere was studied  in situ  by means of transmission electron microscopy (TEM). Specifically, the Pd nanoparticles were dispersed on a planar and amorphous Al 2 O 3  support and were observed during the exposure to 10 mbar technical air at 650 °C. Time-resolved TEM image series reveal that the Pd nanoparticles were immobile and that a few percent of the nanoparticles grew or shrank, indicating a coarsening process mediated by the Ostwald ripening mechanism. The TEM image contrast suggests that the largest nanoparticles tended to wet the Al 2 O 3  support to a higher degree than the smaller nanoparticles and that the distribution of projected particle sizes consequently broadens by the appearance of an asymmetric tail toward the larger particle sizes. A comparison with computer simulations based on a simple mean-field model for the Ostwald ripening process indicates that the observed change in the particle size distribution can be accounted for by wetting of the Al 2 O 3  support by the larger Pd nanoparticles.
Title: Visualizing the mobility of silver during catalytic soot oxidation
Authors: Diego Gardini, Jakob M. Christensen, Christian D. Damsgaard, Anker D. Jensen, Jakob B. Wagner
References: Applied Catalysis B: Environmental 183, 28-36 (2016)
Date: October 2015
Abstract
Title: Visualizing the mobility of silver during catalytic soot oxidation
Authors: Diego Gardini, Jakob M. Christensen, Christian D. Damsgaard, Anker D. Jensen, Jakob B. Wagner
References: Applied Catalysis B: Environmental 183, 28-36 (2016)
Date: October 2015
Abstract: The catalytic activity and mobility of silver nanoparticles used as catalysts in temperature programmed oxidation of soot:silver (1:5 wt:wt) mixtures have been investigated by means of flow reactor experiments and  in situ  environmental transmission electron microscopy (ETEM). The carbon oxidation temperature was significantly lower compared to uncatalyzed soot oxidation with soot and silver loosely stirred together (loose contact) and lowered further with the two components crushed together (tight contact). The  in situ  TEM investigations revealed that the silver particles exhibited significant mobility during the soot oxidation, and this mobility, which increases the soot/catalyst contact, is expected to be an important factor for the lower oxidation temperature. In the intimate tight contact mixture the initial dispersion of the silver particles is greater, and the onset of mobility occurs at a lower temperature which is consistent with the lower oxidation temperature of the tight contact mixture.
Title: In Situ Microscopy and Spectroscopy Applied to Surfaces at Work
Authors: H. L. Han, G. Melaet, S. Alayoglu, G. A. Somorjai
References: ChemCatChem , 7(22), 3625-3638 (2015)
Date: October 2015
Abstract
Title: In Situ Microscopy and Spectroscopy Applied to Surfaces at Work
Authors: H. L. Han, G. Melaet, S. Alayoglu, G. A. Somorjai
References: ChemCatChem , 7(22), 3625-3638 (2015)
Date: October 2015
Abstract: The present review discusses the current state of the art microscopic and spectroscopic characterization techniques available to study surfaces and interfaces under working conditions. Microscopic techniques such as environmental transmission electron microscopy and in situ transmission electron microscopy are first discussed showing their applications in the field of nanomaterials and catalysis. Next sum frequency generation vibrational spectroscopy is discussed, giving probing examples of surface studies in gaseous conditions. Synchrotron based X-ray techniques are also examined with a specific focus on ambient pressure X-ray photoelectron and absorption techniques such as near and extended X-ray absorption fine structure. Each of the techniques is evaluated, whilst the pros and cons are discussed in term of surface sensitivity, spatial resolution and/or time resolution. The second part of the articles is articulated around the future of in situ characterization, giving examples of the probable development of the discussed techniques as well as an introduction of emerging tools such as scanning transmission X-ray microscopy, ptychography, and X-ray photon correlation spectroscopy.
Title: Intermetallic GaPd2 Nanoparticles on SiO2 for Low-Pressure CO2 Hydrogenation to Methanol: Catalytic Performance and In Situ Characterization
Authors: Elisabetta M. Fiordaliso, Irek Sharafutdinov, Hudson W. P. Carvalho, Jan-D. Grunwaldt, Thomas W. Hansen, Ib Chorkendorff, Jakob B. Wagner, and Christian D. Damsgaard
References: ACS Catalysis 5, 5827-5836 (2015)
Date: August 2015
Abstract
Title: Intermetallic GaPd2 Nanoparticles on SiO2 for Low-Pressure CO2 Hydrogenation to Methanol: Catalytic Performance and In Situ Characterization
Authors: Elisabetta M. Fiordaliso, Irek Sharafutdinov, Hudson W. P. Carvalho, Jan-D. Grunwaldt, Thomas W. Hansen, Ib Chorkendorff, Jakob B. Wagner, and Christian D. Damsgaard
References: ACS Catalysis 5, 5827-5836 (2015)
Date: August 2015
Abstract: A nanodispersed intermetallic GaPd2/SiO2 catalyst is prepared by simple impregnation of industrially relevant high-surface-area SiO2 with Pd and Ga nitrates, followed by drying, calcination, and reduction in hydrogen. The catalyst is tested for CO2 hydrogenation to methanol at ambient pressure, revealing that the intrinsic activity of the GaPd2/SiO2 is higher than that of the conventional Cu/ZnO/Al2O3, while the production of the undesired CO is lower. A combination of complementary in situ and ex situ techniques are used to investigate the GaPd2/SiO2 catalyst. In situ X-ray diffraction and in situ extended X-ray absorption fine structure spectroscopy show that the GaPd2 intermetallic phase is formed upon activation of the catalyst via reduction and remains stable during CO2 hydrogenation. Identical location-transmission electron microscopy images acquired ex situ (i.e., micrographs of exactly the same catalyst area recorded at the different steps of activation and reaction procedure) show that nanoparticle size and dispersion are defined upon calcination with no significant changes observed after reduction and methanol synthesis. Similar conclusions can be drawn from electron diffraction patterns and images acquired using environmental TEM (ETEM), indicating that ETEM results are representative for the catalyst treated at ambient pressure. The chemical composition and the crystalline structure of the nanoparticles are identified by scanning TEM energy dispersive X-ray spectroscopy, selected area electron diffraction, and atomically resolved TEM images.
Title: Novel sample preparation for operando TEM of catalysts
Authors: Benjamin K. Miller, Trevor M. Barker, Peter A. Crozier
References: Ultramicroscopy 156, 18-22 (2015)
Date: May 2015
Abstract
Title: Novel sample preparation for operando TEM of catalysts
Authors: Benjamin K. Miller, Trevor M. Barker, Peter A. Crozier
References: Ultramicroscopy 156, 18-22 (2015)
Date: May 2015
Abstract: A new TEM sample preparation method is developed to facilitate  operando  TEM of gas phase catalysis. A porous Pyrex-fiber pellet TEM sample was produced, allowing a comparatively large amount of catalyst to be loaded into a standard Gatan furnace-type tantalum heating holder. The increased amount of catalyst present inside the environmental TEM allows quantitative determination of the gas phase products of a catalytic reaction performed  in-situ  at elevated temperatures. The product gas concentration was monitored using both electron energy loss spectroscopy (EELS) and residual gas analysis (RGA). Imaging of catalyst particles dispersed over the pellet at atomic resolution is challenging, due to charging of the insulating glass fibers. To overcome this limitation, a metal grid is placed into the holder in addition to the pellet, allowing catalyst particles dispersed over the grid to be imaged, while particles in the pellet, which are assumed to experience identical conditions, contribute to the overall catalytic conversion inside the environmental TEM cell. The gas within the cell is determined to be well-mixed, making this assumption reasonable.
Title: Real-Time Observation of Morphological Transformations in II–VI Semiconducting Nanobelts via Environmental Transmission Electron Microscopy
Authors: Rahul Agarwal, Dmitri N. Zakharov, Nadia M. Krook, Wenjing Liu, Jacob S. Berger, Eric A. Stach, and Ritesh Agarwal
References: Nano Letters 15, 3303-3308 (2015)
Date: April 2015
Abstract
Title: Real-Time Observation of Morphological Transformations in II–VI Semiconducting Nanobelts via Environmental Transmission Electron Microscopy
Authors: Rahul Agarwal, Dmitri N. Zakharov, Nadia M. Krook, Wenjing Liu, Jacob S. Berger, Eric A. Stach, and Ritesh Agarwal
References: Nano Letters 15, 3303-3308 (2015)
Date: April 2015
Abstract: It has been observed that wurtzite II-VI semiconducting nanobelts transform into single-crystal, periodically branched nanostructures upon heating. The mechanism of this novel transformation has been elucidated by heating II-VI nanobelts in an environmental transmission electron microscope (ETEM) in oxidizing, reducing, and inert atmospheres while observing their structural changes with high spatial resolution. The interplay of surface reconstruction of high-energy surfaces of the wurtzite phase and environment-dependent anisotropic chemical etching of certain crystal surfaces in the branching mechanism of nanobelts has been observed. Understanding of structural and chemical transformations of materials via in situ microscopy techniques and their role in designing new nanostructured materials is discussed.
Title: Investigations of soot combustion on yttria-stabilized zirconia by environmental transmission electron microscopy (ETEM)
Authors: A. Serve, T. Epicier, M. Aouine, F.J. Cadete Santos Aires, E. Obeid, M. Tsampas, K. Pajot, P. Vernoux
References: Applied Catalysis A: General 504, 74-80 (2015)
Date: March 2015
Abstract
Title: Investigations of soot combustion on yttria-stabilized zirconia by environmental transmission electron microscopy (ETEM)
Authors: A. Serve, T. Epicier, M. Aouine, F.J. Cadete Santos Aires, E. Obeid, M. Tsampas, K. Pajot, P. Vernoux
References: Applied Catalysis A: General 504, 74-80 (2015)
Date: March 2015
Abstract: Environmental transmission electron microscopy (ETEM) equipped with an aberration corrector was used to get further insights into the mechanism of soot oxidation on yttria-stabilized zirconia (YSZ), an O 2−  ionic conductor. In situ observations, with a resolution of around 1 nm, of a "tight" YSZ/real soot mixture were performed at 550 °C in the presence of a few mbar of oxygen (2 and 3 mbar). Preliminary experiments were conducted to validate that moderate electron beam illumination conditions do not control the soot combustion. Video sequences recorded at 550 °C clearly confirmed that bulk YSZ oxygen atoms are the active species for soot oxidation at the soot/YSZ interface as no oxidation takes place without contact. The number of soot/YSZ contact points and their evolution with time are the key parameters for soot oxidation. The contact length between the soot and the YSZ grains could be estimated to be around 20-40 nm only.
Title: Structural Evolution during Photocorrosion of Ni/NiO Core/Shell Cocatalyst on TiO2
Authors: L. Zhang, Q. Liu, T. Aoki, P.A. Crozier
References: The Journal of Physical Chemistry C 119(13), 7207-7214 (2015)
Date: March 2015
Abstract
Title: Structural Evolution during Photocorrosion of Ni/NiO Core/Shell Cocatalyst on TiO2
Authors: L. Zhang, Q. Liu, T. Aoki, P.A. Crozier
References: The Journal of Physical Chemistry C 119(13), 7207-7214 (2015)
Date: March 2015
Abstract: The Ni/NiO core/shell structure is one of the most efficient cocatalysts for solar water splitting when coupled with suitable semiconducting oxides. It has been shown that pretreated Ni/NiO core/shell structures are more active than pure Ni metal, pure NiO, or mixed dispersion of Ni metal and NiO nanoparticles. However, Ni/NiO core/shell structures on TiO2 are only able to generate H2 but not O2 in aqueous water. The nature of the hydrogen evolution reaction in these systems was investigated by correlating photochemical H2 production with atomic-resolution structure determined with aberration-corrected electron microscopy. It was found that the core/shell structure plays an important role for H2 generation but the system undergoes deactivation due to a loss of metallic Ni. During the H2 evolution reaction, the metal core initially formed partial voids which grew, and eventually all the Ni diffused out of the core/shell into solution leaving an inactive hollow void/NiO shell. The H2 evolution was generated by a photochemical reaction involving photocorrosion of Ni metal.
Title: Dynamic Behavior of CuZn Nanoparticles under Oxidizing and Reducing Conditions
Authors: Christian Holse, Christian F. Elkjær, Anders Nierhoff, Jens Sehested, Ib Chorkendorff, Stig Helveg, Jane H. Nielsen
References: J. Phys. Chem. C 119, 2804-2812 (2015)
Date: December 2014
Abstract
Title: Dynamic Behavior of CuZn Nanoparticles under Oxidizing and Reducing Conditions
Authors: Christian Holse, Christian F. Elkjær, Anders Nierhoff, Jens Sehested, Ib Chorkendorff, Stig Helveg, Jane H. Nielsen
References: J. Phys. Chem. C 119, 2804-2812 (2015)
Date: December 2014
Abstract: The oxidation and reduction of CuZn nanoparticles was studied using X-ray photoelectron spectroscopy (XPS) and in situ transmission electron microscopy (TEM). CuZn nanoparticles with a narrow size distribution were produced with a gas-aggregation cluster source in conjunction with mass-filtration. A direct comparison between the spatially averaged XPS information and the local TEM observations was thus made possible. Upon oxidation in O2, the as-deposited metal clusters transform into a polycrystalline cluster consisting of separate CuO and ZnO nanocrystals. Specifically, the CuO is observed to segregate to the cluster surface and partially cover the ZnO nanocrystals. Upon subsequent reduction in H2 the CuO converts into metallic Cu with ZnO nanocrystal covering their surface. In addition, a small amount of metallic Zn is detected suggesting that ZnO is reduced. It is likely that Zn species can migrate to the Cu surface forming a Cu-Zn surface alloy. The oxidation and reduction dynamics of the CuZn nanoparticles is of great importance to industrial methanol synthesis for which the direct interaction of Cu and ZnO nanocrystals synergistically boosts the catalytic activity. Thus, the present results demonstrate a new model approach that should be generally applicable to address metal-support interactions in coprecipitated catalysts and multicomponent nanomaterials.
Title: Modeling of temperature profiles in an environmental transmission electron microscope using computational fluid dynamics
Authors: Peter Mølgaard Mortensen, Thomas Willum Hansen, Jakob Birkedal Wagnerb, Anker Degn Jensen
References: Ultramicroscopy 152, 1-9 (2015)
Date: December 2014
Abstract
Title: Modeling of temperature profiles in an environmental transmission electron microscope using computational fluid dynamics
Authors: Peter Mølgaard Mortensen, Thomas Willum Hansen, Jakob Birkedal Wagnerb, Anker Degn Jensen
References: Ultramicroscopy 152, 1-9 (2015)
Date: December 2014
Abstract: The temperature and velocity field, pressure distribution, and the temperature variation across the sample region inside an environmental transmission electron microscope (ETEM) have been modeled by means of computational fluid dynamics (CFD). Heating the sample area by a furnace type TEM holder gives rise to temperature gradients over the sample area. Three major mechanisms have been identified with respect to heat transfer in the sample area: radiation from the grid, conduction in the grid, and conduction in the gas. A parameter sensitivity analysis showed that the sample temperature was affected by the conductivity of the gas, the emissivity of the sample grid, and the conductivity of the grid. Ideally the grid should be polished and made from a material with good conductivity, e.g. copper. With hydrogen gas, which has the highest conductivity of the gases studied, the temperature difference over the TEM grid is less than 5 °C, at what must be considered typical conditions, and it is concluded that the conditions on the sample grid in the ETEM can be considered as isothermal during general use.
Title: An industrial perspective of the impact of Haldor Topsøe on (in situ) electron microscopy in catalysis
Authors: Stig Helveg
References: Journal of Catalysis 328, 102-110 (2015) 
Date: December 2014
Abstract
Title: An industrial perspective of the impact of Haldor Topsøe on (in situ) electron microscopy in catalysis
Authors: Stig Helveg
References: Journal of Catalysis 328, 102-110 (2015) 
Date: December 2014
Abstract: With recent advances, electron microscopy can now visualize heterogeneous catalysts at the atomic scale and under catalytic meaningful conditions. A selection of the advancements is outlined to reflect Dr. Haldor Topsøe's enthusiasm for electron microscopy as means for improving the fundamental understanding in catalysis.
Title: Vibrational and optical spectroscopies integrated with environmental transmission electron microscopy
Authors: M. Picher, S. Mazzucco, S. Blankenship, R. Sharma
References: Ultramicroscopy 150, 10-15 (2015)
Date: December 2014
Abstract
Title: Vibrational and optical spectroscopies integrated with environmental transmission electron microscopy
Authors: M. Picher, S. Mazzucco, S. Blankenship, R. Sharma
References: Ultramicroscopy 150, 10-15 (2015)
Date: December 2014
Abstract: Here, we present a measurement platform for collecting multiple types of spectroscopy data during high-resolution environmental transmission electron microscopy observations of dynamic processes. Such coupled measurements are made possible by a broadband, high-efficiency, free-space optical system. The critical element of the system is a parabolic mirror, inserted using an independent hollow rod and placed below the sample holder which can focus a light on the sample and/or collect the optical response. We demonstrate the versatility of this optical setup by using it to combine  in situ  atomic-scale electron microscopy observations with Raman spectroscopy. The Raman data is also used to measure the local temperature of the observed sample area. Other applications include, but are not limited to: cathodo- and photoluminescence spectroscopy, and use of the laser as a local, high-rate heating source.
Title: Environmental transmission electron microscopy for catalyst materials using a spherical aberration corrector
Authors: Seiji Takeda, Yasufumi Kuwauchi, Hideto Yoshida
References: Ultramicroscopy 151, 178-190 (2015)
Date: November 2014
Abstract
Title: Environmental transmission electron microscopy for catalyst materials using a spherical aberration corrector
Authors: Seiji Takeda, Yasufumi Kuwauchi, Hideto Yoshida
References: Ultramicroscopy 151, 178-190 (2015)
Date: November 2014
Abstract: Atomic resolution has been obtained using environmental transmission electron microscopy (ETEM) by installing a spherical aberration corrector (Cs-corrector) on the objective lens. Simultaneously, the technology for controlling the environment around a specimen in ETEM has advanced significantly in the past decade. Quantification methodology has recently been established for deriving relevant experimental data in catalyst materials from substantial and systematic ETEM observation at the atomic scale. With this background, this paper summarizes aspects of the evolutional microscopy technique: necessary conditions for atomic resolution in ETEM; reduction of the scattering of electrons by the medium surrounding a specimen; and an environmental cell for structural imaging of a crystalline specimen. The high spatial resolution of a Cs-corrected ETEM is demonstrated for different observation conditions. After statistical analysis combined with numerical image analysis of ETEM data is briefly described, the recent applications of the Cs-corrected ETEM to catalyst materials are reviewed. For gold nanoparticulate catalysts, the structural information on the reaction sites and adsorption sites are deduced. For Pt nanoparticulate catalysts, ETEM studies elucidate the correlation between the catalytic activity and the morphology of the nanoparticles. These studies also reveal oxidation and reduction on the topmost Pt surface layer at the atomic scale. Finally, current issues and the future perspectives of Cs-corrected ETEM are summarized, including the reproducibility of ETEM observation data, the control of environments, the critical evaluation of electron irradiation effects, the full implementation of transmission electron microscopy technology in ETEM, and the safety issues for an ETEM laboratory.
Title: Environmental TEM study of the dynamic nanoscaled morphology of NiO/YSZ during reduction
Authors: Søren Bredmose Simonsen, Karsten Agersted, Karin Vels Hansen, Torben Jacobsen,Jakob Birkedal Wagner, Thomas Willum Hansen, Luise Theil Kuhn
References: Applied Catalysis A: General 489, 147-154 (2015)
Date: October 2014
Abstract
Title: Environmental TEM study of the dynamic nanoscaled morphology of NiO/YSZ during reduction
Authors: Søren Bredmose Simonsen, Karsten Agersted, Karin Vels Hansen, Torben Jacobsen,Jakob Birkedal Wagner, Thomas Willum Hansen, Luise Theil Kuhn
References: Applied Catalysis A: General 489, 147-154 (2015)
Date: October 2014
Abstract: The reduction of a metal oxide is often a critical preparation step for activating catalytic behaviour. This study addresses the reduction process of NiO in pure form and in a composite of NiO/yttria-stabilized zirconia (YSZ) in hydrogen relevant for solid oxide electrochemical cells by comparing results from environmental transmission electron microscopy (ETEM) with thermogravimetric analysis (TGA). The temperature dependent reduction profiles obtained from TGA confirm an inhibitive effect from YSZ on the NiO reduction. The ETEM images show the growth of Ni in decaying NiO and reveal the nanoscale morphological changes such as pore formation in NiO above 280 °C and densification and collapse of the pore structures above 400 °C. The accelerated Ni front in NiO illustrates the autocatalysis of the reaction. A rapid temperature ramping from room temperature to 780 °C in hydrogen in 1 second resulted in immediate morphological changes at the nanoscale from dense NiO to dense Ni. The analysis suggests that the inhibitive effect of YSZ on the NiO reduction reaction is not due to a direct local interaction between YSZ and NiO, but instead due to gas and/or mass transport limitations.
Title: Visualized effect of oxidation on magnetic recording fidelity in pseudo-single-domain magnetite particles
Authors: Trevor P. Almeida, Takeshi Kasama, Adrian R. Muxworthy, Wyn Williams, Lesleis Nagy, Thomas W. Hansen, Paul D. Brown and Rafal E. Dunin-Borkowski
References: Nature Communications 5, article number: 5154 (2014)
Date: October 2014
Abstract
Title: Visualized effect of oxidation on magnetic recording fidelity in pseudo-single-domain magnetite particles
Authors: Trevor P. Almeida, Takeshi Kasama, Adrian R. Muxworthy, Wyn Williams, Lesleis Nagy, Thomas W. Hansen, Paul D. Brown and Rafal E. Dunin-Borkowski
References: Nature Communications 5, article number: 5154 (2014)
Date: October 2014
Abstract: Magnetite (Fe3O4) is an important magnetic mineral to Earth scientists, as it carries the dominant magnetic signature in rocks, and the understanding of its magnetic recording fidelity provides a critical tool in the field of palaeomagnetism. However, reliable interpretation of the recording fidelity of Fe3O4 particles is greatly diminished over time by progressive oxidation to less magnetic iron oxides, such as maghemite (γ-Fe2O3), with consequent alteration of remanent magnetization potentially having important geological significance. Here we use the complementary techniques of environmental transmission electron microscopy and off-axis electron holography to induce and visualize the effects of oxidation on the magnetization of individual nanoscale Fe3O4 particles as they transform towards γ-Fe2O3. Magnetic induction maps demonstrate a change in both strength and direction of remanent magnetization within Fe3O4 particles in the size range dominant in rocks, confirming that oxidation can modify the original stored magnetic information.
Title: In Situ Study of Noncatalytic Metal Oxide Nanowire Growth
Authors: S. Rackauskas, H. Jiang, J.B. Wagner, S.D. Shandakov, T.W. Hansen, E.I. Kauppinen, A.G. Nasibulin
References: Nano Letters , 14(10), 5810-5813 (2014)
Date: September 2014
Abstract
Title: In Situ Study of Noncatalytic Metal Oxide Nanowire Growth
Authors: S. Rackauskas, H. Jiang, J.B. Wagner, S.D. Shandakov, T.W. Hansen, E.I. Kauppinen, A.G. Nasibulin
References: Nano Letters , 14(10), 5810-5813 (2014)
Date: September 2014
Abstract: The majority of the nanowire synthesis methods utilize catalyst particles to guide the nanowire geometry. In contrast, catalyst-free methods are attractive for facile fabrication of pure nanowires without the need for catalyst preparation. Nonetheless, how nanowire growth is guided without a catalyst is still widely disputed and unclear. Here, we show that the nanowire growth during metal oxidation is limited by a nucleation of a new layer. On the basis of in situ transmission electron microscope investigations we found that the growth occurs layer by layer at the lowest specific surface energy planes. Atomic layers nucleate at the edge of twin boundary ridges and form a long-range ordering along the twin boundary. We anticipate our study to be a starting point to employ defects for nanowire growth control and consequently shaping the geometry of nanowires in a similar manner as in the catalyst-assisted growth method
Title: In situ detection of hydrogen-induced phase transitions in individual palladium nanocrystals
Authors: Andrea Baldi, Tarun C. Narayan, Ai Leen Koh, Jennifer A. Dionne
References: Nature Materials 13, 1143-1148 (2014)
Date: September 2014
Abstract
Title: In situ detection of hydrogen-induced phase transitions in individual palladium nanocrystals
Authors: Andrea Baldi, Tarun C. Narayan, Ai Leen Koh, Jennifer A. Dionne
References: Nature Materials 13, 1143-1148 (2014)
Date: September 2014
Abstract: Many energy- and information-storage processes rely on phase changes of nanomaterials in reactive environments. Compared to their bulk counterparts, nanostructured materials seem to exhibit faster charging and discharging kinetics, extended life cycles, and size-tunable thermodynamics. However, in ensemble studies of these materials, it is often difficult to discriminate between intrinsic size-dependent properties and effects due to sample size and shape dispersity. Here, we detect the phase transitions of individual palladium nanocrystals during hydrogenabsorption and desorption, using  in situ  electron energy-loss spectroscopy in an environmental transmission electron microscope. In contrast to ensemble measurements, we find that palladiumnanocrystals undergo sharp transitions between the α and β phases, and that surface effects dictate the size dependence of the hydrogen absorption pressures. Our results provide a general framework for monitoring phase transitions in individual nanocrystals in a reactive environment and highlight the importance of single-particle approaches for the characterization of nanostructured materials.
Title: Direct evidence of active and inactive phases of Fe catalyst nanoparticles for carbon nanotube formation
Authors: Stefano Mazzucco, Ying Wang, Mihaela Tanase, Matthieu Picher, Kai Li, Zhijian Wu, Stephan Irle, Renu Sharma
References: Journal of Catalysis 319, 54-60 (2014)
Date: September 2014
Abstract
Title: Direct evidence of active and inactive phases of Fe catalyst nanoparticles for carbon nanotube formation
Authors: Stefano Mazzucco, Ying Wang, Mihaela Tanase, Matthieu Picher, Kai Li, Zhijian Wu, Stephan Irle, Renu Sharma
References: Journal of Catalysis 319, 54-60 (2014)
Date: September 2014
Abstract: Iron-carbon interactions play an important role in various industrial activities such as liquid fuel production by the Fischer-Tropsch process and carbon nanotube synthesis by chemical vapor deposition. In both cases, catalytic activity is confined to a subset of catalyst nanoparticles. Despite the large number of experimental and theoretical studies on the activity of Fe nanoparticles, very little is known about the difference between the active and inactive particles. We use  in situ  environmental transmission electron microscopy to elucidate the differences between active and inactive nanoparticles with respect to carbon nanotube formation. We present direct evidence that nanoparticles with the cementite (Fe 3 C) structure are active for nanotube growth (C-C bond formation), while carbon-rich particles with Hägg (Fe 5 C 2 ) structure are inactive. Density functional theory calculations suggest that reduced activity may be due to lower carbon mobility and higher C-C bond formation energies on the surface of nanoparticles with Fe 5 C 2  structure.
Title: Oxidation and reduction processes of platinum nanoparticles observed at the atomic scale by environmental transmission electron microscopy
Authors: H. Yoshida, H. Omote and S. Takeda
References: Nanoscale 6, 13113-13118 (2014)
Date: September 2014
Abstract
Title: Oxidation and reduction processes of platinum nanoparticles observed at the atomic scale by environmental transmission electron microscopy
Authors: H. Yoshida, H. Omote and S. Takeda
References: Nanoscale 6, 13113-13118 (2014)
Date: September 2014
Abstract: Oxidation and reduction of the surfaces of Pt nanoparticles were  in situ  examined in reactive gases (O 2 , CO and H 2 O vapor) by aberration-corrected environmental transmission electron microscopy. Atomic layers of Pt oxides were gradually formed on the surface of Pt nanoparticles at room temperature in O 2 . The surface Pt oxides were reduced to Pt promptly in both vacuum and gas including CO. We showed that H 2 O vapor suppressed the surface oxidation. The processes found in this study were induced by gases that were most likely activated by electron irradiation. The observation results provide atomistic insight into the oxidation and reduction process of the surface of Pt nanoparticles that is exposed to activated gases.
Title: Growth Mechanism for Single- and Multi-Layer MoS2 Nanocrystals
Authors: Lars P. Hansen , Erik Johnson , Michael Brorson, Stig Helveg
References: J. Phys. Chem. C 118 (39), 22768-22773 (2014)
Date: September 2014
Abstract
Title: Growth Mechanism for Single- and Multi-Layer MoS2 Nanocrystals
Authors: Lars P. Hansen , Erik Johnson , Michael Brorson, Stig Helveg
References: J. Phys. Chem. C 118 (39), 22768-22773 (2014)
Date: September 2014
Abstract: Transmission electron microscopy (TEM) is used to study growth of MoS2 nanocrystals  in situ . The nanocrystals are formed from a submonolayer molybdenum oxide dispersed on an oxide support by sulfidation in an H2S/H2 atmosphere. From series of time-resolved TEM images, it is revealed that single-layer MoS2 nanocrystals form preferentially and that multi-layer nanocrystals form late in the sulfidation process. The TEM images pinpoint that step sites in the support can act as nucleation centers for single-layer nanocrystals and that single-layer nanocrystals grow along the support surface. Moreover, the TEM images reveal that multi-layer MoS2 nanocrystals form in a layer-by-layer mode by the homogeneous nucleation of additional MoS2 layers onto already formed single-layer MoS2 nanocrystals. Hereby, the atomic-scale observations suggest that the formation of multi-layer MoS2 nanocrystals is an energetically more activated process than growth of single-layers. These findings explain why process parameters, such as temperature, can tune the relative fraction of single- to multi-layer MoS2nanocrystals, which is important for their use in, e.g., hydrotreating catalysis.
Title: Atomic Resolution Single Walled Carbon Nanotube Nucleation Steps on Faceted Catalyst Particle Reveal Potential for Chirality Control
Authors: P. Ann Lin, M. Picher, J.L.G. Ballesteros, P. Balbuena, R. Sharma
References: Microscopy and Microanalysis 20, 1758-1759 (2014)
Date: August 2014
Abstract
Title: Atomic Resolution Single Walled Carbon Nanotube Nucleation Steps on Faceted Catalyst Particle Reveal Potential for Chirality Control
Authors: P. Ann Lin, M. Picher, J.L.G. Ballesteros, P. Balbuena, R. Sharma
References: Microscopy and Microanalysis 20, 1758-1759 (2014)
Date: August 2014
Abstract:  
Title: Optical Spectroscopy Integrated with Environmental Scanning Transmission Electron Microscope: A Comprehensive In Situ Characterization Platform
Authors: M. Picher, S. Mazzucco, S. Blankenship, G. Holland, R. Sharma
References: Microscopy and Microanalysis 20, 1748-1749 (2014)
Date: August 2014
Abstract
Title: Optical Spectroscopy Integrated with Environmental Scanning Transmission Electron Microscope: A Comprehensive In Situ Characterization Platform
Authors: M. Picher, S. Mazzucco, S. Blankenship, G. Holland, R. Sharma
References: Microscopy and Microanalysis 20, 1748-1749 (2014)
Date: August 2014
Abstract:  
Title: In situ observation on hydrogenation of Mg-Ni films using environmental transmission electron microscope with aberration correction
Authors: Junko Matsuda, Kenta Yoshida, Yukichi Sasaki, Naoki Uchiyama and Etsuo Akiba
References: Appl. Phys. Lett. 105, 083903 (2014)
Date: August 2014
Abstract
Title: In situ observation on hydrogenation of Mg-Ni films using environmental transmission electron microscope with aberration correction
Authors: Junko Matsuda, Kenta Yoshida, Yukichi Sasaki, Naoki Uchiyama and Etsuo Akiba
References: Appl. Phys. Lett. 105, 083903 (2014)
Date: August 2014
Abstract: In situ transmission electron microscopy (TEM) was performed to observe the hydrogenation of Mg-Nifilms in a hydrogen atmosphere of 80-100 Pa. An aberration-corrected environmental TEM with a differential pumping system allows us to reveal the Angstrom-scale structure of the films in the initial stage of hydrogenation: first, nucleation and growth of Mg 2NiH4 crystals with a lattice spacing of 0.22 nm in an Mg-rich amorphous matrix of the film occurs within 20 s after the start of the high-resolution observation, then crystallization of MgH2 with a smaller spacing of 0.15 nm happens after approximately 1 min. Our in situ TEM method is also applicable to the analysis of other hydrogen-related materials.
Title: Observing gas-catalyst dynamics at atomic resolution and single-atom sensitivity
Authors: S. Helveg, C. F. Kisielowski, J. R. Jinschek, P. Specht, G. Yuan, H. Frei
References: Micron 68, 176-185 (2014)
Date: August 2014
Abstract
Title: Observing gas-catalyst dynamics at atomic resolution and single-atom sensitivity
Authors: S. Helveg, C. F. Kisielowski, J. R. Jinschek, P. Specht, G. Yuan, H. Frei
References: Micron 68, 176-185 (2014)
Date: August 2014
Abstract: Transmission electron microscopy (TEM) has become an indispensable technique for studying heterogeneous catalysts. In particular, advancements of aberration-corrected electron optics and data acquisition schemes have made TEM capable of delivering images of catalysts with sub-Ångström resolution and single-atom sensitivity. Parallel developments of differentially pumped electron microscopes and of gas cells enable  in situ  observations of catalysts during the exposure to reactive gas environments at pressures of up to atmospheric levels and temperatures of up to several hundred centigrade. Here, we outline how to take advantage of the emerging state-of-the-art instrumentation and methodologies to study surface structures and dynamics to improve the understanding of structure-sensitive catalytic functionality. The concept of using low electron dose-rates in TEM in conjunction with in-line holography and aberration-correction at low voltage (80 kV) is introduced to allow maintaining atomic resolution and sensitivity during  in situ  observations of catalysts. Benefits are illustrated by exit wave reconstructions of TEM images of a nanocrystalline Co 3 O 4  catalyst material acquired  in situ  during their exposure to either a reducing or oxidizing gas environment.
Title: NiO/YSZ Reduction for SOFC/SOEC Studied In Situ by Environmental Transmission Electron Microscopy
Authors: Søren Bredmose Simonsen, Karsten Agersted, Karin Vels Hansen, Torben Jacobsen, Jakob Birkedal Wagner, Thomas Willum Hansen and Luise Theil Kuhn
References: ECS Transactions 64, 73-80 (2014)
Date: August 2014
Abstract
Title: NiO/YSZ Reduction for SOFC/SOEC Studied In Situ by Environmental Transmission Electron Microscopy
Authors: Søren Bredmose Simonsen, Karsten Agersted, Karin Vels Hansen, Torben Jacobsen, Jakob Birkedal Wagner, Thomas Willum Hansen and Luise Theil Kuhn
References: ECS Transactions 64, 73-80 (2014)
Date: August 2014
Abstract: A typical anode for solid oxide fuel cells (SOFC) or cathode for solid oxide electrolysis cells (SOEC) is a complex porous structure of Ni and yttria-stabilized zirconia (YSZ). The porous Ni/YSZ is usually prepared from powder mixtures of NiO and YSZ, tape casted and sintered into a dense structure and finally reduced during start-up of the SOFC/SOEC in H 2  at the operating temperature of the cell (ca. 800 °C). This contribution presents environmental transmission electron microscopy (ETEM) nanoscale observations of the reduction process of a NiO/YSZ powder in H 2  at temperatures up to almost 1000 °C. The study focusses on the temperature dependent dynamical morphology of the NiO/YSZ and on the possible influence of YSZ on the NiO reduction.
Title: Nucleation of Graphene and Its Conversion to Single-Walled Carbon Nanotubes
Authors: Matthieu Picher, Pin Ann Lin, Jose L. Gomez-Ballesteros, Perla B. Balbuena, and Renu Sharma
References: Nano Letters 14 (11), 6104-6108 (2014)
Date: August 2014
Abstract
Title: Nucleation of Graphene and Its Conversion to Single-Walled Carbon Nanotubes
Authors: Matthieu Picher, Pin Ann Lin, Jose L. Gomez-Ballesteros, Perla B. Balbuena, and Renu Sharma
References: Nano Letters 14 (11), 6104-6108 (2014)
Date: August 2014
Abstract: We use an environmental transmission electron microscope to record atomic-scale movies showing how carbon atoms assemble together on a catalyst nanoparticle to form a graphene sheet that progressively lifts-off to convert into a nanotube. Time-resolved observations combined with theoretical calculations confirm that some nanoparticle facets act like a vice-grip for graphene, offering anchoring sites, while other facets allow the graphene to lift-off, which is the essential step to convert into a nanotube.
Title: Structurally inhomogeneous nanoparticulate catalysts in cobalt-catalyzed carbon nanotube growth
Authors: Y. Kohigashi, H. Yoshida, Y. Homma and S. Takeda
References: Appl. Phys. Lett. 105, 073108 (2014)
Date: August 2014
Abstract
Title: Structurally inhomogeneous nanoparticulate catalysts in cobalt-catalyzed carbon nanotube growth
Authors: Y. Kohigashi, H. Yoshida, Y. Homma and S. Takeda
References: Appl. Phys. Lett. 105, 073108 (2014)
Date: August 2014
Abstract: The structure of nanoparticulate catalysts involved in cobalt-catalyzed chemical vapor deposition growthof carbon nanotubes (CNTs) was investigated by in situ environmental transmission electron microscopy (ETEM). In contrast to previous studies, the analyses of ETEM images showed that the nanoparticulatecatalysts were structurally inhomogeneous during CNT growth in the source gas of acetylene at a rate of pressure increase of about 3 Pa/h and at 550 °C. The lattice fringes observed in the nanoparticulatecatalysts can be accounted for by not a single crystalline structure but by several possible pairs ofstructures including pure Co and cobalt carbides. The inhomogeneous structures were unstable with time. The possible origin of the inhomogeneous structures is discussed.
Title: In situ ETEM synthesis of NiGa alloy nanoparticles from nitrate salt solution
Authors: Christian D. Damsgaard, Linus D. Leonhard Duchstein, Irek Sharafutdinov, Morten G. Nielsen, Ib Chorkendorff, Jakob B. Wagner
References: Microscopy (Tokyo) 63 (5), 397-401 (2014)
Date: June 2014
Abstract
Title: In situ ETEM synthesis of NiGa alloy nanoparticles from nitrate salt solution
Authors: Christian D. Damsgaard, Linus D. Leonhard Duchstein, Irek Sharafutdinov, Morten G. Nielsen, Ib Chorkendorff, Jakob B. Wagner
References: Microscopy (Tokyo) 63 (5), 397-401 (2014)
Date: June 2014
Abstract: Metallic alloy nanoparticles (NPs) are synthesized  in situ  in an environmental transmission electron microscope. Atomic level characterization of the formed alloy NPs is carried out at synthesis conditions by use of high-resolution transmission electron microscopy, electron diffraction and electron energy-loss spectroscopy.
Title: Low-pressure ETEM Studies of Au assisted MgO Nanorod Growth
Authors: Linus DL Duchstein, Christian D Damsgaard, Thomas W Hansen, Jakob B Wagner
References: Journal of Physics: Conference Series 522, 012010 (2014)
Date: June 2014
Abstract
Title: Low-pressure ETEM Studies of Au assisted MgO Nanorod Growth
Authors: Linus DL Duchstein, Christian D Damsgaard, Thomas W Hansen, Jakob B Wagner
References: Journal of Physics: Conference Series 522, 012010 (2014)
Date: June 2014
Abstract: Environmental transmission electron microscopy (ETEM) studies MgO nanorod growth from Au catalyst nanoparticles in a controlled gas atmosphere have been performed, in order to elucidate the mobility of Au surface atoms and the configuration of the Au/MgO interface. MgO nanorod growth is driven by the electron beam and found to be strongly dependent on the gaseous environment in the microscope and electron beam current density.
Title: ETEM observation of Pt/C electrode catalysts in a moisturized Cathode atmosphere
Authors: K. Yoshida, X. Zhang, N. Tanaka, E. D. Boyes, and P. L. Gai
References: Journal of Physics: Conference Series 522, 012007 (2014)
Date: June 2014
Abstract
Title: ETEM observation of Pt/C electrode catalysts in a moisturized Cathode atmosphere
Authors: K. Yoshida, X. Zhang, N. Tanaka, E. D. Boyes, and P. L. Gai
References: Journal of Physics: Conference Series 522, 012007 (2014)
Date: June 2014
Abstract: There have been reports of challenges in designing platinum carbon (Pt/C) electrode catalysts for PEMFC. Pt/C electrode catalysts deactivate much faster on the cathode (in moisturized O2) than on the anode (in H2). To understand influences of moisture and oxygen on the deactivation of the Pt/C catalysts in proton-exchange-membrane fuel cells (PEMFCs), spherical-aberration-corrected environmental transmission electron microscopy (AC-ETEM) was applied with a high-speed CCD camera. Structural changes of the Pt/C electrode catalysts were dynamically recorded in moisturized nitrogen, oxygen and hydrogen. The mass spectrometry confirmed the moisture content (between 5 to 30 %) of nitrogen driving gas through a humidifier. Coalescence of platinum nanoparticles (D = 3.24 nm) was carefully evaluated in pure N2 and moisturized N2atmosphere. The Pt/C showed considerable structural weakness in a moisturized N2 atmosphere. Comparable results obtained by AC-ETEM in different gas atmospheres also suggested ways to improve the oxygen reduction reaction (ORR). In this paper, the deactivation process due to moisture (hydroxylation) of carbon supports is discussed using for comparison the movement of platinum nanoparticles measured in moisturized nitrogen and pure nitrogen atmospheres.
Title: Analysis of Catalytic Gas Products Using Electron Energy-Loss Spectroscopy and Residual Gas Analysis for Operando Transmission Electron Microscopy
Authors: Benjamin K. Miller and Peter A. Crozier
References: Microscopy and Microanalysis 20(03), 815-824 (2014)
Date: May 2014
Abstract
Title: Analysis of Catalytic Gas Products Using Electron Energy-Loss Spectroscopy and Residual Gas Analysis for Operando Transmission Electron Microscopy
Authors: Benjamin K. Miller and Peter A. Crozier
References: Microscopy and Microanalysis 20(03), 815-824 (2014)
Date: May 2014
Abstract:  
Title: The Stanford Nanocharacterization Laboratory (SNL) and Recent Applications of an Aberration-Corrected Environmental Transmission Electron Microscope
Authors: Robert Sinclair, Paul Joseph Kempen, Richard Chin and Ai Leen Koh
References: Advanced Engineering Materials 16(5), 476-481 (2014)
Date: April 2014
Abstract
Title: The Stanford Nanocharacterization Laboratory (SNL) and Recent Applications of an Aberration-Corrected Environmental Transmission Electron Microscope
Authors: Robert Sinclair, Paul Joseph Kempen, Richard Chin and Ai Leen Koh
References: Advanced Engineering Materials 16(5), 476-481 (2014)
Date: April 2014
Abstract: This article describes the establishment, over a period of 10 years or so, of a multi-user, institution-wide facility for the characterization of materials and devices at the nanoscale. Emphasis is placed on the type of equipment that we have found to be most useful for our users, and the business strategy that maintains its operations. A central component of our facility is an aberration-corrected environmental transmission electron microscope and its application is summarized in the studies of plasmon energies of silver nanoparticles, the band gap of PbS quantum dots, atomic site occupancy near grain boundaries in yttria stabilized zirconia, the lithiation of silicon nanoparticles, in situ observations on carbon nanotube oxidation and the electron tomography of varicella zoster virus nucleocapsids.
Title: Revealing the Atomic Restructuring of Pt–Co Nanoparticles
Authors: Huolin L. Xin, Selim Alayoglu, Runzhe Tao, Arda Genc, Chong-Min Wang, Libor Kovarik, Eric A. Stach, Lin-Wang Wang, Miquel Salmeron, Gabor A. Somorjai, and Haimei Zheng
References: Nano Letters 14 (6), 3203-3207 (2014)
Date: April 2014
Abstract
Title: Revealing the Atomic Restructuring of Pt–Co Nanoparticles
Authors: Huolin L. Xin, Selim Alayoglu, Runzhe Tao, Arda Genc, Chong-Min Wang, Libor Kovarik, Eric A. Stach, Lin-Wang Wang, Miquel Salmeron, Gabor A. Somorjai, and Haimei Zheng
References: Nano Letters 14 (6), 3203-3207 (2014)
Date: April 2014
Abstract: We studied Pt-Co bimetallic nanoparticles during oxidation in O2 and reduction in H2atmospheres using an aberration corrected environmental transmission electron microscope. During oxidation Co migrates to the nanoparticle surface forming a strained epitaxial CoO film. It subsequently forms islands via strain relaxation. The atomic restructuring is captured as a function of time. During reduction cobalt migrates back to the bulk, leaving a monolayer of platinum on the surface.
Title: Catalysts under Controlled Atmospheres in the Transmission Electron Microscope
Authors: Thomas W. Hansen and Jakob B. Wagner
References: ACS Catal. 4 (6), 1673-1685 (2014)
Date: April 2014
Abstract
Title: Catalysts under Controlled Atmospheres in the Transmission Electron Microscope
Authors: Thomas W. Hansen and Jakob B. Wagner
References: ACS Catal. 4 (6), 1673-1685 (2014)
Date: April 2014
Abstract: Over time, there has been an increasing interest in observing catalysts in their operating environment at high spatial resolution and ultimately to determine the structure of a catalytically active surface. One tool with the potential to do exactly this in direct space is the transmission electron microscope, and since its invention by Ernst Ruska, the idea of imaging samples under gaseous atmospheres was envisioned. However, microscopes have traditionally been operated in high vacuum due to sensitive electron sources, sample contamination, and electron scattering off gas molecules resulting in loss of resolution. Using suitably clean gases, modified pumping schemes, and short pathways through dense gas regions, these issues are now circumvented. Here we provide an account of best practice using environmental transmission electron microscopy on catalytic systems illustrated using select examples from the literature showing how in situ electron microscopy can provide new insight into the state of catalysts under reactive environments.
Title: Graphene Edges Dictate the Morphology of Nanoparticles during Catalytic Channeling
Authors: Filippo Pizzocchero, Marco Vanin, Jens Kling, Thomas W. Hansen, Karsten W. Jacobsen, Peter Bøggild, and Timothy J. Booth
References: J. Phys. Chem. C 118 (8), 4296-4302 (2014)
Date: February 2014
Abstract
Title: Graphene Edges Dictate the Morphology of Nanoparticles during Catalytic Channeling
Authors: Filippo Pizzocchero, Marco Vanin, Jens Kling, Thomas W. Hansen, Karsten W. Jacobsen, Peter Bøggild, and Timothy J. Booth
References: J. Phys. Chem. C 118 (8), 4296-4302 (2014)
Date: February 2014
Abstract: We perform in-situ transmission electron microscopy (TEM) experiments of silver nanoparticles channeling on mono-, bi-, and few-layer graphene and discover that the interactions in the one-dimensional particle-graphene contact line are sufficiently strong so as to dictate the three-dimensional shape of the nanoparticles. We find a characteristic faceted shape in particles channeling along graphene ⟨100⟩ directions that is lost during turning and thus represents a dynamic equilibrium state of the graphene-particle system. We propose a model for the mechanism of zigzag edge formation and an explanation of the rate-limiting step for this process, supported by density functional theory (DFT) calculations, and obtain a good agreement between the DFT-predicted and experimentally obtained activation energies of 0.39 and 0.56 eV, respectively. Understanding the origin of the channels' orientation and the strong influence of the graphene lattice on the dynamic behavior of the particle morphology could be crucial for obtaining deterministic nanopatterning on the atomic scale.
Title: Oxidation mechanism of nickel particles studied in an environmental transmission electron microscope
Authors: Q. Jeangros, T. W. Hansen, J. B. Wagner, R. E. Dunin-Borkowski, C. Hébert, J. Van herle, A. Hessler-Wysera
References: Acta Materialia 67, 362-372 (2014)
Date: February 2014
Abstract
Title: Oxidation mechanism of nickel particles studied in an environmental transmission electron microscope
Authors: Q. Jeangros, T. W. Hansen, J. B. Wagner, R. E. Dunin-Borkowski, C. Hébert, J. Van herle, A. Hessler-Wysera
References: Acta Materialia 67, 362-372 (2014)
Date: February 2014
Abstract: The oxidation of nickel particles was studied in situ in an environmental transmission electron microscope in 3.2 mbar of O 2  between ambient temperature and 600 °C. Several different transmission electron microscopy imaging techniques, electron diffraction and electron energy-loss spectroscopy were used to study the evolution of the microstructure and the local chemical composition of the particles during oxidation. Our results suggest that built-in field effects control the initial stages of oxidation, with randomly oriented NiO crystallites and internal voids then forming as a result of outward diffusion of Ni 2+  along NiO grain boundaries, self-diffusion of Ni 2+  ions and vacancies, growth of NiO grains and nucleation of voids at Ni/NiO interfaces. We also observed the formation of transverse cracks in a growing NiO film in situ in the electron microscope.
Title: Insights into Chirality Distributions of Single-Walled Carbon Nanotube Grown on Different CoxMg1-xO Solid Solutions
Authors: Maoshuai He, Hua Jiang, Inkeri Kauppi, Pavel V. Fedotov, Alexander I. Chernov, Elena D. Obraztsova, Filippo Cavalca, Jakob B. Wagner, Thomas Hansen, Jani Sainio, Emma sairanen, Juha Lehtonen and Esko Kauppinen
References: J. Mater. Chem. A 2, 5883-5889 (2014)
Date: January 2014
Abstract
Title: Insights into Chirality Distributions of Single-Walled Carbon Nanotube Grown on Different CoxMg1-xO Solid Solutions
Authors: Maoshuai He, Hua Jiang, Inkeri Kauppi, Pavel V. Fedotov, Alexander I. Chernov, Elena D. Obraztsova, Filippo Cavalca, Jakob B. Wagner, Thomas Hansen, Jani Sainio, Emma sairanen, Juha Lehtonen and Esko Kauppinen
References: J. Mater. Chem. A 2, 5883-5889 (2014)
Date: January 2014
Abstract: Low-temperature chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWNTs) was achieved on two different types of Co x Mg 1− x O catalysts prepared by different techniques: atomic layer deposition (ALD) and impregnation. The chirality distribution of SWNTs grown on the ALD-prepared Co x Mg 1− x O catalyst is wider than that of SWNTs grown on the impregnation-prepared Co x Mg 1− x O catalyst. The different chirality distributions of SWNTs are related to their different growth modes. The ALD-prepared Co x Mg 1− x O catalyzes the growth of SWNTs by "tip growth" mode, as revealed by  in situ  environmental transmission electron microscopy studies. In contrast, SWNTs grow on the impregnation-prepared Co x Mg 1− x O by "base growth" mode. "Base growth" is attributed to strong metal-support interactions between the epitaxially formed Co nanoparticles and the underlying MgO support, accounting for the synthesis of SWNTs with high chiral-selectivity. In addition, impregnation-prepared Co x Mg 1− x O catalysts calcinated at different temperatures were systematically studied and their catalytic performances in synthesizing carbon nanotubes were elucidated. This work illustrates the influence of metal-support interactions and catalyst reducibility on the chirality-distribution of the synthesized SWNTs.
Title: Advances in the environmental transmission electron microscope (ETEM) for nanoscale in situ studies of gas–solid interactions
Authors: Joerg R. Jinschek
References: Feature article, Chem. Commun. 50, 2696-2706 (2014)
Date: January 2014
Abstract
Title: Advances in the environmental transmission electron microscope (ETEM) for nanoscale in situ studies of gas–solid interactions
Authors: Joerg R. Jinschek
References: Feature article, Chem. Commun. 50, 2696-2706 (2014)
Date: January 2014
Abstract: Although available since the early days of electron microscopy, recent technology developments of the environmental transmission electron microscope (ETEM) have enabled new research in the study of nanomaterials in gaseous environments. Significant improvements in scanning/transmission electron microscope (S/TEM) technologies, while containing a gaseous environment close to the object under investigation, enable now the atomic scale study of phenomena occurring during gas-solid interactions. A focus behind these developments is the research on nanomaterial-based technologies, for instance for efficient energy conversion, use and storage as well as for environmental protection.  In situ  high spatial resolution characterization provides unique information that is beneficial for understanding the relationship between the structure, properties and function of nanostructures directly on their characteristic length scales. The progress in recent research is reviewed to highlight the potential of the state-of-the-art differentially-pumped microscope platform, based on the latest microscope generation optimized for atomic scale  in situ  investigations. Using cases from current catalysis research, high resolution imaging reveals structural changes in nanocatalysts when being active and is instrumental in understanding deactivation processes; while spectroscopy gives additional access to reactivity. Also, imaging schemes are discussed that focus on enhancing the achievable imaging resolution, while having the effect of electron beam-solid interaction in the nanomaterial under control.
Title: In-Situ TEM visualization of vacancy injection and chemical partition during oxidation of Ni-Cr nanoparticles
Authors: Chong-Min Wang, Arda Genc, Huikai Cheng, Lee Pullan, Donald R. Baer & Stephen M. Bruemmer
References: Scientific Reports 4, Article number: 3683 (2014)
Date: January 2014
Abstract
Title: In-Situ TEM visualization of vacancy injection and chemical partition during oxidation of Ni-Cr nanoparticles
Authors: Chong-Min Wang, Arda Genc, Huikai Cheng, Lee Pullan, Donald R. Baer & Stephen M. Bruemmer
References: Scientific Reports 4, Article number: 3683 (2014)
Date: January 2014
Abstract: Oxidation of alloy often involves chemical partition and injection of vacancies. Chemical partition is the consequence of selective oxidation, while injection of vacancies is associated with the differences of diffusivity of cations and anions. It is far from clear as how the injected vacancies behave during oxidation of metal. Using in-situ transmission electron microscopy, we captured unprecedented details on the collective behavior of injected vacancies during oxidation of metal, featuring an initial multi-site oxide nucleation, vacancy supersaturation, nucleation of a single cavity, sinking of vacancies into the cavity and accelerated oxidation of the particle. High sensitive energy dispersive x-ray spectroscopy mapping reveals that Cr is preferentially oxidized even at the initial oxidation, leading to a structure that Cr oxide is sandwiched near the inner wall of the hollow particle. The work provides a general guidance on tailoring of nanostructured materials involving multi-ion exchange such as core-shell structured composite nanoparticles.
Title: Elucidation of the origin of grown-in defects in carbon nanotubes
Authors: H. Yoshida, S. Takeda
References: Carbon 70, 266-272 (2014)
Date: January 2014
Abstract
Title: Elucidation of the origin of grown-in defects in carbon nanotubes
Authors: H. Yoshida, S. Takeda
References: Carbon 70, 266-272 (2014)
Date: January 2014
Abstract: The origin of grown-in defects in carbon nanotubes (CNTs) is elucidated by in situ atomic-scale environmental transmission electron microscope (ETEM) observations of the chemical vapor deposition growth of CNTs. Our high-resolution ETEM observations clearly demonstrate that the deformation of nanoparticle catalysts (NPCs) during the growth of CNTs triggers the formation of various defects in CNTs. The small deformation of NPCs at the interface with CNTs gives rise to the formation of bends and disorder of the interlayer spacing in CNTs. The changes in the diameter and number of graphitic layers in CNTs are caused by the large protrusion on and shrink deformations of NPCs. This study provides insightful strategies to control the grown-in defects of CNTs.
Title: Measurements of local chemistry and structure in Ni(O)–YSZ composites during reduction using energy-filtered environmental TEM
Authors: Quentin Jeangros, Thomas W. Hansen, Jakob B. Wagner, Rafal E. Dunin-Borkowski, Cécile Hébert, Jan Van herle and Aïcha Hessler-Wysera
References: Chem. Commun. 50, 1808-1810 (2014)
Date: December 2013
Abstract
Title: Measurements of local chemistry and structure in Ni(O)–YSZ composites during reduction using energy-filtered environmental TEM
Authors: Quentin Jeangros, Thomas W. Hansen, Jakob B. Wagner, Rafal E. Dunin-Borkowski, Cécile Hébert, Jan Van herle and Aïcha Hessler-Wysera
References: Chem. Commun. 50, 1808-1810 (2014)
Date: December 2013
Abstract: Energy-filtered transmission electron microscopy images are acquired during the reduction of a NiO-YSZ composite in H 2  up to 600 °C. Temperature-resolved quantitative information about both chemistry and structure is extracted with nm spatial resolution from the data, paving the way for the development of detailed reduction models.
Title: Insights from in situ and environmental TEM on the oriented attachment of α-Fe2O3 nanoparticles during α-Fe2O3 nanorod formation
Authors: Trevor P. Almeida, Michael W. Fay, Thomas W. Hansen, Yanqiu Zhu and Paul D. Brown
References: CrystEngComm 16, 1540-1546 (2014)
Date: November 2013
Abstract
Title: Insights from in situ and environmental TEM on the oriented attachment of α-Fe2O3 nanoparticles during α-Fe2O3 nanorod formation
Authors: Trevor P. Almeida, Michael W. Fay, Thomas W. Hansen, Yanqiu Zhu and Paul D. Brown
References: CrystEngComm 16, 1540-1546 (2014)
Date: November 2013
Abstract: Acicular α-Fe 2 O 3  nanorods (NRs), at an intermediate stage of development, were isolated using a snapshot valve-assisted hydrothermal synthesis (HS) technique, for the purpose of complementary  in situ  transmission electron microscopy ( i TEM) and environmental TEM (ETEM) investigations of the effect of local environment on the oriented attachment (OA) of α-Fe 2 O 3 nanoparticles (NPs) during α-Fe 2 O 3  NR growth. Observations of static snapshot HS samples suggested that α-Fe 2 O 3  NPs undergo reorientation following initial attachment, consistent with an intermediate OA stage, prior to 'envelopment' with the developing NR to adopt a perfect single crystal. Conversely, the heating of partially developed α-Fe 2 O 3  NRs up to 250 °C, under vacuum, during  i TEM, demonstrated the progressive coalescence of loosely packed α-Fe 2 O 3 NPs and the coarsening of α-Fe 2 O 3  NRs, without any direct evidence for an intermediate OA stage. Direct evidence was obtained for the action of an OA mechanism prior to the consumption of α-Fe 2 O 3  NPs at the tips of developing α-Fe 2 O 3  NRs during ETEM investigation, under an He pressure of 5 mbar at 500 °C. However, α-Fe 2 O 3  NPs more strongly attached to the side-walls of developing α-Fe 2 O 3  NRs were more likely to be consumed through a local NP destabilisation and reordering process, in the absence of an OA mechanism. Hence, the emerging ETEM evidence suggests a competition between OA and diffusion processes at the α-Fe 2 O 3  NP coalescence stage of acicular α-Fe 2 O 3  NR crystal development, depending on whether the localised growth conditions facilitate freedom of NP movement.
Title: In situ atomic-scale visualization of oxide islanding during oxidation of Cu surfaces
Authors: Guangwen Zhou, Langli Luo, Liang Li, Jim Ciston, Eric A. Stach, Wissam A. Saidi and Judith C. Yang
References: Chem. Commun . 49, 10862-10864 (2013)
Date: October 2013
Abstract
Title: In situ atomic-scale visualization of oxide islanding during oxidation of Cu surfaces
Authors: Guangwen Zhou, Langli Luo, Liang Li, Jim Ciston, Eric A. Stach, Wissam A. Saidi and Judith C. Yang
References: Chem. Commun . 49, 10862-10864 (2013)
Date: October 2013
Abstract: Oxidation of Cu occurs  via  Cu 2 O islanding on an oxide wetting layer at a critical thickness of two atomic layers. The transition from 2D wetting-layer growth to 3D oxide islanding is driven energetically arising from the Cu-Cu 2 O interfacial interaction.