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“Encapsulation of Noble Metal Nanoparticles through Seeded Emulsion Polymerization as Highly Stable Plasmonic Systems”. Scarabelli L, Schumacher M, Jimenez de Aberasturi D, Merkl J‐P, Henriksen‐Lacey M, Milagres de Oliveira T, Janschel M, Schmidtke C, Bals S, Weller H, Liz‐Marzán LM, Advanced functional materials 29, 1809071 (2019). http://doi.org/10.1002/adfm.201809071
Abstract: The implementation of plasmonic nanoparticles in vivo remains hindered by important limitations such as biocompatibility, solubility in biological fluids, and physiological stability. A general and versatile protocol is presented, based on seeded emulsion polymerization, for the controlled encapsulation of gold and silver nanoparticles. This procedure enables the encapsulation of single nanoparticles as well as nanoparticle clusters inside a protecting polymer shell. Specifically, the efficient coating of nanoparticles of both metals is demonstrated, with final dimensions ranging between 50 and 200 nm, i.e., sizes of interest for bio-applications. Such hybrid nanocomposites display extraordinary stability in high ionic strength and oxidizing environments, along with high cellular uptake, and low cytotoxicity. Overall, the prepared nanostructures are promising candidates for plasmonic applications under biologically relevant conditions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.124
Times cited: 19
DOI: 10.1002/adfm.201809071
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“3D characterization of the structural transformation undergone by Cu@Ag core-shell nanoparticles following CO₂, reduction reaction”. Arenas Esteban D, Pacquets L, Choukroun D, Hoekx S, Kadu AA, Schalck J, Daems N, Breugelmans T, Bals S, Chemistry of materials 35, 6682 (2023). http://doi.org/10.1021/ACS.CHEMMATER.3C00649
Abstract: The increasing use of metallic nanoparticles (NPs) is significantly advancing the field of electrocatalysis. In particular, Cu/Ag bimetallic interfaces are widely used to enhance the electrochemical CO2 reduction reaction (eCO(2)RR) toward CO and, more recently, C-2 products. However, drastic changes in the product distribution and performance when Cu@Ag core-shell configurations are used can often be observed under electrochemical reaction conditions, especially during the first few minutes of the reaction. Possible structural changes that generate these observations remain underexplored; therefore, the structure-property relationship is hardly understood. In this study, we use electron tomography to investigate the structural transformation mechanism of Cu@Ag core-shells NPs during the critical first minutes of the eCO(2)RR. In this manner, we found that the crystallinity of the Cu seed determines whether the formation of a complete and homogeneous Ag shell is possible. Moreover, by tracking the particles' transformations, we conclude that modifications of the Cu-Ag interface and Cu2O enrichment at the surface of the NPs are key factors contributing to the product generation changes. These insights provide a better understanding of how bimetallic core-shell NPs transform under electrochemical conditions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 8.6
Times cited: 1
DOI: 10.1021/ACS.CHEMMATER.3C00649
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“Use of nanoscale carbon layers on Ag-based gas diffusion electrodes to promote CO production”. Pacquets L, Van den Hoek J, Arenas Esteban D, Ciocarlan R-G, Cool P, Baert K, Hauffman T, Daems N, Bals S, Breugelmans T, ACS applied nano materials 5, 7723 (2022). http://doi.org/10.1021/ACSANM.2C00473
Abstract: A promising strategy for the inhibition of the hydrogen evolution reaction along with the stabilization of the electrocatalyst in electrochemical CO2 reduction cells involves the application of a nanoscale amorphous carbon layer on top of the active catalyst layer in a gas diffusion electrode. Without modifying the chemical nature of the electrocatalyst itself, these amorphous carbon layers lead to the stabilization of the electrocatalyst, and a significant improvement with respect to the inhibition of the hydrogen evolution reaction was also obtained. The faradaic efficiencies of hydrogen could be reduced from 31.4 to 2.1% after 1 h of electrolysis with a 5 nm thick carbon layer. Furthermore, the impact of the carbon layer thickness (5–30 nm) on this inhibiting effect was investigated. We determined an optimal thickness of 15 nm where the hydrogen evolution reaction was inhibited and a decent stability was obtained. Next, a thickness of 15 nm was selected for durability measurements. Interestingly, these durability measurements revealed the beneficial impact of the carbon layer already after 6 h by suppressing the hydrogen evolution such that an increase of only 37.9% exists compared to 56.9% without the use of an additional carbon layer, which is an improvement of 150%. Since carbon is only applied afterward, it reveals its great potential in terms of electrocatalysis in general.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Laboratory of adsorption and catalysis (LADCA); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 5.9
Times cited: 3
DOI: 10.1021/ACSANM.2C00473
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“Fast A-site cation cross-exchange at room temperature : single-to double- and triple-cation halide perovskite nanocrystals”. Otero-Martinez C, Imran M, Schrenker NJ, Ye J, Ji K, Rao A, Stranks SD, Hoye RLZ, Bals S, Manna L, Perez-Juste J, Polavarapu L, Angewandte Chemie: international edition in English 61, e202205617 (2022). http://doi.org/10.1002/ANIE.202205617
Abstract: We report here fast A-site cation cross-exchange between APbX(3) perovskite nanocrystals (NCs) made of different A-cations (Cs (cesium), FA (formamidinium), and MA (methylammonium)) at room temperature. Surprisingly, the A-cation cross-exchange proceeds as fast as the halide (X=Cl, Br, or I) exchange with the help of free A-oleate complexes present in the freshly prepared colloidal perovskite NC solutions. This enabled the preparation of double (MACs, MAFA, CsFA)- and triple (MACsFA)-cation perovskite NCs with an optical band gap that is finely tunable by their A-site composition. The optical spectroscopy together with structural analysis using XRD and atomically resolved high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and integrated differential phase contrast (iDPC) STEM indicates the homogeneous distribution of different cations in the mixed perovskite NC lattice. Unlike halide ions, the A-cations do not phase-segregate under light illumination.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 16.6
Times cited: 28
DOI: 10.1002/ANIE.202205617
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“Reversible Clustering of Gold Nanoparticles under Confinement”. Sánchez-Iglesias A, Claes N, Solís DM, Taboada JM, Bals S, Liz-Marzán LM, Grzelczak M, Angewandte Chemie: international edition in English 57, 3183 (2018). http://doi.org/10.1002/anie.201800736
Abstract: A limiting factor of solvent-induced nanoparticle self-assembly is the need for constant sample dilution in assembly/disassembly cycles. Changes in the nanoparticle concentration alter the kinetics of the subsequent assembly process, limiting optical signal recovery. Herein, we show that upon confining hydrophobic nanoparticles in permeable silica nanocapsules, the number of nanoparticles participating in cyclic aggregation remains constant despite bulk changes in solution, leading to highly reproducible plasmon band shifts at different solvent compositions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 11.994
Times cited: 53
DOI: 10.1002/anie.201800736
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“Controlled Living Nanowire Growth: Precise Control over the Morphology and Optical Properties of AgAuAg Bimetallic Nanowires”. Mayer M, Scarabelli L, March K, Altantzis T, Tebbe M, Kociak M, Bals S, Garcia de Abajo FJ, Fery A, Liz-Marzan LM, Nano letters 15, 5427 (2015). http://doi.org/10.1021/acs.nanolett.5b01833
Abstract: Inspired by the concept of living polymerization reaction, we are able to produce silver-gold-silver nanowires with a precise control over their total length and plasmonic properties by establishing a constant silver deposition rate on the tips of penta-twinned gold nanorods used as seed cores. Consequently, the length of the wires increases linearly in time. Starting with approximately 210 nm x 32 nm gold cores, we produce nanowire lengths up to several microns in a highly controlled manner, with a small self-limited increase in thickness of approximately 4 nm, corresponding to aspect ratios above 100, whereas the low polydispersity of the product allows us to detect up to nine distinguishable plasmonic resonances in a single colloidal solution. We analyze the spatial distribution and the nature of the plasmons by electron energy loss spectroscopy and obtain excellent agreement between measurements and electromagnetic simulations, clearly demonstrating that the presence of the gold core plays a marginal role, except for relatively short wires or high-energy modes.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 117
DOI: 10.1021/acs.nanolett.5b01833
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“Micelle-directed chiral seeded growth on anisotropic gold nanocrystals”. González-Rubio G, Mosquera J, Kumar V, Pedrazo-Tardajos A, Llombart P, Solís DM, Lobato I, Noya EG, Guerrero-Martínez A, Taboada JM, Obelleiro F, MacDowell LG, Bals S, Liz-Marzán LM, Science 368, 1472 (2020). http://doi.org/10.1126/science.aba0980
Abstract: Surfactant-assisted seeded growth of metal nanoparticles (NPs) can be engineered to produce anisotropic gold nanocrystals with high chiroptical activity through the templating effect of chiral micelles formed in the presence of dissymmetric cosurfactants. Mixed micelles adsorb on gold nanorods, forming quasihelical patterns that direct seeded growth into NPs with pronounced morphological and optical handedness. Sharp chiral wrinkles lead to chiral plasmon modes with high dissymmetry factors (~0.20). Through variation of the dimensions of chiral wrinkles, the chiroptical properties can be tuned within the visible and near-infrared electromagnetic spectrum. The micelle-directed mechanism allows extension to other systems, such as the seeded growth of chiral platinum shells on gold nanorods. This approach provides a reproducible, simple, and scalable method toward the fabrication of NPs with high chiral optical activity.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 56.9
Times cited: 187
DOI: 10.1126/science.aba0980
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“An Expanded Surface-Enhanced Raman Scattering Tags Library by Combinatorial Encapsulation of Reporter Molecules in Metal Nanoshells”. Rodal-Cedeira S, Vázquez-Arias A, Bodelon G, Skorikov A, Núñez-Sanchez S, La Porta A, Polavarapu L, Bals S, Liz-Marzán LM, Perez-Juste J, Pastoriza-Santos I, Acs Nano (2020). http://doi.org/10.1021/acsnano.0c04368
Abstract: Raman-encoded gold nanoparticles have been widely employed as photostable multifunctional probes for sensing, bioimaging, multiplex diagnostics, and surface-enhanced Raman scattering (SERS)-guided tumor therapy. We report a strategy toward obtaining a particularly large library of Au nanocapsules encoded with Raman codes defined by the combination of different thiol-free Raman reporters, encapsulated at defined molar ratios. The fabrication of SERS tags with tailored size and pre-defined codes is based on the in situ incorporation of Raman reporter molecules inside Au nanocapsules during their formation via Galvanic replacement coupled to seeded growth on Ag NPs. The hole-free closed shell structure of the nanocapsules is confirmed by electron tomography. The unusually wide encoding possibilities of the obtained SERS tags are investigated by means of either wavenumber-based encoding or Raman frequency combined with signal intensity, leading to an outstanding performance as exemplified by 26 and 54 different codes, respectively. We additionally demonstrate that encoded nanocapsules can be readily bioconjugated with antibodies for applications such as SERS-based targeted cell imaging and phenotyping.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 17.1
Times cited: 14
DOI: 10.1021/acsnano.0c04368
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“Hematite iron oxide nanorod patterning inside COK-12 mesochannels as an efficient visible light photocatalyst”. Wee LH, Meledina M, Turner S, Custers K, Kerkhofs S, Van Tendeloo G, Martens JA, Journal of materials chemistry A : materials for energy and sustainability 3, 19884 (2015). http://doi.org/10.1039/C5TA05075H
Abstract: The uniform dispersion of functional oxide nanoparticles on the walls of ordered mesoporous silica to tailor optical, electronic, and magnetic properties for biomedical and environmental applications is a scientific challenge. Here, we demonstrate homogeneous confined growth of 5 nanometer-sized hematite iron oxide (α-Fe2O3) inside mesochannels of ordered mesoporous COK-12 nanoplates. The three-dimensional inclusion of the α-Fe2O3 nanorods in COK-12 particles is studied using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray (EDX) spectroscopy and electron tomography. High resolution imaging and EDX spectroscopy provide information about the particle size, shape and crystal phase of the loaded α-Fe2O3 material, while electron tomography provides detailed information on the spreading of the nanorods throughout the COK-12 host. This nanocomposite material, having a semiconductor band gap energy of 2.40 eV according to diffuse reflectance spectroscopy, demonstrates an improved visible light photocatalytic degradation activity with rhodamine 6G and 1-adamantanol model compounds.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.867
Times cited: 9
DOI: 10.1039/C5TA05075H
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“In Situ Plasma Studies Using a Direct Current Microplasma in a Scanning Electron Microscope”. Grünewald L, Chezganov D, De Meyer R, Orekhov A, Van Aert S, Bogaerts A, Bals S, Verbeeck J, Advanced Materials Technologies (2024). http://doi.org/10.1002/admt.202301632
Abstract: Microplasmas can be used for a wide range of technological applications and to improve the understanding of fundamental physics. Scanning electron microscopy, on the other hand, provides insights into the sample morphology and chemistry of materials from the mm‐ down to the nm‐scale. Combining both would provide direct insight into plasma‐sample interactions in real‐time and at high spatial resolution. Up till now, very few attempts in this direction have been made, and significant challenges remain. This work presents a stable direct current glow discharge microplasma setup built inside a scanning electron microscope. The experimental setup is capable of real‐time in situ imaging of the sample evolution during plasma operation and it demonstrates localized sputtering and sample oxidation. Further, the experimental parameters such as varying gas mixtures, electrode polarity, and field strength are explored and experimental<italic>V</italic>–<italic>I</italic>curves under various conditions are provided. These results demonstrate the capabilities of this setup in potential investigations of plasma physics, plasma‐surface interactions, and materials science and its practical applications. The presented setup shows the potential to have several technological applications, for example, to locally modify the sample surface (e.g., local oxidation and ion implantation for nanotechnology applications) on the µm‐scale.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 6.8
DOI: 10.1002/admt.202301632
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“Symmetry-constrained electron vortex propagation”. Clark L, Guzzinati G, Béché, A, Lubk A, Verbeeck J, Physical review A 93, 063840 (2016). http://doi.org/10.1103/PhysRevA.93.063840
Abstract: Electron vortex beams hold great promise for development in transmission electron microscopy but have yet to be widely adopted. This is partly due to the complex set of interactions that occur between a beam carrying orbital angular momentum (OAM) and a sample. Herein, the system is simplified to focus on the interaction between geometrical symmetries, OAM, and topology. We present multiple simulations alongside experimental data to study the behavior of a variety of electron vortex beams after interacting with apertures of different symmetries and investigate the effect on their OAM and vortex structure, both in the far field and under free-space propagation.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.925
Times cited: 7
DOI: 10.1103/PhysRevA.93.063840
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“Anatase TiO2nanoparticle coating on porous COK-12 platelets as highly active and reusable photocatalysts”. Wee LH, Meledina M, Turner S, Custers K, Kerkhofs S, Sree SP, Gobechiya E, Kirschhock CEA, Van Tendeloo G, Martens JA, RSC advances 6, 46678 (2016). http://doi.org/10.1039/C6RA06141A
Abstract: Nanoscale TiO2 photocatalysts are widely used for biomedical applications, self-cleaning processes and wastewater treatments. The impregnation/deposition of TiO2 nanoparticles is indispensable for facile handling and separation as well as the improvement of their photocatalytic performance. In the present study, ordered mesoporous COK-12 silica thin platelets with a high-aspect-ratio and rough surfaces are demonstrated as a potential nanoporous support for homogeneous TiO2 nanoparticle coatings with high loading up to 16.7 wt%. The photocatalytic composite of COK-12 platelets and TiO2 nanoparticles is characterized in detail by HRSEM, SAXS, XRD, N2 physisorption analysis, solid-state UV-vis spectroscopy, HAADF-STEM, EDX analysis, and electron tomography. HAADF-STEM-EDX and electron tomography studies reveal a homogeneous dispersion of nanosized TiO2 nanoparticles over COK-12 platelets. The final composite material with anatase TiO2 nanoparticles that demonstrate a blueshifted semiconductor band gap energy of 3.2 eV coated on a highly porous COK-12 support shows exceptional photocatalytic catalytic activity for photodegradation of organic dyes (rhodamine 6G and methylene blue) and an organic pollutant (1-adamantanol) under UV light radiation, outperforming the commercial P25 TiO2 (Degussa) catalyst.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 6
DOI: 10.1039/C6RA06141A
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“ROS from Physical Plasmas: Redox Chemistry for Biomedical Therapy”. Privat-Maldonado A, Schmidt A, Lin A, Weltmann K-D, Wende K, Bogaerts A, Bekeschus S, Oxidative medicine and cellular longevity 2019, 1 (2019). http://doi.org/10.1155/2019/9062098
Abstract: Physical plasmas generate unique mixes of reactive oxygen and nitrogen species (RONS or ROS). Only a bit more than a decade ago, these plasmas, operating at body temperature, started to be considered for medical therapy with considerably little mechanistic redox chemistry or biomedical research existing on that topic at that time. Today, a vast body of evidence is available on physical plasma-derived ROS, from their spatiotemporal resolution in the plasma gas phase to sophisticated chemical and biochemical analysis of these species once dissolved in liquids. Data from<italic>in silico</italic>analysis dissected potential reaction pathways of plasma-derived reactive species with biological membranes, and<italic>in vitro</italic>and<italic>in vivo</italic>experiments in cell and animal disease models identified molecular mechanisms and potential therapeutic benefits of physical plasmas. In 2013, the first medical plasma systems entered the European market as class IIa devices and have proven to be a valuable resource in dermatology, especially for supporting the healing of chronic wounds. The first results in cancer patients treated with plasma are promising, too. Due to the many potentials of this blooming new field ahead, there is a need to highlight the main concepts distilled from plasma research in chemistry and biology that serve as a mechanistic link between plasma physics (how and which plasma-derived ROS are produced) and therapy (what is the medical benefit). This inevitably puts cellular membranes in focus, as these are the natural interphase between ROS produced by plasmas and translation of their chemical reactivity into distinct biological responses.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.593
DOI: 10.1155/2019/9062098
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“Arc plasma reactor modification for enhancing performance of dry reforming of methane”. Dinh DK, Trenchev G, Lee DH, Bogaerts A, Journal Of Co2 Utilization 42, 101352 (2020). http://doi.org/10.1016/j.jcou.2020.101352
Abstract: Arc plasma technology is gaining increasing interest for a variety of chemical reaction applications. In this study, we demonstrate how modifying the reactor geometry can significantly enhance the chemical reaction performance. Using dry reforming of methane as a model reaction, we studied different rotating arc reactors (conventional rotating arc reactor and nozzle-type rotating arc reactor) to evaluate the effect of attaching a downstream nozzle. The nozzle structure focuses the heat to a confined reaction volume, resulting in enhanced heat transfer from the arc into gas activation and reduced heat losses to the reactor walls. Compared to the conventional rotating arc reactor, this yields much higher CH4 and CO2 conversion (i.e., 74% and 49%, respectively, versus 40% and 28% in the conventional reactor, at 5 kJ/L) as well as energy efficiency (i.e., 53% versus 36%). The different performance in both reactors was explained by both experiments (measurements of temperature and oscillogram of current and voltage) and numerical modelling of the gas flow dynamics, heat transfer and fluid plasma of the reactor chambers. The results provide important insights for design optimization of arc plasma reactors for various chemical reactions.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 7.7
DOI: 10.1016/j.jcou.2020.101352
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“Effect of plasma-induced surface charging on catalytic processes: application to CO2activation”. Bal KM, Huygh S, Bogaerts A, Neyts EC, Plasma sources science and technology 27, 024001 (2018). http://doi.org/10.1088/1361-6595/aaa868
Abstract: Understanding the nature and effect of the multitude of plasma–surface interactions in plasma catalysis is a crucial requirement for further process development and improvement. A particularly intriguing and rather unique property of a plasma-catalytic setup is the ability of the plasma to modify the electronic structure, and hence chemical properties, of the catalyst through charging, i.e. the absorption of excess electrons. In this work, we develop a quantum chemical model based on density functional theory to study excess negative surface charges in a heterogeneous catalyst exposed to a plasma. This method is specifically applied to investigate plasma-catalytic CO2 activation on supported M/Al2O3 (M=Ti, Ni, Cu) single atom catalysts. We find that (1) the presence of a negative surface charge dramatically improves the reductive power of the catalyst, strongly promoting the splitting of CO2 to CO and oxygen, and (2) the relative activity of the investigated transition metals is also changed upon charging, suggesting that controlled surface charging is a powerful additional parameter to tune catalyst activity and selectivity. These results strongly point to plasma-induced surface charging of the catalyst as an important factor contributing to the plasma-catalyst synergistic effects frequently reported for plasma catalysis.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.302
Times cited: 19
DOI: 10.1088/1361-6595/aaa868
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“Inhibiting recombination to improve the performance of plasma-based CO2 conversion”. Wang K, Ceulemans S, Zhang H, Tsonev I, Zhang Y, Long Y, Fang M, Li X, Yan J, Bogaerts A, Chemical Engineering Journal 481, 148684 (2024). http://doi.org/10.1016/j.cej.2024.148684
Abstract: Warm plasma offers a promising route for CO2 splitting into valuable CO, yet recombination reactions of CO with oxygen, forming again CO2, have recently emerged as critical limitation. This study combines experiments and fluid dynamics + chemical kinetics modelling to comprehensively analyse the recombination reactions upon CO2 splitting in an atmospheric plasmatron. We introduce an innovative in-situ gas sampling technique, enabling 2D spatial mapping of gas product compositions and temperatures, experimentally confirming for the first time the substantial limiting effect of CO recombination reactions in the afterglow region. Our results show that the CO mole fraction at a 5 L/min flow rate drops significantly from 11.9 % at a vertical distance of z = 20 mm in the afterglow region to 8.6 % at z = 40 mm. We constructed a comprehensive 2D model that allows for spatial reaction rates analysis incorporating crucial reactions, and we validated it to kinetically elucidate this phenomenon. CO2 +M⇌O+CO+M and CO2 +O⇌CO+O2 are the dominant reactions, with the forward reactions prevailing in the plasma region and the backward reactions becoming prominent in the afterglow region. These results allow us to propose an afterglow quenching strategy for performance enhancement, which is further demonstrated through a meticulously developed plasmatron reactor with two-stage cooling. Our approach substantially increases the CO2 conversion (e.g., from 6.6 % to 19.5 % at 3 L/min flow rate) and energy efficiency (from 13.5 % to 28.5 %, again at 3 L/min) and significantly shortens the startup time (from ~ 150 s to 25 s). Our study underscores the critical role of inhibiting recombination reactions in plasma-based CO2 conversion and offers new avenues for performance enhancement.
Keywords: A1 Journal Article; Plasma-based CO2 splitting Recombination reactions In-situ gas sampling Fluid dynamics modeling Kinetics modeling Afterglow quenching; Plasma, laser ablation and surface modeling Antwerp (PLASMANT) ;
Impact Factor: 15.1
DOI: 10.1016/j.cej.2024.148684
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“Atomic Layer Deposition of Pt Nanoparticles within the Cages of MIL-101: A Mild and Recyclable Hydrogenation Catalyst”. Leus K, Dendooven J, Tahir N, Ramachandran R, Meledina M, Turner S, Van Tendeloo G, Goeman J, Van der Eycken J, Detavernier C, Van Der Voort P, Nanomaterials 6, 45 (2016). http://doi.org/10.3390/nano6030045
Abstract: We present the in situ synthesis of Pt nanoparticles within MIL-101-Cr (MIL = Materials Institute Lavoisier) by means of atomic layer deposition (ALD). The obtained Pt@MIL-101 materials were characterized by means of N2 adsorption and X-ray powder diffraction (XRPD) measurements, showing that the structure of the metal organic framework was well preserved during the ALD deposition. X-ray fluorescence (XRF) and transmission electron microscopy (TEM) analysis confirmed the deposition of highly dispersed Pt nanoparticles with sizes determined by the MIL-101-Cr pore sizes and with an increased Pt loading for an increasing number of ALD cycles. The Pt@MIL-101 material was examined as catalyst in the hydrogenation of different linear and cyclic olefins at room temperature, showing full conversion for each substrate. Moreover, even under solvent free conditions, full conversion of the substrate was observed. A high concentration test has been performed showing that the Pt@MIL-101 is stable for a long reaction time without loss of activity, crystallinity and with very low Pt leaching.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 3.553
Times cited: 19
DOI: 10.3390/nano6030045
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“Artifact Reduction Based on Sinogram Interpolation for the 3D Reconstruction of Nanoparticles Using Electron Tomography”. Sentosun K, Lobato I, Bladt E, Zhang Y, Palenstijn WJ, Batenburg KJ, Van Dyck D, Bals S, Particle and particle systems characterization 34, 1700287 (2017). http://doi.org/10.1002/ppsc.201700287
Abstract: Electron tomography is a well-known technique providing a 3D characterization of the morphology and chemical composition of nanoparticles. However, several reasons hamper the acquisition of tilt series with a large number of projection images, which deteriorate the quality of the 3D reconstruction. Here, an inpainting method that is based on sinogram interpolation is proposed, which enables one to reduce artifacts in the reconstruction related to a limited tilt series of projection images. The advantages of the approach will be demonstrated for the 3D characterization of nanoparticles using phantoms and several case studies.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Vision lab
Times cited: 2
DOI: 10.1002/ppsc.201700287
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“Merging Metadynamics into Hyperdynamics: Accelerated Molecular Simulations Reaching Time Scales from Microseconds to Seconds”. Bal KM, Neyts EC, Journal of chemical theory and computation 11, 4545 (2015). http://doi.org/10.1021/acs.jctc.5b00597
Abstract: The hyperdynamics method is a powerful tool to simulate slow processes at the atomic level. However, the construction of an optimal hyperdynamics potential is a task that is far from trivial. Here, we propose a generally applicable implementation of the hyperdynamics algorithm, borrowing two concepts from metadynamics. First, the use of a collective variable (CV) to represent the accelerated dynamics gives the method a very large flexibility and simplicity. Second, a metadynamics procedure can be used to construct a suitable history-dependent bias potential on-the-fly, effectively turning the algorithm into a self-learning accelerated molecular dynamics method. This collective variable-driven hyperdynamics (CVHD) method has a modular design: both the local system properties on which the bias is based, as well as the characteristics of the biasing method itself, can be chosen to match the needs of the considered system. As a result, system-specific details are abstracted from the biasing algorithm itself, making it extremely versatile and transparent. The method is tested on three model systems: diffusion on the Cu(001) surface and nickel-catalyzed methane decomposition, as examples of reactive processes with a bond-length-based CV, and the folding of a long polymer-like chain, using a set of dihedral angles as a CV. Boost factors up to 109, corresponding to a time scale of seconds, could be obtained while still accurately reproducing correct dynamics.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 5.245
Times cited: 41
DOI: 10.1021/acs.jctc.5b00597
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“Measurement of atomic electric fields and charge densities from average momentum transfers using scanning transmission electron microscopy”. Muller-Caspary K, Krause FF, Grieb T, Loffler S, Schowalter M, Béché, A, Galioit V, Marquardt D, Zweck J, Schattschneider P, Verbeeck J, Rosenauer A, Ultramicroscopy 178, 62 (2016). http://doi.org/10.1016/j.ultramic.2016.05.004
Abstract: This study sheds light on the prerequisites, possibilities, limitations and interpretation of high-resolution differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM). We draw particular attention to the well-established DPC technique based on segmented annular detectors and its relation to recent developments based on pixelated detectors. These employ the expectation value of the momentum transfer as a reliable measure of the angular deflection of the STEM beam induced by an electric field in the specimen. The influence of scattering and propagation of electrons within the specimen is initially discussed separately and then treated in terms of a two-state channeling theory. A detailed simulation study of GaN is presented as a function of specimen thickness and bonding. It is found that bonding effects are rather detectable implicitly, e.g., by characteristics of the momentum flux in areas between the atoms than by directly mapping electric fields and charge densities. For strontium titanate, experimental charge densities are compared with simulations and discussed with respect to experimental artifacts such as scan noise. Finally, we consider practical issues such as figures of merit for spatial and momentum resolution, minimum electron dose, and the mapping of larger-scale, built-in electric fields by virtue of data averaged over a crystal unit cell. We find that the latter is possible for crystals with an inversion center. Concerning the optimal detector design, this study indicates that a sampling of 5mrad per pixel is sufficient in typical applications, corresponding to approximately 10x10 available pixels.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 93
DOI: 10.1016/j.ultramic.2016.05.004
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“Modelling molecular adsorption on charged or polarized surfaces: a critical flaw in common approaches”. Bal KM, Neyts EC, Physical chemistry, chemical physics 20, 8456 (2018). http://doi.org/10.1039/C7CP08209F
Abstract: A number of recent computational material design studies based on density functional theory (DFT) calculations have put forward a new class of materials with electrically switchable chemical characteristics that can be exploited in the development of tunable gas storage and electrocatalytic applications. We find systematic flaws in almost every computational study of gas adsorption on polarized or charged surfaces, stemming from an improper and unreproducible treatment of periodicity, leading to very large errors of up to 3 eV in some cases. Two simple corrective procedures that lead to consistent results are proposed, constituting a crucial course correction to the research in the field.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.123
Times cited: 8
DOI: 10.1039/C7CP08209F
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“Direct observation of realistic-temperature fuel combustion mechanisms in atomistic simulations”. Bal KM, Neyts EC, Chemical science 7, 5280 (2016). http://doi.org/10.1039/C6SC00498A
Abstract: Atomistic simulations can in principle provide an unbiased description of all mechanisms, intermediates, and products of complex chemical processes. However, due to the severe time scale limitation of conventional simulation techniques, unrealistically high simulation temperatures are usually applied, which are a poor approximation of most practically relevant low-temperature applications. In this work, we demonstrate the direct observation at the atomic scale of the pyrolysis and oxidation of n-dodecane at temperatures as low as 700 K through the use of a novel simulation technique, collective variable-driven hyperdynamics (CVHD). A simulated timescale of up to 39 seconds is reached. Product compositions and dominant mechanisms are found to be strongly temperature-dependent, and are consistent with experiments and kinetic models. These simulations provide a first atomic-level look at the full dynamics of the complicated fuel combustion process at industrially relevant temperatures and time scales, unattainable by conventional molecular dynamics simulations.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 8.668
Times cited: 22
DOI: 10.1039/C6SC00498A
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“How bead size and dielectric constant affect the plasma behaviour in a packed bed plasma reactor: a modelling study”. Van Laer K, Bogaerts A, Plasma sources science and technology 26, 085007 (2017). http://doi.org/10.1088/1361-6595/aa7c59
Abstract: Packed bed plasma reactors (PBPRs) are gaining increasing interest for use in environmental applications, such as greenhouse gas conversion into value-added chemicals or renewable fuels and volatile pollutant removal (e.g. NOx, VOC, K), as they enhance the conversion and energy efficiency of the process compared to a non-packed reactor. However, the plasma behaviour in a PBPR is not well understood. In this paper we demonstrate, by means of a fluid model, that the discharge behaviour changes considerably when changing the size of the packing beads and their dielectric constant, while keeping the interelectrode spacing constant. At low dielectric constant, the plasma is spread out over the full discharge gap, showing significant density in the voids as well as in the connecting void channels. The electric current profile shows a strong peak during each half cycle. When the dielectric constant increases, the plasma becomes localised in the voids, with a current profile consisting of many smaller peaks during each half cycle. For large bead sizes, the shift from full gap discharge to localised discharges takes place at a higher dielectric constant than for smaller beads. Furthermore, smaller beads or beads with a lower dielectric constant require a higher breakdown voltage to cause plasma formation.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.302
Times cited: 22
DOI: 10.1088/1361-6595/aa7c59
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“Accelerated molecular dynamics simulation of large systems with parallel collective variable-driven hyperdynamics”. Fukuhara S, Bal KM, Neyts EC, Shibuta Y, Computational Materials Science 177, 109581 (2020). http://doi.org/10.1016/j.commatsci.2020.109581
Abstract: The limitation in time and length scale is a major issue of molecular dynamics (MD) simulation. Although several methods have been developed to extend the MD time scale, their performance usually deteriorates with increasing system size. Therefore, an acceleration method which is applicable to large systems is required to bridge the gap between the MD simulations and target phenomena. In this study, an accelerated MD method for large system is developed based on the collective variable-driven hyperdynamics (CVHD) method [K.M. Bal and E.C. Neyts, 2015]. The key idea is to run CVHD in parallel with rate control and accelerate multiple possible events simultaneously. Using this novel method, carbon diffusion in bcc-iron bicrystal with grain boundary is examined as an application for practical materials. Carbon atoms reaching at the grain boundary are trapped whereas carbon atoms in the bulk region diffuse randomly, and both dynamic regimes can be simultaneously accelerated with the parallel CVHD technique.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.3
DOI: 10.1016/j.commatsci.2020.109581
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“Electrodeposition of Highly Porous Pt Nanoparticles Studied by Quantitative 3D Electron Tomography: Influence of Growth Mechanisms and Potential Cycling on the Active Surface Area”. Ustarroz J, Geboes B, Vanrompay H, Sentosun K, Bals S, Breugelmans T, Hubin A, ACS applied materials and interfaces 9, 16168 (2017). http://doi.org/10.1021/acsami.7b01619
Abstract: Nanoporous Pt nanoparticles (NPs) are promising fuel cell catalysts due to their large surface area and increased electrocatalytic activity towards the oxygen reduction reaction (ORR). Herein, we report on the infuence of the growth mechanisms on the surface properties of electrodeposited Pt dendritic NPs with large surface areas. The electrochemically active surface was studied by hydrogen underpotential deposition (HUPD) and compared for the rst time to high angle annular dark eld scanning transmission electron microscopy (HAADF-STEM) quantitative 3D electron tomography of individual nanoparticles. Large nucleation overpotential leads to a large surface coverage of Pt roughened spheroids, which provide large roughness factor (Rf ) but low mass-specic electrochemically active surface area (EASA). Lowering the nucleation overpotential leads to highly porous Pt NPs with pores protruding to the center of the structure. At the expense of smaller Rf , the obtained EASA values of these structures are in the range of these of large surface area supported fuel cell catalysts. The active surface area of the Pt dendritic NPs was measured by electron tomography and it was found that the potential cycling in the H adsorption/desorption and Pt oxidation/reduction region, which is generally performed to determine the EASA, leads to a signicant reduction of that surface area due to a partial collapse of their dendritic and porous morphology. Interestingly, the extrapolation of the microscopic tomography results to macroscopic electrochemical parameters indicated that the surface properties measured by H UPD are comparable to the values measured on individual NPs by electron tomography after the degradation caused by the H UPD measurement. These results highlight that the combination of electrochemical and quantitative 3D surface analysis techniques is essential to provide insights into the surface properties, the electrochemical stability and, hence, the applicability of these materials. Moreover, it indicates that care must be taken with widely used electrochemical methods of surface area determination, especially in the case of large surface area and possibly unstable nanostructures, since the measured surface can be strongly aected by the measurement itself.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 7.504
Times cited: 24
DOI: 10.1021/acsami.7b01619
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“Plasma treatment causes structural modifications in lysozyme, and increases cytotoxicity towards cancer cells”. Attri P, Kaushik NK, Kaushik N, Hammerschmid D, Privat-Maldonado A, De Backer J, Shiratani M, Choi EH, Bogaerts A, International Journal Of Biological Macromolecules 182, 1724 (2021). http://doi.org/10.1016/j.ijbiomac.2021.05.146
Abstract: Bacterial and mammalian proteins, such as lysozyme, are gaining increasing interest as anticancer drugs. This study aims to modify the lysozyme structure using cold atmospheric plasma to boost its cancer cell killing effect. We investigated the structure at acidic and neutral pH using various experimental techniques (circular dichroism, fluorescence, and mass spectrometry) and molecular dynamics simulations. The controlled structural modification of lysozyme at neutral pH enhances its activity, while the activity was lost at acidic pH at the same treatment conditions. Indeed, a larger number of amino acids were oxidized at acidic pH after plasma treatment, which results in a greater distortion of the lysozyme structure, whereas only limited structural changes were observed in lysozyme after plasma treatment at neutral pH. We found that the plasma-treated lysozyme significantly induced apoptosis to the cancer cells. Our results reveal that plasma-treated lysozyme could have potential as a new cancer cell killing drug.
Keywords: A1 Journal Article; Lysozyme; Cold atmospheric plasma; Cancer cell death; Plasma, laser ablation and surface modeling Antwerp (PLASMANT) ;
Impact Factor: 3.671
DOI: 10.1016/j.ijbiomac.2021.05.146
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“Free energy barriers from biased molecular dynamics simulations”. Bal KM, Fukuhara S, Shibuta Y, Neyts EC, Journal Of Chemical Physics 153, 114118 (2020). http://doi.org/10.1063/5.0020240
Abstract: Atomistic simulation methods for the quantification of free energies are in wide use. These methods operate by sampling the probability density of a system along a small set of suitable collective variables (CVs), which is, in turn, expressed in the form of a free energy surface (FES). This definition of the FES can capture the relative stability of metastable states but not that of the transition state because the barrier height is not invariant to the choice of CVs. Free energy barriers therefore cannot be consistently computed from the FES. Here, we present a simple approach to calculate the gauge correction necessary to eliminate this inconsistency. Using our procedure, the standard FES as well as its gauge-corrected counterpart can be obtained by reweighing the same simulated trajectory at little additional cost. We apply the method to a number of systems—a particle solvated in a Lennard-Jones fluid, a Diels–Alder reaction, and crystallization of liquid sodium—to demonstrate its ability to produce consistent free energy barriers that correctly capture the kinetics of chemical or physical transformations, and discuss the additional demands it puts on the chosen CVs. Because the FES can be converged at relatively short (sub-ns) time scales, a free energy-based description of reaction kinetics is a particularly attractive option to study chemical processes at more expensive quantum mechanical levels of theory.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.4
DOI: 10.1063/5.0020240
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“The role of SnF₂, additive on interface formation in all lead-free FASnI₃, perovskite solar cells”. Zillner J, Boyen H-G, Schulz P, Hanisch J, Gauquelin N, Verbeeck J, Kueffner J, Desta D, Eisele L, Ahlswede E, Powalla M, Advanced functional materials , 2109649 (2022). http://doi.org/10.1002/ADFM.202109649
Abstract: Tin-based perovskites are promising alternative absorber materials for leadfree perovskite solar cells but need strategies to avoid fast tin (Sn) oxidation. Generally, this reaction can be slowed down by the addition of tin fluoride (SnF2) to the perovskite precursor solution, which also improves the perovskite layer morphology. Here, this work analyzes the spatial distribution of the additive within formamidinium tin triiodide (FASnI(3)) films deposited on top of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transporting layers. Employing time-of-flight secondary ion mass spectrometry and a combination of hard and soft X-ray photoelectron spectroscopy, it is found that Sn F2 preferably accumulates at the PEDOT:PSS/perovskite interface, accompanied by the formation of an ultrathin SnS interlayer with an effective thickness of approximate to 1.2 nm.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19
Times cited: 22
DOI: 10.1002/ADFM.202109649
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“A new way of producing electron vortex probes for STEM”. Verbeeck J, Tian H, Béché, A, Ultramicroscopy 113, 83 (2012). http://doi.org/10.1016/j.ultramic.2011.10.008
Abstract: A spiral holographic aperture is used in the condensor plane of a scanning transmission electron microscope to produce a focussed electron vortex probe carrying a topological charge of either −1, 0 or +1. The spiral aperture design has a major advantage over the previously used forked aperture in that the three beams with topological charge m=−1, 0, and 1 are not side by side in the specimen plane, but rather on top of each other, focussed at different heights. This allows us to have only one selected beam in focus on the sample while the others contribute only to a background signal. In this paper we describe the working principle as well as first experimental results demonstrating atomic resolution HAADF STEM images obtained with electron vortex probes. These results pave the way for atomic resolution magnetic information when combined with electron energy loss spectroscopy.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 62
DOI: 10.1016/j.ultramic.2011.10.008
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“Depth-resolved resonant inelastic x-ray scattering at a superconductor/half-metallic-ferromagnet interface through standing wave excitation”. Kuo C-T, Lin S-C, Ghiringhelli G, Peng Y, De Luca GM, Di Castro D, Betto D, Gehlmann M, Wijnands T, Huijben M, Meyer-Ilse J, Gullikson E, Kortright JB, Vailionis A, Gauquelin N, Verbeeck J, Gerber T, Balestrino G, Brookes NB, Braicovich L, Fadley CS, Physical review B 98, 235146 (2018). http://doi.org/10.1103/PHYSREVB.98.235146
Abstract: We demonstrate that combining standing wave (SW) excitation with resonant inelastic x-ray scattering (RIXS) can lead to depth resolution and interface sensitivity for studying orbital and magnetic excitations in correlated oxide heterostructures. SW-RIXS has been applied to multilayer heterostructures consisting of a superconductor La1.85Sr0.15CuO4 (LSCO) and a half-metallic ferromagnet La0.67Sr0.33MnO3 (LSMO). Easily observable SW effects on the RIXS excitations were found in these LSCO/LSMO multilayers. In addition, we observe different depth distribution of the RIXS excitations. The magnetic excitations are found to arise from the LSCO/LSMO interfaces, and there is also a suggestion that one of the dd excitations comes from the interfaces. SW-RIXS measurements of correlated-oxide and other multilayer heterostructures should provide unique layer-resolved insights concerning their orbital and magnetic excitations, as well as a challenge for RIXS theory to specifically deal with interface effects.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 5
DOI: 10.1103/PHYSREVB.98.235146
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