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“Effectiveness of reducing the influence of CTAB at the surface of metal nanoparticles during in situ heating studies by TEM”. De Meyer R, Albrecht W, Bals S, Micron 144, 103036 (2021). http://doi.org/10.1016/j.micron.2021.103036
Abstract: In situ TEM is a valuable technique to offer novel insights in the behavior of nanomaterials under various conditions. However, interpretation of in situ experiments is not straightforward since the electron beam can impact the outcome of such measurements. For example, ligands surrounding metal nanoparticles transform into a protective carbon layer upon electron beam irradiation and may impact the apparent thermal stability during in situ heating experiments. In this work, we explore the effect of different treatments typically proposed to remove such ligands. We found that plasma treatment prior to heating experiments for Au nanorods and nanostars increased the apparent thermal stability of the nanoparticles, while an activated carbon treatment resulted in a decrease of the observed thermal stability. Treatment with HCl barely changed the experimental outcome. These results demonstrate the importance of carefully selecting pre-treatments procedures during in situ heating experiments.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.98
DOI: 10.1016/j.micron.2021.103036
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“Understanding and Controlling the Crystallization Process in Reconfigurable Plasmonic Superlattices”. Bagiński M, Pedrazo-Tardajos A, Altantzis T, Tupikowska M, Vetter A, Tomczyk E, Suryadharma RNS, Pawlak M, Andruszkiewicz A, Górecka E, Pociecha D, Rockstuhl C, Bals S, Lewandowski W, Acs Nano , acsnano.0c09746 (2021). http://doi.org/10.1021/acsnano.0c09746
Abstract: The crystallization of nanomaterials is a primary source of solid-state, photonic structures. Thus, a detailed understanding of this process is of paramount importance for the successful application of photonic nanomaterials in emerging optoelectronic technologies. While colloidal crystallization has been thoroughly studied, for example, with advanced in situ electron microscopy methods, the noncolloidal crystallization (freezing) of nanoparticles (NPs) remains so far unexplored. To fill this gap, in this work, we present proof-of principle experiments decoding a crystallization of reconfigurable assemblies of NPs at a solid state. The chosen material corresponds to an excellent testing bed, as it enables both in situ and ex situ investigation using X-ray diffraction (XRD), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), atomic force microscopy (AFM), and optical spectroscopy in visible and ultraviolet range (UV−vis) techniques. In particular, ensemble measurements with small-angle XRD highlighted the dependence of the correlation length in the NPs assemblies on the number of heating/cooling cycles and the rate of cooling. Ex situ TEM imaging further supported these results by revealing a dependence of domain size and structure on the sample preparation route and by showing we can control the domain size over 2 orders of magnitude. The application of HAADF-STEM tomography, combined with in situ thermal control, provided three-dimensional single-particle level information on the positional order evolution within assemblies. This combination of real and reciprocal space provides insightful information on the anisotropic, reversibly reconfigurable assemblies of NPs. TEM measurements also highlighted the importance of interfaces in the polydomain structure of nanoparticle solids, allowing us to understand experimentally observed differences in UV−vis extinction spectra of the differently prepared crystallites. Overall, the obtained results show that the combination of in situ heating HAADF-STEM tomography with XRD and ex situ TEM techniques is a powerful approach to study nanoparticle freezing processes and to reveal the crucial impact of disorder in the solid-state aggregates of NPs on their plasmonic properties.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 13.942
Times cited: 10
DOI: 10.1021/acsnano.0c09746
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“A simple method to clean ligand contamination on TEM grids”. Li C, Tardajos AP, Wang D, Choukroun D, Van Daele K, Breugelmans T, Bals S, Ultramicroscopy 221, 113195 (2021). http://doi.org/10.1016/j.ultramic.2020.113195
Abstract: Colloidal nanoparticles (NPs) including nanowires and nanosheets made by chemical methods involve many organic ligands. When the structure of NPs is investigated via transmission electron microscopy (TEM), the organic ligands act as a source for e-beam induced deposition and this causes substantial build-up of carbon layers in the investigated areas, which is typically referred to as “contamination” in the eld of electron mi- croscopy. This contamination is often more severe for scanning TEM, a technique that is based on a focused electron beam and hence higher electron dose rate. In this paper, we report a simple and effective method to clean drop-cast TEM grids that contain NPs with ligands. Using a combination of activated carbon and ethanol, this method effectively reduces the amount of ligands on TEM grids, and therefore greatly improves the quality of electron microscopy images and subsequent analytical measurements. This ef cient and facile method can be helpful during electron microscopy investigation of different kinds of nanomaterials that suffer from ligand- induced contamination.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 2.843
Times cited: 10
DOI: 10.1016/j.ultramic.2020.113195
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“Three-dimensional atomic structure of supported Au nanoparticles at high temperature”. Liu P, Arslan Irmak E, De Backer A, De wael A, Lobato I, Béché, A, Van Aert S, Bals S, Nanoscale 13 (2021). http://doi.org/10.1039/D0NR08664A
Abstract: Au nanoparticles (NPs) deposited on CeO2 are extensively used as thermal catalysts since the morphology of the NPs is expected to be stable at elevated temperatures. Although it is well known that the activity of Au NPs depends on their size and surface structure, their three-dimensional (3D) structure at the atomic scale has not been completely characterized as a function of temperature. In this paper, we overcome the limitations of conventional electron tomography by combining atom counting applied to aberration-corrected scanning transmission electron microscopy images and molecular dynamics relaxation. In this manner, we are able to perform an atomic resolution 3D investigation of supported Au NPs. Our results enable us to characterize the 3D equilibrium structure of single NPs as a function of temperature. Moreover, the dynamic 3D structural evolution of the NPs at high temperatures, including surface layer jumping and crystalline transformations, has been studied.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 13
DOI: 10.1039/D0NR08664A
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“Tuning the turnover frequency and selectivity of photocatalytic CO2 reduction to CO and methane using platinum and palladium nanoparticles on Ti-Beta zeolites”. Blommaerts N, Hoeven N, Arenas Esteban D, Campos R, Mertens M, Borah R, Glisenti A, De Wael K, Bals S, Lenaerts S, Verbruggen SW, Cool P, Chemical Engineering Journal 410, 128234 (2021). http://doi.org/10.1016/j.cej.2020.128234
Abstract: A Ti-Beta zeolite was used in gas phase photocatalytic CO2 reduction to reduce the charge recombination rate and increase the surface area compared to P25 as commercial benchmark, reaching 607 m2 g-1. By adding Pt nanoparticles, the selectivity can be tuned toward CO, reaching a value of 92% and a turnover frequency (TOF) of 96 µmol.gcat-1.h-1, nearly an order of magnitude higher in comparison with P25. By adding Pd nanoparticles the selectivity can be shifted from CO (70% for a bare Ti-Beta zeolite), toward CH4 as the prevalent species (60%). In this way, the selectivity toward CO or CH4 can be tuned by either using Pt or Pd. The TOF values obtained in this work outperform reported state-of-the-art values in similar research. The improved activity by adding the nanoparticles was attributed to an improved charge separation efficiency, together with a plasmonic contribution of the metal nanoparticles under the applied experimental conditions.
Keywords: A1 Journal article; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL); Electron microscopy for materials research (EMAT); Laboratory of adsorption and catalysis (LADCA); AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 6.216
Times cited: 15
DOI: 10.1016/j.cej.2020.128234
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“Fast versus conventional HAADF-STEM tomography of nanoparticles: advantages and challenges”. Vanrompay H, Skorikov A, Bladt E, Béché, A, Freitag B, Verbeeck J, Bals S, Ultramicroscopy 221, 113191 (2021). http://doi.org/10.1016/j.ultramic.2020.113191
Abstract: HAADF-STEM tomography is a widely used experimental technique for analyzing nanometer-scale crystalline structures of a large variety of materials in three dimensions. Unfortunately, the acquisition of conventional HAADF-STEM tilt series can easily take up one hour or more, depending on the complexity of the experiment. It is therefore far from straightforward to investigate samples that do not withstand long acquisition or to acquire large amounts of tilt series during a single TEM experiment. The latter would lead to the ability to obtain statistically meaningful 3D data, or to perform in situ 3D characterizations with a much shorter time resolution. Various HAADF-STEM acquisition strategies have been proposed to accelerate the tomographic acquisition and reduce the required electron dose. These methods include tilting the holder continuously while acquiring a projection “movie” and a hybrid, incremental, methodology which combines the benefits of the conventional and continuous technique. However, until now an experimental evaluation has been lacking. In this paper, the different acquisition strategies will be experimentally compared in terms of speed, resolution and electron dose. This evaluation will be performed based on experimental tilt series acquired for various metallic nanoparticles with different shapes and sizes. We discuss the data processing involved with the fast HAADF-STEM tilt series and provide a general guideline when which acquisition strategy should be preferentially used.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 15
DOI: 10.1016/j.ultramic.2020.113191
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“Alloy CsCdxPb1–xBr3Perovskite Nanocrystals: The Role of Surface Passivation in Preserving Composition and Blue Emission”. Imran M, Ramade J, Di Stasio F, De Franco M, Buha J, Van Aert S, Goldoni L, Lauciello S, Prato M, Infante I, Bals S, Manna L, Chemistry Of Materials 32, acs.chemmater.0c03825 (2020). http://doi.org/10.1021/acs.chemmater.0c03825
Abstract: Various strategies have been proposed to engineer the band gap of metal halide perovskite nanocrystals (NCs) while preserving their structure and composition and thus ensuring spectral stability of the emission color. An aspect that has only been marginally investigated is how the type of surface passivation influences the structural/color stability of AMX3 perovskite NCs composed of two different M2+ cations. Here, we report the synthesis of blue-emitting Cs-oleate capped CsCdxPb1–xBr3 NCs, which exhibit a cubic perovskite phase containing Cd-rich domains of Ruddlesden–Popper phases (RP phases). The RP domains spontaneously transform into pure orthorhombic perovskite ones upon NC aging, and the emission color of the NCs shifts from blue to green over days. On the other hand, postsynthesis ligand exchange with various Cs-carboxylate or ammonium bromide salts, right after NC synthesis, provides monocrystalline NCs with cubic phase, highlighting the metastability of RP domains. When NCs are treated with Cs-carboxylates (including Cs-oleate), most of the Cd2+ ions are expelled from NCs upon aging, and the NCs phase evolves from cubic to orthorhombic and their emission color changes from blue to green. Instead, when NCs are coated with ammonium bromides, the loss of Cd2+ ions is suppressed and the NCs tend to retain their blue emission (both in colloidal dispersions and in electroluminescent devices), as well as their cubic phase, over time. The improved compositional and structural stability in the latter cases is ascribed to the saturation of surface vacancies, which may act as channels for the expulsion of Cd2+ ions from NCs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.6
Times cited: 44
DOI: 10.1021/acs.chemmater.0c03825
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“Near-Edge Ligand Stripping and Robust Radiative Exciton Recombination in CdSe/CdS Core/Crown Nanoplatelets”. Leemans J, Singh S, Li C, Ten Brinck S, Bals S, Infante I, Moreels I, Hens Z, Journal Of Physical Chemistry Letters 11, 3339 (2020). http://doi.org/10.1021/acs.jpclett.0c00870
Abstract: We address the relation between surface chemistry and optoelectronic properties in semiconductor nanocrystals using core/crown CdSe/CdS nanoplatelets passivated by cadmium oleate (Cd(Ol)2) as model systems. We show that addition of butylamine to a nanoplatelet (NPL) dispersion maximally displaces ∼40% of the original Cd(Ol)2 capping. On the basis of density functional theory simulations, we argue that this behavior reflects the preferential displacement of Cd(Ol)2 from (near)-edge surface sites. Opposite from CdSe core NPLs, core/crown NPL dispersions can retain 45% of their initial photoluminescence efficiency after ligand displacement, while radiative exciton recombination keeps dominating the luminescent decay. Using electron microscopy observations, we assign this robust photoluminescence to NPLs with a complete CdS crown, which prevents charge carrier trapping in the near-edge surface sites created by ligand displacement. We conclude that Z-type ligands such as cadmium carboxylates can provide full electronic passivation of (100) facets yet are prone to displacement from (near)-edge surface sites.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.7
Times cited: 24
DOI: 10.1021/acs.jpclett.0c00870
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“Fast Electron Tomography for Nanomaterials”. Albrecht W, Bals S, Journal Of Physical Chemistry C , acs.jpcc.0c08939 (2020). http://doi.org/10.1021/acs.jpcc.0c08939
Abstract: Electron tomography (ET) has become a well-established technique to visualize nanomaterials in three dimensions. A vast richness in information can be gained by ET, but the conventional acquisition of a tomography series is an inherently slow process on the order of 1 h. The slow acquisition limits the applicability of ET for monitoring dynamic processes or visualizing nanoparticles, which are sensitive to the electron beam. In this Perspective, we summarize recent work on the development of emerging experimental and computational schemes to enhance the data acquisition process. We particularly focus on the application of these fast ET techniques for beam-sensitive materials and highlight insight into dynamic transformations of nanoparticles under external stimuli, which could be gained by fast in situ ET. Moreover, we discuss challenges and possible solutions for simultaneously increasing the speed and quality of fast ET.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 3.7
Times cited: 26
DOI: 10.1021/acs.jpcc.0c08939
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“Luminescent Colloidal InSb Quantum Dots from In Situ Generated Single-Source Precursor”. Busatto S, Ruiter M de, Jastrzebski JTBH, Albrecht W, Pinchetti V, Brovelli S, Bals S, Moret M-E, de Mello Donega C, Acs Nano 14, 13146 (2020). http://doi.org/10.1021/acsnano.0c04744
Abstract: Despite recent advances, the synthesis of colloidal InSb quantum dots (QDs) remains underdeveloped, mostly due to the lack of suitable precursors. In this work, we use Lewis acid–base interactions between Sb(III) and In(III) species formed at room temperature in situ from commercially available compounds (viz., InCl3, Sb[NMe2]3 and a primary alkylamine) to obtain InSb adduct complexes. These complexes are successfully used as precursors for the synthesis of colloidal InSb QDs ranging from 2.8 to 18.2 nm in diameter by fast coreduction at sufficiently high temperatures (≥230 °C). Our findings allow us to propose a formation mechanism for the QDs synthesized in our work, which is based on a nonclassical nucleation event, followed by aggregative growth. This yields ensembles with multimodal size distributions, which can be fractionated in subensembles with relatively narrow polydispersity by postsynthetic size fractionation. InSb QDs with diameters below 7.0 nm have the zinc blende crystal structure, while ensembles of larger QDs (≥10 nm) consist of a mixture of wurtzite and zinc blende QDs. The QDs exhibit photoluminescence with small Stokes shifts and short radiative lifetimes, implying that the emission is due to band-edge recombination and that the direct nature of the bandgap of bulk InSb is preserved in InSb QDs. Finally, we constructed a sizing curve correlating the peak position of the lowest energy absorption transition with the QD diameters, which shows that the band gap of colloidal InSb QDs increases with size reduction following a 1/d dependence.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 17.1
Times cited: 21
DOI: 10.1021/acsnano.0c04744
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“Ligand-Mode Directed Selectivity in Cu–Ag Core–Shell Based Gas Diffusion Electrodes for CO2Electroreduction”. Irtem E, Arenas Esteban D, Duarte M, Choukroun D, Lee S, Ibáñez M, Bals S, Breugelmans T, Acs Catalysis , 13468 (2020). http://doi.org/10.1021/acscatal.0c03210
Abstract: Bimetallic nanoparticles with tailored size and specific composition have shown promise as stable and selective catalysts for electrochemical reduction of CO2 (CO2R) in batch systems. Yet, limited effort was devoted to understand the effect of ligand coverage and postsynthesis treatments on CO2 reduction, especially under industrially applicable conditions, such as at high currents (>100 mA/cm2) using gas diffusion electrodes (GDE) and flow reactors. In this work, Cu–Ag core–shell nanoparticles (11 ± 2 nm) were prepared with three different surface modes: (i) capped with oleylamine, (ii) capped with monoisopropylamine, and (iii) surfactant free with a reducing borohydride agent; Cu–Ag (OAm), Cu–Ag (MIPA), and Cu–Ag (NaBH4), respectively. The ligand exchange and removal was evidenced by infrared spectroscopy (ATR-FTIR) analysis, whereas high-resolution scanning transmission electron microscopy (HAADF-STEM) showed their effect on the interparticle distance and nanoparticle rearrangement. Later on, we developed a process-on-substrate method to track these effects on CO2R. Cu–Ag (OAm) gave a lower on-set potential for hydrocarbon production, whereas Cu–Ag (MIPA) and Cu–Ag (NaBH4) promoted syngas production. The electrochemical impedance and surface area analysis on the well-controlled electrodes showed gradual increases in the electrical conductivity and active surface area after each surface treatment. We found that the increasing amount of the triple phase boundaries (the meeting point for the electron–electrolyte–CO2 reactant) affect the required electrode potential and eventually the C+2e̅/C2e̅ product ratio. This study highlights the importance of the electron transfer to those active sites affected by the capping agents—particularly on larger substrates that are crucial for their industrial application.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 12.9
Times cited: 23
DOI: 10.1021/acscatal.0c03210
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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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“3D Characterization and Plasmon Mapping of Gold Nanorods Welded by Femtosecond Laser Irradiation”. Milagres de Oliveira T, Albrecht W, González-Rubio G, Altantzis T, Lobato Hoyos IP, Béché, A, Van Aert S, Guerrero-Martínez A, Liz-Marzán LM, Bals S, Acs Nano 14, acsnano.0c02610 (2020). http://doi.org/10.1021/acsnano.0c02610
Abstract: Ultrafast laser irradiation can induce morphological and structural changes in plasmonic nanoparticles. Gold nanorods (Au NRs), in particular, can be welded together upon irradiation with femtosecond laser pulses, leading to dimers and trimers through the formation of necks between individual nanorods. We used electron tomography to determine the 3D (atomic) structure at such necks for representative welding geometries and to characterize the induced defects. The spatial distribution of localized surface plasmon modes for different welding configurations was assessed by electron energy loss spectroscopy. Additionally, we were able to directly compare the plasmon line width of single-crystalline and welded Au NRs with single defects at the same resonance energy, thus making a direct link between the structural and plasmonic properties. In this manner, we show that the occurrence of (single) defects results in significant plasmon broadening.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 17.1
Times cited: 25
DOI: 10.1021/acsnano.0c02610
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“Tuning Size and Seed Position in Small Silver Nanorods”. Sánchez-Iglesias A, Zhuo X, Albrecht W, Bals S, Liz-Marzán LM, ACS materials letters 2, 1246 (2020). http://doi.org/10.1021/acsmaterialslett.0c00388
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 9
DOI: 10.1021/acsmaterialslett.0c00388
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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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“Real‐Time Reconstruction of Arbitrary Slices for Quantitative and In Situ 3D Characterization of Nanoparticles”. Vanrompay H, Buurlage J‐W, Pelt DM, Kumar V, Zhuo X, Liz‐Marzán LM, Bals S, Batenburg KJ, Particle &, Particle Systems Characterization 37, 2000073 (2020). http://doi.org/10.1002/ppsc.202000073
Abstract: A detailed 3D investigation of nanoparticles at a local scale is of great importance to connect their structure and composition to their properties. Electron tomography has therefore become an important tool for the 3D characterization of nanomaterials. 3D investigations typically comprise multiple steps, including acquisition, reconstruction, and analysis/quantification. Usually, the latter two steps are performed offline, at a dedicated workstation. This sequential workflow prevents on-the-fly control of experimental parameters to improve the quality of the 3D reconstruction, to select a relevant nanoparticle for further characterization or to steer an in-situ tomography experiment. Here, we present an efficient approach to overcome these limitations, based on the real-time reconstruction of arbitrary 2D reconstructed slices through a 3D object. Implementation of this method may lead to generalized implementation of electron tomography for routine nanoparticle characterization in 3D.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 2.7
Times cited: 10
DOI: 10.1002/ppsc.202000073
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“Improving extracellular vesicles visualization: From static to motion”. Reclusa P, Verstraelen P, Taverna S, Gunasekaran M, Pucci M, Pintelon I, Claes N, de Miguel-Pérez D, Alessandro R, Bals S, Kaushal S, Rolfo C, Scientific Reports 10, 6494 (2020). http://doi.org/10.1038/s41598-020-62920-0
Abstract: In the last decade extracellular vesicles (EVs) have become a hot topic. The findings on EVs content and effects have made them a major field of interest in cancer research. EVs, are able to be internalized through integrins expressed in parental cells, in a tissue specific manner, as a key step of cancer progression and pre-metastatic niche formation. However, this specificity might lead to new opportunities in cancer treatment by using EVs as devices for drug delivery. For future applications of EVs in cancer, improved protocols and methods for EVs isolation and visualization are required. Our group has put efforts on developing a protocol, able to track the EVs for in vivo internalization analysis. We showed, for the first time, the videos of labeled EVs uptake by living lung cancer cells.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.6
Times cited: 25
DOI: 10.1038/s41598-020-62920-0
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“Manganese‐Doping‐Induced Quantum Confinement within Host Perovskite Nanocrystals through Ruddlesden–Popper Defects”. Paul S, Bladt E, Richter AF, Döblinger M, Tong Y, Huang H, Dey A, Bals S, Debnath T, Polavarapu L, Feldmann J, Angewandte Chemie-International Edition 59, 6794 (2020). http://doi.org/10.1002/anie.201914473
Abstract: The concept of doping Mn2+ ions into II–VI semiconductor nanocrystals (NCs) was recently extended to perovskite NCs. To date, most studies on Mn2+ doped NCs focus on enhancing the emission related to the Mn2+ dopant via an energy transfer mechanism. Herein, we found that the doping of Mn2+ ions into CsPbCl3 NCs not only results in a Mn2+‐related orange emission, but also strongly influences the excitonic properties of the host NCs. We observe for the first time that Mn2+ doping leads to the formation of Ruddlesden–Popper (R.P.) defects and thus induces quantum confinement within the host NCs. We find that a slight doping with Mn2+ ions improves the size distribution of the NCs, which results in a prominent excitonic peak. However, with increasing the Mn2+ concentration, the number of R.P. planes increases leading to smaller single‐crystal domains. The thus enhanced confinement and crystal inhomogeneity cause a gradual blue shift and broadening of the excitonic transition, respectively.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 16.6
Times cited: 64
DOI: 10.1002/anie.201914473
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“Defect‐Directed Growth of Symmetrically Branched Metal Nanocrystals”. Smith JD, Bladt E, Burkhart JAC, Winckelmans N, Koczkur KM, Ashberry HM, Bals S, Skrabalak SE, Angewandte Chemie (International ed. Print) 132, 953 (2020). http://doi.org/10.1002/ange.201913301
Abstract: Branched plasmonic nanocrystals (NCs) have attracted much attention due to electric field enhancements at their tips. Seeded growth provides routes to NCs with defined branching patterns and, in turn, near‐field distributions with defined symmetries. Here, a systematic analysis was undertaken in which seeds containing different distributions of planar defects were used to grow branched NCs in order to understand how their distributions direct the branching. Characterization of the products by multimode electron tomography and analysis of the NC morphologies at different overgrowth stages indicate that the branching patterns are directed by the seed defects, with the emergence of branches from the seed faces consistent with minimizing volumetric strain energy at the expense of surface energy. These results contrast with growth of branched NCs from single‐crystalline seeds and provide a new platform for the synthesis of symmetrically branched plasmonic NCs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
DOI: 10.1002/ange.201913301
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“Formation of Hollow Gold Nanocrystals by Nanosecond Laser Irradiation”. González-Rubio G, Milagres de Oliveira T, Albrecht W, Díaz-Núñez P, Castro-Palacio JC, Prada A, González RI, Scarabelli L, Bañares L, Rivera A, Liz-Marzán LM, Peña-Rodríguez O, Bals S, Guerrero-Martínez A, Journal Of Physical Chemistry Letters 11, 670 (2020). http://doi.org/10.1021/acs.jpclett.9b03574
Abstract: The irradiation of spherical gold nanoparticles (AuNPs) with nanosecond laser pulses induces shape transformations yielding nanocrystals with an inner cavity. The concentration of the stabilizing surfactant, the use of moderate pulse fluences, and the size of the irradiated AuNPs determine the efficiency of the process and the nature of the void. Hollow nanocrystals are obtained when molecules from the surrounding medium (e.g., water and organic matter derived from the surfactant) are trapped during laser pulse irradiation. These experimental observations suggest the existence of a subtle balance between the heating and cooling processes experienced by the nanocrystals, which induce their expansion and subsequent recrystallization keeping exogenous matter inside. The described approach provides valuable insight into the mechanism of interaction of pulsed nanosecond laser with AuNPs, along with interesting prospects for the development of hollow plasmonic nanoparticles with potential applications related to gas and liquid storage at the nanoscale.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 5.7
Times cited: 15
DOI: 10.1021/acs.jpclett.9b03574
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“Plasmonic gold-embedded TiO2 thin films as photocatalytic self-cleaning coatings”. Peeters H, Keulemans M, Nuyts G, Vanmeert F, Li C, Minjauw M, Detavernier C, Bals S, Lenaerts S, Verbruggen SW, Applied Catalysis B-Environmental 267, 118654 (2020). http://doi.org/10.1016/j.apcatb.2020.118654
Abstract: Transparent photocatalytic TiO2 thin films hold great potential in the development of self-cleaning glass sur-
faces, but suffer from a poor visible light response that hinders the application under actual sunlight. To alleviate this problem, the photocatalytic film can be modified with plasmonic nanoparticles that interact very effectively with visible light. Since the plasmonic effect is strongly concentrated in the near surroundings of the nano- particle surface, an approach is presented to embed the plasmonic nanostructures in the TiO2 matrix itself, rather than deposit them loosely on the surface. This way the interaction interface is maximised and the plasmonic effect can be fully exploited. In this study, pre-fabricated gold nanoparticles are made compatible with the organic medium of a TiO2 sol-gel coating suspension, resulting in a one-pot coating suspension. After spin coating, homogeneous, smooth, highly transparent and photoactive gold-embedded anatase thin films are ob- tained.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Sustainable Energy, Air and Water Technology (DuEL)
Impact Factor: 22.1
Times cited: 57
DOI: 10.1016/j.apcatb.2020.118654
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“Locating and controlling the Zn content in In(Zn)P quantum dots”. Kirkwood N, De Backer A, Altantzis T, Winckelmans N, Longo A, Antolinez FV, Rabouw FT, De Trizio L, Geuchies JJ, Mulder JT, Renaud N, Bals S, Manna L, Houtepen AJ, Chemistry of materials 32, 557 (2019). http://doi.org/10.1021/acs.chemmater.9b04407
Abstract: Zinc is routinely employed in the synthesis of InP quantum dots (QDs) to improve the photoluminescence efficiency and carrier mobility of the resulting In(Zn)P alloy nanostructures. The exact location of Zn in the final structures and the mechanism by which it enhances the optoelectronic properties of the QDs is debated. We use synchrotron X-ray absorbance spectroscopy to show that the majority of Zn in In(Zn)P QDs is located at their surface as Zn-carboxylates. However, a small amount of Zn is present inside the bulk of the QDs with the consequent contraction of their lattice, as confirmed by combining high resolution high-angle annular dark-field imaging scanning transmission electron microscopy (HAADF-STEM) with statistical parameter estimation theory. We further demonstrate that the Zn content and its incorporation into the QDs can be tuned by the ligation of commonly employed Zn carboxylate precursors: the use of highly reactive Zn-acetate leads to the formation of undesired Zn3P2 and the final nanostructures being characterized by broad optical features, whereas Zn-carboxylates with longer carbon chains lead to InP crystals with much lower zinc content and narrow optical features. These results can explain the differences between structural and optical properties of In(Zn)P samples reported across the literature, and provide a rational method to tune the amount of Zn in InP nanocrystals and to drive the incorporation of Zn either as surface Zn-carboxylate, as a substitutional dopant inside the InP crystal lattice, or even predominantly as Zn3P2.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 39
DOI: 10.1021/acs.chemmater.9b04407
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“Quantitative 3D Characterization of Elemental Diffusion Dynamics in Individual Ag@Au Nanoparticles with Different Shapes”. Skorikov A, Albrecht W, Bladt E, Xie X, van der Hoeven JES, van Blaaderen A, Van Aert S, Bals S, ACS nano 13, 13421 (2019). http://doi.org/10.1021/acsnano.9b06848
Abstract: Anisotropic bimetallic nanoparticles are promising candidates for plasmonic and catalytic applications. Their catalytic performance and plasmonic properties are closely linked to the distribution of the two metals, which can change during applications in which the particles are exposed to heat. Due to this fact, correlating the thermal stability of complex heterogeneous nanoparticles to their microstructural properties is of high interest for the practical applications of such materials. Here, we employ quantitative electron tomography in high-angle annular dark-field scanning transmission electron microscopy (HAADFSTEM) mode to measure the 3D elemental diffusion dynamics in individual anisotropic Au−Ag nanoparticles upon heating in situ. This approach allows us to study the elemental redistribution in complex, asymmetric nanoparticles on a single particle level, which has been inaccessible to other techniques so far. In this work, we apply the proposed method to compare the alloying dynamics of Au−Ag nanoparticles with different shapes and compositions and find that the shape of the nanoparticle does not exhibit a significant effect on the alloying speed whereas the composition does. Finally, comparing the experimental results to diffusion simulations allows us to estimate the diffusion coefficients of the metals for individual nanoparticles.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 13.942
Times cited: 29
DOI: 10.1021/acsnano.9b06848
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“Chemical and Structural Configuration of Pt Doped Metal Oxide Thin Films Prepared by Atomic Layer Deposition”. Ramachandran RK, Filez M, Solano E, Poelman H, Minjauw MM, Van Daele M, Feng J-Y, La Porta A, Altantzis T, Fonda E, Coati A, Garreau Y, Bals S, Marin GB, Detavernier C, Dendooven J, Chemistry of materials 31, 9673 (2019). http://doi.org/10.1021/acs.chemmater.9b03066
Abstract: Pt doped semiconducting metal oxides and Pt metal clusters embedded in an oxide matrix are of interest for applications such as catalysis and gas sensing, energy storage and memory devices. Accurate tuning of the dopant level is crucial for adjusting the properties of these materials. Here, a novel atomic layer deposition (ALD) based method for doping Pt into In2O3 in specific, and metals in metal oxides in general, is demonstrated. This approach combines alternating exposures of Pt and In2O3 ALD processes in a single ‘supercycle’, followed by supercycle repetition leading to multilayered nanocomposites. The atomic level control of ALD and its conformal nature make the method suitable for accurate dopant control even on high surface area supports. Oxidation state, local structural environment and crystalline phase of the embedded Pt dopants were obtained by means of X-ray characterization methods and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In addition, this approach allows characterization of the nucleation stages of metal ALD processes, by stacking those states multiple times in an oxide matrix. Regardless of experimental conditions, a few Pt ALD cycles leads to the formation of oxidized Pt species due to their highly dispersed nature, as proven by X-ray absorption spectroscopy (XAS). Grazing-incidence small-angle X-ray scattering (GISAXS) and highresolution scanning transmission electron microscopy, combined with energy dispersive X-ray spectroscopy (HR-STEM/EDXS) show that Pt is evenly distributed in the In2O3 metal oxide matrix without the formation of clusters. For a larger number of Pt ALD
cycles, typ. > 10, the oxidation state gradually evolves towards fully metallic, and metallic Pt clusters are obtained within the In2O3 metal oxide matrix. This work reveals how tuning of the ALD supercycle approach for Pt doping allows controlled engineering of the Pt compositional and structural configuration within a metal oxide matrix.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 9.466
Times cited: 6
DOI: 10.1021/acs.chemmater.9b03066
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“Corrosion protection of Cu by atomic layer deposition”. Cremers V, Rampelberg G, Baert K, Abrahami S, Claes N, de Oliveira TM, Terryn H, Bals S, Dendooven J, Detavernier C, Journal of vacuum science and technology: A: vacuum surfaces and films 37, 060902 (2019). http://doi.org/10.1116/1.5116136
Abstract: Atomic layer deposition (ALD) is a vapor phase technique that is able to deposit uniform, conformal thin films with an excellent thickness control at the atomic scale. 18 nm thick Al2O3 and TiO2 coatings were deposited conformaly and pinhole-free onto micrometer-sized Cu powder, using trimethylaluminum and tetrakis(dimethylamido)titanium(IV), respectively, as a precursor and de-ionized water as a reactant. The capability of the ALD coating to protect the Cu powder against corrosion was investigated. Therefore, the stability of the coatings was studied in solutions with different pH in the range of 0–14, and in situ raman spectroscopy was used to detect the emergence of corrosion products of Cu as an indication that the protective coating starts to fail. Both ALD coatings provide good protection at standard pH values in the range of 5–7. In general, the TiO2 coating shows a better barrier protection against corrosion than the Al2O3 coating. However, for the most extreme pH conditions, pH 0 and pH 14, the TiO2 coating starts also to degrade.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.374
Times cited: 7
DOI: 10.1116/1.5116136
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“Unraveling Structural Information of Turkevich Synthesized Plasmonic Gold-Silver Bimetallic Nanoparticles”. Blommaerts N, Vanrompay H, Nuti S, Lenaerts S, Bals S, Verbruggen SW, Small 15, 1902791 (2019). http://doi.org/10.1002/smll.201902791
Abstract: For the synthesis of gold-silver bimetallic nanoparticles, the Turkevich method has been the state-of-the-art method for several decades. It has been presumed that this procedure results in a homogeneous alloy, although this has been debatable for many years. In this work, it is shown that neither a full alloy, nor a perfect core-shell particle is formed but rather a core-shell-like particle with altering metal composition along the radial direction. In-depth wet-chemical experiments are performed in combination with advanced transmission electron microscopy, including EDX tomography, and Finite Element Method modeling to support the observations. From the electron tomography results, the core-shell structure could be clearly visualized and the spatial distribution of gold and silver atoms could be quantified. Theoretical simulations are performed to demonstrate that even though UV-Vis spectra show only one plasmon band, this still originates from core-shell type structures. The simulations also indicate that the core-shell morphology does not so much affect the location of the plasmon band, but mainly results in significant band broadening. Wet-chemistry experiments provide the evidence that the synthesis pathway starts with gold enriched alloy cores, and later on in the synthesis mainly silver is incorporated to end up with a silver enriched alloy shell.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Sustainable Energy, Air and Water Technology (DuEL)
Impact Factor: 8.643
Times cited: 26
DOI: 10.1002/smll.201902791
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“Thermal Stability of Gold/Palladium Octopods Studied in Situ in 3D: Understanding Design Rules for Thermally Stable Metal Nanoparticles”. Albrecht W, Bladt E, Vanrompay H, Smith JD, Skrabalak SE, Bals S, ACS nano 13, 6522 (2019). http://doi.org/10.1021/acsnano.9b00108
Abstract: Multifunctional metal nanoparticles (NPs) such as anisotropic multimetallic NPs are crucial for boosting nanomaterial based applications. Advanced synthetic protocols exist to make a large variety of such nanostructures. However, a major limiting factor for the usability of them in real life applications is their stability. Here, we show that Au/Pd octopods, 8-branched nanocrystals with Oh symmetry, with only a low amount of Pd exhibited a high thermal stability and maintained strong plasmon resonances up to 600 ◦C. Furthermore, we study the influence of the composition, morphology and environment on the thermal stability and define key parameters for the design of thermally stable multifunctional NPs.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 13.942
Times cited: 46
DOI: 10.1021/acsnano.9b00108
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“3D characterization of heat-induced morphological changes of Au nanostars by fast in situ electron tomography”. Vanrompay H, Bladt E, Albrecht W, Béché, A, Zakhozheva M, Sánchez-Iglesias A, Liz-Marzán LM, Bals S, Nanoscale 10, 22792 (2018). http://doi.org/10.1039/C8NR08376B
Abstract: A thorough understanding of the thermal stability and potential reshaping of anisotropic gold nanostars is required for various potential applications. Combination of a tomographic heating holder with fast tilt series acquisition has been used to monitor temperature-induced morphological changes of Au nanostars. The outcome of our 3D investigations can be used as an input for boundary element method simulations, enabling us to investigate the influence of reshaping on the nanostars’ plasmonic properties. Our work leads to a better understanding of the mechanism behind thermal reshaping. In addition, the approach presented here is generic and can hence be applied to a wide variety of nanoparticles made of different materials and with arbitrary morphology.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 55
DOI: 10.1039/C8NR08376B
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“Chemistry of Shape-Controlled Iron Oxide Nanocrystal Formation”. Feld A, Weimer A, Kornowski A, Winckelmans N, Merkl J-P, Kloust H, Zierold R, Schmidtke C, Schotten T, Riedner M, Bals S, Weller PD Horst, ACS nano 13, 152 (2018). http://doi.org/10.1021/acsnano.8b05032
Abstract: Herein we demonstrate that meticulous and in-depth analysis of the reaction mechanisms of nanoparticle formation is rewarded by full control of size, shape and crystal structure of superparamagnetic iron oxide nanocrystals during synthesis. Starting from two iron sources – iron(II)- and iron(III) carbonate -a strict separation of oleate formation from the generation of reactive pyrolysis products and concomitant nucleation of iron oxide nanoparticles was achieved. This protocol enabled us to analyze each step of nanoparticle formation independently in depth. Progress of the entire reaction was monitored via matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and gas chromatography (GC) gaining insight into the formation of various iron oleate species prior to nucleation. Interestingly, due to the intrinsic strongly reductive pyrolysis conditions of the oleate intermediates and redox process in early stages of the synthesis, pristine iron oxide nuclei were composed exclusively from wustite, irrespective of the oxidation state of the iron source. Controlling the reaction conditions provided a very broad range of size- and shape defined monodisperse iron oxide nanoparticles. Curiously, after nucleation star shaped nanocrystals were obtained, which underwent metamorphism towards cubic shaped particles. EELS tomography revealed ex post oxidation of the primary wustite nanocrystal providing a full 3D image of Fe2+ and Fe3+ distribution within. Overall, we developed a highly flexible synthesis, yielding multigram amounts of well-defined iron oxide nanocrystals of different sizes and morphologies.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 13.942
Times cited: 54
DOI: 10.1021/acsnano.8b05032
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“Fe2+Deficiencies, FeO Subdomains, and Structural Defects Favor Magnetic Hyperthermia Performance of Iron Oxide Nanocubes into Intracellular Environment”. Lak A, Cassani M, Mai BT, Winckelmans N, Cabrera D, Sadrollahi E, Marras S, Remmer H, Fiorito S, Cremades-Jimeno L, Litterst FJ, Ludwig F, Manna L, Teran FJ, Bals S, Pellegrino T, Nano letters 18, 6856 (2018). http://doi.org/10.1021/acs.nanolett.8b02722
Abstract: Herein, by studying a stepwise phase transformation of 23 nm FeO-Fe3O4 core-shell nanocubes into Fe3O4, we identify a composition at which the magnetic heating performance of the nanocubes is not affected by the medium viscosity and aggregation. Structural and magnetic characterizations reveal the transformation of the FeO-Fe3O4 nanocubes from having stoichiometric phase compositions into Fe2+ deficient Fe3O4 phases. The resultant nanocubes contain tiny compressed and randomly distributed FeO sub-domains as well as structural defects. This phase transformation causes a tenfold increase in the magnetic losses of the nanocubes, which remains exceptionally insensitive to the medium viscosity as well as aggregation unlike similarly sized single-phase magnetite nanocubes. We observe that the dominant relaxation mechanism switches from Néel in fresh core-shell nanocubes to Brownian in partially oxidized nanocubes and once again to Néel in completely treated nanocubes. The Fe2+ deficiencies and structural defects appear to reduce the magnetic energy barrier and anisotropy field, thereby driving the overall relaxation into Néel process. The magnetic losses of the particles remain unchanged through a progressive internalization/association to ovarian cancer cells. Moreover, the particles induce a significant cell death after being exposed to hyperthermia treatment. Here, we present the largest heating performance that has been reported to date for 23 nm iron oxide nanoparticles under cellular and intracellular conditions. Our findings clearly demonstrate the positive impacts of the Fe2+ deficiencies and structural defects in the Fe3O4 structure on the heating performance under cellular and intracellular conditions.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 51
DOI: 10.1021/acs.nanolett.8b02722
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