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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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“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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“Electrochemical stability of rhodium-platinum core-shell nanoparticles : an identical location scanning transmission electron microscopy study”. Vega-Paredes M, Aymerich-Armengol R, Arenas Esteban D, Marti-Sanchez S, Bals S, Scheu C, Manjon AG, ACS nano 17, 16943 (2023). http://doi.org/10.1021/ACSNANO.3C04039
Abstract: Rhodium-platinum core-shell nanoparticleson a carbonsupport (Rh@Pt/C NPs) are promising candidates as anode catalystsfor polymer electrolyte membrane fuel cells. However, their electrochemicalstability needs to be further explored for successful applicationin commercial fuel cells. Here we employ identical location scanningtransmission electron microscopy to track the morphological and compositionalchanges of Rh@Pt/C NPs during potential cycling (10 000 cycles,0.06-0.8 V-RHE, 0.5 H2SO4)down to the atomic level, which are then used for understanding thecurrent evolution occurring during the potential cycles. Our resultsreveal a high stability of the Rh@Pt/C system and point toward particledetachment from the carbon support as the main degradation mechanism.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 17.1
Times cited: 2
DOI: 10.1021/ACSNANO.3C04039
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“Self-assembly of gas-phase synthesized magnesium nanoparticles on room temperature substrates”. Venturi F, Calizzi M, Bals S, Perkisas T, Pasquini L, Materials research express 2, 015007 (2015). http://doi.org/10.1088/2053-1591/2/1/015007
Abstract: Magnesium nanoparticles (NPs) with initial size in the 10-50 nmrange were synthesized by inert gas condensation under helium flow and deposited on room temperature substrates. The morphology and crystal structure of the NPs ensemble were investigated as a function of the deposition time by complementary electron microscopy techniques, including high resolution imaging and chemical mapping. With increasing amount of material, strong coarsening phenomena were observed at room temperature: small NPs disappeared while large faceted NPs developed, leading to a 5-fold increase of the average NPs size within a few minutes. The extent of coarsening and the final morphology depended also on the nature of the substrate. Furthermore, large single-crystal NPs were seen to arise from the self-organization of primary NPs units, providing a mechanism for crystal growth. The dynamics of the self-assembly process involves the basic steps of NPs sticking, diffusion on substrate, coordinated rotation and attachment/coalescence. Key features are the surface energy anisotropy, reflected by the faceted shape of the NPs, and the low melting point of the material. The observed phenomena have strong implications in relation to the synthesis and stability of nanostructures based on Mg or other elements with similar features.
Keywords: A1 Journal article; Engineering Management (ENM); Electron microscopy for materials research (EMAT)
Impact Factor: 1.068
Times cited: 14
DOI: 10.1088/2053-1591/2/1/015007
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“Electronic reconstruction at n-type SrTiO3/LaAlO3 interfaces”. Verbeeck J, Bals S, Lamoen D, Luysberg M, Huijben M, Rijnders G, Brinkman A, Hilgenkamp H, Blank DHA, Van Tendeloo G, Physical review : B : condensed matter and materials physics 81, 085113 (2010). http://doi.org/10.1103/PhysRevB.81.085113
Abstract: Electron-energy-loss spectroscopy (EELS) is used to investigate single layers of LaAlO3 grown on SrTiO3 having an n-type interface as well as multilayers of LaAlO3 and SrTiO3 in which both n- and p-type interfaces occur. Only minor changes in Ti valence at the n-type interface are observed. This finding seems to contradict earlier experiments for other SrTiO3/LaAlO3 systems where large deviations in Ti valency were assumed to be responsible for the conductivity of these interfaces. Ab initio calculations have been carried out in order to interpret our EELS results. Using the concept of Bader charges, it is demonstrated that the so-called polar discontinuity is mainly resolved by lattice distortions and to a far lesser extent by changes in valency for both single layer and multilayer geometries.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 25
DOI: 10.1103/PhysRevB.81.085113
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“Photocatalytic acetaldehyde oxidation in air using spacious TiO2 films prepared by atomic layer deposition on supported carbonaceous sacrificial templates”. Verbruggen SW, Deng S, Kurttepeli M, Cott DJ, Vereecken PM, Bals S, Martens JA, Detavernier C, Lenaerts S, Applied catalysis : B : environmental 160, 204 (2014). http://doi.org/10.1016/j.apcatb.2014.05.029
Abstract: Supported carbon nanosheets and carbon nanotubes served as sacrificial templates for preparing spacious TiO2 photocatalytic thin films. Amorphous TiO2 was deposited conformally on the carbonaceous template material by atomic layer deposition (ALD). Upon calcination at 550 °C, the carbon template was oxidatively removed and the as-deposited continuous amorphous TiO2 layers transformed into interlinked anatase nanoparticles with an overall morphology commensurate to the original template structure. The effect of type of template, number of ALD cycles and gas residence time of pollutant on the photocatalytic activity, as well as the stability of the photocatalytic performance of these thin films was investigated. The TiO2 films exhibited excellent photocatalytic activity toward photocatalytic degradation of acetaldehyde in air as a model reaction for photocatalytic indoor air pollution abatement. Optimized films outperformed a reference film of commercial PC500.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Sustainable Energy, Air and Water Technology (DuEL)
Impact Factor: 9.446
Times cited: 37
DOI: 10.1016/j.apcatb.2014.05.029
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“Plasmonic ‘rainbow&rsquo, photocatalyst with broadband solar light response for environmental applications”. Verbruggen SW, Keulemans M, Goris B, Blommaerts N, Bals S, Martens JA, Lenaerts S, Applied catalysis : B : environmental 188, 147 (2016). http://doi.org/10.1016/j.apcatb.2016.02.002
Abstract: We propose the concept of a ‘rainbow’ photocatalyst that consists of TiO2 modified with gold-silver alloy nanoparticles of various sizes and compositions, resulting in a broad plasmon absorption band that covers the entire UV–vis range of the solar spectrum. It is demonstrated that this plasmonic ‘rainbow’ photocatalyst is 16% more effective than TiO2 P25 under both simulated and real solar light for pollutant degradation at the solid-gas interface. With this we provide a promising strategy to maximize the spectral response for solar to chemical energy conversion.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Sustainable Energy, Air and Water Technology (DuEL)
Impact Factor: 9.446
Times cited: 47
DOI: 10.1016/j.apcatb.2016.02.002
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“PdPb-catalyzed decarboxylation of proline to pyrrolidine : highly selective formation of a biobased amine in water”. Verduyckt J, Van Hoof M, De Schouwer F, Wolberg M, Kurttepeli M, Eloy P, Gaigneaux EM, Bals S, Kirschhock CEA, De Vos DE, ACS catalysis 6, 7303 (2016). http://doi.org/10.1021/ACSCATAL.6B02561
Abstract: Amino acids have huge potential as platform chemicals in the biobased industry. Pd-catalyzed decarboxylation is a very promising route for the valorization of these natural compounds derived from protein waste or fermentation. We report that the highly abundant and nonessential amino acid L-proline is very reactive in the Pd-catalyzed decarboxylation. Full conversions are obtained with Pd/C and different Pd/MeOx catalysts; this allowed the identification of the different side reactions and the mapping of the reaction network. Due to the high reactivity of pyrrolidine, the selectivity for pyrrolidine was initially low. By carefully modifying Pd/ZrO2 with Pb in a controlled manner-via two incipient wetness impregnation steps-the selectivity increased remarkably. Finally, a thorough investigation of the reaction parameters resulted in an increased activity of this modified catalyst and an even further enhanced selectivity under a low H-2 pressure of 4 bar at 235 degrees C in water. This results in a very selective and sustainable production route for the highly interesting pyrrolidine.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 10.614
Times cited: 27
DOI: 10.1021/ACSCATAL.6B02561
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“3D arrangement of epitaxial graphene conformally grown on porousified crystalline SiC”. Veronesi S, Pfusterschmied G, Fabbri F, Leitgeb M, Arif O, Esteban DA, Bals S, Schmid U, Heun S, Carbon 189, 210 (2022). http://doi.org/10.1016/j.carbon.2021.12.042
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 10.9
Times cited: 3
DOI: 10.1016/j.carbon.2021.12.042
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“High-Throughput Morphological Chirality Quantification of Twisted and Wrinkled Gold Nanorods”. Vlasov E, Heyvaert W, Ni B, Van Gordon K, Girod R, Verbeeck J, Liz-Marzán LM, Bals S, ACS Nano (2024). http://doi.org/10.1021/acsnano.4c02757
Abstract: Chirality in gold nanostructures offers an exciting opportunity to tune their differential optical response to left- and right-handed circularly polarized light, as well as their interactions with biomolecules and living matter. However, tuning and understanding such interactions demands quantification of the structural features that are responsible for the chiral behavior. Electron tomography (ET) enables structural characterization at the single-particle level and has been used to quantify the helicity of complex chiral nanorods. However, the technique is time-consuming and consequently lacks statistical value. To address this issue, we introduce herein a high-throughput methodology that combines images acquired by secondary electron-based electron beam-induced current (SEEBIC) with quantitative image analysis. As a result, the geometric chirality of hundreds of nanoparticles can be quantified in less than 1 h. When combining the drastic gain in data collection efficiency of SEEBIC with a limited number of ET data sets, a better understanding of how the chiral structure of individual chiral nanoparticles translates into the ensemble chiroptical response can be reached.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 17.1
DOI: 10.1021/acsnano.4c02757
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“Secondary electron induced current in scanning transmission electron microscopy: an alternative way to visualize the morphology of nanoparticles”. Vlasov E, Skorikov A, Sánchez-Iglesias A, Liz-Marzán LM, Verbeeck J, Bals S, ACS materials letters , 1916 (2023). http://doi.org/10.1021/acsmaterialslett.3c00323
Abstract: Electron tomography (ET) is a powerful tool to determine the three-dimensional (3D) structure of nanomaterials in a transmission electron microscope. However, the acquisition of a conventional tilt series for ET is a time-consuming process and can therefore not provide 3D structural information in a time-efficient manner. Here, we propose surface-sensitive secondary electron (SE) imaging as an alternative to ET for the investigation of the morphology of nanomaterials. We use the SE electron beam induced current (SEEBIC) technique that maps the electrical current arising from holes generated by the emission of SEs from the sample. SEEBIC imaging can provide valuable information on the sample morphology with high spatial resolution and significantly shorter throughput times compared with ET. In addition, we discuss the contrast formation mechanisms that aid in the interpretation of SEEBIC data.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 1
DOI: 10.1021/acsmaterialslett.3c00323
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“Nanoparticle-MediatedIn SituMolecular Reprogramming of Immune Checkpoint Interactions for Cancer Immunotherapy”. Walters AA, Santacana-Font G, Li J, Routabi N, Qin Y, Claes N, Bals S, Tzu-Wen Wang J, Al-Jamal KT, Acs Nano 15, 17549 (2021). http://doi.org/10.1021/acsnano.1c04456
Abstract: Immune checkpoint blockade involves targeting immune
regulatory molecules with antibodies. Preclinically, complex multiantibody
regimes of both inhibitory and stimulatory targets are a promising
candidate for the next generation of immunotherapy. However, in this
setting, the antibody platform may be limited due to excessive toxicity
caused by off target effects as a result of systemic administration. RNA
can be used as an alternate to antibodies as it can both downregulate
immunosuppressive checkpoints (siRNA) or induce expression of
immunostimulatory checkpoints (mRNA). In this study, we demonstrate
that the combination of both siRNA and mRNA in a single
formulation can simultaneously knockdown and induce expression of
immune checkpoint targets, thereby reprogramming the tumor
microenvironment from immunosuppressive to immunostimulatory
phenotype. To achieve this, RNA constructs were synthesized and
formulated into stable nucleic acid lipid nanoparticles (SNALPs); the SNALPs produced were 140−150 nm in size with >80%
loading efficiency. SNALPs could transfect macrophages and B16F10 cells in vitro resulting in 75% knockdown of inhibitory
checkpoint (PDL1) expression and simultaneously express high levels of stimulatory checkpoint (OX40L) with minimal
toxicity. Intratumoral treatment with the proposed formulation resulted in statistically reduced tumor growth, a greater
density of CD4+ and CD8+ infiltrates in the tumor, and immune activation within tumor-draining lymph nodes. These data
suggest that a single RNA-based formulation can successfully reprogram multiple immune checkpoint interactions on a
cellular level. Such a candidate may be able to replace future immune checkpoint therapeutic regimes composed of both
stimulatory- and inhibitory-receptor-targeting antibodies.
Keywords: A1 Journal article; Pharmacology. Therapy; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 13.942
Times cited: 11
DOI: 10.1021/acsnano.1c04456
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“Binary icosahedral clusters of hard spheres in spherical confinement”. Wang D, Dasgupta T, van der Wee EB, Zanaga D, Altantzis T, Wu Y, Coli GM, Murray CB, Bals S, Dijkstra M, van Blaaderen A, Nature Physics , 1 (2020). http://doi.org/10.1038/S41567-020-1003-9
Abstract: The influence of geometry on the local and global packing of particles is important to many fundamental and applied research themes, such as the structure and stability of liquids, crystals and glasses. Here we show by experiments and simulations that a binary mixture of hard-sphere-like nanoparticles crystallizing into a MgZn(2)Laves phase in bulk spontaneously forms icosahedral clusters in slowly drying droplets. Using advanced electron tomography, we are able to obtain the real-space coordinates of all the spheres in the icosahedral clusters of up to about 10,000 particles. The local structure of 70-80% of the particles became similar to that of the MgCu(2)Laves phase. These observations are important for photonic applications. In addition, we observed in simulations that the icosahedral clusters nucleated away from the spherical boundary, which is distinctly different from that of the single species clusters. Our findings open the way for particle-level studies of nucleation and growth of icosahedral clusters, and of binary crystallization. The authors investigate out-of-equilibrium crystallization of a binary mixture of sphere-like nanoparticles in small droplets. They observe the spontaneous formation of an icosahedral structure with stable MgCu(2)phases, which are promising for photonic applications.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 19.6
Times cited: 38
DOI: 10.1038/S41567-020-1003-9
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“Structural diversity in three-dimensional self-assembly of nanoplatelets by spherical confinement”. Wang D, Hermes M, Najmr S, Tasios N, Grau-Carbonell A, Liu Y, Bals S, Dijkstra M, Murray CB, van Blaaderen A, Nature communications 13, 6001 (2022). http://doi.org/10.1038/S41467-022-33616-Y
Abstract: Nanoplatelets offer many possibilities to construct advanced materials due to new properties associated with their (semi)two-dimensional shapes. However, precise control of both positional and orientational order of the nanoplatelets in three dimensions, which is required to achieve emerging and collective properties, is challenging to realize. Here, we combine experiments, advanced electron tomography and computer simulations to explore the structure of supraparticles self-assembled from nanoplatelets in slowly drying emulsion droplets. We demonstrate that the rich phase behaviour of nanoplatelets, and its sensitivity to subtle changes in shape and interaction potential can be used to guide the self-assembly into a wide range of different structures, offering precise control over both orientation and position order of the nanoplatelets. Our research is expected to shed light on the design of hierarchically structured metamaterials with distinct shape- and orientation- dependent properties. Nanoplatelets can be used as anisotropic building blocks for constructing novel optoelectronic materials. Here, Wang et al. show a route of assembling nanoplatelets with controllable positional and orientational order in three dimensions facilitated by the surface tension of drying emulsion droplets.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 16.6
Times cited: 7
DOI: 10.1038/S41467-022-33616-Y
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“Quantitative 3D real-space analysis of Laves phase supraparticles”. Wang D, van der Wee EB, Zanaga D, Altantzis T, Wu Y, Dasgupta T, Dijkstra M, Murray CB, Bals S, van Blaaderen A, Nature Communications 12, 3980 (2021). http://doi.org/10.1038/S41467-021-24227-0
Abstract: 3D real-space analysis of thick nanoparticle crystals is non-trivial. Here, the authors demonstrate the structural analysis of a bulk-like Laves phase by imaging an off-stoichiometric binary mixture of hard-sphere-like nanoparticles in spherical confinement by electron tomography, enabling defect analysis on the single-particle level. Assembling binary mixtures of nanoparticles into crystals, gives rise to collective properties depending on the crystal structure and the individual properties of both species. However, quantitative 3D real-space analysis of binary colloidal crystals with a thickness of more than 10 layers of particles has rarely been performed. Here we demonstrate that an excess of one species in the binary nanoparticle mixture suppresses the formation of icosahedral order in the self-assembly in droplets, allowing the study of bulk-like binary crystal structures with a spherical morphology also called supraparticles. As example of the approach, we show single-particle level analysis of over 50 layers of Laves phase binary crystals of hard-sphere-like nanoparticles using electron tomography. We observe a crystalline lattice composed of a random mixture of the Laves phases. The number ratio of the binary species in the crystal lattice matches that of a perfect Laves crystal. Our methodology can be applied to study the structure of a broad range of binary crystals, giving insights into the structure formation mechanisms and structure-property relations of nanomaterials.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 12.124
Times cited: 10
DOI: 10.1038/S41467-021-24227-0
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“Tuning of the size and the lattice parameter of ion-beam synthesized Pb nanoparticles embedded in Si”. Wang H, Cuppens J, Biermans E, Bals S, Fernandez-Ballester L, Kvashnina KO, Bras W, van Bael MJ, Temst K, Vantomme A, Journal of physics: D: applied physics 45, 035301 (2012). http://doi.org/10.1088/0022-3727/45/3/035301
Abstract: The size and lattice constant evolution of Pb nanoparticles (NPs) synthesized by high fluence implantation in crystalline Si have been studied with a variety of experimental techniques. Results obtained from small-angle x-ray scattering showed that the Pb NPs grow with increasing implantation fluence and annealing duration. The theory of NP growth kinetics can be applied to qualitatively explain the size evolution of the Pb NPs during the implantation and annealing processes. Moreover, the lattice constant of the Pb NPs was evaluated by conventional x-ray diffraction. The lattice dilatation was observed to decrease with increasing size of the Pb NPs. Such lattice constant tuning can be attributed to the pseudomorphism caused by the lattice mismatch between the Pb NPs and the Si matrix.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.588
Times cited: 5
DOI: 10.1088/0022-3727/45/3/035301
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“Modifying the Stöber Process: Is the Organic Solvent Indispensable?”.Wang J, Zhang K, Kavak S, Bals S, Meynen V, Chemistry-A European Journal (2022). http://doi.org/10.1002/chem.202202670
Abstract: The Stöber method is one of the most important and fundamental processes for the synthesis of inorganic (nano)materials but has the drawback of using a large amount of organic solvent. Herein, ethanol was used as an example to explore if the organic solvent in a typical Stöber method can be omitted. It was found that ethanol increases the particle size of the obtained silica spheres and aids the formation of uniform silica particles rather than forming a gel. Nevertheless, the results indicated that an organic solvent in the initial synthesis mixture is not indispensable. An initially immiscible synthesis method was discovered, which can replace the organic solvent-based Stöber method to successfully synthesize silica particles with the same size ranges as the original Stöber process without addition of organic solvents. Moreover, this process can be of further value for the extension to synthesis processes of other materials based on the Stöber process.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 4.3
Times cited: 3
DOI: 10.1002/chem.202202670
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“Stabilization and encapsulation of gold nanostars mediated by dithiols”. Wang Y, Belén Serrano A, Sentosun K, Bals S, Liz-Marzán LM, Small 11, 4314 (2015). http://doi.org/10.1002/smll.201500703
Abstract: Surface chemistry plays a pivotal role in regulating the morphology of nanoparticles, maintaining colloidal stability, and mediating the interaction with target analytes toward practical applications such as surface-enhanced Raman scattering (SERS)-based sensing and imaging. The use of a binary ligand mixture composed of 1,4-benzenedithiol (BDT) and hexadecyltrimethylammonium chloride (CTAC) to provide gold nanostars with long-term stability is reported. This is despite BDT being a bifunctional ligand, which usually leads to bridging and loss of colloidal stability. It is found however that neither BDT nor CTAC alone are able to provide sufficient colloidal and chemical stability. BDT-coated Au nanostars are additionally used as seeds to direct the encapsulation with a gold outer shell, leading to the formation of unusual nanostructures including semishell-coated gold nanostars, which are characterized by high-resolution electron microscopy and electron tomography. Finally, BDT is exploited as a probe to reveal the enhanced local electric fields in the different nanostructures, showing that the semishell configuration provides significantly high SERS signals as compared to other coreshell configurations obtained during seeded growth, including full shells.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 36
DOI: 10.1002/smll.201500703
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“Engineering Structural Diversity in Gold Nanocrystals by Ligand-Mediated Interface Control”. Wang Y, Sentosun K, Li A, Coronado-Puchau M, Sánchez-Iglesias A, Li S, Su X, Bals S, Liz-Marzán LM, Chemistry of materials 27, 8032 (2015). http://doi.org/10.1021/acs.chemmater.5b03600
Abstract: Surface and interface control is fundamentally important for crystal growth engineering, catalysis, surface enhanced spectroscopies, and self-assembly, among other processes and applications. Understanding the role of ligands in regulating surface properties of plasmonic metal nanocrystals during growth has received considerable attention. However, the underlying mechanisms and the diverse functionalities of ligands are yet to be fully addressed. In this contribution,
we report a systematic study of ligand-mediated interface control in seeded growth of gold nanocrystals, leading to diverse and exotic nanostructures with an improved surface enhanced Raman scattering (SERS) activity. Three dimensional transmission electron microscopy (3D TEM) revealed an intriguing gold shell growth process mediated by the bifunctional ligand 1,4-benzenedithiol (BDT), which leads to a unique crystal growth mechanism as compared to other ligands, and subsequently to the concept of interfacial energy control mechanism. Volmer-Weber growth mode was proposed to be responsible for BDT-mediated seeded growth, favoring the strongest interfacial energy and generating an asymmetric island growth pathway with internal crevices/gaps. This additionally favors incorporation of BDT at the plasmonic nanogaps, thereby generating strong SERS activity with a maximum efficiency for a core-semishell configuration obtained along seeded growth. Numerical modeling was used to explain this observation. Interestingly, the same strategy can be used to engineer the structural diversity of this system, by using gold nanoparticle seeds with various sizes and shapes, and varying the [Au3+]/[Au0] ratio. This rendered a series of diverse and exotic plasmonic nanohybrids such as semishell-coated gold nanorods, with embedded Raman-active tags and Janus surface with distinct surface functionalities.
These would greatly enrich the plasmonic nanostructure toolbox for various studies and applications such as anisotropic nanocrystal engineering, SERS, and high-resolution Raman bioimaging or nanoantenna devices.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 18
DOI: 10.1021/acs.chemmater.5b03600
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“Quantitatively linking morphology and optical response of individual silver nanohedra”. Wang Y, Sztranyovszky Z, Zilli A, Albrecht W, Bals S, Borri P, Langbein W, Nanoscale 14, 11028 (2022). http://doi.org/10.1039/D2NR02131E
Abstract: The optical response of metal nanoparticles is governed by plasmonic resonances, which are dictated by the particle morphology. A thorough understanding of the link between morphology and optical response requires quantitatively measuring optical and structural properties of the same particle. Here we present such a study, correlating electron tomography and optical micro-spectroscopy. The optical measurements determine the scattering and absorption cross-section spectra in absolute units, and electron tomography determines the 3D morphology. Numerical simulations of the spectra for the individual particle geometry, and the specific optical set-up used, allow for a quantitative comparison including the cross-section magnitude. Silver nanoparticles produced by photochemically driven colloidal synthesis, including decahedra, tetrahedra and bi-tetrahedra are investigated. A mismatch of measured and simulated spectra is found in some cases when assuming pure silver particles, which is explained by the presence of a few atomic layers of tarnish on the surface, not evident in electron tomography. The presented method tightens the link between particle morphology and optical response, supporting the predictive design of plasmonic nanomaterials.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6.7
Times cited: 1
DOI: 10.1039/D2NR02131E
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“Transport, magnetic, and structural properties of La0.7Ce0.3MnO3 thin films: evidence for hole-doping”. Werner R, Raisch C, Leca V, Ion V, Bals S, Van Tendeloo G, Chasse T, Kleiner R, Koelle D, Physical review : B : solid state 79, 054416 (2009). http://doi.org/10.1103/PhysRevB.79.054416
Abstract: Cerium-doped manganite thin films were grown epitaxially by pulsed laser deposition at 720 °C and oxygen pressure pO2=125 Pa and were subjected to different annealing steps. According to x-ray diffraction (XRD) data, the formation of CeO2 as a secondary phase could be avoided for pO28 Pa. However, transmission electron microscopy shows the presence of CeO2 nanoclusters even in those films which appear to be single phase in XRD. With O2 annealing, the metal-to-insulator transition temperature increases, while the saturation magnetization decreases and stays well below the theoretical value for electron-doped La0.7Ce0.3MnO3 with mixed Mn3+/Mn2+ valences. The same trend is observed with decreasing film thickness from 100 to 20 nm, indicating a higher oxygen content for thinner films. Hall measurements on a film which shows a metal-to-insulator transition clearly reveal holes as dominating charge carriers. Combining data from x-ray photoemission spectroscopy, for determination of the oxygen content, and x-ray absorption spectroscopy (XAS), for determination of the hole concentration and cation valences, we find that with increasing oxygen content the hole concentration increases and Mn valences are shifted from 2+ to 4+. The dominating Mn valences in the films are Mn3+ and Mn4+, and only a small amount of Mn2+ ions can be observed by XAS. Mn2+ and Ce4+ XAS signals obtained in surface-sensitive total electron yield mode are strongly reduced in the bulk-sensitive fluorescence mode, which indicates hole-doping in the bulk for those films which do show a metal-to-insulator transition.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 25
DOI: 10.1103/PhysRevB.79.054416
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“Structure and vacancy distribution in copper telluride nanoparticles influence plasmonic activity in the near-infrared”. Willhammar T, Sentosun K, Mourdikoudis S, Goris B, Kurttepeli M, Bercx M, Lamoen D, Partoens B, Pastoriza-Santos I, Pérez-Juste J, Liz-Marzán LM, Bals S, Van Tendeloo G, Nature communications 8, 14925 (2017). http://doi.org/10.1038/ncomms14925
Abstract: Copper chalcogenides find applications in different domains including photonics, photothermal therapy and photovoltaics. CuTe nanocrystals have been proposed as an alternative to noble metal particles for plasmonics. Although it is known that deviations from stoichiometry are a prerequisite for plasmonic activity in the near-infrared, an accurate description of the material and its (optical) properties is hindered by an insufficient understanding of the atomic structure and the influence of defects, especially for materials in their nanocrystalline form. We demonstrate that the structure of Cu1.5±xTe nanocrystals canbe determined using electron diffraction tomography. Real-space high-resolution electron tomography directly reveals the three-dimensional distribution of vacancies in the structure. Through first-principles density functional theory, we furthermore demonstrate that the influence of these vacancies on the optical properties of the nanocrystals is determined. Since our methodology is applicable to a variety of crystalline nanostructured materials, it is expected to provide unique insights concerning structure–property correlations.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 12.124
Times cited: 37
DOI: 10.1038/ncomms14925
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“Multimode Electron Tomography as a Tool to Characterize the Internal Structure and Morphology of Gold Nanoparticles”. Winckelmans N, Altantzis T, Grzelczak M, Sánchez-Iglesias A, Liz-Marzán LM, Bals S, The journal of physical chemistry: C : nanomaterials and interfaces 122, 13522 (2018). http://doi.org/10.1021/acs.jpcc.7b12379
Abstract: Three dimensional (3D) characterization of structural defects in nanoparticles by transmission electron microscopy is far from straightforward. We propose the use of a dose-efficient approach, so-called multimode tomography, during which tilt series of low and high angle annular dark field scanning transmission electron microscopy projection images are acquired simultaneously. In this manner, not only reliable information can be obtained concerning the shape of the nanoparticles, but also the twin planes can be clearly visualized in 3D. As an example, we demonstrate the application of this approach to identify the position of the seeds with respect to the twinning planes in anisotropic gold nanoparticles synthesized using a seed mediated growth approach.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.536
Times cited: 23
DOI: 10.1021/acs.jpcc.7b12379
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“Catalytic upcycling of PVC waste-derived phthalate esters into safe, hydrogenated plasticizers”. Windels S, Diefenhardt T, Jain N, Marquez C, Bals S, Schlummer M, De Vos DE, Green chemistry : cutting-edge research for a greener sustainable future 24, 754 (2022). http://doi.org/10.1039/D1GC03864H
Abstract: Recycling of end-of-life polyvinyl chloride (PVC) calls for solutions to deal with the vast amounts of harmful phthalate plasticizers that have historically been incorporated in PVC. Here, we report on the upcycling of such waste-extracted phthalate esters into analogues of the much safer diisononyl 1,2-cyclohexanedicarboxylate plasticizer (DINCH), via a catalytic one-pot (trans)esterification-hydrogenation process. For most of the virgin phthalates, Ru/Al2O3 is a highly effective hydrogenation catalyst, yielding >99% ring-hydrogenated products under mild reaction conditions (0.1 mol% Ru, 80 degrees C, 50 bar H-2). However, applying this reaction to PVC-extracted phthalates proved problematic, (1) as benzyl phthalates are hydrogenolyzed to benzoic acids that inhibit the Ru-catalyst, and (2) because impurities in the plasticizer extract (PVC, sulfur) further retard the hydrogenation. These complications were solved by coupling the hydrogenation to an in situ (trans)esterification with a higher alcohol, and by pretreating the extract with an activated carbon adsorbent. In this way, a real phthalate extract obtained from post-consumer PVC waste was eventually completely (>99%) hydrogenated to phthalate-free, cycloaliphatic plasticizers.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.8
Times cited: 8
DOI: 10.1039/D1GC03864H
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“3D Magnetic Induction Maps of Nanoscale Materials Revealed by Electron Holographic Tomography”. Wolf D, Rodriguez LA, Béché, A, Javon E, Serrano L, Magen C, Gatel C, Lubk A, Lichte H, Bals S, Van Tendeloo G, Fernández-Pacheco A, De Teresa JM, Snoeck E, Chemistry of materials 27, 6771 (2015). http://doi.org/10.1021/acs.chemmater.5b02723
Abstract: The investigation of three-dimensional (3D) ferromagnetic nanoscale materials constitutes one of the key research areas of the current magnetism roadmap, and carries great potential to impact areas such as data storage, sensing and biomagnetism. The properties of such nanostructures are closely connected with their 3D magnetic nanostructure, making their determination highly valuable. Up to now, quantitative 3D maps providing both the internal magnetic and electric configuration of the same specimen with high spatial resolution are missing. Here, we demonstrate the quantitative 3D reconstruction of the dominant axial component of the magnetic induction and electrostatic potential within a cobalt nanowire (NW) of 100 nm in diameter with spatial resolution below 10 nanometers by applying electron holographic tomography. The tomogram was obtained using a dedicated TEM sample holder for acquisition, in combination with advanced alignment and tomographic reconstruction routines. The powerful approach presented here is widely applicable to a broad range of 3D magnetic nanostructures and may trigger the progress of novel spintronic non-planar nanodevices.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 50
DOI: 10.1021/acs.chemmater.5b02723
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“Stabilization effects in binary colloidal Cu and Ag nanoparticle electrodes under electrochemical CO₂, reduction conditions”. Wu L, Kolmeijer KE, Zhang Y, An H, Arnouts S, Bals S, Altantzis T, Hofmann JP, Costa Figueiredo M, Hensen EJM, Weckhuysen BM, van der Stam W, Nanoscale 13, 4835 (2021). http://doi.org/10.1039/D0NR09040A
Abstract: Nanoparticle modified electrodes constitute an attractive way to tailor-make efficient carbon dioxide (CO2) reduction catalysts. However, the restructuring and sintering processes of nanoparticles under electrochemical reaction conditions not only impedes the widespread application of nanoparticle catalysts, but also misleads the interpretation of the selectivity of the nanocatalysts. Here, we colloidally synthesized metallic copper (Cu) and silver (Ag) nanoparticles with a narrow size distribution (<10%) and utilized them in electrochemical CO2 reduction reactions. Monometallic Cu and Ag nanoparticle electrodes showed severe nanoparticle sintering already at low overpotential of -0.8 V vs. RHE, as evidenced by ex situ SEM investigations, and potential-dependent variations in product selectivity that resemble bulk Cu (14% for ethylene at -1.3 V vs. RHE) and Ag (69% for carbon monoxide at -1.0 V vs. RHE). However, by co-deposition of Cu and Ag nanoparticles, a nanoparticle stabilization effect was observed between Cu and Ag, and the sintering process was greatly suppressed at CO2 reducing potentials (-0.8 V vs. RHE). Furthermore, by varying the Cu/Ag nanoparticle ratio, the CO2 reduction reaction (CO2RR) selectivity towards methane (maximum of 20.6% for dense Cu-2.5-Ag-1 electrodes) and C-2 products (maximum of 15.7% for dense Cu-1-Ag-1 electrodes) can be tuned, which is attributed to a synergistic effect between neighbouring Ag and Cu nanoparticles. We attribute the stabilization of the nanoparticles to the positive enthalpies of Cu-Ag solid solutions, which prevents the dissolution-redeposition induced particle growth under CO2RR conditions. The observed nanoparticle stabilization effect enables the design and fabrication of active CO2 reduction nanocatalysts with high durability.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 7.367
Times cited: 24
DOI: 10.1039/D0NR09040A
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“Highly active, selective, and stable Pd single-atom catalyst anchored on N-doped hollow carbon sphere for electrochemical H₂O₂, synthesis under acidic conditions”. Xi J, Yang S, Silvioli L, Cao S, Liu P, Chen Q, Zhao Y, Sun H, Hansen JN, Haraldsted J-PB, Kibsgaard J, Rossmeisl J, Bals S, Wang S, Chorkendorff I, Journal Of Catalysis 393, 313 (2021). http://doi.org/10.1016/J.JCAT.2020.11.020
Abstract: Single-atom catalysts (SACs) have recently attracted broad scientific interests due to their unique structural feature, the single-atom dispersion. Optimized electronic structure as well as high stability are required for single-atom catalysts to enable efficient electrochemical production of H2O2. Herein, we report a facile synthesis method that stabilizes atomic Pd species on the reduced graphene oxide/Ndoped carbon hollow carbon nanospheres (Pd1/N-C). Pd1/N-C exhibited remarkable electrochemical H2O2 production rate with high faradaic efficiency, reaching 80%. The single-atom structure and its high H2O2 production rate were maintained even after 10,000 cycle stability test. The existence of single-atom Pd as well as its coordination with N species is responsible for its high activity, selectivity, and stability. The N coordination number and substrate doping around Pd atoms are found to be critical for an optimized adsorption energy of intermediate *OOH, resulting in efficient electrochemical H2O2 production. (C) 2020 Elsevier Inc. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.844
Times cited: 40
DOI: 10.1016/J.JCAT.2020.11.020
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“Seeded growth combined with cation exchange for the synthesis of anisotropic Cu2-xS/ZnS, Cu2-xS, and CuInS2 nanorods”. Xia C, Pedrazo-Tardajos A, Wang D, Meeldijk JD, Gerritsen HC, Bals S, de Donega CM, Chemistry of materials 33, 102 (2021). http://doi.org/10.1021/ACS.CHEMMATER.0C02817
Abstract: Colloidal copper(I) sulfide (Cu2-xS) nanocrystals (NCs) have attracted much attention for a wide range of applications because of their unique optoelectronic properties, driving scientists to explore the potential of using Cu2-xS NCs as seeds in the synthesis of heteronanocrystals to achieve new multifunctional materials. Herein, we developed a multistep synthesis strategy toward Cu2-xS/ZnS heteronanorods. The Janus-type Cu2-xS/ZnS heteronanorods are obtained by the injection of hexagonal high-chalcocite Cu2-xS seed NCs in a hot zinc oleate solution in the presence of suitable surfactants, 20 s after the injection of sulfur precursors. The Cu2-xS seed NCs undergo rapid aggregation and coalescence in the first few seconds after the injection, forming larger NCs that act as the effective seeds for heteronucleation and growth of ZnS. The ZnS heteronucleation occurs on a single (100) facet of the Cu2-xS seed NCs and is followed by fast anisotropic growth along a direction that is perpendicular to the c-axis, thus leading to Cu2-xS/ZnS Janus-type heteronanorods with a sharp heterointerface. Interestingly, the high-chalcocite crystal structure of the injected Cu2-xS seed NCs is preserved in the Cu2-xS segments of the heteronanorods because of the highthermodynamic stability of this Cu2-xS phase. The Cu2-xS/ZnS heteronanorods are subsequently converted into single-component Cu2-xS and CuInS2 nanorods by postsynthetic topotactic cation exchange. This work expands the possibilities for the rational synthesis of colloidal multicomponent heteronanorods by allowing the design principles of postsynthetic heteroepitaxial seeded growth and nanoscale cation exchange to be combined, yielding access to a plethora of multicomponent heteronanorods with diameters in the quantum confinement regime.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 10
DOI: 10.1021/ACS.CHEMMATER.0C02817
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“Near-Infrared-Emitting CuInS2/ZnS Dot-in-Rod Colloidal Heteronanorods by Seeded Growth”. Xia C, Winckelmans N, Prins PT, Bals S, Gerritsen HC, de Mello Donegá, C, Journal of the American Chemical Society 140, 5755 (2018). http://doi.org/10.1021/jacs.8b01412
Abstract: Synthesis protocols for anisotropic CuInX2 (X = S, Se, Te)-based heteronanocrystals (HNCs) are scarce due to the difficulty in balancing the reactivities of multiple precursors and the high solid-state diffusion rates of the cations involved in the CuInX2 lattice. In this work, we report a multistep seeded growth synthesis protocol that yields colloidal wurtzite CuInS2/ZnS dot core/rod shell HNCs with photoluminescence in the NIR (∼800 nm). The wurtzite CuInS2 NCs used as seeds are obtained by topotactic partial Cu+ for In3+ cation exchange in template Cu2–xS NCs. The seed NCs are injected in a hot solution of zinc oleate and hexadecylamine in octadecene, 20 s after the injection of sulfur in octadecene. This results in heteroepitaxial growth of wurtzite ZnS primarily on the Sulfur-terminated polar facet of the CuInS2 seed NCs, the other facets being overcoated only by a thin (∼1 monolayer) shell. The fast (∼21 nm/min) asymmetric axial growth of the nanorod proceeds by addition of [ZnS] monomer units, so that the polarity of the terminal (002) facet is preserved throughout the growth. The delayed injection of the CuInS2 seed NCs is crucial to allow the concentration of [ZnS] monomers to build up, thereby maximizing the anisotropic heteroepitaxial growth rates while minimizing the rates of competing processes (etching, cation exchange, alloying). Nevertheless, a mild etching still occurred, likely prior to the onset of heteroepitaxial overgrowth, shrinking the core size from 5.5 to ∼4 nm. The insights provided by this work open up new possibilities in designing multifunctional Cu-chalcogenide based colloidal heteronanocrystals.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 43
DOI: 10.1021/jacs.8b01412
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“Waste-derived copper-lead electrocatalysts for CO₂, reduction”. Yang S, An H, Anastasiadou D, Xu W, Wu L, Wang H, de Ruiter J, Arnouts S, Figueiredo MC, Bals S, Altantzis T, van der Stam W, Weckhuysen BM, ChemCatChem 14, e202200754 (2022). http://doi.org/10.1002/CCTC.202200754
Abstract: It remains a real challenge to control the selectivity of the electrocatalytic CO2 reduction (eCO(2)R) reaction to valuable chemicals and fuels. Most of the electrocatalysts are made of non-renewable metal resources, which hampers their large-scale implementation. Here, we report the preparation of bimetallic copper-lead (CuPb) electrocatalysts from industrial metallurgical waste. The metal ions were extracted from the metallurgical waste through simple chemical treatment with ammonium chloride, and CuxPby electrocatalysts with tunable compositions were fabricated through electrodeposition at varying cathodic potentials. X-ray spectroscopy techniques showed that the pristine electrocatalysts consist of Cu-0, Cu1+ and Pb2+ domains, and no evidence for alloy formation was found. We found a volcano-shape relationship between eCO(2)R selectivity toward two electron products, such as CO, and the elemental ratio of Cu and Pb. A maximum Faradaic efficiency towards CO was found for Cu9.00Pb1.00, which was four times higher than that of pure Cu, under the same electrocatalytic conditions. In situ Raman spectroscopy revealed that the optimal amount of Pb effectively improved the reducibility of the pristine Cu1+ and Pb2+ domains to metallic Cu and Pb, which boosted the selectivity towards CO by synergistic effects. This work provides a framework of thinking to design and tune the selectivity of bimetallic electrocatalysts for CO2 reduction through valorization of metallurgical waste.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 4.5
Times cited: 7
DOI: 10.1002/CCTC.202200754
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