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“Estimation of temperature homogeneity in MEMS-based heating nanochips via quantitative HAADF-STEM tomography”. Chen Q, Skorikov A, van der Hoeven JES, van Blaaderen A, Albrecht W, Perez-Garza HH, Bals S, Particle and particle systems characterization 41, 1 (2023). http://doi.org/10.1002/PPSC.202300070
Abstract: Sample holders for transmission electron microscopy (TEM) based on micro-electro-mechanical systems (MEMS) have recently become popular for investigating the behavior of nanomaterials under in situ or environmental conditions. The accuracy and reproducibility of these in situ holders are essential to ensure the reliability of experimental results. In addition, the uniformity of an applied temperature trigger across the MEMS chip is a crucial parameter. In this work, it is measured the temperature homogeneity of MEMS-based heating sample supports by locally analyzing the dynamics of heat-induced alloying of Au@Ag nanoparticles located in different regions of the support through quantitative fast high-angle annular dark-field scanning TEM tomography. These results demonstrate the superior temperature homogeneity of a microheater design based on a heating element shaped as a circular spiral with a width decreasing outwards compared to a double spiral-shaped designed microheater. The proposed approach to measure the local temperature homogeneity based on the thermal properties of bimetallic nanoparticles will support the future development of MEMS-based heating supports with improved thermal properties and in situ studies where high precision in the temperature at a certain position is required. This schematic delineates an approach to quantifying potential localized temperature deviation within a nanochip. Employing two comparable nanoparticles as thermal probes in discrete nanochip regions, the alloying kinetics of these nanoparticles are monitorable using in situ quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography, thus enabling the precise estimation of local temperature deviations.image
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 2.7
DOI: 10.1002/PPSC.202300070
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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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“Recent Advances in Transmission Electron Microscopy for Materials Science at the EMAT Lab of the University of Antwerp”. Guzzinati G, Altantzis T, Batuk M, De Backer A, Lumbeeck G, Samaee V, Batuk D, Idrissi H, Hadermann J, Van Aert S, Schryvers D, Verbeeck J, Bals S, Materials 11, 1304 (2018). http://doi.org/10.3390/ma11081304
Abstract: The rapid progress in materials science that enables the design of materials down to the nanoscale also demands characterization techniques able to analyze the materials down to the same scale, such as transmission electron microscopy. As Belgium’s foremost electron microscopy group, among the largest in the world, EMAT is continuously contributing to the development of TEM techniques, such as high-resolution imaging, diffraction, electron tomography, and spectroscopies, with an emphasis on quantification and reproducibility, as well as employing TEM methodology at the highest level to solve real-world materials science problems. The lab’s recent contributions are presented here together with specific case studies in order to highlight the usefulness of TEM to the advancement of materials science.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.654
Times cited: 15
DOI: 10.3390/ma11081304
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“Oxidation barrier of Cu and Fe powder by Atomic Layer Deposition”. Cremers V, Rampelberg G, Barhoum A, Walters P, Claes N, Oliveira TM de, Assche GV, Bals S, Dendooven J, Detavernier C, Surface and coatings technology 349, 1032 (2018). http://doi.org/10.1016/j.surfcoat.2018.06.048
Abstract: Atomic layer deposition (ALD) is a vapor based technique which allows to deposit uniform, conformal films with a thickness control at the atomic scale. In this research, Al 2 O 3 coatings were deposited on micrometer-sized Fe and Cu powder (particles) using the thermal trimethylaluminum (TMA)/ water (H 2 O) process in a rotary pump-type ALD reactor. Rotation of the powder during deposition was required to obtain a pinhole-free ALD coating. The protective nature of the coating was evaluated by quantifying its effectiveness in protecting the metal particles during oxidative annealing treatments. The Al 2 O 3 coated powders were annealed in ambient air while in-situ thermogravimetric analysis (TGA) and in-situ x-ray diffraction (XRD) data were acquired. The thermal stability of a series of Cu and Fe powder with different Al 2 O 3 thicknesses were determined with TGA. In both samples a clear shift in oxidation temperature is visible. For Cu and Fe powder coated with 25 nm Al 2 O 3 , we observed an increase of the oxidation temperature with 300-400°C. For the Cu powder a thin film of only 8 nm is required to obtain an initial increase in oxidation temperature of 200°C. In contrast, for Fe powder a thicker coating of 25 nm is required. In both cases, the oxidation temperature increases with increasing thickness of the Al 2 O 3 coating. These results illustrate that the Al 2 O 3 thin film, deposited by the thermal ALD process (TMA/H 2 O) can be an efficient and pinhole-free barrier layer for micrometer-sized powder particles, provided that the powder is properly agitated during the process to ensure sufficient vapour-solid interaction.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.589
Times cited: 10
DOI: 10.1016/j.surfcoat.2018.06.048
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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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“Optimized fabrication of high-quality La0.67Sr0.33MnO3 thin films considering all essential characteristics”. Boschker H, Huijben M, Vailinois A, Verbeeck J, Van Aert S, Luysberg M, Bals S, Van Tendeloo G, Houwman EP, Koster G, Blank DHA, Rijnders G, Journal of physics: D: applied physics 44, 205001 (2011). http://doi.org/10.1088/0022-3727/44/20/205001
Abstract: In this paper, an overview of the fabrication and properties of high-quality La0.67Sr0.33MnO3 (LSMO) thin films is given. A high-quality LSMO film combines a smooth surface morphology with a large magnetization and a small residual resistivity, while avoiding precipitates and surface segregation. In the literature, typically only a few of these issues are adressed. We therefore present a thorough characterization of our films, which were grown by pulsed laser deposition. The films were characterized with reflection high energy electron diffraction, atomic force microscopy, x-ray diffraction, magnetization and transport measurements, x-ray photoelectron spectroscopy and scanning transmission electron microscopy. The films have a saturation magnetization of 4.0 µB/Mn, a Curie temperature of 350 K and a residual resistivity of 60 µΩ cm. These results indicate that high-quality films, combining both large magnetization and small residual resistivity, were realized. A comparison between different samples presented in the literature shows that focussing on a single property is insufficient for the optimization of the deposition process. For high-quality films, all properties have to be adressed. For LSMO devices, the thin-film quality is crucial for the device performance. Therefore, this research is important for the application of LSMO in devices.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.588
Times cited: 99
DOI: 10.1088/0022-3727/44/20/205001
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“On the use of TEM in the characterization of nanocomposites”. Monticelli O, Musina Z, Russo S, Bals S, Materials letters 61, 3446 (2007). http://doi.org/10.1016/j.matlet.2006.11.086
Abstract: Both an organically modified commercial clay of montmorillonite type (MMT) and its nanocomposites, based either on polyamide 6 (PA6) or an epoxy resin, as matrix polymer, have been characterized by transmission electron microscopy (TEM). Sample micrographs, taken at increasing exposure times (t(e)), have shown the gradual disappearance of clay layers, because of an amorphisation of the MMT crystalline structures caused by prolonged sample exposure to electron beam. Indeed, the above phenomenon, which is mostly evident in the case of intercalated nanocomposites, makes the detection of the layered silicate dispersion in the polymer matrix rather difficult and compels to perform TEM measurements using very short exposure times. Moreover, the microscopy accelerating voltage has turned out to affect sample stability; namely, when decreasing the above parameter, the disappearance of clay structure occurs at lower exposure times. (C) 2006 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.572
Times cited: 28
DOI: 10.1016/j.matlet.2006.11.086
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“Exploring the effects of graphene and temperature in reducing electron beam damage: A TEM and electron diffraction-based quantitative study on Lead Phthalocyanine (PbPc) crystals”. Jain N, Hao Y, Parekh U, Kaltenegger M, Pedrazo-Tardajos A, Lazzaroni R, Resel R, Geerts YH, Bals S, Van Aert S, Micron 169, 103444 (2023). http://doi.org/10.1016/j.micron.2023.103444
Abstract: High-resolution transmission electron microscopy (TEM) of organic crystals, such as Lead Phthalocyanine (PbPc), is very challenging since these materials are prone to electron beam damage leading to the breakdown of the crystal structure during investigation. Quantification of the damage is imperative to enable high-resolution imaging of PbPc crystals with minimum structural changes. In this work, we performed a detailed electron diffraction study to quantitatively measure degradation of PbPc crystals upon electron beam irradiation. Our study is based on the quantification of the fading intensity of the spots in the electron diffraction patterns. At various incident dose rates (e/Å2/s) and acceleration voltages, we experimentally extracted the decay rate (1/s), which directly correlates with the rate of beam damage. In this manner, a value for the critical dose (e/Å2) could be determined, which can be used as a measure to quantify beam damage. Using the same methodology, we explored the influence of cryogenic temperatures, graphene TEM substrates, and graphene encapsulation in prolonging the lifetime of the PbPc crystal structure during TEM investigation. The knowledge obtained by diffraction experiments is then translated to real space high-resolution TEM imaging of PbPc.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.4
Times cited: 1
DOI: 10.1016/j.micron.2023.103444
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“A new Bi4Mn1/3W2/3O8Cl Sillén-Aurivillius intergrowth: synthesis and structural characterisation by quantitative transmission electron microscopy”. Avila-Brande D, Otero-Díaz LC, Landa-Cánovas AR, Bals S, Van Tendeloo G, European journal of inorganic chemistry , 1853 (2006). http://doi.org/10.1002/ejic.200501021
Abstract: The synthesis and structural characterisation of a new phase with nominal composition Bi4Mn1/3W2/3O8Cl is presented. Conventional and analytical transmission electron microscopy are used to determine the composition, unit-cell symmetry and space group of the compound, whereas a structural model is deducted by exit-wave reconstruction in the transmission electron microscope. This technique allows the microscope information limit of 1.1 angstrom to be reached and the (light) oxygen atoms in the presence of heavier atoms (Bi, W, Mn) to be imaged. The average structure is refined from Xray powder diffraction data using the Rietveld method yielding an orthorhombic unit cell with lattice parameters a 5.467(4) angstrom, b = 5.466(7) angstrom and c = 14.159(3) angstrom and space group Cm2m, which could be described as a Sillen-Aurivillius intergrowth. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.444
Times cited: 12
DOI: 10.1002/ejic.200501021
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“The influence of acids on tuning the pore size of mesoporous TiO2 templated by non-ionic block copolymers”. Loreto S, Vanrompay H, Mertens M, Bals S, Meynen V, European journal of inorganic chemistry 2018, 62 (2018). http://doi.org/10.1002/EJIC.201701266
Abstract: <script type='text/javascript'>document.write(unpmarked('We show the possibility to tune the pore size of mesoporous TiO2 templated by non-ionic block copolymers by adding different inorganic acids at well-chosen concentration. The effect of the inorganic anions on both the TiO2 cluster formation and the non-ionic block copolymers micelles is investigated to explain the experimental results.'));
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Laboratory of adsorption and catalysis (LADCA)
Impact Factor: 2.444
Times cited: 6
DOI: 10.1002/EJIC.201701266
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“A decade of atom-counting in STEM: From the first results toward reliable 3D atomic models from a single projection”. De Backer A, Bals S, Van Aert S, Ultramicroscopy , 113702 (2023). http://doi.org/10.1016/j.ultramic.2023.113702
Abstract: Quantitative structure determination is needed in order to study and understand nanomaterials at the atomic scale. Materials characterisation resulting in precise structural information is a crucial point to understand the structure–property relation of materials. Counting the number of atoms and retrieving the 3D atomic structure of nanoparticles plays an important role here. In this paper, an overview will be given of the atom-counting methodology and its applications over the past decade. The procedure to count the number of atoms will be discussed in detail and it will be shown how the performance of the method can be further improved. Furthermore, advances toward mixed element nanostructures, 3D atomic modelling based on the atom-counting results, and quantifying the nanoparticle dynamics will be highlighted.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
Times cited: 3
DOI: 10.1016/j.ultramic.2023.113702
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“Structural characterization of Er-doped Li2O-Al2O3-SiO2 glass ceramics”. Krsmanovic R, Bals S, Bertoni G, Van Tendeloo G, Optical materials 30, 1183 (2008). http://doi.org/10.1016/j.optmat.2007.05.045
Abstract: Particularly favourable properties of glass ceramics are developed on the basis of two key advantages of these materials: the variation of chemical composition and of microstructure. Therefore, detailed structural and chemical information are necessary to get insight in novel glass ceramic materials. We present here two examples of Er-doped Li2O-Al2O3-SiO2, with different quantities of ZrO2, both obtained with sol-gel synthesis. Different transmission electron microscopy techniques: conventional TEM, HRTEM, and EELS are used and the results are compared with those previously obtained with XRD and Rietveld analysis. We also demonstrate the 3D reconstruction, obtained from HAADF-STEM imaging, to determine the morphology of nanosize precipitates in these composites. (c) 2007 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.238
Times cited: 12
DOI: 10.1016/j.optmat.2007.05.045
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“Phase formation and texture of thin nickel germanides on Ge(001) and Ge(111)”. De Schutter B, Van Stiphout K, Santos NM, Bladt E, Jordan-Sweet J, Bals S, Lavoie C, Comrie CM, Vantomme A, Detavernier C, Journal of applied physics 119, 135305 (2016). http://doi.org/10.1063/1.4945317
Abstract: We studied the solid-phase reaction between a thin Nifilm and a single crystal Ge(001) or Ge(111) substrate during a ramp anneal. The phase formation sequence was determined using in situX-ray diffraction and in situRutherford backscattering spectrometry (RBS), while the nature and the texture of the phases were studied using X-ray pole figures and transmission electron microscopy. The phase sequence is characterized by the formation of a single transient phase before NiGe forms as the final and stable phase. X-ray pole figures were used to unambiguously identify the transient phase as the ϵ-phase, a non-stoichiometric Ni-rich germanide with a hexagonal crystal structure that can exist for Ge concentrations between 34% and 48% and which forms with a different epitaxial texture on both substrate orientations. The complementary information gained from both RBS and X-ray pole figure measurements revealed a simultaneous growth of both the ϵ-phase and NiGe over a small temperature window on both substrate orientations.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.068
Times cited: 14
DOI: 10.1063/1.4945317
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“Controlling the formation and stability of ultra-thin nickel silicides : an alloying strategy for preventing agglomeration”. Geenen FA, van Stiphout K, Nanakoudis A, Bals S, Vantomme A, Jordan-Sweet J, Lavoie C, Detavernier C, Journal of applied physics 123, 075303 (2018). http://doi.org/10.1063/1.5009641
Abstract: The electrical contact of the source and drain regions in state-of-the-art CMOS transistors is nowadays facilitated through NiSi, which is often alloyed with Pt in order to avoid morphological agglomeration of the silicide film. However, the solid-state reaction between as-deposited Ni and the Si substrate exhibits a peculiar change for as-deposited Ni films thinner than a critical thickness of t(c) = 5 nm. Whereas thicker films form polycrystalline NiSi upon annealing above 450 degrees C, thinner films form epitaxial NiSi2 films that exhibit a high resistance toward agglomeration. For industrial applications, it is therefore of utmost importance to assess the critical thickness with high certainty and find novel methodologies to either increase or decrease its value, depending on the aimed silicide formation. This paper investigates Ni films between 0 and 15 nm initial thickness by use of “thickness gradients,” which provide semi-continuous information on silicide formation and stability as a function of as-deposited layer thickness. The alloying of these Ni layers with 10% Al, Co, Ge, Pd, or Pt renders a significant change in the phase sequence as a function of thickness and dependent on the alloying element. The addition of these ternary impurities therefore changes the critical thickness t(c). The results are discussed in the framework of classical nucleation theory. Published by AIP Publishing.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.068
Times cited: 23
DOI: 10.1063/1.5009641
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“Seeing and measuring in 3D with electrons”. Bals S, Goris B, Altantzis T, Heidari H, Van Aert S, Van Tendeloo G, Comptes rendus : physique 15, 140 (2014). http://doi.org/10.1016/j.crhy.2013.09.015
Abstract: Modern TEM enables the investigation of nanostructures at the atomic scale. However, TEM images are only two-dimensional (2D) projections of a three-dimensional (3D) object. Electron tomography can overcome this limitation. The technique is increasingly focused towards quantitative measurements and reaching atomic resolution in 3D has been the ultimate goal for many years. Therefore, one needs to optimize the acquisition of the data, the 3D reconstruction techniques as well as the quantification methods. Here, we will review a broad range of methodologies and examples. Finally, we will provide an outlook and will describe future challenges in the field of electron tomography.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.048
Times cited: 15
DOI: 10.1016/j.crhy.2013.09.015
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“Assisted spray pyrolysis production and characterisation of ZnO nanoparticles with narrow size distribution”. Turner S, Tavernier SMF, Huyberechts G, Bals S, Batenburg KJ, Van Tendeloo G, Journal of nanoparticle research 12, 615 (2010). http://doi.org/10.1007/s11051-009-9630-1
Abstract: Nano-sized ZnO particles with a narrow size distribution and high crystallinity were prepared from aqueous solutions with high concentrations of Zn2+ containing salts and citric acid in a conventional spray pyrolysis setup. Structure, morphology and size of the produced material were compared to ZnO material produced by simple spray pyrolysis of zinc nitrates in the same experimental setup. Using transmission electron microscopy and electron tomography it has been shown that citric acid-assisted spray pyrolysed material is made up of micron sized secondary particles comprising a shell of lightly agglomerated, monocrystalline primary ZnO nanoparticles with sizes in the 2030 nm range, separable by a simple ultrasonic treatment step.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.02
Times cited: 27
DOI: 10.1007/s11051-009-9630-1
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“Intracellular fate of hydrophobic nanocrystal self-assemblies in tumor cells”. Nicolas-Boluda A, Yang Z, Dobryden I, Carn F, Winckelmans N, Pechoux C, Bonville P, Bals S, Claesson PM, Gazeau F, Pileni MP, Advanced Functional Materials 30, 2004274 (2020). http://doi.org/10.1002/ADFM.202004274
Abstract: Control of interactions between nanomaterials and cells remains a biomedical challenge. A strategy is proposed to modulate the intralysosomal distribution of nanoparticles through the design of 3D suprastructures built by hydrophilic nanocrystals (NCs) coated with alkyl chains. The intracellular fate of two water-dispersible architectures of self-assembled hydrophobic magnetic NCs: hollow deformable shells (colloidosomes) or solid fcc particles (supraballs) is compared. These two self-assemblies display increased cellular uptake by tumor cells compared to dispersions of the water-soluble NC building blocks. Moreover, the self-assembly structures increase the NCs density in lysosomes and close to the lysosome membrane. Importantly, the structural organization of NCs in colloidosomes and supraballs are maintained in lysosomes up to 8 days after internalization, whereas initially dispersed hydrophilic NCs are randomly aggregated. Supraballs and colloidosomes are differently sensed by cells due to their different architectures and mechanical properties. Flexible and soft colloidosomes deform and spread along the biological membranes. In contrast, the more rigid supraballs remain spherical. By subjecting the internalized suprastructures to a magnetic field, they both align and form long chains. Overall, it is highlighted that the mechanical and topological properties of the self-assemblies direct their intracellular fate allowing the control intralysosomal density, ordering, and localization of NCs.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19
Times cited: 11
DOI: 10.1002/ADFM.202004274
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“Enhanced self-assembly of metal oxides and metal-organic frameworks from precursors with magnetohydrodynamically induced long-lived collective spin states”. Breynaert E, Emmerich J, Mustafa D, Bajpe SR, Altantzis T, Van Havenbergh K, Taulelle F, Bals S, Van Tendeloo G, Kirschhock CEA, Martens JA;, Advanced materials 26, 5173 (2014). http://doi.org/10.1002/adma.201400835
Abstract: Magneto-hydrodynamic generation of long-lived collective spin states and their impact on crystal morphology is demonstrated for three different, technologically relevant materials: COK-16 metal organic framework, manganese oxide nanotubes, and vanadium oxide nano-scrolls.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 7
DOI: 10.1002/adma.201400835
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“Advanced electron microscopy for advanced materials”. Van Tendeloo G, Bals S, Van Aert S, Verbeeck J, van Dyck D, Advanced materials 24, 5655 (2012). http://doi.org/10.1002/adma.201202107
Abstract: The idea of this Review is to introduce newly developed possibilities of advanced electron microscopy to the materials science community. Over the last decade, electron microscopy has evolved into a full analytical tool, able to provide atomic scale information on the position, nature, and even the valency atoms. This information is classically obtained in two dimensions (2D), but can now also be obtained in 3D. We show examples of applications in the field of nanoparticles and interfaces.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 19.791
Times cited: 107
DOI: 10.1002/adma.201202107
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“Three-dimensional characterization of helical silver nanochains mediated by protein assemblies”. Leroux F, Gysemans M, Bals S, Batenburg KJ, Snauwaert J, Verbiest T, van Haesendonck C, Van Tendeloo G, Advanced materials 22, 2193 (2010). http://doi.org/10.1002/adma.200903657
Abstract: Characterization methods for the structural investigation of biotemplates for nanodevices remain widely unexplored, despite the fact that biotemplating methods for nanodevice fabrication are becoming more widespread. In this study several techniques are used to characterize the morphology and 3D distribution of silver nanoparticles deposited on insulin fibrils.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 19.791
Times cited: 51
DOI: 10.1002/adma.200903657
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“End-to-end assembly of shape-controlled nanocrystals via a nanowelding approach mediated by gold domains”. Figuerola A, Franchini IR, Fiore A, Mastria R, Falqui A, Bertoni G, Bals S, Van Tendeloo G, Kudera S, Cingolani R, Manna L, Advanced materials 21, 550 (2009). http://doi.org/10.1002/adma.200801928
Abstract: Welding nanocrystals for assembly: The welding of Au domains grown on the tips of shape-controlled cadmium chalcogenide colloidal nanocrystals is used as a strategy for their assembly. Iodine-induced coagulation of selectively grown Au domains leads to assemblies such as flowerlike structures based on bullet-shaped nanocrystals, linear and cross-linked chains of nanorods, and globular networks with tetrapods as building blocks.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 110
DOI: 10.1002/adma.200801928
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“A new approach for electron tomography: annular dark-field transmission electron microscopy”. Bals S, Van Tendeloo G, Kisielowski C, Advanced materials 18, 892 (2006). http://doi.org/10.1002/adma.200502201
Abstract: Annular dark-field transmission electron microscopy uses an annular objective aperture that blocks the central beam and all electrons scattered up to a certain serniangle. A contrast suitable for electron tomography is generated and 3D reconstructions of CdTe tetrapods and C nanotubes (see figure) are successfully obtained. With short exposure times and high contrast, the technique could be useful not only for materials science, but also for biological applications.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 53
DOI: 10.1002/adma.200502201
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“Imaging heterogeneously distributed photo-active traps in perovskite single crystals”. Yuan H, Debroye E, Bladt E, Lu G, Keshavarz M, Janssen KPF, Roeffaers MBJ, Bals S, Sargent EH, Hofkens J, Advanced materials 30, 1705494 (2018). http://doi.org/10.1002/ADMA.201705494
Abstract: Organic-inorganic halide perovskites (OIHPs) have demonstrated outstanding energy conversion efficiency in solar cells and light-emitting devices. In spite of intensive developments in both materials and devices, electronic traps and defects that significantly affect their device properties remain under-investigated. Particularly, it remains challenging to identify and to resolve traps individually at the nanoscopic scale. Here, photo-active traps (PATs) are mapped over OIHP nanocrystal morphology of different crystallinity by means of correlative optical differential super-resolution localization microscopy (Delta-SRLM) and electron microscopy. Stochastic and monolithic photoluminescence intermittency due to individual PATs is observed on monocrystalline and polycrystalline OIHP nanocrystals. Delta-SRLM reveals a heterogeneous PAT distribution across nanocrystals and determines the PAT density to be 1.3 x 10(14) and 8 x 10(13) cm(-3) for polycrystalline and for monocrystalline nanocrystals, respectively. The higher PAT density in polycrystalline nanocrystals is likely related to an increased defect density. Moreover, monocrystalline nanocrystals that are prepared in an oxygen and moisture-free environment show a similar PAT density as that prepared at ambient conditions, excluding oxygen or moisture as chief causes of PATs. Hence, it is conduded that the PATs come from inherent structural defects in the material, which suggests that the PAT density can be reduced by improving crystalline quality of the material.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 29
DOI: 10.1002/ADMA.201705494
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“Spontaneous self-assembly of Perovskite nanocrystals into electronically coupled supercrystals : toward filling the green gap”. Tong Y, Yao E-P, Manzi A, Bladt E, Wang K, Doeblinger M, Bals S, Mueller-Buschbaum P, Urban AS, Polavarapu L, Feldmann J, Advanced materials 30, 1801117 (2018). http://doi.org/10.1002/ADMA.201801117
Abstract: Self-assembly of nanoscale building blocks into ordered nanoarchitectures has emerged as a simple and powerful approach for tailoring the nanoscale properties and the opportunities of using these properties for the development of novel optoelectronic nanodevices. Here, the one-pot synthesis of CsPbBr3 perovskite supercrystals (SCs) in a colloidal dispersion by ultrasonication is reported. The growth of the SCs occurs through the spontaneous self-assembly of individual nanocrystals (NCs), which form in highly concentrated solutions of precursor powders. The SCs retain the high photoluminescence (PL) efficiency of their NC subunits, however also exhibit a redshifted emission wavelength compared to that of the individual nanocubes due to interparticle electronic coupling. This redshift makes the SCs pure green emitters with PL maxima at approximate to 530-535 nm, while the individual nanocubes emit a cyan-green color (approximate to 512 nm). The SCs can be used as an emissive layer in the fabrication of pure green light-emitting devices on rigid or flexible substrates. Moreover, the PL emission color is tunable across the visible range by employing a well-established halide ion exchange reaction on the obtained CsPbBr3 SCs. These results highlight the promise of perovskite SCs for light emitting applications, while providing insight into their collective optical properties.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 161
DOI: 10.1002/ADMA.201801117
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“A Facet-Specific Quantum Dot Passivation Strategy for Colloid Management and Efficient Infrared Photovoltaics”. Kim Y, Che F, Jo JW, Choi J, de Arquer FPG, Voznyy O, Sun B, Kim J, Choi M-J, Quintero-Bermudez R, Fan F, Tan CS, Bladt E, Walters G, Proppe AH, Zou C, Yuan H, Bals S, Hofkens J, Roeffaers MBJ, Hoogland S, Sargent EH, Advanced materials 31, 1805580 (2019). http://doi.org/10.1002/ADMA.201805580
Abstract: Colloidal nanocrystals combine size- and facet-dependent properties with solution processing. They offer thus a compelling suite of materials for technological applications. Their size- and facet-tunable features are studied in synthesis; however, to exploit their features in optoelectronic devices, it will be essential to translate control over size and facets from the colloid all the way to the film. Larger-diameter colloidal quantum dots (CQDs) offer the attractive possibility of harvesting infrared (IR) solar energy beyond absorption of silicon photovoltaics. These CQDs exhibit facets (nonpolar (100)) undisplayed in small-diameter CQDs; and the materials chemistry of smaller nanocrystals fails consequently to translate to materials for the short-wavelength IR regime. A new colloidal management strategy targeting the passivation of both (100) and (111) facets is demonstrated using distinct choices of cations and anions. The approach leads to narrow-bandgap CQDs with impressive colloidal stability and photoluminescence quantum yield. Photophysical studies confirm a reduction both in Stokes shift (approximate to 47 meV) and Urbach tail (approximate to 29 meV). This approach provides a approximate to 50% increase in the power conversion efficiency of IR photovoltaics compared to controls, and a approximate to 70% external quantum efficiency at their excitonic peak.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 74
DOI: 10.1002/ADMA.201805580
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“3D Atomic‐Scale Dynamics of Laser‐Light‐Induced Restructuring of Nanoparticles Unraveled by Electron Tomography”. Albrecht W, Arslan Irmak E, Altantzis T, Pedrazo‐Tardajos A, Skorikov A, Deng T‐S, van der Hoeven JES, van Blaaderen A, Van Aert S, Bals S, Advanced Materials , 2100972 (2021). http://doi.org/10.1002/adma.202100972
Abstract: Understanding light–matter interactions in nanomaterials is crucial for
optoelectronic, photonic, and plasmonic applications. Specifically, metal
nanoparticles (NPs) strongly interact with light and can undergo shape
transformations, fragmentation and ablation upon (pulsed) laser excitation.
Despite being vital for technological applications, experimental insight into
the underlying atomistic processes is still lacking due to the complexity of
such measurements. Herein, atomic resolution electron tomography is performed
on the same mesoporous-silica-coated gold nanorod, before and after
femtosecond laser irradiation, to assess the missing information. Combined
with molecular dynamics (MD) simulations based on the experimentally
determined 3D atomic-scale morphology, the complex atomistic rearrangements,
causing shape deformations and defect generation, are unraveled.
These rearrangements are simultaneously driven by surface diffusion, facet
restructuring, and strain formation, and are influenced by subtleties in the
atomic distribution at the surface.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 19.791
Times cited: 8
DOI: 10.1002/adma.202100972
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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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“Surfactant layers on gold nanorods”. Mosquera J, Wang D, Bals S, Liz-Marzan LM, Accounts of chemical research 56, 1204 (2023). http://doi.org/10.1021/ACS.ACCOUNTS.3C00101
Abstract: Gold nanorods (Au NRs) are an exceptionally promising tool in nanotechnology due to three key factors: (i) their strong interaction with electromagnetic radiation, stemming from their plasmonic nature, (ii) the ease with which the resonance frequency of their longitudinal plasmon mode can be tuned from the visible to the near-infrared region of the electromagnetic spect r u m based on their aspect ratio, and (iii) their simple and cost-effective preparation through seed-mediated chemical growth. In this synthetic method, surfactants play a critical role in controlling the size, shape, and colloidal stabi l i t y of Au NRs. For example, surfactants can stabilize specific crystallographic facets during the formation of Au NRs, leading to t h e formation of NRs with specific morphologies. The process of surfactant adsorption onto the NR surface may result in various assemblies of surfactant molecules, such as spherical micelles, elongated micelles, or bilayers. Again, the assembly mode is critical toward determining the further availabi l i t y of the Au NR surface to the surrounding medium. Despite its importance and a great deal of research effort, the interaction between Au NPs and surfactants remains insufficiently understood, because the assembly process is influenced by numerous factors, including the chemical nature of the surfactant, the surface morphology of Au NPs, and solution parameters. Therefore, gaining a more comprehensive understanding of these interactions is essential to unlock the full potential of the seed-mediated growth method and the applications of plasmonic NPs. A plethora of characterization techniques have been applied to reach such an understanding , but many open questions remain. In this Account, we review the current knowledge on the interactions between surfactants and Au NRs. We briefly introduce the state-of-the-art methods for synthesizing Au NRs and highlight the crucial role of cationic surfactants during this process. The self-assembly and organization of surfactants on the Au NR surface is then discussed to better understand their role in seed-mediated growth. Subsequently, we provide examples and elucidate how chemical additives can be used to modulate micellar assemblies, in turn allowing for a finer control over the growth of Au NRs, including chiral NRs. Next, we review the main experimental characterization and computational modeling techniques that have been applied to shed light on the arrangement of surfactants on Au NRs and summarize the advantages and disadvantages for each technique. The Account ends with a “Conclusions and Outlook” section, outlining promising future research directions and developments that we consider are sti l l required, mostly related to the application of electron microscopy in liquid and in 3D. Finally, we remark on the potential of exploiting machine learning techniques to predict synthetic routes for NPs with predefined structures and properties.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 18.3
Times cited: 8
DOI: 10.1021/ACS.ACCOUNTS.3C00101
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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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“Charging of vitreous samples in cryogenic electron microscopy mitigated by graphene”. Zhang Y, van Schayck JP, Pedrazo-Tardajos A, Claes N, Noteborn WEM, Lu P-H, Duimel H, Dunin-Borkowski RE, Bals S, Peters PJ, Ravelli RBG, ACS nano 17, 15836 (2023). http://doi.org/10.1021/ACSNANO.3C03722
Abstract: Cryogenic electronmicroscopy can provide high-resolution reconstructionsof macromolecules embedded in a thin layer of ice from which atomicmodels can be built de novo. However, the interactionbetween the ionizing electron beam and the sample results in beam-inducedmotion and image distortion, which limit the attainable resolutions.Sample charging is one contributing factor of beam-induced motionsand image distortions, which is normally alleviated by including partof the supporting conducting film within the beam-exposed region.However, routine data collection schemes avoid strategies wherebythe beam is not in contact with the supporting film, whose rationaleis not fully understood. Here we characterize electrostatic chargingof vitreous samples, both in imaging and in diffraction mode. We mitigatesample charging by depositing a single layer of conductive grapheneon top of regular EM grids. We obtained high-resolution single-particleanalysis (SPA) reconstructions at 2 & ANGS; when the electron beamonly irradiates the middle of the hole on graphene-coated grids, usingdata collection schemes that previously failed to produce sub 3 & ANGS;reconstructions without the graphene layer. We also observe that theSPA data obtained with the graphene-coated grids exhibit a higher b factor and reduced particle movement compared to dataobtained without the graphene layer. This mitigation of charging couldhave broad implications for various EM techniques, including SPA andcryotomography, and for the study of radiation damage and the developmentof future sample carriers. Furthermore, it may facilitate the explorationof more dose-efficient, scanning transmission EM based SPA techniques.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 17.1
DOI: 10.1021/ACSNANO.3C03722
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