“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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“Optical enhancement of a printed organic tandem solar cell using diffractive nanostructures”. Mayer JA, Offermans T, Chrapa M, Pfannmöller M, Bals S, Ferrini R, Nisato G, Optics express 26, A240 (2018). http://doi.org/10.1364/OE.26.00A240
Abstract: Solution processable organic tandem solar cells offer a promising approach to achieve cost-effective, lightweight and flexible photovoltaics. In order to further enhance the efficiency of optimized organic tandem cells, diffractive light-management nanostructures were designed for an optimal redistribution of the light as function of both wavelength and propagation angles in both sub-cells. As the fabrication of these optical structures is compatible with roll-to-roll production techniques such as hot-embossing or UV NIL imprinting, they present an optimal cost-effective solution for printed photovoltaics. Tandem cells with power conversion efficiencies of 8-10% were fabricated in the ambient atmosphere by doctor blade coating, selected to approximate the conditions during roll-to-roll manufacturing. Application of the light management structure onto an 8.7% efficient encapsulated tandem cell boosted the conversion efficiency of the cell to 9.5%. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.307
Times cited: 9
DOI: 10.1364/OE.26.00A240
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“Linearized radially polarized light for improved precision in strain measurements using micro-Raman spectroscopy”. Prabhakara V, Nuytten T, Bender H, Vandervorst W, Bals S, Verbeeck J, Optics Express 29, 34531 (2021). http://doi.org/10.1364/OE.434726
Abstract: Strain engineering in semiconductor transistor devices has become vital in the semiconductor industry due to the ever-increasing need for performance enhancement at the nanoscale. Raman spectroscopy is a non-invasive measurement technique with high sensitivity to mechanical stress that does not require any special sample preparation procedures in comparison to characterization involving transmission electron microscopy (TEM), making it suitable for inline strain measurement in the semiconductor industry. Indeed, at present, strain measurements using Raman spectroscopy are already routinely carried out in semiconductor devices as it is cost effective, fast and non-destructive. In this paper we explore the usage of linearized radially polarized light as an excitation source, which does provide significantly enhanced accuracy and precision as compared to linearly polarized light for this application. Numerical simulations are done to quantitatively evaluate the electric field intensities that contribute to this enhanced sensitivity. We benchmark the experimental results against TEM diffraction-based techniques like nano-beam diffraction and Bessel diffraction. Differences between both approaches are assigned to strain relaxation due to sample thinning required in TEM setups, demonstrating the benefit of Raman for nondestructive inline testing.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.307
Times cited: 2
DOI: 10.1364/OE.434726
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“Evaluation of top, angle, and side cleaned FIB samples for TEM analysis”. Montoya E, Bals S, Rossell MD, Schryvers D, Van Tendeloo G, Microscopy research and technique 70, 1060 (2007). http://doi.org/10.1002/jemt.20514
Abstract: ITEM specimens of a LaAlO3/SrTiO3 multilayer are prepared by FIB with internal lift out. Using a Ga+1 beam of 5 kV, a final cleaning step yielding top, top-angle, side, and bottom-angle cleaning is performed. Different cleaning procedures, which can be easily implemented in a dual beam FIB system, are described and compared; all cleaning types produce thin lamellae, useful for HRTEM and HAADF-STEM work up to atomic resolution. However, the top cleaned lamellae are strongly affected by the curtain effect. Top-angle cleaned specimens show an amorphous layer of around 5 nm at the specimen surfaces, due to damage and redeposition. Furthermore, it is observed that the LaAlO3 layers are preferentially destroyed and transformed into amorphous material, during the thinning process.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.147
Times cited: 36
DOI: 10.1002/jemt.20514
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“Transmission electron microscopy on interface engineered superconducting thin films”. Bals S, Van Tendeloo G, Rijnders G, Huijben M, Leca V, Blank DHA, IEEE transactions on applied superconductivity 13, 2834 (2003). http://doi.org/10.1109/TASC.2003.812023
Abstract: Transmission electron microscopy is used to evaluate different deposition techniques, which optimize the microstructure and physical properties of superconducting thin films. High-resolution electron microscopy proves that the use of an YBa2Cu2Ox buffer layer can avoid a variable interface configuration in YBa2Cu3O7-delta thin films grown on SrTiO3. The growth can also be controlled at an atomic level by, using sub-unit cell layer epitaxy, which results in films with high quality and few structural defects. Epitaxial strain in Sr0.85La0.15CuO2 infinite layer thin films influences the critical temperature of these films, as well as the microstructure. Compressive stress is released by a modulated or a twinned microstructure, which eliminates superconductivity. On the other hand, also tensile strain seems to lower the critical temperature of the infinite layer.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 13
DOI: 10.1109/TASC.2003.812023
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“Ultrastructure and composition of cell wall appositions in the roots of Asplenium (Polypodiales)”. Leroux O, Leroux F, Bagniewska-Zadworna, Knox JP, Claeys M, Bals S, Viane RLL, Micron 42, 863 (2011). http://doi.org/10.1016/j.micron.2011.06.002
Abstract: Cell wall appositions (CWAs), formed by the deposition of extra wall material at the contact site with microbial organisms, are an integral part of the response of plants to microbial challenge. Detailed histological studies of CWAs in fern roots do not exist. Using light and electron microscopy we examined the (ultra)structure of CWAs in the outer layers of roots of Asplenium species. All cell walls studded with CWAs were impregnated with yellow-brown pigments. CWAs had different shapes, ranging from warts to elongated branched structures, as observed with scanning and transmission electron microscopy. Ultrastructural study further showed that infecting fungi grow intramurally and that they are immobilized by CWAs when attempting to penetrate intracellularly. Immunolabelling experiments using monoclonal antibodies indicated pectic homogalacturonan, xyloglucan, mannan and cellulose in the CWAs, but tests for lignins and callose were negative. We conclude that these appositions are defense-related structures made of a non-lignified polysaccharide matrix on which phenolic compounds are deposited in order to create a barrier protecting the root against infections.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.98
Times cited: 20
DOI: 10.1016/j.micron.2011.06.002
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“Effectiveness of reducing the influence of CTAB at the surface of metal nanoparticles during in situ heating studies by TEM”. De Meyer R, Albrecht W, Bals S, Micron 144, 103036 (2021). http://doi.org/10.1016/j.micron.2021.103036
Abstract: In situ TEM is a valuable technique to offer novel insights in the behavior of nanomaterials under various conditions. However, interpretation of in situ experiments is not straightforward since the electron beam can impact the outcome of such measurements. For example, ligands surrounding metal nanoparticles transform into a protective carbon layer upon electron beam irradiation and may impact the apparent thermal stability during in situ heating experiments. In this work, we explore the effect of different treatments typically proposed to remove such ligands. We found that plasma treatment prior to heating experiments for Au nanorods and nanostars increased the apparent thermal stability of the nanoparticles, while an activated carbon treatment resulted in a decrease of the observed thermal stability. Treatment with HCl barely changed the experimental outcome. These results demonstrate the importance of carefully selecting pre-treatments procedures during in situ heating experiments.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.98
DOI: 10.1016/j.micron.2021.103036
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“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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“Barrier efficiency of sponge-like La2Zr2O7 buffer layers for YBCO-coated conductors”. Molina L, Tan H, Biermans E, Batenburg KJ, Verbeeck J, Bals S, Van Tendeloo G, Superconductor science and technology 24, 065019 (2011). http://doi.org/10.1088/0953-2048/24/6/065019
Abstract: Solution derived La2Zr2O7 films have drawn much attention for potential applications as thermal barriers or low-cost buffer layers for coated conductor technology. Annealing and coating parameters strongly affect the microstructure of La2Zr2O7, but different film processing methods can yield similar microstructural features such as nanovoids and nanometer-sized La2Zr2O7 grains. Nanoporosity is a typical feature found in such films and the implications for the functionality of the films are investigated by a combination of scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) and quantitative electron tomography. Chemical solution based La2Zr2O7 films deposited on flexible Ni5 at.%W substrates with a {100}lang001rang biaxial texture were prepared for an in-depth characterization. A sponge-like structure composed of nanometer-sized voids is revealed by high-angle annular dark-field scanning transmission electron microscopy in combination with electron tomography. A three-dimensional quantification of nanovoids in the La2Zr2O7 film is obtained on a local scale. Mostly non-interconnected highly faceted nanovoids compromise more than one-fifth of the investigated sample volume. The diffusion barrier efficiency of a 170 nm thick La2Zr2O7 film is investigated by STEM-EELS, yielding a 1.8 ± 0.2 nm oxide layer beyond which no significant nickel diffusion can be detected and intermixing is observed. This is of particular significance for the functionality of YBa2Cu3O7 − δ coated conductor architectures based on solution derived La2Zr2O7 films as diffusion barriers.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.878
Times cited: 31
DOI: 10.1088/0953-2048/24/6/065019
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“The superconducting proximity effect in epitaxial Al/Pb nanocomposites”. Wang H, Picot T, Houben K, Moorkens T, Grigg J, Van Haesendonck C, Biermans E, Bals S, Brown SA, Vantomme A, Temst K, Van Bael MJ;, Superconductor science and technology 27, 015008 (2014). http://doi.org/10.1088/0953-2048/27/1/015008
Abstract: We have investigated the superconducting properties of Pb nanoparticles with a diameter ranging from 8 to 20 nm, synthesized by Pb+ ion implantation in a crystalline Al matrix. A detailed structural characterization of the nanocomposites reveals the highly epitaxial relation between the Al crystalline matrix and the Pb nanoparticles. The Al/Pb nanocomposites display a single superconducting transition, with the critical temperature T-c increasing with the Pb content. The dependence of T-c on the Pb/Al volume ratio was compared with theoretical models of the superconducting proximity effect based on the bulk properties of Al and Pb. A very good correspondence with the strong-coupling proximity effect model was found, with an electron-phonon coupling constant in the Pb nanoparticles slightly reduced compared to bulk Pb. Our result differs from other studies on Pb nanoparticle based proximity systems where weak-coupling models were found to better describe the T-c dependence. We infer that the high interface quality resulting from the ion implantation synthesis method is a determining factor for the superconducting properties. Critical field and critical current measurements support the high quality of the nanocomposite superconducting films.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.878
Times cited: 2
DOI: 10.1088/0953-2048/27/1/015008
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“Selectivity in ligand functionalization of photocatalytic metal oxide nanoparticles for phase transfer and self‐assembly applications”. Borah R, Ninakanti R, Nuyts G, Peeters H, Pedrazo-Tardajos A, Nuti S, Vande Velde C, De Wael K, Lenaerts S, Bals S, Verbruggen S, Chemistry-A European Journal , chem.202100029 (2021). http://doi.org/10.1002/CHEM.202100029
Abstract: Functionalization of photocatalytic metal oxide nanoparticles of TiO 2 , ZnO, WO 3 and CuO with amine‐terminated (oleylamine) and thiol‐terminated (1‐dodecanethiol) alkyl chained ligands was studied under ambient conditions. A high selectivity was observed in the binding specificity of a ligand towards nanoparticles of these different oxides. It was observed that oleylamine binds stably to only TiO 2 and WO 3 , while 1‐dodecanethiol binds stably only to ZnO and CuO. Similarly, polar to non‐polar solvent phase transfer of TiO 2 and WO 3 nanoparticles could be achieved by using oleylamine, but not by 1‐dodecanethiol, while the contrary holds for ZnO and CuO. The surface chemistry of ligand functionalized nanoparticles was probed by ATR‐FTIR spectroscopy, that enabled to elucidate the occupation of the ligands at the active sites. The photo‐stability of the ligands on the nanoparticle surface was determined by the photocatalytic self‐cleaning properties of the material. While TiO 2 and WO 3 degrade the ligands within 24 hours under both UV and visible light, ligands on ZnO and CuO remain unaffected. The gathered insights are also highly relevant from an application point of view. As an example, since the ligand functionalized nanoparticles are hydrophobic in nature, they can thus be self‐assembled at the air‐water interface, for obtaining nanoparticle films with demonstrated photocatalytic as well as anti‐fogging properties.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Sustainable Energy, Air and Water Technology (DuEL); Intelligence in PRocesses, Advanced Catalysts and Solvents (iPRACS)
Impact Factor: 5.317
Times cited: 15
DOI: 10.1002/CHEM.202100029
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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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“AuNP/MIL-88B-NH₂, nanocomposite for the valorization of nitroarene by green catalytic hydrogenation”. Lelouche SNK, Lemir I, Biglione C, Craig T, Bals S, Horcajada P, Chemistry: a European journal , 1 (2024). http://doi.org/10.1002/CHEM.202400442
Abstract: The efficiency of a catalytic process is assessed based on conversion, yield, and time effectiveness. However, these parameters are insufficient for evaluating environmentally sustainable research. As the world is urged to shift towards green catalysis, additional factors such as reaction media, raw material availability, sustainability, waste minimization and catalyst biosafety, need to be considered to accurately determine the efficacy and sustainability of the process. By combining the high porosity and versatility of metal organic frameworks (MOFs) and the activity of gold nanoparticles (AuNPs), efficient, cyclable and biosafe composite catalysts can be achieved. Thus, a composite based on AuNPs and the nanometric flexible porous iron(III) aminoterephthalate MIL-88B-NH2 was successfully synthesized and fully characterized. This nanocomposite was tested as catalyst in the reduction of nitroarenes, which were identified as anthropogenic water pollutants, reaching cyclable high conversion rates at short times for different nitroarenes. Both synthesis and catalytic reactions were performed using green conditions, and even further tested in a time-optimizing one-pot synthesis and catalysis experiment. The sustainability and environmental impact of the catalytic conditions were assessed by green metrics. Thus, this study provides an easily implementable synthesis, and efficient catalysis, while minimizing the environmental and health impact of the process.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.3
DOI: 10.1002/CHEM.202400442
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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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“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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“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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“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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“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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“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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“Multimode electron tomography sheds light on synthesis, structure, and properties of complex metal-based nanoparticles”. Jenkinson K, Liz-Marzan LM, Bals S, Advanced materials 34, 2110394 (2022). http://doi.org/10.1002/ADMA.202110394
Abstract: Electron tomography has become a cornerstone technique for the visualization of nanoparticle morphology in three dimensions. However, to obtain in-depth information about a nanoparticle beyond surface faceting and morphology, different electron microscopy signals must be combined. The most notable examples of these combined signals include annular dark-field scanning transmission electron microscopy (ADF-STEM) with different collection angles and the combination of ADF-STEM with energy-dispersive X-ray or electron energy loss spectroscopies. Here, the experimental and computational development of various multimode tomography techniques in connection to the fundamental materials science challenges that multimode tomography has been instrumental to overcoming are summarized. Although the techniques can be applied to a wide variety of compositions, the study is restricted to metal and metal oxide nanoparticles for the sake of simplicity. Current challenges and future directions of multimode tomography are additionally discussed.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 29.4
Times cited: 10
DOI: 10.1002/ADMA.202110394
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“Chiral Seeded Growth of Gold Nanorods Into 4‐Fold Twisted Nanoparticles with Plasmonic Optical Activity”. Ni B, Mychinko M, Gómez‐Graña S, Morales‐Vidal J, Obelleiro‐Liz M, Heyvaert W, Vila‐Liarte D, Zhuo X, Albrecht W, Zheng G, González‐Rubio G, Taboada JM, Obelleiro F, López N, Pérez‐Juste J, Pastoriza‐Santos I, Cölfen H, Bals S, Liz‐Marzán LM, Advanced materials , 2208299 (2022). http://doi.org/10.1002/adma.202208299
Abstract: A robust and reproducible methodology to prepare stable inorganic nanoparticles with chiral morphology might hold the key to the practical utilization of these materials. We describe herein an optimized chiral growth method to prepare 4-fold twisted gold nanorods, where the amino acid cysteine is used as a dissymmetry inducer. Four tilted ridges were found to develop on the surface of single-crystal nanorods upon repeated reduction of HAuCl4, in the presence of cysteine as the chiral inducer and ascorbic acid as a reducing agent. From detailed electron microscopy analysis of the crystallographic structures, we propose that dissymmetry results from the development of chiral facets in the form of protrusions (tilted ridges) on the initial nanorods, eventually leading to a twisted shape. The role of cysteine is attributed to assisting enantioselective facet evolution, which is supported by density functional theory simulations of the surface energies, modified upon adsorption of the chiral molecule. The development of R-type and S-type chiral structures (small facets, terraces, or kinks) would thus be non-equal, removing the mirror symmetry of the Au NR and in turn resulting in a markedly chiral morphology with high plasmonic optical activity.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 29.4
Times cited: 35
DOI: 10.1002/adma.202208299
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“Direct operando visualization of metal support interactions induced by hydrogen spillover during CO₂, hydrogenation”. Jenkinson K, Spadaro MC, Golovanova V, Andreu T, Morante JR, Arbiol J, Bals S, Advanced materials 35, 2306447 (2023). http://doi.org/10.1002/ADMA.202306447
Abstract: The understanding of catalyst active sites is a fundamental challenge for the future rational design of optimized and bespoke catalysts. For instance, the partial reduction of Ce4+ surface sites to Ce3+ and the formation of oxygen vacancies are critical for CO2 hydrogenation, CO oxidation, and the water gas shift reaction. Furthermore, metal nanoparticles, the reducible support, and metal support interactions are prone to evolve under reaction conditions; therefore a catalyst structure must be characterized under operando conditions to identify active states and deduce structure-activity relationships. In the present work, temperature-induced morphological and chemical changes in Ni nanoparticle-decorated mesoporous CeO2 by means of in situ quantitative multimode electron tomography and in situ heating electron energy loss spectroscopy, respectively, are investigated. Moreover, operando electron energy loss spectroscopy is employed using a windowed gas cell and reveals the role of Ni-induced hydrogen spillover on active Ce3+ site formation and enhancement of the overall catalytic performance.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 29.4
DOI: 10.1002/ADMA.202306447
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“Decoding Excimer Formation in Covalent–Organic Frameworks Induced by Morphology and Ring Torsion”. Chakraborty J, Chatterjee A, Molkens K, Nath I, Arenas Esteban D, Bourda L, Watson G, Liu C, Van Thourhout D, Bals S, Geiregat P, Van der Voort P, Advanced Materials (2024). http://doi.org/10.1002/adma.202314056
Abstract: A thorough and quantitative understanding of the fate of excitons in covalent–organic frameworks (COFs) after photoexcitation is essential for their augmented optoelectronic and photocatalytic applications via precise structure tuning. The synthesis of a library of COFs having identical chemical backbone with impeded conjugation, but varied morphology and surface topography to study the effect of these physical properties on the photophysics of the materials is herein reported. The variation of crystallite size and surface topography substantified different aggregation pattern in the COFs, which leads to disparities in their photoexcitation and relaxation properties. Depending on aggregation, an inverse correlation between bulk luminescence decay time and exciton binding energy of the materials is perceived. Further transient absorption spectroscopic analysis confirms the presence of highly localized, immobile, Frenkel excitons (of diameter 0.3–0.5 nm) via an absence of annihilation at high density, most likely induced by structural torsion of the COF skeletons, which in turn preferentially relaxes via long‐lived (nanosecond to microsecond) excimer formation (in femtosecond scale) over direct emission. These insights underpin the importance of structural and topological design of COFs for their targeted use in photocatalysis.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 29.4
DOI: 10.1002/adma.202314056
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“Decoding Excimer Formation in Covalent–Organic Frameworks Induced by Morphology and Ring Torsion”. Chakraborty J, Chatterjee A, Molkens K, Nath I, Arenas Esteban D, Bourda L, Watson G, Liu C, Van Thourhout D, Bals S, Geiregat P, Van der Voort P, Advanced Materials (2024). http://doi.org/10.1002/adma.202314056
Abstract: A thorough and quantitative understanding of the fate of excitons in covalent–organic frameworks (COFs) after photoexcitation is essential for their augmented optoelectronic and photocatalytic applications via precise structure tuning. The synthesis of a library of COFs having identical chemical backbone with impeded conjugation, but varied morphology and surface topography to study the effect of these physical properties on the photophysics of the materials is herein reported. The variation of crystallite size and surface topography substantified different aggregation pattern in the COFs, which leads to disparities in their photoexcitation and relaxation properties. Depending on aggregation, an inverse correlation between bulk luminescence decay time and exciton binding energy of the materials is perceived. Further transient absorption spectroscopic analysis confirms the presence of highly localized, immobile, Frenkel excitons (of diameter 0.3–0.5 nm) via an absence of annihilation at high density, most likely induced by structural torsion of the COF skeletons, which in turn preferentially relaxes via long‐lived (nanosecond to microsecond) excimer formation (in femtosecond scale) over direct emission. These insights underpin the importance of structural and topological design of COFs for their targeted use in photocatalysis.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 29.4
DOI: 10.1002/adma.202314056
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“Combination of HAADF-STEM and ADF-STEM Tomography for Core-Shell Hybrid Materials”. Sentosun K, Sanz Ortiz MN, Batenburg KJ, Liz-Marzán LM, Bals S, Particle and particle systems characterization 32, 1063 (2015). http://doi.org/10.1002/ppsc.201500097
Abstract: Characterization of core-shell type nanoparticles in 3D by transmission electron microscopy (TEM) can be very challenging. Especially when both heavy and light elements co-exist within the same nanostructure, artefacts in the 3D reconstruction are often present. A representative example would be a particle comprising an anisotropic metallic (Au) nanoparticle coated with a (mesoporous) silica shell. To obtain a reliable 3D characterization of such an object, we propose a dose-efficient strategy to simultaneously acquire high angle annular dark field scanning TEM and annular dark field tilt series for tomography. The 3D reconstruction is further improved by applying an advanced masking and interpolation approach to the acquired data. This new methodology enables us to obtain high quality reconstructions from which also quantitative information can be extracted. This approach is broadly applicable to investigate hybrid core-shell materials.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 4.474
Times cited: 13
DOI: 10.1002/ppsc.201500097
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“Quantitative structure determination of large three-dimensional nanoparticle assemblies”. Altantzis T, Goris B, Sánchez-Iglesias A, Grzelczak M, Liz-Marzán LM, Bals S, Particle and particle systems characterization 30, 84 (2013). http://doi.org/10.1002/ppsc.201200045
Abstract: Thumbnail image of graphical abstract To investigate nanoassemblies in three dimensions, electron tomography is an important tool. For large nanoassemblies, it is not straightforward to obtain quantitative results in three dimensions. An optimized acquisition technique, incoherent bright field scanning transmission electron microscopy, is combined with an advanced 3D reconstruction algorithm. The approach is applied to quantitatively analyze large nanoassemblies in three dimensions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.474
Times cited: 23
DOI: 10.1002/ppsc.201200045
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“A New Method for Quantitative XEDS Tomography of Complex Heteronanostructures”. Zanaga D, Altantzis T, Polavarapu L, Liz-Marzán LM, Freitag B, Bals S, Particle and particle systems characterization 33, 396 (2016). http://doi.org/10.1002/ppsc.201600021
Abstract: Reliable quantification of 3D results obtained by X-ray Energy Dispersive Spectroscopy (XEDS) tomography is currently hampered by the presence of shadowing effects and poor spatial resolution. Here, we present a method that overcomes these problems by synergistically combining quantified XEDS data and High Angle Annular Dark Field – Scanning Transmission Electron Microscopy (HAADF-STEM) tomography. As a proof of principle, the approach is applied to characterize a complex Au/Ag nanorattle obtained through a galvanic replacement reaction. However, the technique we propose here is widely applicable to a broad range of nanostructures.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.474
Times cited: 29
DOI: 10.1002/ppsc.201600021
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