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“Single-cell yolk-shell nanoencapsulation for long-term viability with size-dependent permeability and molecular recognition”. Wang L, Li Y, Yang X-Y, Zhang B-B, Ninane N, Busscher HJ, Hu Z-Y, Delneuville C, Jiang N, Xie H, Van Tendeloo G, Hasan T, Su B-L, National Science Review 8 (2021). http://doi.org/10.1093/NSR/NWAA097
Abstract: Like nanomaterials, bacteria have been unknowingly used for centuries. They hold significant economic potential for fuel and medicinal compound production. Their full exploitation, however, is impeded by low biological activity and stability in industrial reactors. Though cellular encapsulation addresses these limitations, cell survival is usually compromised due to shell-to-cell contacts and low permeability. Here, we report ordered packing of silica nanocolloids with organized, uniform and tunable nanoporosities for single cyanobacterium nanoencapsulation using protamine as an electrostatic template. A space between the capsule shell and the cell is created by controlled internalization of protamine, resulting in a highly ordered porous shell-void-cell structure formation. These unique yolk-shell nano structures provide long-term cell viability with superior photosynthetic activities and resistance in harsh environments. In addition, engineering the colloidal packing allows tunable shell-pore diameter for size-dependent permeability and introduction of new functionalities for specific molecular recognition. Our strategy could significantly enhance the activity and stability of cyanobacteria for various nanobiotechnological applications.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.843
DOI: 10.1093/NSR/NWAA097
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“Triple-Modal Imaging of Magnetically-Targeted Nanocapsules in Solid TumoursIn Vivo”. Bai J, Wang JT-W, Rubio N, Protti A, Heidari H, Elgogary R, Southern P, Al-Jamal W' T, Sosabowski J, Shah AM, Bals S, Pankhurst QA, Al-Jamal KT, Theranostics 6, 342 (2016). http://doi.org/10.7150/thno.11918
Abstract: Triple-modal imaging magnetic nanocapsules, encapsulating hydrophobic superparamagnetic iron oxide nanoparticles, are formulated and used to magnetically target solid tumours after intravenous administration in tumour-bearing mice. The engineered magnetic polymeric nanocapsules m-NCs are ~200 nm in size with negative Zeta potential and shown to be spherical in shape. The loading efficiency of superparamagnetic iron oxide nanoparticles in the m-NC was ~100%. Up to ~3- and ~2.2-fold increase in tumour uptake at 1 and 24 h was achieved, when a static magnetic field was applied to the tumour for 1 hour. m-NCs, with multiple imaging probes (e.g. indocyanine green, superparamagnetic iron oxide nanoparticles and indium-111), were capable of triple-modal imaging (fluorescence/magnetic resonance/nuclear imaging) in vivo. Using triple-modal imaging is to overcome the intrinsic limitations of single modality imaging and provides complementary information on the spatial distribution of the nanocarrier within the tumour. The significant findings of this study could open up new research perspectives in using novel magnetically-responsive nanomaterials in magnetic-drug targeting combined with multi-modal imaging.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.712
Times cited: 54
DOI: 10.7150/thno.11918
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“Cation ordering within the perovskite block of a six-layer Ruddlesden-Popper oxide from layer-by-layer growth artificial interfaces in complex unit cells”. Yan L, Niu HJ, Duong GV, Suchomel MR, Bacsa J, Chalker PR, Hadermann J, Van Tendeloo G, Rosseinsky MJ, Chemical science 2, 261 (2011). http://doi.org/10.1039/c0sc00482k
Abstract: The (AO)(ABO3)n Ruddlesden-Popper structure is an archetypal complex oxide consisting of two distinct structural units, an (AO) rock salt layer separating an n-octahedra thick perovskite block. Conventional high-temperature oxide synthesis methods cannot access members with n > 3, but low-temperature layer-by-layer thin film methods allow the preparation of materials with thicker perovskite blocks, exploiting high surface mobility and lattice matching with the substrate. This paper describes the growth of an n = 6 member CaO[(CSMO)2(LCMO)2 (CSMO)2] in which the six unit cell perovskite block is sub-divided into two central La0.67Ca0.33MnO3 (LCMO) and two terminal Ca0.85Sm0.15MnO3 (CSMO) layers to allow stabilization of the rock salt layer and variation of the transition metal charge.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.668
Times cited: 16
DOI: 10.1039/c0sc00482k
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“Engineered spatial inversion symmetry breaking in an oxide heterostructure built from isosymmetric room-temperature magnetically ordered components”. Alaria J, Borisov P, Dyer MS, Manning TD, Lepadatu S, Cain MG, Mishina ED, Sherstyuk NE, Ilyin NA, Hadermann J, Lederman D, Claridge JB, Rosseinsky MJ;, Chemical science 5, 1599 (2014). http://doi.org/10.1039/c3sc53248h
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.668
Times cited: 24
DOI: 10.1039/c3sc53248h
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“Mixed-valent, heteroleptic homometallic diketonates as templates for the design of volatile heterometallic precursors”. Lieberman CM, Filatov AS, Wei Z, Rogachev AY, Abakumov AM, Dikarev EV, Chemical science 6, 2835 (2015). http://doi.org/10.1039/c4sc04002c
Abstract: A novel series of mixed-valent, heteroleptic transition metal diketonates that can be utilized as prospective single-source precursors for the low-temperature preparation of oxide materials are reported. The first mixed-valent iron beta-diketonates with different Fe-III/Fe-II ratios have been synthesized by applying the mixed-ligand approach. Based on nearly quantitative reaction yields and analysis of iron-oxygen bonds, these compounds were formulated as [Fe-III(acac)(3)][Fe-II(hfac)(2)] (1) and [Fe-II(hfac)(2)][Fe-III(acac)(3)][Fe-II(hfac)(2)] (2). In the above heteroleptic complexes, the Lewis acidic, coordinatively unsaturated Fe-II centers chelated by two hfac (hexafluoroacetylacetonate) ligands with electron-withdrawing substituents maintain bridging interactions with oxygen atoms of electron-donating acac (acetylacetonate) groups that chelate the neighboring Fe-III atoms. Switching the ligands on Fe-III and Fe-II atoms in starting reagents resulted in the instant ligand exchange between iron centers and in yet another polynuclear homometallic diketonate [Fe-II(hfac)(2)][Fe-III(acac)(2)(hfac)][Fe-II(hfac)(2)] (3) that adheres to the same bonding pattern as in complexes 1 and 2. The proposed synthetic methodology has been extended to design heterometallic diketonates with different M : M' ratios. Homometallic parent molecules have been used as templates to obtain heterometallic mixed-valent [Fe-III(acac)(3)][Mn-II(hfac)(2)] (4) and [Ni-II(hfac)(2)] – [Fe-III(acac)(3)][Ni-II(hfac)(2)] (5) complexes. The combination of two different diketonate ligands with electron-donating and electron-withdrawing substituents was found to be crucial for maintaining the above mixed-valent heterometallic assemblies. Theoretical investigation of two possible “isomers”, [Fe-III(acac)(3)][Mn-II(hfac)(2)] (4) and [Mn-III(acac)(3)][Fe-II(hfac)(2)] (40) provided an additional support for the metal site assignment giving a preference of 9.78 kcal mol(-1) for the molecule 4. Heterometallic complexes obtained in the course of this study have been found to act as effective single-source precursors for the synthesis of mixed-transition metal oxide materials MxM2-xO3 and MxMi-xO. The title highly volatile precursors can be used for the low-temperature preparation of both amorphous and crystalline heterometallic oxides in the form of thin films or nanosized particles that are known to operate as efficient catalysts in oxygen evolution reaction.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.668
Times cited: 13
DOI: 10.1039/c4sc04002c
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“_BiMnFe2O6, a polysynthetically twinned hcp MO structure”. Yang T, Abakumov AM, Hadermann J, Van Tendeloo G, Nowik I, Stephens PW, Hamberger J, Tsirlin AA, Ramanujachary KV, Lofland S, Croft M, Ignatov A, Sun J, Greenblatt M, Chemical science 1, 751 (2010). http://doi.org/10.1039/c0sc00348d
Abstract: The most efficient use of spatial volume and the lowest potential energies in the metal oxide structures are based on cubic close packing (ccp) or hexagonal close packing (hcp) of anions with cations occupying the interstices. A promising way to tune the composition of close packed oxides and design new compounds is related to fragmenting the parent structure into modules by periodically spaced planar interfaces, such as twin planes at the unit cell scale. The unique crystal chemistry properties of cations with a lone electron pair, such as Bi3+ or Pb2+, when located at interfaces, enables them to act as chemical scissors, to help relieve configurational strain. With this approach, we synthesized a new oxide, BiMnFe2O6, where fragments of the hypothetical hcp oxygen-based MO structure (the NiAs structure type), for the first time, serve as the building modules in a complex transition metal oxide. Mn3+ and Fe3+ ions are randomly distributed in two crystallographically independent sites (M1 and M2). The structure consists of quasi two-dimensional blocks of the 2H hexagonal close packed MO structure cut along the (114) crystal plane of the hcp lattice and stacked along the c axis. The blocks are related by a mirror operation that allows BiMnFe2O6 to be considered as a polysynthetically twinned 2H hcp MO structure. The transition to an AFM state with an incommensurate spin configuration at [similar] 212 K is established by 57Fe Mössbauer spectroscopy, magnetic susceptibility, specific heat and low temperature powder neutron diffraction.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.668
Times cited: 12
DOI: 10.1039/c0sc00348d
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“Gel-based morphological design of zirconium metal-organic frameworks”. Bueken B, Van Velthoven N, Willhammar T, Stassin T, Stassen I, Keen DA, Baron GV, Denayer JFM, Ameloot R, Bals S, De Vos D, Bennett TD, Chemical science 8, 3939 (2017). http://doi.org/10.1039/C6SC05602D
Abstract: The ability of metal-organic frameworks (MOFs) to gelate under specific synthetic conditions opens up new opportunities in the preparation and shaping of hierarchically porous MOF monoliths, which could be directly implemented for catalytic and adsorptive applications. In this work, we present the first examples of xero-or aerogel monoliths consisting solely of nanoparticles of several prototypical Zr4+-based MOFs: UiO-66-X (X – H, NH2, NO2, (OH)(2)), UiO-67, MOF-801, MOF-808 and NU-1000. High reactant and water concentrations during synthesis were observed to induce the formation of gels, which were converted to monolithic materials by drying in air or supercritical CO2. Electron microscopy, combined with N-2 physisorption experiments, was used to show that irregular nanoparticle packing leads to pure MOF monoliths with hierarchical pore systems, featuring both intraparticle micropores and interparticle mesopores. Finally, UiO-66 gels were shaped into monolithic spheres of 600 mm diameter using an oil-drop method, creating promising candidates for packed-bed catalytic or adsorptive applications, where hierarchical pore systems can greatly mitigate mass transfer limitations.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.668
Times cited: 168
DOI: 10.1039/C6SC05602D
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“Single-site metal-organic framework catalysts for the oxidative coupling of arenes via C-H/C-H activation”. Van Velthoven N, Waitschat S, Chavan SM, Liu P, Smolders S, Vercammen J, Bueken B, Bals S, Lillerud KP, Stock N, De Vos DE, Chemical science 10, 3616 (2019). http://doi.org/10.1039/C8SC05510F
Abstract: C-H activation reactions are generally associated with relatively low turnover numbers (TONs) and high catalyst concentrations due to a combination of low catalyst stability and activity, highlighting the need for recyclable heterogeneous catalysts with stable single-atom active sites. In this work, several palladium loaded metal-organic frameworks (MOFs) were tested as single-site catalysts for the oxidative coupling of arenes (e.g. o-xylene) via C-H/C-H activation. Isolation of the palladium active sites on the MOF supports reduced Pd(0) aggregate formation and thus catalyst deactivation, resulting in higher turnover numbers (TONs) compared to the homogeneous benchmark reaction. Notably, a threefold higher TON could be achieved for palladium loaded MOF-808 due to increased catalyst stability and the heterogeneous catalyst could efficiently be reused, resulting in a cumulative TON of 1218 after three runs. Additionally, the palladium single-atom active sites on MOF-808 were successfully identified by Fourier transform infrared (FTIR) and extended X-ray absorption fine structure (EXAFS) spectroscopy.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.668
Times cited: 68
DOI: 10.1039/C8SC05510F
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“Dynamic motion of Ru-polyoxometalate ions (POMs) on functionalized few-layer graphene”. Ke X, Turner S, Quintana M, Hadad C, Montellano-López A, Carraro M, Sartorel A, Bonchio M, Prato M, Bittencourt C, Van Tendeloo G;, Small 9, 3922 (2013). http://doi.org/10.1002/smll.201300378
Abstract: The interaction and stability of Ru4POM on few layer graphene via functional groups is investigated by time-dependent imaging using aberration-corrected transmission electron microscopy. The Ru4POM demonstrates dynamic motion on the graphene surface with its frequency and amplitude of rotation related to the nature of the functional group used. The stability of the Ru4POMgraphene hybrid corroborates its long-term robustness when applied to multielectronic catalytic processes.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 16
DOI: 10.1002/smll.201300378
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“Fluorescent nanodiamonds embedded in biocompatible translucent shells”. Rehor I, Slegerova J, Kucka J, Proks V, Petrakova V, Adam MP, Treussart F, Turner S, Bals S, Sacha P, Ledvina M, Wen AM, Steinmetz NF, Cigler P;, Small 10, 1106 (2014). http://doi.org/10.1002/smll.201302336
Abstract: High pressure high temperature (HPHT) nanodiamonds (NDs) represent extremely promising materials for construction of fluorescent nanoprobes and nanosensors. However, some properties of bare NDs limit their direct use in these applications: they precipitate in biological solutions, only a limited set of bio-orthogonal conjugation techniques is available and the accessible material is greatly polydisperse in shape. In this work, we encapsulate bright 30-nm fluorescent nanodiamonds (FNDs) in 1020-nm thick translucent (i.e., not altering FND fluorescence) silica shells, yielding monodisperse near-spherical particles of mean diameter 66 nm. High yield modification of the shells with PEG chains stabilizes the particles in ionic solutions, making them applicable in biological environments. We further modify the opposite ends of PEG chains with fluorescent dyes or vectoring peptide using click chemistry. High conversion of this bio-orthogonal coupling yielded circa 2000 dye or peptide molecules on a single FND. We demonstrate the superior properties of these particles by in vitro interaction with human prostate cancer cells: while bare nanodiamonds strongly aggregate in the buffer and adsorb onto the cell membrane, the shell encapsulated NDs do not adsorb nonspecifically and they penetrate inside the cells.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 79
DOI: 10.1002/smll.201302336
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“Nitrogen and luminescent nitrogen-vacancy defects in detonation nanodiamond”. Vlasov II, Shenderova O, Turner S, Lebedev OI, Basov AA, Sildos I, Rähn M, Shiryaev AA, Van Tendeloo G, Small 6, 687 (2010). http://doi.org/10.1002/smll.200901587
Abstract: An efficient method to investigate the microstructure and spatial distribution of nitrogen and nitrogen-vacancy (N-V) defects in detonation nanodiamond (DND) with primary particle sizes ranging from approximately 3 to 50 nm is presented. Detailed analysis reveals atomic nitrogen concentrations as high as 3 at% in 50% of diamond primary particles with sizes smaller than 6 nm. A non-uniform distribution of nitrogen within larger primary DND particles is also presented, indicating a preference for location within the defective central part or at twin boundaries. A photoluminescence (PL) spectrum with well-pronounced zero-phonon lines related to the N-V centers is demonstrated for the first time for electron-irradiated and annealed DND particles at continuous laser excitation. Combined Raman and PL analysis of DND crystallites dispersed on a Si substrate leads to the conclusion that the observed N-V luminescence originates from primary particles with sizes exceeding 30 nm. These findings demonstrate that by manipulation of the size/nitrogen content in DND there are prospects for mass production of nanodiamond photoemitters based on bright and stable luminescence from nitrogen-related defects.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 84
DOI: 10.1002/smll.200901587
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“Prussian blue analogues of reduced dimensionality”. Gengler RYN, Toma LM, Pardo E, Lloret F, Ke X, Van Tendeloo G, Gournis D, Rudolf P, Small 8, 2532 (2012). http://doi.org/10.1002/smll.201200517
Abstract: Mixed-valence polycyanides (Prussian Blue analogues) possess a rich palette of properties spanning from room-temperature ferromagnetism to zero thermal expansion, which can be tuned by chemical modifications or the application of external stimuli (temperature, pressure, light irradiation). While molecule-based materials can combine physical and chemical properties associated with molecular-scale building blocks, their successful integration into real devices depends primarily on higher-order properties such as crystal size, shape, morphology, and organization. Herein a study of a new reduced-dimensionality system based on Prussian Blue analogues (PBAs) is presented. The system is built up by means of a modified Langmuir-Blodgett technique, where the PBA is synthesized from precursors in a self-limited reaction on a clay mineral surface. The focus of this work is understanding the magnetic properties of the PBAs in different periodic, low-dimensional arrangements, and the influence of the “on surface” synthesis on the final properties and dimensionality of the system.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 17
DOI: 10.1002/smll.201200517
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“Stabilization and encapsulation of gold nanostars mediated by dithiols”. Wang Y, Belén Serrano A, Sentosun K, Bals S, Liz-Marzán LM, Small 11, 4314 (2015). http://doi.org/10.1002/smll.201500703
Abstract: Surface chemistry plays a pivotal role in regulating the morphology of nanoparticles, maintaining colloidal stability, and mediating the interaction with target analytes toward practical applications such as surface-enhanced Raman scattering (SERS)-based sensing and imaging. The use of a binary ligand mixture composed of 1,4-benzenedithiol (BDT) and hexadecyltrimethylammonium chloride (CTAC) to provide gold nanostars with long-term stability is reported. This is despite BDT being a bifunctional ligand, which usually leads to bridging and loss of colloidal stability. It is found however that neither BDT nor CTAC alone are able to provide sufficient colloidal and chemical stability. BDT-coated Au nanostars are additionally used as seeds to direct the encapsulation with a gold outer shell, leading to the formation of unusual nanostructures including semishell-coated gold nanostars, which are characterized by high-resolution electron microscopy and electron tomography. Finally, BDT is exploited as a probe to reveal the enhanced local electric fields in the different nanostructures, showing that the semishell configuration provides significantly high SERS signals as compared to other coreshell configurations obtained during seeded growth, including full shells.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 36
DOI: 10.1002/smll.201500703
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“Au2Sx/CdS nanorods by cation exchange : mechanistic insights into the competition between cation-exchange and metal ion reduction”. Kundu S, Kundu P, Van Tendeloo G, Ravishankar N, Small 10, 3895 (2014). http://doi.org/10.1002/smll.201400524
Abstract: Thumbnail image of graphical abstract It is well known that metals with higher electron affinity like Au tend to undergo reduction rather than cation-exchange. It is experimentally shown that under certain conditions cation-exchange is dominant over reduction. Thermodynamic calculation further consolidates the understanding and paves the way for better predictability of cation-exchange/reduction reactions for other systems.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 8
DOI: 10.1002/smll.201400524
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“Thermally induced structural and morphological changes of CdSe/CdS octapods”. Goris B, van Huis MA, Bals S, Zandbergen HW, Manna L, Van Tendeloo G, Small 8, 937 (2012). http://doi.org/10.1002/smll.201101897
Abstract: Branched nanostructures are of great interest because of their promising optical and electronic properties. For successful and reliable integration in applications such as photovoltaic devices, the thermal stability of the nanostructures is of major importance. Here the different domains (CdSe cores, CdS pods) of the heterogeneous octapods are shown to have different thermal stabilities, and heating is shown to induce specific shape changes. The octapods are heated from room temperature to 700 °C, and investigated using (analytical and tomographic) transmission electron microscopy (TEM). At low annealing temperatures, pure Cd segregates in droplets at the outside of the octapods, indicating non-stochiometric composition of the octapods. Furthermore, the tips of the pods lose their faceting and become rounded. Further heating to temperatures just below the sublimation temperature induces growth of the zinc blende core at the expense of the wurtzite pods. At higher temperatures, (500700 °C), sublimation of the octapods is observed in real time in the TEM. Three-dimensional tomographic reconstructions reveal that the four pods pointing into the vacuum have a lower thermal stability than the four pods that are in contact with the support.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 20
DOI: 10.1002/smll.201101897
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“Two-fold emission from the S-shell of PbSe/CdSe core/shell quantum dots”. Grodzińska D, Evers WH, Dorland R, van Rijssel J, van Huis MA, Meijerink A, de Mello Donegá, C, Vanmaekelbergh D, Small 7, 3493 (2011). http://doi.org/10.1002/smll.201101819
Abstract: The optical properties of PbSe/CdSe core/shell quantum dots with core sizes smaller than 4 nm in the 5300 K range are reported. The photoluminescence spectra show two peaks, which become increasingly separated in energy as the core diameter is reduced below 4 nm. It is shown that these peaks are due to intrinsic exciton transitions in each quantum dot, rather than emission from different quantum dot sub-ensembles. Most likely, the energy separation between the peaks is due to inter-valley coupling between the L-points of PbSe. The temperature dependence of the relative intensities of the peaks implies that the two emitting states are not in thermal equilibrium and that dark exciton states must play an important role.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 23
DOI: 10.1002/smll.201101819
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“Well shaped Mn3O4 nano-octahedra with anomalous magnetic behavior and enhanced photodecomposition properties”. Li Y, Tan H, Yang X-Y, Goris B, Verbeeck J, Bals S, Colson P, Cloots R, Van Tendeloo G, Su B-L, Small 7, 475 (2011). http://doi.org/10.1002/smll.201001403
Abstract: Very uniform and well shaped Mn3O4 nano-octahedra are synthesized using a simple hydrothermal method under the help of polyethylene glycol (PEG200) as a reductant and shape-directing agent. The nano-octahedra formation mechanism is monitored. The shape and crystal orientation of the nanoparticles is reconstructed by scanning electron microscopy and electron tomography, which reveals that the nano-octahedra only selectively expose {101} facets at the external surfaces. The magnetic testing demonstrates that the Mn3O4 nano-octahedra exhibit anomalous magnetic properties: the Mn3O4 nano-octahedra around 150 nm show a similar Curie temperature and blocking temperature to Mn3O4 nanoparticles with 10 nm size because of the vertical axis of [001] plane and the exposed {101} facets. With these Mn3O4 nano-octahedra as a catalyst, the photodecomposition of rhodamine B is evaluated and it is found that the photodecomposition activity of Mn3O4 nano-octahedra is much superior to that of commercial Mn3O4 powders. The anomalous magnetic properties and high superior photodecomposition activity of well shaped Mn3O4 nano-octahedra should be related to the special shape of the nanoparticles and the abundantly exposed {101} facets at the external surfaces. Therefore, the shape preference can largely broaden the application of the Mn3O4 nano-octahedra.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 131
DOI: 10.1002/smll.201001403
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“Encapsulation of Single Plasmonic Nanoparticles within ZIF-8 and SERS Analysis of the MOF Flexibility”. Zheng G, de Marchi S, Lopez-Puente V, Sentosun K, Polavarapu L, Perez-Juste I, Hill EH, Bals S, Liz-Marzan LM, Pastoriza-Santos I, Perez-Juste J, Small 12, 3935 (2016). http://doi.org/10.1002/smll.201600947
Abstract: Hybrid nanostructures composed of metal nanoparticles and metal-organic frameworks (MOFs) have recently received increasing attention toward various applications due to the combination of optical and catalytic properties of nanometals with the large internal surface area, tunable crystal porosity and unique chemical properties of MOFs. Encapsulation of metal nanoparticles of well-defined shapes into porous MOFs in a core-shell type configuration can thus lead to enhanced stability and selectivity in applications such as sensing or catalysis. In this study, the encapsulation of single noble metal nanoparticles with arbitrary shapes within zeolitic imidazolate-based metal organic frameworks (ZIF-8) is demonstrated. The synthetic strategy is based on the enhanced interaction between ZIF-8 nanocrystals and metal nanoparticle surfaces covered by quaternary ammonium surfactants. High resolution electron microscopy and tomography confirm a complete core-shell morphology. Such a well-defined morphology allowed us to study the transport of guest molecules through the ZIF-8 porous shell by means of surface-enhanced Raman scattering by the metal cores. The results demonstrate that even molecules larger than the ZIF-8 aperture and pore size may be able to diffuse through the framework and reach the metal core.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 140
DOI: 10.1002/smll.201600947
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“Unraveling Structural Information of Turkevich Synthesized Plasmonic Gold-Silver Bimetallic Nanoparticles”. Blommaerts N, Vanrompay H, Nuti S, Lenaerts S, Bals S, Verbruggen SW, Small 15, 1902791 (2019). http://doi.org/10.1002/smll.201902791
Abstract: For the synthesis of gold-silver bimetallic nanoparticles, the Turkevich method has been the state-of-the-art method for several decades. It has been presumed that this procedure results in a homogeneous alloy, although this has been debatable for many years. In this work, it is shown that neither a full alloy, nor a perfect core-shell particle is formed but rather a core-shell-like particle with altering metal composition along the radial direction. In-depth wet-chemical experiments are performed in combination with advanced transmission electron microscopy, including EDX tomography, and Finite Element Method modeling to support the observations. From the electron tomography results, the core-shell structure could be clearly visualized and the spatial distribution of gold and silver atoms could be quantified. Theoretical simulations are performed to demonstrate that even though UV-Vis spectra show only one plasmon band, this still originates from core-shell type structures. The simulations also indicate that the core-shell morphology does not so much affect the location of the plasmon band, but mainly results in significant band broadening. Wet-chemistry experiments provide the evidence that the synthesis pathway starts with gold enriched alloy cores, and later on in the synthesis mainly silver is incorporated to end up with a silver enriched alloy shell.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Sustainable Energy, Air and Water Technology (DuEL)
Impact Factor: 8.643
Times cited: 26
DOI: 10.1002/smll.201902791
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“Strain Anisotropy and Magnetic Domains in Embedded Nanomagnets”. Nord M, Semisalova A, Kákay A, Hlawacek G, MacLaren I, Liersch V, Volkov OM, Makarov D, Paterson GW, Potzger K, Lindner J, Fassbender J, McGrouther D, Bali R, Small , 1904738 (2019). http://doi.org/10.1002/smll.201904738
Abstract: Nanoscale modifications of strain and magnetic anisotropy can open pathways to engineering magnetic domains for device applications. A periodic magnetic domain structure can be stabilized in sub‐200 nm wide linear as well as curved magnets, embedded within a flat non‐ferromagnetic thin film. The nanomagnets are produced within a non‐ferromagnetic B2‐ordered Fe60Al40 thin film, where local irradiation by a focused ion beam causes the formation of disordered and strongly ferromagnetic regions of A2 Fe60Al40. An anisotropic lattice relaxation is observed, such that the in‐plane lattice parameter is larger when measured parallel to the magnet short‐axis as compared to its length. This in‐plane structural anisotropy manifests a magnetic anisotropy contribution, generating an easy‐axis parallel to the short axis. The competing effect of the strain and shape anisotropies stabilizes a periodic domain pattern in linear as well as spiral nanomagnets, providing a versatile and geometrically controllable path to engineering the strain and thereby the magnetic anisotropy at the nanoscale.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 2
DOI: 10.1002/smll.201904738
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“The Influence of Size, Shape, and Twin Boundaries on Heat‐Induced Alloying in Individual Au@Ag Core–Shell Nanoparticles”. Mychinko M, Skorikov A, Albrecht W, Sánchez‐Iglesias A, Zhuo X, Kumar V, Liz‐Marzán LM, Bals S, Small , 2102348 (2021). http://doi.org/10.1002/smll.202102348
Abstract: Environmental conditions during real-world application of bimetallic core–shell nanoparticles (NPs) often include the use of elevated temperatures, which are known to cause elemental redistribution, in turn significantly altering the properties of these nanomaterials. Therefore, a thorough understanding of such processes is of great importance. The recently developed combination of fast electron tomography with in situ heating holders is a powerful approach to investigate heat-induced processes at the single NP level, with high spatial resolution in 3D. In combination with 3D finite-difference diffusion simulations, this method can be used to disclose the influence of various NP parameters on the diffusion dynamics in Au@Ag core–shell systems. A detailed study of the influence of heating on atomic diffusion and alloying for Au@Ag NPs with varying core morphology and crystallographic details is carried out. Whereas the core shape and aspect ratio of the NPs play a minor role, twin boundaries are found to have a strong influence on the elemental diffusion.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 8
DOI: 10.1002/smll.202102348
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“Interface Pattern Engineering in Core‐Shell Upconverting Nanocrystals: Shedding Light on Critical Parameters and Consequences for the Photoluminescence Properties”. Hudry D, De Backer A, Popescu R, Busko D, Howard IA, Bals S, Zhang Y, Pedrazo‐Tardajos A, Van Aert S, Gerthsen D, Altantzis T, Richards BS, Small , 2104441 (2021). http://doi.org/10.1002/smll.202104441
Abstract: Advances in controlling energy migration pathways in core-shell lanthanide (Ln)-based hetero-nanocrystals (HNCs) have relied heavily on assumptions about how optically active centers are distributed within individual HNCs. In this article, it is demonstrated that different types of interface patterns can be formed depending on shell growth conditions. Such interface patterns are not only identified but also characterized with spatial resolution ranging from the nanometer- to the atomic-scale. In the most favorable cases, atomic-scale resolved maps of individual particles are obtained. It is also demonstrated that, for the same type of core-shell architecture, the interface pattern can be engineered with thicknesses of just 1 nm up to several tens of nanometers. Total alloying between the core and shell domains is also possible when using ultra-small particles as seeds. Finally, with different types of interface patterns (same architecture and chemical composition of the core and shell domains) it is possible to modify the output color (yellow, red, and green-yellow) or change (improvement or degradation) the absolute upconversion quantum yield. The results presented in this article introduce an important paradigm shift and pave the way toward the emergence of a new generation of core-shell Ln-based HNCs with better control over their atomic-scale organization.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 8.643
Times cited: 17
DOI: 10.1002/smll.202104441
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“Measuring Dynamic Structural Changes of Nanoparticles at the Atomic Scale Using Scanning Transmission Electron Microscopy”. De wael A, De Backer A, Jones L, Varambhia A, Nellist PD, Van Aert S, Physical Review Letters 124, 106105 (2020). http://doi.org/10.1103/PhysRevLett.124.106105
Abstract: We propose a new method to measure atomic scale dynamics of nanoparticles from experimental high-resolution annular dark field scanning transmission electron microscopy images. By using the so-called hidden Markov model, which explicitly models the possibility of structural changes, the number of atoms in each atomic column can be quantified over time. This newly proposed method outperforms the current atom-counting procedure and enables the determination of the probabilities and cross sections for surface diffusion. This method is therefore of great importance for revealing and quantifying the atomic structure when it evolves over time via adatom dynamics, surface diffusion, beam effects, or during in situ experiments.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.6
DOI: 10.1103/PhysRevLett.124.106105
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“Unraveling the Role of Lattice Substitutions on the Stabilization of the Intrinsically Unstable Pb2Sb2O7Pyrochlore: Explaining the Lightfastness of Lead Pyroantimonate Artists&rsquo, Pigments”. Marchetti A, Saniz R, Krishnan D, Rabbachin L, Nuyts G, De Meyer S, Verbeeck J, Janssens K, Pelosi C, Lamoen D, Partoens B, De Wael K, Chemistry Of Materials 32, 2863 (2020). http://doi.org/10.1021/acs.chemmater.9b04821
Abstract: The pyroantimonate pigments Naples yellow and lead tin antimonate yellow are recognized as some of the most stable synthetic yellow pigments in the history of art. However, this exceptional lightfastness is in contrast with experimental evidence suggesting that this class of mixed oxides is of semiconducting nature. In this study the electronic structure and light-induced behavior of the lead pyroantimonate pigments were determined by means of a combined multifaceted analytical and computational approach (photoelectrochemical measurements, UV-vis diffuse reflectance spectroscopy, STEM-EDS, STEM-HAADF, and density functional theory calculations). The results demonstrate both the semiconducting nature and the lightfastness of these pigments. Poor optical absorption and minority carrier mobility are the main properties responsible for the observed stability. In addition, novel fundamental insights into the role played by Na atoms in the stabilization of the otherwise intrinsically unstable Pb2Sb2O7 pyrochlore were obtained.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 8.6
Times cited: 8
DOI: 10.1021/acs.chemmater.9b04821
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“Secondary-Phase-Assisted Grain Boundary Migration in CuInSe2”. Li C, Sanli ES, Barragan-Yani D, Stange H, Heinemann M-D, Greiner D, Sigle W, Mainz R, Albe K, Abou-Ras D, van Aken P A, Physical Review Letters 124, 095702 (2020). http://doi.org/10.1103/PhysRevLett.124.095702
Abstract: Significant structural evolution occurs during the deposition of CuInSe2 solar materials when the Cu content increases. We use in situ heating in a scanning transmission electron microscope to directly observe how grain boundaries migrate during heating, causing nondefected grains to consume highly defected grains. Cu substitutes for In in the near grain boundary regions, turning them into a Cu-Se phase topotactic with the CuInSe2 grain interiors. Together with density functional theory and molecular dynamics calculations, we reveal how this Cu-Se phase makes the grain boundaries highly mobile.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.6
DOI: 10.1103/PhysRevLett.124.095702
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“Alloy CsCdxPb1–xBr3Perovskite Nanocrystals: The Role of Surface Passivation in Preserving Composition and Blue Emission”. Imran M, Ramade J, Di Stasio F, De Franco M, Buha J, Van Aert S, Goldoni L, Lauciello S, Prato M, Infante I, Bals S, Manna L, Chemistry Of Materials 32, acs.chemmater.0c03825 (2020). http://doi.org/10.1021/acs.chemmater.0c03825
Abstract: Various strategies have been proposed to engineer the band gap of metal halide perovskite nanocrystals (NCs) while preserving their structure and composition and thus ensuring spectral stability of the emission color. An aspect that has only been marginally investigated is how the type of surface passivation influences the structural/color stability of AMX3 perovskite NCs composed of two different M2+ cations. Here, we report the synthesis of blue-emitting Cs-oleate capped CsCdxPb1–xBr3 NCs, which exhibit a cubic perovskite phase containing Cd-rich domains of Ruddlesden–Popper phases (RP phases). The RP domains spontaneously transform into pure orthorhombic perovskite ones upon NC aging, and the emission color of the NCs shifts from blue to green over days. On the other hand, postsynthesis ligand exchange with various Cs-carboxylate or ammonium bromide salts, right after NC synthesis, provides monocrystalline NCs with cubic phase, highlighting the metastability of RP domains. When NCs are treated with Cs-carboxylates (including Cs-oleate), most of the Cd2+ ions are expelled from NCs upon aging, and the NCs phase evolves from cubic to orthorhombic and their emission color changes from blue to green. Instead, when NCs are coated with ammonium bromides, the loss of Cd2+ ions is suppressed and the NCs tend to retain their blue emission (both in colloidal dispersions and in electroluminescent devices), as well as their cubic phase, over time. The improved compositional and structural stability in the latter cases is ascribed to the saturation of surface vacancies, which may act as channels for the expulsion of Cd2+ ions from NCs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.6
Times cited: 44
DOI: 10.1021/acs.chemmater.0c03825
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“From 2D to 3D : bridging self-assembled monolayers to a substrate-induced polymorph in a molecular semiconductor”. Hao Y, Velpula G, Kaltenegger M, Bodlos WR, Vibert F, Mali KS, De Feyter S, Resel R, Geerts YH, Van Aert S, Beljonne D, Lazzaroni R, Chemistry of materials 34, 2238 (2022). http://doi.org/10.1021/ACS.CHEMMATER.1C04038
Abstract: In this study, a new bottom-up approach is proposed to predict the crystal structure of the substrate-induced polymorph (SIP) of an archetypal molecular semiconductor. In spite of intense efforts, the formation mechanism of SIPs is still not fully understood, and predicting their crystal structure is a very delicate task. Here, we selected lead phthalocyanine (PbPc) as a prototypical molecular material because it is a highly symmetrical yet nonplanar molecule and we demonstrate that the growth and crystal structure of the PbPc SIPs can be templated by the corresponding physisorbed self-assembled molecular networks (SAMNs). Starting from SAMNs of PbPc formed at the solution/graphite interface, the structural and energetic aspects of the assembly were studied by a combination of in situ scanning tunneling microscopy and multiscale computational chemistry approach. Then, the growth of a PbPc SIP on top of the physisorbed monolayer was modeled without prior experimental knowledge, from which the crystal structure of the SIP was predicted. The theoretical prediction of the SIP was verified by determining the crystal structure of PbPc thin films using X-ray diffraction techniques, revealing the formation of a new polymorph of PbPc on the graphite substrate. This study clearly illustrates the correlation between the SAMNs and SIPs, which are traditionally considered as two separate but conceptually connected research areas. This approach is applicable to molecular materials in general to predict the crystal structure of their SIPs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.6
DOI: 10.1021/ACS.CHEMMATER.1C04038
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“Study of the Mechanism and Increasing Crystallinity in the Self-Templated Growth of Ultrathin PbS Nanosheets”. van der Sluijs MM, Salzmann BBV, Arenas Esteban D, Li C, Jannis D, Brafine LC, Laning TD, Reinders JWC, Hijmans NSA, Moes JR, Verbeeck J, Bals S, Vanmaekelbergh D, Chemistry of materials (2023). http://doi.org/10.1021/acs.chemmater.3c00300
Abstract: Colloidal 2D semiconductor nanocrystals, the analogue of solid-state quantum wells, have attracted strong interest in material science and physics. Molar quantities of suspended quantum objects with spectrally pure absorption and emission can be synthesized. For the visible region, CdSe nanoplatelets with atomically precise thickness and tailorable emission have been (almost) perfected. For the near-infrared region, PbS nanosheets (NSs) hold strong promise, but the photoluminescence quantum yield is low and many questions on the crystallinity, atomic structure, intriguing rectangular shape, and formation mechanism remain to be answered. Here, we report on a detailed investigation of the PbS NSs prepared with a lead thiocyanate single source precursor. Atomically resolved HAADF-STEM imaging reveals the presence of defects and small cubic domains in the deformed orthorhombic PbS crystal lattice. Moreover, variations in thickness are observed in the NSs, but only in steps of 2 PbS monolayers. To study the reaction mechanism, a synthesis at a lower temperature allowed for the study of reaction intermediates. Specifically, we studied the evolution of pseudo-crystalline templates towards mature, crystalline PbS NSs. We propose a self-induced templating mechanism based on an oleylamine-lead-thiocyanate (OLAM-Pb-SCN) complex with two Pb-SCN units as a building block; the interactions between the long-chain ligands regulate the crystal structure and possibly the lateral dimensions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.6
Times cited: 2
DOI: 10.1021/acs.chemmater.3c00300
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“Spontaneous Chirality Evolved at the Au–Ag Interface in Plasmonic Nanorods”. Sa J, Hu N, Heyvaert W, Van Gordon K, Li H, Wang L, Bals S, Liz-Marzán LM, Ni W, Chemistry of materials (2023). http://doi.org/10.1021/acs.chemmater.3c01044
Abstract: Chiral ligands are considered a required ingredient during the synthesis of dissymmetric plasmonic metal nanocrystals. The mechanism behind the generation of chiral structures involves the formation of high Miller index chiral facets, induced by the adsorption of such chiral ligands. We found however that, chirality can also evolve spontaneously, without the involvement of any chiral ligands, during the co-deposition of Au and Ag on Au nanorods. When using a specific Au/Ag ratio, phase segregation of the two metals leads to an interface within the obtained AuAg shell, which can be exposed by removing the Ag component via oxidative etching. Although a close-to-racemic mixture of chiral Au nanorods with right and left handedness is found in solution, electron tomography analysis evidences left- and righthanded helicities, both at the Au-Ag interface and at the exposed surface of Au NRs after Ag etching. The helicity profile of the NRs indicates dominating inclination angles in a range from 30° to 60°. Single-particle optical characterization also reveals random handedness in the plasmonic response of individual nanorods. We hypothesize that, the origin of chirality is related with symmetry breaking during the co-deposition of Au and Ag, through an initial perturbation in a small region on the Au-Ag interface that eventually leads to chiral segregation throughout the nanocrystal.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.6
DOI: 10.1021/acs.chemmater.3c01044
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“3D characterization of the structural transformation undergone by Cu@Ag core-shell nanoparticles following CO₂, reduction reaction”. Arenas Esteban D, Pacquets L, Choukroun D, Hoekx S, Kadu AA, Schalck J, Daems N, Breugelmans T, Bals S, Chemistry of materials 35, 6682 (2023). http://doi.org/10.1021/ACS.CHEMMATER.3C00649
Abstract: The increasing use of metallic nanoparticles (NPs) is significantly advancing the field of electrocatalysis. In particular, Cu/Ag bimetallic interfaces are widely used to enhance the electrochemical CO2 reduction reaction (eCO(2)RR) toward CO and, more recently, C-2 products. However, drastic changes in the product distribution and performance when Cu@Ag core-shell configurations are used can often be observed under electrochemical reaction conditions, especially during the first few minutes of the reaction. Possible structural changes that generate these observations remain underexplored; therefore, the structure-property relationship is hardly understood. In this study, we use electron tomography to investigate the structural transformation mechanism of Cu@Ag core-shells NPs during the critical first minutes of the eCO(2)RR. In this manner, we found that the crystallinity of the Cu seed determines whether the formation of a complete and homogeneous Ag shell is possible. Moreover, by tracking the particles' transformations, we conclude that modifications of the Cu-Ag interface and Cu2O enrichment at the surface of the NPs are key factors contributing to the product generation changes. These insights provide a better understanding of how bimetallic core-shell NPs transform under electrochemical conditions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 8.6
Times cited: 1
DOI: 10.1021/ACS.CHEMMATER.3C00649
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