“Real-time tilt undersampling optimization during electron tomography of beam sensitive samples using golden ratio scanning and RECAST3D”. Craig TM, Kadu AA, Batenburg KJ, Bals S, Nanoscale 15, 5391 (2023). http://doi.org/10.1039/D2NR07198C
Abstract: Electron tomography is a widely used technique for 3D structural analysis of nanomaterials, but it can cause damage to samples due to high electron doses and long exposure times. To minimize such damage, researchers often reduce beam exposure by acquiring fewer projections through tilt undersampling. However, this approach can also introduce reconstruction artifacts due to insufficient sampling. Therefore, it is important to determine the optimal number of projections that minimizes both beam exposure and undersampling artifacts for accurate reconstructions of beam-sensitive samples. Current methods for determining this optimal number of projections involve acquiring and post-processing multiple reconstructions with different numbers of projections, which can be time-consuming and requires multiple samples due to sample damage. To improve this process, we propose a protocol that combines golden ratio scanning and quasi-3D reconstruction to estimate the optimal number of projections in real-time during a single acquisition. This protocol was validated using simulated and realistic nanoparticles, and was successfully applied to reconstruct two beam-sensitive metal–organic framework complexes.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6.7
Times cited: 1
DOI: 10.1039/D2NR07198C
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“Collective Plasmonic Properties in Few-Layer Gold Nanorod Supercrystals”. Hamon C, Novikov SM, Scarabelli L, Solís DM, Altantzis T, Bals S, Taboada JM, Obelleiro F, Liz-Marzán LM, ACS Photonics 2, 1482 (2015). http://doi.org/10.1021/acsphotonics.5b00369
Abstract: Gold nanorod supercrystals have been widely employed for the detection of relevant bioanalytes with detection limits ranging from nano- to picomolar levels,
confirming the promising nature of these structures for biosensing. Even though a relationship between the height of the supercrystal (i.e., the number of stacked nanorod layers)and the enhancement factor has been proposed, no systematic
study has been reported. In order to tackle this problem, we prepared gold nanorod supercrystals with varying numbers of stacked layers and analyzed them extensively by atomic force microscopy, electron microscopy and surface enhanced Raman scattering. The experimental results were compared to numerical
simulations performed on real-size supercrystals composed of thousands of nanorod building blocks. Analysis of the hot spot distribution in the simulated supercrystals showed the presence of standing waves that were distributed at different depths, depending on the number of layers in each supercrystal. On the basis of these theoretical results, we interpreted the experimental
data in terms of analyte penetration into the topmost layer only, which indicates that diffusion to the interior of the supercrystals would be crucial if the complete field enhancement produced by the stacked nanorods is to be exploited. We propose that our conclusions will be of high relevance in the design of next generation plasmonic devices.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6.756
Times cited: 70
DOI: 10.1021/acsphotonics.5b00369
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“Exciton Fine Structure and Lattice Dynamics in InP/ZnSe Core/Shell Quantum Dots”. Brodu A, Ballottin MV, Buhot J, van Harten EJ, Dupont D, La Porta A, Prins PT, Tessier MD, Versteegh MAM, Zwiller V, Bals S, Hens Z, Rabouw FT, Christianen PCM, de Donega CM, Vanmaekelbergh D, ACS Photonics 5, 3353 (2018). http://doi.org/10.1021/ACSPHOTONICS.8B00615
Abstract: Nanocrystalline InP quantum dots (QDs) hold promise for heavy-metal-free optoelectronic applications due to their bright and size tunable emission in the visible range. Photochemical stability and high photoluminescence (PL) quantum yield are obtained by a diversity of epitaxial shells around the InP core. To understand and optimize the emission line shapes, the exciton fine structure of InP core/shell QD systems needs be investigated. Here, we study the exciton fine structure of InP/ZnSe core/shell QDs with core diameters ranging from 2.9 to 3.6 nm (PL peak from 2.3 to 1.95 eV at 4 K). PL decay measurements as a function of temperature in the 10 mK to 300 K range show that the lowest exciton fine structure state is a dark state, from which radiative recombination is assisted by coupling to confined acoustic phonons with energies ranging from 4 to 7 meV, depending on the core diameter. Circularly polarized fluorescence line-narrowing (FLN) spectroscopy at 4 K under high magnetic fields (up to 30 T) demonstrates that radiative recombination from the dark F = +/- 2 state involves acoustic and optical phonons, from both the InP core and the ZnSe shell. Our data indicate that the highest intensity FLN peak is an acoustic phonon replica rather than a zero-phonon line, implying that the energy separation observed between the F = +/- 1 state and the highest intensity peak in the FLN spectra (6 to 16 meV, depending on the InP core size) is larger than the splitting between the dark and bright fine structure exciton states.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6.756
Times cited: 40
DOI: 10.1021/ACSPHOTONICS.8B00615
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“Ferroelectric gating of narrow band-gap nanocrystal arrays with enhanced light-matter coupling”. Greboval C, Chu A, Vale Magalhaes D, Ramade J, Qu J, Rastogi P, Khalili A, Chee S-S, Aubin H, Vincent G, Bals S, Delerue C, Lhuillier E, Acs Photonics 8, 259 (2021). http://doi.org/10.1021/ACSPHOTONICS.0C01464
Abstract: As narrow band gap nanocrystals become a considerable building block for the design of infrared sensors, device design needs to match their actual operating conditions. While in the near and shortwave infrared, room-temperature operation has been demonstrated, longer wavelengths still require low-temperature operations and thus specific design. Here, we discuss how field-effect transistors (FETs) can be compatible with low-temperature detection. To reach this goal, two key developments are proposed. First, we report the gating of nanocrystal films from SrTiO3 which leads to high gate capacitance with leakage and breakdown free operation in the 4-100 K range. Second, we demonstrate that this FET is compatible with a plasmonic resonator whose role is to achieve strong light absorption from a thin film used as the channel of the FET. Combining three resonances, broadband absorption from 1.5 to 3 mu m reaching 30% is demonstrated. Finally, combining gate and enhanced light-matter coupling, we show that detectivity can be as high as 10(12) Jones for a device presenting a 3 mu m cutoff wavelength and 30 K operation.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6.756
Times cited: 21
DOI: 10.1021/ACSPHOTONICS.0C01464
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“Third-Order Nonlinear Optical Properties and Saturation of Two-Photon Absorption in Lead-Free Double Perovskite Nanocrystals under Femtosecond Excitation”. Mushtaq A, Pradhan B, Kushavah D, Zhang Y, Wolf M, Schrenker N, Fron E, Bals S, Hofkens J, Debroye E, Pal SK, Acs Photonics 8, 3365 (2021). http://doi.org/10.1021/acsphotonics.1c01351
Abstract: Lead halide perovskites have been widely explored
in the field of photovoltaics, light-emitting diodes, and lasers due to
their outstanding linear and nonlinear optical (NLO) properties.
But, the presence of lead toxicity and low chemical stability remain
serious concerns. Lead-free double perovskite with excellent
optical properties and chemical stability could be an alternative.
However, proper examination of the NLO properties of such a
material is crucial to identify their utility for future nonlinear device
applications. Herein, we have made use of femtosecond (fs) Z-scan
technique to explore the NLO properties of Cs2AgIn0.9Bi0.1Cl6
nanocrystals (NCs). Our measurements suggest that under
nonresonant fs excitation, perovskite NCs exhibit strong twophoton
absorption (TPA). The observed saturation of TPA at high
light intensities has been explained by a customized model. Furthermore, we have demonstrated a change in the nonlinear refractive
index of the NCs under varying input intensities. The strong TPA absorption of lead-free double perovskite NCs could be used for
Kerr nonlinearity-based nonlinear applications such as optical shutters for picosecond lasers.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6.756
Times cited: 25
DOI: 10.1021/acsphotonics.1c01351
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“In Situ Plasma Studies Using a Direct Current Microplasma in a Scanning Electron Microscope”. Grünewald L, Chezganov D, De Meyer R, Orekhov A, Van Aert S, Bogaerts A, Bals S, Verbeeck J, Advanced Materials Technologies (2024). http://doi.org/10.1002/admt.202301632
Abstract: Microplasmas can be used for a wide range of technological applications and to improve the understanding of fundamental physics. Scanning electron microscopy, on the other hand, provides insights into the sample morphology and chemistry of materials from the mm‐ down to the nm‐scale. Combining both would provide direct insight into plasma‐sample interactions in real‐time and at high spatial resolution. Up till now, very few attempts in this direction have been made, and significant challenges remain. This work presents a stable direct current glow discharge microplasma setup built inside a scanning electron microscope. The experimental setup is capable of real‐time in situ imaging of the sample evolution during plasma operation and it demonstrates localized sputtering and sample oxidation. Further, the experimental parameters such as varying gas mixtures, electrode polarity, and field strength are explored and experimental<italic>V</italic>–<italic>I</italic>curves under various conditions are provided. These results demonstrate the capabilities of this setup in potential investigations of plasma physics, plasma‐surface interactions, and materials science and its practical applications. The presented setup shows the potential to have several technological applications, for example, to locally modify the sample surface (e.g., local oxidation and ion implantation for nanotechnology applications) on the µm‐scale.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 6.8
DOI: 10.1002/admt.202301632
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“Molecular shape-selectivity of MFI zeolite nanosheets in n-decane isomerization and hydrocracking”. Verheyen E, Jo C, Kurttepeli M, Vanbutsele G, Gobechiya E, Korányi TI, Bals S, Van Tendeloo G, Ryoo R, Kirschhock CEA, Martens JA;, Journal of catalysis 300, 70 (2013). http://doi.org/10.1016/j.jcat.2012.12.017
Abstract: MFI zeolite nanosheets with thickness of 2 and 8 nm were synthesized, transformed into bifunctional catalysts by loading with platinum and tested in n-decane isomerization and hydrocracking. Detailed analysis of skeletal isomers and hydrocracked products revealed that the MFI nanosheets display transition-state shape-selectivity similar to bulk MFI zeolite crystals. The suppressed formation of bulky skeletal isomers and C5 cracking products are observed both in the nanosheets and the bulk crystals grown in three dimensions. This is typical for restricted transition-state shape-selectivity, characteristic for the MFI type pores. It is a first clear example of transition-state shape-selectivity inside a zeolitic nanosheet. Owing to the short diffusion path across the sheets, expression of diffusion-based discrimination of reaction products in the MFI nanosheets was limited. The 2-methylnonane formation among monobranched C10 isomers and 2,7-dimethyloctane among dibranched C10 isomers, which in MFI zeolite are favored by product diffusion, was much less favored on the nanosheets compared to the reference bulk ZSM-5 material.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.844
Times cited: 121
DOI: 10.1016/j.jcat.2012.12.017
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“Quantitative determination of residual silver distribution in nanoporous gold and its influence on structure and catalytic performance”. Mahr C, Kundu P, Lackmann A, Zanaga D, Thiel K, Schowalter M, Schwan M, Bals S, Wittstock A, Rosenauer A, Journal of catalysis 352, 52 (2017). http://doi.org/10.1016/j.jcat.2017.05.002
Abstract: Large efforts have been made trying to understand the origin of the high catalytic activity of dealloyed nanoporous gold as a green catalyst for the selective promotion of chemical reactions at low temperatures. Residual silver, left in the sample after dealloying of a gold-silver alloy, has been shown to have a strong influence on the activity of the catalyst. But the question of how the silver is distributed within the porous structure has not finally been answered yet. We show by quantitative energy dispersive X-ray tomography measurements that silver forms clusters that are distributed irregularly, both on the surface and inside the ligaments building up the porous structure. Furthermore, we find that the role of the residual silver is ambiguous. Whereas CO oxidation is supported by more residual silver, methanol oxidation to methyl formate is hindered. Structural characterisation reveals larger ligaments and pores for decreasing residual silver concentration.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.844
Times cited: 42
DOI: 10.1016/j.jcat.2017.05.002
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“Highly active, selective, and stable Pd single-atom catalyst anchored on N-doped hollow carbon sphere for electrochemical H₂O₂, synthesis under acidic conditions”. Xi J, Yang S, Silvioli L, Cao S, Liu P, Chen Q, Zhao Y, Sun H, Hansen JN, Haraldsted J-PB, Kibsgaard J, Rossmeisl J, Bals S, Wang S, Chorkendorff I, Journal Of Catalysis 393, 313 (2021). http://doi.org/10.1016/J.JCAT.2020.11.020
Abstract: Single-atom catalysts (SACs) have recently attracted broad scientific interests due to their unique structural feature, the single-atom dispersion. Optimized electronic structure as well as high stability are required for single-atom catalysts to enable efficient electrochemical production of H2O2. Herein, we report a facile synthesis method that stabilizes atomic Pd species on the reduced graphene oxide/Ndoped carbon hollow carbon nanospheres (Pd1/N-C). Pd1/N-C exhibited remarkable electrochemical H2O2 production rate with high faradaic efficiency, reaching 80%. The single-atom structure and its high H2O2 production rate were maintained even after 10,000 cycle stability test. The existence of single-atom Pd as well as its coordination with N species is responsible for its high activity, selectivity, and stability. The N coordination number and substrate doping around Pd atoms are found to be critical for an optimized adsorption energy of intermediate *OOH, resulting in efficient electrochemical H2O2 production. (C) 2020 Elsevier Inc. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.844
Times cited: 40
DOI: 10.1016/J.JCAT.2020.11.020
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“Controlled Alloying of Au@Ag Core–Shell Nanorods Induced by Femtosecond Laser Irradiation”. González‐Rubio G, Díaz‐Núñez P, Albrecht W, Manzaneda‐González V, Bañares L, Rivera A, Liz‐Marzán LM, Peña‐Rodríguez O, Bals S, Guerrero‐Martínez A, Advanced Optical Materials , 2002134 (2021). http://doi.org/10.1002/adom.202002134
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.875
Times cited: 10
DOI: 10.1002/adom.202002134
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“High resolution electron tomography”. Bals S, Van Aert S, Van Tendeloo G, Current opinion in solid state and materials science 17, 107 (2013). http://doi.org/10.1016/j.cossms.2013.03.001
Abstract: Reaching atomic resolution in 3D has been the ultimate goal in the field of electron tomography for many years. Significant progress, both on the theoretical as well as the experimental side has recently resulted in several exciting examples demonstrating the ability to visualise atoms in 3D. In this paper, we will review the different steps that have pushed the resolution in 3D to the atomic level. A broad range of methodologies and practical examples together with their impact on materials science will be discussed. Finally, we will provide an outlook and will describe future challenges in the field of high resolution electron tomography.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.938
Times cited: 24
DOI: 10.1016/j.cossms.2013.03.001
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“The uptake and elimination of ZnO and CuO nanoparticles in Daphnia magna under chronic exposure scenarios”. Adam N, Leroux F, Knapen D, Bals S, Blust R, Water research 68, 249 (2015). http://doi.org/10.1016/j.watres.2014.10.001
Abstract: In this study, the uptake and elimination of ZnO and CuO nanoparticles in Daphnia magna was tested. Daphnids were exposed during 10 days to sublethal concentrations of ZnO and CuO nanoparticles and corresponding metal salts (ZnCl2 and CuCl2.2H2O), after which they were transferred to unexposed medium for another 10 days. At different times during the exposure and none-exposure, the total and internal zinc or copper concentration of the daphnids was determined and the nanoparticles were localized in the organism using electron microscopy. The exposure concentrations were characterized by measuring the dissolved, nanoparticle and aggregated fraction in the medium. The results showed that the ZnO nanoparticles quickly dissolved after addition to the medium. Contrarily, only a small fraction (corresponding to the dissolved metal salt) of the CuO nanoparticles dissolved, while most of these nanoparticles formed large aggregates. Despite an initial increase in zinc and copper concentration during the first 48 hour to 5 day exposure, the body concentration reached a plateau level that was comparable for the ZnO nanoparticles and ZnCl2, but much higher for the CuO nanoparticles (with visible aggregates accumulating in the gut) than CuCl2.2H2O. During the remaining exposure and subsequent none-exposure phase, the zinc and copper concentration decreased fast to concentrations comparable with the unexposed daphnids. The results indicate that D. magna can regulate its internal zinc and copper concentration after exposure to ZnO and CuO nanoparticles, similar as after exposure to metal salts. The combined dissolution, accumulation and toxicity results confirm that the toxicity of ZnO and CuO nanoparticles is caused by the dissolved fraction. Keywords nano; zinc; copper; dissolution; aggregation; electron microscopy
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Veterinary physiology and biochemistry
Impact Factor: 6.942
Times cited: 51
DOI: 10.1016/j.watres.2014.10.001
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“Hybrid core–shell nanoparticles for cell-specific magnetic separation and photothermal heating”. de la Encarnación C, Jungwirth F, Vila-Liarte D, Renero-Lecuna C, Kavak S, Orue I, Wilhelm C, Bals S, Henriksen-Lacey M, Jimenez de Aberasturi D, Liz-Marzán LM, Journal of materials chemistry B : materials for biology and medicine (2023). http://doi.org/10.1039/D3TB00397C
Abstract: Hyperthermia, as the process of heating a malignant site above 42 °C to trigger cell death, has emerged as an effective and selective cancer therapy strategy. Various modalities of hyperthermia have been proposed, among which magnetic and photothermal hyperthermia are known to benefit from the use of nanomaterials. In this context, we introduce herein a hybrid colloidal nanostructure comprising plasmonic gold nanorods (AuNRs) covered by a silica shell, onto which iron oxide nanoparticles (IONPs) are subsequently grown. The resulting hybrid nanostructures are responsive to both external magnetic fields and near-infrared irradiation. As a result, they can be applied for the targeted magnetic separation of selected cell populations – upon targeting by antibody functionalization – as well as for photothermal heating. Through this combined functionality, the therapeutic effect of photothermal heating can be enhanced. We demonstrate both the fabrication of the hybrid system and its application for targeted photothermal hyperthermia of human glioblastoma cells.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 7
Times cited: 1
DOI: 10.1039/D3TB00397C
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“Photothermal circular dichroism measurements of single chiral gold nanoparticles correlated with electron tomography”. Spaeth P, Adhikari S, Heyvaert W, Zhuo X, Garcia I, Liz-Marzan LM, Bals S, Orrit M, Albrecht W, ACS Photonics 9, 3995 (2022). http://doi.org/10.1021/ACSPHOTONICS.2C01457
Abstract: Chemically synthesized metal nanoparticles with morphological chiral features are known to exhibit strong circular dichroism. However, we still lack understanding of the correlation between morphological and chiroptical features of plasmonic nanoparticles. To shed light on that question, single nanoparticle experiments are required. We performed photothermal circular dichroism measurements of single chiral and achiral gold nanoparticles and correlated the chiroptical response to the 3D morphology of the same nanoparticles retrieved by electron tomography. In contrast to an ensemble measurement, we show that individual particles within the ensemble display a broad distribution of strength and handedness of circular dichroism signals. Whereas obvious structural chiral features, such as helical wrinkles, translate into chiroptical ones, nanoparticles with less obvious chiral morphological features can also display strong circular dichroism signals. Interestingly, we find that even seemingly achiral nanoparticles can display large g-factors. The origin of this circular dichroism signal is discussed in terms of plasmonics and other potentially relevant factors.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7
Times cited: 5
DOI: 10.1021/ACSPHOTONICS.2C01457
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“High-throughput characterization of single-quantum-dot emission spectra and spectral diffusion by multiparticle spectroscopy”. Mangnus MJJ, de Wit JW, Vonk SJW, Geuchies JJ, Albrecht W, Bals S, Houtepen AJ, Rabouw FT, ACS Photonics 10, 2688 (2023). http://doi.org/10.1021/ACSPHOTONICS.3C00420
Abstract: In recent years, quantum dots (QDs) have emerged as bright,color-tunablelight sources for various applications such as light-emitting devices,lasing, and bioimaging. One important next step to advance their applicabilityis to reduce particle-to-particle variations of the emission propertiesas well as fluctuations of a single QD's emission spectrum,also known as spectral diffusion (SD). Characterizing SD is typicallyinefficient as it requires time-consuming measurements at the single-particlelevel. Here, however, we demonstrate multiparticle spectroscopy (MPS)as a high-throughput method to acquire statistically relevant informationabout both fluctuations at the single-particle level and variationsat the level of a synthesis batch. In MPS, we simultaneously measureemission spectra of many (20-100) QDs with a high time resolution.We obtain statistics on single-particle emission line broadening fora batch of traditional CdSe-based core-shell QDs and a batchof the less toxic InP-based core-shell QDs. The CdSe-basedQDs show significantly narrower homogeneous line widths, less SD,and less inhomogeneous broadening than the InP-based QDs. The timescales of SD are longer in the InP-based QDs than in the CdSe-basedQDs. Based on the distributions and correlations in single-particleproperties, we discuss the possible origins of line-width broadeningof the two types of QDs. Our experiments pave the way to large-scale,high-throughput characterization of single-QD emission propertiesand will ultimately contribute to facilitating rational design offuture QD structures.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7
Times cited: 1
DOI: 10.1021/ACSPHOTONICS.3C00420
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“Sustainable formation of tricarballylic acid from citric acid over highly stable Pd/Nb2O5.nH2O catalysts”. Stuyck W, Bugaev AL, Nelis T, de Oliveira-Silva R, Smolders S, Usoltsev OA, Arenas Esteban D, Bals S, Sakellariou D, De Vos D, Journal of catalysis (2022). http://doi.org/10.1016/j.jcat.2022.02.013
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 7.3
Times cited: 5
DOI: 10.1016/j.jcat.2022.02.013
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“Atomic layer deposition-based tuning of the pore size in mesoporous thin films studied by in situ grazing incidence small angle X-ray scattering”. Dendooven J, Devloo-Casier K, Ide M, Grandfield, Kurttepeli, Ludwig KF, Bals S, Van der Voort P, Detavernier C, Nanoscale 6, 14991 (2014). http://doi.org/10.1039/c4nr05049e
Abstract: Atomic layer deposition (ALD) enables the conformal coating of porous materials, making the technique suitable for pore size tuning at the atomic level, e.g., for applications in catalysis, gas separation and sensing. It is, however, not straightforward to obtain information about the conformality of ALD coatings deposited in pores with diameters in the low mesoporous regime (<10 nm). In this work, it is demonstrated that in situ synchrotron based grazing incidence small angle X-ray scattering (GISAXS) can provide valuable information on the change in density and internal surface area during ALD of TiO2 in a porous titania film with small mesopores (3-8 nm). The results are shown to be in good agreement with in situ X-ray fluorescence data representing the evolution of the amount of Ti atoms deposited in the porous film. Analysis of both datasets indicates that the minimum pore diameter that can be achieved by ALD is determined by the size of the Ti-precursor molecule.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 41
DOI: 10.1039/c4nr05049e
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“Band structure quantization in nanometer sized ZnO clusters”. Schouteden K, Zeng Y-J, Lauwaet K, Romero CP, Goris B, Bals S, Van Tendeloo G, Lievens P, Van Haesendonck C, Nanoscale 5, 3757 (2013). http://doi.org/10.1039/c3nr33989k
Abstract: Nanometer sized ZnO clusters are produced in the gas phase and subsequently deposited on clean Au(111) surfaces under ultra-high vacuum conditions. The zinc blende atomic structure of the approximately spherical ZnO clusters is resolved by high resolution scanning transmission electron microscopy. The large band gap and weak n-type conductivity of individual clusters are determined by scanning tunnelling microscopy and spectroscopy at cryogenic temperatures. The conduction band is found to exhibit clear quantization into discrete energy levels, which can be related to finite-size effects reflecting the zero-dimensional confinement. Our findings illustrate that gas phase cluster production may provide unique possibilities for the controlled fabrication of high purity quantum dots and heterostructures that can be size selected prior to deposition on the desired substrate under controlled ultra-high vacuum conditions.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 13
DOI: 10.1039/c3nr33989k
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“Dimethylformamide-mediated synthesis of water-soluble platinum nanodendrites for ethanol oxidation electrocatalysis”. Mourdikoudis S, Chirea M, Altantzis T, Pastoriza-Santos I, Perez-Juste J, Silva F, Bals S, Liz-Marzan LM, Nanoscale 5, 4776 (2013). http://doi.org/10.1039/c3nr00924f
Abstract: Herein we describe the synthesis of water-soluble platinum nanodendrites in dimethylformamide (DMF), in the presence of polyethyleneimine (PEI) as a stabilizing agent. The average size of the dendrites is in the range of 20-25 nm while their porosity can be tuned by modifying the concentration of the metal precursor. Electron tomography revealed different crystalline orientations of nanocrystallites in the nanodendrites and allowed a better understanding of their peculiar branching and porosity. The high surface area of the dendrites (up to 22 m(2) g(-1)) was confirmed by BET measurements, while X-ray diffraction confirmed the abundance of high-index facets in the face-centered-cubic crystal structure of Pt. The prepared nanodendrites exhibit excellent performance in the electrocatalytic oxidation of ethanol in alkaline solution. Sensing, selectivity, cycleability and great tolerance toward poisoning were demonstrated by cyclic voltammetry measurements.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 50
DOI: 10.1039/c3nr00924f
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“Multifunctional self-assembled composite colloids and their application to SERS detection”. La Porta A, Sanchez-Iglesias A, Altantzis T, Bals S, Grzelczak M, Liz-Marzan LM, Nanoscale 7, 10377 (2015). http://doi.org/10.1039/c5nr01264c
Abstract: We present a simple method for the co-encapsulation of gold nanostars and iron-oxide nanoparticles into hybrid colloidal composites that are highly responsive to both light and external magnetic fields. Self-assembly was driven by hydrophobic interactions between polystyrene capped gold nanostars and iron oxide nanocrystals stabilized with oleic acid, upon addition of water. A block copolymer was then used to encapsulate the resulting spherical colloidal particle clusters, which thereby became hydrophilic. Electron microscopy analysis unequivocally shows that each composite particle comprises a single Au nanostar surrounded by a few hundreds of iron oxide nanocrystals. We demonstrate that this hybrid colloidal system can be used as an efficient substrate for surface enhanced Raman scattering, using common dyes as model molecular probes. The co-encapsulation of iron oxide nanoparticles renders the system magnetically responsive, so that application of an external magnetic field leads to particle accumulation and limits of detection are in the nM range.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 51
DOI: 10.1039/c5nr01264c
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“Governing the morphology of PtAu heteronanocrystals with improved electrocatalytic performance”. Mourdikoudis S, Chirea M, Zanaga D, Altantzis T, Mitrakas M, Bals S, Marzán LM, Pérez-Juste J, Pastoriza-Santos I, Nanoscale 7, 8739 (2015). http://doi.org/10.1039/C4NR07481E
Abstract: Platinumgold heteronanostructures comprising either dimer (PtAu) or coresatellite (Pt@Au) configurations were synthesized by means of a seeded growth procedure using platinum nanodendrites as seeds. Careful control of the reduction kinetics of the gold precursor can be used to direct the nucleation and growth of gold nanoparticles on either one or multiple surface sites simultaneously, leading to the formation of either dimers or coresatellite nanoparticles, respectively, in high yields. Characterization by electron tomography and high resolution electron microscopy provided a better understanding of the actual three-dimensional particle morphology, as well as the AuPt interface, revealing quasi-epitaxial growth of Au on Pt. The prepared PtAu bimetallic nanostructures are highly efficient catalysts for ethanol oxidation in alkaline solution, showing accurate selectivity, high sensitivity, and improved efficiency by generating higher current densities than their monometallic counterparts.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 41
DOI: 10.1039/C4NR07481E
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“Synthesis of a 3D network of Pt nanowires by atomic layer deposition on a carbonaceous template”. Deng S, Kurttepeli M, Deheryan S, Cott DJ, Vereecken PM, Martens JA, Bals S, Van Tendeloo G, Detavernier C, Nanoscale 6, 6939 (2014). http://doi.org/10.1039/c4nr00982g
Abstract: The formation of a 3D network composed of free standing and interconnected Pt nanowires is achieved by a two-step method, consisting of conformal deposition of Pt by atomic layer deposition (ALD) on a forest of carbon nanotubes and subsequent removal of the carbonaceous template. Detailed characterization of this novel 3D nanostructure was carried out by transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS). The characterization showed that this pure 3D nanostructure of platinum is self-supported and offers an enhancement of the electrochemically active surface area by a factor of 50.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 14
DOI: 10.1039/c4nr00982g
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“Synthesis of uniformly dispersed anatase nanoparticles inside mesoporous silica thin films via controlled breakup and crystallization of amorphous TiO2 deposited using atomic layer deposition”. Sree SP, Dendooven J, Masschaele K, Hamed HM, Deng S, Bals S, Detavernier C, Martens JA, Nanoscale 5, 5001 (2013). http://doi.org/10.1039/c3nr00594a
Abstract: Amorphous titanium dioxide was introduced into the pores of mesoporous silica thin films with 75% porosity and 12 nm average pore diameter via Atomic Layer Deposition (ALD) using alternating pulses of tetrakis(dimethylamino)titanium and water. Calcination provoked fragmentation of the deposited amorphous TiO2 phase and its crystallization into anatase nanoparticles inside the nanoporous film. The narrow particle size distribution of 4 ± 2 nm and the uniform dispersion of the particles over the mesoporous silica support were uniquely revealed using electron tomography. These anatase nanoparticle bearing films showed photocatalytic activity in methylene blue degradation. This new synthesis procedure of the anatase nanophase in mesoporous silica films using ALD is a convenient fabrication method of photocatalytic coatings amenable to application on very small as well as very large surfaces
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 22
DOI: 10.1039/c3nr00594a
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“Quantitative 3D analysis of huge nanoparticle assemblies”. Zanaga D, Bleichrodt F, Altantzis T, Winckelmans N, Palenstijn WJ, Sijbers J, de Nijs B, van Huis MA, Sanchez-Iglesias A, Liz-Marzan LM, van Blaaderen A, Joost Batenburg K, Bals S, Van Tendeloo G, Nanoscale 8, 292 (2016). http://doi.org/10.1039/c5nr06962a
Abstract: Nanoparticle assemblies can be investigated in 3 dimensions using electron tomography. However, it is not straightforward to obtain quantitative information such as the number of particles or their relative position. This becomes particularly difficult when the number of particles increases. We propose a novel approach in which prior information on the shape of the individual particles is exploited. It improves the quality of the reconstruction of these complex assemblies significantly. Moreover, this quantitative Sparse Sphere Reconstruction approach yields directly the number of particles and their position as an output of the reconstruction technique, enabling a detailed 3D analysis of assemblies with as many as 10 000 particles. The approach can also be used to reconstruct objects based on a very limited number of projections, which opens up possibilities to investigate beam sensitive assemblies where previous reconstructions with the available electron tomography techniques failed.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 7.367
Times cited: 34
DOI: 10.1039/c5nr06962a
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“Decoupling the shape parameter to assess gold nanorod uptake by mammalian cells”. Kinnear C, Rodriguez-Lorenzo L, Clift MJD, Goris B, Bals S, Rothen B, Fink AS, Nanoscale 8, 16416 (2016). http://doi.org/10.1039/C6NR03543D
Abstract: The impact of nanoparticles (NPs) upon biological systems can be fundamentally associated with their physicochemical parameters. A further often-stated tenet is the importance of NP shape on rates of endocytosis. However, given the convoluted parameters concerning the NP-cell interaction, it is experimentally challenging to attribute any findings to shape alone. Herein we demonstrate that shape, below a certain limit, which is specific to nanomedicine, is not important for the endocytosis of spherocylinders by either epithelial or macrophage cells in vitro. Through a systematic approach, we reshaped a single batch of gold nanorods into different aspect ratios resulting in near-spheres and studied their cytotoxicity, (pro-)inflammatory status, and endocytosis/exocytosis. It was found that on a length scale of ~10-90 nm and at aspect ratios less than 5, NP shape has little impact upon their entry into either macrophages or epithelial cells. Conversely, nanorods with an aspect ratio above 5 were preferentially endocytosed by epithelial cells, whereas there was a lack of shape dependent uptake following exposure to macrophages in vitro. These findings have implications both in the understanding of nanoparticle reshaping mechanisms, as well as in the future rational design of nanomaterials for biomedical applications.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 23
DOI: 10.1039/C6NR03543D
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“Three-dimensional atomic models from a single projection using Z-contrast imaging: verification by electron tomography and opportunities”. De Backer A, Jones L, Lobato I, Altantzis T, Goris B, Nellist PD, Bals S, Van Aert S, Nanoscale 9, 8791 (2017). http://doi.org/10.1039/C7NR02656K
Abstract: In order to fully exploit structure–property relations of nanomaterials, three-dimensional (3D) characterization at the atomic scale is often required. In recent years, the resolution of electron tomography has reached the atomic scale. However, such tomography typically requires several projection images demanding substantial electron dose. A newly developed alternative circumvents this by counting the number of atoms across a single projection. These atom counts can be used to create an initial atomic model with which an energy minimization can be applied to obtain a relaxed 3D reconstruction of the nanoparticle. Here, we compare, at the atomic scale, this single projection reconstruction approach with tomography and find an excellent agreement. This new approach allows for the characterization of beam-sensitive materials or where the acquisition of a tilt series is impossible. As an example, the utility is illustrated by the 3D atomic scale characterization of a nanodumbbell on an in situ heating holder of limited tilt range.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 33
DOI: 10.1039/C7NR02656K
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“Nanorattles with tailored electric field enhancement”. Schnepf MJ, Mayer M, Kuttner C, Tebbe M, Wolf D, Dulle M, Altantzis T, Formanek P, Förster S, Bals S, König TAF, Fery A, Nanoscale 9, 9376 (2017). http://doi.org/10.1039/C7NR02952G
Abstract: Nanorattles are metallic core–shell particles with core and shell separated by a dielectric spacer. These
nanorattles have been identified as a promising class of nanoparticles, due to their extraordinary high
electric-field enhancement inside the cavity. Limiting factors are reproducibility and loss of axial symmetry
owing to the movable metal core; movement of the core results in fluctuation of the nanocavity dimensions
and commensurate variations in enhancement factor. We present a novel synthetic approach for
the robust fixation of the central gold rod within a well-defined box, which results in an axisymmetric
nanorattle. We determine the structure of the resulting axisymmetric nanorattles by advanced transmission
electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Optical absorption and scattering
cross-sections obtained from UV-vis-NIR spectroscopy quantitatively agree with finite-difference
time-domain (FDTD) simulations based on the structural model derived from SAXS. The predictions of
high and homogenous field enhancement are evidenced by scanning TEM electron energy loss spectroscopy
(STEM-EELS) measurement on single-particle level. Thus, comprehensive understanding of
structural and optical properties is achieved for this class of nanoparticles, paving the way for photonic
applications where a defined and robust unit cell is crucial.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 69
DOI: 10.1039/C7NR02952G
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“Morphological and chemical transformations of single silica-coated CdSe/CdS nanorods upon fs-laser excitation”. Albrecht W, Goris B, Bals S, Hutter EM, Vanmaekelbergh D, van Huis MA, van Blaaderen A, Nanoscale 9, 4810 (2017). http://doi.org/10.1039/C6NR09879G
Abstract: Radiation-induced modifications of nanostructures are of fundamental interest and constitute a viable out-of-equilibrium approach to the development of novel nanomaterials. Herein, we investigated the structural transformation of silica-coated CdSe/CdS nanorods (NRs) under femtosecond (fs) illumination. By comparing the same nanorods before and after illumination with different fluences we found that the silica-shell did not only enhance the stability of the NRs but that the confinement of the NRs also led to novel morphological and chemical transformations. Whereas uncoated CdSe/CdS nanorods were found to sublimate under such excitations the silica-coated nanorods broke into fragments which deformed towards a more spherical shape. Furthermore, CdS decomposed which led to the formation of metallic Cd, confirmed by high-resolution electron microscopy and energy dispersive X-ray spectrometry (EDX), whereby an epitaxial interface with the remaining CdS lattice was formed. Under electron beam exposure similar transformations were found to take place which we followed in situ.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 4
DOI: 10.1039/C6NR09879G
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“Shape control in ZIF-8 nanocrystals and metal nanoparticles@ZIF-8 heterostructures”. Zheng G, Chen Z, Sentosun K, Pérez-Juste I, Bals S, Liz-Marzán LM, Pastoriza-Santos I, Pérez-Juste J, Hong M, Nanoscale 9, 16645 (2017). http://doi.org/10.1039/C7NR03739B
Abstract: Shape control in metal-organic frameworks still remains a challenge. We propose a strategy based on the capping agent modulator method to control the shape of ZIF-8 nanocrystals. This approach requires the use of a surfactant, cetyltrimethylammonium bromide (CTAB), and a second capping agent, tris(hydroxymethyl)aminomethane (TRIS), to obtain ZIF-8 nanocrystals with morphology control in aqueous media. Semiempirical computational simulations suggest that both shape-inducing agents adsorb onto different surface facets of ZIF-8, thereby slowing down their crystal growth rates. While CTAB molecules preferentially adsorb onto the {100} facets, leading to ZIF-8 particles with cubic morphology, TRIS preferentially stabilizes the {111} facets, inducing the formation of octahedral crystals. Interestingly, the presence of both capping agents leads to nanocrystals with irregular shapes and higher index facets, such as hexapods and burr puzzles. Additionally, the combination of ZIF-8 nanocrystals with other materials is expected to impart additional properties due to the hybrid nature of the resulting nanocomposites. In the present case, the presence of CTAB and TRIS molecules as capping agents facilitates the synthesis of metal nanoparticle@ZIF-8 nanocomposites, due to synergistic effects which could be of use in a number of applications such as catalysis, gas sensing and storage.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 109
DOI: 10.1039/C7NR03739B
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“Gold nanoclusters with bright near-infrared photoluminescence”. Pramanik G, Humpolickova J, Valenta J, Kundu P, Bals S, Bour P, Dracinsky M, Cigler P, Nanoscale 10, 3792 (2018). http://doi.org/10.1039/C7NR06050E
Abstract: The increase in nonradiative pathways with decreasing emission energy reduces the luminescence quantum yield (QY) of near-infrared photoluminescent (NIR PL) metal nanoclusters. Efficient surface ligand chemistry can significantly improve the luminescence QY of NIR PL metal nanoclusters. In contrast to the widely reported but modestly effective thiolate ligand-to-metal core charge transfer, we show that metal-to-ligand charge transfer (MLCT) can be used to greatly enhance the luminescence QY of NIR PL gold nanoclusters (AuNCs). We synthesized water-soluble and colloidally stable NIR PL AuNCs with unprecedentedly high QY (similar to 25%) upon introduction of triphenylphosphonium moieties into the surface capping layer. By using a combination of spectroscopic and theoretical methods, we provide evidence for gold core-to-ligand charge transfer occurring in AuNCs. We envision that this work can stimulate the development of these unusually bright AuNCs for promising optoelectronic, bioimaging, and other applications.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 97
DOI: 10.1039/C7NR06050E
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