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“Encapsulation of Noble Metal Nanoparticles through Seeded Emulsion Polymerization as Highly Stable Plasmonic Systems”. Scarabelli L, Schumacher M, Jimenez de Aberasturi D, Merkl J‐P, Henriksen‐Lacey M, Milagres de Oliveira T, Janschel M, Schmidtke C, Bals S, Weller H, Liz‐Marzán LM, Advanced functional materials 29, 1809071 (2019). http://doi.org/10.1002/adfm.201809071
Abstract: The implementation of plasmonic nanoparticles in vivo remains hindered by important limitations such as biocompatibility, solubility in biological fluids, and physiological stability. A general and versatile protocol is presented, based on seeded emulsion polymerization, for the controlled encapsulation of gold and silver nanoparticles. This procedure enables the encapsulation of single nanoparticles as well as nanoparticle clusters inside a protecting polymer shell. Specifically, the efficient coating of nanoparticles of both metals is demonstrated, with final dimensions ranging between 50 and 200 nm, i.e., sizes of interest for bio-applications. Such hybrid nanocomposites display extraordinary stability in high ionic strength and oxidizing environments, along with high cellular uptake, and low cytotoxicity. Overall, the prepared nanostructures are promising candidates for plasmonic applications under biologically relevant conditions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.124
Times cited: 19
DOI: 10.1002/adfm.201809071
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“Fully inorganic Ruddlesden-Popper double CI-I and triple CI-Br-I lead halide perovskite nanocrystals”. Akkerman QA, Bladt E, Petralanda U, Dang Z, Sartori E, Baranov D, Abdelhady AL, Infante I, Bals S, Manna L, Chemistry of materials 31, 2182 (2019). http://doi.org/10.1021/ACS.CHEMMATER.9B00489
Abstract: The vast majority of lead halide perovskite (LHP) nanocrystals (NCs) are currently based on either a single halide composition (CsPbCl3, CsPbBr3, and CsPbI3) or an alloyed mixture of bromide with either Cl- or I- [i.e., CsPb(Br:Cl)(3) or CsPb(Br:I)(3)]. In this work, we present the synthesis as well as a detailed optical and structural study of two halide alloying cases that have not previously been reported for LHP NCs: Cs2PbI2Cl2 NCs and triple halide CsPb(Cl:Br:I)(3) NCs. In the case of Cs2PbI2Cl2, we observe for the first time NCs with a fully inorganic Ruddlesden-Popper phase (RPP) crystal structure. Unlike the well-explored organic-inorganic RPP, here, the RPP formation is triggered by the size difference between the halide ions. These NCs exhibit a strong excitonic absorption, albeit with a weak photoluminescence quantum yield (PLQY). In the case of the triple halide CsPb(Cl:Br:I)(3) composition, the NCs comprise a CsPbBr2Cl perovskite crystal lattice with only a small amount of incorporated iodide, which segregates at RPP planes' interfaces within the CsPb(Cl:Br:I)(3) NCs. Supported by density functional theory calculations and postsynthetic surface treatments to enhance the PLQY, we show that the combination of iodide segregation and defective RPP interfaces are most likely linked to the strong PL quenching observed in these nanostructures. In summary, this work demonstrates the limits of halide alloying in LHP NCs because a mixture that contains halide ions of very different sizes leads to the formation of defective RPP interfaces and a severe quenching of LHP NC's optical properties.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 58
DOI: 10.1021/ACS.CHEMMATER.9B00489
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“Highly porous palladium nanodendrites : wet-chemical synthesis, electron tomography and catalytic activity”. Mourdikoudis S, Montes-Garcia V, Rodal-Cedeira S, Winckelmans N, Perez-Juste I, Wu H, Bals S, Perez-Juste J, Pastoriza-Santos I, Journal of the Chemical Society : Dalton transactions 48, 3758 (2019). http://doi.org/10.1039/C9DT00107G
Abstract: A simple procedure to obtain highly porous hydrophilic palladium nanodendrites in one-step is described. The synthetic strategy is based on the thermal reduction of a Pd precursor in the presence of a positively charged polyelectrolyte such as polyethylenimine (PEI). Advanced electron microscopy techniques combined with X-ray diffraction (XRD), thermogravimetry and BET analysis demonstrate the polycrystalline nature of the nanodendrites as well as their high porosity and active surface area, facilitating a better understanding of their unique morphology. Besides, catalytic studies performed using Raman scattering and UV-Vis spectroscopies revealed that the nanodendrites exhibit a superior performance as recyclable catalysts towards hydrogenation reaction compared to other noble metal nanoparticles.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 23
DOI: 10.1039/C9DT00107G
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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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“Chemical cutting of perovskite nanowires into single-photon emissive low-aspect-ratio CsPbX3(X = Cl, Br, I) nanorods”. Tong Y, Fu M, Bladt E, Huang H, Richter AF, Wang K, Mueller-Buschbaum P, Bals S, Tamarat P, Lounis B, Feldmann J, Polavarapu L, Angewandte Chemie: international edition in English 57, 16094 (2018). http://doi.org/10.1002/ANIE.201810110
Abstract: Post-synthetic shape-transformation processes provide access to colloidal nanocrystal morphologies that are unattainable by direct synthetic routes. Herein, we report our finding about the ligand-induced fragmentation of CsPbBr3 perovskite nanowires (NWs) into low aspect-ratio CsPbX3 (X = Cl, Br and I) nanorods (NRs) during halide ion exchange reaction with PbX2-ligand solution. The shape transformation of NWs-to-NRs resulted in an increase of photoluminescence efficiency owing to a decrease of nonradiative decay rates. Importantly, we found that the perovskite NRs exhibit single photon emission as revealed by photon antibunching measurements, while it is not detected in parent NWs. This work not only reports on the quantum light emission of low aspect ratio perovskite NRs, but also expands our current understanding of shape-dependent optical properties of perovskite nanocrystals.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 11.994
Times cited: 70
DOI: 10.1002/ANIE.201810110
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“Corrosion protection of Cu by atomic layer deposition”. Cremers V, Rampelberg G, Baert K, Abrahami S, Claes N, de Oliveira TM, Terryn H, Bals S, Dendooven J, Detavernier C, Journal of vacuum science and technology: A: vacuum surfaces and films 37, 060902 (2019). http://doi.org/10.1116/1.5116136
Abstract: Atomic layer deposition (ALD) is a vapor phase technique that is able to deposit uniform, conformal thin films with an excellent thickness control at the atomic scale. 18 nm thick Al2O3 and TiO2 coatings were deposited conformaly and pinhole-free onto micrometer-sized Cu powder, using trimethylaluminum and tetrakis(dimethylamido)titanium(IV), respectively, as a precursor and de-ionized water as a reactant. The capability of the ALD coating to protect the Cu powder against corrosion was investigated. Therefore, the stability of the coatings was studied in solutions with different pH in the range of 0–14, and in situ raman spectroscopy was used to detect the emergence of corrosion products of Cu as an indication that the protective coating starts to fail. Both ALD coatings provide good protection at standard pH values in the range of 5–7. In general, the TiO2 coating shows a better barrier protection against corrosion than the Al2O3 coating. However, for the most extreme pH conditions, pH 0 and pH 14, the TiO2 coating starts also to degrade.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.374
Times cited: 7
DOI: 10.1116/1.5116136
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“A titanium(IV)-based metal-organic framework featuring defect-rich Ti-O sheets as an oxidative desulfurization catalyst”. Smolders S, Willhammar T, Krajnc A, Şentosun K, Wharmby MT, Lomachenko KA, Bals S, Mali G, Roeffaers MBJ, De Vos DE, Bueken B, Angewandte Chemie: international edition in English 58, 9160 (2019). http://doi.org/10.1002/ANIE.201904347
Abstract: While titanium-based metal-organic frameworks (MOFs) have been widely studied for their (photo) catalytic potential, only a few Ti-IV MOFs have been reported owing to the high reactivity of the employed titanium precursors. The synthesis of COK-47 is now presented, the first Ti carboxylate MOF based on sheets of (TiO6)-O-IV octahedra, which can be synthesized with a range of different linkers. COK-47 can be synthesized as an inherently defective nanoparticulate material, rendering it a highly efficient catalyst for the oxidation of thiophenes. Its structure was determined by continuous rotation electron diffraction and studied in depth by X-ray total scattering, EXAFS, and solid-state NMR. Furthermore, its photoactivity was investigated by electron paramagnetic resonance and demonstrated by catalytic photodegradation of rhodamine 6G.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 11.994
Times cited: 97
DOI: 10.1002/ANIE.201904347
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“Locating and controlling the Zn content in In(Zn)P quantum dots”. Kirkwood N, De Backer A, Altantzis T, Winckelmans N, Longo A, Antolinez FV, Rabouw FT, De Trizio L, Geuchies JJ, Mulder JT, Renaud N, Bals S, Manna L, Houtepen AJ, Chemistry of materials 32, 557 (2019). http://doi.org/10.1021/acs.chemmater.9b04407
Abstract: Zinc is routinely employed in the synthesis of InP quantum dots (QDs) to improve the photoluminescence efficiency and carrier mobility of the resulting In(Zn)P alloy nanostructures. The exact location of Zn in the final structures and the mechanism by which it enhances the optoelectronic properties of the QDs is debated. We use synchrotron X-ray absorbance spectroscopy to show that the majority of Zn in In(Zn)P QDs is located at their surface as Zn-carboxylates. However, a small amount of Zn is present inside the bulk of the QDs with the consequent contraction of their lattice, as confirmed by combining high resolution high-angle annular dark-field imaging scanning transmission electron microscopy (HAADF-STEM) with statistical parameter estimation theory. We further demonstrate that the Zn content and its incorporation into the QDs can be tuned by the ligation of commonly employed Zn carboxylate precursors: the use of highly reactive Zn-acetate leads to the formation of undesired Zn3P2 and the final nanostructures being characterized by broad optical features, whereas Zn-carboxylates with longer carbon chains lead to InP crystals with much lower zinc content and narrow optical features. These results can explain the differences between structural and optical properties of In(Zn)P samples reported across the literature, and provide a rational method to tune the amount of Zn in InP nanocrystals and to drive the incorporation of Zn either as surface Zn-carboxylate, as a substitutional dopant inside the InP crystal lattice, or even predominantly as Zn3P2.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 39
DOI: 10.1021/acs.chemmater.9b04407
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“Defect-directed growth of symmetrically branched metal nanocrystals”. Smith JD, Bladt E, Burkhart JAC, Winckelmans N, Koczkur KM, Ashberry HM, Bals S, Skrabalak SE, Angewandte Chemie-International Edition 59, 943 (2020). http://doi.org/10.1002/ANIE.201913301
Abstract: Branched plasmonic nanocrystals (NCs) have attracted much attention due to electric field enhancements at their tips. Seeded growth provides routes to NCs with defined branching patterns and, in turn, near-field distributions with defined symmetries. Here, a systematic analysis was undertaken in which seeds containing different distributions of planar defects were used to grow branched NCs in order to understand how their distributions direct the branching. Characterization of the products by multimode electron tomography and analysis of the NC morphologies at different overgrowth stages indicate that the branching patterns are directed by the seed defects, with the emergence of branches from the seed faces consistent with minimizing volumetric strain energy at the expense of surface energy. These results contrast with growth of branched NCs from single-crystalline seeds and provide a new platform for the synthesis of symmetrically branched plasmonic NCs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 16.6
Times cited: 23
DOI: 10.1002/ANIE.201913301
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“Pr/ZrO2 prepared by atomic trapping : an efficient catalyst for the conversion of glycerol to lactic acid with concomitant transfer hydrogenation of cyclohexene”. Tang Z, Liu P, Cao H, Bals S, Heeres HJ, Pescarmona PP, ACS catalysis 9, 9953 (2019). http://doi.org/10.1021/ACSCATAL.9B02139
Abstract: A series of heterogeneous catalysts consisting of highly dispersed Pt nanoparticles supported on nanosized ZrO2 (20 to 60 nm) was synthesized and investigated for the one-pot transfer hydrogenation between glycerol and cyclohexene to produce lactic acid and cyclohexane, without any additional H-2. Different preparation methods were screened, by varying the calcination and reduction procedures with the purpose of optimizing the dispersion of Pt species (i.e., as single-atom sites or extra-fine Pt nanoparticles) on the ZrO2 support. The Pt/ZrO2 catalysts were characterized by means of transmission electron microscopy techniques (HAADF-STEM, TEM), elemental analysis (ICP-OES, EDX mapping), N-2-physisorption, H-2 temperature-programmed-reduction (H-2-TPR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Based on this combination of techniques it was possible to correlate the temperature of the calcination and reduction treatments with the nature of the Pt species. The best catalyst consisted of subnanometer Pt clusters (<1 nm) and atomically dispersed Pt (as Pt2+ and Pt4+) on the ZrO2 support, which were converted into extra-fine Pt nanoparticles (average size = 1.4 nm) upon reduction. These nanoparticles acted as catalytic species for the transfer hydrogenation of glycerol with cyclohexene, which gave an unsurpassed 95% yield of lactic acid salt at 96% glycerol conversion (aqueous glycerol solution, NaOH as promoter, 160 degrees C, 4.5 h, at 20 bar N-2). This is the highest yield and selectivity of lactic acid (salt) reported in the literature so far. Reusability experiments showed a partial and gradual loss of activity of the Pt/ZrO2 catalyst, which was attributed to the experimentally observed aggregation of Pt nanoparticles.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 10.614
Times cited: 46
DOI: 10.1021/ACSCATAL.9B02139
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“Defect‐Directed Growth of Symmetrically Branched Metal Nanocrystals”. Smith JD, Bladt E, Burkhart JAC, Winckelmans N, Koczkur KM, Ashberry HM, Bals S, Skrabalak SE, Angewandte Chemie (International ed. Print) 132, 953 (2020). http://doi.org/10.1002/ange.201913301
Abstract: Branched plasmonic nanocrystals (NCs) have attracted much attention due to electric field enhancements at their tips. Seeded growth provides routes to NCs with defined branching patterns and, in turn, near‐field distributions with defined symmetries. Here, a systematic analysis was undertaken in which seeds containing different distributions of planar defects were used to grow branched NCs in order to understand how their distributions direct the branching. Characterization of the products by multimode electron tomography and analysis of the NC morphologies at different overgrowth stages indicate that the branching patterns are directed by the seed defects, with the emergence of branches from the seed faces consistent with minimizing volumetric strain energy at the expense of surface energy. These results contrast with growth of branched NCs from single‐crystalline seeds and provide a new platform for the synthesis of symmetrically branched plasmonic NCs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
DOI: 10.1002/ange.201913301
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“Manganese‐Doping‐Induced Quantum Confinement within Host Perovskite Nanocrystals through Ruddlesden–Popper Defects”. Paul S, Bladt E, Richter AF, Döblinger M, Tong Y, Huang H, Dey A, Bals S, Debnath T, Polavarapu L, Feldmann J, Angewandte Chemie-International Edition 59, 6794 (2020). http://doi.org/10.1002/anie.201914473
Abstract: The concept of doping Mn2+ ions into II–VI semiconductor nanocrystals (NCs) was recently extended to perovskite NCs. To date, most studies on Mn2+ doped NCs focus on enhancing the emission related to the Mn2+ dopant via an energy transfer mechanism. Herein, we found that the doping of Mn2+ ions into CsPbCl3 NCs not only results in a Mn2+‐related orange emission, but also strongly influences the excitonic properties of the host NCs. We observe for the first time that Mn2+ doping leads to the formation of Ruddlesden–Popper (R.P.) defects and thus induces quantum confinement within the host NCs. We find that a slight doping with Mn2+ ions improves the size distribution of the NCs, which results in a prominent excitonic peak. However, with increasing the Mn2+ concentration, the number of R.P. planes increases leading to smaller single‐crystal domains. The thus enhanced confinement and crystal inhomogeneity cause a gradual blue shift and broadening of the excitonic transition, respectively.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 16.6
Times cited: 64
DOI: 10.1002/anie.201914473
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“Fast versus conventional HAADF-STEM tomography of nanoparticles: advantages and challenges”. Vanrompay H, Skorikov A, Bladt E, Béché, A, Freitag B, Verbeeck J, Bals S, Ultramicroscopy 221, 113191 (2021). http://doi.org/10.1016/j.ultramic.2020.113191
Abstract: HAADF-STEM tomography is a widely used experimental technique for analyzing nanometer-scale crystalline structures of a large variety of materials in three dimensions. Unfortunately, the acquisition of conventional HAADF-STEM tilt series can easily take up one hour or more, depending on the complexity of the experiment. It is therefore far from straightforward to investigate samples that do not withstand long acquisition or to acquire large amounts of tilt series during a single TEM experiment. The latter would lead to the ability to obtain statistically meaningful 3D data, or to perform in situ 3D characterizations with a much shorter time resolution. Various HAADF-STEM acquisition strategies have been proposed to accelerate the tomographic acquisition and reduce the required electron dose. These methods include tilting the holder continuously while acquiring a projection “movie” and a hybrid, incremental, methodology which combines the benefits of the conventional and continuous technique. However, until now an experimental evaluation has been lacking. In this paper, the different acquisition strategies will be experimentally compared in terms of speed, resolution and electron dose. This evaluation will be performed based on experimental tilt series acquired for various metallic nanoparticles with different shapes and sizes. We discuss the data processing involved with the fast HAADF-STEM tilt series and provide a general guideline when which acquisition strategy should be preferentially used.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 15
DOI: 10.1016/j.ultramic.2020.113191
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“Tuning Size and Seed Position in Small Silver Nanorods”. Sánchez-Iglesias A, Zhuo X, Albrecht W, Bals S, Liz-Marzán LM, ACS materials letters 2, 1246 (2020). http://doi.org/10.1021/acsmaterialslett.0c00388
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 9
DOI: 10.1021/acsmaterialslett.0c00388
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“Nanocrystals of lead chalcohalides : a series of kinetically trapped metastable nanostructures”. Toso S, Akkerman QA, Martin-Garcia B, Prato M, Zito J, Infante I, Dang Z, Moliterni A, Giannini C, Bladt E, Lobato I, Ramade J, Bals S, Buha J, Spirito D, Mugnaioli E, Gemmi M, Manna L, Journal Of The American Chemical Society 142, 10198 (2020). http://doi.org/10.1021/JACS.0C03577
Abstract: We report the colloidal synthesis of a series of surfactant-stabilized lead chalcohalide nanocrystals. Our work is mainly focused on Pb4S3Br2, a chalcohalide phase unknown to date that does not belong to the ambient-pressure PbS-PbBr2 phase diagram. The Pb4S3Br2 nanocrystals herein feature a remarkably narrow size distribution (with a size dispersion as low as 5%), a good size tunability (from 7 to similar to 30 nm), an indirect bandgap, photoconductivity (responsivity = 4 +/- 1 mA/W), and stability for months in air. A crystal structure is proposed for this new material by combining the information from 3D electron diffraction and electron tomography of a single nanocrystal, X-ray powder diffraction, and density functional theory calculations. Such a structure is closely related to that of the recently discovered high-pressure chalcohalide Pb4S3I2 phase, and indeed we were able to extend our synthesis scheme to Pb4S3I2 colloidal nanocrystals, whose structure matches the one that has been published for the bulk. Finally, we could also prepare nanocrystals of Pb3S2Cl2, which proved to be a structural analogue of the recently reported bulk Pb3Se2Br2 phase. It is remarkable that one high-pressure structure (for Pb4S3I2) and two metastable structures that had not yet been reported (for Pb4S3Br2 and Pb3S2Cl2) can be prepared on the nanoscale by wet-chemical approaches. This highlights the important role of colloidal chemistry in the discovery of new materials and motivates further exploration into metal chalcohalide nanocrystals.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 15
Times cited: 32
DOI: 10.1021/JACS.0C03577
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“S,O-functionalized metal-organic frameworks as heterogeneous single-site catalysts for the oxidative alkenylation of arenes via C- H activation”. Van Velthoven N, Henrion M, Dallenes J, Krajnc A, Bugaev AL, Liu P, Bals S, Soldatov A, Mali G, De Vos DE, Acs Catalysis 10, 5077 (2020). http://doi.org/10.1021/ACSCATAL.0C00801
Abstract: Heterogeneous single-site catalysts can combine the R precise active site design of organometallic complexes with the efficient recovery of solid catalysts. Based on recent progress on homogeneous thioether ligands for Pd-catalyzed C-H activation reactions, we here develop a scalable metal-organic framework-based heterogeneous single-site catalyst containing S,O-moieties that increase the catalytic activity of Pd(II) for the oxidative alkenylation of arenes. The structure of the Pd@MOF-808-L1 catalyst was characterized in detail via solid-state nuclear magnetic resonance spectroscopy, N-2 physisorption, and high-angle annular dark field scanning transmission electron microscopy, and the structure of the isolated palladium active sites could be identified by X-ray absorption spectroscopy. A turnover frequency (TOF) of 8.4 h(-1) was reached after 1 h of reaction time, which was 3 times higher than the TOF of standard Pd(OAc)(2), ranking Pd@MOF-808-L1 among the most active heterogeneous catalysts ever reported for the nondirected oxidative alkenylation of arenes. Finally, we showed that the single-site catalyst promotes the oxidative alkenylation of a broad range of electron-rich arenes, and the applicability of this heterogeneous system was demonstrated by the gram-scale synthesis of industrially relevant products.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.9
Times cited: 37
DOI: 10.1021/ACSCATAL.0C00801
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“Near-Edge Ligand Stripping and Robust Radiative Exciton Recombination in CdSe/CdS Core/Crown Nanoplatelets”. Leemans J, Singh S, Li C, Ten Brinck S, Bals S, Infante I, Moreels I, Hens Z, Journal Of Physical Chemistry Letters 11, 3339 (2020). http://doi.org/10.1021/acs.jpclett.0c00870
Abstract: We address the relation between surface chemistry and optoelectronic properties in semiconductor nanocrystals using core/crown CdSe/CdS nanoplatelets passivated by cadmium oleate (Cd(Ol)2) as model systems. We show that addition of butylamine to a nanoplatelet (NPL) dispersion maximally displaces ∼40% of the original Cd(Ol)2 capping. On the basis of density functional theory simulations, we argue that this behavior reflects the preferential displacement of Cd(Ol)2 from (near)-edge surface sites. Opposite from CdSe core NPLs, core/crown NPL dispersions can retain 45% of their initial photoluminescence efficiency after ligand displacement, while radiative exciton recombination keeps dominating the luminescent decay. Using electron microscopy observations, we assign this robust photoluminescence to NPLs with a complete CdS crown, which prevents charge carrier trapping in the near-edge surface sites created by ligand displacement. We conclude that Z-type ligands such as cadmium carboxylates can provide full electronic passivation of (100) facets yet are prone to displacement from (near)-edge surface sites.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.7
Times cited: 24
DOI: 10.1021/acs.jpclett.0c00870
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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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“Effectiveness of reducing the influence of CTAB at the surface of metal nanoparticles during in situ heating studies by TEM”. De Meyer R, Albrecht W, Bals S, Micron 144, 103036 (2021). http://doi.org/10.1016/j.micron.2021.103036
Abstract: In situ TEM is a valuable technique to offer novel insights in the behavior of nanomaterials under various conditions. However, interpretation of in situ experiments is not straightforward since the electron beam can impact the outcome of such measurements. For example, ligands surrounding metal nanoparticles transform into a protective carbon layer upon electron beam irradiation and may impact the apparent thermal stability during in situ heating experiments. In this work, we explore the effect of different treatments typically proposed to remove such ligands. We found that plasma treatment prior to heating experiments for Au nanorods and nanostars increased the apparent thermal stability of the nanoparticles, while an activated carbon treatment resulted in a decrease of the observed thermal stability. Treatment with HCl barely changed the experimental outcome. These results demonstrate the importance of carefully selecting pre-treatments procedures during in situ heating experiments.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.98
DOI: 10.1016/j.micron.2021.103036
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“The design of magneto-plasmonic nanostructures formed by magnetic Prussian Blue-type nanocrystals decorated with Au nanoparticles”. Sanchis-Gual R, Susic I, Torres-Cavanillas R, Arenas-Esteban D, Bals S, Mallah T, Coronado-Puchau M, Coronado E, Chemical Communications 57, 1903 (2021). http://doi.org/10.1039/D0CC08034A
Abstract: We have developed a general protocol for the preparation of hybrid nanostructures formed by nanoparticles (NPs) of molecule-based magnets based on Prussian Blue Analogues (PBAs) decorated with plasmonic Au NPs of different shapes. By adjusting the pH, Au NPs can be attached preferentially along the edges of the PBA or randomly on the surface. The protocol allows tuning the plasmonic properties of the hybrids in the whole visible spectrum.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.319
Times cited: 5
DOI: 10.1039/D0CC08034A
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“Halide perovskite-lead chalcohalide nanocrystal heterostructures”. Imran M, Peng L, Pianetti A, Pinchetti V, Ramade J, Zito J, Di Stasio F, Buha J, Toso S, Song J, Infante I, Bals S, Brovelli S, Manna L, Journal Of The American Chemical Society 143, 1435 (2021). http://doi.org/10.1021/JACS.0C10916
Abstract: We report the synthesis of colloidal CsPbX3-Pb4S3Br2 (X = Cl, Br, I) nanocrystal heterostructures, providing an example of a sharp and atomically resolved epitaxial interface between a metal halide perovskite and a non-perovskite lattice. The CsPbBr3-Pb4S3Br2 nanocrystals are prepared by a two-step direct synthesis using preformed subnanometer CsPbBr3 clusters. Density functional theory calculations indicate the creation of a quasi-type II alignment at the heterointerface as well as the formation of localized trap states, promoting ultrafast separation of photogenerated excitons and carrier trapping, as confirmed by spectroscopic experiments. Postsynthesis reaction with either Cl- or I- ions delivers the corresponding CsPbCI3-Pb4S3Br2 and CsPbI3-Pb4S3Br2 heterostructures, thus enabling anion exchange only in the perovskite domain. An increased structural rigidity is conferred to the perovskite lattice when it is interfaced with the chalcohalide lattice. This is attested by the improved stability of the metastable gamma phase (or “black” phase) of CsPbI3 in the CsPbI3-Pb4S3Br2 heterostructure.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 54
DOI: 10.1021/JACS.0C10916
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“Seeded growth combined with cation exchange for the synthesis of anisotropic Cu2-xS/ZnS, Cu2-xS, and CuInS2 nanorods”. Xia C, Pedrazo-Tardajos A, Wang D, Meeldijk JD, Gerritsen HC, Bals S, de Donega CM, Chemistry of materials 33, 102 (2021). http://doi.org/10.1021/ACS.CHEMMATER.0C02817
Abstract: Colloidal copper(I) sulfide (Cu2-xS) nanocrystals (NCs) have attracted much attention for a wide range of applications because of their unique optoelectronic properties, driving scientists to explore the potential of using Cu2-xS NCs as seeds in the synthesis of heteronanocrystals to achieve new multifunctional materials. Herein, we developed a multistep synthesis strategy toward Cu2-xS/ZnS heteronanorods. The Janus-type Cu2-xS/ZnS heteronanorods are obtained by the injection of hexagonal high-chalcocite Cu2-xS seed NCs in a hot zinc oleate solution in the presence of suitable surfactants, 20 s after the injection of sulfur precursors. The Cu2-xS seed NCs undergo rapid aggregation and coalescence in the first few seconds after the injection, forming larger NCs that act as the effective seeds for heteronucleation and growth of ZnS. The ZnS heteronucleation occurs on a single (100) facet of the Cu2-xS seed NCs and is followed by fast anisotropic growth along a direction that is perpendicular to the c-axis, thus leading to Cu2-xS/ZnS Janus-type heteronanorods with a sharp heterointerface. Interestingly, the high-chalcocite crystal structure of the injected Cu2-xS seed NCs is preserved in the Cu2-xS segments of the heteronanorods because of the highthermodynamic stability of this Cu2-xS phase. The Cu2-xS/ZnS heteronanorods are subsequently converted into single-component Cu2-xS and CuInS2 nanorods by postsynthetic topotactic cation exchange. This work expands the possibilities for the rational synthesis of colloidal multicomponent heteronanorods by allowing the design principles of postsynthetic heteroepitaxial seeded growth and nanoscale cation exchange to be combined, yielding access to a plethora of multicomponent heteronanorods with diameters in the quantum confinement regime.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 10
DOI: 10.1021/ACS.CHEMMATER.0C02817
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“Three-Dimensional Nanoparticle Transformations Captured by an Electron Microscope”. Albrecht W, Van Aert S, Bals S, Accounts Of Chemical Research 54, 1189 (2021). http://doi.org/10.1021/acs.accounts.0c00711
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 20.268
Times cited: 12
DOI: 10.1021/acs.accounts.0c00711
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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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“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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“Fast electron low dose tomography for beam sensitive materials”. Esteban DA, Vanrompay H, Skorikov A, Béché, A, Verbeeck J, Freitag B, Bals S, Microscopy And Microanalysis 27, 2116 (2021). http://doi.org/10.1017/S1431927621007649
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.891
DOI: 10.1017/S1431927621007649
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“Linearized radially polarized light for improved precision in strain measurements using micro-Raman spectroscopy”. Prabhakara V, Nuytten T, Bender H, Vandervorst W, Bals S, Verbeeck J, Optics Express 29, 34531 (2021). http://doi.org/10.1364/OE.434726
Abstract: Strain engineering in semiconductor transistor devices has become vital in the semiconductor industry due to the ever-increasing need for performance enhancement at the nanoscale. Raman spectroscopy is a non-invasive measurement technique with high sensitivity to mechanical stress that does not require any special sample preparation procedures in comparison to characterization involving transmission electron microscopy (TEM), making it suitable for inline strain measurement in the semiconductor industry. Indeed, at present, strain measurements using Raman spectroscopy are already routinely carried out in semiconductor devices as it is cost effective, fast and non-destructive. In this paper we explore the usage of linearized radially polarized light as an excitation source, which does provide significantly enhanced accuracy and precision as compared to linearly polarized light for this application. Numerical simulations are done to quantitatively evaluate the electric field intensities that contribute to this enhanced sensitivity. We benchmark the experimental results against TEM diffraction-based techniques like nano-beam diffraction and Bessel diffraction. Differences between both approaches are assigned to strain relaxation due to sample thinning required in TEM setups, demonstrating the benefit of Raman for nondestructive inline testing.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.307
Times cited: 2
DOI: 10.1364/OE.434726
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“From CdSe nanoplatelets to quantum rings by thermochemical edge reconfiguration”. Salzmann BBV, Vliem JF, Maaskant DN, Post LC, Li C, Bals S, Vanmaekelbergh D, Chemistry Of Materials 33, 6853 (2021). http://doi.org/10.1021/ACS.CHEMMATER.1C01618
Abstract: The variation in the shape of colloidal semiconductor nanocrystals (NCs) remains intriguing. This interest goes beyond crystallography as the shape of the NC determines its energy levels and optoelectronic properties. While thermodynamic arguments point to a few or just a single shape(s), terminated by the most stable crystal facets, a remarkable variation in NC shape has been reported for many different compounds. For instance, for the well-studied case of CdSe, close-to-spherical quantum dots, rods, two-dimensional nanoplatelets, and quantum rings have been reported. Here, we report how two-dimensional CdSe nanoplatelets reshape into quantum rings. We monitor the reshaping in real time by combining atomically resolved structural characterization with optical absorption and photoluminescence spectroscopy. We observe that CdSe units leave the vertical sides of the edges and recrystallize on the top and bottom edges of the nanoplatelets, resulting in a thickening of the rims. The formation of a central hole, rendering the shape into a ring, only occurs at a more elevated temperature.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 7
DOI: 10.1021/ACS.CHEMMATER.1C01618
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“Phase transformation behavior of a two-dimensional zeolite”. Bae J, Cichocka MO, Zhang Y, Bacsik Z, Bals S, Zou X, Willhammar T, Hong SB, Angewandte Chemie: international edition in English 58, 10230 (2019). http://doi.org/10.1002/ANIE.201904825
Abstract: Understanding the molecular-level mechanisms of phase transformation in solids is of fundamental interest for functional materials such as zeolites. Two-dimensional (2D) zeolites, when used as shape-selective catalysts, can offer improved access to the catalytically active sites and a shortened diffusion length in comparison with their 3D analogues. However, few materials are known to maintain both their intralayer microporosity and structure during calcination for organic structure-directing agent (SDA) removal. Herein we report that PST-9, a new 2D zeolite which has been synthesized via the multiple inorganic cation approach and fulfills the requirements for true layered zeolites, can be transformed into the small-pore zeolite EU-12 under its crystallization conditions through the single-layer folding process, but not through the traditional dissolution/recrystallization route. We also show that zeolite crystal growth pathway can differ according to the type of organic SDAs employed.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 2
DOI: 10.1002/ANIE.201904825
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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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