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“Direct Observation of Luminescent Silver Clusters Confined in Faujasite Zeolites”. Altantzis T, Coutino-Gonzalez E, Baekelant W, Martinez GT, Abakumov AM, Van Tendeloo G, Roeffaers MBJ, Bals S, Hofkens J, ACS nano 10, 7604 (2016). http://doi.org/10.1021/acsnano.6b02834
Abstract: One of the ultimate goals in the study of metal clusters is the correlation between the atomic-scale organization and their physicochemical properties. However, direct observation of the atomic organization of such minuscule metal clusters is heavily hindered by radiation damage imposed by the different characterization techniques. We present direct evidence of the structural arrangement, at an atomic level, of luminescent silver species stabilized in faujasite (FAU) zeolites using aberration-corrected scanning transmission electron microscopy. Two different silver clusters were identified in Ag-FAU zeolites, a trinuclear silver species associated with green emission and a tetranuclear silver species related to yellow emission. By combining direct imaging with complementary information obtained from X-ray powder diffraction and Rietveld analysis, we were able to elucidate the main differences at an atomic scale between luminescent (heat-treated) and nonluminescent (cation-exchanged) Ag-FAU zeolites. It is expected that such insights will trigger the directed synthesis of functional metal nanocluster-zeolite composites with tailored luminescent properties.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.942
Times cited: 57
DOI: 10.1021/acsnano.6b02834
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“Facile morphology-controlled synthesis of organolead iodide perovskite nanocrystals using binary capping agents”. Debroye E, Yuan H, Bladt E, Baekelant W, Van der Auweraer M, Hofkens J, Bals S, Roeffaers MBJ, ChemNanoMat : chemistry of nanomaterials for energy, biology and more 3, 223 (2017). http://doi.org/10.1002/CNMA.201700006
Abstract: Controlling the morphology of organolead halide perovskite crystals is crucial to a fundamental understanding of the materials and to tune their properties for device applications. Here, we report a facile solution-based method for morphology-controlled synthesis of rod-like and plate-like organolead halide perovskite nanocrystals using binary capping agents. The morphology control is likely due to an interplay between surface binding kinetics of the two capping agents at different crystal facets. By high-resolution scanning transmission electron microscopy, we show that the obtained nanocrystals are monocrystalline. Moreover, long photoluminescence decay times of the nanocrystals indicate long charge diffusion lengths and low trap/defect densities. Our results pave the way for large-scale solution synthesis of organolead halide perovskite nanocrystals with controlled morphology for future device applications.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 2.937
Times cited: 19
DOI: 10.1002/CNMA.201700006
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“Imaging heterogeneously distributed photo-active traps in perovskite single crystals”. Yuan H, Debroye E, Bladt E, Lu G, Keshavarz M, Janssen KPF, Roeffaers MBJ, Bals S, Sargent EH, Hofkens J, Advanced materials 30, 1705494 (2018). http://doi.org/10.1002/ADMA.201705494
Abstract: Organic-inorganic halide perovskites (OIHPs) have demonstrated outstanding energy conversion efficiency in solar cells and light-emitting devices. In spite of intensive developments in both materials and devices, electronic traps and defects that significantly affect their device properties remain under-investigated. Particularly, it remains challenging to identify and to resolve traps individually at the nanoscopic scale. Here, photo-active traps (PATs) are mapped over OIHP nanocrystal morphology of different crystallinity by means of correlative optical differential super-resolution localization microscopy (Delta-SRLM) and electron microscopy. Stochastic and monolithic photoluminescence intermittency due to individual PATs is observed on monocrystalline and polycrystalline OIHP nanocrystals. Delta-SRLM reveals a heterogeneous PAT distribution across nanocrystals and determines the PAT density to be 1.3 x 10(14) and 8 x 10(13) cm(-3) for polycrystalline and for monocrystalline nanocrystals, respectively. The higher PAT density in polycrystalline nanocrystals is likely related to an increased defect density. Moreover, monocrystalline nanocrystals that are prepared in an oxygen and moisture-free environment show a similar PAT density as that prepared at ambient conditions, excluding oxygen or moisture as chief causes of PATs. Hence, it is conduded that the PATs come from inherent structural defects in the material, which suggests that the PAT density can be reduced by improving crystalline quality of the material.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 29
DOI: 10.1002/ADMA.201705494
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“Dopant-induced electron localization drives CO2 reduction to C2 hydrocarbons”. Zhou Y, Che F, Liu M, Zou C, Liang Z, De Luna P, Yuan H, Li J, Wang Z, Xie H, Li H, Chen P, Bladt E, Quintero-Bermudez R, Sham T-K, Bals S, Hofkens J, Sinton D, Chen G, Sargent EH, Nature chemistry 10, 974 (2018). http://doi.org/10.1038/S41557-018-0092-X
Abstract: The electrochemical reduction of CO2 to multi-carbon products has attracted much attention because it provides an avenue to the synthesis of value-added carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the efficiency of CO2 conversion to C-2 products remains below that necessary for its implementation at scale. Modifying the local electronic structure of copper with positive valence sites has been predicted to boost conversion to C-2 products. Here, we use boron to tune the ratio of Cu delta+ to Cu-0 active sites and improve both stability and C-2-product generation. Simulations show that the ability to tune the average oxidation state of copper enables control over CO adsorption and dimerization, and makes it possible to implement a preference for the electrosynthesis of C-2 products. We report experimentally a C-2 Faradaic efficiency of 79 +/- 2% on boron-doped copper catalysts and further show that boron doping leads to catalysts that are stable for in excess of similar to 40 hours while electrochemically reducing CO2 to multi-carbon hydrocarbons.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 25.87
Times cited: 700
DOI: 10.1038/S41557-018-0092-X
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“A Facet-Specific Quantum Dot Passivation Strategy for Colloid Management and Efficient Infrared Photovoltaics”. Kim Y, Che F, Jo JW, Choi J, de Arquer FPG, Voznyy O, Sun B, Kim J, Choi M-J, Quintero-Bermudez R, Fan F, Tan CS, Bladt E, Walters G, Proppe AH, Zou C, Yuan H, Bals S, Hofkens J, Roeffaers MBJ, Hoogland S, Sargent EH, Advanced materials 31, 1805580 (2019). http://doi.org/10.1002/ADMA.201805580
Abstract: Colloidal nanocrystals combine size- and facet-dependent properties with solution processing. They offer thus a compelling suite of materials for technological applications. Their size- and facet-tunable features are studied in synthesis; however, to exploit their features in optoelectronic devices, it will be essential to translate control over size and facets from the colloid all the way to the film. Larger-diameter colloidal quantum dots (CQDs) offer the attractive possibility of harvesting infrared (IR) solar energy beyond absorption of silicon photovoltaics. These CQDs exhibit facets (nonpolar (100)) undisplayed in small-diameter CQDs; and the materials chemistry of smaller nanocrystals fails consequently to translate to materials for the short-wavelength IR regime. A new colloidal management strategy targeting the passivation of both (100) and (111) facets is demonstrated using distinct choices of cations and anions. The approach leads to narrow-bandgap CQDs with impressive colloidal stability and photoluminescence quantum yield. Photophysical studies confirm a reduction both in Stokes shift (approximate to 47 meV) and Urbach tail (approximate to 29 meV). This approach provides a approximate to 50% increase in the power conversion efficiency of IR photovoltaics compared to controls, and a approximate to 70% external quantum efficiency at their excitonic peak.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 74
DOI: 10.1002/ADMA.201805580
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“Edge stabilization in reduced-dimensional perovskites”. Quan LN, Ma D, Zhao Y, Voznyy O, Yuan H, Bladt E, Pan J, de Arquer FPG, Sabatini R, Piontkowski Z, Emwas A-H, Todorovic P, Quintero-Bermudez R, Walters G, Fan JZ, Liu M, Tan H, Saidaminov M I, Gao L, Li Y, Anjum DH, Wei N, Tang J, McCamant DW, Roeffaers MBJ, Bals S, Hofkens J, Bakr OM, Lu Z-H, Sargent EH, Nature Communications 11, 170 (2020). http://doi.org/10.1038/S41467-019-13944-2
Abstract: Reduced-dimensional perovskites are attractive light-emitting materials due to their efficient luminescence, color purity, tunable bandgap, and structural diversity. A major limitation in perovskite light-emitting diodes is their limited operational stability. Here we demonstrate that rapid photodegradation arises from edge-initiated photooxidation, wherein oxidative attack is powered by photogenerated and electrically-injected carriers that diffuse to the nanoplatelet edges and produce superoxide. We report an edge-stabilization strategy wherein phosphine oxides passivate unsaturated lead sites during perovskite crystallization. With this approach, we synthesize reduced-dimensional perovskites that exhibit 97 +/- 3% photoluminescence quantum yields and stabilities that exceed 300 h upon continuous illumination in an air ambient. We achieve green-emitting devices with a peak external quantum efficiency (EQE) of 14% at 1000 cd m(-2); their maximum luminance is 4.5 x 10(4) cd m(-2) (corresponding to an EQE of 5%); and, at 4000 cd m(-2), they achieve an operational half-lifetime of 3.5 h.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 16.6
Times cited: 147
DOI: 10.1038/S41467-019-13944-2
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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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“State of the art and prospects for Halide Perovskite Nanocrystals”. Dey A, Ye J, De A, Debroye E, Ha SK, Bladt E, Kshirsagar AS, Wang Z, Yin J, Wang Y, Quan LN, Yan F, Gao M, Li X, Shamsi J, Debnath T, Cao M, Scheel MA, Kumar S, Steele JA, Gerhard M, Chouhan L, Xu K, Wu X-gang, Li Y, Zhang Y, Dutta A, Han C, Vincon I, Rogach AL, Nag A, Samanta A, Korgel BA, Shih C-J, Gamelin DR, Son DH, Zeng H, Zhong H, Sun H, Demir HV, Scheblykin IG, Mora-Sero I, Stolarczyk JK, Zhang JZ, Feldmann J, Hofkens J, Luther JM, Perez-Prieto J, Li L, Manna L, Bodnarchuk M I, Kovalenko M V, Roeffaers MBJ, Pradhan N, Mohammed OF, Bakr OM, Yang P, Muller-Buschbaum P, Kamat P V, Bao Q, Zhang Q, Krahne R, Galian RE, Stranks SD, Bals S, Biju V, Tisdale WA, Yan Y, Hoye RLZ, Polavarapu L, Acs Nano 15, 10775 (2021). http://doi.org/10.1021/ACSNANO.0C08903
Abstract: Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 13.942
Times cited: 538
DOI: 10.1021/ACSNANO.0C08903
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“Atomic-scale detection of individual lead clusters confined in Linde Type A zeolites”. Fatermans J, Romolini G, Altantzis T, Hofkens J, Roeffaers MBJ, Bals S, Van Aert S, Nanoscale (2022). http://doi.org/10.1039/D2NR01819E
Abstract: Structural analysis of metal clusters confined in nanoporous materials is typically performed by X-ray-driven techniques. Although X-ray analysis has proved its strength in the characterization of metal clusters, it provides averaged structural information. Therefore, we here present an alternative workflow for bringing the characterization of confined metal clusters towards the local scale. This workflow is based on the combination of aberration-corrected transmission electron microscopy (TEM), TEM image simulations, and powder X-ray diffraction (XRD) with advanced statistical techniques. In this manner, we were able to characterize the clustering of Pb atoms in Linde Type A (LTA) zeolites with Pb loadings as low as 5 wt%. Moreover, individual Pb clusters could be directly detected. The proposed methodology thus enables a local-scale characterization of confined metal clusters in zeolites. This is important for further elucidation of the connection between the structure and the physicochemical properties of such systems.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 6.7
Times cited: 2
DOI: 10.1039/D2NR01819E
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“Additivity of Atomic Strain Fields as a Tool to Strain-Engineering Phase-Stabilized CsPbI3Perovskites”. Teunissen JL, Braeckevelt T, Skvortsova I, Guo J, Pradhan B, Debroye E, Roeffaers MBJ, Hofkens J, Van Aert S, Bals S, Rogge SMJ, Van Speybroeck V, The Journal of Physical Chemistry C 127, 23400 (2023). http://doi.org/10.1021/acs.jpcc.3c05770
Abstract: CsPbI3 is a promising perovskite material for photovoltaic applications in its photoactive perovskite or black phase. However, the material degrades to a photovoltaically inactive or yellow phase at room temperature. Various mitigation strategies are currently being developed to increase the lifetime of the black phase, many of which rely on inducing strains in the material that hinder the black-to-yellow phase transition. Physical insight into how these strategies exactly induce strain as well as knowledge of the spatial extent over which these strains impact the material is crucial to optimize these approaches but is still lacking. Herein, we combine machine learning potential-based molecular dynamics simulations with our in silico strain engineering approach to accurately quantify strained large-scale atomic structures on a nanosecond time scale. To this end, we first model the strain fields introduced by atomic substitutions as they form the most elementary strain sources. We demonstrate that the magnitude of the induced strain fields decays exponentially with the distance from the strain source, following a decay rate that is largely independent of the specific substitution. Second, we show that the total strain field induced by multiple strain sources can be predicted to an excellent approximation by summing the strain fields of each individual source. Finally, through a case study, we illustrate how this additive character allows us to explain how complex strain fields, induced by spatially extended strain sources, can be predicted by adequately combining the strain fields caused by local strain sources. Hence, the strain additivity proposed here can be adopted to further our insight into the complex strain behavior in perovskites and to design strain from the atomic level onward to enhance their sought-after phase stability.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 3.7
DOI: 10.1021/acs.jpcc.3c05770
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“Achieving High Moisture Tolerance in Pseudohalide Perovskite Nanocrystals for Light-Emitting Diode Application”. Bhatia H, Keshavarz M, Martin C, Van Gaal L, Zhang Y, de Coen B, Schrenker NJ, Valli D, Ottesen M, Bremholm M, Van de Vondel J, Bals S, Hofkens J, Debroye E, ACS Applied Optical Materials 1, 1184 (2023). http://doi.org/10.1021/acsaom.3c00096
Abstract: The addition of potassium thiocyanate (KSCN) to the FAPbBr3 structure and subsequent post-treatment of nanocrystals (NCs) lead to high quantum confinement, resulting in a photoluminescent quantum yield (PLQY) approaching unity and microsecond decay times. This synergistic approach demonstrated exceptional stability under humid conditions, retaining 70% of the PLQY for over a month, while the untreated NCs degrade within 24 h. Additionally, the devices incorporating the post-treated NCs displayed 1.5% external quantum efficiency (EQE), a 5-fold improvement over untreated devices. These results provide promising opportunities for the use of perovskites in moisture-stable optoelectronics.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
DOI: 10.1021/acsaom.3c00096
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“Optical encoding of luminescent carbon nanodots in confined spaces”. Bartholomeeusen E, De Cremer G, Kennes K, Hammond C, Hermans I, Lu J-B, Schryvers D, Jacobs PA, Roeffaers MBJ, Hofkens J, Sels BF, Coutino-Gonzalez E, Chemical Communications 57, 11952 (2021). http://doi.org/10.1039/D1CC04777A
Abstract: Stable emissive carbon nanodots were generated in zeolite crystals using near infrared photon irradiation gradually converting the occluded organic template, originally used to synthesize the zeolite crystals, into discrete luminescent species consisting of nano-sized carbogenic fluorophores, as ascertained using Raman microscopy, and steady-state and time-resolved spectroscopic techniques. Photoactivation in a confocal laser fluorescence microscope allows 3D resolved writing of luminescent carbon nanodot patterns inside zeolites providing a cost-effective and non-toxic alternative to previously reported metal-based nanoclusters confined in zeolites, and opens up opportunities in bio-labelling and sensing applications.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.319
DOI: 10.1039/D1CC04777A
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“Deciphering the role of water in promoting the optoelectronic performance of surface-engineered lead halide perovskite nanocrystals”. Bhatia H, Martin C, Keshavarz M, Dovgaliuk I, Schrenker NJ, Ottesen M, Qiu W, Fron E, Bremholm M, Van de Vondel J, Bals S, Roeffaers MBJ, Hofkens J, Debroye E, ACS applied materials and interfaces 15, 7294 (2023). http://doi.org/10.1021/ACSAMI.2C20605
Abstract: Lead halide perovskites are promising candidates for applicability is limited by their structural instability toward moisture. Although a deliberate addition of water to the precursor solution has recently been shown to improve the crystallinity and optical properties of perovskites, the corresponding thin films still do not exhibit a near-unity quantum yield. Herein, we report that the direct addition of a minute amount of water to post-treated substantially enhances the stability while achieving a 95% photoluminescence quantum yield in a NC thin film. We unveil the mechanism of how moisture assists in the formation of an additional NH4Br component. Alongside, we demonstrate the crucial role of moisture in assisting localized etching of the perovskite crystal, facilitating the partial incorporation of NH4+, which is key for improved performance under ambient conditions. Finally, as a proof-of-concept, the application of post-treated and watertreated perovskites is tested in LEDs, with the latter exhibiting a superior performance, offering opportunities toward commercial application in moisture-stable optoelectronics.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.5
Times cited: 3
DOI: 10.1021/ACSAMI.2C20605
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“Cs3Bi2Br9 nanoparticles decorated C3N4 nanotubes composite photocatalyst for highly selective oxidation of benzylic alcohol”. Ding Y, Wang C, Bandaru S, Pei L, Zheng R, Hau Ng Y, Arenas Esteban D, Bals S, Zhong J, Hofkens J, Van Tendeloo G, Roeffaers MBJ, Chen L-H, Su B-L, Journal of Colloid and Interface Science 672, 600 (2024). http://doi.org/10.1016/j.jcis.2024.06.017
Abstract: Solar-light driven oxidation of benzylic alcohols over photocatalysts endows significant prospects in value-added organics evolution owing to its facile, inexpensive and sustainable process. However, the unsatisfactory performance of actual photocatalysts due to the inefficient charge separation, low photoredox potential and sluggish surface reaction impedes the practical application of this process. Herein, we developed an innovative Z-Scheme Cs3BiBr9 nanoparticles@porous C3N4 tubes (CBB-NP@P-tube-CN) heterojunction photocatalyst for highly selective benzyl alcohol oxidation. Such composite combining increased photo-oxidation potential, Z-Scheme charge migration route as well as the structural advantages of porous tubular C3N4 ensures the accelerated mass and ions diffusion kinetics, the fast photoinduced carriers dissociation and sufficient photoredox potentials. The CBB-NP@P-tube-CN photocatalyst demonstrates an exceptional performance for selective photo-oxidation of benzylic alcohol into benzaldehyde with 19, 14 and 3 times higher benzylic alcohols conversion rate than those of C3N4 nanotubes, Cs3Bi2Br9 and Cs3Bi2Br9@bulk C3N4 photocatalysts, respectively. This work offers a sustainable photocatalytic system based on lead-free halide perovskite toward large scale solar-light driven value-added chemicals production.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 9.9
DOI: 10.1016/j.jcis.2024.06.017
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“Investigation of the Octahedral Network Structure in Formamidinium Lead Bromide Nanocrystals by Low-Dose Scanning Transmission Electron Microscopy”. Schrenker NJ, Braeckevelt T, De Backer A, Livakas N, Yu C-P, Friedrich T, Roeffaers MBJ, Hofkens J, Verbeeck J, Manna L, Van Speybroeck V, Van Aert S, Bals S, Nano Letters 24, 10936 (2024). http://doi.org/10.1021/acs.nanolett.4c02811
Abstract: Metal halide perovskites (MHP) are highly promising semiconductors. In this study, we focus on FAPbBr3 nanocrystals, which are of great interest for green light-emitting diodes. Structural parameters significantly impact the properties of MHPs and are linked to phase instability, which hampers long-term applications. Clearly, there is a need for local and precise characterization techniques at the atomic scale, such as transmission electron microscopy. Because of the high electron beam sensitivity of MHPs, these investigations are extremely challenging. Here, we applied a low-dose method based on four-dimensional scanning transmission electron microscopy. We quantified the observed elongation of the projections of the Br atomic columns, suggesting an alternation in the position of the Br atoms perpendicular to the Pb–Br–Pb bonds. Together with molecular dynamics simulations, these results remarkably reveal local distortions in an on-average cubic structure. Additionally, this study provides an approach to prospectively investigating the fundamental degradation mechanisms of MHPs.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 10.8
DOI: 10.1021/acs.nanolett.4c02811
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“The beneficial effect of CO2 in the low temperature synthesis of high quality carbon nanofibers and thin multiwalled carbon nanotubes from CH_{4} over Ni catalysts”. Corthals S, van Noyen J, Geboers J, Vosch T, Liang D, Ke X, Hofkens J, Van Tendeloo G, Jacobs P, Sels B, Carbon 50, 372 (2012). http://doi.org/10.1016/j.carbon.2011.08.047
Abstract: A low temperature chemical vapor deposition method is described for converting CH4 into high-quality carbon nanofibers (CNFs) using a Ni catalyst supported on either spinel or perovskite oxides in the presence of CO2. The addition of CO2 has a significant influence on CNF purity and stability, while the CNF diameter distribution is significantly narrowed. Ultimately, the addition of CO2 changes the CNF structure from fishbone fibers to thin multiwalled carbon nanotubes. A new in situ cooling principle taking into account dry reforming chemistry and thermodynamics is introduced to account for the structural effects of CO2.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.337
Times cited: 26
DOI: 10.1016/j.carbon.2011.08.047
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“Control of surface plasmon localization via self-assembly of silver nanoparticles along silver nanowires”. Tran ML, Centeno SP, Hutchison JA, Engelkamp H, Liang D, Van Tendeloo G, Sels BF, Hofkens J, Uji-i H, Journal of the American Chemical Society 130, 17240 (2008). http://doi.org/10.1021/ja807218e
Abstract: A simple and low-cost method to create metal−metal hybrid nanostructures possessing fairly regularly spaced hot-spots of surface plasmon resonances is proposed. The nanohybrid structure was prepared via self-assembly during a simple drop-casting procedure, using chemically synthesized silver nanowires and silver nanoparticles prepared in a single batch of a polyol process. Wide field illumination of these nanohybrids produced hot-spots with spacings of around 500 nm to 1 ìm. The intensity of the emission/scattering from the hot-spots fluctuates over time. The proposed structure can be useful for the development of molecular-sensors or as a substrate for surface enhanced Raman/fluorescence spectroscopy.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 51
DOI: 10.1021/ja807218e
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“Light-assisted nucleation of silver nanowires during polyol synthesis”. Lin H, Ohta T, Paul A, Hutchison JA, Kirilenko D, Lebedev O, Van Tendeloo G, Hofkens J, Uji-i H, Journal of photochemistry and photobiology: A: chemistry 221, 220 (2011). http://doi.org/10.1016/j.jphotochem.2011.04.015
Abstract: This report describes the effect of light irradiation on the synthesis of silver nanowires by the well-known polyol method. High quality nanowires are produced in high yields when the reaction suspension is irradiated with 400500 nm light during the nucleation stage. These studies suggest that light accelerates the formation of the nanoparticle seeds most appropriate for nanowire growth.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.625
Times cited: 24
DOI: 10.1016/j.jphotochem.2011.04.015
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“Luminescence of oxyfluoride glasses co-doped with Ag nanoclusters and Yb3+ ions”. Tikhomirov VK, Vosch T, Fron E, Rodríguez VD, Velázquez JJ, Kirilenko D, Van Tendeloo G, Hofkens J, Van der Auweraer M, Moshchalkov VV, RSC advances 2, 1496 (2012). http://doi.org/10.1039/c1ra01026c
Abstract: Bulk oxyfluoride glasses co-doped with Ag nanoclusters and Yb3+ ions have been prepared by a melt quenching technique. When excited in the absorption band of the Ag nanoclusters between 300 to 500 nm, these glasses emit a broad band characteristic of the Ag nanoclusters between 400 to 750 nm as well as an emission band between 900 to 1100 nm, originating from Yb3+ ions. The intensity ratio of the Yb3+/Ag emission bands increases with the Ag doping level at a fixed concentration of Yb3+, indicating the presence of energy transfer mechanism from the Ag nanoclusters to the Yb3+ ions. Comparison of time-resolved decay kinetics of the luminescence in the respectively Ag nanocluster-Yb3+ co-doped and single Ag nanocluster doped glasses, hints towards an energy transfer from the red and infrared emitting Ag nanoclusters to the Yb3+ ions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 46
DOI: 10.1039/c1ra01026c
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“Single layer vs bilayer graphene : a comparative study of the effects of oxygen plasma treatment on their electronic and optical properties”. Nourbakhsh A, Cantoro M, Klekachev AV, Pourtois G, Vosch T, Hofkens J, van der Veen MH, Heyns MM, de Gendt S, Sels BF, The journal of physical chemistry: C : nanomaterials and interfaces 115, 16619 (2011). http://doi.org/10.1021/jp203010z
Abstract: This contribution presents the effects of a mild O2 plasma treatment on the structural, optical, and electrical properties of single-layer (SLG) and bilayer graphene (BLG). Unexpectedly, we observe only photoluminescence in the SLG parts of a graphene flake composed of regions of various thickness upon O2 plasma treatment, whereas the BLG and few-layer graphene (FLG) parts remain optically unchanged. Confirmed with X-ray photoelectron spectroscopy (XPS) that O2 plasma induces epoxide and hydroxyl-like groups in graphene, density functional theory (DFT) calculations are carried out on representative epoxidized and hydroxylated SLG and BLG models to predict density of states (DOS) and band structures. Sufficiently oxidized SLG shows a bandgap and thus loss of semimetallic behavior, while oxidized BLG maintains its semimetallic behavior even at high oxygen density in agreement with the results of the photoluminescence spectroscopy (PL) experiments. DFT calculations confirm that the Fermi velocity in epoxidized BLG is remarkably comparable with that of pristine SLG, pointing to a similarity of electronic band structure. The similarity is also experimentally demonstrated by the electrical characterization of a plasma-treated BLG-FET. As expected from the electronegative oxygen adatoms in the graphene, epoxidized BLG presents conductive features typical of hole doping. Moreover, the electrical characteristics suggest band structures closely related to that of epoxidized graphene while deviating from that of hydroxylated graphene. Finally, upon O2 plasma treatment of BLG, the four-component 2D peak around 2700 cm1 in the Raman spectrum evolves into a single Lorentzian line, very like the 2D peak of pristine SLG. Summarizing, the data in this contribution recommend that a controlled O2 plasma treatment, which is compatible with CMOS process flow in contrast to wet chemical oxidation methods, provides an efficient and valuable technique to exploit the transport properties of the bottom layer of BLG.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.536
Times cited: 46
DOI: 10.1021/jp203010z
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“Luminescence of fixed site Ag nanoclusters in a simple oxyfluoride glass host and plasmon absorption of amorphous Ag nanoparticles in a complex oxyfluoride glass host”. Shestakov MV, Meledina M, Turner S, Baekelant W, Verellen N, Chen X, Hofkens J, Van Tendeloo G, Moshchalkov VV, Proceedings of the Society of Photo-optical Instrumentation Engineers
T2 –, 8th International Conference on Photonics, Devices, and System VI, AUG 27-29, 2014, Prague, CZECH REPUBLIC , Unsp 94501n (2015). http://doi.org/10.1117/12.2068198
Abstract: Ag nanocluster-doped glasses have been prepared by a conventional melt-quenching method. The effect of melt temperature and dwell time on the formation of Ag nanoclusters and Ag nanoparticles in simple host oxyfluoride glasses has been studied. The increase of melt temperature and dwell time results in the dissolution of Ag nanoparticles and substantial red-shift of absorption and photoluminescence spectra of the prepared glasses. The quantum yield of the glasses is similar to 5% and does not depend on melt temperature and dwell time. The prepared glasses may be used as red phosphors or down-conversion layers for solar-cells.
Keywords: P1 Proceeding; Electron microscopy for materials research (EMAT)
DOI: 10.1117/12.2068198
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“Response to mixed substrate feeds of the structure and activity of a linuron-degrading triple-species biofilm”. Bruegelmans P, Horemans B, Hofkens J, Springael D, Research in microbiology 161, 660 (2010). http://doi.org/10.1016/J.RESMIC.2010.06.006
Abstract: We sought to determine whether the pesticide-degrading performance of a multi-species bacterial biofilm is affected by co-occurrence of multiple nutrient sources Thus, the 3-(3,4-dichlorophenyl)-l-methoxy-l-methyl urea (linuron)-degrading activity of a triple-species linuron-degrading consortium, cultivated in continuous flow biofilm systems, was monitored when exposed to mixed substrate feeds which contained, in addition to linuron, readily assimilated carbon (i e citrate and trypticase soy broth) and/or nitrogen (i e ammonium) sources The addition of alternative carbon sources at different concentrations resulted in diminished linuron degradation efficiency In addition, the efficiency of removal of the linuron metabolite 3,4-dichloroaniline was affected These effects might be attributed to catabolic repression of the linuron metabolic pathway in the presence of alternative carbon substrates Moreover, each nutrient condition resulted in a particular biofilm composition and a particular spatial and structural organization, which might also be related to the performance of the biofilm community Results show that the activity of pesticide-degrading biofilms strongly depends on prevailing nutrient conditions and that the ideal biofilm configuration and activity, as observed under selective conditions, does not exist in real-life environmental conditions where mixtures of substrates are often present (C) 2010 Elsevier Masson SAS All rights reserved.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1016/J.RESMIC.2010.06.006
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“Rashba-type band splitting effect in 2D (PEA)₂PbI₄, perovskites and its impact on exciton-phonon coupling”. Ghosh S, Pradhan B, Bandyopadhyay A, Skvortsova I, Zhang Y, Sternemann C, Paulus M, Bals S, Hofkens J, Karki KJ, Materny A, The journal of physical chemistry letters 15, 7970 (2024). http://doi.org/10.1021/ACS.JPCLETT.4C01957
Abstract: Despite a few recent reports on Rashba effects in two-dimensional (2D) Ruddlesden-Popper (RP) hybrid perovskites, the precise role of organic spacer cations in influencing Rashba band splitting remains unclear. Here, using a combination of temperature-dependent two-photon photoluminescence (2PPL) and time-resolved photoluminescence spectroscopy, alongside density functional theory (DFT) calculations, we contribute to significant insights into the Rashba band splitting found for 2D RP hybrid perovskites. The results demonstrate that the polarity of the organic spacer cation is crucial in inducing structural distortions that lead to Rashba-type band splitting. Our investigations show that the intricate details of the Rashba band splitting occur for organic cations with low polarity but not for more polar ones. Furthermore, we have observed stronger exciton-phonon interactions due to the Rashba-type band splitting effect. These findings clarify the importance of selecting appropriate organic spacer cations to manipulate the electronic properties of 2D perovskites.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 5.7
DOI: 10.1021/ACS.JPCLETT.4C01957
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