12 research outputs found

    From Paracrystalline Ru(CO)<sub>4</sub> 1D Polymer to Nanosized Ruthenium Metal: A Case of Study through Total Scattering Analysis

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    The highly defective 1D polymer [RuĀ­(CO)<sub>4</sub>]<sub><i>n</i></sub> species, in which Ru atoms are arranged in parallel chains well separated by the ligand shell, is here investigated by total scattering Debye function analysis on synchrotron powder diffraction data. A new chain packing model based on the presence of 2D paracrystalline effects in the <b>ab</b> plane is successfully proposed and well accounts for the unusual combination of sharp and very broad diffraction peaks not compatible with conventional size or strain models. Upon thermolysis, the collinear metal arrangement of the parallel [RuĀ­(CO)<sub>4</sub>]<sub><i>n</i></sub> bundles in the polymer is not maintained in the Ru particles, whose nanocrystals are not significantly elongated and show a faulted hcp structure with much smaller domains than in the parent organometallic species. These results thus dismiss the appealing hypothesis that, by using a chain-like precursor, highly anisotropically shaped Ru-metal nanorods can be formed upon controlled pyrolysis

    Bending by Faulting: A Multiple Scale Study of Copper and Silver Nitropyrazolates

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    A multiscale approach, combining structural and microstructural characterizations, was applied to tackle an uncommon and so far unsolved structural problem occurring in group 11 nitropyrazolates. To this goal, the average structure of the [AgĀ­(4-NO<sub>2</sub>-pz)]<sub>3</sub> and [CuĀ­(4-NO<sub>2</sub>-pz)]<sub>3</sub> species was determined through ab initio X-ray powder diffraction techniques on high-resolution synchrotron data, and used to infer molecular models of randomly distributed defects within molecular stacks of trimeric molecules of <i>D</i><sub>3<i>h</i></sub> idealized symmetry. By cross-coupling the size and shape information on nanocrystalline coherent domains derived from tailored Debye function simulations with those obtained from scanning electron miscroscopy images on multidomain particles, the mechanism of structural disorder disrupting crystal periodicity is proposed. Such a model was further supported through the derivation of the pair distribution function, which affords local features to be sought independently from the presence of structural periodicity. Finally, the effects of stacking faults on the electrical properties of [AgĀ­(4-NO<sub>2</sub>-pz)]<sub>3</sub> have been experimentally evaluated

    Energy Transfer from Magnetic Iron Oxide Nanoparticles: Implications for Magnetic Hyperthermia

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    ACS Appl. Nano Mater. 2023, 6, 12914ā€“12921https://doi.org/10.1021/acsanm.3c01643Magnetic iron oxide nanoparticles (IONPs) have gained momentum in the field of biomedical applications. They can be remotely heated via alternating magnetic fields, and such heat can be transferred from the IONPs to the local environment. However, the microscopic mechanism of heat transfer is still debated. By X-ray total scattering experiments and first-principles simulations, we show how such heat transfer can occur. After establishing structural and microstructural properties of the maghemite phase of the IONPs, we built a maghemite model functionalized with aminoalkoxysilane, a molecule used to anchor (bio)molecules to oxide surfaces. By a linear response theory approach, we reveal that a resonance mechanism is responsible for the heat transfer from the IONPs to the surroundings. Heat transfer occurs not only via covalent linkages with the IONP but also through the solvent hydrogen-bond network. This result may pave the way to exploit the directional control of the heat flow from the IONPs to the anchored moleculesā”€i.e., antibiotics, therapeutics, and enzymesā”€for their activation or release in a broader range of medical and industrial applications.</p

    Selecting the Desired Solid Form by Membrane Crystallizers: Crystals or Cocrystals

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    This work aims to describe a systematic study on the conditions promoting the selective formation of carbamazepine-saccharin cocrystals or single component crystals from water/ethanol solvent mixtures, by using a membrane crystallization process. Results revealed the ability to operate in the proper zone of the phase diagram of the system when opportunely choosing the initial solution conditions and limiting the maximum level of supersaturation by using the membrane-based technology. Control in the selective crystallization of a specific solid form can be achieved by adjusting the solvent evaporation through the micropores of the membrane. Furthermore, the direct correlation between transmembrane flow and polymorphic composition in the case of carbamazepine precipitation confirmed the possibility to produce particular metastable phases upon increasing the supersaturation rate

    Magnetiteā€“Maghemite Nanoparticles in the 5ā€“15 nm Range: Correlating the Coreā€“Shell Composition and the Surface Structure to the Magnetic Properties. A Total Scattering Study.

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    Very small superparamagnetic iron oxide nanoparticles were characterized by innovative synchrotron X-ray total scattering methods and Debye function analysis. Using the information from both Bragg and diffuse scattering, size-dependent coreā€“shell magnetiteā€“maghemite compositions and full size (number- and mass-based) distributions were derived within a coherent approach. The magnetite core radii in 10 nm sized NPs well match the magnetic domain sizes and show a clear correlation to the saturation magnetization values, while the oxidized shells seem to be magnetically silent. Very broad superstructure peaks likely produced by the polycrystalline nature of the surface layers were experimentally detected in room temperature oxidized samples. Effective magnetic anisotropy constants, derived by taking the knowledge of the full size-distributions into account, show an inverse dependence on the NPs size, witnessing a major surface contribution. Finally, an additional amorphous component was uncovered within the diffuse scattering of the ā€œorderedā€ magnetiteā€“maghemite NPs. Under the hypothesis that this material may form an external dead layer, an additional thickness varying between 0.3 and 1.0 nm should be added to the overall coreā€“shell NPs size

    Resolving the Core and the Surface of CdSe Quantum Dots and Nanoplatelets Using Dynamic Nuclear Polarization Enhanced PASSā€“PIETA NMR Spectroscopy

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    Understanding the surface of semiconductor nanocrystals (NCs) prepared using colloidal methods is a long-standing goal of paramount importance for all their potential optoelectronic applications, which remains unsolved largely because of the lack of site-specific physical techniques. Here, we show that multidimensional <sup>113</sup>Cd dynamic nuclear polarization (DNP) enhanced NMR spectroscopy allows the resolution of signals originating from different atomic and magnetic surroundings in the NC cores and at the surfaces. This enables the determination of the structural perfection, and differentiation between the surface and core atoms in all major forms of size- and shape-engineered CdSe NCs: irregularly faceted quantum dots (QDs) and atomically flat nanoplatelets, including both dominant polymorphs (zinc-blende and wurtzite) and their epitaxial nanoheterostructures (CdSe/CdS core/shell quantum dots and CdSe/CdS core/crown nanoplatelets), as well as magic-sized CdSe clusters. Assignments of the NMR signals to specific crystal facets of oleate-terminated ZB structured CdSe NCs are proposed. Significantly, we discover far greater atomistic complexity of the surface structure and the species distribution in wurtzite as compared to zinc-blende CdSe QDs, despite an apparently identical optical quality of both QD polymorphs

    Resolving the Core and the Surface of CdSe Quantum Dots and Nanoplatelets Using Dynamic Nuclear Polarization Enhanced PASSā€“PIETA NMR Spectroscopy

    No full text
    Understanding the surface of semiconductor nanocrystals (NCs) prepared using colloidal methods is a long-standing goal of paramount importance for all their potential optoelectronic applications, which remains unsolved largely because of the lack of site-specific physical techniques. Here, we show that multidimensional <sup>113</sup>Cd dynamic nuclear polarization (DNP) enhanced NMR spectroscopy allows the resolution of signals originating from different atomic and magnetic surroundings in the NC cores and at the surfaces. This enables the determination of the structural perfection, and differentiation between the surface and core atoms in all major forms of size- and shape-engineered CdSe NCs: irregularly faceted quantum dots (QDs) and atomically flat nanoplatelets, including both dominant polymorphs (zinc-blende and wurtzite) and their epitaxial nanoheterostructures (CdSe/CdS core/shell quantum dots and CdSe/CdS core/crown nanoplatelets), as well as magic-sized CdSe clusters. Assignments of the NMR signals to specific crystal facets of oleate-terminated ZB structured CdSe NCs are proposed. Significantly, we discover far greater atomistic complexity of the surface structure and the species distribution in wurtzite as compared to zinc-blende CdSe QDs, despite an apparently identical optical quality of both QD polymorphs

    Exploration of Near-Infrared-Emissive Colloidal Multinary Lead Halide Perovskite Nanocrystals Using an Automated Microfluidic Platform

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    Hybrid organicā€“inorganic and fully inorganic lead halide perovskite nanocrystals (NCs) have recently emerged as versatile solution-processable light-emitting and light-harvesting optoelectronic materials. A particularly difficult challenge lies in warranting the practical utility of such semiconductor NCs in the red and infrared spectral regions. In this context, all three archetypal A-site monocationic perovskitesī—øCH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, CHĀ­(NH<sub>2</sub>)<sub>2</sub>PbI<sub>3</sub>, and CsPbI<sub>3</sub>ī—øsuffer from either chemical or thermodynamic instabilities in their bulk form. A promising approach toward the mitigation of these challenges lies in the formation of multinary compositions (mixed cation and mixed anion). In the case of multinary colloidal NCs, such as quinary Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbĀ­(Br<sub>1ā€“<i>y</i></sub>I<sub><i>y</i></sub>)<sub>3</sub> NCs, the outcome of the synthesis is defined by a complex interplay between the bulk thermodynamics of the solid solutions, crystal surface energies, energetics, dynamics of capping ligands, and the multiple effects of the reagents in solution. Accordingly, the rational synthesis of such NCs is a formidable challenge. Herein, we show that droplet-based microfluidics can successfully tackle this problem and synthesize Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbI<sub>3</sub> and Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbĀ­(Br<sub>1ā€“<i>y</i></sub>I<sub><i>y</i></sub>)<sub>3</sub> NCs in both a time- and cost-efficient manner. Rapid <i>in situ</i> photoluminescence and absorption measurements allow for thorough parametric screening, thereby permitting precise optical engineering of these NCs. In this showcase study, we fine-tune the photoluminescence maxima of such multinary NCs between 700 and 800 nm, minimize their emission line widths (to below 40 nm), and maximize their photoluminescence quantum efficiencies (up to 89%) and phase/chemical stabilities. Detailed structural analysis revealed that the Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbĀ­(Br<sub>1ā€“<i>y</i></sub>I<sub><i>y</i></sub>)<sub>3</sub> NCs adopt a cubic perovskite structure of FAPbI<sub>3</sub>, with iodide anions partially substituted by bromide ions. Most importantly, we demonstrate the excellent transference of reaction parameters from microfluidics to a conventional flask-based environment, thereby enabling up-scaling and further implementation in optoelectronic devices. As an example, Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbĀ­(Br<sub>1ā€“<i>y</i></sub>I<sub><i>y</i></sub>)<sub>3</sub> NCs with an emission maximum at 735 nm were integrated into light-emitting diodes, exhibiting a high external quantum efficiency of 5.9% and a very narrow electroluminescence spectral bandwidth of 27 nm

    Exploration of Near-Infrared-Emissive Colloidal Multinary Lead Halide Perovskite Nanocrystals Using an Automated Microfluidic Platform

    No full text
    Hybrid organicā€“inorganic and fully inorganic lead halide perovskite nanocrystals (NCs) have recently emerged as versatile solution-processable light-emitting and light-harvesting optoelectronic materials. A particularly difficult challenge lies in warranting the practical utility of such semiconductor NCs in the red and infrared spectral regions. In this context, all three archetypal A-site monocationic perovskitesī—øCH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, CHĀ­(NH<sub>2</sub>)<sub>2</sub>PbI<sub>3</sub>, and CsPbI<sub>3</sub>ī—øsuffer from either chemical or thermodynamic instabilities in their bulk form. A promising approach toward the mitigation of these challenges lies in the formation of multinary compositions (mixed cation and mixed anion). In the case of multinary colloidal NCs, such as quinary Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbĀ­(Br<sub>1ā€“<i>y</i></sub>I<sub><i>y</i></sub>)<sub>3</sub> NCs, the outcome of the synthesis is defined by a complex interplay between the bulk thermodynamics of the solid solutions, crystal surface energies, energetics, dynamics of capping ligands, and the multiple effects of the reagents in solution. Accordingly, the rational synthesis of such NCs is a formidable challenge. Herein, we show that droplet-based microfluidics can successfully tackle this problem and synthesize Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbI<sub>3</sub> and Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbĀ­(Br<sub>1ā€“<i>y</i></sub>I<sub><i>y</i></sub>)<sub>3</sub> NCs in both a time- and cost-efficient manner. Rapid <i>in situ</i> photoluminescence and absorption measurements allow for thorough parametric screening, thereby permitting precise optical engineering of these NCs. In this showcase study, we fine-tune the photoluminescence maxima of such multinary NCs between 700 and 800 nm, minimize their emission line widths (to below 40 nm), and maximize their photoluminescence quantum efficiencies (up to 89%) and phase/chemical stabilities. Detailed structural analysis revealed that the Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbĀ­(Br<sub>1ā€“<i>y</i></sub>I<sub><i>y</i></sub>)<sub>3</sub> NCs adopt a cubic perovskite structure of FAPbI<sub>3</sub>, with iodide anions partially substituted by bromide ions. Most importantly, we demonstrate the excellent transference of reaction parameters from microfluidics to a conventional flask-based environment, thereby enabling up-scaling and further implementation in optoelectronic devices. As an example, Cs<sub><i>x</i></sub>FA<sub>1ā€“<i>x</i></sub>PbĀ­(Br<sub>1ā€“<i>y</i></sub>I<sub><i>y</i></sub>)<sub>3</sub> NCs with an emission maximum at 735 nm were integrated into light-emitting diodes, exhibiting a high external quantum efficiency of 5.9% and a very narrow electroluminescence spectral bandwidth of 27 nm

    Strongly Confined CsPbBr<sub>3</sub> Quantum Dots as Quantum Emitters and Building Blocks for Rhombic Superlattices

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    The success of the colloidal semiconductor quantum dots (QDs) field is rooted in the precise synthetic control of QD size, shape, and composition, enabling electronically well-defined functional nanomaterials that foster fundamental science and motivate diverse fields of applications. While the exploitation of the strong confinement regime has been driving commercial and scientific interest in InP or CdSe QDs, such a regime has still not been thoroughly explored and exploited for lead-halide perovskite QDs, mainly due to a so far insufficient chemical stability and size monodispersity of perovskite QDs smaller than about 7 nm. Here, we demonstrate chemically stable strongly confined 5 nm CsPbBr3 colloidal QDs via a postsynthetic treatment employing didodecyldimethylammonium bromide ligands. The achieved high size monodispersity (7.5% Ā± 2.0%) and shape-uniformity enables the self-assembly of QD superlattices with exceptional long-range order, uniform thickness, an unusual rhombic packing with an obtuse angle of 104Ā°, and narrow-band cyan emission. The enhanced chemical stability indicates the promise of strongly confined perovskite QDs for solution-processed single-photon sources, with single QDs showcasing a high single-photon purity of 73% and minimal blinking (78% ā€œonā€ fraction), both at room temperature
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