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
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
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
ACS Appl. Nano Mater. 2023, 6, 12914ā12921https://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 moleculesāi.e., antibiotics, therapeutics, and enzymesāfor 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
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
MagnetiteāMaghemite Nanoparticles in the 5ā15 nm Range: Correlating the CoreāShell Composition and the Surface Structure to the Magnetic Properties. A Total Scattering Study.
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 coreāshell magnetiteāmaghemite
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 āorderedā magnetiteāmaghemite
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 coreāshell NPs size
Resolving the Core and the Surface of CdSe Quantum Dots and Nanoplatelets Using Dynamic Nuclear Polarization Enhanced PASSāPIETA NMR Spectroscopy
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 PASSāPIETA NMR Spectroscopy
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
Hybrid organicāinorganic 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 perovskitesīøCH<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>īøsuffer 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
Hybrid organicāinorganic 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 perovskitesīøCH<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>īøsuffer 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
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% āonā fraction), both at room temperature