94 research outputs found
Folding a 2-D powder diffraction image into a 1-D scan: a new procedure
A new procedure aiming at folding a powder diffraction 2-D into a 1-D scan is
presented. The technique consists of three steps: tracking the beam centre by
means of a Simulated Annealing (SA) of the diffraction rings along the same
axis, detector tilt and rotation determination by a Hankel Lanczos Singular
Value Decomposition (HLSVD) and intensity integration by an adaptive binning
algorithm. The X-ray powder diffraction (XRPD) intensity profile of the
standard NIST Si 640c sample is used to test the performances. Results show the
robustness of the method and its capability of efficiently tagging the pixels
in a 2-D readout system by matching the ideal geometry of the detector to the
real beam-sample-detector frame. The whole technique turns out in a versatile
and user-friendly tool for the scanning of 2-D XRPD profiles.Comment: 11 pages, 1 table, 2 figure
Testing the Debye Function Approach on a Laboratory X-ray Powder Diffraction Equipment. A Critical Study
Total Scattering Methods are nowadays widely used for the characterization of defective and nanosized materials. They commonly rely on highly accurate neutron and synchrotron diffraction data collected at dedicated beamlines. Here, we compare the results obtained on conventional laboratory equipment and synchrotron radiation when adopting the Debye Function Analysis method on a simple nanocrystalline material (a synthetic iron oxide with average particle size near to 10nm). Such comparison, which includes the cubic lattice parameter, the sample stoichiometry and the microstructural (size-distribution) analyses, highlights the limitations, but also some strengthening points, of dealing with conventional powder diffraction data collections on nanocrystalline material
Energy Transfer from Magnetic Iron Oxide Nanoparticles: Implications for Magnetic Hyperthermia
Magnetic 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 molecules─i.e., antibiotics, therapeutics, and enzymes─for their activation or release in a broader range of medical and industrial applications
The International Summer School on "Diffraction at the Nanoscale: Nanocrystals, Defective & Amorphous Materials”
Testing the Debye Function Approach on a Laboratory X-ray Powder Diffraction Equipment. A Critical Study.
Heterovalent BiIII/PbII ionic substitution in one-dimensional trimethylsulfoxonium halide pseudo-perovskites (X = I, Br)
We report on the synthesis and characterization of novel lead and bismuth hybrid (organic 12inorganic) iodide and bromide pseudo-perovskites (ABX3) containing the trimethylsulfoxonium cation (CH3)3SO+ (TMSO) in the A site, Pb/Bi in the Bsite, and Br or I as X anions. All of these compounds are isomorphic and crystallize in the orthorhombic Pnma space group. Lead-based
pseudo-perovskites consist of one-dimensional (1D) chains of facesharing [PbX6] octahedra, while in the bismuth-based ones, the chains of [BiX6] are interrupted, with one vacancy every third site,leading to a zero-dimensional (0D) local structure based on separated [Bi2I9] 3 12 dimers. Five solid solutions for the iodide with different Pb2 +/Bi3 + ratios between (TMSO)PbI3 and
(TMSO)3Bi2I9, and two for the bromide counterparts, were synthetized. Due to the charge compensation mechanism, these systems are best described by the (TMSO)3Pb3xBi2(1 12x)I9 (x =
0.98, 0.92, 0.89, 0.56, and 0.33) and (TMSO)3Pb3xBi2(1 12x)Br9 (x = 0.83 and 0.37) formulae. X-ray powder diffraction (XRPD) measurements were employed to determine the crystal structure of all studied species and further used to test the metal cation miscibility within monophasic samples not showing cation segregation. These systems can be described through an ionic defectivity
on the pseudo-perovskite B site, where the Pb2+/Bi3+ replacement is compensated by one Pb2+ vacancy for every Bi3+ pair. This leads to a wide range of possible different (numerical and geometrical) chain configurations, leading to the unique features observed in XRPD patterns. The optical band gap of the iodide samples falls in the 2.11 122.74 eV range and decreases upon increasing the Bi3+
content. Interestingly, even a very low loading of Bi3+ (1%) is sufficient to reduce the band gap substantially from 2.74 to 2.25 eV. Periodic density functional theory (DFT) calculations were used to simulate the atomic and electronic structures of our samples, with predicted band gap trends in good agreement with the experimental ones. This work highlights the structural flexibility of such
systems and accurately interprets the ionic defectivity of the different pseudo-perovskite structures
The role of nanoparticle structure and morphology in the dissolution kinetics and nutrient release of nitrate‑doped calcium phosphate nanofertilizers
Bio-inspired synthetic calcium phosphate (CaP) nanoparticles (NPs), mimicking the mineral
component of bone and teeth, are emergent materials for sustainable applications in agriculture.
These sparingly soluble salts show self-inhibiting dissolution processes in undersaturated
aqueous media, the control at the molecular and nanoscale levels of which is not fully elucidated.
Understanding the mechanisms of particle dissolution is highly relevant to the efcient delivery of
macronutrients to the plants and crucial for developing a valuable synthesis-by-design approach. It
has also implications in bone (de)mineralization processes. Herein, we shed light on the role of size,
morphology and crystallinity in the dissolution behaviour of CaP NPs and on their nitrate doping
for potential use as (P,N)-nanofertilizers. Spherical fully amorphous NPs and apatite-amorphous
nanoplatelets (NPLs) in a core-crown arrangement are studied by combining forefront Small-Angle
and Wide-Angle X-ray Total Scattering (SAXS and WAXTS) analyses. Ca2+ ion release rates difer
for spherical NPs and NPLs demonstrating that morphology plays an active role in directing the
dissolution kinetics. Amorphous NPs manifest a rapid loss of nitrates governed by surface-chemistry.
NPLs show much slower release, paralleling that of Ca2+ ions, that supports both detectable nitrate
incorporation in the apatite structure and dissolution from the core basal faces.Fondazione Cariplo
2016-0648FEDER/Ministerio de Ciencia, Innovacion y Universidades-Agencia Estatal de Investigacion (FEDER/MCIU/AEI, Spain) through the project NanoVIT
RTI-2018-095794-A-C22FEDER/Ministerio de Ciencia, Innovacion y Universidades-Agencia Estatal de Investigacion (FEDER/MCIU/AEI, Spain) through the project NanoSmart
RYC-2016-21042FEDER/MCIU/AEI within the Juan de la Cierva Program (JdC2017
Colloidal Synthesis and Characterization of Tetrapod-Shaped Magnetic Nanocrystals
Tetrapod-shaped maghemite nanocrystals are synthesized by manipulating the decomposition of iron pentacarbonyl in a ternary surfactant mixture under mild thermal conditions. Adjustment of the reaction parameters allows for the systematic tuning of both the width and the length of the tetrapod arms, which grow preferentially along the 〈111〉 easy axis direction. Such degree of control leads to modulation of the magnetic behavior of the nanocrystals, which evolves systematically as their surface magnetization phase and shape anisotropy are progressively increased
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