32 research outputs found
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
Medium chain length (mcl)-pha-based nanocomposites for biomedical applications: system evaluation through xrd
Medium-chain polyhydroxyalkanoates (mcl-PHA) are flexible, elastomeric polymers produced by wide range of
bacteria as intercellular storage of carbon and energy. They represent attractive components in biomaterial design
because they are biocompatible, biodegradable and can be obtained using variety of carbon sources including
waste streams[1]. However, being semi-crystalline, all mcl-PHAs are characterized by low melting temperature and
poor tensile strength which can interfere with processing methods and wider biomedical application. Simple way
to improve mcl-PHAs properties is to incorporate a nanophase within biopolymer to obtain nanocomposites.
Nano-sized constituents interact with biopolymer more intimately affecting in turn the obtained nanocomposite
properties as well as functionality. Among inorganic nanofillers, TiO2 nanostructures with high aspect ratio (e.g.
nanofibers) have unique properties that support osteogenic phenotype which makes them suitable for bone tissue
engineering [2]
Localized vs. delocalized character of charge carriers in LaAlO3/ SrTiO3 superlattices
Understanding the nature of electrical conductivity, superconductivity and
magnetism between layers of oxides is of immense importance for the design of
electronic devices employing oxide heterostructures. We demonstrate that
resonant inelastic X-ray scattering can be applied to directly probe the
carriers in oxide heterostructures. Our investigation on epitaxially grown
LaAlO3/SrTiO3 superlattices unambiguously reveals the presence of both
localized and delocalized Ti 3d carriers. These two types of carriers are
caused by oxygen vacancies and electron transfer due to the polar discontinuity
at the interface. This result allows explaining the reported discrepancy
between theoretically calculated and experimentally measured carrier density
values in LaAlO3/SrTiO3 heterostructures.Comment: 14 pages, 3 figure
Tetramethylbenzidine-TetrafluoroTCNQ: A narrow-gap semiconducting salt with room temperature relaxor ferroelectric behavior
We present an extension and revision of the spectroscopic and structural data
of the mixed stack charge transfer (CT) crystal
3,3,5,5-tetramethylbenzidine--tetrafluoro-tetracyanoquinodimethane
(TMB-TCNQF4), associated with new electric and dielectric measurements.
Refinement of syncrotron structural data at low temperature has led to revise
the previously reported [Phys. Rev. Mat. 2, 024602 (2018)] structure.
The revised structure is , with two dimerized stacks per unit cell, and
is consistent with the vibrational data. However, polarized Raman data in the
low-frequency region also indicate that by increasing temperature above 200 K
the structure presents an increasing degree of disorder mainly along the stack
axis. X-ray diffraction data at room temperature have confirmed that the
correct structure is -- no phase transitions -- but did not allow to
definitely substantiate the presence of disorder. On the other hand, dielectric
measurement have evidenced a typical relaxor ferroelectric behavior already at
room temperature, with a peak in real part of dielectric constant
around 200 K and 0.1 Hz. The relaxor behavior is explained
in terms of the presence of spin solitons separating domains of opposite
polarity that yield to ferroelectric nanodomains. TMB-TCNQF4 is confirmed to be
a narrow gap band semiconductor ( eV) with room temperature
conductivity of cm.Comment: 21 pages, including the Supporting Information in the same file.
Version 3 updates the x-ray structural data at room temperatur
Crystal Symmetry of Stripe Ordered La1.88Sr0.12CuO4
We present a combined x-ray and neutron diffraction study of the stripe
ordered superconductor \lscox{0.12}. The average crystal structure is
consistent with the orthorhombic space group as commonly reported in the
literature. This structure however is not symmetry compatible with a second
order phase transition into the stripe order phase, and, as we report here
numerous Bragg peaks forbidden in the space group are observed. We have
studied and analysed these -forbidden Bragg reflections. Fitting of the
diffraction intensities yields monoclinic lattice distortions that are symmetry
consistent with charge stripe order.Comment: 7 pages, 3 figures, 5 Table
Weak-signal extraction enabled by deep-neural-network denoising of diffraction data
Removal or cancellation of noise has wide-spread applications for imaging and
acoustics. In every-day-life applications, denoising may even include
generative aspects which are unfaithful to the ground truth. For scientific
applications, however, denoising must reproduce the ground truth accurately.
Here, we show how data can be denoised via a deep convolutional neural network
such that weak signals appear with quantitative accuracy. In particular, we
study X-ray diffraction on crystalline materials. We demonstrate that weak
signals stemming from charge ordering, insignificant in the noisy data, become
visible and accurate in the denoised data. This success is enabled by
supervised training of a deep neural network with pairs of measured low- and
high-noise data. This way, the neural network learns about the statistical
properties of the noise. We demonstrate that using artificial noise (such as
Poisson and Gaussian) does not yield such quantitatively accurate results. Our
approach thus illustrates a practical strategy for noise filtering that can be
applied to challenging acquisition problems.Comment: 8 pages, 4 figure
Diffraction from Nanocrystal Superlattices
Diffraction from a lattice of periodically spaced crystals is a topic of current interest because of the great development of self-organised superlattices (SL) of nanocrystals (NC). The self-organisation of NC into SL has theoretical interest, but especially a rich application prospect, as the coherent organisation has large effects on a wide range of material properties. Diffraction is a key method to understand the type and quality of SL ordering. Hereby, the characteristic diffraction signature of an SL of NC—together with the characteristic types of disorder—are theoretically explored