The representation of coupling interactions in the Material Properties Open Database (MPOD)

International audience; The Material Properties Open Database (MPOD, http//mpod.cimav.edu.mx) is a functional element of the web-based open databases system linked with crystallography. MPOD delivers single-crystal tensor properties in several representations, ranging from numerical matrices to 3D printing. Longitudinal moduli surfaces can be displayed in computers as well as in smart cell phones. Properties are stored as '.mpod' files. IUCr formatting standards (CIF) are followed. The original published paper containing the data is cited. Structural and experimental information is also registered and linked. 'Coupling properties', say piezo-effects and magnetoelectricity, represent interactions linking different subsystems in a material. Currently, piezoelectricity occupies a significant fraction of cases in MPOD. The implications of crystal symmetry in piezoelectricity are systematically taken into account. Matrices' elements and longitudinal moduli surfaces are checked for consistency with the Neumann principle. The inclusion of magnetoelectric axial tensors introduces exciting features into MPOD

Assessment of chemical species of lead accumulated in tidemarks of human articular cartilage by X-ray absorption near-edge structure analysis

Lead is a toxic trace element that shows a highly specific accumulation in the transition zone between calcified and non-calcified articular cartilage, the so-called ‘tidemark’. Excellent agreement has been found between XANES spectra of synthetic Pb-doped carbonated hydroxyapatite and spectra obtained in the tidemark region and trabecular bone of normal human samples, confirming that in both tissues Pb is incorporated into the hydroxyapatite crystal structure of bone. During this study the µ-XANES set-up at the SUL-X beamline at ANKA was tested and has proven to be well suited for speciation of lead in human mineralized tissue samples

The large area detector onboard the eXTP mission

The Large Area Detector (LAD) is the high-throughput, spectral-timing instrument onboard the eXTP mission, a flagship mission of the Chinese Academy of Sciences and the China National Space Administration, with a large European participation coordinated by Italy and Spain. The eXTP mission is currently performing its phase B study, with a target launch at the end-2027. The eXTP scientific payload includes four instruments (SFA, PFA, LAD and WFM) offering unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. The LAD instrument is based on the design originally proposed for the LOFT mission. It envisages a deployed 3.2 m2 effective area in the 2-30 keV energy range, achieved through the technology of the large-area Silicon Drift Detectors - offering a spectral resolution of up to 200 eV FWHM at 6 keV - and of capillary plate collimators - limiting the field of view to about 1 degree. In this paper we will provide an overview of the LAD instrument design, its current status of development and anticipated performance

GIMPy: a software for the simulation of X-ray fluorescence and reflectivity of layered materials

X-ray fluorescence (XRF) analysis is an established technique for quantitative elemental analysis. Grazing incidence X-ray fluorescence analysis (GIXRF) extends the application of XRF to thin films because of the improved sensibility. GIXRF shares the phenomenological basis with X-ray reflectivity, a scattering technique typically used for thin-film metrology, offering sensitivity to elemental depth. This work presents the GIMPy (Grazing Incidence Material analysis with Python) software developed for the analysis of GIXRF spectra by combining a fundamental parameter approach to quantitative XRF analysis and the electric field calculation in stratified media, which also delivers the total reflected intensity as measured in X-ray reflectivity experiments. An XRF experiment can be modelled from the source, modulation of the primary beam, interactions with a layered sample, absorption of the emitted fluorescence intensities, and the response function of semiconductor energy dispersive detectors obtaining a simulation of the expected spectrum that can be directly compared with the acquired one. The fundamental parameter part includes signal enhancements by cascade effect and secondary fluorescence. The code offers the possibility to take into account the effects originated by deviations from ideal conditions: non-monochromatic excitation, beam divergence, beam size and shape, sample-inspected area, and solid angle of detection. The functionality of the code is demonstrated on a set of semiconductor substrates (Si, Ge, and GaAs) and shallow dopant distributions of arsenic in silicon

MPOD: A Material Property Open Database linked to structural information

Inspired by the Crystallography Open Database (COD), the Material Properties Open Database (MPOD) was given birth. MPOD aims at collecting and making publicly available at no charge tensorial properties (including scalar properties) of phases and linking such properties to structural information of the COD when available. MPOD files are written with the STAR file syntax, used and developed for the Crystallographic Information Files. A dictionary containing new definitions has been written according to the Dictionary Definition Language 1, although some tricks were adopted to allow for multiple entries still avoiding ambiguousness. The initial set includes mechanical properties, elastic stiffness and compliance, internal friction; electrical properties, resistivity, dielectric permittivity and stiffness, thermodynamic properties, heat capacity, thermal conductivity, diffusivity and expansion; electromechanical properties, piezoelectricity, electrostriction, electromechanical coupling; optical properties; piezooptic and photoelastic properties; superconducting properties, critical fields, penetration and coherence lengths. Properties are reported in MPOD files where the original published paper containing the data is cited and structural and experimental information is also given. One MPOD file contains information relative to only one publication and one phase. The files and the information contained therein can also be consulted on-line at http://www.materialproperties.org

A Compact Current- and Voltage-Mode Model of Antenna-Coupled FET Terahertz Detectors

In this article a comprehensive modeling of cold-biased field-effect transistors (FETs) used as terahertz (THz) detectors is developed. The described model is based upon the transistor Enz-Krummenacher-Vittoz (EKV) model in order to provide valid quantities also near and below the transistor threshold by using available technology parameters, without any extra fitting nor calibration. Important aspects such as the antenna coupling and the effect of amplitude modulation of the THz source are considered in a single, handy, analytical model. THz measurements performed on specifically designed FET detectors confirm its validity, providing a powerful tool and giving a clear insight of the role of available variables. The model can anticipate time-consuming numerical simulations or more physically accurate models requiring experimental parameters calibration, that may complement the results for better accuracy