The disordered structure of the columnar misfit ∼ PbCr2S4 phase (∼ character indicates that it is close to the stoichiometric composition but slightly away) has been revealed by means of transmission electron microscopy (TEM) varied techniques such as selected area electron diffraction (SAED), high-resolution TEM (HRTEM), dark-field TEM and high-angle annular dark field (HAADF) in scanning-transmision (STEM) mode. The structure consists of a hexagonal framework (Cr21S36), with unit cell parameters a0 = b0 = 21.407 (1) Å and c0 3.476 (1), and with hexagonal (Pb6Cr2S6) and trigonal columns (Pb3S) with the same a and b parameters and different c: c3 = 3.98 Å; c6 = 5.62 Å, measured by electron diffraction. While the framework exhibit no crystalline disorder, the arrangement of the two types of columns is disordered. This disorder is shown by electron diffraction as diffuse scattering planes which are perpendicular to the framework c axis and parallel to the a∗b∗ plane. While the disorder between hexagonal columns is due to the lack of correlation between different columns, we observe in the trigonal columns also the presence of intra-columnar atomic disorder. X-ray wavelength dispersive spectroscopy (XWDS) analyses produce Pb0.81(1)Cr2S3.97(6) composition. TEM imaging techniques suggest lack of correlation between trigonal columns as the cause for the observed disorder as well as inside-the-column structural disorder in Pb3S trigonal columns.
A. Gómez-Herrero, A. R. Landa-Cánovas, and L. C. Otero-Díaz, “TEM study of ∼PbCr2S4 columnar misfit phases,” J. Solid State Chem. 319, 123826 (2023)
Kagome antiferromagnetic lattices are of high interest because the geometric frustration is expected to give rise to highly degenerated ground states that may host exotic properties such as quantum spin liquid (QSL). Ca10Cr7O28 has been reported to display all the features expected for a QSL. At present, most of the literature reports on samples synthesized with starting materials ratio CaO/Cr2O3 3:1, which leads to a material with small amounts of CaCrO4 and CaO as secondary phases; this impurity excess affects not only the magnetic properties but also the structural ones. In this work, samples with starting material ratios CaO/Cr2O3 3:1, 2.9:1, 2.85:1, and 2.8:1 have been synthesized and studied by X-ray diffraction with Rietveld refinements, selected area electron diffraction
measurements, high-resolution transmission electron microscopy (HRTEM), low-temperature magnetometry, and magnetic calorimetry. This result shows that a highly pure Ca10Cr7O28 phase is obtained for a CaO/Cr2O3 ratio of 2.85:1 instead of the 3:1 usually reported; the incorrect stoichiometric ratio leads to a larger distortion of the corner-sharing triangular arrangement of magnetic ions Cr+5 with S = 1/2 in the Kagome lattice. In addition, our study reveals that there exists another frustration pathway which is an asymmetric zigzag spin ladder along the directions , [12−1], and [1−1−1], in which the Cr−Cr distances are shorter than in the Kagome layers.
D. R. Alshalawi, J. M. Alonso, A. R. Landa-Cánovas, and P. de la Presa, «Coexistence of Two Spin Frustration Pathways in the Quantum Spin Liquid Ca10Cr7O28,» Inorg. Chem. 61, 16228 (2022).
MoO2 thin films were subjected to a laser localized oxidation process that allowed to obtain different well defined MoOx phases. In particular, spatially resolved MoO2, α-MoO3, β-MoO3, amorphous a-MoO3, and Mo4O11 regions were obtained as a function of the laser power and the distance to the laser focus. The origin of this spatial phase separation was investigated through a careful and exhaustive Raman mapping study covering several micrometres away from the laser focus and taking into account the thermochemical properties of the species involved. It was found that a sublimation/deposition process, driven by the different vapour pressures of the species, was responsible for the phase separation. At higher laser power, a solid state reaction was observed to contribute as well. In the laser annealed tracks, distant lateral sidebands of oxide deposition were observed with composition that depended on the laser power and the distance to the centre of the track. Electrical measurements between irradiated and non-irradiated regions showed a strong rectifying behaviour, revealing a transformation from metal-like to semiconducting Mo oxide phases, which may open the way to the development of laser written all-oxide electronic circuits.
O. de Melo, F. Agulló-Rueda and V. Torres-Costa, “Spatially resolved MoOx phases by laser localized oxidation of MoO2: A possible route for all-molybdenum-oxide devices,” J. Mater. Chem. C 9, 6579–6588 (2021).
Publicado en laser irradiation, microscopy, nanocharacterization, Raman spectroscopy, semiconductor, Sin categoría, transition metal oxides
Etiquetado article, coating, heating, laser irradiation, oxide, Raman spectroscopy, thin film
Jon Canca Ruiz va a defender su tesis doctoral «Fenómenos de orden-desorden en óxidos con estructura tipo rutilo y su aplicación como soportes en catalizadores heterogéneos» dentro del Programa de Doctorado de Química Aplicada de la Universidad Autónoma de Madrid. El acto tendrá lugar el viernes 26 de marzo de 2021 a las 11:00am en el Salón de Actos del Instituto de Ciencia de Materiales de Madrid, CSIC. El aforo está limitado a 40 personas y se aplicará el protocolo anti COVID-19.
Publicado en microscopy, nanocharacterization, nanoscience, People, Ph.D. thesis, Raman spectroscopy, rutile crystal structure, transition metal oxides
Etiquetado antimony, FeSbO4, FeSBVO4, HRTEM, iron, Keggin, molybdenum, nanocharacterization, order-disorder, oxide, phase transition, polyoxometalate, Raman spectroscopy, SbVO4, short range order, thesis, vanadium, vanadium oxide, VO2
A. Gómez‐Herrero, A. R. Landa‐Cánovas and L. C. Otero‐Díaz, “New Order in (BiS)1.19(Bi1/3Cr2S4) Misfit Layer Compound,” Z. Anorg. Allg. Chem. 647, 1–7 (2021).
In a sample with nominal composition BiCr2S5 a new misfit layer compound has been synthesized and studied via transmission electron microscopy (TEM). It presents a composite modulated structure with a composition that can be formulated as (BiS)1.19[(CrS2)-Bi1/3-(CrS2)]. It consists of the periodic stacking of a Q layer (BiS) with two H layers (CrS2), …QHHQHH…, with additional bismuth atoms inserted between the H layers. Selected area electron diffraction (SAED) patterns show an almost commensurate fit between the pseudo-tetragonal Q (BiS) and the pseudo-orthohexagonal H (Bi1/3Cr2S4) subcells along the misfit direction a, being b the same for both sublattices and c the layers stacking direction. In addition to the characteristic misfit modulation between the two sub-structures, a second modulation is observed in the H sub-structure produced by the ordering of bismuth atoms within the Van der Waals gap that occurs between consecutive H layers. High resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) images show ordered stacking sequences between the (BiS) and (Bi1/3Cr2S4) layers. Besides, disordered intergrowths have been occasionally found as well as different kinds of twinning defects.
En una muestra con composición nominal BiCr2S5 un nuevo compuesto de «misfit layer» ha sido sintetizado y estudiado a través de microscopía electrónica de transmisión (TEM). Presenta una estructura modulada compuesta con una composición que puede formularse como (BiS)1.19[(CrS2)-Bi1/3-(CrS2)]. Consiste en el apilamiento periódico de una capa Q (BiS) con dos capas H (CrS2), … QHHQHH…, con átomos de bismuto adicionales insertados entre las capas H. Los patrones de difracción de electrones de área seleccionada (SAED) muestran un ajuste casi conmensurable entre las subceldas pseudo-tetragonal Q (BiS) y la pseudo-ortohexagonal H (Bi1/3Cr2S4) a lo largo de la dirección de «misfit» a, siendo b el mismo para ambos sublátices y c la dirección de apilamiento de las capas. Además de la modulación de «misfit» característica entre los dos subestructuras, se observa una segunda modulación en la subestructura H producido por el orden de los átomos de bismuto dentro de la brecha de Van der Waals que se produce entre capas H consecutivas. La microscopía electrónica de transmisión de alta resolución (HRTEM) y las imágenes de microscopía electrónica de transmisión de barrido (STEM) muestran secuencias de apilamiento ordenadas entre capas (BiS) y (Bi1/3Cr2S4). Además, los intercrecimientos desordenados han sido ocasionalmente defectos de macla.
Published in Zeitschrift für anorganische und allgemeine Chemie (Journal of Inorganic and General Chemistry)
A. Fernández García, V. Torres-Costa, O. de Melo, F. Agulló-Rueda, G. R. Castro and M. Manso Silvan, “Growth of out-of-plane standing MoTe2(1−x)Se2x/MoSe2 composite flake films by sol-gel nucleation of MoOy and isothermal closed space telluro-selenization,” Appl. Surf. Sci. 546, 149076 (2021)
N. Naveas, M. Manso-Silván, R. Pulido, F. Agulló-Rueda, V. Torres-Costa, T. Plaza, H. Pesenti, G. Recio, and J. Hernandez-Montelongo, “Fabrication and characterization of nanostructured porous silicon-silver composite layers by cyclic deposition: dip-coating vs spin-coating,“ Nanotechnol. 31, 365704 (2020)
P. Pellacani, V. Torres-Costa, F. Agulló-Rueda, R. Vanna, C. Morasso, M. Manso Silván, “Laser writing of nanostructured silicon arrays for the SERS detection of biomolecules with inhibited oxidation,” Colloids Surf. B 174, 174–180 (2019)
Publicado en laser irradiation, microscopy, nanocharacterization, nanoscience, nanotechnology, Publications, Raman spectroscopy, silicon
Etiquetado analytics, article, biological materials, coating, laser irradiation, nanocharacterization, Raman spectroscopy, semiconductor, silicon
A. R. Landa-Cánovas, J. Santiso, F. Agulló-Rueda, P. Herrero, E. Navarrete-Astorga, E. Ochoa-Martínez, J. R. Ramos-Barrado, and M. Gabás, “Nanostructural changes upon substitutional Al doping in ZnO sputtered films,” Ceram. Int. 45, 6319–6327 (2019).
Al:ZnO layers, with low and high Al content, 0.2% and 2.1% cat. respectively, have been prepared using the RF magnetron sputtering technique. Noticeable differences in the optical and electrical properties have been detected in these films. With doping, the resistivity decreases and the band-gap increases. The alterations in the films crystalline structure are explained in terms of the nanostructural changes induced by Al substitutional doping, such as a higher concentration of edge dislocation defects and a higher rotation of crystalline nanodomains in the plane of the films (normal to the preferential orientation c-axis) for the high content Al:ZnO layer. A complete description of such effects has been accomplished using several characterization techniques, such as X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The combination of these techniques provides an exhaustive understanding of the films nanostructure.
Publicado en HRTEM, microscopy, nanocharacterization, nanoscience, Publications, Raman spectroscopy, transparent conductive oxides, zinc oxide
Etiquetado coating, doping, HRTEM, nanocharacterization, Raman spectroscopy, thin film, transparent conductive oxide (TCO), zinc oxide, ZnO
P. Pellacani, V. Torres-Costa, F. Agulló-Rueda, R. Vanna, C. Morasso, M. Manso Silván, “Laser writing of nanostructured silicon arrays for the SERS detection of biomolecules with inhibited oxidation,” Colloids Surf., B, accepted (2018).
The present work reports the processing of laser irradiated Si arrays (LISi) and underlines their surface enhanced Raman scattering (SERS) functionality. A nanostructured Si/SiOx surface forms providing additional fluidic and photoprotective properties. Because of their optical and surface characteristics, the arrays exhibit a SERS analytical enhancing factor of 500, without any noble metals such as gold or silver. Micro-Raman maps allowed studying LISi properties, identifying maximum amplification in nanostructured areas characterized by the presence of 7 nm Si nanocrystals. These structures are confined by a SiOx layer as illustrated by XPS valence band measurements. The highly hydrophilic LISi areas allow a pre-concentration of target molecules prior to SERS analysis. A relevant application of LISi was found in the detection of apomorphine (APO), a drug used for the treatment of Parkinson’s disease. In contrast with what is obtained by using gold SERS substrates, LISi allows the detection of APO with no sign of oxidation. This invites for the use of the Si/SiOx SERS detection in future systems for the personalized delivery of APO.
Publicado en microscopy, nanocharacterization, nanoscience, nanotechnology, Publications, Raman spectroscopy, silicon
Etiquetado article, biological materials, coating, oxide, Raman spectroscopy, semiconductor, silicon