Person: Díaz-Guerra Viejo, Carlos
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First Name
Carlos
Last Name
Díaz-Guerra Viejo
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Física Aplicada
Identifiers
4 results
Search Results
Now showing 1 - 4 of 4
Item Femtosecond double-pulse laser ablation and deposition of Co-doped ZnS thin films(Nanomaterials, 2020) López Quintas, Ignacio; Rebollar, Esther; Ávila Brande, David; Izquierdo, Jesús G.; Díaz-Guerra Viejo, Carlos; Urbieta Quiroga, Ana Irene; Castillejo, Marta; Nalda, Rebeca de; Martín Fernández, MargaritaNanostructured thin films of Co-doped zinc sulfide were synthesized through femtosecond pulsed laser deposition. The scheme involved ablation of physically mixed Co and ZnS with pairs of ultrashort pulses separated in time in the 0-300 ps range. In situ monitorization of the deposition process was carried out through a simultaneous reflectivity measurement. The crystallinity of generated nanoparticles and the inclusion of Co in the ZnS lattice is demonstrated by transmission electron microscopy and energy dispersive X-ray microanalysis (TEM-EDX) characterization. Surface morphology, Raman response, and photoluminescence of the films have also been assessed. The role of interpulse temporal separation is most visible in the thickness of the films obtained at the same total fluence, with much thicker films deposited with short delays than with individual uncoupled pulses. The proportion of Co in the synthesized doped ZnS nanoparticles is found to be substantially lower than the original proportion, and practically independent on interpulse delay.Item Anisotropy of the electric field gradient in two-dimensional alpha-MoO_(3) investigated by (57)^Mn((57)^Fe) emission mossbauer spectroscopy(Crystals, 2022) Schell, Juliana; Zyabkin, Dmitry; Bharuth-Ram, Krish; Gonçalves, Joao N.; Díaz-Guerra Viejo, Carlos; Gunnlaugsson, Haraldur P.; Tarazaga Martín-Luengo, Aitana; Schaaf, Peter; Bonanni, Alberta; Masenda, Hilary; otros, ...Van der Waals alpha-MoO_(3) samples offer awide range of attractive catalytic, electronic, and optical properties. We present herein an emission Mossbauer spectroscopy (eMS) study of the electric-field gradient (EFG) anisotropy in crystalline free-standing alpha-MoO_(3) samples. Although alpha-MoO3 is a twodimensional (2D) material, scanning electron microscopy shows that the crystals are 0.5-5-mu m thick. The combination of X-ray diffraction and micro-Raman spectroscopy, performed after sample preparation, provided evidence of the phase purity and crystal quality of the samples. The eMS measurements were conducted following the implantation of (57)^Mn (t(1/ 2) = 1.5 min), which decays to the (57)^Fe, 14.4 keV Mossbauer state. The eMS spectra of the samples are dominated by a paramagnetic doublet (D1) with an angular dependence, pointing to the Fe^(2+) probe ions being in a crystalline environment. It is attributed to an asymmetric EFG at the eMS probe site originating from strong in-plane covalent bonds and weak out-of-plane van derWaals interactions in the 2D material. Moreover, a second broad component, D2, can be assigned to Fe^(3+) defects that are dynamically generated during the online measurements. The results are compared to ab initio simulations and are discussed in terms of the in-plane and out-of-plane interactions in the system- Project number: 104
Item Diseño de herramientas de dinamización del aula adaptables a distintos escenarios de docencia (presenciales o en línea)(2022) Fernández Sánchez, Paloma; Arroyo Bujase, Alex Miguel; Díaz-Guerra Viejo, Carlos; Fernández Jiménez, Rubén; Garrido Díaz, Esther; Hidalgo Alcalde, Pedro; Panis Maramba, Carlo Dexter; Romero Izquierdo, Carlos; Sotillo Buzarra, Belén; Urbieta Quiroga, Ana Irene Item Temperature dependence of the hyperfine magnetic field at Fe sites in Ba-Doped BiFeO_(3) thin films studied by emission Mossbauer spectroscopy(Crystals, 2023) Heiniger-Schell, Juliana; Bharuth-Ram, Krish; Naicker, Kimara; Masondo, Vusumuzi; Dang, Thien Thanh; Escobar, Marianela; Díaz-Guerra Viejo, Carlos; Marschick, Georg; Masenda, Hilary; Gunnlaugsson, Haraldur P.; Qi, Bingcui; Unzueta, Iraultza; Olafsson, Sveinn; Adhikari, Rajdeep; Peters, Gerrard; Naidoo, Deena; Schaaf, Peter; Zyabkin, Dmitry; Johnston, Karl; Becker, Sven; Jakob, GerhardEmission Fe-57 Mossbauer spectroscopy (eMS), following the implantation of radioactive Mn-57(+) ions, has been used to study the temperature dependence of the hyperfine magnetic field at Fe sites in Ba-doped BiFeO3 (BFO) thin films. 57Mn fi decays (t(1/ 2) = 90 s) to the 14.4 keV Mossbauer state of Fe-57, thus allowing online eMS measurements at a selection of sample temperatures during Mn implantation. The eMS measurements were performed on two thin film BFO samples, 88 nm and 300 nm thick, and doped to 15% with Ba ions. The samples were prepared by pulsed laser deposition on SrTiO_3 substrates. X-ray diffraction analyses of the samples showed that the films grew in a tetragonal distorted structure. The Mossbauer spectra of the two films, measured at absorber temperatures in the range 301 K-700 K, comprised a central pair of paramagnetic doublets and a magnetic sextet feature in the wings. The magnetic component was resolved into (i) a component attributed to hyperfine interactions at Fe^(3+) ions located in octahedral sites (B_(hf)); and (ii) to Fe^(3+) ions in implantation induced lattice defects, which were characterized by a distribution of the magnetic field B_(Distr). The hyperfine magnetic field at the Fe probes in the octahedral site has a room temperature value of B_(hf) = 44.5(9) T. At higher sample temperatures, the Bhf becomes much weaker, with the Fe3+ hyperfine magnetic contribution disappearing above 700 K. Simultaneous analysis of the Ba-BFO eMS spectra shows that the variation of the hyperfine field with temperature follows the Brillouin curve for S = 5/2.