Person: Rojo Alaminos, Juan Manuel
Universidad Complutense de Madrid
Faculty / Institute
Ciencia de los Materiales e Ingeniería Metalúrgica
Now showing 1 - 3 of 3
PublicationReduced hardness at the onset of plasticity in nanoindented titanium dioxide(American Physical Society, 2008-12) Navarro, V.; Rodríguez de la Fuente, Óscar; Mascaraque Susunaga, Arantzazu; Rojo Alaminos, Juan ManuelTitanium dioxide rutile crystals have been nanoindented and studied by a combination of atomic force microscopy imaging and analysis of force vs penetration curves. In all the experiments, gold crystals have been used as a reference. A concept of nanoindentation effective volume is introduced to differentiate the bulk behavior from that of a small defect-free volume around the indentation. In the latter volume, a reversible Hertzian elastic stage is identified with a Young modulus comparable to that of the bulk. At higher loads, an incipient plastic range is recognized in which the load is linear on the penetration and permanent traces are left behind at the surface upon tip retraction. In that range, the hardness is constant, about five times smaller than the yield strength and more than three times smaller than the corresponding bulk value. This reduced hardness is explained in terms of the operation of dislocation sources with a low-energy barrier. PublicationUncommon dislocation processes at the incipient plasticity of stepped gold surfaces(American Physical Society, 2008-03-14) Navarro, V.; Rodríguez de la Fuente, Óscar; Mascaraque Susunaga, Arantzazu; Rojo Alaminos, Juan ManuelGold vicinal surfaces (788), with a high density of steps, along with (111) flat surfaces taken as a reference, have been nanoindented and their resulting penetration curves and related defect structure comparatively analyzed by AFM and atomistic simulations. Stepped surfaces are shown to yield at smaller loads than (111) ones in agreement with calculations of the critical resolved shear stress needed to nucleate a dislocation. In the stepped surfaces, a novel intermediate state is identified in which the penetration curves depart from a Hertzian behavior prior to the appearance of pop-ins. This state is shown to result from heterogeneous nucleation at preexisting surface steps of dislocation loops, most of which retract and vanish when the indenter load is removed. PublicationFormation of titanium monoxide (001) single-crystalline thin film induced by ion bombardment of titanium dioxide (110)(Nature Publishing Group, 2015-02) Martínez Pabón, María Beatriz; Beltrán Finez, Juan Ignacio; Sánchez Santolino, Gabriel; Palacio, I.; López Sánchez, Jesús; Rubio Zuazo, J.; Rojo Alaminos, Juan Manuel; Ferrer, P.; Mascaraque Susunaga, Arantzazu; Muñoz, M. C.; Varela del Arco, María; Castro, G. R.; Rodríguez de la Fuente, ÓscarA plethora of technological applications justify why titanium dioxide is probably the most studied oxide, and an optimal exploitation of its properties quite frequently requires a controlled modification of the surface. Low-energy ion bombardment is one of the most extended techniques for this purpose and has been recently used in titanium oxides, among other applications, to favour resistive switching mechanisms or to form transparent conductive layers. Surfaces modified in this way are frequently described as reduced and defective, with a high density of oxygen vacancies. Here we show, at variance with this view, that high ion doses on rutile titanium dioxide (110) induce its transformation into a nanometric and single-crystalline titanium monoxide (001) thin film with rocksalt structure. The discovery of this ability may pave the way to new technical applications of ion bombardment not previously reported, which can be used to fabricate heterostructures and interfaces.