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© 2015 Macmillan Publishers Limited. Financial support from the Spanish Ministry of Economy and Competitiveness under projects MAT2012-38045-C04-03 and MAT2012-38045-C04-04 is acknowledged. A.M. also acknowledges project MAT2010-21156-C03-02 for financial support. We thank A. Tejeda for critical discussions. We acknowledge the Spanish Ministry of Economy and Competitiveness and Consejo Superior de Investigaciones Científicas for both financial support under project PIE 201060E013 and provision of synchrotron radiation facilities. We would also like to thank the SpLine beamline staff for their assistance during the SR experiments. GSS and the microscopy effort were supported by the ERC starting Investigator Award, grant #239739 STEMOX. Electron microscopy observations were carried out at the Centro Nacional de Microscopía Electrónica, CNME-UCM. Part of the XRD measurements were performed at the C.A.I. de Difracción de Rayos X-UCM. Computational calculations were performed at the Supercomputing Centre of Galicia (CESGA). Author contributions: O.R.d.l.F. conceived the project and coordinated the research. B.M., I.P. and O.R.d.l.F. prepared the samples and performed the Auger and LEED measurements and the ion beam modifications. B.M., I.P., A.M., J.L.-S, O.R.d.l.F., J.R.-Z., P.F. and G.C. performed the X ray diffraction measurements. G.S.-S. and M.V. performed the STEM measurements. J.I.B. and M.C.M. carried out the Density Functional Theory calculations. All authors wrote and revised the manuscript and extensively discussed the results and their interpretation. Supplementary Information: accompanies this paper at http://www.nature.com/ naturecommunications., A 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., Unión Europea. FP7, Ministerio de Economía y Competitividad (MINECO), España, Consejo Superior de Investigaciones Científicas (CSIC), España, ERC starting Investigator Awards, European Research Council (ERC), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 The American Physical Society. The authors acknowledge financial support from the Comunidad de Madrid Project No. CAM-S-0505/PPQ/0316, from Santander-UCM Project No.PR27/05-13926, and from the Spanish Ministerio de Educación y Ciencia Project No. MAT2006-13149-C02-01., Titanium 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., Comunidad de Madrid, Santander-UCM, Spanish Ministerio de Educacion y Ciencia, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2008 The American Physical Society. The authors thank J.E. Ortega for providing us the Au(788) sample. Financial support from the Spanish MEC, Project No. MAT2006-13149-C02-01 and from the CAM Projects Nos. CAM-S-0505/PPQ/0316 and GR/ MAT/0632/2004 are gratefully acknowledged. V. N. thanks MEC through No. MAT2003-08627-C02-01., Gold 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., Spanish MEC, CAM, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

En conjunción con experimentos de nanoindentación en AFM, podemos relacionar estas configuraciones de dislocación con los fenómenos plásticos registrados en las curvas de fuerza frente a desplazamiento (pop-ins). Empleando el modelo de contacto de Hertz, efectuamos una estimación cuantitativa del límite elástico y obtenemos un valor similar al teórico para un cristal perfecto, con lo que ponemos de manifiesto que las propiedades mecánicas de la superficie son distintas de las del volumen. Comprobamos que estos fenómenos plásticos generan huellas permanentes en la superficie y configuraciones de dislocación estables a temperatura ambiente. A diferencia de esta clase de defectos generados por nanoindentación, mostramos que los defectos producidos por el bombardeo iónico a temperatura ambiente y en el rango de dosis estudiado presentan una evolución temporal significativa, donde el barrido de la punta en determinadas condiciones, la anisotropía introducida por la reconstrucción y la difusión superficial influyen de forma relevante.

En conjunción con experimentos de nanoindentación en AFM, podemos relacionar estas configuraciones de dislocación con los fenómenos plásticos registrados en las curvas de fuerza frente a desplazamiento (pop-ins). Empleando el modelo de contacto de Hertz, efectuamos una estimación cuantitativa del límite elástico y obtenemos un valor similar al teórico para un cristal perfecto, con lo que ponemos de manifiesto que las propiedades mecánicas de la superficie son distintas de las del volumen. Comprobamos que estos fenómenos plásticos generan huellas permanentes en la superficie y configuraciones de dislocación estables a temperatura ambiente. A diferencia de esta clase de defectos generados por nanoindentación, mostramos que los defectos producidos por el bombardeo iónico a temperatura ambiente y en el rango de dosis estudiado presentan una evolución temporal significativa, donde el barrido de la punta en determinadas condiciones, la anisotropía introducida por la reconstrucción y la difusión superficial influyen de forma relevante.