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Lopez-Polin G.,Autonomous University of Madrid | Gomez-Navarro C.,Autonomous University of Madrid | Parente V.,CSIC - Institute of Materials Science | Guinea F.,CSIC - Institute of Materials Science | And 3 more authors.
Nature Physics | Year: 2015

The extraordinary strength, stiffness and lightness of graphene have generated great expectations of its application in flexible electronics and as a mechanical reinforcement agent. However, the presence of lattice defects, unavoidable in sheets obtained by scalable routes, might degrade its mechanical properties. Here we report a systematic study on the elastic modulus and strength of graphene with a controlled density of defects. Counter-intuitively, the in-plane Youngâ €™ s modulus increases with increasing defect density up to almost twice the initial value for a vacancy content of â 1/40.2%. For a higher density of vacancies, the elastic modulus decreases with defect inclusions. The initial increase in Youngâ €™ s modulus is explained in terms of a dependence of the elastic coefficients on the momentum of flexural modes predicted for two-dimensional membranes. In contrast, the fracture strength decreases with defect density according to standard fracture continuum models. These quantitative structure-property relationships, measured in atmospheric conditions, are of fundamental and technological relevance and provide guidance for applications in which graphene mechanics represents a disruptive improvement. © 2014 Macmillan Publishers Limited. All rights reserved.

Munoz M.,CSIC - National Center of Microelectronics | Prieto J.L.,Technical University of Madrid
Nature Communications | Year: 2011

Nanofabrication has allowed the development of new concepts such as magnetic logic and race-track memory, both of which are based on the displacement of magnetic domain walls on magnetic nanostripes. One of the issues that has to be solved before devices can meet the market demands is the stochastic behaviour of the domain wall movement in magnetic nanostripes. Here we show that the stochastic nature of the domain wall motion in permalloy nanostripes can be suppressed at very low fields (0.6-2.7 Oe). We also find different field regimes for this stochastic motion that match well with the domain wall propagation modes. The highest pinning probability is found around the precessional mode and, interestingly, it does not depend on the external field in this regime. These results constitute an experimental evidence of the intrinsic nature of the stochastic pinning of domain walls in soft magnetic nanostripes. © 2011 Macmillan Publishers Limited. All rights reserved.

Bausells J.,CSIC - National Center of Microelectronics
Microelectronic Engineering | Year: 2015

Microfabricated cantilevers have enabled a wide range of applications in scanning probe microscopies (SPM) and in high-sensitivity nanomechanical sensors. The use of piezoresistivity for self-sensing the cantilever motion is preferred to the standard optical readout for some applications, in view of the advantages that it offers in terms of miniaturization, operation in non-transparent liquid media and capability of simultaneously addressing arrays of devices. Although in principle piezoresistive cantilevers should have a lower resolution than their optical counterparts, current devices can achieve similar performances. This is because a large amount of work has been devoted in the past two decades to their development. This paper provides a short review of the field of piezoresistive cantilevers. We discuss the device performances for the measurement of forces or surface stresses in static operation, or masses in dynamic operation. We then describe the fabrication technologies and materials that are typically used to manufacture the cantilevers. Finally, the main applications in the domains of SPM and nanomechanical sensing are presented. © 2015 Elsevier B.V. All rights reserved.

Chiesa M.,CSIC - National Center of Microelectronics | Garcia R.,CSIC - National Center of Microelectronics
Applied Physics Letters | Year: 2010

We have measured the surface potential and the space charge generated during the first stages of atomic force microscopy field-induced oxidation. Space charge densities are about 1017 cm-3 for oxidation times below 10 ms. In a dry atmosphere, the surface potential is negative. However, in humid air the surface potential could be either positive or negative. This effect is attributed to a screening effect of the water molecules. These results explain and support the use of local oxidation patterns as templates for building molecular architectures. They also establish the space charge build up as an intrinsic feature in local oxidation experiments. © 2010 American Institute of Physics.

Martin J.,CSIC - National Center of Microelectronics | Martin-Gonzalez M.,CSIC - National Center of Microelectronics
Nanoscale | Year: 2012

Large area silicon nitride (SiN x) nanoporous surfaces are fabricated using poly(ether-ether-ketone) (PEEK) nanorod arrays as a template. The procedure involves manipulation of nanoporous anodic aluminum oxide (AAO) templates in order to form an ordered array of PEEK nanopillars with high temperature resistant characteristics. In this context, self-ordered AAO templates are infiltrated with PEEK melts via the "precursor film" method. Once the melts have been crystallized in the porous structure of AAO, the basis alumina layer is removed, yielding an ordered array of PEEK nanopillars. The resulting structure is a high temperature and chemical resistant polymeric nanomold, which can be utilized in the synthesis of nanoporous materials under aggressive conditions. Such conditions are high temperatures (up to 320°C), vacuum, or extreme pH. For example, SiN x nanopore arrays have been grown by plasma enhanced chemical vapor deposition at 300°C, which can be of interest as mold for nanoimprint lithography, due to its hardness and low surface energy. The SiN x nanopore array portrays the same characteristics as the original AAO template: 120 nm diameter pores and an interpore distance of 430 nm. Furthermore, the aspect ratio of the SiN x nanopores can be tuned by selecting an AAO template with appropriate conditions. The use of PEEK as a nanotemplate extends the applicability of polymeric nanopatterns into a temperature regime up to now not accessible and opens up the simple fabrication of novel nanoporous inorganic surfaces. This journal is © The Royal Society of Chemistry 2012.

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