J. Sánchez-Marcos

Raman spectroscopy for the study of reduction mechanisms and optimization of conductivity in graphene oxide thin films

Highly reduced few-layer graphene oxide films with conductivities of up to 500 S cm−1 are obtained. The thin films with an optimized compromise between sheet resistance (3.1 kΩ sq−1) and transparency (around 80% to 90%) are suitable for touch screens and transparent electrodes in OLEDs. We discuss the effects of low temperature annealing and chemical reduction on the properties of the films and present an optimized reduction process that allows the original 2D/G Raman intensity ratio of few-layer graphene to be recovered. The Raman spectrum of graphene oxide is found to be only related to oxygen-free graphene-like regions with Raman bands at 1130 and 3155 cm−1 that probably involve C–H vibrations of rings and edges, while a band at 1700 cm−1 is assigned to irregular rings such as Stone Wales defects. All the bands involve resonant Raman processes and disappear in highly reduced samples. Clear correlations of the D band width with the sp2 content in thin films and resistivity have been observed, indicating that this is a good Raman parameter for evaluating the quality of the samples. The structural defects produced by the release of embedded water and some of the oxygen functional groups during annealing are detrimental for intra-grain conductivity but greatly enhance inter-grain connectivity.

Enhancement and Directionality of Spontaneous Emission in Hybrid Self‐Assembled Photonic–Plasmonic Crystals

J.F. Galisteo-Lopez was supported by the JAE Postdoctoral Program. M. Lopez-Garcia was supported by the FPI PhD program from the MICINN. This work was supported by the Spanish MICINN CSD2007-0046 (Nanolightes) and MAT2006-09062 projects. A. Garcia-Martin also acknowledges financial support from the Spanish MICINN (MAGPLAS MAT2008-06765-C02-01/NAN, Funcoat Consolider Ingenio 2010 CSD2008-00023), and European Commission (NMP3-SL-2008-214107-Nanomagma).

Electrical stimuli to increase cell proliferation on carbon nanotubes/mesoporous silica composites for drug delivery

The development of smart materials as bone implants is nowadays a challenging task to optimize their fast osteointegration. Nevertheless, no attempts have been done in joining the possibility of using electrical stimulation and drug delivery together in a material intended for bone tissue engineering. Moreover, the use of this synergy to induce bone healing is still limited until novel drug reservoirs material formulations allow an efficient applicability of the electrical stimuli. Herein, we present the biological response of osteoblasts cells, cultured over carbon nanotubes-mesoporous silica composites while exposed to external electrical stimulus. Moreover, its ability to function as drug delivery systems is also demonstrated. Bone cell metabolism was stimulated and mitochondrial activity was increased up to seven times in the presence of these composites under electrical stimulus, suggesting their potential application in bone regeneration processes.

Carbon nanotubes—mesoporous silica composites as controllable biomaterials

A composite based on mesoporous ordered silica (SBA-15) and carbon nanotubes (CNTs), has been synthesized to be used in biomedical applications as a conductor composite for cell stimulation and regeneration. The influence of the CNT addition time on the SBA-15–CNTs composite synthesis has been studied and optimized attending to morphology and structure, to produce a homogeneous material with both structures preserved. With the addition of the CNTs, the electrical resistance has decreased 8 orders in magnitude in comparison to the SBA-15 itself. The potential of these materials to be used as bioimplants has been evaluated in vitro by soaking the composite in simulated body fluid (SBF) at 37 °C.

Exchange bias in iron oxide nanoclusters

Iron oxide nanoclusters have been prepared by the gas-phase aggregation technique to form thin film structures with very high exchange bias values (up to 3000xa0Oe at low temperatures). Composition has been analysed by x-ray absorption and Mössbauer spectroscopies in order to elucidate the actual origin of the observed magnetic behaviour. The formation of a metal-oxide core-shell arrangement to explain the observed exchange bias has to be discarded since results show no metallic iron content and the main presence of α-Fe(2)O(3). The observed weak ferromagnetism and exchange bias are in agreement with the obtained size of α-Fe(2)O(3) nanoparticles: weak ferromagnetism because of the well-known spin canting in this antiferromagnetic structure and exchange bias because of the interaction between different spin sublattice configurations promoted by the modification of iron coordination in α-Fe(2)O(3) nanoparticles. Moreover, the preparation method is proposed for tuning both magnetization and exchange bias values by modification of the preparation conditions of α-Fe(2)O(3) nanoparticles, which open new possibilities in the design of new materials with required properties.

Elastic properties of B-C-N films grown by N2-reactive sputtering from boron carbide targets

Boron-carbon-nitrogen films were grown by RF reactive sputtering from a B4C target and N2 as reactive gas. The films present phase segregation and are mechanically softer than boron carbide films (a factor of more than 2 in Youngs modulus). This fact can turn out as an advantage in order to select buffer layers to better anchor boron carbide films on substrates eliminating thermally induced mechanical tensions.