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The following article appeared in Scientific Reports 10 (2020): 16039 and may be found at https://www.nature.com/articles/s41598-020-73029-9, In this work we report on the characterization and biological functionalization of 2D MoS2 fakes, epitaxially grown on sapphire, to develop an optical biosensor for the breast cancer biomarker miRNA21. The MoS2 fakes were modifed with a thiolated DNA probe complementary to the target biomarker. Based on the photoluminescence of MoS2, the hybridization events were analyzed for the target (miRNA21c) and the control non-complementary sequence (miRNA21nc). A specifc redshift was observed for the hybridization with miRNA21c, but not for the control, demonstrating the biomarker recognition via PL. The homogeneity of these MoS2 platforms was verifed with microscopic maps. The detailed spectroscopic analysis of the spectra reveals changes in the trion to excitation ratio, being the redshift after the hybridization ascribed to both peaks. The results demonstrate the benefts of optical biosensors based on MoS2 monolayer for future commercial devices, The research is supported by the MINECO (CTQ2017-84309-C2-2-R, CTQ2017-84309-C2-1-R, ELECTROBIONET, RED2018-102412-T) and Comunidad de Madrid (TRANSNANOAVANSENS, P2018/NMT4349) projects. ARC acknowledges Ramón y Cajal program (under contract number RYC-2015-18047)

In this work, we present our recent results on the applicability of optical microcavities based on Cr doped Ga_2O_3 wires to operate as a nanothermometer in a wide temperature range (at least from 150 up to 550 K) and achieving a temperature precision of around 1 K. To this purpose, DBR (distributed Bragg reflectors) have been used to enhance the reflectivity at the lateral ends of the wires. The transduction mechanism encompasses both the luminescence features of the characteristic R-lines of Cr^(3+) ions in this host as well as the interferometric effects of the Fabry-Perot resonances within the cavity.

Remote temperature sensing at the micro- and nanoscale is key in fields such as photonics, electronics, energy, or biomedicine, with optical properties being one of the most used transducing mechanisms for such sensors. Ga

The doping strategy of hybrid perovskites is being extensively explored not only for higher efficiency but also to overcome issues in photovoltaic materials such as self-degradation pathways in an ambient atmosphere or under visible irradiation. Here, BiI3 is introduced in the synthesis of MAPbI3 films (MA: CH3–NH3+) to stabilize the material. Around 25% of nominal Bi3+ is accommodated in the perovskite structure, producing a shrinking of the unit cell and a small increase of the band gap. The presence of empty Bi gap states quenches the 770 nm red interband emission and results in a near-infrared emission at 1100 nm. However, high enough visible irradiation density induces a progressive segregation of Bi3+ out of the perovskite lattice and promotes the re-emergence of the red emission. This emission is blue-shifted, and its intensity increases strongly with time until it reaches a saturation value which remains stable in the transformed films for extremely high power densities, around 1000 times higher t...

The optical and electrical properties of fluorinated tin oxide (FTO) films deposited at room temperature by sputtering have been investigated varying the fluorine content and the hydrogen atmosphere. The complex behavior of the obtained films is disclosed using a wide set of characterization techniques that reveals the combined effects of these two parameters on the generated defects. These defects control the electrical transport (carrier density, mobility and conductivity), the optical properties (band gap and defects-related absorption and photoluminescence) and finally promote the amorphization of the samples. H2 in the sputtering gas does not modify the H content in the films but induces the partial reduction of tin (from Sn4 to Sn2) and the consequent generation of oxygen vacancies with shallow energy levels close to the valence band. A variation of up to four orders of magnitude in electrical conductivity is reported in samples with the appropriate fluorine doping and hydrogen fraction in the sputtering gas, maintaining excellent optical transparency. Optimized room temperature grown electrodes reach sheet resistance ~20 Omega and transparency 90%. This room temperature deposition process enables film preparation on flexible organic substrates, such as polyethylene terephthalate (PET), with identical performance of doubtless interest in flexible and large scale electronics. We would like to thank IDIVAL for financial support, Projects N°NVAL16/17, INNVAL19/18 and NVAL18/07. CRL thanks the MINECO for the Juan de la Cierva Formación grant (ref. FJCI-2015-25306). This work has been supported by the Spanish MINECO, Instituto de Salud Carlos III, the European Union FEDER funds under Projects ref. PI16/00496 (AES 2016), PI19/00349 and DTS19/00033 (AES 2019). The authors are grateful to Dr F Madrazo and the Laser Microscopy Unit of the IDIVAL Institute for the use of the Confocal Raman Imaging Microscope.

The relatively low stability of solar cells based on hybrid halide perovskites is the main issue to be solved for the implementation in real life of these extraordinary materials. Degradation is accelerated by temperature, moisture, oxygen, and light and mediated by halide easy hopping. The approach here is to incorporate pristine graphene, which is hydrophobic and impermeable to gases and likely limits ionic diffusion while maintaining adequate electronic conductivity. Low concentrations of few-layer graphene platelets (up to 24 × 10–3 wt %) were incorporated to MAPbI3 films for a detailed structural, optical, and transport study whose results are then used to fabricate solar cells with graphene-doped active layers. The lowest graphene content delays the degradation of films with time and light irradiation and leads to enhanced photovoltaic performance and stability of the solar cells, with relative improvement over devices without graphene of 15% in the power conversion efficiency, PCE. A higher graphene content further stabilizes the perovskite films but is detrimental for in-operation devices. A trade-off between the possible sealing effect of the perovskite grains by graphene, that limits ionic diffusion, and the reduction of the crystalline domain size that reduces electronic transport, and, especially, the detected increase of film porosity, that facilitates the access to atmospheric gases, is proposed to be at the origin of the observed trends. This work demonstrated how the synergy between these materials can help to develop cost-effective routes to overcome the stability barrier of metal halide perovskites, introducing active layer design strategies that allow commercialization to take off. We acknowledge financial support by the Spanish Ministry of Science and Innovation under Projects PID2020-115514RB-I00 (C.C.), MAT2015-65356-C3-2-R (A.A), and PID2019-107314RB-I00 (I.M-S). This work was partially supported by European Research Council (ERC) via Consolidator Grant (724424-No-LIMIT) (I.M-S), AYUDA PUENTE 2020 URJC (C.C.). Associated Lab LABCADIO belonging to Community of Madrid, CM, net laboratories ref 351 is also acknowledged (C.C.). T.S.R. acknowledges funding from CM and European Social Fund (ESF) under the Talento fellowship 2017-T2/IND-5586 and project F660 financed by CM and Rey Juan Carlos University under action 1, “Encouragement of Young Phd students investigation". C.R-O. acknowledges funding from the Spanish Ministry of Science and Innovation under a FPI predoctoral contract (PRE2019-088433).

In this work we report on the characterization and biological functionalization of 2D MoS2 flakes, epitaxially grown on sapphire, to develop an optical biosensor for the breast cancer biomarker miRNA21. The MoS2 flakes were modified with a thiolated DNA probe complementary to the target biomarker. Based on the photoluminescence of MoS2, the hybridization events were analyzed for the target (miRNA21c) and the control non-complementary sequence (miRNA21nc). A specific redshift was observed for the hybridization with miRNA21c, but not for the control, demonstrating the biomarker recognition via PL. The homogeneity of these MoS2 platforms was verified with microscopic maps. The detailed spectroscopic analysis of the spectra reveals changes in the trion to excitation ratio, being the redshift after the hybridization ascribed to both peaks. The results demonstrate the benefits of optical biosensors based on MoS2 monolayer for future commercial devices.

A new approach for in-situ specific functionalization of graphene with carboxylic groups through a single-step growth is presented. Depending on the fabrication parameters, it is possible to synthesize functionalized single layer or multilayer graphene. The homogeneity and functionalization degree are evaluated combining micro-Raman and XPS spectroscopies. The obtained COOH content reaches around 5%, similar to the values obtained by the other methods but with significantly lower contents of the other oxygen groups (carbonyl and hydroxyl) and of other sp defects which are detrimental for electronic transport. The obtained COOH- functionalized single-layer graphene presents optimum values of the sheet resistance, around 8 kΩ, and high mobility, around 800 cmVs. Anchoring of antibodies is demonstrated through the immobilization of IgG1–FITC by the carbodiimide method, showing that these COOH- functionalized single-layer graphene can be very promising materials for electronic sensing applications., Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under Project MAT2015-65356-C3-1-R and Comunidad de Madrid Excellence Network under Project S2013/MIT-2740 is acknowledged. S.C. acknowledges BES-2016-076440 and L.A.-F. BES-2013-062759 FPI grants from MINECO.

Chemical vapor deposition (CVD) is one of the best ways to scalably grow low cost, high quality graphene on metal substrates; unfortunately, it not ideal for producing graphene on dielectric substrates. Here, we demontrate production of a high quality graphene layer on Sapphire using CVD with a copper catalyst. The catalyst consists of a thin copper film grown epitaxially on α- Al 2 O 3 (0001). After CVD growth of Graphene, the copper can be removed by simple evaporation in the presence of a carbon source ( C 2 H 4 ). We characterized the resulting graphene layer using Raman spectroscopy, atomic force microscopy (AFM), optical transmission and helium atom scattering (HAS). The sample exhibited a reduced Raman D peak and an excellent 2D to G ratio. AFM and HAS show large graphene domains over a macroscopic region. We measured > 86 % transparency over the visible spectrum.

The optical and electrical properties of fluorinated tin oxide (FTO) films deposited at room temperature by sputtering were investigated. In addition to small amount of oxygen to preserve highly transparent films, electrical resistivity become decreased two orders of magnitude by using appropriate hydrogen content in the sputtering gas. Films deposited with Ar(93%)/O2(5%)/H2(2%) gas mixture show maximal values of conductivity, charge carrier density and mobility as well as excellent transparency. Taking into account the film characterization carried out by Rutherford backscattering spectrometry (RBS), a mechanism is proposed to explain the observed optical and electrical dependence with the hydrogen content in the film.

Enhancing the stability of spectrally selective coatings (SSC) at high temperatures in air is necessary to push the concentrated solar power (CSP) technology to the next level. To avoid failures that might not be discovered for years, advanced knowledge of the chemical properties related to the degradation mechanisms with temperature is required. For this purpose, the Mo local environment is investigated here for Mo–Si3N4 and MoSi2–Si3N4 nanocomposites SSCs. The atomic short-range order around Mo proves that MoSi2 is the stable form that appears in high temperature vacuum annealing and that MoO3 formation is associated with optical degradation in air annealing. Deposition of Al2O3 capping layers with different techniques is found of paramount relevance in the long term performance of MoSi2–Si3N4 based SSCs. MoSi2–Si3N4 hybrid composite with Al2O3 capping layer shows exceptional functional stability even after 2900 h at 600 °C in air. Antireflective Al2O3 layer synthesized by atomic layer deposition (ALD) ...

Remote temperature sensing at the micro- and nanoscale is key in fields such as photonics, electronics, energy, or biomedicine, with optical properties being one of the most used transducing mechanisms for such sensors. Ga_2O_3presents very high chemical and thermal stability, as well as high radiation resistance, becoming of great interest to be used under extreme conditions, for example, electrical and/or optical high-power devices and harsh environments. In this work, a luminescent and interferometric thermometer is proposed based on Fabry-Perot (FP) optical microcavities built on Cr-doped Ga_2O_3 nanowires. It combines the optical features of the Cr^(3+) -related luminescence, greatly sensitive to temperature, and spatial confinement of light, which results in strong FP resonances within the Cr^(3+) broad band. While the chromium-related R lines energy shifts are adequate for low-temperature sensing, FP resonances extend the sensing range to high temperatures with excellent sensitivity. This thermometry system achieves micron-range spatial resolution, temperature precision of around 1 K, and a wide operational range, demonstrating to work at least in the 150-550 K temperature range. Besides, the temperature-dependent anisotropic refractive index and thermo-optic coefficient of this oxide have been further characterized by comparison to experimental, analytical, and finite-difference time-domain simulation results.

Size, shape and hot spots are crucial to optimize Raman amplification from metallic nanoparticle (NPs). The amplification from radius = 1.8 ± 0.4 nm ultra-small silver NPs was explored. Increasing NP density redshifts and widens their plasmon that, according to simulations for NPs arrays, is originated by the reduction of the interparticle distance, d, becoming remarkable for d ≤ R. Inter-particle interaction red-shifts (>130 nm) and widens (>90 nm) the standard plasmon of non-interacting spherical particles. Graphene partly delocalizes the carriers enhancing the NIR spectral weight. Raman amplification of graphene phonons is moderate and depends smoothly on d while that of Rhodamine 6G (R6G) varies almost exponentially due to their location at hot-spots that depend strongly on d. The experimental correlation between amplification and plasmon position is well reproduced by simulations. The amplification originated by the ultra-small NPs is compared to that of larger particles, granular silver films with 7 < R < 15 nm grains, with similar extinction values. The amplification is found to be larger for the 1.8 nm NPs due to the higher surface/volume ration that allows higher density of hot spots. It is demonstrated that Raman amplification can be efficiently increased by depositing low density layers of ultra-small NPs on top of granular films. The research leading to these results has received funding from Ministerio de Ciencia, Innovación y Universidades (RTI2018-096918-B-C41). S.C. acknowledges the grant BES-2016-076440 from MINECO. L.M. acknowledges the European Union (grant number ERC-2013-SyG 610256 NANOCOSMOS).

© 2020 by the authors., The detection of Raman signals from diluted molecules or biomaterials in complex media is still a challenge. Besides the widely studied Raman enhancement by nanoparticle plasmons, interference mechanisms provide an interesting option. A novel approach for amplification platforms based on supported thin alumina membranes was designed and fabricated to optimize the interference processes. The dielectric layer is the extremely thin alumina membrane itself and, its metallic aluminum support, the reflecting medium. A CVD (chemical vapor deposition) single-layer graphene is transferred on the membrane to serve as substrate to deposit the analyte. Experimental results and simulations of the interference processes were employed to determine the relevant parameters of the structure to optimize the Raman enhancement factor (E.F.). Highly homogeneous E.F. over the platform surface are obtained, typically 370 ± (5%), for membranes with ~100 nm pore depth, ~18 nm pore diameter and the complete elimination of the Al2O3 bottom barrier layer. The combined surface enhanced Raman scattering (SERS) and interference amplification is also demonstrated by depositing ultra-small silver nanoparticles. This new approach to amplify the Raman signal of analytes is easily obtained, low-cost and robust with useful enhancement factors (~400) and allows only interference or combined enhancement mechanisms, depending on the analyte requirements., The research leading to these results has received funding from Ministerio de Ciencia, Innovación y Universidades (RTI2018-096918-B-C41) and RTI2018-094040-B-I00) and by the Agency for Management of University and Research Grants (AGAUR) 2017-SGR-1527. S.C. acknowledges the grant BES-2016-076440 from MINECO.

This article belongs to the Special Issue Physics and Chemistry of Graphene: From Fundamentals to Applications. The search for novel platforms and metamaterials for the enhancement of optical and particularly Raman signals is still an objective since optical techniques offer affordable, noninvasive methods with high spatial resolution and penetration depth adequate to detect and image a large variety of systems, from 2D materials to molecules in complex media and tissues. Definitely, plasmonic materials produce the most efficient enhancement through the surface-enhanced Raman scattering (SERS) process, allowing single-molecule detection, and are the most studied ones. Here we focus on less explored aspects of SERS such as the role of the inter-nanoparticle (NP) distance and the ultra-small NP size limit (down to a few nm) and on novel approaches involving graphene and graphene-related materials. The issues on reproducibility and homogeneity for the quantification of the probe molecules will also be discussed. Other light enhancement mechanisms, in particular resonant and interference Raman scatterings, as well as the platforms that allow combining several of them, are presented in this review with a special focus on the possibilities that graphene offers for the design and fabrication of novel architectures. Recent fluorescence enhancement platforms and strategies, so important for bio-detection and imaging, are reviewed as well as the relevance of graphene oxide and graphene/carbon nanodots in the field. The research leading to these results has received funding from Ministerio de Ciencia e Innovación (RTI2018-096918-B-C41). S.C. acknowledges the grant BES-2016-076440 from MINECO.

Graphene is grown by chemical vapour deposition on ruthenium ultrathin films down to a nominal thickness of 5 nm. While at 910 °C multilayer graphitic films are obtained, single layer defective graphene is formed at 1000 °C. The extremely thin Ru films allow the formation of a novel nano-crystalline ruthenium carbide phase to be discerned by combining synchrotron X-ray diffraction, synchrotron X-ray absorption spectroscopy and electron diffraction. The ruthenium carbide (Ru-C) phase formed at or above 1000 °C presents cubic symmetry (cP) with a lattice parameter of 2.927 Å and a Ru-C distance of around 2.31 Å. The increase of C solubility in ruthenium seems to be sufficient to trigger the stabilization of the Ru-C phase during graphene growth preferentially in grains with orientation different to (0001). The structural transition from hcp Ru to cP Ru-C is not limited to a shell; it occurs for the whole grain. The formation of the carbide seems to favour the synthesis of single layer graphene by hindering the segregation of carbon to the surface during cooling. This simple method allows nano-crystalline ruthenium-carbide films to be obtained as well as graphene covered Ru nanograins, both with size control. These new materials are foreseen to present interesting mechanical, catalytic and sensing properties.http://doi.org/10.1039/C7TC02855E, Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under Project MAT2015-65356-C3-1-R and Comunidad de Madrid Excellence Network under Project S2013/MIT-2740 is acknowledged. We also acknowledge the MINECO for financial support and provision of synchrotron radiation facilities at the BM25 SpLine of The Spanish CRG Beamline at the ESRF. L. A.-F. acknowledges a FPI grant (BES-2013-062759) from MINECO.

We report on the formation of highly stable and robust hybrid semitransparent electrodes based on a percolated mesoscale copper grid covered with graphene. Copper films sputtered on transparent substrates are used to synthesize graphene by CVD and annealed to form metallic grids covered with graphene. The copper grid density can be controlled by varying annealing temperature and time, obtaining excellent sheet resistance ( < 0.7 Omega/sq). The single layer graphene that covers the whole sample modifies the preferred crystalline orientation favoring (110) copper grains when treated up to 1050 degrees C. However, when annealed few degrees below bulk copper melting temperature, graphene is partially eliminated, probably due to the high pressure of copper vapor generated underneath, and copper forms isolated dots with mainly (111) orientation. During graphene synthesis, similar to 70% of the copper film is evaporated but, once graphene layer is completed the remaining copper fraction is constant up to almost bulk copper melting temperature demonstrating that graphene is an excellent barrier against copper evaporation. Contrary to the enhanced oxidation of copper foils with graphene, these graphene-Cu grids are extremely stable in ambient conditions maintaining an almost unchanged performance for years. The copper based meso-grids are highly stable and robust and present a suitable surface for organic- and biomolecules provided by the continuous graphene layer.

[EN] 2D monolayer molybdenum disulphide (MoS) has been the focus of intense research due to its direct bandgap compared with the indirect bandgap of its bulk counterpart; however its photoluminescence (PL) intensity is limited due to its low absorption efficiency. Herein, we use gallium hemispherical nanoparticles (Ga NPs) deposited by thermal evaporation on top of chemical vapour deposited MoS monolayers in order to enhance its luminescence. The influence of the NP radius and the laser wavelength is reported in PL and Raman experiments. In addition, the physics behind the PL enhancement factor is investigated. The results indicate that the prominent enhancement is caused by the localized surface plasmon resonance of the Ga NPs induced by a charge transfer phenomenon. This work sheds light on the use of alternative metals, besides silver and gold, for the improvement of MoS luminescence., The research is supported by the MINECO (CTQ2014-53334-C2-2-R, MAT2015-65356-C3-1-R and CTQ2017-84309-C2-2-R) and Comunidad de Madrid (NANOAVANSENS ref. S2013/MIT-3029) and UAM-Santander (2017/EEUU/14) projects. ARC acknowledges the Ramón y Cajal program (under contract number RYC-2015-18047). FN acknowledges support from the Marie Sklodowska-Curie grant agreement No. 641899 from the European Union's Horizon 2020 research and innovation programme.

Understanding the interaction between graphene and its supporting substrate is of paramount importance for the development of graphene based applications. In this work the interplay of the technologically relevant graphene-Cu system is investigated in detail as a function of substrate grain orientation in Cu polycrystalline foils. While (100) and (111) Cu grains show the well-known graphene-enhanced oxidation, (110) grains present a superior oxidation resistance compared to uncovered Cu and an anomalous shift of its graphene 2D Raman band which cannot be explained by the known effects of strain and doping. These results are interpreted in terms of a weak graphene-Cu coupling at the (110) grains, and show that graphene can actually be used as anticorrosion coating, contrary to previously reported. The anomalous shift is suggested to be the result of an enhanced outer Raman scattering process which surpasses the usually dominant inner process. Since Raman spectroscopy is widely used as first and main characterization tool of graphene, the existence of an anomalous shift on its 2D band not only challenges the current theory of Raman scattering in graphene, but also has profound implications from an experimental point of view.

2D monolayer molybdenum disulphide (MoS

A cheap and green technology based on electro-erosion, performed at room conditions and scalable to large area (cm2) is demonstrated for structuring graphene and graphene oxide films on any substrate. This one-step technique based on electrical discharges produced by a direct current voltage source competes favorably with laser patterning. The threshold voltage for complete graphene elimination as determined by Raman mapping is around 20 V. At low relative humidity conditions (30%) the transformation to graphene oxide is also detected for operating voltages above 40 V, the oxidation being probably mediated by the residual adsorbed water at the surface. We also show the close correlation of atomic force microscopy (AFM) phase images with the modified graphene characteristics while AFM topographic images are dominated by extrinsic aspects. The use of a spring probe relaxes the requirement of precision for the tip-sample distance and sample flatness to around 10 μm which is very convenient for large scale applications. Furthermore, this technique allows the formation of high quality nanographene, with size around 18 nm, and graphene micro-ribbon lattices in a very fast way and very well defined edges, with dimensions down to 1 μm width and mm length, very promising for terahertz graphene plasmonic applications., X.D. acknowledges a FPI scholarship from Spanish MINECO and C.M. thanks financial support from the “Juan de la Cierva” postdoctoral program JCI-2011-08815. The research leading to these results has received funding from Spanish MINECO under projects MAT2012-37276-C03-01, MAT2012-37276-C03-03 and MAT2011-27470-C02-02, from Comunidad de Madrid under Project S2013/MIT-2740 (PHAMA_2.0-CM) as well as from the European Union Seventh Framework Program under grant agreement No. 604391 “Graphene Flagship.”

8 pags.; 8 figs., Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. The light emission properties of anatase TiO2/Eu3+ thin films prepared by electrophoretic deposition and of the corresponding precursor nanoparticulate sols and xerogels with different Eu3+ contents are reported. Transparent anatase TiO2 thin films were successfully obtained by electrophoretic deposition after dilution of the original sols with ethanol in order to inhibit the water hydrolysis and facilitate the drying process. The topography of the films shows a high homogeneous distribution in terms of grain size and roughness of the surface of the thin films. The film thickness varied from 50 nm to 800 nm and it was found to be strongly dependent on the Eu3+ content of the sols, probably because of uncompensated electrical charges provided by Eu3+ ions located at the surface of the nanoparticles. A spontaneous densification of the films occurs at a thickness above 400 nm and, concomitantly, a significant increase of the Eu3+ emission efficiency is detected. Transparent and nanoparticulate anatase TiO2/Eu3+ thin films were obtained by electrophoretic deposition. A densification of the films occurs at a thickness above 400 nm and, concomitantly, a significant increase of the Eu3+ emission efficiency is detected. Similar values of PL efficiency to those of the xerogels (bulk material) could be achieved., This study has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) through projects MAT2012- 31090, TEC2012-38901-C02-01 and MAT2012-37276-C03-01. M. B. thanks the Consejo Superior de Investigaciones Científicas (CSIC) for the concession of a grant (JAE-Pre 083).

Using a novel instrument previously reported by our group [1], we have been able to perform Local Anodic Oxidation (LAO) over monolayer graphene to create unprecedented large areas (larger than mm2) of single layer Graphene Oxide (GO) with any shape and in a very short time (a few minutes). Our instrument is equipped with three electromechanical steppers with 0.05 µm accuracy and 1 µm precision, and each stepper with a linear piezoactuator. It operates at speeds up to 15 mm/s, and includes a steel/Ni spring probe of typically 6 µm radius to work in tapping or contact mode. The equipment is provided with a humidity control system that allows maintaining a stable Relative Humidity (RH) environment, together with a system of supply and electrical monitoring. Thus, electrical signal coming from the tip-sample interaction is continuously monitored (by means of a high speed oscilloscope). When the tip approaches to graphene on a wet atmosphere (RH higher than 40%), it is commonly accepted that a water bridge is created between them. When a negative bias is applied to the tip respect to the grounded graphene (in our case we operate between 20V - 40 V), the LAO phenomena takes place [2] (Fig. 1a). The process firstly consists on electrical water ionization in H+ and OH- ions. Hydroxyl anions are then conducted to the graphene surface, which is thus oxidized. Within a specific RH range, the oxide patterns created show a good reproducibility and regular shape (Fig. 1b). Controlling the movement of the tip, we can draw the desired patterns over the graphene or any other 2D-substrate (Fig. 1c). We have extensively studied and optimized the influence of the experimental variables affecting the process, like applied bias, contact time or relative humidity. This LAO procedure is so a very powerful tool for the fabrication of electrical devices. Also, the possibility of chemical functionalization of GO allow us to design a large variety of utilities like (bio)chemical sensors, supported catalysts, etc. In addition, we have been able to record the electrochemical trace generated during the oxidation reaction of graphene. To our knowledge, it is the first time these records have been reported. Moreover, based on these data, we have formulated a theoretical model based just on classical first principles that predicts the behavior of the LAO process over graphene. This model shows a very accurate fit for the dependence of the oxide pattern expansion with the applied voltage (Fig. 2a), with the contact time (Fig. 2b), and also for the evolution of the recorded transient electric current (Fig. 2c). This model reveals very relevant information about the processes governing LAO. First, at the beginning (< 20 ms), most of the total current I(t) passing through the tip-substrate junction does not come from the electrochemical reaction but from residual conductance of the non-oxidized graphene. We call this component drift current, IT(t). Second, for longer times (>200 ms), the total current becomes dominated just by the electrochemical reaction, and the drift component almost vanishes. We call this component electrochemical current, IEC(t) (Fig. 2c). Third, the process is mainly driven by the electric field increase at the edge of the pattern. And fourth, the GO generated has a very high oxidation degree. This work opens new promising fields for development of extensive fabrication methods, technical applications and the study of anodic oxidation processes of conducting and any 2d material at large scales. References [1] Rev. Sci. Instrum. 2015, 86, 84704-6. [2] Carbon 2018, 129, 281. Figure 1

The detection, identification, and quantification of different types of molecules and the optical imaging of, for example, cellular processes are important challenges. Here, we present how interference-enhanced Raman scattering (IERS) in adequately designed heterostructures can provide amplification factors relevant for both detection and imaging. Calculations demonstrate that the key factor is maximizing the absolute value of the refractive indices' difference between dielectric and metal layers. Accordingly, Si/Al/AlO/graphene heterostructures have been fabricated by optimizing the thickness and roughness and reaching enhancement values up to 700 for 488 nm excitation. The deviation from the calculated enhancement, 1200, is mainly due to reflectivity losses and roughness of the Al layer. The IERS platforms are also demonstrated to improve significantly the quality of white light images of graphene and are foreseen to be adequate to reveal the morphology of 2D and biological materials. A graphene top layer is adequate for most organic molecule deposition and often quenches possible fluorescence, permitting Raman signal detection, which, for a rhodamine 6G (R6G) monolayer, presents a gain of 400. Without graphene, the nonquenched R6G fluorescence is similarly amplified. The wavelength dependence of the involved refractive indices predicts much higher amplification (around 10) for NIR excitation. These interference platforms can therefore be used to gain contrast and intensity in white light, Raman, and fluorescence imaging. We also demonstrate that surface-enhanced Raman scattering and IERS amplifications can be efficiently combined, leading to a gain of >10 (at 488 nm) by depositing a Ag nanostructured transparent film on the IERS platform. When the plasmonic structures deposited on the IERS platforms are optimized, singlemolecule detection can be actively envisaged., L.A.-F. acknowledges a FPI grant (BES-2013-062759) from Spanish Ministerio de Economía y Competitividad (MINECO). The research leading to these results has received funding from MINECO (MAT2012-37276-C03-01 and MAT2015-65356-C3-1-R) and Comunidad de Madrid (S2013/MIT-2740, PHAMA2.0-CM).

The oxidation and corrosion of copper are fundamental issues studied for many decades due to their ubiquitous and transversal impact. However, the oxidation of copper used as catalyst for graphene synthesis has opened a singular problem not yet solved. Contradictory results are reported about the protecting or enhancing role of graphene in copper oxidation. We study short- and long-term oxidation of copper with different characteristics, such as oxygen content and morphology, with and without graphene, and in polycrystalline copper foils and almost totally textured (100) and (111) copper films on MgO and sapphire substrates, respectively. We propose a mechanism to explain the enhanced oxidation of polycrystalline copper originated by oxygen encapsulated by the graphene impermeable layer during graphene growth. The initial oxygen content and the existence of grain boundaries are the main factors that determine the relevance of this process. Graphene is shown to prevent oxidation from the atmosphere for any of the copper substrates but also promotes slow oxidation derived by the release of out-of-equilibrium encapsulated oxygen. The formation of bubbles after several months evidence this slow release. The occluded oxygen in graphene covered copper is demonstrated by comparing the oxygen to copper ratio at different depths using hard X-ray photoelectron spectroscopy for samples with and without graphene., Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under Projects MAT2015-65356-C3-1-R and MAT2012-37276-C03-01 and Comunidad de Madrid Excellence Network under Project S2013/MIT-2740 is acknowledged. We also acknowledge the MINECO for financial support and provision of synchrotron radiation facilities at BM25 SpLine The Spanish CRG Beamline at the ESRF. L.A-F. acknowledges a FPI grant (BES-2013-062759) from MINECO.

In addition to the known effect of the substrate on the interfacial properties of perovskite films, here we show that the bulk properties of hybrid lead halide perovskite films depend on the type of substrate used for film growth. Despite the relative large film thickness, ∼600 nm, the roughness and nature of the substrate layer (glass, FTO, TiO and PEDOT:PSS) affect not just the degree of preferential orientation and crystal grain size but also the lattice parameters of CHNHPbI films synthesized from the PbCl precursor. The obtained changes in lattice parameters indicate that the Pb-Pb distance varies by around 0.7%. We suggest that the substrate roughness and chemical nature determine the concentration of defects mainly by varying the chlorine content and probably by the incorporation of oxygen and iodine vacancies during film nucleation and growth. These differences also have consequences in the observed light induced transformations. Upon laser illumination, the formation of additional defects, most probably related to oxygen, is revealed by 110 and 165 cm Raman peaks. With increasing laser power the chemical transformation into PbO is clearly identified by the 140 and 275 cm Raman peaks. The irreversible photoluminescence enhancement observed at low power with illumination time, also dependent on the substrate nature, is proposed to be due to the localization of the electron-hole excitons created in the vicinity of the light generated defects. These results shed light on the performance of the perovskite layer and help to understand how bulk processes, where ion migration is a conspicuous example, are severely affected by interfacial properties such as those imposed by the substrate., Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under Projects MAT2015-65356-C3-1-R and 2-R, MAT2014-54852-R and MAT2015-70611-ERC and Comunidad de Madrid Excellence Network under Project S2013/MIT-2740 (and Associated Lab LABCADIO belonging to CM net labs ref. 351) is acknowledged. We also acknowledge the MINECO for financial support and provision of synchrotron radiation facilities at ESRF, and thank María Vila for her assistance in using beamline BM25-SpLine. B. C. H. is grateful to the support of the National Council of Technological and Scientific Development (CNPq), Brazil, through the Science without Borders program.

Stable Graphene/gas/Cu bubbles are formed by the spontaneous oxidation at room conditions of the Cu substrates used as the catalyst agent in chemical vapor deposition growth of graphene. The non homogeneous copper oxidation produces discontinuous CuO films where atmospheric molecules get trapped by the impermeable graphene layer forming bubbles. Raman Interference effects are calculated both for graphene and CuO phonons in graphene/CuO/Cu system using the transfer matrix method finding that CuO thickness is limited to 20 nm and maximum Raman enhancement of graphene is 10. Nevertheless, enhancement values up to 60 are detected for micrometric graphene bubbles on copper which, according to the simulations, are 70 nm height. AFM measurements confirm the bubble dimensions and show that they are mechanically softer than graphene on copper. Consistently, the Raman characteristics of the graphene bubbles coincide with free standing undoped graphene with small strain, in the range 0-0.3%, while graphene on CuO presents hole doping and larger strain fields. The simulations indicate that interference Raman enhancement can reach values >10 in graphene/dielectric/Aluminum trilayers (dielectric = gas, oxide or polymer). These systems are therefore interesting platforms for optical sensing where graphene is the adequate bio-compatible layer for metallic nanoparticles and molecules deposition., A-F. acknowledges a FPI grant from Spanish Ministerio de Economía y Competitividad (MINECO) (BES-2013-062759) and E.C-P from the European Union Seventh Framework Program under grant agreement n° 604391 “Graphene Flagship”. The research leading to these results has received funding from Spanish MINECO (MAT2012-37276-C03-01 and MAT2015-65356-C3-1-R) and Comunidad Autónoma de Madrid (S2013/MIT-2740, PHAMA2.0-CM).

The influence of particle size in both the structure and thermochromic behavior of 4H-SrMnO3 related perovskite is described. Microsized SrMnO3 suffers a structural transition from hexagonal (P63/mmc) to orthorhombic (C2221) symmetry at temperature close to 340 K. The orthorhombic distortion is due to the tilting of the corner-sharing Mn2O9 units building the 4H structural type. When temperature decreases, the distortion becomes sharper reaching its maximal degree at ∼125 K. These structural changes promote the modification of the electronic structure of orthorhombic SrMnO3 phase originating the observed color change. nano-SrMnO3 adopts the ideal 4H hexagonal structure at room temperature, the orthorhombic distortion being only detected at temperature below 170 K. A decrease in the orthorhombic distortion degree, compared to that observed in the microsample, may be the reason why a color change is not observed at low temperature (77 K).

With the correct choice of the solvothermal conditions, we have achieved the unprecedented in situ formation of the free radical form of the anthraquinone-1,5-disulfonate molecule, and its favorable organization. The semiquinone radicals are coordinated to rare-earth cations to produce a 2D framework with a very high charge mobility and electric conductivity through the π-π-interactions. The existence of AQDS 3- anion radicals is proven on the base of: i) the electrical neutrality: elemental analyses for the different lanthanide RPF-8 bulks, the maximum residual electron densities in the structure, rule out the existence of any other neutralizing ion, ii) the geometrical modifications in the antraquinone molecules, and iii) although less definitive, due to the low magnetic moment μ = 0.39 μ B, the exhibited paramagnetism for the La (3+) with no unpaired electrons. © 2012 The Royal Society of Chemistry., This work has been supported by Spanish MCYT Projects Mat 2007-60822, 2010-17571, and 2008-06542-C04, the Project Consolider-Ingenio CSD2006-2001, and the Project of Comunidad Autónoma de Madrid (S2009/MAT-1756).

We report on a new p-type organic semiconductor single crystal, 5,10,15-trimethyl-10,15-dihydro-5H-diindolo[3,2-a:3’,2’-c]carbazole (N-trimethyltriindole). This molecule crystallizes forming a highly ordered columnar structure in which stacked molecules are situated at two alternating distances (3.53 A and 3.68 A) along the column as determined by single crystal X-ray diffraction analysis. These short intermolecular distances between adjacent units, make this system an ideal candidate for charge-transport processes along the stacks. Relevant parameters for transport (i.e. internal reorganization energies, transfer integral) have been estimated by DFT calculations at a 6-311G(d,p)/B3LYP level of theory. As a double check for the transfer integral, the electronic band structure of a one-dimensional stack of molecules has been computed. The electronic properties of this material have been studied both theoretically and experimentally. Its HOMO value is found to coincide with Au work function (ΦAu = 5.1 eV), thus low barriers are expected for hole injection from gold electrodes. The hole mobility of this material has been predicted theoretically considering a hopping-type mechanism for the charge-transport and determined experimentally at the space charge limited current (SCLC) regime of the current–voltage measurements. Both theoretical and experimental values are in good agreement. The high hole mobility (μmin = 0.4 cm2 V−1 s−1) of this material points towards its useful application in the organic electronics arena. N-Trimethyltriindole single crystals constitute an essential model to study transport properties of triindole-based materials and to design new derivatives with improved electronic performance.

We report a new method to produce high-quality, transparent graphene/sapphire samples, using Cu as a catalyst. The starting point is a high-quality graphene layer prepared by CVD on Cu(111)/AlO. Graphene on sapphire is obtained in situ by evaporation of the Cu film in UHV. He-diffraction, atomic force microscopy (AFM), Raman spectroscopy and optical transmission have been used to assess the quality of graphene in a metal free area. We used helium atom scattering as a sensitive probe of the crystallinity of the graphene on sapphire. The observation of high reflectivity and clear diffraction peaks demonstrates the presence of flat and homogeneous graphene domains over lateral scales of microns, consistent with the AFM results. Surprisingly, putting graphene on sapphire improves the quality of the He-diffraction spectra. Graphene forms a moiré pattern with a (11 × 11) periodicity, aligned with the (1 × 1) sapphire unit cell. The lattice constant of graphene on sapphire is a = (2.44 ± 0.02) Å. The phonon dispersion of the graphene flexural mode has been measured. This allowed the determination of the bending rigidity k = 0.61 ± 0.15 eV, and the graphene-sapphire coupling strength g = (5.8 ± 0.4) × 10 N m. The uniformity of the graphene has also been investigated by Raman mapping. Judging by the ratio of the 2D to G peaks, the quality of the graphene is not degraded by Cu removal. The high transparency (80%) measured in the visible range makes this system suitable for many applications that require hybrid properties commonly associated with metals (conductivity) and insulators (transparency). Our study shows that He-diffraction and Raman provide crucial information on quite different, complementary aspects of the same samples., This project was sponsored by the European Union, Seventh Framework Programme: Theme NMP.2012.1.4-3 Grant no. 309672. AMW and HKY acknowledge support from the Alexander von Humboldt Foundation, the Max Planck EPFL Center for Molecular Nanoscience and Technology as well as the Deutsche Forschungsgemeinschaft under CRC 1073. Additionally, a part of the research has been supported by the Spanish MINECO, under project MAT2012-37276-C03-01, and by Comunidad de Madrid, under project S2013/MIT-2740 (PHAMA_2.0-CM). S2013/MIT-2740/PHAMA_2.0-CM

Current manufacturing technologies for OLEDs involve the use of expensive high vacuum techniques and call for thermal stability requirements which are not fulfilled by many materials. These problems disappear when the OLED films are deposited directly from solution. In this study, we have designed, synthesized and characterized a novel octacoordinated complex, Tris(1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedionate)mono(bathophenanthroline) europium(III), to be used as a >complex-only> emissive layer in wet-processed OLEDs. Upon excitation in the UV region, very efficient energy transfer from the ligands to Eu3+ takes place, giving rise to intense red emission with very high monochromaticity (R=19), both in powder and as a thin film. The decay times of 754 μs (powder) and 620 μs (thin film) are comparable to those of the most efficient Eu3+ β-diketonate complexes reported to date. The same energy transfer leading to saturated red and narrow emission is also observed in the OLED device (glass/ITO/PEDOT:PSS/[Eu(cbtfa)3(bath)]/Ca/Al) when biased at >5.2 V. Its high quantum efficiency (∼60%), good thermal stability up to 200 °C and adequate thin film forming properties make this material a promising chromophore for cost-effective OLEDs., P. Martín-Ramos thanks Fundación Iberdrola for its financial support. CEMDRX group is grateful to Fundação para a Ciência e a Tecnologia (FCT) for providing funds under grant PTDC/FIS/102284/2008 and PEst-C/FIS/UI0036/2011. Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under projects MAT2012-37276-C03 and MAT2012-37276-C01 is gratefully acknowledged by the URJC and ICMM groups.

Eu3+/TiO2 xerogels have been obtained from colloidal sols by drying at room conditions. Anatase with traces of brookite phases are obtained from the synthesis and the stability of both with temperature is higher (from 400°C up to 800°C) when Eu3+ is present. Raman phonons have been used to detect the different phases and follow the structural transitions. The observed changes with calcination temperature of anatase modes (Eg,1, B1g,1 Ag/B1g,2, and Eg,3) are found to be mainly related to the grain size. The anatase grain size increases more and at lower temperatures for undoped than for Eu3+-doped samples favoring the transition to rutile. The stability of the brookite phase is also influenced by the doping being higher in the doped xerogels (700°C) than in the undoped ones (400°C). No concentration quenching of the f-f Eu3+ emission bands is observed up to 3% Eu3+ at low temperatures but the maximum emission is found at lower temperatures for higher Eu3+ content may be due to quenching related to Eu3+ migration. The narrower f-f emission bands of the as-prepared samples are consistent with the presence of Eu3+ ions at the surface with a weak interaction with the TiO2 nanoparticles. A diffusion process of Eu3+ ions occurs during calcination from the surface to different positions of the anatase lattice close to the surface producing an inhomogeneous broadening. Finally, the formation of the pyrochlore phase Eu2Ti2O7 is detected which explains the decrease on the emission efficiency and the increase of the Eu3+ environment symmetry., This study has been supported by the Spanish Ministry of Economy and Competitiveness through projects MAT2012‐31090 and MAT2012‐37276‐C03‐01. Dr. M. Borlaf thanks CSIC for the concession of a grant (JAE‐Pre 083).

We propose a strategy to study the elastic properties of extremely thin graphene oxide (GO) films using Brillouin spectroscopy. The dependence of the surface acoustic wave of a gold capping layer on the structural, chemical and morphological changes occurring to the underneath GO film with temperature is reported and analyzed. At room temperature the shear constant c44 is ∼17 GPa and hardens up to 28 GPa at 100 °C due to the partial elimination of embedded water layers and to interlayer distance shrinking. At 200 °C the almost complete elimination of water induces layer stacking disorder, further GO–GO distance reduction and a significant increase of all elastic constants. The in-plane constants harden due to the partial restoration of the sp2 C network (c11: from 268 to 620 GPa) and the out of plane constants harden due to the H bonds that now directly connect the neighbouring GO layers (c44 ≈ 80 GPa). The obtained Young's moduli are significantly higher than those reported for GO paper because the ultra-thin GO films are highly ordered and there is no macroscopic applied strain during the measurement. The results obtained here are associated with the intrinsic properties of GO as in-plane and inter-layer bonding., X.D. acknowledges a FPI scholarship from Spanish MINECO. The research leading to these results has received funding from Spanish MINECO under project MAT2012-37276-C03-01, from Comunidad de Madrid, project S2013/MIT-2740 (PHAMA_2.0-CM) and from the European Union Seventh Framework Program under grant agreement no. 604391 “Graphene Flagship.” info:eu-repo/grantAgreement/EC/FP7/604391

Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform., Gil Gonçalves thanks the Fundação para a Ciência e Tecnologia (FCT) for the PostDoc grant (SFRH/BDP/84419/2012). A de Andres thanks MINECO (MAT2012-37276-C03-01) project. M Vila thanks the FCT for the 2013 investigator grant. We would like to thank Fundação para a Ciência e a Tecnologia (FCT, Portugal), the European Union, QREN, FEDER, COMPETE, for funding the TEMA Research Unit (PEst-C/QUI/UI0062/2013). The authors acknowledge the SUDOE and ERDF within the Territorial Cooperation Programme IVB funding through the project CarbonInspired 2.0 (Grant Agreement SOE4/P1/E793).

El pdf del artículo es la versión post-print.-- et al., We have developed a lactate biosensor based on a bionanocomposite (BNC) composed of titanium dioxide nanoparticles (TiO2-NPs), photocatalytically reduced graphene, and lactate oxidase. Graphene oxide was photochemically reduced (without using any chemical reagents) in the presence of TiO2-NPs to give graphene nanosheets that were characterized by atomic force microscopy, Raman and X-ray photoelectron spectroscopy. The results show the nanosheets to possess few oxygen functionalities only and to be decorated with TiO2-NPs. These nanosheets typically are at least 1 μm long and have a thickness of 4.2 nm. A BNC was obtained by mixing lactate oxidase with the nanosheets and immobilized on the surface of a glassy carbon electrode. The resulting biosensor was applied to the determination of lactate. Compared to a sensor without TiO2-NPs, the sensor exhibits higher sensitivity (6.0 μA mM-1), a better detection limit (0.6 μM), a wider linear response (2.0 μM to 0.40 mM), and better reproducibility (3.2 %). [Figure not available: see fulltext.] © 2013 Springer-Verlag Wien., This work has been supported by Comunidad Autónoma de Madrid (project No. S2009/PPQ-1642, AVANSENS), Ministerio de Ciencia e Innovación (project No. CTQ2011-28157) and Ministerio de Economía y Competitividad (project No. FIS2012-38866-C05-05).