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Cellulose acetate (CA) fibers were obtained by electrospinning and their properties analyzed by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction (XRD), differential scanning calorimeter (DSC) and thermogravimetric analysis. The effect of the polymer concentration on crystallinity and fiber diameter of the obtained material was studied by DSC. The application of the pure polymeric fibers to the discoloration of methylene blue (MB) aqueous solutions in dark and under sunlight irradiation was evaluated with UV–Vis absorption and photoluminescence spectroscopies. Also, the photodegradation of the dye was compared using CA powder and fibers under UV irradiation. The results revealed that the dye molecule discoloration with CA fibers mesh was higher under sunlight irradiation than in dark conditions. The maximum absorption band (664 nm) of MB decreased with the time in the absence and presence of polymer under either solar natural exposition or UV irradiation. The dye organic discoloration efficiency obtained by using electrospun CA mesh was 28% and 98% in dark conditions and under natural solar illumination, respectively. The FTIR showed the interaction of dye organic or sub-products generated with the polymeric component. This work provides a simple method for the discoloration of wastewater effluents using microfibers composed of only one abundant polymeric material, allowing the reduction in the amount of material needed and therefore the manufacturing costs of the adsorbent material.

In this work, copper selenide (Cu3Se2 umangite phase) was synthesized by two routes, using a chemical reaction and the hydrothermal method to obtain CuSe-A and CuSe-H, respectively. The synthesis o...

In this work, a high-resolution atomic force acoustic microscopy imaging technique is developed in order to obtain the local indentation modulus at the nanoscale level. The technique uses a model that gives a qualitative relationship between a set of contact resonance frequencies and the indentation modulus. It is based on white-noise excitation of the tip–sample interaction and uses system theory for the extraction of the resonance modes. During conventional scanning, for each pixel, the tip–sample interaction is excited with a white-noise signal. Then, a fast Fourier transform is applied to the deflection signal that comes from the photodiodes of the atomic force microscopy (AFM) equipment. This approach allows for the measurement of several vibrational modes in a single step with high frequency resolution, with less computational cost and at a faster speed than other similar techniques. This technique is referred to as stochastic atomic force acoustic microscopy (S-AFAM), and the frequency shifts of the free resonance frequencies of an AFM cantilever are used to determine the mechanical properties of a material. S-AFAM is implemented and compared with a conventional technique (resonance tracking-atomic force acoustic microscopy, RT-AFAM). A sample of a graphite film on a glass substrate is analyzed. S-AFAM can be implemented in any AFM system due to its reduced instrumentation requirements compared to conventional techniques.

Graphite, as a well-known carbon-based solid, is a paradigmatic example of the so-called van der Waals layered materials, which display a large anisotropy in their physical properties. Here we study quantum effects in structural and elastic properties of graphite by using path-integral molecular dynamics simulations in the temperature range from 50 to 1500~K. This method takes into account quantization and anharmonicity of vibrational modes in the material. Our results are compared with those found by using classical molecular dynamics simulations. We analyze the volume and in-plane area as functions of temperature and external stress. The quantum motion is essential to correctly describe the in-plane and out-of-plane thermal expansion. Quantum effects cause also changes in the elastic properties of graphite with respect to a classical model. At low temperature we find an appreciable decrease in the linear elastic constants, mainly in $C_{12}$ and $C_{44}$. Quantum corrections in stiffness constants can be in some cases even larger than 20\%. The bulk modulus and Poisson's ratio are reduced in a 4\% and 19\%, respectively, due to zero-point motion of the C atoms. These quantum effects in structural and elastic properties of graphite are nonnegligible up to temperatures higher than 300~K., 15 pages, 10 figures, 5 tables

We fabricated a ZnO-based Schottky diode via the deposition of a ZnO film co-doped with Al + In (4 at.%) on a boron-doped ZnO film (8 at.%). Each film was prepared by layering coatings (2, 3, 4, and 5 layers) by sol–gel deposition. The finished diode consists of the combination of seven layers (each layer with a thickness of around 90 nm). The total thickness of the diode is around 700 nm. The films were previously studied and structurally, optically and electrically characterized. Additionally, for comparative purposes, we fabricated and characterized un-doped ZnO films. The energy bandgap values of the un-doped films, mono-doped films, and co-doped films were 3.30 eV, 3.32 eV, and 3.34 eV, respectively. X-ray diffraction did not show traces of different phases from hexagonal Wurtzite-type ZnO. The electrical resistivity values obtained were 386, 4.44 × 104, and 3.37 Ω-cm, respectively. The junction diodes were built by depositing layers of the high-resistivity material (ZnO:B) on ITO conductor substrates, followed by the deposition of layers of the low-resistivity material (ZnO:Al + In) on the same substrate. The I–V characteristics of these diodes were analyzed in terms of the number of the deposited layers (or the different thickness of the films). The results show a Schottky-type behavior in the dark and under light (spot lamp of 160 W), which is controlled by the thickness of the resistive layer. From the I–V curves, the characteristic parameters including barrier height, ideality factor, and series resistance were calculated. From the transconductance (gm=dI/dV), it was possible to identify the presence of all the layer–layer interfaces. Depending on the thickness of the resistive ZnO:B film, we found a region of negative differential resistance and a region of visible light detection.

Primary intent of the present paper is to correlate the effectiveness of surface preparation type (pre-bonding), such as solvent cleaning, sanding (mechanical abrade), chemical etching (alkaline and acid), and peeling of sacrificial surface layer (peel ply) of carbon fiber reinforced composite (CFRC) test specimens, with the corresponding effect to the final strength of adhesive bonding. The analysis was performed by means of several spectroscopic and microscopic techniques, such as XPS, SEM, AFM, and a contact angle measurement technique which provides a direct, fast and easy measurement of the surface energy of the fiber composites. The adhesively bonded carbon fiber composites based on the different surface treatments were mechanically tested by employing the ASTM D 5528-0 (reapproved 2007) standard. The double cantilever beam (DCB) specimen geometry was used to evaluate the value known as opening Mode I inter-laminar fracture toughness (GIC) in adhesive bonds of carbon fiber composite materials. The results were varying between 1 and 1.8 kJ/m2 for GIC analysis and around 50 mm for delamination lengths. The mechanics of the linear elastic fracture is considered a tool for the failure of the laminate in composite materials with cracks or cuts in the plane, due to the presence of damaged zones in the tip of the crack; which is therefore applied to the study of delamination or fracture toughness.

Graphane is a layered material consisting of a sheet of hydrogenated graphene, with a C:H ratio of 1:1. We study isotopic effects in the properties of chair graphane, where H atoms alternate in a chairlike arrangement on both sides of the carbon layer. We use path-integral molecular dynamics simulations, which allows one to analyze the influence of nuclear quantum effects on equilibrium variables of materials. Finite-temperature properties of graphane are studied in the range 50--1500~K as functions of the isotopic mass of the constituent atoms, using an efficient tight-bonding potential. Results are presented for kinetic and internal energy, atomic mean-square displacements, fluctuations in the C--H bond direction, plus interatomic distances and layer area. At low temperature, substituting $^{13}$C for $^{12}$C gives a fractional change of $-2.6 \times 10^{-4}$ in C--C distance and $-3.9 \times 10^{-4}$ in the graphane layer area. Replacing $^2$H for $^1$H causes a larger fractional change in the C--H bond of $-5.7 \times 10^{-3}$. The isotopic effect in C--C bond distance increases (decreases) by applying a tensile (compressive) in-plane stress. These results are interpreted in terms of a quasiharmonic approximation for the vibrational modes. Similarities and differences with isotopic effects in graphene are discussed., 17 pages, 11 figures, 2 tables

Exposure of nanomaterials (NMs) to biological medium results in their direct interaction with biomolecules and the formation of a dynamic biomolecular layer known as the biomolecular corona. Despite numerous published data on nano-biointeractions, the role of protein glycosylation in the formation, characteristics, and fate of such nano-biocomplexes has been almost completely neglected, although most serum proteins are glycosylated. This study aimed to systematically investigate the differences in interaction of metallic NPs with glycosylated vs nonglycosylated transferrin. To reach this aim, we compared interaction mechanisms between differently sized, shaped, and surface-functionalized silver NMs and gold NMs to commercially available human transferrin (TRF), a glycosylated protein, and to its nonglycosylated recombinant form (ngTRF). Bovine serum albumin (BSA) was also included in the study for comparative purposes. Characterization of NMs was performed using transmission electron microscopy and dynamic and electrophoretic light scattering techniques. Fluorescence quenching and circular dichroism methods were used to evaluate protein binding constants on the nanosurface and conformational changes after the protein–NM interactions, respectively. Competitive binding of TRF, ngTRF, and BSA to the surface of different NMs was evaluated by separating them after extraction from protein corona by gel electrophoresis following quantification with a commercial protein assay. The results showed that the binding strength between NMs and transferrin and the changes in the secondary protein structure largely depend not only on NM physicochemical properties but also on the protein glycosylation status. Data gained by this study highlight the relevance of protein glycosylation for all future design, development, and efficacy and safety assessment of NMs., This study is based upon collaborative work from COST Action CA 17140 “Cancer Nanomedicine from the Bench to the Bedside” supported by COST (European Cooperation in Science and Technology). It was financially supported by the “Research Cooperability” Program of the Croatian Science Foundation funded by the European Union from the European Social Fund under the Operational Programme Efficient Human Resources 2014–2020 (grant HRZZ-PZS-2019-02-4323), Ministerio de Ciencia e Innovacion (Spain, grant BIO2017–84246-C2–1-R), Fondo Social de la DGA (grupos DGA), and Croatian Science Foundation (grant number HRZZ-IP-2016-06-2436). The authors would like to acknowledge the use of the Advanced Microscopy Laboratory (INMA-Universidad de Zaragoza) for access to their instrumentation and expertise.

Isotopic effects are relevant to understand several properties of solids, and have been thoroughly analyzed along the years. These effects may depend on the dimensionality of the considered solid. Here we assess their magnitude for structural properties of graphene, a paradigmatic two-dimensional material. We use path-integral molecular dynamics simulations, a well-suited technique to quantify the influence of nuclear quantum effects on equilibrium variables, especially in cases where anharmonic effects are important. Emphasis is put on interatomic distances and mean-square displacements, as well as on the in-plane area of the graphene layer. At low temperature, the relative difference in C--C distance for $^{13}$C and $^{14}$C, with respect to $^{12}$C, is found to be $-2.5$ and $-4.6 \times 10^{-4}$, respectively, larger than in three-dimensional carbon-based materials such as diamond. For the in-plane area, the relative changes amount to $-3.9$ and $-6.9 \times 10^{-4}$. The magnitude of anharmonicity in the lattice vibrations is estimated by comparing the internal energy and atomic vibrational amplitudes with those derived from a harmonic approximation., 12 pages, 8 figures

A metal-semiconductor interface is an integral part of numerous electronic devices such as Schottky barrier diodes, photodetectors, photovoltaic detectors, photoelectric converters for UV radiation, among others. On the other hand, semiconductor thin films of cadmium sulfide have been applied to several electronic devices. This study presents the synthesis of semiconductor thin films of pure cadmium sulfide and those doped with Al, Sn, and Eu by a chemical bath deposition technique. XRD, SEM, EDS, XPS, UV-Vis spectroscopy, I-V, and photocurrent measurement analyzed these semiconductor thin films. Afterwards, the doped and undoped CdS thin films were applied to the manufacture of Schottky diodes. The doped CdS thin films reveals differences in the size of the crystallites, which decreased by 5.7%, 11.5%, and 60.1% after doping with aluminum, tin, and europium, respectively. The CdS thin films show morphological differences, decreasing grain size by 5.3% in the case of tin doping and increasing by 21.9% with aluminum and 32.6% after being doped with europium. Additionally, the energy bandgap of the doped CdS thin films show a blue shift, except when doped with Eu, which shows a red shift. This enables the design of window layers by choosing the suitable dopant of CdS. The effect of the CdS doping on the electrical photoresponse of the Schottky diodes was also analyzed. Due to the incorporation of dopants, the photoresponse of the aluminum-doped CdS Schottky diodes improved by 176% compared to its undoped counterpart and by up to 493% with other reports in the literature. The Schottky diodes manufactured in this work show variation in height of the potential barrier, increasing by 6% in the case of aluminum doping and decreasing by 5% and 25% after being doped with europium and tin respectively. These results demonstrated the beneficial impact of dopants on the characteristics of the CdS-based Schottky diodes and elaborated photodiodes, exhibiting an impressive enhancement in their photoresponse, in the potential barrier reached for photosensitivity and in the energy band gap value. Overall, our extensive study reveals that there is great potential in the design of affordable multifunctional optoelectronic devices.

Zinc oxide (ZnO) thin films were deposited on commercial glass substrates at room temperature by RF magnetron sputtering. The effect of the sputtering variables such as RF power, argon flow and deposition time on the structural, electrical and optical properties was studied and discussed using a full 3k design of experiments. The properties of the deposited films were determined from x-ray diffraction, 3D optical microscopy, four-point probe and UV–Vis spectroscopy measurements. The x-ray diffraction patterns revealed a wurtzite-like crystalline structure of the ZnO films, with preferential orientation along the (002) direction. Depending on deposition parameters, the thickness of the films varied in the range of 23–163 nm and their resistivity was in the range from 100 Ω cm to 105 Ω cm. Additionally, all films show good optical transmittance (higher than 70%) in the visible spectral region and energy band gap values in the range of 2.27–2.31 eV. On the other hand, a multiple linear regression analysis was performed to predict the responses (average thickness, resistivity, and energy band gap) in terms of the significant factors. The results suggest that the time, power-time and flow-time are significant predictors for the thickness model; meanwhile, flow, flow2, power-flow, and power-time are significant for the resistivity model. In the energy band gap model, power, flow, time and flow2 were significant.

In this work, the obtaining of Cu7.2S4 hexapods by a hydrothermal process of two stages is reported. First, hexapods of Cu2O were obtained using copper chloride, and then in the second stage, sodium sulfite was used at different weight ratios in relation with Cu2O for the transformation into Cu7.2S4. The XRD, SEM, Raman, and XPS studies show that at 1:1 wt-ratio the conversion is not completely achieved and the presence of the two phases in the hexapod is detected. By increasing the weight-ratio to 1:2, Cu7.2S4 hexapods with smooth surface were totally transformed into Cu7.2S4 ones with modified surface completely covered by nanosheets.

Thin transparent films of tin-doped cadmium sulfide (CdS) on different substrates were obtained by an ammonia-free chemical bath deposition technique assisted by ultraviolet illumination with a wavelength of 265 nm. Several sets of films were deposited by varying the amount of SnCl2 in the reaction bath and analyzed by X-ray diffraction, scanning electron microscopy, optical transmission and reflection spectroscopy and current versus voltage measurements. In the doped films, the position of the main X-ray diffraction peak is shifted to larger angles showing a decrease of the crystal lattice constant; this is attributed to the substitution of tin by cadmium in the doping process. The morphological characterization of the doped films shows homogeneously distributed spherical grains with an average grain size of 58.5 nm. The grains are composed of crystallites with an average size of 23 nm; the surface of the doped films does not show conglomerates that are typical for materials grown by the chemical bath deposition technique. The electrical properties reveal a decrement in the resistivity of an order of magnitude with respect to the films without doping. The optical results exhibit variation in the band gap that we consider as the consequence of the films' porosity; the theoretical analysis presented confirms this point. The films show a reflectance at a normal incidence less than 30%, which is an indication of their good optical quality. The main effects of the tin doping on the CdS films were observed as changes in the crystal structure and electrical resistivity.

This article presents an experimental study on the hygric performance of brick masonry with a special focus on the hydraulic characterization of the brick-mortar interface. The hygric behavior was studied at the level of the constituent materials as well as at the composite scale. An extruded fired-clay brick and two types of mortar –Portland cement mortar and natural hydraulic lime mortar– were chosen as target materials. The hygric properties were determined following prescribed experimental procedures. The experimental program included vacuum saturation tests, static gravimetric tests for adsorption/desorption isotherms, dry/wet cup tests, capillary absorption tests, and isothermal one-dimensional drying. The results allowed for a comprehensive identification of the main hygric features of the target materials. Fired-clay brick and lime mortar revealed low hygroscopicity and a strong capillary-active behavior with negligible hysteresis, whereas cement mortar showed activity in both hygroscopic and capillary ranges with a distinct moisture storage hysteresis. Different curing conditions led to dissimilar properties between the lime mortar prepared in molds and the same mortar cured in masonry bed joints. Water absorption in fired-clay bricks showed a marked anisotropic behavior, likely derived from the extrusion process. The existence of an imperfect hydraulic contact at the brick-mortar interface was demonstrated for water absorption. Conversely, the interfacial effect on drying kinetics was not evident.

An unusual reaction between GO, DBU and DMF, that typically uses base and solvent, has been thoroughly analyzed providing valuable basic knowledge about the reactivity of GO, which is essential to control functionalization and therefore the properties of graphene derivatives. A combination of characterization techniques, experiments and theoretical calculations allowed us to propose a structure for the materials and a plausible mechanism. The catalytic activity of the new basic materials was also analyzed.

We report a simple sol–gel process for the deposition of poly(methyl methacrylate) (PMMA)–ZrO2 organic–inorganic hybrid films at low temperature and studied their properties as a function of the molar ratios of the precursors in the hybrid sol–gel solution, which included zirconium propoxide as the inorganic (zirconia) source, methyl methacrylate as the organic source, and 3-trimethoxy-silyl-propyl-methacrylate (TMSPM) as the coupling agent to enhance the compatibility between the organic and inorganic phases. The hybrid thin-film deposition was done on glass slide substrates by the dip-coating method. After deposition, the films were heat-treated at 100 °C for 24 h. The analysis of the hybrid films included Fourier transform infrared spectroscopy to identify their chemical groups and thermogravimetric analysis to determine the content of their organic and inorganic components. In addition, capacitance–voltage (C–V) and current–voltage (I–V) curves in metal–insulator–metal structures, using gold as metal ...

CuxS thin films were deposited on commercial glass substrates at different temperatures by an ammonia-free chemical bath deposition process. The deposition process is based in a copper chloride- sodium citrate- thiourea system. The pH value in the reactive solution was adjusted at 10 by addition of KOH and buffer solution. In order to investigate the effect of the deposition temperature and time, four reaction baths were prepared and set at temperatures 25, 40, 55 and 70 °C. The deposited films were studied by X-ray diffraction, Raman spectroscopy, 3D optical microscopy, energy dispersive X-ray spectroscopy, electron probe X-ray microanalysis, UV–vis spectroscopy and two-points probe electrical measurements. The chemically deposited CuxS films showed good adherence to the substrate, homogeneity, metallic luster and light reddish-brown appearance. The thickness of the films varied in the range of 40–80 nm, depending on the deposition conditions. The X-ray diffraction revealed that the films present amorphous nature, excepting those deposited at the highest temperature, which had CuS covellite crystalline structure. The chemical composition of the films exhibited the presence of the covellite phase with excess of sulphur atoms in all cases. The electrical analysis showed a strong decrease in the resistivity with increasing the deposition temperature with values in the range from 106 to 10−2 Ωcm.

The stabilization of δ-phase of poly(vinylidene fluoride) PVDF in a 14 µm-thickness ferroelectric membrane is achieved by a simple route based on the use of a dimethylformamide (DMF)/acetone solvent, in which the application of external electric field is not required. X-ray diffraction and calorimetric experiments on heating reveal that, at 154 °C, the original mixture between ferroelectric δ-phase and paraelectric α-phase transits to a system with only this latter phase in the crystalline fraction. A gradual and slight increment of amorphous fraction up to the melting at 161 °C is also observed. The existence of δ-phase is corroborated by the occurrence of a broad maximum around 154 °C in dielectric permittivity measurements, as well as the hysteresis loops observed at room temperature. These results suggest a wide thermal window for a stable δ-phase, between room temperature and 154 °C, a subsequent transition into α-phase and the corresponding melting at 161 °C. The broad dielectric maximum observed around 154 °C in dielectric and calorimetric measurements, can be associated with a diffuse ferroelectric-paraelectric transition.

The aim of this work is the development of highly protective agents to be administered locally within the middle ear to avoid cisplatin-induced ototoxicity, which affects to 100% of the clinical patients at ultra-high concentrations (16 mg/kg). The protective agents are based on polymeric nanoparticles loaded with dexamethasone or α-tocopheryl succinate as anti-inflammarory and anti-apoptotic molecules. Dexamethasone and α-tocopheryl succinate are poorly soluble in water and present severe side effects when systemic administered during long periods of time. Their incorporation in the hydrophobic core of nanoparticles with the appropriate hydrodynamic properties provides the desired effects in vitro (lower cisplatin-induced toxicity, decreasing of caspase 3/7 activity, and lower IL-1β release) and in vivo (reducing the hearing loss at the local level). The local administration of the nanoparticles by bullostomy provides an adequate dose of drug without systemic interference with the chemotherapeutic effect of cisplatin. Statement of Significance 100% of the cancer patients receiving ultra-high doses of CDDP (16 mg/kg) suffer severe hearing loss, being a limiting factor in antineoplastic treatments. In this paper we describe the application of polymeric nanoparticles loaded with dexamethasone or α-tocopheryl succinate to palliate the cisplatin ototoxicity derived from chemotherapy treatment. These new nanoparticles, that encapsulate, transport, and deliver dexamethasone or α-tocopheryl succinate in the middle ear, are able to partially prevent ototoxicity derived from high doses of CDDP. This is an interdisciplinary study in which in vitro and in vivo experiments are described and extensively discussed. The importance of the results opens an excellent opportunity to the translation to the clinic.

Ruthenium belongs to the family of metals widely used in anticancer therapy (platinum, arsenic, antimony, bismuth, gold, vanadium, iron, rhodium, titanium, gallium). This paper deals with a new kind of ruthenium terminated carbosilane dendrimers (CRD), consisting of carbosilane dendrons functionalized with N-, NH 2 -donor monodentate and N,N-chelating ruthenium complexes. The biophysical characterization, hemolytic activity and the cytotoxicity towards cancer (HL-60) and normal (B-14) cell lines of CRDs have been determined. The data indicate that: (1) generation 0 metallodendrimers are the most effective drugs, being non-toxic for normal cells but induced significant cytotoxicity (>90%) in cancer cells; (2) an increase of generation leads both increased cytotoxicity of CRDs and the levelling of the difference in their action on normal and cancer cells; (3) coordination modes of ruthenium in a dendrimer scaffold did not correlate with their cytotoxicity towards normal and cancer cells. Results suggest that ruthenium dendrimers can be considered as alternative anticancer therapeutic agent.

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.

Graphene bilayers display peculiar electronic and mechanical characteristics associated to their two-dimensional character and relative disposition of the sheets. Here we study nuclear quantum effects in graphene bilayers by using path-integral molecular dynamics simulations, which allow us to consider quantization of vibrational modes and study the effect of anharmonicity on physical variables. Finite-temperature properties are analyzed in the range from 12 to 2000~K. Our results for graphene bilayers are compared with those found for graphene monolayers and graphite. Nuclear quantum effects turn out to be appreciable in the layer area and interlayer distance at finite temperatures. Differences in the behavior of in-plane and real areas of the graphene sheets are discussed. The interlayer spacing has a zero-point expansion of $1.5 \times 10^{-2}$ \AA\ with respect to the classical minimum. The compressibility of graphene bilayers in the out-of-plane direction is found to be similar to that of graphite at low temperature, and increases faster as temperature is raised. The low-temperature compressibility increases by a 6\% due to zero-point motion. Especial emphasis is laid upon atomic vibrations in the out-of-plane direction. Quantum effects are present in these vibrational modes, but classical thermal motion becomes dominant over quantum delocalization for large system size. The significance of anharmonicities in this atomic motion is estimated by comparing with a harmonic approximation for the vibrational modes in graphene bilayers., Comment: 15 pages, 10 figures

In this study, polymethyl methacrylate (PMMA)-based organic–inorganic hybrid films were deposited by the sol–gel technique by mixing the methyl methacrylate (MMA) organic precursor solution with an inorganic precursor solution of bismuth sodium titanate (Bi0.5Na0.5TiO3 or commonly known as BNT). 3-(trimethoxysilyl) propyl methacrylate (TMSPM) was used as coupling agent to improve the compatibility between the phases. The chemical composition and thermal stability were monitored by FTIR spectroscopy and thermogravimetric analysis. The high thermal stability observed together with the appearance of functional groups related to Si–O–metal interactions confirms the formation of a hybrid organic–inorganic material. A study of the optical properties by UV–Vis was also performed, where the refractive index between 2.1 and 2.6 was obtained, corroborating a good coupling between the organic and inorganic phases in the hybrid films. Atomic force microscopy measurements were also made to determine the surface morphology and roughness of the hybrid films and bear out their homogeneity. Finally, electrical measurements were performed by capacitance–voltage (C–V) and current–voltage (I–V), to obtain the dielectric permittivity constant with values from 15.5 to 18.5 and density current from 1 × 10−5 to 1 × 10−6 A cm−2. In comparison with other PMMA-based hybrid materials such as those containing the precursors TiO2 or SiO2, the PMMA–BNT hybrid material shows an improvement in its optical and dielectric properties.

Metal clusters stabilized in zeolites have emerged as promising candidates for optoelectronic applications due to their remarkable luminescent properties. These optical properties have been exploited to develop fast and highly sensitive methods for optical sensing in environmental monitoring. However, to date, these materials have not been proposed as a detection method based on their luminescent response for sensing toxic metal ions. In this report, we synthesized luminescent lead (Pb) clusters into the cavities of synthetic F9-NaX zeolites, which were used as scaffolds to confine and detect Pb2+ ions in water through a fluorimetric mode. These Pb-F9 samples display an intense cyan emission in dehydrated form. Also, a correlation between the luminescence intensity of the materials and the lead loadings was observed, obtaining a low limit of detection of 1.248 ppb and a limit of quantification of 3.782 ppb. The results clearly demonstrate the potential of luminescent lead-exchanged F9 zeolites as one-step method for lead monitoring in water using a rapid and low-cost strategy.

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.

The increase of charge mobility in transparent conductive indium molybdenum oxide (IMO) films is correlated with the presence of hydroxyl groups. The introduction of H in the chamber during sputtering deposition compensates the excess charge introduced by cationic Mo doping of indium oxide either by oxygen or hydroxyl interstitials. Films present a linear increase of carrier mobility correlated with H content only after vacuum annealing. This behavior is explained because vacuum annealing favors the removal of oxygen interstitials over that of hydroxyl groups. Since hydroxyl groups offer lower effective charge and smaller lattice distortions than those associated with interstitial oxygen, this compensation mechanism offers the conditions for the observed increase in mobility. Additionally, the short-range order around molybdenum is evaluated by extended X-ray absorption fine structure (EXAFS) spectroscopy, showing that Mo is placed at the In site of the indium oxide., We acknowledge financial support to Spanish MINECO, Madrid Regional Government and CSIC though contracts MAT2012-37276-C03-01, P2013/MIT-2740 and 201660E016, respectively.

Polycrystalline thin films of cadmium hydroxide Cd(OH) 2 with high purity and good adhesion to the substrate were synthesized by an ammonia free chemical bath deposition method. The as-deposited films have a monoclinic crystalline structure with lattice constants a = 6.5768 A, b = 10.2704 A, c = 3.4125 A, α = 90.00°, β = 120.16°, γ = 90.00°, and crystallite size 26.1 ± 0.9 nm. The cubic phase of cadmium oxide with lattice constants a = 4.7155 A and crystallite size of 10.9 ± 0.9 nm was obtained by heating the as-deposited films at 220 °C. The absorption bands in the 3500–3600 cm − 1 range observed in the infrared spectra of the as-deposited films were used to detect the presence Cd(OH) 2 compound. The possible ways to optimize the synthesis of Cd(OH) 2 to be used as precursor for production of chalcogenide films is discussed.

ZnO thin films were processed by radio frequency magnetron sputtering at room temperature on p-Si/SiO2 substrates under pure argon (Ar:O2 = 100:0 vol.%) and argon–oxygen mixture (Ar:O2 = 99:1 vol.%) gas environment. Morphological, optical and electrical characteristics of the ZnO films are reported, and they show a clear relationship with the gas mixture employed for the sputtering process. Scanning Electron Microscopy revealed the formation of grains of 15.3 and 19.9 nm average sizes and thicknesses of 59 nm and 82 nm for films growth in pure argon and argon–oxygen, respectively. Photoluminescence measurements at room temperature showed the violet emission band (centered at 3 eV) which was only detected in the ZnO film grown under pure argon. From thermally stimulated conductivity measurements two traps with 0.27 and 0.14 eV activation energies were identified for films grown in pure argon and argon–oxygen mixture, respectively. The trap at 0.27 eV is associated with a level located below the conduction band edge and it is supported by the PL band centered at 3 eV. Both types of ZnO films were used as the active channel layer in thin film transistors with thermal SiO2 as gate dielectric. Field effect mobility, threshold voltage and current ratio were improved in the devices with ZnO channel deposited with the argon–oxygen mixture (99% Ar/1% O2 vol.). Threshold voltage decreased from 25 V to 15 V, field effect mobility and current ratio increased from 0.8 to 2.4 cm2/Vs and from 102 to 106, in that order.

The modulation of electrical and Raman properties of ultrafine (∼4 nm) Ag nanoparticle/graphene/SiO hybrid material at low coverage is evaluated with gradual nanoparticle incorporation by the gas aggregation deposition technique. The different contributing factors, such as doping, impurity scattering or strain, are assessed. Incorporation of Ag nanoparticles produce a very efficient n-type doping of graphene (∼7.5 e per particle) maintaining a constant mobility for particle coverage below ∼0.3 monolayers. Doping efficiency is determined by the probability for nanoparticles to be deposited in contact with graphene. The Fermi level upshift is modeled within the charged impurity scattering mechanism in the whole coverage range. A crossover to the regime where impurity scattering dominates is evidenced at large particle concentration. Surface-enhanced Raman scattering is detected in graphene phonons in the limit of vanishing plasmon resonance and very low coverage (∼0.08) that correspond to ∼1500 nanoparticles at the laser spot. Small distortions of the graphene lattice (±0.012%) induced by the nanoparticles overcome the predicted changes in Raman phonons related to carrier doping and originate I/I damping. This evolution of physical properties with gradual incorporation of Ag nanoparticles is anticipated to provide valuable hints to tune the optical and electronic performance of these graphene-based hybrid systems., This work is supported by MINECO (MAT2012-37276-C03-01) and from Comunidad de Madrid, project S2013/MIT-2740 (PHAMA_2.0-CM).

We assessed the effects of ultra dry-air plasma surface treatments on the properties of Al2O3-GPTMS-PMMA hybrid dielectric layers for applications to high-performance amorphous Indium Gallium Zinc Oxide (a-IGZO) thin film transistors (TFTs). The hybrid layers were deposited by an easy dip coating sol-gel process at low temperature and then treated with dry-air plasma at 1, 2 and 3 consecutive cycles. Their properties were analyzed as a function of the number of plasma cycles and contrasted with those of the untreated ones. The dielectric characteristics of the hybrid layers were determined from I–V and C–f measurements performed on metal–insulator–metal and metal–insulator–semiconductor devices. The results show that the plasma treatments increase the surface energy and wettability of the hybrid films. There is also a reduction of the OH groups and oxygen vacancies in the hybrid network improving the dielectric properties. The incorporation of nitrogen into the hybrid films surface is also observed. The plasma-treated hybrid dielectric layers were applied as dielectric gate in the fabrication of a-IGZO TFTs. The best electrical performance of the fabricated TFTs was achieved with the 3 cycles plasma-treated hybrid dielectric gate, showing high mobility, 29.3 cm2 V−1 s−1, low threshold voltage, 2.9 V, high I ON/OFF current ratio, 106, and low subthreshold swing of 0.42 V dec−1.

The aim of this report is to synthesize copper oxide nanocubes (CuO NCs) at room temperature, using sodium borohydride as a reducing agent, and Cetyl Trimethyl Ammonium Bromide (CTAB) as a stabilizing agent. The crystallinity and morphology of the synthesized CuO NCs are investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The optical properties were analyzed by means of UV-visible absorbance and Raman spectroscopy. The existence of specific functional groups and structural stability were established via FTIR spectroscopy and thermogravimetric analysis (TGA). Furthermore, the catalytic efficiency of the as-prepared CuO NCs was tested using catalytic and photocatalytic studies of para-nitrophenol (p-NP) reduction and methylene blue (MB) degradation, respectively. The catalytic results demonstrated the nanocubes' excellent catalytic and photocatalytic responses with respect to the abatement of p-NP and MB within 50 s and 240 min, with kinetic rate constants of 3.9 × 10-2 s-1 and 6.47 × 10-3 min-1, respectively.

Organic-inorganic Eu3+-doped PMMA-SiO2 and PMMA-TiO2 hybrid systems were synthesized by sol-gel. The doping ions were used as ion-probe luminescence to analyze the differences in the microstructure of the hybrid matrices. The local symmetry environment of the Eu3+ ions in the hybrid matrices was described by the asymmetry parameter (R), defined as the intensity ratio of the 5D0 → 7F2/5D0 → 7F1 transitions. The photoluminescence of PMMA-SiO2 with quenched emission and lower R is consistent with a symmetric, hydrated environment surrounding the Eu3+ ions. Meanwhile, the higher value of R and the higher emission intensity, observed for PMMA-TiO2, reveal a lower symmetric environment of the Eu3+ ions. Furthermore, the emission and excitation bands of the 5D0 − 7F0 transition shows a red shift in the PMMA-TiO2 spectra, indicating higher Eu-O covalence degree. The calculated values of the Judd-Ofelt parameters are in agreement with the higher Eu-O covalence degree in this hybrid material.

Even though there are reports on NiO-p/Si-n based photodetector, work along 1D NiO/Si self-powered photodetector remains unexplored. 1D materials offer better electron mobility and can provide ballistic transport channel, which helps in achieving high responsivity. In this work, direct single-step deposition of p-type NiO nanowires on n-type Si as a self-powered photodetector was successfully fabricated by engaging simple electrospinning technique. The structural properties as observed from XRD indicate highly crystalline NiO nanowires and FESEM images revealed 60-75 nm diameter with uniform distribution. Growth of nanowires by using stimuli polymer and its completely removal at high temperature was confirmed using TGA and XPS analysis. The responsivity of the fabricated photodetector was calculated to be 9.1 mA W−1 at zero bias, which can be attributed to the p-type NiO interface with the n-type Silicon, which creates an internal electrical field thereby assisting in the effective separation of the photogenerated carriers. Further, under illumination, at zero bias, the photogenerated current still exists suggesting a generation of internal voltage, which makes the fabricated device as self-powered. This fabrication method will enhance the photodetection properties, and it can be implemented in the fields of optoelectronic devices, sensors, and flexible electronics.

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.

Application of Fibre Reinforced Polymers (FRPs) as external reinforcement for masonry structures has been found to be a promising technique, but the long-term behavior of such systems still needs attention. This study presents an overview of the experimental activities followed by the authors on durability of externally bonded FRP-masonry components subjected to water immersion and accelerated hygrothermal exposure. Both moist and hygrothermal environments were found to be extremely deteriorating in the studied materials and led to significant degradation of mechanical properties and loss in bond strength. The effect of mechanical surface treatment on the bond durability performance was also investigated., This work was supported by the Competitivity Factor Operational Program (COMPETE) and the Foundation for Science and Technology (FCT) within the scope of the project POCI-01-0145-FEDER-007633. The first author would like to acknowledge the financial support of the Ministerio da Ciencia, Tecnologia e Ensino Superior, FCT, Portugal, under the grant SFRH/BD/117114/2016.

[EN] We report on an alternative route based on nanomechanical folding induced by an AFM tip to obtain weakly interacting multilayer graphene (wi-MLG) from a chemical vapor deposition (CVD)-grown single-layer graphene (SLG). The tip first cuts and then pushes and folds graphene during zigzag movements. The pushed graphene has been analyzed using various Raman microscopy plots- AD/ AG × EL4 vs ΓG, ω2D vs Γ2D, Γ2D vs ΓG, ω2D+/- vs Γ2D+/-, and A2D-/ A2D+ vs A2D/ AG. We show that the SLG in-plane properties are maintained under the folding process and that a few tens of graphene layers are stacked, with a limited number of structural defects. A blue shift of about 20 cm-1 of the 2D band is observed. The relative intensity of the 2D- and 2D+ bands have been related to structural defects, giving evidence of their role in the inner and outer processes at play close to the Dirac cone., Funding by the Spanish Ministerio de Economía y Competitividad under Project MAT2015-65356-C3-1-R is acknowledged. French PACA Region is acknowledged

Aluminum dopant effect upon cadmium sulfide (CdS) films was analyzed as well as its impact of the resultant properties in the functional device, ITO/CdS:Al/C. The optical and electrical properties of the CdS films were affected due to the aluminum doping, and as a result, the Schottky diode performance shows dependency on the Al doping concentration. The Al-doped CdS films and devices were characterized electrically and optically. The results show that as the dopant concentration increases, the film resistivity its reduced from 108 to 107 Ω cm, the work function decreases from 4.7 to 4.3 eV and the energy bandgap slightly increases from 2.45 to 2.48 eV. Regarding the devices, the on/off ratio ∼106, and the ideality factor shows an improvement from 3 to 1.5. The diode presents a final leakage current around ∼10−3 A. The doping effect on CdS films results in the improvement of the overall performance of the device. We can conclude that this treatment can be used in optoelectronic devices such as solar cells or photodiodes.

Indium-doped zinc oxide (IZO) polycrystalline thin films were grown on polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and as reference on 7059 Corning glass substrates at room temperature by radio frequency magnetron sputtering from a target prepared with a mixture of ZnO and In2O3 powders. The structural, optical, and electrical properties of the films were analyzed and compared. The IZO polycrystalline films showed n-type conductivity. The electrical resistivity drops significantly, and the carrier concentration increases as a consequence of In incorporation within the ZnO crystalline lattice. In both cases the changes are of several orders of magnitude. The resistivity obtained was 3.1 ± 0.5 x 10-3 Ω-cm for an IZO sample grown on PET with a carrier concentration of 3.1 ± 0.7 x 1020 cm-3, the best mobility obtained was 27.7 ± 0.8 cm2V-1s-1 for an IZO sample grown on PEN. From the results, we conclude that n-type IZO polycrystalline films with high transmittance, high mobility and low resistivity were obtained on flexible transparent substrates.

In this work, the effects on the preparation of bis(thiourea) cadmium chloride crystals when illuminated with ultraviolet (UV) light at a wavelength of 367 nm using the chemical bath deposition technique are studied comparatively. Two experiments are performed to make a comparison: one without UV light and the other with the aid of UV light. Both experiments are performed under equal conditions, at a temperature of 343 K and with a pH of 3.2. The precursors used are cadmium chloride (CdCl(2)) and thiourea [CS(NH(2))(2)], which are dissolved in 50 mL of deionized water with an acidic pH. In this experiment, the interaction of electromagnetic radiation is sought at the moment the chemical reaction is carried out. The results demonstrate the existence of an interaction between the crystals and the UV light; the UV light assistance causes crystal growths in an acicular shape. Also, the final product obtained is cadmium sulfide and shows no evident difference when synthesized with or without the use of UV light.

At a critical spinodal in-plane stress τC, a planar crystalline graphene layer becomes mechanically unstable. We present a model of the critical behavior of the membrane area near τC and show that it is in complete agreement with path-integral simulations and with recent experiments based on interferometric profilometry and Raman spectroscopy. Close to the critical stress, τC, the in-plane strain behaves as τC−τ1/2 for τ < τC.At a critical spinodal in-plane stress τC, a planar crystalline graphene layer becomes mechanically unstable. We present a model of the critical behavior of the membrane area near τC and show that it is in complete agreement with path-integral simulations and with recent experiments based on interferometric profilometry and Raman spectroscopy. Close to the critical stress, τC, the in-plane strain behaves as τC−τ1/2 for τ < τC.

Thermal properties of graphene display peculiar characteristics associated to the two-dimensional nature of this crystalline membrane. These properties can be changed and tuned in the presence of applied stresses, both tensile and compressive. Here we study graphene monolayers under tensile stress by using path-integral molecular dynamics (PIMD) simulations, which allows one to take into account quantization of vibrational modes and analyze the effect of anharmonicity on physical observables. The influence of the elastic energy due to strain in the crystalline membrane is studied for increasing tensile stress and for rising temperature (thermal expansion). We analyze the internal energy, enthalpy, and specific heat of graphene, and compare the results obtained from PIMD simulations with those given by a harmonic approximation for the vibrational modes. This approximation turns out to be precise at low temperatures, and deteriorates as temperature and pressure are increased. At low temperature the specific heat changes as $c_p \sim T$ for stress-free graphene, and evolves to a dependence $c_p \sim T^2$ as the tensile stress is increased. Structural and thermodynamic properties display nonnegligible quantum effects, even at temperatures higher than 300~K. Moreover, differences in the behavior of the in-plane and real areas of graphene are discussed, along with their associated properties. These differences show up clearly in the corresponding compressibility and thermal expansion coefficient., 15 pages, 9 figures. arXiv admin note: text overlap with arXiv:1709.05148

Cadmium sulfide (CdS) thin films were deposited, on glass substrates, at 70°C for 120 min using an ammonium-free chemical bath deposition process. After deposition, the films were placed in a CuCl2 solution for 45, 60, 75, and 90 min, respectively, for their ion exchange, generating CdxCu1-xS films. The obtained films were analyzed by X-ray diffraction, Raman spectroscopy, X-ray wavelength dispersion spectrometry, and scanning electron microscopy. The reference CdS films showed a homogeneous appearance and a yellowish color; elapsing the immersion time, the films changed their color showing a greenish appearance. The X-ray analysis indicated that the CdS films developed a hexagonal structure with preferential orientation along the plane (002). During the ion exchange, a decrease in the intensity of the reflection (002) was observed as well as a slight displacement of this reflection towards higher values of 2θ derived from the substitution of Cd atoms by Cu atoms. The WDS analysis revealed that approximately 10% of the cadmium atoms were replaced by copper ones after 90 min of immersion.

Finite-temperature properties of graphene monolayers under tensile stress have been studied by path-integral molecular dynamics (PIMD) simulations. This method allows one to consider the quantization of vibrational modes in these crystalline membranes and to analyze the influence of anharmonic effects on the membrane properties. Quantum nuclear effects turn out to be appreciable on the structural and thermodynamic properties of graphene at low temperature, and they can even be noticeable at room temperature. Such quantum effects become more relevant as the applied stress is increased, mainly for properties related to out-of-plane atomic vibrations. The relevance of quantum dynamics in the out-of-plane motion depends on the system size, and is enhanced by tensile stress. For applied tensile stresses, we analyze the contribution of the elastic energy to the internal energy of graphene. Results of PIMD simulations are compared with calculations based on a harmonic approximation for the vibrational modes of the graphene lattice. This approximation describes rather well the structural properties of graphene, provided that the frequencies of ZA (flexural) acoustic modes in the transverse direction include a pressure-dependent correction., This work was supported by Dirección General de Investigación, MINECO (Spain) through Grants FIS2012-31713 and FIS2015-64222-C2.

Electroluminescence (EL) has been obtained and studied in two different wide band gap oxide crystals: MgO:Li (7.8 eV) and Al2O3:Mg (8.8 eV). EL requires crystal doping with Li or Mg to induce p-type conductivity and the formation of F-type centers which are the deep levels within the band gap for electron–hole recombination. Oxidizing treatments are required in Al2O3:Mg to reach adequate conductivities. The main EL emissions are at 2.35 eV (528 nm) for MgO:Li crystals and at 3.8 eV (327 nm) for Al2O3:Mg. Trace impurities also produce EL in the visible region, their control may be used for color designed LEDs., We acknowledge financial support from Spanish MINECO, MAT2012-37276-C03-01, and Comunidad Autónoma de Madrid PHAMAS2009/MAT-1756.

Transparent and well adhered Cu doped ZnS films were obtained on glass substrates by the chemical bath deposition process. The resulting films were prepared with reaction solutions containing Zn and Cu salts, ethylenediamine tetra-acetic acid disodium and thiocetamide. An analysis derived from Raman spectroscopy revealed the presence of the cubic structure or β-ZnS in the ZnS:Cu films, with an impurity phase corresponding to the insertion of Cu ions in interstitial sites or defects of the lattice. The presence of Cu in these films, formed by elongated aggregates instead of the rounded ones shown by the undoped ZnS films, was also confirmed by energy dispersive spectrometry. Changes in the optical properties as well as in the resistivity of the films have been observed due to the incorporation of Cu. In addition, it was confirmed by the rectification method that the ZnS:Cu films have p-type conductivity.