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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 performed systematic studies on the oxidation of zinc nitride metastable layers using a climate chamber with controlled temperature and relative humidity. The electrical properties of the samples were in situ analyzed using a programmable microprocessor with a voltage divider, while the structural and optical properties were ex situ measured by scanning electron microscopy, elastic recoil detection analysis, and spectroscopic ellipsometry. Our results show that zinc nitride transformation proceeds in a top-down way, with a progressive substitution of N by O, which leads to the formation of pores and a remarkable swelling effect. The overall behavior is well explained by a universal logistic growth model. Considering this model, we successfully fabricated and tested a zinc nitride-based dehydration sensor for biomedical applications.

Current higher education context is very demanding and academic leadership is facing a lot of pressure coming from different stakeholders; they question the efforts on outcomes, such as: higher employability rate, lower drop-out rate, higher student satisfaction, higher number of strategic partnerships. No matter what relationships are established between higher education institutions and other stakeholders, the interconnection between all components of the institutional mission is a starting point for a change. A huge interest has been quite recently put on the higher education institutions role on societal engagement; nevertheless, the investment in new strategies for teaching and learning has revealed several good practices on open lab model. Specific literature review shows that this model can be considered as a win-win strategy model, all partners gaining successful results. This paper explains how an open-lab model functions and how academic leadership can contribute to make the teaching and learning strategy an effective one. The research methodology is based on a literature review, as well as on a brainstorming session and a questionnaire-based approach revealing the perceptions of academic leadership in moving forward to such a model. Main objectives include: to understand the open-lab teaching and learning model; to explain the open lab experience in a Civic European University; to reveal the academic leadership perceptions on developing the model; to build a possible strategy for an open-lab teaching and learning. Main findings prove that academic leadership is aware about the importance of moving towards open-lab challenges, but not effectively prepared for it.

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.

Plasmonic gallium (Ga) nanoparticles (NPs) are well known to exhibit good performance in numerous applications such as surface enhanced fluorescence and Raman spectroscopy or biosensing. However, to reach the optimal optical performance, the strength of the localized surface plasmon resonances (LSPRs) must be enhanced particularly by suitable narrowing the NP size distribution among other factors. With this purpose, our last work demonstrated the production of hexagonal ordered arrays of Ga NPs by using templates of aluminium (Al) shallow pit arrays, whose LSPRs were observed in the VIS region. The quantitative analysis of the optical properties by spectroscopic ellipsometry confirmed an outstanding improvement of the LSPR intensity and full width at half maximum (FWHM) due to the imposed ordering. Here, by engineering the template dimensions, and therefore by tuning Ga NPs size, we expand the LSPRs of the Ga NPs to cover a wider range of the electromagnetic spectrum from the UV to the IR regions. More interestingly, the factors that cause this optical performance improvement are studied with the universal plasmon ruler equation, supported with discrete dipole approximation simulations. The results allow us to conclude that the plasmonic coupling between NPs originated in the ordered systems is the main cause for the optimized optical response, The research is supported by the MINECO (CTQ2014-53334-C2-2-R, CTQ2017-84309-C2-2-R and MAT201676824-C3-1-R) and Comunidad de Madrid (P2018/NMT4349 and S2018/NMT-4321 NANOMAGCOST) projects. ARC acknowledges Ramón y Cajal program (under contract number RYC-2015-18047)

Zinc oxynitride layers are becoming popular as semiconductor materials for thin film transistors. However, the formation of these ternary phases with a high N content is challenging because of the different crystalline structures and stability of the binaries involved. In this work, we study both the formation and stability of ternary ZnOxNy phases grown by RF sputtering at different oxygen flux ratios (f). The preferential incorporation of O into the layers is confirmed even for small f values. A singular X-ray amorphous phase is detected for f = 1.7%, denoting the transition towards the hexagonal phase. The exact composition of this phase is accurately determined by elastic recoil detection analysis with a time-of-flight telescope, finding a maximum content of 11% N. For contents below it, all the phases show clear hexagonal signatures in the diffractograms. These hexagonal phases exhibit more than one absorption edge, indicating the formation of a diluted ternary phase into a predominant ZnO matrix. Due to this diluted character of the ternary phase, all the ZnOxNy layers have a remarkable stability in humid environments.

A novel procedure, based in a closed space vapor transport (CSVT) configuration, has been devised to grow films or flakes of pure MoO2 in a reductive atmosphere, at relatively low temperature and using MoO3 as the source. In contrast with conventional CSVT technique, in the proposed method a temperature gradient is not required for the growth to take place, which occurs through an intermediate volatile transport species that is produced in the complex reduction reaction of MoO3. An added value of this simple method is the possibility of transforming the MoO2 into MoTe2, one of the most interesting members of the transition metal dichalcogenide family. This is achieved in a sequential process that includes the growth of Mo oxide and its (in-situ) tellurization in two consecutive steps.

In this work, we use Joule-effect thermal evaporation to produce hybrid structures made of Ga and In nanoparticles (NPs) on Si (100) substrates. Taking advantage of the protective oxide shell, In NPs can be used as a template for a second deposition step without structural changes, enabling the hybridization of NPs of materials. These complex structures of mixed NPs present a spectrally broad plasmonic absorption that can be optically tuned with a wide range of photon energies from UV to IR regions with a full width at half maximum range of ∼400 to 800 nm. The results suggest that the localized surface plasmon resonance (LSPR) of the hybrid NPs is mainly due to the plasmonic coupling of the in-plane modes. Furthermore, different scenarios studied by discrete dipole approximation simulations show that the interconnection between NPs is extremely sensitive to the size and the local arrangement of the nanostructures. This kind of broadening and tunable LSPR may have interest for energy transfer applications, biosensing platforms and solar cells.

The physics of collective optical response of molecular assemblies, pioneered by Dicke in 1954, has long been at the center of theoretical and experimental scrutiny. The influence of the environment on such phenomena is also of great interest due to various important applications in, e.g., energy conversion devices. In this Letter, we demonstrate both experimentally and theoretically the spatial modulations of the collective decay rates of molecules placed in proximity to a metal interface. We show in a very simple framework how the cooperative optical response can be analyzed in terms of intermolecular correlations causing interference between the response of different molecules and the polarization induced on a nearby metallic boundary and predict similar collective interference phenomena in excitation energy transfer between molecular aggregates.

In this work, the characterization of high mobility thin-film transistors based on zinc nitride films deposited at room temperature by magnetron radio-frequency sputtering is presented. The values extracted of field-effect mobility were > 2 cm 2 /Vs for long channel devices. For short channel devices, a reduction of the mobility values is found and, as a result of the analysis of the width-normalized resistance for different channel lengths and gate voltages, the reduction is attributed to the effects of a high contact resistance. The impact of the gate dielectric thickness on electrical characteristics is also presented.

Zinc nitride (Zn3N2) is a metastable material in ambient conditions because of its high reactivity with water molecules. In this work we perform a systematic analysis of the oxidation of Zn3N2 layers grown by RF magnetron sputtering at room temperature. The aging and transformation of the layers toward a ZnO film is explored by means of spectroscopic ellipsometry and scanning electron microscopy for conditions with different relative humidity (RH). Accurate depth profiling by means of elastic recoil detection analysis with a time-of-flight telescope demonstrated the substitutional reaction between O and N and the important effect of the RH in this process. Because of this metastability the resistivity of the layers changes several orders of magnitude. Taking advantage of this principle, we develop electronic indicators and characterize the transformation of their electrical properties as a function of the ambient RH, finding a good correlation between the transformation time and the RH level.

Almost all, if not all, general purpose codes for analysis of Ion Beam Analysis data have been originally developed to handle laterally homogeneous samples only. This is the case of RUMP, NDF, SIMNRA, and even of the Monte Carlo code Corteo. General-purpose codes usually include only limited support for lateral inhomogeneity. In this work, we show analytical simulations of samples that consist of a layer of parallel oriented nanowires on a substrate, using a model implemented in NDF. We apply the code to real samples, made of vertical ZnO nanowires on a sapphire substrate. Two configurations of the nanowires were studied: 40 nm diameter, 4.1 μm height, 3.5% surface coverage; and 55 nm diameter, 1.1 μm height, 42% surface coverage. We discuss the accuracy and limits of applicability of the analysis, Authors thank funding from projects CTQ2014-53334-C2-2-R (MINECO, Spain) and NANOAVANSENS S2013/MIT 3029 (Comunidad de Madrid). A.R.C. acknowledges Juan de la Cierva program (under contract number JCI-2012-14509). This work was partially funded by Fundação para a Ciência e Tecnologia under grant UID/Multi/04349/2013

In this work, the electrical stability of zinc nitride (Zn3N2) Thin-film Transistors (TFTs) under negative bias stress (NBS) and positive bias stress (PBS) is presented. The Zn3N2 TFTs were fabricated on plastic substrates. Spin-on glass was used as gate dielectric. The threshold voltage shift (ΔVT) and its recovery are analyzed during a long stress time and after a period of rest. The hysteresis of the transfer characteristics after the electrical stress is also analyzed. In order to explain the mechanism of instability in the Zn3N2 TFTs, MOS capacitors were fabricated and characterized under NBS and PBS. The behavior exhibited in MOS capacitors under NBS and PBS, is in agreement with the ΔVT exhibited in the Zn3N2 TFTs under NBS and PBS, respectively.

This Accepted Manuscript will be available for reuse under a CC BY-NC-ND licence after 24 months of embargo period, A novel electrochemiluminescence (ECL) sensor for the sensitive detection of taurine was developed. Taurine contains an aliphatic amine that gives it co-reactant properties. The ECL response of the taurine/[Ru(bpy)3]2+ system was analyzed on two different electrodes surfaces, screen-printed graphene and gold electrodes, before and after modification with ZnO nanowires (ZnO NWs). The ZnO NWs modified electrode yielded an enhanced ECL signal, allowing rapid detection of taurine at 5.5 × 10−6 mol L−1 detection limit. The ECL signal is stable and reproducible. The sensor has been applied to the determination of taurine in a commercial taurine supplement, The financial supports from the Spanish Ministerio de Ciencia, Innovación y Universidades (CTQ2017-84309-C2-1-R and CTQ2017-84309-C2-2-R) and Comunidad Autónoma de Madrid (NANOAVANSENS Program) are gratefully acknowledged. IMDEA Nanociencia acknowledges support from the 'Severo Ochoa' Programme for Centres of Excellence in R&D (Ministerio de Ciencia, Innovación y Universidades, Grant SEV-2016-0686). C.G-S. and T.G-E. acknowledges the Atracción de Talento Project (2017-T1/BIO-5435) and youth employment program (PEJD-2017-PRE/SAL-3834) from the Comunidad de Madrid, respectively. Authors wish to thank SIdI (Servicio Interdepartamental de Investigación, UAM) for the HPLC measurements

[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.

Graphene Oxide (GO) is considered an ideal candidate for the fabrication of hydrogen gas (H2 (g)) sensors due to its excellent capabilities for direct wiring, thanks to the presence of functional groups, which provide an opportunity to modify its chemical functionalities. In this study, we have fabricated a H2 (g) sensor based on the precise positioning of GO flakes across sputtered aluminium-doped ZnO (AZO) electrodes on a glass substrate using a positive dielectrophoretic force (DEP). GO flakes assembly was performed between AZO electrodes gap of 4 μm and optimized by controlling the DEP parameters. A chemical reduction using a solution of 10 mM sodium borohydride was used to enhance the conductivity of the GO flakes up to two orders of magnitude. The arrangement of the GO flakes, the efficiency of the reduction process, the morphology and the surface potential of these was analyzed by Atomic Force and Kelvin Probe Microscopies. A reduced Graphene Oxide (rGO) work function in the range of 4.7–4.9 eV was obtained. Moreover, the H2 (g) response of rGO/AZO sensor was studied by two types of tests. First test consists of a single 10 min exposure of pure H2 (g), collecting the IV directly data in order to obtain the sensitivity of the rGO to be of ∼100 % at 1 V. Second test consists of a batch of different time exposures to analyze the stress performance and the saturation level of the sensor. Finally, the impact of the ambient conditions on our sensor sensitivity was studied.

Mechanical manipulation of nanowires (NWs) for their integration in electronics is still problematic because of their reduced dimensions, risking to produce mechanical damage to the NW structure and electronic properties during the assembly process. In this regard, contactless NW manipulation based methods using non-uniform electric fields, like dielectrophoresis (DEP) are usually much softer than mechanical methods, offering a less destructive alternative for integrating nanostructures in electronic devices. Here, we report a feasible and reproducible dielectrophoretic method to assemble single GaAs NWs (with radius 35–50 nm, and lengths 3–5 μm) on conductive electrodes layout with assembly yields above 90% per site, and alignment yields of 95%. The electrical characteristics of the dielectrophoretic contact formed between a GaAs NW and conductive electrodes have been measured, observing Schottky barrier like contacts. Our results also show the fast fabrication of diodes with rectifying characteristics due to the formation of a low-resistance contact between the Ga catalytic droplet at the tip of the NW when using Al doped ZnO as electrode. The current-voltage characteristics of a single Ga-terminated GaAs NW measured in dark and under illumination exhibit a strong sensitivity to visible light under forward bias conditions (around two orders of magnitude), mainly produced by a change on the series resistance of the device.

2D monolayer molybdenum disulphide (MoS

This Accepted Manuscript is available for reuse under a CC BY-NC-ND 3.0 licence after the 12 month embargo period provided that all the terms of the licence are adhered to, Core-shell gallium nanoparticles (Ga NPs) have recently been proposed as an ultraviolet plasmonic material for different applications but only at room temperature. Here, the thermal stability as a function of the size of the NPs is reported over a wide range of temperatures. We analyze the chemical and structural properties of the oxide shell by x-ray photoelectron spectroscopy and atomic force microscopy. We demonstrate the inverse dependence of the shell breaking temperature with the size of the NPs. Spectroscopic ellipsometry is used for tracking the rupture and its mechanism is systematically investigated by scanning electron microscopy, grazing incidence x-ray diffraction and cathodoluminescence. Taking advantage of the thermal stability of the NPs, we perform complete oxidations that lead to homogenous gallium oxide NPs. Thus, this study set the physical limits of Ga NPs to last at high temperatures, and opens up the possibility to achieve totally oxidized NPs while keeping their sphericity, The research is supported by the MINECO (CTQ2014-53334-C2-2-R, CTQ2017-84309-C2-2-R, MAT2016-80394-R, MAT 2015-65274-R/FEDER and MAT2017-85089-C2-1-R) and Comunidad de Madrid (NANOAVANSENS ref. S2013/MIT-3029) projects. ARC acknowledges Ramón y Cajal program (under contract number RYC-2015-18047). FN acknowledges support from Marie Sklodowska-Curie grant agreement No. 641899 from the European Union´s Horizon 2020 research and innovation programme

Ga nanoparticles (GaNPs) produced by thermal evaporation or epitaxial methods on graphene sheets present strong plasmonic effects that can couple to graphene phonons. In this work, GaNPs are deposited on graphene monolayers supported on Cu, quartz, and SiO2/Si substrates. The use of graphene increases the interparticle distance and improves the size uniformity. The enhancement of G and 2D graphene Raman lines is analyzed for the different substrates under excitation at 633 and 532 nm. The plasmonic effects are investigated using spectroscopic ellipsometry, finding a strong resonant mode at energies between 1.7 and 2.0 eV and an incidence angle of 55.6°. Finally, the heterogeneous surfaces are functionalized for the preparation of optical biosensors exposing the surface to 3,3′-dithiodipropionic acid di(N-succinimidyl ester) (DTSP). A significant energy shift of the ellipsometric signal on the Ga/graphene surfaces is observed in comparison to Ga/Si surfaces. Sketch of GaNPs atop graphene and biofunctionalizing agent (DTSP). Dip in the Psi ellipsometric function, and associated step in the Delta function, found around the GaNPs–graphene coupling resonance at an incident angle of 55.6°.

In this paper, zinc nitride (Zn3N2)-based flexible thin-film transistors (TFTs) are presented. The zinc nitride thin film is deposited by magnetron radio frequency sputtering at room temperature, while spin-on glass and aluminum were used as gate insulator and source/drain electrode, respectively. Polyethylene terephthalate is used as flexible substrate. The flexible Zn3N2 TFTs were characterized while bent to 5-mm tensile radius. The flexible TFTs exhibit an electron mobility of 3.8 cm $^{2}/\text{V}\cdot \text{s}$ and an ON/OFF current ratio close to 105 after several cycles of bending and being exposed to air ambient for 30 days.

This Accepted Manuscript is available for reuse under a CC BY-NC-ND 3.0 licence after the 12 month embargo period provided that all the terms of the licence are adhered to, The effect of the oxidation of gallium nanoparticles (Ga NPs) on their plasmonic properties is investigated. Discrete dipole approximation has been used to study the wavelength of the out-of-plane localized surface plasmon resonance in hemispherical Ga NPs, deposited on silicon substrates, with oxide shell (Ga2O3) of different thickness. Thermal oxidation treatments, varying temperature and time, were carried out in order to increase experimentally the Ga2O3 shell thickness in the NPs. The optical, structural and chemical properties of the oxidized NPs have been studied by spectroscopic ellipsometry, scanning electron microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. A clear redshift of the peak wavelength is observed, barely affecting the intensity of the plasmon resonance. A controllable increase of the Ga2O3 thickness as a consequence of the thermal annealing is achieved. In addition, simulations together with ellipsometry results have been used to determine the oxidation rate, whose kinetics is governed by a logarithmic dependence. These results support the tunable properties of the plasmon resonance wavelength in Ga NPs by thermal oxidation at low temperatures without significant reduction of the plasmon resonance intensity, This research is supported by the MINECO (CTQ2014-53334-C2-2-R and MAT2016-80394-R) and Comunidad de Madrid (NANOAVANSENS ref. S2013/MIT-3029) projects. ARC acknowledges Ramón y Cajal program (under contract number RYC-2015-18047). FN acknowledges support from Marie Sklodowska-Curie grant agreement No 641899 from the European Union’s Horizon 2020 research and innovation programme

F. Nucciarelli, I. Bravo, L. Vázquez, E. Lorenzo, J. L. Pau, "Gallium nanoparticles colloids synthesis for UV bio-optical sensors", SPIE Optics + Optoelectronics Proc. SPIE 10231 (16 May 2017) Copyright 2017 Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. Proceedings of the Optical Sensors Conference (Prague, Czech Republic) doi: https://doi.org/10.1117/12.2265883, A new method for the synthesis of colloidal gallium nanoparticles (Ga NPs) based on the thermal evaporation of Ga on an expendable aluminum zinc oxide (AZO) layer is presented here. The growth of AZO layers was investigated on different substrates at room temperature and 300 °C. By means of physical evaporation process, nanoparticles were deposited with a distribution ranging from 10 nm to 80 nm in diameter. A study of their endurance in acidic environment was carried out in order to assure the NPs shape and size stability during the etching process. Smaller particles start to disappear between 1h and 2h immersion time in a pH=1 solution, while bigger particles reduce their dimension. The NPs were dispersed in tetrahydrofuran (THF) organic solvent and optically characterized, showing strong UV absorption with a band centered at 280 nm. The colloids size distribution of as-evaporated samples was compared with the distribution obtained in droplets of the solution after drop-casting. By Dipole Discrete Approximation simulations, a close relationship between the UV absorption and the NPs with diameter smaller than ∼40 nm was found. Because of the gallium oxide (Ga1-xOx) outer shell that surrounds the Ga NPs, an enhancement of their hydrophobicity occurs. Hence, the low agglomeration state between NPs in tetrahydrofuran allows to obtain narrow absorption band in the optical spectrum, We are also grateful to the international PROMIS project, framed in the Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 641899. This research is supported by the MINECO (CTQ2014-53334-C2-2-R and MAT2016-80394-R) and Comunidad de Madrid (NANOAVANSES ref. S2013/MIT-3029) Project

Zinc oxide (ZnO) nanowires (NWs) based ultraviolet (UV) sensors have been fabricated using different assembly techniques to form functional structures, aiming at the improvement of the performance of NW-based sensors for optoelectronic applications. NWs with diameters and lengths varying between 90–870 nm and 2–20 μm, respectively, were synthesized by controlling the growth conditions in a chemical vapor transport system. Optical properties of NWs were studied by means of transmission spectroscopy. Electrical properties of single ZnO NW-based sensors were analyzed in dark and under UV illumination (at photon wavelength of λ < 370 nm) as a function of the NW diameter. Results of the study indicate that reduction of the NW diameter below 200 nm leads to an improvement of the photocurrent (at λ < 370 nm) up to 102 μA and a decrease of the decay time around 150 s. These enhancements may help to improve the performance of ZnO-based optoelectronic devices.

Plasmonics has emerged as an attractive field driving the development of optical systems in order to control and exploit light-matter interactions. The increasing interest around plasmonic systems is pushing the research of alternative plasmonic materials, spreading the operability range from IR to UV. Within this context, gallium appears as an ideal candidate, potentially active within a broad spectral range (UV-VIS-IR), whose optical properties are scarcely reported. Importantly, the smart design of active plasmonic materials requires their characterization at high spatial and spectral resolution to access the optical fingerprint of individual nanostructures, attainable by transmission electron microscopy techniques (i.e., by means of electron energy-loss spectroscopy, EELS). Therefore, the optical response of individual Ga nanoparticles (NPs) by means of EELS measurements is analyzed, in order to spread the understanding of the plasmonic response of Ga NPs. The results show that single Ga NPs may support several plasmon modes, whose nature is extensively discussed.

In this work, an unusual ambipolar behavior in zinc nitride (Zn3N2) based thin film transistors (TFTs) on plastic substrates is presented. Polyethylene terephthalate is used as flexible substrate. The Zn3N2 thin film is deposited by magnetron radio-frequency sputtering at room temperature, whereas spin-on glass is used as gate insulator. The transfer and output characteristics are the typical reported for ambipolar TFTs. The extracted linear mobility was 1.8 cm2 V−1 s−1 for the n-type region and 0.15 cm2 V−1 s−1 for the p-type region. Using a physically-based simulator, the ambipolar output characteristics are simulated. The results presented are promising to develop novel ambipolar Zn3N2 TFTs.

This letter presents the characterization results of nanowire (NW) Schottky photodiodes fabricated from the dielectrophoretic contact between a ZnO NW and a Cu electrode. The device counter-electrode is fabricated using Pt focused ion beam deposition. The current–voltage characteristics exhibit rectifying properties with a leakage current as low as 40 pA at −40 V. The fitting of the forward characteristics reveals a barrier height lowering under UV illumination along with a large reduction of the series resistance. At forward bias, responsivities of $\sim 10^{\mathrm { {5}}}$ A/W are obtained above the bandgap energy. Under reverse bias, the responsivity reduces up to $10^{\mathrm { {4}}}$ A/W, but a higher ultraviolet/visible contrast and a faster response are observed. In those conditions, the barrier height lowering is fostered by the drift of photogenerated holes toward the interface with the Cu electrode, yielding lower barrier height values under illumination.

A simple strategy for covalent immobilizing DNA sequences, based on the formation of stable diazonized conducting platforms, is described. The electrochemical reduction of 4-nitrobenzenediazonium salt onto screen-printed carbon electrodes (SPCE) in aqueous media gives rise to terminal grafted amino groups. The presence of primary aromatic amines allows the formation of diazonium cations capable to react with the amines present at the DNA capture probe. As a comparison a second strategy based on the binding of aminated DNA capture probes to the developed diazonized conducting platforms through a crosslinking agent was also employed. The resulting DNA sensing platforms were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and spectroscopic ellipsometry. The hybridization event with the complementary sequence was detected using hexaamineruthenium (III) chloride as electrochemical indicator. Finally, they were applied to the analysis of a 145-bp sequence from the human gene MRP3, reaching a detection limit of 210 pg μL(-1).

This work analyzes the morphological, compositional and electrical modification of zinc nitride (Zn3N2) films through arc discharges produced by biasing a metal tip at a micrometric distance of the surface. Polycrystalline nitride layers are prepared by radio-frequency magnetron sputtering from a pure Zn target on glass substrates using N2 as working gas. Film properties after arc discharges are investigated by using scanning electron microscopy (SEM), ion beam analysis (IBA) techniques and four-probe resistivity measurements. Electrical discharge lithography performed at low bias voltages reveals as an effective mechanism to reduce resistivity by electrical breakdown of the thin oxide layer formed on top of the nitride. At higher voltages, electrical discharges along the scan increase nitride resistivity due to the severe modification of the structural properties. Additionally, compositional analysis reveals that nitrogen leaves the structure being replaced by ambient oxygen. This characteristic behavior leads to the formation of facetted submicron ZnO crystals whose size depends on the original Zn3N2 grain size and the probe voltage used. The excess of zinc forms self-assembled microstructures along the scan edge.

GaAs nanowires (NWs) were grown by Ga-assisted chemical beam epitaxy on Si(111) substrates covered by a thin oxide layer using different substrate temperatures and growth times. Ga droplet terminated NWs with hexagonal footprint and cross section were observed by scanning electron microscopy, with diameters and lengths in the range of 40–65 nm and 0.3–1.2 µm, respectively. Transmission electron microscopy (TEM) images show evidences of vapor–liquid–solid growth mechanisms which lead to different droplet-nanowire interface quality depending on Ga-catalyst wetting area of NW sidewalls. TEM and Raman spectroscopy demonstrates the existence of a single zincblende phase in the NW body, without any evidence of wurtzite phase domains.

Carlos García Núñez, Alejandro F. Braña, Nair López, José L. Pau, Basilio J. García, "Photodetector fabrication by dielectrophoretic assembly of GaAs nanowires grown by a two-steps method", Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications. Proc. SPIE 10353 (29 August 2017); doi: 10.1117/12.2274007. Copyright 2017 Society of Photo-Optical Instrumentation Engineers, One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited, Proceedings of Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications Conference (San Diego, California, United States), GaAs nanowires (NWs) are promising advanced materials for the development of high performance photodetectors in the visible and infrared range. In this work, we optimize the epitaxial growth of GaAs NWs compared to conventional procedures, by introducing a novel two-steps growth method that exhibits an improvement of the resulting NW aspectratio and an enhancement of the NW growth rate. Moreover, we investigate the contactless manipulation of NWs using non-uniform electric fields to assemble a single GaAs NW on conductive electrodes, resulting in assembly yields above 90%/site and an alignment yields of around 95%. The electrical characteristics of the dielectrophoretic contact formed between the NW and the electrode have been measured, observing that the use of n-type Al-doped ZnO (AZO) as electrode material for NW alignment produces Schottky barrier contacts with the GaAs NW body. Moreover, our results show the fast fabrication of diodes with rectifying characteristics due to the formation of a low-resistance contact between the Ga catalytic droplet at the tip of the NW and the AZO electrode. The current-voltage measurements of a single GaAs NW diode under different illumination conditions show a strong light responsivity of the forward bias characteristic mainly produced by a change on the series resistance, N. López acknowledges support of the European Commission by Marie Curie International Incoming Fellowship PIIF-GA-2012-326579. The authors also acknowledge the support from MINECO under TEC2013-48350-R and TEC2016-78433-R projects

S. Catalán-Gómez, M. Briones, A. Redondo-Cubero, F. J. Palomares, F. Nucciarelli, E. Lorenzo, J. L. Pau, "The role of the oxide shell in the chemical functionalization of plasmonic gallium nanoparticles", SPIE Optics + Optoelectronics Proc. SPIE 10231 (16 May 2017); doi: 10.1117/12.2265665; Copyright 2017 Society of Photo‑Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited., Plasmonic Ga nanoparticles (NPs) were thermally oxidized at low temperature in order to increase the native Ga 2 O 3 shell thickness and to improve their stability during the chemical functionalization. The optical, structural and chemical properties of the oxidized NPs have been studied by spectroscopic ellipsometry, scanning electron microscopy, grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy. A clear redshift of the peak wavelength is observed with the increasing annealing time due to the Ga 2 O 3 thickness increase, and barely affecting the intensity of the plasmon resonance. This oxide layer enhances the stability of the NPs upon immersion in ethanol or water. The surface sensitivity properties of the as-grown and oxidized NPs were investigated by linking a thiol group from 6-Mercapto-1-hexanol through immersion. Ellipsometric spectra at the reversal polarization handedness (RPH) condition are in agreement with the Langmuir absorption model, indicating the formation of a thiol monolayer on the NPs.

New methods for the production of colloidal Ga nanoparticles (GaNPs) are introduced based on the evaporation of gallium on expendable aluminum zinc oxide (AZO) layer. The nanoparticles can be prepared in aqueous or organic solvents such as tetrahydrofuran in order to be used in different sensing applications. The particles had a quasi mono-modal distribution with diameters ranging from 10 nm to 80 nm, and their aggregation status depended on the solvent nature. Compared to common chemical synthesis, our method assures higher yield with the possibility of tailoring particles size by adjusting the deposition time. The GaNPs have been studied by spectrophotometry to obtain the absorption spectra. The colloidal solutions exhibit strong plasmonic absorption in the ultra violet (UV) region around 280 nm, whose width and intensity mainly depend on the nanoparticles dimensions and their aggregation state. With regard to the colloidal GaNPs flocculate behavior, the water solvent case has been investigated for different pH values, showing UV-visible absorption because of the formation of NPs clusters. Using discrete dipole approximation (DDA) method simulations, a close connection between the UV absorption and NPs with a diameter smaller than ~40 nm was observed., We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)., This research is supported by the MINECO (CTQ2014-53334-C2-2-R, MAT2014-54231-C4-1-P and MAT2016-80394-R) and Comunidad de Madrid (NANOAVANSES ref. S2013/MIT-3029) project. I.B. gratefully acknowledges the FPI-2012 Grant from Spanish Ministerio de Economía y Competitividad.

A label-free DNA and single nucleotide polymorphism (SNP) sensing method is described. It is based on the use of the pseudodielectric function of gallium plasmonic nanoparticles (GaNPs) deposited on Si (100) substrates under reversal of the polarization handedness condition. Under this condition, the pseudodielectric function is extremely sensitive to changes in the surrounding medium of the nanoparticle surface providing an excellent sensing platform competitive to conventional surface plasmon resonance. DNA sensing has been carried out by immobilizing a thiolated capture probe sequence from Helicobacter pylori onto GaNP/Si substrates; complementary target sequences of Helicobacter pylori can be quantified over the range of 10 pM to 3.0 nM with a detection limit of 6.0 pM and a linear correlation coefficient of R(2) = 0.990. The selectivity of the device allows the detection of a single nucleotide polymorphism (SNP) in a specific sequence of Helicobacter pylori, without the need for a hybridization suppressor in solution such as formamide. Furthermore, it also allows the detection of this sequence in the presence of other pathogens, such as Escherichia coli in the sample. The broad applicability of the system was demonstrated by the detection of a specific gene mutation directly associated with cystic fibrosis in large genomic DNA isolated from blood cells.

Zinc nitride (Zn3N2) films were prepared by radio-frequency magnetron sputtering from a pure Zn target in a N2 ambient. Films were deposited on glass and Si(100) substrates at 298- and 473-K substrate temperatures (Ts). Ion beam analysis (IBA) techniques, spectroscopic ellipsometry (SE) and transmission spectroscopy were used to characterize the samples as a function of Ts and time. IBA studies showed that the Zn and N concentrations matched the stoichiometric values 3:2 of the cubic anti-bixbyte structure and revealed the partial transformation of Zn3N2 into zinc oxide (ZnO) due to the exposure to ambient air. IBA and SE techniques revealed films grown at higher Ts were less affected by the oxidation process. Transmission spectroscopy showed that the band gap energy blue shifted as Ts decreased. It was also found that the oxidation process produced a blue shift of the band gap energy. For the sake of comparison, ZnO/Zn3N2 heterostructures were synthesized using the same system and characterized in parallel to unintentionally oxidized nitride layers. SE studies of the heterostructure showed that the deposition of a ZnO layer helped to prevent nitride oxidation.

Zinc nitride films were prepared by radio-frequency magnetron sputtering in N2/Ar ambient using different substrates (glass and thermally-oxidized-Si) and buffer layers (low-temperature Zn3N2 and ZnO). Resonant Rutherford backscattering (RBS) allowed determining ZnxNy stoichiometry and thickness. Despite the sputtering system was operated in high vacuum conditions, unintentional oxygen incorporation during growth was detected. Calculations of the relative oxygen concentration showed that the oxygen content was very dependent on the growth rate. Ex-situ oxidation was also analyzed by resonant RBS and compared with the results of as-grown layers. Scanning electron microscopy and X-ray diffraction revealed that surface morphology and crystal orientation were strongly dependent on the substrate temperature (Ts). In addition, optical transmission measurements show a reduction of the optical energy band gap from 1.46 to 1.25 eV as Ts increased. The electrical properties were examined as a function of growth rate, total working gas flux and Ts aiming to maximize electron mobility. From those studies, it was found that Hall mobility increased significantly as the growth rate decreased. A maximum mobility of 100 cm2/Vs and a minimum carrier concentration of 3.2 × 1018 cm−3 were achieved at a Ts of 423 K and a growth rate of 4.44 nm/min.

Zn is sputter-deposited on melted Sn films by radio-frequency magnetron sputtering in oxidizing plasma. The samples present an absorption cut-off wavelength close to the one of ZnO, and an optical transparency higher than 50% in the visible range. Ex-situ thermal annealing improves visible transparency and produces a slight blue-shift in the optical bandgap. X-ray diffraction patterns show typical spectra due to polycrystalline ZnO with evidence of the presence of crystalline SnO, before annealing, and Zn 2 SnO 4 , after annealing. Rutherford Backscattering studies reveal the existence of a ZnO layer on top of an O-rich (Zn, Sn)O thin film. After optimal thermal treatment, electrical characterization exhibits carrier concentrations of 10 16 –10 17 cm − 3 and mobilities of 20–80 cm 2 V − 1 s − 1 for the resulting (Zn, Sn)O n-type films.

Growths of blue and green multi-quantum wells (MQWs) and light-emitting diodes (LEDs) are realized on lateral epitaxial overgrowth (LEO) GaN, and compared with identical structures grown on conventional GaN. Atomic force microscopy is used to confirm the significant reduction of dislocations in the wing region of our LEO samples before active-region growth. Differences between surface morphologies of blue and green MQWs are analyzed. These MQWs are integrated into LEDs. All devices show a blue shift in the electroluminescence (EL) peak and narrowing in EL spectra with increasing injection current, both characteristics attributed to the band-gap renormalization. Green LEDs show a larger EL peak shift and a broader EL spectrum due to larger piezoelectric field and more indium segregation in the MQWs, respectively. Blue LEDs on LEO GaN show a higher performance than those on conventional GaN; however, no performance difference is observed for green LEDs on LEO GaN versus conventional GaN. The performance of the green LEDs is shown to be primarily limited by the active layer growth quality.

The authors report on the current-voltage (I-V) characteristic under forward biases obtained in low leakage, small size p-(In,Ga)N-GaN-n multiquantum well diodes. Under barrier illumination, the devices present a high optical response with capabilities to detect optical powers in the pW range without further amplification. This response is attributed to the screening of the internal electric fields. Recombination times of a few seconds are found to be associated to this mechanism. Moreover, a step-like feature is found in the I-V characteristic before the diode turn-on voltage. Our model proposes tunneling current through the multiquantum-well structure as responsible of this feature. Fast modulation of the tunneling effect under barrier illumination is used to evaluate the detection of low photon fluxes.

This chapter focuses on the plasmonic effects that appear in the ellipsometric functions and the pseudodielectric function when metal thin films and nanoparticles are analyzed by spectroscopic ellipsometry in the visible, near infrared and ultraviolet regions of the electromagnetic spectrum. The chapter is structured in two large sections. The first section reviews the basics of total internal reflection ellipsometry (TIRE), based on the excitation of surface polaritons in metal thin films. The conditions required to excite polaritons in TIRE systems are analyzed along with the main characteristics of those electromagnetic waves. The second section of the chapter is devoted to study the optical properties of plasmonic resonances in nanostructures and the characteristics introduced in the dielectric functions. The treatment of optical anisotropies and Fano resonances in the ellipsometric models is discussed. The last section of the chapter reviews the state of the art of the technique in biosensing applications.

The high temperature characterization of GaN-based devices, including high electron mobility transistors (HEMTs), p-i-n photodiodes and surface acoustic wave (SAW) filters is reported. Transmission line method (TLM) measurements reveal the reversible behaviour of both the ohmic contact resistance and the two-dimensional electron gas (2DEG) mobility. AlGaN/GaN HEMTs on sapphire and SiC substrates present a reduction of the drain current and the transconductance as temperature increases. The responsivity of InGaN/GaN photodiodes is enhanced and shifted to larger wavelengths with temperature, recovering its original value after the thermal cycle. The temperature coefficient of frequency of SAW filters on AlN epilayers on different substrates has been measured. The influence of temperature on the different surface acoustic modes is compared.

We report on a study of the electrical and optical properties of strained M-plane GaN films grown on LiAlO2 substrates. We have electrically characterized Schottky barrier devices fabricated on strained M-plane GaN films. The current leakage found in these devices is probably related to a surface effect. The influence of the current direction for in-plane transport in M-plane GaN was also studied. Polarized photoluminescence spectroscopy shows the effect of residual biaxial strain on the optical selection rules, allowing to identify intrinsic transitions involving holes from the two uppermost valence bands. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Noise characteristics of InGaN/GaN multiple-quantum-well (MQW) photodiodes (PD) and photoconductors (PC) were studied. 1/f-type noise was examined in MQW PDs as a function of reverse bias, In content and temperature. Superposed multilevel Random Telegraph Signal Noise was observed under reverse and forward biases. The dominant presence of this type of noise in MQW PCs seems to indicate that its origin was related to localization effects in the InGaN QWs. Detectivity of the MQW PDs was determined at various voltages for a wide range of temperatures.

Gallium nanoparticles (GaNPs) of different sizes are deposited on Si(100) substrates by thermal evaporation. Through ellipsometric analysis, it is possible to investigate the plasmonic effects in the GaNPs and exploit them to develop biosensors. The excitation of the resonant modes for certain incidence angles leads to negative values of the imaginary part of the pseudodielectric function (, This research is partially supported by the Ministry of Economy and Competitiveness (CTQ2014- 53334-C2-1-R and 2-R) and Comunidad de Madrid (NANOAVANSENS ref. S2013/MIT- 3029)

Although nanowires (NWs) may improve the performance of many optoelectronic devices such as light emitters and photodetectors, the mass commercialization of these devices is limited by the difficult task of finding reliable and reproducible methods to integrate the NWs on foreign substrates. This work shows the fabrication of zinc oxide NWs photodetectors on conventional glass using transparent conductive electrodes to effectively integrate the NWs at specific locations by dielectrophoresis (DEP). The paper describes the careful preparation of NW dispersions by sedimentation and the dielectrophoretic alignment of NWs in a home-made system. This system includes an impedance technique for the assessment of the alignment quality in real time. Following this procedure, ultraviolet photodetectors based on the electrical contacts formed by the DEP process on the transparent electrodes are fabricated. This cost-effective mean of contacting NWs enables front-and back-illumination operation modes, the latter eliminating shadowing effects caused by the deposition of metals. The electro-optical characterization of the devices shows uniform responsivities in the order of 106 A/W below 390 nm under both modes, as well as, time responses of a few seconds, This research is partially supported by the Comunidad de Madrid (NANOAVANSENS; ref. S2013/MIT-3029), the Ministry of Science and Innovation of Spain TEC2010-20796 projects and the research funding from UAM-Banco Santander