The effect of X-ray nano-beam irradiation has been investigated, along with a subsequent electric discharge between the metallic electrodes of memristive-like devices fabricated on top of rutile single crystals. X-ray irradiation with a photon flux of about 6 x 10(12) photons/second impinging on an area of 74 x 60 nm(2), and with irradiation times of the order of tens of seconds per point, has been able to pattern a conducting path between the electrodes, which has guided the electric discharge process. The results from Ti K-edge XANES mapping with submicron spatial resolution show small changes in the configuration of the pre-edge peaks, suggesting the presence of anatase phase in the affected region, which is also confirmed by micro-Raman mapping. This implies the occurrence of very intense Joule heating during the electric discharge (T > 2140 K), followed by a very quick cooling process. This conversion of rutile to anatase represents a novel electrical method for the formation of localized anatase nanoparticles from rutile single crystals, which may be of help for specific applications.

Solar energy is rapidly becoming a robust renewable energy source to conventional finite resources such as fossil fuels. It is harvested using interconnected photovoltaic panels typically built with crystalline silicon cells, i.e. semiconducting materials that convert effectively the solar radiation into electricity. However, crystalline silicon is fragile and vulnerable to cracking over time or in predictive maintenance tasks, which can lead to electric isolation of parts of the solar cell and even failure, thus affecting the panel performance and reducing electricity generation. This work aims to developing a system for detecting cell cracks in solar panels to anticipate and alert of a potential failure of the photovoltaic system by using computer vision techniques. Three scenarios are defined where these techniques will bring value. In scenario A, images are taken manually and the system detecting failures in the solar cells is not subject to any computational constraints. In this case, the InceptionV3 model, with a multilabel dataset, reached over 93% accuracy. In scenario B, an Edge device is placed near the solar farm, able to make inferences. For these conditions, an EfficientNetB0 model shrunk into full integer quantization proved to be the most suitable model, reaching 85% accuracy. Finally, in scenario C, a small microcontroller is placed in a drone flying over the solar farm and making inferences about the solar cells' states. In this situation, customized CNN architectures are the most suitable solutions since traditional ones are too big to be exported onto microcontrollers. Here, a machine learning model built with VGG16 blocks achieved 82% accuracy on a binarized dataset.

Bismuth selenide, a benchmark topological insulator, grows in a trigonal structure at ambient conditions and exhibits a number of enticing properties related to the formation of Dirac surface states. Besides this polytype, a metastable orthorhombic modification with Pnma space group has been produced by electrodeposition and high-pressure high-temperature synthesis displaying upon Sb doping significant thermoelectric properties in the midtemperature range. However, very little experimental information is available on the fundamental properties of this polytype, such as, e.g., the electronic band gap and the lattice dynamics. We report here the temperature dependence of the Raman spectra of orthorhombic Bi2Se3 between 10 K and 300 K, which displays an anharmonic behavior of the optical phonons that can be modelled with a two-phonon decay channel. In order to analyze the data we performed ab initio calculations of the electronic bandstructure, the phonon frequencies at the center of the Brillouin zone, and the phonon dispersion relations along the main symmetry directions, examining the effect of spin-orbit coupling in both phonon and electronic energies. Lastly, we report here cathodoluminescence experiments at 83 K that set a lower limit to the electronic bandgap at 0.835 eV, pointing to an indirect nature, in agreement with our calculations. These results shed light to essential properties of orthorhombic Bi2Se3 for further understanding of the potential of this semiconductor for thermoelectrics and new applications.

The integration of both optical and electronic components on a single chip, despite several challenges, holds the promise of compatibility with complementary metal-oxide semiconductor (CMOS) technology and high scalability. Among all candidate materials, III-V semiconductors exhibit great potential for optoelectronics and quantum-optics based devices, such as light emitters and harvesters. The control over geometry, and dimensionality of the III-V nanostructures, enables one to modify the band structures, and hence provide a powerful tool for tailoring the optoelectronic properties of III-V compounds. One of the most creditable approaches towards such growth control is the combination of using a patterned wafer and the self-assembled epitaxy. This work presents monolithically integrated catalyst-free InP nanowires grown selectively on Si nanotip-patterned, CMOS compatible (001) Si substrates using gas-source molecular-beam epitaxy. We use nanoheteroepitaxy approach to selectively grow InP nanowires on Si nanotips, which holds benefits due to its peculiar substrate design. In addition, our methodology allows the switching of dimensionality of the InP structures between one-dimensional nanowires and three-dimensional bulklike InP nanoislands by thermally modifying the shape of silicon nanotips surrounded by the silicon dioxide layer during the thermal cleaning of the substrate. The structural and optical characterization of nanowires indicates the coexistence of both zincblende and wurtzite InP crystal phases in nanowires. The two different crystal structures were aligned with a type-II band alignment. The luminescence from InP nanowires was measured up to 300 K, which reveals their promising optical quality for integrated photonics and optoelectronic applications.

The use of semiconductor technologies for the development of qubits is having a strong development. This paper reports the development of technological solutions to enable the experimentation on semiconductor qubits. Two technological approaches are followed: spin qubits in quantum dots and Majorana qubits for topological quantum computing. This is complemented by research on advanced characterization of the fabricated qubit nanostructures.

We have modified the electrical properties of rutile TiO2 with a 17 keV X-ray beam about 50x50 nm2 in size. We have drawn a conducting channel in an insulating matrix, guided the electroforming of a conducting filament and modified the rectifying properties of a Schottky barrier. We have also observed changes in the surface morphology and a more intense Raman activity in the irradiated regions. Computer simulations show that temperature spikes at the nanoscale are expected in correspondence with the synchrotron pulses, and preliminary measurements via single crystal X-ray diffraction confirm that local heating takes place during irradiation.

GaP as one of the III-V semiconductors has an indirect band gap in its natural zinc-blend (ZB) crystal phase, limiting its applications in optoelectronics. The atomic arrange-ments of the ZB GaP, however, can be changed by adding energy to the system, for example, using strain and defects. In such a way, GaP can be crystallized in the wurtzite (WZ) phase with a direct band gap in the yellow-green range and promising new optical properties. GaP nanostructures offer the great possibility to induce strain, and hence, one can expect to obtain the WZ phase by modifying the geometry and dimensionality of GaP. In this work, we present GaP nanowires (NWs) grown on SiO2 substrates by gas-source molecular beam epitaxy. Raman measurements on individual GaP NWs indicate that NWs are poly-type crystal structures with the starting growth of the WZ phase, transforming into the ZB phase, and ending as the WZ phase. Photoluminescence at 9 K from an ensemble of NWs shows emissions at 2.09-2.14 eV, which are related to the direct band gap of the WZ phase and peaks between 2.26 and 2.3 eV due to the ZB phase. The emission of the WZ GaP phase is observable up to 160 K. Cathodoluminescence at 83 K shows directly the emission between 2.09 and 2.14 eV along the single NWs, indicating the presence of the WZ phase. Our results demonstrate the realization of poly-type, ZB, and WZ GaP NWs on SiO2 by gas-source molecular beam epitaxy.

The synthesis and characterization of ion exchange polymer poly(4-acryloylaminobenzoic acid) (poly(4-AABA)), which contains amide and carboxylic acid functional groups on each repeating unit are reported. The polymer was used as reducing and stabilizing agent in the synthesis of gold nanoparticles, silver nanoparticles, and gold silver nanoparticles at room temperature and 75 C. The poly(4-AABA)-stabilized metallic nanoparticles were characterized by ultraviolet-visible spectroscopy, transmission electron microscopy, X-ray diffraction, and infrared spectroscopy. It was found that the amide group of the repeating unit of poly(4-AABA) confers the ability to reduce gold and silver ions by transferring the free electrons from the N atom. UV-Vis results showed that the process of reduction of the metallic ions by poly(4-AABA) at room temperature occurs slowly, and the obtention of the nanoparticles take place after several days. On increasing the temperature to 75 C, the reduction rate increases considerably, and the formation of nanoparticles occurs over a few minutes. Conformational arrangement of poly(4-AABA) play an important role in controlling the size and shape of the nano particles. The composition of the Au-Ag nanoparticles strongly depends on the reaction temperature, changing from an Au-rich alloy when the temperature is 25 C to an Ag-rich alloy at 75 C. The poly(4-AABA) stabilizing to the nanoparticles in aqueous solution through the electro-steric stabilization mechanism, since through the carboxylic acid groups it interacts electrostatically with the surface of the particles and due to the long length of the polymeric chains, the poly(4-AABA) also envelops to particles controlling their growth and preventing agglomeration. Probable mechanism for formation of colloidal metallic nanoparticles in aqueous solution of poly (4-AABA) is proposed is discussed.

The luminescence of SrTiO3 depends on the sample type, either doped or stoichiometric, as grown or treated, the excitation conditions, and temperature. The origin of the luminescence emissions, blue, green, and infrared, remains controversial. In particular, the role played by defects, mainly oxygen vacancies, impurities, and selftrapped holes and electrons on the different emissions are far to be elucidated. We present a cathodoluminescence (CL) and photoluminescence (PL) study of undoped and Nb-doped samples. The different excitation conditions of CL and PL permit to distinguish the luminescence emission from the bulk (CL) and from a surface skin region (PL). Significant differences between both techniques are seen for the undoped sample, while the Nb-doped sample presents less differences, highlighting the role played by the surface defects and the doped electrons. The study is complemented by the temperature dependence of the luminescence spectra and the emission due to defects generated by plastic deformation.

Abstract The integration of both optical and electronic components on a single chip, despite the challenge, holds the promise of compatibility with CMOS technology and high scalability. Among all candidate materials, III-V semiconductor nanostructures are key ingredients for opto-electronics and quantum optics devices, such as light emitters and harvesters. The control over geometry, and dimensionality of the nanostructures, enables one to modify the band structures, and hence provide a powerful tool for tailoring the opto-electronic properties of III-V compounds. One of the most creditable approaches towards such growth control is the combination of using patterned wafer and the self-assembled epitaxy. This work presents monolithically integrated catalyst-free InP nanowires grown selectively on nanotip-patterned (001)Si substrates using gas-source molecular-beam epitaxy. The substrates are fabricated using CMOS nanotechnology. The dimensionality of the InP structures can be switched between two-dimensional nanowires and three-dimensional bulk-like InP islands by thermally modifying the shape of Silicon nanotips, surrounded by the SiO2 layer during the oxide-off process. The structural and optical characterization of nanowires indicate the coexistence of both zincblende and wurtzite InP crystal phases in nanowires. The two different crystal structures were aligned with a type-II heterointerface.

Ecuadorian pottery is renowned for its beauty and the particularly rich colour of its pigments. However, a major challenge for art historians is the proper assessment of the provenance of individual pieces due to their lack of archaeological context. Of particular interest is the Jama-Coaque culture, which produced fascinating anthropomorphic and zoomorphic pottery from ca. 240 B.C. until the Spanish Conquest of 1532 A.D. in the coastal region of Ecuador. Using a combination of microscopic and spectroscopic techniques, i.e., transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), energy-dispersive x-ray spectroscopy (EDX), and scanning electron microscopy (SEM); we are able to characterize these pieces. We have found several kinds of iron-oxide based nanostructures in all the colour pigments we investigated for the Jama-Coaque culture, suggesting the same unique volcanic source material was used for their clay. Such nanostructures were absent from the pigment samples studied from other contemporary coastal-Ecuadorian cultures, i.e., the Tumaco-La Tolita and Bahía cultures. In the yellow pigments of goethite we find carbon nanofibres, indicating these pigments were subjected to a thermal treatment. Finally, in the blue, green, and black pigments we detect modern pigments (phthalocyanine blue, lithopone, and titanium white), suggesting modern restoration. Our results demonstrate the power of TEM, Raman, FTIR, EDX, and SEM archaeometric techniques for characterizing pieces without a clear archaeological context. Furthermore, the characterization of nanostructures present in such pieces could be used as a possible fingerprint for a provenance study.

The high pressure lattice dynamics of rhombohedral antimony have been studied by a combination of diffuse scattering and inelastic x-ray scattering. The evolution of the phonon behavior as a function of pressure was analyzed by means of two theoretical approaches: density functional perturbation theory and symmetry-based phenomenological phase transition analysis. This paper focuses on the first structural phase transition, SbI-SbIV, and the role of vibrations in leading the transition. The phonon dispersion exhibits complex behavior as one approaches the structural transition, with the branches, corresponding to the two transitions happening at high pressure in the Va elements (A7-to-BCC and A7-to-PC) both showing softening.

This paper presents the study of the magnetic properties exhibited by a highly porous strontium ferrite with a copper metal cover. The analyzed samples consisted of a mix of the M - and X-type ferrimagnetic phases. The characterization included optical microscopy, X-ray diffraction, and the Rietveld refinement method. Microstructural characteristics and magnetic properties were studied at different amounts of electrodeposited copper. Results show the emergence of strong ferrimagnetic coupling between the M and the X phases, whereas the copper layer enhances the squareness remanence (M-r/M-s). A reduction in the width of the switching field distribution (SFD) curves observed in the porous structures indicates an intense competition between the exchange and magnetostatic interactions, which results in the emergence of a cooperative switching of the particles. This interesting phenomenon is a product of a conjunction of the porous structure together with the ferrimagnetic coupling of the ferrimagnetic phases.

This paper presents an intelligent system aimed at detecting a person's posture when sitting in a wheelchair. The main use of the proposed system is to warn an improper posture to prevent major health issues. A network of sensors is used to collect data that are analyzed through a scheme involving the following stages: selection of prototypes using condensed nearest neighborhood rule (CNN), data balancing with the Kennard-Stone algorithm, and reduction of dimensionality through principal component analysis. In doing so, acquired data can be both stored and processed into a micro controller. Finally, to carry out the posture classification over balanced, pre-processed data, and the K-nearest neighbors algorithm is used. It turns to be an intelligent system reaching a good tradeoff between the necessary amount of data and performance is accomplished. As a remarkable result, the amount of required data for training is significantly reduced while an admissible classification performance is achieved being a suitable trade given the device conditions.

We investigate the hydrostatic pressure dependence of the zone center optical phonons of c-plane and aplane wurtzite InN epilayers grown on GaN substrates. The longitudinal to transverse mode splitting for the A1 and E1 modes was found to increase with increasing pressure, whereas the associated transverse effective charge decreases for both modes as eT (A1) = 2.93−9.9×10−3P and eT (E1) = 2.80−10.6×10−3P (in units of elementary charge and P in GPa). These observations are well in line with results for other II-VI, III-V, and group-IV semiconductor compounds as far as the relation between the magnitude and sign of the pressure derivative of eT and the bond ionicity is concerned. As the latter increases so does |∂eT/∂P| with a sign change from positive to negative for bond ionicities around fi = 0.46 for compounds with anions belonging to the first row of the periodic table. A comparison of the results for InN and other nine tetrahedrally bonded compounds indicate that the pressure behavior of the transverse effective charge is mainly determined by the strength of the Pauli repulsion between cation valence electrons and those of the anion core. We also perform ab-initio calculations in order to address the origin of the observed increase in linewidth of the E 2 mode which is found to arise from a pressure-induced increase in the rate of two-phonon decay processes. This broadening is associated with tuning into resonance of a steep edge in the two-phonon density of states around 460 cm−1 with the frequency of the E 2 mode. PACS numbers: 07.35.+k, 62.50.-p,78.30.Am, 63.20.-e

ABSTRACTMetal nanoparticles are obtained by different chemical reactions using reducing agents that are not environmentally friendly. This work report the synthesis of Au nanoparticles in colloidal solution using three monodisperse macroelectrolytes, with peripheral sulfonic acid groups bonded covalently, without toxic reducing agents. During the synthesis of Au nanoparticles were used the new macroelectrolytes as reducing and stabilizing agents in aqueous solution or ethylene glycol. The macroelectrolytes were synthesized using hexachlorocyclotriphosphazene as core, and o‐ or p‐aminobenzenesulfonic acid, obtaining acid macroelectrolytes with two and six sulfonic acid groups in ortho‐ position, and four sulfonic acid groups in para‐ position. The ultraviolet–visible (UV–vis) absorption spectroscopy and transmission electron microscopy study show that the macroelectrolytes with sulfonic acid groups in ortho‐ position are reducing agents for Au+++ ions in colloidal solution and produced Au nanoparticles with anisotropic shapes, such as decahedrons and prisms. The macroelectrolyte with sulfonic acid groups in para‐ position is reducing agent for Au+++ and produces quasispherical Au nanoparticles with sizes between 8 and 40 nm. The colloidal solutions with Au nanoparticles were stable by several months due to the protection of imine and sulfonic groups of macroelectrolytes on the Au nanoparticles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45888.

Sleep stage classification is a highly addressed issue in polysomnography; It is considered a tedious and time-consuming task if done manually by the specialist; therefore, from the engineering point of view, several methods have been proposed to perform an automatic sleep stage classification. In this paper an unsupervised approach to automatic sleep stage clustering of EEG signals is proposed which uses spectral features related to signal power, coherences, asymmetries, and Wavelet coefficients; the set of features is classified using a clustering algorithm that optimizes a cost function of minimum sum of squares. Accuracy and kappa coefficients are comparable to those of the current literature as well as individual stage classification results. Methods and results are discussed in the light of the current literature, as well as the utility of the groups of features to differentiate the states of sleep. Finally, clustering techniques are recommended for implementation in support systems for sleep stage scoring.

We report evidence of a nonadiabatic Kohn anomaly in boron-doped diamond, using a joint theoretical and experimental analysis of the phonon dispersion relations. We demonstrate that standard calculations of phonons using density-functional perturbation theory are unable to reproduce the dispersion relations of the high-energy phonons measured by high-resolution inelastic x-ray scattering. On the contrary, by taking into account nonadiabatic effects within a many-body field-theoretic framework, we obtain excellent agreement with our experimental data. This result indicates a breakdown of the Born-Oppenheimer approximation in the phonon dispersion relations of boron-doped diamond.