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8 pags., 8 figs., 1 tab., We report the existence of moir\'e patterns and magic angle physics in all families of chiral collapsed carbon nanotubes. A detailed study of the electronic structure of all types of chiral nanotubes, previously collapsed via molecular dynamics, has been performed. We find that each family possesses a unique geometry and moir\'e disposition, as well as a characteristic number of flat bands. Remarkably, all kinds of nanotubes behave the same with respect to magic angle tuning, showing a monotonic behavior that gives rise to magic angles in full agreement with those of twisted bilayer graphene. Therefore, magic angle behavior is universally found in chiral collapsed nanotubes with a small chiral angle, giving rise to moir\'e patterns. Our approach comprises first-principles and semi-empirical calculations of the band structure, density of states and spatial distribution of the localized states signaled by flat bands., We thank the Centro de Supercomputación de Galicia, CESGA, (www.cesga.es, Santiago de Compostela, Spain) for providing access to their supercomputing facilities. This work was supported by grant PID2019-106820RB-C21 funded by MCIN/AEI/ 10.13039/501100011033/ and by “ERDF A way of making Europe”, by grant TED2021-129457B-I0 funded by MCIN/AEI/10.13039/501100011033/ and by the “European Union NextGenerationEU/PRTR” and by grant PRE2019-088874 funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. ESM acknowledges financial support from FONDECYT Regular, Chile 1221301, and LC gratefully acknowledges the support from Comunidad de Madrid (Spain) under the Multiannual Agreement with Universidad Complutense de Madrid, Program of Excellence of University Professors, in the context of the V Plan Regional de Investigación Científica e Innovación Tecnológica (PRICIT).

An accurate knowledge of the optical properties of β-Ga2O3 is key to developing the full potential of this oxide for photonics applications. In particular, the dependence of these properties on temperature is still being studied. Optical micro- and nanocavities are promising for a wide range of applications. They can be created within microwires and nanowires via distributed Bragg reflectors (DBR), i.e., periodic patterns of the refractive index in dielectric materials, acting as tunable mirrors. In this work, the effect of temperature on the anisotropic refractive index of β-Ga2O3 n(λ,T) was analyzed with ellipsometry in a bulk crystal, and temperature-dependent dispersion relations were obtained, with them being fitted to Sellmeier formalism in the visible range. Micro-photoluminescence (μ-PL) spectroscopy of microcavities that developed within Cr-doped β-Ga2O3 nanowires shows the characteristic thermal shift of red–infrared Fabry–Perot optical resonances when excited with different laser powers. The origin of this shift is mainly related to the variation in the temperature of the refractive index. A comparison of these two experimental results was performed by finite-difference time-domain (FDTD) simulations, considering the exact morphology of the wires and the temperature-dependent, anisotropic refractive index. The shifts caused by temperature variations observed by μ-PL are similar, though slightly larger than those obtained with FDTD when implementing the n(λ,T) obtained with ellipsometry. The thermo-optic coefficient was calculated. This work was supported by MICINN projects (RTI2018-097195-B-I00, RTI2018-096918-B-C41, PID2021-122562NB-I00 and PID2021-123190OB-I00/AEI/10.13039/501100011033/FEDER, UE). The authors acknowledge the financial support of the excellence research network RED2018-102609-T by MINECO. The authors acknowledge the support from the Air Force Office of Scientific Research under Award No. FA8655-20-1-7013 (Program Manager: Ali Sayir). M.A.-O. acknowledges financial support from MICINN (FPU contract No. FPU15/01982) and thanks the Central Research Development Fund (CRDF) of the University of Bremen for funding (ZF04/2021). J.S.M. and J.J. were supported by the Air Force Office of Scientific Research under award number FA9550–21–1–0507, monitored by Dr. Ali Sayir. Any opinions, finding, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the United States Air Force.

Multiphase coexistence has attracted significant interest in recent years because its control has entailed a significant breakthrough for the piezoelectric activity enhancement of lead-free piezoelectric oxides. However, the comprehension of phase coexistence still has many controversies including an adequate synthesis process and/or the role played by crystalline phases in functional properties. In this study, functional barium titanate [BaTiO_(3), (BTO)]-based materials with tunable functional properties were obtained by compositional modification via Bismuth (Bi) doping. Towards this aim, we systematically synthesized BTO-based materials by a sol-gel method, focusing on the control of Bi substitution in the BaTiO_(3) structure. In particular, we found that the substitution of Bi^(+3) leads to the stabilization of a monoclinic-tetragonal (M-T) phase boundary close to room temperature, which facilities the polarization process of the system. As a surprising result, we believe that the simple and cost-effective strategy and design principles described in this work open up the possibility of obtaining BTO-based lead-free ceramics with enhanced properties induced by the stabilization of the phase coexistence, expanding their application range.

17 páginas, 12 figuras, 1 tabla, In the quest for effective gas sensors for breath analysis, magnetoelastic resonance-based gas sensors (MEGSs) are remarkable candidates. Thanks to their intrinsic contactless operation, they can be used as non-invasive and portable devices. However, traditional monitoring techniques are bound to slow detection, which hinders their application to fast bio-related reactions. Here we present a method for real-time monitoring of the resonance frequency, with a proof of concept for real-time monitoring of gaseous biomarkers based on resonance frequency. This method was validated with a MEGS based on a Metglass 2826 MB microribbon with a polyvinylpyrrolidone (PVP) nanofiber electrospun functionalization. The device provided a low-noise (RMS = 1.7 Hz), fast (, Author A.P. received funding from grant PRE2019-0875001234, Ministerio de Ciencia e Innovación (MCI), Spain. D.M. received funding from Comfuturo, Consejo Superior de Investigaciones Científicas, Spain. Authors A.P., D.M., P.M. and C.H. received funding from projects RTI2018-095856- B-C21 and RTI2018-095856-B-C22, Ministerio de Ciencia e Innovación, Spain. A.P. and P.M. received funding S2018/NMT-4321, Comunidad de Madrid. J.D.A received funding from Next Generation EU, Ministerio de Trabajo y Economía, Comunidad de Madrid, Spain, Programa Investigo from grant 96-UCM-INV.

We use angle-resolved photoemission to map the Fermi surface and quasiparticle dispersion of bulk-like thin films of SrMoO$_3$ grown by pulsed laser deposition. The electronic self-energy deduced from our data reveals weak to moderate correlations in SrMoO$_3$, consistent with our observation of well-defined electronic states over the entire occupied band width. We further introduce spectral function calculations that combine dynamical mean-field theory with an unfolding procedure of density functional calculations and demonstrate good agreement of this approach with our experiments.

Hypothesis: As a fluid approaches three phase coexistence, adsorption may take place by the successive formation of two intervening wetting films. The equilibrium thickness of these wetting layers is the result of a delicate balance of intermolecular forces, as dictated by an underlying interface potential. The van der Waals forces for the two variable adsorption layers may be formulated exactly from Dzyaloshinskii-Lifshitz-Pitaevskii theory, and analytical approximations may be derived that extent well beyond the validity of conventional Hamaker theory. Calculations: We consider the adsorption equilibrium of water vapor on Silver Iodide where both ice and a water layers can form simultaneously and compete for the vapor as the triple point is approached. We perform numerical calculations of Lifshitz theory for this complex system and work out analytical approximations which provide quantitative agreement with the numerical results. Findings: At the three phase contact line between AgI/water/air, surface forces promote growth of ice both on the AgI/air and the water/vapor interfaces, lending support to a contact nucleation mode of AgI in the atmosphere. Our approach provides a framework for the description of adsorption at three phase coexistence, and allows for the study of ice nucleation efficiency on atmospheric aerosols., Accepted Manuscript

Sensing behaviour of samples belonging to the system ZnO:CuO has been investigated. Samples with different proportions of ZnO and CuO have been sintered and exposed to a reducing agent as ethanol (C_2H_5OH). All the samples have been characterized not only from the point of view of the sensing properties but also regarding morphology, composition, crystallinity and luminescent properties in order to correlate these properties to the sensing behaviour. Sensitivity, response times, recovery and stability have been measured under exposure to ethanol vapour in concentrations 800, 4700 and 16000 ppm. Sensing cycles have been performed at three different temperatures: 25, 50 and 100 degrees C.

Here in we present the fabrication and performance of waveguide tapers produced by femtosecond laser induced element redistribution in modified phosphate glasses. More particularly, it is demonstrated that by controlling the scan velocity during the writing process it is possible to adequately tune both the size of the modified area and the refractive index contrast to produce waveguides that can cope with mode field diameters in the range of 7 mu m. In addition, we fabricated tapered structures through the induction of an acceleration in the laser scanning velocity, resulting in a device that can efficiently convert a wide range of mode fields. The fine control achieved over the index contrast in the range of 10^(-3) and 10^(-2) would allow the production of a wide variety of tapers that could potentially be used to couple numerous photonic devices.

Abstract We performed ground-based experiments on the sample polystyrene–toluene–cyclohexane in order to complement the experimental activities in microgravity conditions related to the ESA projects DCMIX4 and Giant Fluctuations. After applying a stabilizing thermal gradient by heating from above a layer of the fluid mixture, we studied over many hours the density variations in the bidimensional horizontal field by means of a Shadowgraph optical setup. The resulting images evidence the appearance of convective instability after a diffusive time associated with the binary molecular solvent consisting of toluene and cyclohexane, confirming the negative sign of the Soret coefficient of this mixture. After a larger diffusive time related to mass diffusion of the polystyrene in the binary solvent, convection was suppressed by the increasing stabilizing density gradient originated by the Soret-induced concentration gradient of the polymer. This is compatible with a positive sign of the Soret coefficient of the polymer in the binary solvent. Graphic Abstract

The aim of this work is to clarify how in-plane magnetic anisotropy and magnetoelasticity depend on the thickness of Ga-rich FeGa layers. Samples with an Fe72Ga28 composition were grown by sputtering in the ballistic regime in oblique incidence. Although for these growth conditions uniaxial magnetic anisotropy could be expected, in-plane anisotropy is only present when the sample thickness is above 100 nm. By means of differential X-ray absorption spectroscopy, we have determined the influence of both Ga pairs and tetragonal cell distortion on the evolution of the magnetic anisotropy with the increase of FeGa thickness. On the other hand, we have used the cantilever beam technique with capacitive detection to also determine the evolution of the magnetoelastic parameters with the thickness increase. In this case, experimental results can be understood considering the grain distribution. Therefore, the different physical origins for anisotropy and magnetoelasticity open up the possibility to independently tune these two characteristics in Ga-rich FeGa films., This work has been financially supported through the projects MAT2015-66888-C3-3-R and MAT2015-66726-R (MINECO/FEDER) of the Spanish Ministry of Economy and Competitiveness, RTI2018-097895-B-C43 of the Spanish Ministry of Science, Innovation, and Universities, and Gobierno de Aragón (Grant E10-17D) and Fondo Social Europeo. A.M.-N. is thankful for the contract from Universidad Complutense and Comunidad de Madrid “Atracción de Talento” program 2018-T1/IND-10360, and A.B. thanks MINECO for the Ph.D. grant BES-2016-076482.

The growth mechanism of layered alpha-MoO_3 nano- and microplates on the surface of Mo wires during Joule heating has been investigated by application of an external electric field to the current carrying wire. The observed rapid growth of the structures, involving enhanced diffusion processes associated to the intense electric current, is further enhanced by the external field leading to a near instantaneous formation of MoO_3 plates. Thermally assisted electromigration in the Mo wire with the additional effect of the electric field appears as a very time effective method to grow MoO_3 layered low dimensional structures. Other molybdenum oxide nanostructures, such as nanospheres and nanocrystallites with different shapes, have been found to grow by deposition from the Mo wire on the electrodes used to apply the external electric field. The growth on the electrodes takes place by a thermally assisted electric-field-driven process.

The quest for Majorana zero modes in the laboratory is an active field of research in condensed matter physics. In this regard, there have been many theoretical proposals; however, their experimental detection remains elusive. In this article, we present a realistic setting by considering a quantum ring with Rashba spin-orbit coupling and threaded by a magnetic flux, in contact with a topological superconducting nanowire. We focus on spin-polarized persistent currents to assess the existence of Majorana zero modes. We find that the Rashba spin-orbit coupling allows for tuning the position of the zero energy crossings in the flux parameter space and has sizable effects on spin-polarized persistent currents. We believe that our results will contribute towards probing the existence of Majorana zero modes.

[EN] Fe3C/few-layered graphene core/shell nanoparticles embedded in a carbon matrix are synthesized by a novel two-step surfactant sol-gel strategy, where the processes of hydrolysis, polycondensation and drying take place in a one-pot. The present approach is based on the combined action of oleic acid and oleylamine, which act sterically on the precursor micelles when a densification temperature is performed in a reducing atmosphere. The structural and magnetic evolution of the formed compounds is investigated, ranging from iron oxides such as Fe3O4 and FeO, to the formation of pure Fe3C/C samples from 700 ºC onwards. Interestingly, Fe3C nanoparticles with a size of ~20 nm crystallize immersed in the carbon matrix and the surrounding environment forms an oriented encapsulation built by few-layered graphene. The nanostructures show a saturation magnetization of ~43 emu/g and a moderate coercivity of ~500 Oe. Thereby, an innovative chemical route to produce single phase Fe3C nanoparticles is described, and an effective method of few-layered graphene passivation is proposed, yielding a product with a high magnetic response and high chemical stability against environmental corrosion., Ministerio de Ciencia de Innovación (MCINN), Spain, through the projects: MAT2015–65445-C2–1-R, MAT2017–86450-C4–1-R, MAT2015–67557-C2–1-P, RTI2018–095856-B-C21, RTI2018–095303-A-C52, PIE: 2021-60-E030, PIE: 2010–6-OE-013; and Comunidad de Madrid, Spain, by S2013/MIT-2850 NANOFRONTMAG and S2018/NMT-4321 NANOMAGCOST. The authors are also grateful for the electron microscopy characterization performed in the Centro Nacional de Microscopía Electrónica at the Universidad Complutense de Madrid (ICTS ELECMI, UCM), support from MCINN grant # RTI2018–097895-B-43. C.G.-M. acknowledges the financial support from MICINN through the “Juan de la Cierva” Program (FJC2018–035532-I).

Lanthanide-based upconverting nanoparticles (UCNPs) are trustworthy workhorses in luminescent nanothermometry. The use of UCNPs-based nanothermometers has enabled the determination of the thermal properties of cell membranes and monitoring of in vivo thermal therapies in real time. However, UCNPs boast low thermal sensitivity and brightness, which, along with the difficulty in controlling individual UCNP remotely, make them less than ideal nanothermometers at the single-particle level. In this work, it is shown how these problems can be elegantly solved using a thermoresponsive polymeric coating. Upon decorating the surface of NaYF4:Er3+,Yb3+ UCNPs with poly(N-isopropylacrylamide) (PNIPAM), a >10-fold enhancement in optical forces is observed, allowing stable trapping and manipulation of a single UCNP in the physiological temperature range (20–45 °C). This optical force improvement is accompanied by a significant enhancement of the thermal sensitivity— a maximum value of 8% °C+1 at 32 °C induced by the collapse of PNIPAM. Numerical simulations reveal that the enhancement in thermal sensitivity mainly stems from the high-refractive-index polymeric coating that behaves as a nanolens of high numerical aperture. The results in this work demonstrate how UCNP nanothermometers can be further improved by an adequate surface decoration and open a new avenue toward highly sensitive single-particle nanothermometry, This work was supported by the Ministerio de Ciencia e Innovación de España (PID2019-106211RB-I00 PID2019-105195RA-I00 and MAT2017- 83111R), by the Comunidad de Madrid (S2017/BMD-3867 RENIM-CM), co-financed by European Structural and Investment Fund and by the Universidad Autónoma de Madrid and Comunidad Autónoma de Madrid (SI1/PJI/2019-00052 and PR38/21-36 ANTICIPA-CM). D.L. acknowledges a scholarship from the China Scholarship Council (201808350097). J.R.B. acknowledges the support from Carl Tryggers Foundation (CTS18:229). M.I.M acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación, through the “María de Maeztu” Programme for Units of Excellence in R&D (CEX2018-000805-M) and the MELODIA PGC2018-095777-B-C22 projec

[EN] In this work, we demonstrate the use of electrical impedance spectroscopy (EIS) for the disentanglement of several dielectric contributions in encapsulated single graphene layers. The dielectric data strongly vary qualitatively with the nominal graphene resistance. In the case of sufficiently low resistance of the graphene layers, the dielectric spectra are dominated by inductive contributions, which allow for disentanglement of the electrode/graphene interface resistance from the intrinsic graphene resistance by the application of an adequate equivalent circuit model. Higher resistance of the graphene layers leads to predominantly capacitive dielectric contributions, and the deconvolution is not feasible due to the experimental high frequency limit of the EIS technique., This research was funded by the EU graphene flagship (grant Graphene Core3 881603), the EU FLAG-ERA project To2Dox (JTC-2019-009) and the Spanish MINECO (grant PID2020-118078RBI00).

[EN] The use of rare-earth-based permanent magnets is one of the critical points for the development of the current technology. On the one hand, industry of the rare-earths is highly polluting due to the negative environmental impact of their extraction and, on the other hand, the sector is potentially dependent on China. Therefore, investigation is required both in the development of rare-earth-free permanent magnets and in sintering processes that enable their greener fabrication with attractive magnetic properties at a more competitive price. This work presents the use of a cold sintering process (CSP) followed by a post-annealing at 1100 °C as a new way to sinter composite permanent magnets based on strontium ferrite (SFO). Composites that incorporate a percentage ≤ 10% of an additional magnetic phase have been prepared and the morphological, structural and magnetic properties have been evaluated after each stage of the process. CSP induces a phase transformation of SFO in the composites, which is partially recovered by the post-thermal treatment improving the relative density to 92% and the magnetic response of the final magnets with a coercivity of up to 3.0 kOe. Control of the magnetic properties is possible through the composition and the grain size in the sintered magnets. These attractive results show the potential of the sintering approach as an alternative to develop modern rare-earth-free composite permanent magnets., This work has been supported by the Ministerio Español de Ciencia e Innovación (MICINN), Spain, through the projects MAT2017-86540-C4-1-R and RTI2018-095303-A-C52, and by the European Commission through Project H2020 No. 720853 (Amphibian). C.G.-M. and A.Q. acknowledge financial support from MICINN through the “Juan de la Cierva” program (FJC2018-035532-I) and the “Ramón y Cajal” contract (RYC-2017-23320). S. R.-G. gratefully acknowledges the financial support of the Alexander von Humboldt foundation, Germany. A.S. acknowledges the financialsupport from the Comunidad de Madrid, Spain, for an “Atracción de Talento Investigador” contract (No. 2017-t2/IND5395).

Spent batteries recycling is an important way to obtain low-cost graphite. Nevertheless, the obtaining of crystalline graphite with a rather low density of defects is required for many applications. In the present work, high-quality graphites have been obtained from different kinds of spent batteries. Black masses from spent alkaline batteries (batteries black masses, BBM), and lithium-ion batteries from smartphones (smartphone black masses, SBM) and electric and/or hybrid vehicles (lithium-ion black masses, LBM) were used as starting materials. A hydrometallurgical process was then used to obtain recycled graphites by acidic leaching. Different leaching conditions were used depending on the type of the initial black mass. The final solids were characterized by a wide set of complementary techniques. The performance as Li ion batteries anode of the sample with better structural quality was assessed., This work has been funded by the European Union′s Horizon 2020 research and innovation program under grant agreement No 776851 (CarE Service), the Spanish Ministry of Economy and Competitiveness (MINECO) under project MAT2017-84118-C2-2-R and by Banco Santander-UCM through project PR87/19-22613.

When exposed to an alternating magnetic field, superparamagnetic nanoparticles can elicit the required hyperthermic effect while also being excellent magnetic resonance imaging (MRI) contrast agents. Their main drawback is that they diffuse out of the area of interest in one or two days, thus preventing a continuous application during the typical several-cycle multi-week treatment. To solve this issue, our aim was to synthesise an implantable, biodegradable membrane infused with magnetite that enabled long-term treatment while having adequate MRI contrast and hyperthermic capabilities. To immobilise the nanoparticles inside the scaffold, they were synthesised inside hydrogel fibres. First, polysuccinimide (PSI) fibres were produced by electrospinning and crosslinked, and then, magnetitc iron oxide nanoparticles (MIONs) were synthesised inside and in-between the fibres of the hydrogel membranes with the well-known co-precipitation method. The attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) investigation proved the success of the chemical synthesis and the presence of iron oxide, and the superconducting quantum interference device (SQUID) study revealed their superparamagnetic property. The magnetic hyperthermia efficiency of the samples was significant. The given alternating current (AC) magnetic field could induce a temperature rise of 5 °C (from 37 °C to 42 °C) in less than 2 min even for five quick heat-cool cycles or for five consecutive days without considerable heat generation loss in the samples. Short-term (1 day and 7 day) biocompatibility, biodegradability and MRI contrast capability were investigated in vivo on Wistar rats. The results showed excellent MRI contrast and minimal acute inflammation.

Finding suitable p-type dopants, as well as reliable doping and characterization methods for the emerging wide bandgap semiconductor beta-Ga_2O_3 could strongly influence and contribute to the development of the next generation of power electronics. In this work, we combine easily accessible ion implantation, diffusion and nuclear transmutation methods to properly incorporate the Cd dopant into the beta-Ga_2O_3 lattice, being subsequently characterized at the atomic scale with the Perturbed Angular Correlation (PAC) technique and Density Functional Theory (DFT) simulations. The acceptor character of Cd in beta-Ga_2O_3 is demonstrated, with Cd sitting in the octahedral Ga site having a negative charge state, showing no evidence of polaron deformations nor extra point defects nearby. The possibility to determine the charge state of Cd will allow assessing the doping type, in particular proving p-type character, without the need for ohmic contacts. Furthermore, a possible approach for contactless charge mobility studies is demonstrated, revealing thermally activated free electrons for temperatures above similar to 648 K with an activation energy of 0.54(1) and local electron transport dominated by a tunneling process between defect levels and the Cd probes at lower temperatures.

Zn_2GeO_4 microrods obtained by thermal evaporation of a compacted powder mixture of ZnO and Ge exhibit quite intense UV luminescence at low temperatures. Herein, the luminescence properties of Zn_2GeO_4 microrods are studied for 2:1 and 1:1 ZnO:Ge ratio in the precursor mixture. In both cases, Zn2GeO4 microrods of high crystal quality produce a 355 nm emission under aforementioned bandgap excitation conditions at low temperatures. However, this emission vanishes at room temperature (RT) in the 1:1 samples while it is kept in the 2:1 ones. Herein this work, the thermal quenching of the UV luminescence is studied by means of steady and time-resolved photoluminescence techniques from 4 K up to RT for both Zn_2GeO_4 microrods. The analysis of the results leads us to conclude that although the luminescence mechanisms are the same in both cases, a higher decay rate is observed in the 1:1 in both intensity and lifetime, which explain the observed thermal quenching at RT.

Perovskite La_0.3Ca_0.7Fe_0.7Cr_0.3O_(3-delta) (LCFCr) is a mixed ionic and electronic conductor (MIEC) that can be employed as an electrode material in reversible solid oxide fuel cells (RSOFCs). In this work, an ultra-fast (15 min) one-step microwave (MW)-assisted combustion synthesis route has been developed to obtain phase pure and highly crystalline LCFCr powder. The synthesized powders exhibited a sponge-like microstructure with increased electrochemical reaction sites. Neutron thermodiffraction analysis revealed a structural transition above 500 degrees C from the room temperature (RT) orthorhombic Pnma to a rhombohedral R3c perovskite phase. The oxygen vacancy concentration was found to increase from delta = 0.272(7) at RT to delta = 0.333(5) at 900 degrees C. Furthermore, a 3-dimensional G-type antiferromagnetic structure was detected at RT. MW-sintering of pressed green ceramic pellets was carried out at 950 degrees C for 1 h, using a MW-transparent quartz fiber crucible or alternatively a SiC crucible acting as a MW-absorber. Impedance spectroscopy data on sintered ceramic pellets revealed electronic inhomogeneity as demonstrated by the occurrence of three dielectric relaxation processes associated with two grain boundary (GB)-like contributions and one bulk. The dielectric inhomogeneity encountered may be restricted to the extrinsic GB areas, which may be rather thin. More homogeneous dielectric properties of the GBs were found in the pellet that was sintered in the SiC crucible.

We analyze the micromagnetics of short longitudinal modulations of a high-magnetization material in cylindrical nanowires made of a soft-magnetic material of lower magnetization such as permalloy, combining magnetic microscopy, analytical modeling, and micromagnetic simulations. The mismatch of magnetization induces curling of magnetization around the axis in the modulations, in an attempt to screen the interfacial magnetic charges. The curling angle increases with modulation length, until a plateau is reached with nearly full charge screening for a specific length scale~$\Delta_\mathrm{mod}$, larger than the dipolar exchange length of any of the two materials. The curling circulation can be switched by the Oersted field arising from a charge current with typical magnitude $10^{12} A/m^{2}$ for a diameter of $\sim$100 nm, and reaching a maximum for $\Delta_\mathrm{mod}$.

Au/SiO2 SBA-15 materials were prepared using supercritical CO2 (scCO2) and by wet impregnation. First, SiO2 SBA-15 was functionalized with thiol groups at different grafting densities using 3-(Mercaptopropyl)trimethoxysilane dissolved in scCO2. The support was then impregnated with HAuCl4·3H2O in scCO2 modified with EtOH. Wet impregnation of the supports with HAuCl4·3H2O in ethanol was also performed. Materials were calcined at 500 ºC to remove the organic matter and promote particle growth. Materials prepared on the highest thiol grafting density support showed Au NP between 2.5-5 nm homogeneously distributed within the mesopores. Slightly larger Au NPs were obtained in scCO2 modified with EtOH. Materials prepared on the low thiol grafting density support showed a bimodal particle size distribution with particles up to 7 nm located inside the mesopores and larger ones of 10-20 nm on the external surface. A possible reaction mechanism was proposed. These materials can be used in catalysis, sensing and biomedicine.

Different studies carried out in the last three decades on the magnetic susceptibility of the spinel ZnFeO ferrite have revealed the positive character of its Curie–Weiss temperature, contradicting its observed antiferromagnetic behavior which is characterized by a well-defined susceptibility peak centered around the Neel temperature (10 K). Some approaches based on ab initio calculations and mixture of interactions have been attempted to explain this anomaly. This work shows how for very low values of the inversion parameter, the small percentage of Fe atoms located in tetrahedral sites gives rise to the appearance of ferrimagnetic clusters around them. Superparamagnetism of these clusters is the main cause of the anomalous Curie–Weiss behavior. This finding is supported experimentally from the thermal dependence of the inverse susceptibility and its evolution with the degree of inversion., This research was funded by Spanish Ministries of Science Innovation and Universities and of Economy and Competitiveness by means of the AFORMAR (PID2019-109334RB), RTI2018-095303-B-C51 and RTI2018-095856-B-C21 projects. The support of the grants from the Community of Madrid numbers S2018/NMT-4381-MAT4.0-CM and P2018/NMT-4321 is also recognized.

Kagome antiferromagnetic lattices are of high interest because the geometric frustration is expected to give rise to highly degenerated ground states that may host exotic properties such as quantum spin liquid (QSL). Ca_10Cr_7O_28 has been reported to display all the features expected for a QSL. At present, most of the literature reports on samples synthesized with starting materials ratio CaO/Cr_2O_3 3:1, which leads to a material with small amounts of CaCrO_4 and CaO as secondary phases; this impurity excess affects not only the magnetic properties but also the structural ones. In this work, samples with starting material ratios CaO/Cr_2O_3 3:1, 2.9:1, 2.85:1, and 2.8:1 have been synthesized and studied by X-ray diffraction with Rietveld refinements, selected area electron diffraction measurements, high-resolution transmission electron microscopy (HRTEM), low-temperature magnetometry, and magnetic calorimetry. This result shows that a highly pure Ca_10Cr_7O_28 phase is obtained for a CaO/Cr_2O_3 ratio of 2.85:1 instead of the 3:1 usually reported; the incorrect stoichiometric ratio leads to a larger distortion of the corner-sharing triangular arrangement of magnetic ions Cr+5 with S = 1/2 in the Kagome lattice. In addition, our study reveals that there exists another frustration pathway which is an asymmetric zigzag spin ladder along the directions [211], [12-1], and [1- 1-1], in which the Cr-Cr distances are shorter than in the Kagome layers.

5 pags., 5 figs., Li metal has been deposited on the surface of a Ru(0001) single crystal containing patches of monolayer-thick epitaxial graphene islands. The use of low-energy electron microscopy and diffraction allowed us to {\em in situ} monitor the process by measuring the local work function as well as to study the system in real and reciprocal space, comparing the changes taking place on the graphene with those on the bare Ru(0001) surface. It is found that Li deposition decreases the work function of the graphene islands but to a much smaller degree than of the Ru(0001) surface, as corresponds to its intercalation below the graphene overlayer. Finally, the diffusion process of Li out of the graphene islands has been monitored by photoelectron microscopy using a visible-light laser., This work is supported by grant RTI2018-095303-B-C51, funded by MCIN/AEI/10.13039/501100011033 and by ‘‘ERDF A way of making Europe’’, by grant PID2020-117024GB-C43 (Ministerio de Ciencia e Innovación) and by grant S2018-NMT-4321, funded by the Regional Government of Madrid, Spain and by ‘‘ERDF A way of making Europe’’. L.M.G. acknowledges a sabbatical grant from DGAPA-UNAM

A systematic study on laser-induced heating carried out in two biological windows (800 nm and 1053 nm) for Fe3O4 nanoparticles in water suspension showed evidence of the strong dependence of the specific absorption rate (SAR) on extrinsic parameters such as the vessel volume or laser spot size. The results show that a minimum of 100 μL must be used in order to obtain vessel-size-independent SARs. In addition, at a constant intensity but different laser powers and spot size ratios, the SARs can differ by a three-fold factor, showing that the laser power and irradiated area strongly affect the heating curves for both wavelengths. The infrared molecular absorber IRA 980B was characterized under the same experimental conditions, and the results confirm the universality of the SARs’ dependence on these extrinsic parameters. Based on these results, we propose using solutions of IRA 980B as a standard probe for SAR measurements and employing the ratio SARiron oxide/SARIRA 980B to compare different measurements performed in different laboratories. This measurement standardization allows us to extract more accurate information about the heating performance of different nanoparticles.

Correction for ‘A feasible pathway to stabilize monoclinic and tetragonal phase coexistence in barium titanate-based ceramics’ by Jallouli Necib et al., J. Mater. Chem. C, 2022, 10, 17743–17756, https://doi.org/10.1039/D2TC04265G.

In this work, Gd-filled skutterudite GdxCo4Sb12 has been prepared in one-step method under high-pressure conditions in a piston-cylinder press at 3.5 GPa and moderate temperature of 800 °C. A detailed structural characterization was performed using synchrotron X-ray diffraction (SXRD), revealing a filling fraction of x = 0.066(4) and an average bond length of 3.3499(3) Å. The lattice thermal expansion accessed via temperature-dependent SXRD led to a precise determination of a Debye temperature of 322(3) K, from the fitting of the unit-cell volume expansion using the second order Grüneisen approximation. Such parameter, when evaluated from the mean square displacements of Co and Sb, displayed a value of 265(2) K, meaning that the application of the harmonic Debye theory underestimates the Debye temperature in skutterudites. Regarding the Gd atom, its intrinsic disorder value is ~5× and ~25× higher than those of Co and Sb, respectively, denoting that Gd has a strong rattling behavior with an Einstein temperature of θE = 67(2) K. As a result, an ultra-low thermal conductivity of ~0.89 W/m·K at 773 K was obtained, leading to a thermoelectric efficiency zT of ~0.5 at 673 K.

Artículo con 10 figuras, In this work, NbO layers with highly improved electrical properties respect to pristine material have been produced by ultrafast-laser powder bed fusion process. The conditions required for producing uniform and compact layers of NbO from powder material have been studied and optimized. It has been established that ultrafast-laser irradiation, performed in air at room temperature, leads to the formation of dense NbO layers with the high temperature monoclinic crystal structure (H-NbO) but oxygen deficient. The layers show a preferential crystal orientation with the short axis of the monoclinic structure lying in the structure plane. This preferential orientation can be controlled by the laser irradiation conditions. Anisotropic resistivity has been observed as a consequence of the induced microstructure, while the overall material resistivity is decreased by more than eight orders of magnitude due to the oxygen deficiency. These results indicate that it is feasible to use ultrafast laser processing to promote high-temperature non-stoichiometric niobium oxide phases in a few seconds and with low energy consumption. The highly improved electrical properties of the laser irradiated NbO layers are extremely interesting for different electronic and sensing applications., The authors are grateful to the Comunidad de Madrid for support via the Project PR65/19-22464 (Proyectos de I+D para jóvenes doctores) and MCIN/AEI/10.13039/501100011033 for the financial support through grant PID2020-112770RB-C21. This work has also been funded by Complutense University of Madrid and Banco Santander via the project UCM-Santander 2019 (PR87/19-22613). B. Sotillo acknowledges financial support from Comunidad de Madrid (Ayudas del Programa de Atracción de Talento 2017-T2/IND-5465). We acknowledge the Technical Services of CENIM-CSIC for the XPS measurements.

11 pags., 5 figs., 1 tab. -- This article belongs to the Special Issue Multifunctional Magnetic Nanowires and Nanotubes, The use of metallic nanowires is mostly reduced to scientific areas where a small quantity of nanostructures are needed. In order to broaden the applicability of these nanomaterials, it is necessary to establish novel synthesis protocols that provide a larger amount of nanowires than the conventional laboratory fabrication processes at a more competitive cost. In this work, we propose several modifications to the conventional electrochemical synthesis of nanowires in order to increase the production with considerably reduced production time and cost. To that end, we use a soft anodization procedure of recycled aluminum at room temperature to produce the alumina templates, followed by galvanostatic growth of CoFe nanowires. We studied their morphology, composition and magnetic configuration, and found that their properties are very similar to those obtained by conventional methods., This research was partially funded by the Spanish Agencia Estatal de Investigación through projects MAT2017-87072-C4-2-P and RTI2018-095303-B-C53, by The Ministerio de Ciencia y Universidades through project RTI2018-095303-A-C52, through the Ramón y Cajal Contract RYC2017-23320, The European Commission through the H2020 Project No. 720853 (AMPHIBIAN) and by the Comunidad de Madrid through Project NANOMAGCOST-CM P2018/NMT-4321.

In this work, we have explored the possibility of using light to remove the adsorbed hydrogen layer that blocks the GaAs surface when electrodepositing Bi thin films on lower-doped n-GaAs(111)B substrates. A light pulse of a few seconds applied under open-circuit (zero-current) conditions before starting the electrodepositionof Bi in darkness has a small effect on the structural, morphological and interfacial electrical properties of the Bi film in comparison to layers deposited without the use of light. The potentiostatic curves recorded during the Bi nucleation show that the light pulse does not remove the adsorbed hydrogen layer but modifies the n-GaAs surface, inhibiting the reduction of Bi(III) ions. The atomic force microscopy analysis of the n-GaAs surface corroborates that the light degrades the surface by inducing photo-oxidation reactions, phenomenon that is correlated to the photocorrosion of the substrate. To maintain the electrical neutrality during photocorrosion, proton reduction and electroless deposition of Bi occur in parallel to the photo-oxidations. The simultaneity of these processes and the inhibition of Bi(III) ions to get reduced on those areas of the n-GaAs surface chemically altered enables the electroless deposition of unconnected Bi flakes with morphological, structural and interfacial electrical properties close to the state of the art of Bi thin films. Only the out of plane crystal quality of the Bi flakes show a small detriment whereas the Schottky barrier height slightly increases.

Ruddlesden–Popper oxides, (AO)(ABO3) n , occupy a prominent place in the landscape of materials research because of their intriguing potential applications. Compositional modifications to the cation sublattices, A or B, have been explored in order to achieve enhanced functionalities. However, changes to the anionic sublattice have been much less explored. In this work, new oxygen-deficient manganese Ruddlesden–Popper-related phases, La0.5Ca2.5Mn2O6.5 and La0.5Ca2.5Mn2O6.25, have been synthesized by controlled reduction of the fully oxidized n = 2 term La0.5Ca2.5Mn2O7. A complete structural and compositional characterization, by means of neutron diffraction, electron diffraction and atomically resolved scanning transmission electron microscopy and electron energy-loss spectroscopy techniques, allows the proposition of a topotactic reduction pathway through preferential oxygen removal in the [MnO2] layers along [031] and [0{\bar 1}3] directions. The gradual decrease of the Mn oxidation state, accommodated by short-range ordering of anionic vacancies, reasonably explains the breaking of ferromagnetic interactions reinforcing the emergence of antiferromagnetic ones. Additional short-range order–disorder phenomena of La and Ca cations have been detected in the reduced La0.5Ca2.5Mn2O7−δ, as previously reported in the parent compound.

International audience; Rare earth (RE)-doped GaN nanowires (NWs), combining the well-defined and controllable optical emission lines of trivalent RE ions with the high crystalline quality, versatility, and small dimension of the NW host, are promising building blocks for future nanoscale devices in optoelectronics and quantum technologies. Europium doping of GaN NWs was performed by ion implantation, and structural and optical properties were assessed in comparison to thin film reference samples. Despite some surface degradation for high implantation fluences, the NW core remains of high crystalline quality with lower concentrations of extended defects than observed in ion-implanted thin films. Strain introduced by implantation defects is efficiently relaxed in NWs and the measured deformation stays much below that in thin films implanted in the same conditions. Optical activation is achieved for all samples after annealing, and while optical centers are similar in all samples, Eu3+ emission from NW samples is shown to be less affected by residual implantation damage than for the case of thin films. The incorporation of Eu in GaN NWs was further investigated by nano-cathodoluminescence and X-ray absorption spectroscopy (XAS). Maps of the Eu-emission intensity within a single NW agree well with the Eu-distribution predicted by Monte Carlo simulations, suggesting that no pronounced Eu-diffusion takes place. XAS shows that 70–80% of Eu is found in the 3+ charge state while 20–30% is 2+ attributed to residual implantation defects. A similar local environment was found for Eu in NWs and thin films: for low fluences, Eu is mainly incorporated on substitutional Ga-sites, while for high fluences XAS points at the formation of a local EuN-like next neighbor structure. The results reveal the high potential of ion implantation as a processing tool at the nanoscale.

This study reports on the deposition of highly transparent, n-type ZnO thin films on glass substrate at 450 C using spray pyrolysis processing, with the simultaneous insertion of yttrium (Y) at different percentages (0, 2, 5, 7 at%) as a dopant. The effect of Y doping on the structure, morphology and optical properties of Y doped ZnO (ZnO:Y) was investigated for optoelectronic applications. The obtained thin films were characterized by means of X-ray diffraction, field-emission scanning electron microscopy (FESEM), UV visible absorbance measurements, photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. The as-prepared films exhibit well-defined hexagonal wurtzite structure grown along [002]. Field emission scanning electron microscope micrographs of the pure ZnO and ZnO:Y showed that the films acquired a dominance of hexagonal-like grains, the morphology was influenced by Y incorporation. All the films showed high transparency in the visible domain with an average transmittance of 83%. The band gap energy, Eg, increased from 3.12 eV to 3.18 eV by increasing the Y doping concentration up to 5 at% and then decreased to 3.15 eV for 7 at% Y content. The PL and CL measurements reveal a strong ultraviolet (UV) emission, suggesting that the as-prepared ZnO:Y thin films can potentially be used in optoelectronic devices.

Anatase TiO2 nanoparticles doped with iron ions have been synthesized via the green chemistry method using aqueous extract of lemongrass (Cymbopogon citratus) obtained from Soxhlet extraction and doped by wet impregnation. The TiO2 anatase phase has been doped with Fe3+ (0.05, 0.075, and 0.1 Fe3+ : Ti molar ratio) at 550°C and 350°C, respectively. The scanning electron microscopy with energy-dispersive X-ray (SEM-EDS) shows nanoparticle clusters and efficiencies of impregnations between 66.5 and 58.4% depending on the theoretical dopant amount. The electron transmission microscopy (TEM) reveals final particle sizes ranging between 7 and 26 nm depending on the presence or not of the dopant. The cathodoluminescence (CL) and photoluminescence (PL) studies of the doped and undoped nanoparticles show a luminescence signal attributed to surface oxygen vacancies (visible CL emission 380–700 nm and PL emission 350–800 nm); additionally, a decrease in emission intensity is observed due the inhibition of the recombination of the photogenerated electron-holes pairs; moreover, nanopowders were analyzed by UV-Vis spectrophotometry of diffuse reflectance, and the absorption edge of the Fe-TiO2 in comparison to undoped TiO2 is extended greatly toward the visible light. The six bands (A1g + 2B1g + 3Eg) found by Raman spectroscopy and the x-ray diffraction pattern (XRD) confirm that synthesized TiO2 is only anatase phase, which is commonly used as a catalyst in waste water treatment, specifically in heterogeneous photocatalytic processes.

[EN] The purpose of this work is to fabricate self-assembled microstructures by the sol–gel method and study the morphological, structural and compositional dependence of 3-Fe2O3 nanoparticles embedded in silica when glycerol (GLY) and cetyl-trimethylammonium bromide (CTAB) are added as steric agents simultaneously. The combined action of a polyalcohol and a surfactant significantly modifies the morphology of the sample giving rise to a different microstructure in each of the studied cases (1, 3 and 7 days of magnetic stirring time). This is due to the fact that the addition of these two compounds leads to a considerable increase in gelation time as GLY can interact with the alkoxide group on the surface of the iron oxide precursor micelle and/or be incorporated into the hydrophilic chains of CTAB. This last effect causes the iron oxide precursor micelles to be interconnected forming aggregates whose size and structure depend on the magnetic stirring time of the sol–gel synthetic route. In this paper, crystalline structure, composition, purity and morphology of the sol–gel coatings densified at 960 ºC are examined. Emphasis is placed on the nominal percentage of the different iron oxides found in the samples and on the morphological and structural differences. This work implies the possibility of patterning 3-Fe2O3 nanoparticles in coatings and controlling their purity by an easy one-pot sol–gel method., Spanish Ministry of Industry, Economy and Competitiveness for financing the project MAT2015-65445-C2-1-R, MAT2017-86450-C4-1-R, MAT2015-67557-C2-1-P, by the Comunidad de Madrid S2013/MIT-2850 NANOFRONTMAG and H2020 AMPHIBIAN Project ID: 720853. The authors are also grateful to the BM25-SpLine staff for their valuable technical support beyond their duties and for the financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) and The Spanish National Research Council (CSIC) under Grant No. PIE 2010- 6OE-013, The ESRF – The European Synchrotron, MICIU and CSIC are acknowledged for provision of synchrotron radiation facilities. A. S. acknowledges the Financial support from the Comunidad de Madrid for an “Atracción de Talento Investigador” contract (No. 2017-t2/IND5395).

A thermal actuator based on thin flexible lamellas of Ga_2O_3 was designed in order to demonstrate the potential of this semiconductor for micro-opto-electro-mechanical applications (MOEMs). The working principle of these devices is based on the thermal expansion that induces a vertical movement resultant of the lamella elongation due the self-heating/Joule effect. Upon excitation with photons, electrons or ions, intrinsic luminescence bands associated with self-trapped excitons and donor-acceptor pair recombination dominate the emission spectrum. When a current passes through the device, simultaneously with the thermal expansion, this luminescence is strongly quenched. Based on systematic Photoluminescence and Raman studies as a function of temperature and as a function of the applied power it is demonstrated that the observed luminescence quenching is directly related with the Joule heating effect. This work presents for the first time a thermal actuator based on Ga_2O_3 and it intends to be a stimulus for future works on MOEMs applications based on this semiconductor.

TiO2 is currently one of the most employed material in photocatalysis and optoelectronic applications. By doping with different elements, tailored luminescent and optoelectronic properties can be obtained, which further enhances its applicability. The achievement of deeper knowledge and control on the recombination processes via light-metal doping engineering promises a wider use in optoelectronic applications. In this work, the luminescent properties of undoped and Li-doped anatase TiO2 nanoparticles obtained by hydrolysis process are studied, by means of photoluminescence (PL) measurements from 10 K to room-temperature. TiO2 presents a wide emission which covers the visible range, while Li-doping quenches the emission on the low visible region. By terms of time-resolved luminescence (TR-PL), lifetime of the recombination processes can be obtained, in which a decrease on lifetime values can be observed for the doped samples.

In this review, we describe different families of metastable materials, some of them with relevant technological applications, which can be stabilized at moderate pressures 2–3.5 GPa in a piston-cylinder press. The synthesis of some of these systems had been previously reported under higher hydrostatic pressures (6–10 GPa), but can be accessed under milder conditions in combination with reactive precursors prepared by soft-chemistry techniques. These systems include perovskites with transition metals in unusual oxidation states (e.g., RNiO3 with Ni3+, R = rare earths); double perovskites such as RCu3Mn4O12 with Jahn–Teller Cu2+ ions at A sites, pyrochlores derived from Tl2Mn2O7 with colossal magnetoresistance, pnictide skutterudites MxCo4Sb12 (M = La, Yb, Ce, Sr, K) with thermoelectric properties, or metal hydrides Mg2MHx (M = Fe, Co, Ni) and AMgH3 (A: alkali metals) with applications in hydrogen storage. The availability of substantial amounts of sample (0.5–1.5 g) allows a complete characterization of the properties of interest, including magnetic, transport, thermoelectric properties and so on, and the structural characterization by neutron or synchrotron X-ray diffraction techniques.

In this work we have explored the growth by high pressure sputtering (HPS) of materials intended for novel selective contacts for photovoltaic cells. This technique shows promise for the low-damage low-temperature deposition of PV materials. We studied the deposition of ITO, MoO x and TiO x using pure Ar and mixed Ar/O 2 atmospheres as well as ceramic or metallic targets. We show that HPS deposition of these materials is feasible. The growth rate is greatly reduced when oxygen is added to the argon sputtering atmosphere. The best sputtering RF power was 20–45 W for the pressure range studied. Finally, as-deposited films present high surface recombination, but a mild hot plate anneal at 200°C recovers long effective lifetimes.

12 pags., 8 figs., 1 tab., We study the effect of the Rashba spin-orbit coupling on the Fermi arcs of topological Dirac semimetals. The Rashba coupling is induced by breaking the inversion symmetry at the surface. Remarkably, this coupling could be enhanced by the interaction with the substrate and controlled by an external electric field. We study analytically and numerically the rotation of the spin of the surface states as a function of the electron's momentum and the coupling strength. Furthermore, a detailed analysis of the spin-dependent two-terminal conductance is presented in the clean limit and with the addition of a random distribution of impurities. Depending on the magnitude of the quadratic terms in the Hamiltonian, the spin-flip conductance may become dominant, thus showing the potential of the system for spintronic applications, since the effect is robust even in the presence of disorder., We acknowledge financial support through Spanish grants PGC2018-094180-B-I00 (MCIU/AEI/FEDER, EU), MAT2016-75955, MAT2017-86717-P and PID2019-106820RB-C21 (MINECO/FEDER, EU), CAM/FEDER Project No. S2018/TCS-4342 (QUITEMAD-CM) and CSIC Research Platform PTI-001. G P also acknowledges support from the DFG within SBF 1277 and from the ‘UA: Matemática Aplicada a la Teoría de la Materia Condensada’ with the Carlos III University.

We investigate the effect of a non-magnetic donor impurity located at the surface of the SnTe topological crystalline insulator. In particular, the changes on the surface states due to a Sb impurity atom are analyzed by means of ab initio simulations of pristine and impurity-doped SnTe. Both semi-infinite and slab geometries are considered within the first-principles approach. Furthermore, minimal and Green's function continuum models are proposed with the same goal. We find that the Dirac cones are shifted down in energy upon doping; this shift strongly depends on the position of the impurity with respect to the surface. In addition, we observe that the width of the impurity band presents an even-odd behavior by varying the position of the impurity. This behavior is related to the position of the nodes of the wave function with respect to the surface, and hence it is a manifestation of confinement effects. We compare slab and semi-infinite geometries within the ab initio approach, demonstrating that the surface states remain gapless and their spin textures are unaltered in the doped semi-infinite system. In the slab geometry, a gap opens due to hybridization of the states localized at opposite surfaces. Finally, by means of a continuum model, we extrapolate our results to arbitrary positions of the impurity, clearly showing a non-monotonic behavior of the Dirac cone., Comment: Paper published as Open Access

A comprehensive work in plasmonic chiral and achiral nanostructures is presented. The bottom-up fabricated structures range from simple building blocks such as metallic and dielectric disk dimers or rods, to more complex nanostructures built from these individual blocks, arranged in the plane (two dimensional structures) or out of plane (three dimensional structures). The fabrication process uses hole-mask colloidal lithography and multiaxial evaporation, a powerful and cost-effective fabrication technique able to obtain a variety of structures in large areas. Besides morphology changes, parameters such as the composition and the spatial arrangement of the building blocks which compose them have been varied to comprehend their role in the optical response of the structures. These parameters are tailored to obtain active chiral meta-structures with optimum properties. The fabricated structures are morphologically, optically and magneto-optically characterized in depth. A thorough and step-by-step experimental study to explain the chiro-optical response of complex chiral plasmonic nanostructures from the achiral responses of its constituents is shown. To fully characterize the physical properties hidden in the measurements of these structures, an alternative analysis of the Mueller matrix elements is developed. Using this method, the optical, chiro-optical and magnetooptical properties of these complex nano-systems are validated...

This article belongs to the Special Issue Magnetic Nanoparticles as High-Frequency Nano-Heater., The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing have been seeking to push the forefront towards some new clinical trials. As many, they did not go at the expected pace. Today, fruitful international cooperation and the wisdom gain after a careful analysis of the lessons learned from seminal clinical trials allow us to have a future with better guarantees for a more definitive takeoff of this genuine nanotherapy against cancer. Deliberately giving prominence to a number of critical aspects, this opinion review offers a blend of state-of-the-art hints and glimpses into the future of the therapy, considering the expected evolution of science and technology behind magnetic hyperthermia., This work was supported by the NoCanTher project, which has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 685795. The authors acknowledge support from the COST Association through the COST actions “RADIOMAG” (TD1402) and “MyWAVE” (CA17115). D.O., A.S.-O. and I.R.-R. acknowledge financial support from the Community of Madrid under Contracts No. PEJD-2017-PRE/IND-3663 and PEJ-2018-AI/IND-11069, from the Spanish Ministry of Science through the Ramón y Cajal grant RYC2018-025253-I and Research Networks RED2018-102626-T, as well as the Ministry of Economy and Competitiveness through the grants MAT2017-85617-R, MAT2017-88148R and the “Severo Ochoa” Program for Centers of Excellence in R&D (SEV-2016-0686). M.B. and N.T.K.T. would like to thank EPSRC for funding (grant EP/K038656/1 and EP/M015157/1) and AOARD (FA2386-17-1-4042) award. This work was additionally supported by the EMPIR program co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation program, grant no. 16NRM04 “MagNaStand”. The work was further supported by the DFG grant CRC “Matrix in Vision” (SFB 1340/1 2018, no 372486779, project A02).

Hybrid nanoparticles allow exploiting the interplay of confinement, proximity between different materials and interfacial effects. However, to harness their properties an in-depth understanding of their (meta)stability and interfacial characteristics is crucial. This is especially the case of nanosystems based on functional oxides working under reducing conditions, which may severely impact their properties. In this work, the in-situ electron-induced selective reduction of Mn3O4 to MnO is studied in magnetic Fe3O4/Mn3O4 and Mn3O4/Fe3O4 core/shell nanoparticles by means of high-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Such in-situ transformation allows mimicking the actual processes in operando environments. A multi-stage image analysis using geometric phase analysis combined with particle image velocity enables direct monitoring of the relationship between structure, chemical composition and strain relaxation during the Mn3O4 reduction. In the case of Fe3O4/Mn3O4 core/shell the transformation occurs smoothly without the formation of defects. However, for the inverse Mn3O4/Fe3O4 core/shell configuration the electron beam-induced transformation occurs in different stages that include redox reactions and void formation followed by strain field relaxation via formation of defects. This study highlights the relevance of understanding the local dynamics responsible for changes in the particle composition in order to control stability and, ultimately, macroscopic functionality., Research supported by the European Research Council Starting Investigator Award STEMOX # 239739 (M.R. and J. S.), JSPS Postdoctoral Fellowship for Research Abroad (R.I.) and by Spanish MAT2015-066888-C3-3-R and RTI2018-097895-B-C43 (MINECO/FEDER). Electron microscopy observations at Oak Ridge National Laboratory (ORNL) supported by the U.S. Department of Energy (DOE), Basic Energy Sciences (BES), Materials Sciences and Engineering Division and through a user project supported by ORNL’s Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. A.M. and G.S.A. thank the financial support of the Knut and Alice Wallenberg Foundation through the project 3DEM-NATUR. The work at INC2 has been supported by the 2017-SGR-292 project of the Generalitat de Catalunya and by the MAT2016-77391-R project of the Spanish MINECO. ALO acknowledges the Spanish Ministerio de Economía y Competitividad through the Juan de la Cierva Program (IJCI-2014-21530). ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. ICN2 also acknowledges support from the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, grant no. SEV-2017-0706). S. J. P. thanks the National University of Singapore for funding. M. E. Acknowledges the Spanish MINECO for her Ramón y Cajal Fellowship (RYC2018-024396-I).

For flowing quantum gases, it has been found that at long times an initial black-hole laser (BHL) configuration exhibits only two possible states: the ground state or a periodic self-oscillating state of continuous emission of solitons. So far, all the works on this subject are based on a highly idealized model, quite difficult to implement experimentally. Here we study the instability spectrum and the time evolution of a recently proposed realistic model of a BHL, thus providing a useful theoretical tool for the clear identification of black-hole lasing in future experiments. We further confirm the existence of a well-defined phase diagram at long times, which bespeaks universality in the long-time behavior of a BHL. Additionally, we develop a complementary model in which the same potential profile is applied to a subsonic homogeneous flowing condensate that, despite not forming a BHL, evolves towards the same phase diagram as the associated BHL model. This result reveals an even stronger form of robustness in the long-time behavior with respect to the transient, which goes beyond what has been described in the previous literature., 14 pages, 8 figures. Final version of the manuscript

Achieving nanostructures with high surface area is one of the most challenging tasks as this metric usually plays a key role in technological applications, such as energy storage, gas sensing or photocatalysis, fields in which NiO is gaining increasing attention recently. Furthermore, the advent of modern NiO-based devices can take advantage of a deeper knowledge of the doping process in NiO, and the fabrication of p-n heterojunctions. By controlling experimental conditions such as dopant concentration, reaction time, temperature or pH, NiO morphology and doping mechanisms can be modulated. In this work, undoped and Sn doped nanoparticles and NiO/SnO2 nanostructures with high surface areas were obtained as a result of Sn incorporation. We demonstrate that Sn incorporation leads to the formation of nanosticks morphology, not previously observed for undoped NiO, promoting p-n heterostructures. Consequently, a surface area value around 340 m2/g was obtained for NiO nanoparticles with 4.7 at.% of Sn, which is nearly nine times higher than that of undoped NiO. The presence of Sn with different oxidation states and variable Ni3+/Ni2+ ratio as a function of the Sn content were also verified by XPS, suggesting a combination of two charge compensation mechanisms (electronic and ionic) for the substitution of Ni2+ by Sn4+. These results make Sn doped NiO nanostructures a potential candidate for a high number of technological applications, in which implementations can be achieved in the form of NiO–SnO2 p-n heterostructures.

In this work we investigate novel spherical core–shell nanoparticles with band inversion. The core and the embedding medium are normal semiconductors while the shell material is assumed to be a topological insulator . The envelope functions are found to satisfy a Dirac-like equation that can be solved in a closed form. The core–shell nanoparticle supports midgap bound states located at both interfaces due to band inversion. These states are robust since they are topologically protected. The energy spectrum presents mirror symmetry due to the chiral symmetry of the Dirac-like Hamiltonian. As a major result, we show that the thickness of the shell acts as an additional parameter for the fine tuning of the energy levels, which paves the way for electronics and optoelectronics applications.

Nickel oxide (NiO) is one of the very few p-type semiconducting oxides, the study of which is gaining increasing attention in recent years due to its potential applicability in many emerging fields of technological research. Actually, a growing number of scientific works focus on NiO-based electrochromic devices, high-frequency spintronics, fuel cell electrodes, supercapacitors, photocatalyst, chemical/gas sensors, or magnetic devices, among others. However, less has been done so far in the development of NiO-based optical devices, a field in which this versatile transition metal oxide still lags in performance despite its potential applicability. This review could contribute with novelty and new forefront insights on NiO micro and nanostructures with promising applicability in optical and optoelectronic devices. As some examples, NiO lighting devices, optical microresonators, waveguides, optical limiters, and neuromorphic applications are reviewed and analyzed in this work. These emerging functionalities, together with some other recent developments based on NiO micro and nanostructures, can open a new field of research based on this p-type material which still remains scarcely explored from an optical perspective, and would pave the way to future research and scientific advances.