Llibertat Abad Muñoz

• Ph.D.
• Senior Researcher at Spanish National Research Council

Modulation of magnetic properties through voltage-driven ion motion and redox processes, i.e., magneto-ionics, is a unique approach to control magnetism with electric field for low-power memory and spintronic applications. So far, magneto-ionics has been achieved through direct electrical connections to the actuated material. Here we evidence that...

Modulation of magnetic properties through voltage-driven ion motion and redox processes, i.e., magneto-ionics, is a unique approach to control magnetism with electric field for low-power memory and spintronic applications. So far, magneto-ionics has been achieved through direct electrical connections to the actuated material. Here we evidence that...

Magneto-ionics refers to the control of magnetic properties of materials through voltage-driven ion motion. To generate effective electric fields, either solid or liquid electrolytes are utilized, which also serve as ion reservoirs. Thin solid electrolytes have difficulties in (i) withstanding high electric fields without electric pinholes and (ii)...

The use of slurries of conducting particles has been considered a way to extend the electrode area in some energy storage electrochemical cells. When suspensions of conducting particles are used in electrolytes a decreased impedance is observed, even for concentrations much lower than the theoretical percolation limits. Indeed, it is known that pol...

Bipolar electrochemistry allows the development of processes in a wireless manner, with reactions occurring at the induced anodes and cathodes of an immersed conducting material in the electrolyte. As a result, a gradient oxidation state may appear along the main axis field on the surface or bulk of the material depending on the type of reaction av...

The utility of electrical resistivity as an indicator of magnetoionic performance in stoichiometrically and structurally similar thin-film systems is demonstrated. A series of highly nanocrystalline cobalt nitride (Co−N) thin films (85 nm thick) with a broad range of electrical properties exhibit markedly different magnetoionic behaviors. Semicondu...

Magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. Here, we demonstrate room-temperature voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a CoN film. Nitrogen magneto-ionics in CoN is compared to oxygen magneto-ionics...

Voltage control of magnetism through electric field‐induced oxygen motion (magneto‐ionics) could represent a significant breakthrough in the pursuit for new strategies to enhance energy efficiency in magnetically actuated devices. Boosting the induced changes in magnetization, magneto‐ionic rates and cyclability continue to be key challenges to tur...

Magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. Here, we demonstrate room-temperature voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a CoN film. Nitrogen magneto-ionics in CoN is compared to oxygen magneto-ionics...

So far, magneto-ionics, understood as voltage-driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ion/vacancy and, to a lesser extent, lithium and hydrogen. Here, we demonstrate efficient, room-temperature, voltage-driven nitrogen transport (i.e., nitrogen magneto-ionics) by electrolyte-gating of a singl...

We report the anomalous bulk transformation of vapor deposited stable glasses into the liquid state. The transformation proceeds through two competing parallel processes: partial rejuvenation of the stable glass and nucleation and growth of liquid patches within the glass. The kinetics of the transformation extracted from heat capacity curves after...

Voltage control of magnetism through electric field-induced oxygen motion (magneto-ionics) could represent a significant breakthrough in the pursuit for new strategies to enhance energy efficiency in a large variety of magnetic devices, such as magnetic micro-electro-mechanical systems (MEMS), magnetic logics, spin electronics, or neuromorphic comp...

Growth monitoring during the early stages of vapor deposition is of prime importance to understand the growth process, the microstructure, and thus the overall layer properties. We demonstrate that phonons can be used as an extremely sensitive probe to monitor the real-time evolution of film microstructure during growth, from incipient clustering t...

Implantable electrodes act with direct electrical contact although recent work has shown that electrostimulation is also possible through non-contact wireless settings, through the generation of dipoles at the borders of the material by bipolar electrochemistry. The experimental observations with neural cell cultures demonstrate a clear difference...

Thermoelectricity (TE) is proving to be a promising way to harvest energy for small applications and to produce a new range of thermal sensors. Recently, several thermoelectric generators (TEGs) based on nanomaterials have been developed, outperforming the efficiencies of many previous bulk generators. Here, we presented the thermoelectric characte...

Ultrathin Si films have a reduced thermal conductivity in comparison to Si bulk due to phonon scattering at the surfaces. Furthermore, the small thickness guarantees a reduced thermal mass (in the µJ/K range), which opens up the possibility of developing thermal sensors with a high sensitivity. Based on these premises, a thermoelectric (TE) microse...

We show the use as a thermal photosensor of a thermoelectric (TE) microsensor based on ultrathin suspended Si films. The reduced thickness of the structural films enhances the extremely large thermal insulation of the sensing area (~43 µW/K), since phonons scatter in the surfaces, and guarantees a reduced thermal mass (in the µJ/K range). The sensi...

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Porous materials display enhanced scattering mechanisms that greatly influence their transport properties. Metal-assisted chemical etching (MACE) enables fabrication of porous silicon nanowires starting from a doped Si wafer by using a metal template that catalyzes the etching process. Here, we report on the low thermal conductivity (κ) of individu...

Growth monitoring during the early stages of film formation is of prime importance to understand the growth process, the microstructure and thus the overall layer properties. In this work, we demonstrate that phonons can be used as sensitive probes to monitor real time evolution of film microstructure during growth, from incipient clustering to con...

Growth monitoring during the early stages of film formation is of prime importance to understand the growth process, the microstructure and thus the overall layer properties. In this work, we demonstrate that phonons can be used as sensitive probes to monitor real time evolution of film microstructure during growth, from incipient clustering to con...

Vapour-deposited organic glasses are currently in use in many optoelectronic devices. Their operation temperature is limited by the glass transition temperature of the organic layers and thermal management strategies become increasingly important to improve the lifetime of the device. Here we report the unusual finding that molecular orientation he...

Vapour-deposited organic glasses are currently in use in many optoelectronic devices. Their operation temperature is limited by the glass transition temperature of the organic layers and thermal management strategies become increasingly important to improve the lifetime of the device. Here we report the unusual finding that molecular orientation he...

This work describes the design and fabrication of a miniaturized flow cell for the chronoamperometric detection of Mieloperoxidase (MPO), a cardiac biomarker. The flow cell consists of a microfluidic cartridge made of a series of cyclo-olefin polymer (COP) and pressure sensitive adhesive (PSA) layers, featuring four independent channels and their c...

In this work we report on the production of a low cost microfluidic device for the multiplexed electrochemical detection of magneto bioassays. As a proof of concept, the device has been used to detect myeloperoxidase (MPO), a cardiovascular biomarker. With this purpose, two bioassays have been optimized in parallel onto magnetic beads (MBs) for the...

We measure the thermal conductivity of a 17.5-nm-thick single crystalline Si layer by using a suspended structure developed from a silicon-on-insulator wafer, in which the Si layer bridges the suspended platforms. The obtained value of 19 Wm−1 K−1 at room temperature represents a tenfold reduction with respect to bulk Si. This design paves the way...

Interdigitated microband electrodes are important electroanalytical tools, and have been used in the construction of advanced sensing and biosensing devices for a long time. Nanoband-based systems, on the other hand, are more difficult to come by, as their fabrication involves the use of costly and scarce e-beam lithography resources. In this work...

We report the development of a Si-based micro thermogenerator build from silicon-on-insulator by using standard CMOS processing. Ultrathin single-crystalline Si membranes, 100 nm in thickness, with embedded n and p-type doped regions electrically connected in series and thermally in parallel, are the active elements of the thermoelectric device tha...

A spatially-controlled synthesis of nanowire bundles of the functional crystalline coordination polymer (CP) Ag(I)TCNQ (tetracyanoquinodimethane) from previously fabricated and trapped monovalent silver CP (Ag(I)- Cys (cysteine)) using a room-temperature microfluidic-assisted templated growth method is demonstrated. The incorporation of microengine...

This work demonstrates the design and fabrication of an all cyclo-olefin polymer based microfluidic device capable of capturing magnetic beads and performing electrochemical detection in a series of gold electrodes. The size of chip is of a microscope slide and features six independent measuring cells for multianalyte detection purposes. The aim of...

This work demonstrates the implementation of iridium oxide films (IROF) grown on silicon-based thin-film platinum microelectrodes, their utilization as a pH sensor, and their successful formatting into a urea pH sensor. In this context, Pt electrodes were fabricated on Silicon by using standard photolithography and lift-off procedures and IROF thin...

We report a non-enzymatic glucose sensor that is based on a gold micropillar array electrode and was fabricated by using a combination of photolithographic techniques and electroplating. The electrode exhibits (a) a larger electroactive area, (b) enhanced surface roughness, and (c) enhanced catalytic activity toward the electro-oxidation of glucose...

Iridium oxohydroxide thin coatings have been prepared by a dynamic oxidation electrodeposition method from complex oxalate solutions that induce template effects in the final coating at the nanoscale. The preparation method induces the formation of a oxohydroxide with reproducible stoichiometry and sponge-like quasiamorphous open structure, high io...

Titanium oxides have anti-inflammatory activity and tunable electrochemical properties that make them attractive materials for biomedical applications. This work investigated the compatibility of nanometric coatings of low-temperature phases of TiO2 with neurons in 4-day and 10-day cultures, using different cell densities to quantify cell survival...

Surface and interface magnetisms in oxide thin films and heterostructures have been a recurrent topic during the past years due to their relevance in the implementation of magnetoelectronic devices. Magneto-optical techniques, such as x-ray magnetic circular dichroism, turn out to be a very efficient tool to study surface magnetism due to their sen...

We investigated the use of the focused ion-beam (FIB) technique as a nanofabrication tool for the implementation of oxide-based magnetic and magnetoelectronic functional devices. In particular, we studied the effect of using FIB lithography for the patterning of La(2/3)Ca(1/3)MnO(3) magnetic oxide thin films. Results obtained show that the transpor...

The transport properties across perovskite oxides heterointerfaces are analyzed. Epitaxial La(2/3)Ca(1/3)MnO3/SrTiO3 (LCMO/STO) heterostructures with different STO insulating-barrier thicknesses are systematically investigated and their behavior compared with LCMO/metal junctions. Atomic force microscopy (AFM) measurements in current-sensing mode s...

The transport properties across La2/3Ca1/3MnO3/SrTiO3 (LCMO/STO) heterostructures with different thicknesses of the STO insulating barrier have been studied by using atomic force microscopy measurements in the current sensing (CS) mode. To avoid intrinsic problems of the CS method we have developed a nanostructured contact geometry of Au dots. The...

Microstructural features of La2/3Ca1/3MnO3 layers of various thicknesses grown on top of (001) LaAlO3 substrates are studied by using transmission electron microscopy and electron energy loss spectroscopy. Films are of high microstructural quality but exhibit some structural relaxation and mosaicity both when increasing thickness or after annealing...

Complex oxides with perovskite structure are the ideal arena to study a plethora of physical properties including superconductivity, ferromagnetism, ferroelectricity, piezoelectricity and more. Among them, transition metal oxides are especially relevant since they present large electronic correlations leading to a strong competition between lattice...

Surface magnetic properties of perovskite manganites have been a recurrent topic during last years since they play a major role in the implementation of magnetoelectronic devices. Magneto-optical techniques, such as X-ray magnetic circular dichroism, turn out to be a very efficient tool to study surface magnetism due to their sensitivity to magneti...

Magneto-optical techniques in reflection geometry turn out to be a very efficient tool to study the surface magnetism due to their sensitivity to magnetic and chemical variations across the sample depth. The existence of a surface layer of about one to five unit cells with strongly depressed magnetic properties, when compared with the rest of the f...

The oxidation state of Mn in La 2/3 Ca 1/3 MnO 3 thin films grown on single crystalline SrTiO 3 , LaAlO 3 and NdGaO 3 substrates has been analyzed by soft x-ray absorption spectroscopy. The spectra at the Mn-L 2/3 edges and at the O-K edge indicate the presence of a Mn 2+ component, besides the expected Mn 3+ /Mn 4+ mixed valence state being charac...

The O K -edge pre-edge structure in the x-ray absorption spectra of high quality La _2/3 Ca _1/3 Mn O ₃ epitaxial thin films grown on top of (001) Sr Ti O ₃ and Nd Ga O ₃ substrates is analyzed as a function of structural strain and temperature. A clear correlation between temperature dependent s...

In this work we present results of contact resistance between La2/3Ca1/3MnO3 (LCMO) and Pt system. LCMO epitaxial thin films have been grown by rf sputtering on top of LaAlO3 (LAO) substrate. The contact between the manganite film and the metal have been prepared by exsitu deposition of a 30 nm thick Pt layer on top of the manganite film by e-beam...

Magnetotransport properties of very high quality fully strained epitaxial thin films of La2/3Ca1/3MnO3 (LCMO), grown on top of SrTiO3 (STO) (001) substrates, are analyzed. As-grown fully strained epitaxial films are ferromagnetic and metallic but exhibit depressed transport and magnetic properties (low TC and MS). Detailed analysis of the structura...

A Mn valence instability on La2/3Ca1/3MnO3 thin films, grown on LaAlO3 (001)substrates is observed by x-ray absorption spectroscopy at the Mn L-edge and O K-edge. As-grown samples, in situ annealed at 800 C in oxygen, exhibit a Curie temperature well below that of the bulk material. Upon air exposure a reduction of the saturation magnetization, MS,...

The growth mechanisms and surface morphology of colossal magnetoresistance (CMR) La0.67Ca0.33MnO3 films deposited by rf magnetron sputtering on SrTiO3(001) substrates are investigated. The films are epitaxial, coherently strained and ferromagnetic. It is found that at early growth stages, in nanometric films, a layer-by-layer mechanism dominates, w...

To fabricate magnetic tunnel junctions the morphology of the films is a key issue, and two dimensional (2D) growth and very smooth film surfaces are required. In the epitaxy of manganites like La0.67Ca0.33MnO3 (LCMO) above a relatively low thickness a roughening transition is frequently found: growth starts by a layer-by-layer mode, but roughness i...

The role of the surface layers in La _2/3 Ca _1/3 Mn O ₃ magnetic oxide epitaxial thin films is analyzed. We show that the topmost layers do play a very relevant role on the transport properties acting as an insulating barrier. Atomic force microscopy (AFM) measurements in the current sensing mode exhibit typical feat...

We report on the chemical stability of La2/3Ca1/3MnO3 thin films. X-ray absorption spectroscopy at the Mn L-edge and O K-edge makes evident deviations from the nominally expected (2/3-1/3) Mn3+/Mn4+ ratio after the growth of thin films on LaAlO3 substrates. As-grown thin films, exhibiting Curie temperature, TC, well below that of the LCMO bulk mate...

Transverse resistance measurements are reported on patterned epitaxial thin films of optimally doped La2/3Ca1/3MnO3 oxides. We show that the voltage drop measured across a micron-size patterned track displays a temperature dependence that, particularly in a temperature region around the Curie temperature, cannot be explained solely by the contribut...