arXiv subjects

J. Gazquez

Publications and source records attributed to J. Gazquez.

11 recordsLinked to original sources

arXiv2025

Sustainable wafer-scale integration of epitaxial ZnO on silicon for piezoelectric devices

To sustainably support the ongoing energetic transition, we need functional metal oxides capable of converting energy, and produce storage, and sensing devices. However, these materials suffer from a high economic cost of manufacturing, and their production in a sustainable way is, to date, a milestone. Additionally, the technical challenges, such as scalability and integration of silicon for industrial processing using microelectronic technologies, impose strict conditions for the entire materials process. In this work, we engineer {\alpha}-quartz virtual substrates up to 4 inches facilitating the large-scale and sustainable integration of multifunctional epitaxial ZnO metal oxide microwire films on silicon. These materials are exclusively manufactured on silicon using solution chemistry, providing single-chip solutions that can meet strict economic constraints for developing sustainable devices at a lower cost. Through this integrative technology, we demonstrate the microfabrication of epitaxial (110)ZnO/(100){\alpha}-quartz/(100)silicon piezoelectric membrane resonators at the wafer-scale with potential applications in energy conversion and sensing. We combined four dimensional (4D)-STEM diffraction technology and Piezoelectric Force Microscopy (PFM) to establish a correlation between out of plane crystalline strain and piezoelectric response in epitaxial (110) ZnO at the microscale. Finally, we proved the fabrication of 800 nm thick (110) ZnO suspended membranes that can be transferred to flexible substrates, making them suitable for flexible devices.

cond-mat.mtrl-sci↗

arXiv2020

Enhancement in Thermally Generated Spin Voltage at Pd/NiFe$_2$O$_4$ Interfaces by the Growth on Lattice-Matched Substrates

Efficient spin injection from epitaxial ferrimagnetic NiFe$_2$O$_4$ thin films into a Pd layer is demonstrated via spin Seebeck effect measurements in the longitudinal geometry. The NiFe$_2$O$_4$ films (60 nm to 1 $μ$m) are grown by pulsed laser deposition on isostructural spinel MgAl$_2$O$_4$, MgGa$_2$O$_4$, and CoGa$_2$O$_4$ substrates with lattice mismatch varying between 3.2% and 0.2%. For the thinner films ($\leq$ 330 nm), an increase in the spin Seebeck voltage is observed with decreasing lattice mismatch, which correlates well with a decrease in the Gilbert damping parameter as determined from ferromagnetic resonance measurements. High resolution transmission electron microscopy studies indicate substantial decrease of antiphase boundary and interface defects that cause strain-relaxation, i.e., misfit dislocations, in the films with decreasing lattice mismatch. This highlights the importance of reducing structural defects in spinel ferrites for efficient spin injection. It is further shown that angle-dependent spin Seebeck effect measurements provide a qualitative method to probe for in-plane magnetic anisotropies present in the films.

cond-mat.mtrl-sci↗

arXiv2019

Nanostructure engineering of epitaxial piezoelectric α-quartz thin films on silicon

The monolithic integration of sub-micron quartz structures on silicon substrates is a key issue for the future development of telecommunication to the GHz frequencies. Here we report unprecedented large-scale fabrication of ordered arrays of piezoelectric epitaxial quartz nanostructures on silicon substrates by the combination of soft-chemistry and three cost effective lithographic techniques: (i) laser transfer lithography, (ii) soft nanoimprint lithography on Sr-doped SiO2 sol-gel thin films and (iii) self-assembled SrCO3 nanoparticles reactive nanomasks. Epitaxial α-quartz nanopillars with different diameters (down to 50 nm) and heights (up to 2000 nm) were obtained for the first time. This work proves the control over the shape, micro- and nano-patterning of quartz thin films while preserving its crystallinity, texture and piezoelectricity. This work opens up the opportunity to fabricate new high frequency resonators and high sensitivity sensors relevant in different fields of application.

physics.app-ph↗

arXiv2019

Enhanced ferroelectricity in epitaxial Hf0.5Zr0.5O2 thin films integrated with Si(001) using SrTiO3 templates

SrTiO3 templates have been used to integrate epitaxial bilayers of ferroelectric Hf0.5Zr0.5O2 and La2/3Sr1/3MnO3 bottom electrode on Si(001). The Hf0.5Zr0.5O2 films show enhanced properties in comparison to equivalent films on SrTiO3(001) single crystalline substrates. The films, thinner than 10 nm, have very high remnant polarization of 34 uC/cm2. Hf0.5Zr0.5O2 capacitors at operating voltage of 4 V present long retention time well beyond 10 years and high endurance against fatigue up to 109 cycles. The robust ferroelectric properties displayed by the epitaxial Hf0.5Zr0.5O2 films on Si(001) using SrTiO3 templates paves the way for the monolithic integration on silicon of emerging memory devices based on epitaxial HfO2.

physics.app-ph↗

arXiv2017

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nanometer to micrometer and mosaicity effects

High-quality thermoelectric LaxSr1-xTiO3 (LSTO) layers (here with x = 0.2), with thicknesses ranging from 20 nm to 700 nm, have been epitaxially grown on SrTiO3(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 x 10-4 ohm.cm at room temperature), one order of magnitude lower than commercial Nb-doped SrTiO3 single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of around -60 microV/K have been found for all films, accordingly. Finally, a correlation is given between the mosaicity and the (thermo)electric properties. These functional LSTO films can be integrated on Si in opto-microelectronic devices as transparent conductor, thermoelectric elements or in non-volatile memory structures.

cond-mat.mtrl-sci↗

arXiv2015

Multiple-stable anisotropic magnetoresistance memory in antiferromagnetic MnTe

A common perception assumes that magnetic memories require ferromagnetic materials with a non-zero net magnetic moment. However, it has been recently proposed that compensated antiferromagnets with a zero net moment may represent a viable alternative to ferromagnets. So far, experimental research has focused on bistable memories in antiferromagnetic metals. In the present work we demonstrate a multiple-stable memory device in epitaxial manganese telluride (MnTe) which is an antiferromagnetic counterpart of common II-VI semiconductors. Favorable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly varying antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the applied magnetic field, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states which we set by heat-assisted magneto-recording and by changing the angle of the writing field. We explore the dependence of the magnitude of the zero-field read-out signal on the strength of the writing field and demonstrate the robustness of the antiferromagnetic memory states against strong magnetic field perturbations. We ascribe the multiple-stability in our antiferromagnetic memory to different distributions of domains with the Néel vector aligned along one of the three $c$-plane magnetic easy axes in the hexagonal MnTe film. The domain redistribution is controlled during the heat-assisted recording by the strength and angle of the writing field and freezes when sufficiently below the Néel temperature.

cond-mat.mtrl-sci↗

arXiv2014

Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs

Recent studies have demonstrated the potential of antiferromagnets as the active component in spintronic devices. This is in contrast to their current passive role as pinning layers in hard disk read heads and magnetic memories. Here we report the epitaxial growth of a new high-temperature antiferromagnetic material, tetragonal CuMnAs, which exhibits excellent crystal quality, chemical order and compatibility with existing semiconductor technologies. We demonstrate its growth on the III-V semiconductors GaAs and GaP, and show that the structure is also lattice matched to Si. Neutron diffraction shows collinear antiferromagnetic order with a high Neél temperature. Combined with our demonstration of room-temperature exchange coupling in a CuMnAs/Fe bilayer, we conclude that tetragonal CuMnAs films are suitable candidate materials for antiferromagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2013

Orientational tuning of the 2D-superconductivity in LaAlO3/SrTiO3 interfaces

The discovery of a two-dimensional (2D) electron gas at the (110)-oriented LaAlO3/SrTiO3 in- terface provided us with the opportunity to probe the effect of crystallographic orientation and the ensuing electronic reconstructions on interface properties beyond the conventional (001)-orientation. At temperatures below 200 mK, we have measured 2D superconductivity with a spatial extension significantly larger (d approx. 24 - 30 nm) than previously reported for (001)-oriented LaAlO3/SrTiO3 interfaces (d approx. 10 nm). The more extended superconductivity brings about the absence of violation of the Pauli paramagnetic limit for the upper critical fields, signaling the distinctive nature of the electronic structure of the (110)-oriented interface with respect to their (001)-counterparts

cond-mat.str-el↗

arXiv2013

Storing magnetic information in IrMn/MgO/Ta tunnel junctions via field-cooling

Tunneling junctions containing no ferromagnetic elements have been fabricated and we show that distinct resistance states can be set by field cooling the devices from above the Néel along different orientations. Variations of the resistance up to 10% are found upon field cooling in applied fields of 2T, in-plane or out of plane. Below TN, we found that the metastable states are insensitive to magnetic fields thus constituting a memory element robust against external magnetic fields. Our work provides the demonstration of an electrically readable magnetic memory device, which contains no ferromagnetic elements and stores the information in an antiferromagnetic active layer.

cond-mat.mes-hall↗

arXiv2013

Solving and refining novel thin film phases using Cu X-ray radiation: the epitaxy-induced CuMnAs tetragonal phase

We present a combined experimental and computational method which enables the precise determination of the atomic positions in a thin film using CuKα radiation, only. The capabilities of this technique surpass simple structure refinement and allow solving unknown phases stabilized by substrate-induced stress. We derive the appropriate corrections to transform the measured integrated intensities into structure factors. Data collection was performed entirely on routinely available laboratory diffractometers (CuKα radiation); the subsequent analysis was carried out by single-crystal direct methods (δ recycling procedure) followed by the least-squares refinement of the structural parameters of the unit cell content. We selected an epitaxial thin film of CuMnAs grown on top of a GaAs substrate, which formed a crystal structure with tetragonal symmetry, differing from the bulk material which is orthorhombic. Here we demonstrate the new tetragonal form of epitaxial CuMnAs grown on GaAs substrate and present consistent high-resolution scanning transmission electron microscopy and stoichiometry analyses.

cond-mat.mtrl-sci↗

arXiv2012

Electron transfer and ionic displacements at the origin of the 2D electron gas at the LAO/STO interface: Direct measurements with atomic-column spatial resolution

The discovery that the interface between two band gap insulators LaAlO3 and SrTiO3 is highly conducting has raised an enormous interest in the field of oxide electronics. The LAlO3/SrTiO3 interface can be tuned using an electric field and switched from a superconducting to an insulating state. Conducting paths in an insulating background can be written applying a voltage with the tip of an atomic force microscope, creating great promise for the development of a new generation of nanoscale electronic devices. However, the mechanism for interface conductivity in LaAlO3/SrTiO3 has remained elusive. The theoretical explanation based on an intrinsic charge transfer (electronic reconstruction) has been strongly challenged by alternative descriptions based on point defects. In this work, thanks to modern aberration-corrected electron probes with atomic-scale spatial resolution, interfacial charge and atomic displacements originating the electric field within the system can be simultaneously measured, yielding unprecedented experimental evidence in favor of an intrinsic electronic reconstruction.

cond-mat.str-el↗