Andres Redondo-Cubero

Autonomous University of Madrid | UAM · Department of Applied Physics

Bismuth-antimony alloys are among the most studied topological insulators and also have very promising thermoelectric properties. In addition, in the amorphous state they exhibit superconductivity with critical temperatures in the range 6.0–6.4 K. In this work, we have prepared and studied different polycrystalline films of B i 100 – x S b x (x = 0...

In this work, the characterization of zinc nitride (Zn3N2) Thin-film Transistors (TFTs) as phototransistors is presented. Polyethylene terephthalate is used as recyclable plastic substrate. A zinc oxide (ZnO) film is used as passivation layer. The Zn3N2 and ZnO films are deposited at room temperature using a magnetron sputtering. The sensitivity, r...

The integration of nanostructures on top of solar cells has been previously demonstrated as an effective method to increase the collection efficiency by coupling to sunlight. In this work, this approach is implemented by using core-shell gallium nanoparticles (Ga-NPs) as functional light scatterers on III-V solar cells, investigating how the Ga-NPs...

Heart rate and blood oxygen saturation level are essential medical parameters that can be measured optically by photoplethysmography. However, certain individuals present variability in skin absorption that can affect the proper quantification of both pulse and blood oxygen level. In this work, we designed an optical device capable of measuring the...

Surface nanopatterning induced by ion beam irradiation (IBI) has emerged as an effective nanostructuring technique since it induces patterns on large areas of a wide variety of materials, in short time, and at low cost. Nowadays, two main subfields can be distinguished within IBI nanopatterning depending on the irrelevant or relevant role played by...

The dynamics of the pattern induced on a silicon surface by oblique incidence of a 40 keV Fe ion beam is studied. The results are compared with those obtained for two reference systems namely, a noble gas ion beam either without or with Fe co-deposition. The techniques employed include Atomic Force Microscopy, Rutherford Backscattering Spectrometry...

This book collects the lectures presented in the first COST TUMIEE Training School held in Greece in 2019, supplemented with specific applications that illustrate how the multi-scale approach is implemented in specific cases of interest. The book is intended both as a reference in the field and as a textbook for people becoming interested or enteri...

In this work, we performed systematic studies on the oxidation of zinc nitride metastable layers using a climate chamber with controlled temperature and relative humidity. The electrical properties of the samples were in situ analyzed using a programmable microprocessor with a voltage divider, while the structural and optical properties were ex sit...

In article number 2100141, Catalán-Gómez, Vázquez and co-workers perform the modulation of the mechanical properties of the core-shell structure of gallium nanoparticles by thermal oxidation processes. The study is carried out by single-particle indentations by atomic force microscopy over a wide range of nanoparticle radius. It is found that the s...

Gallium nanoparticles (Ga NPs) are attracting increasing attention because of their appealing physical‐chemical properties. In particular, their mechanical properties play a key role in the implementation of these core‐shell structures on certain applications, such as soft and stretchable electronics. Thus, efforts are being addressed to modulate t...

We report on the current status of the ion beam laboratory of the Centre of Micro-Analysis of Materials at the Autonomous University of Madrid. The 5 MV accelerator facility provides MeV ion beams of any stable element. Six main beam lines are under operation, allowing the analysis and modification of materials through ion beam methods. Although th...

In this work we report on the characterization and biological functionalization of 2D MoS2 flakes, epitaxially grown on sapphire, to develop an optical biosensor for the breast cancer biomarker miRNA21. The MoS2 flakes were modified with a thiolated DNA probe omplementary to the target biomarker. Based on the photoluminescence of MoS2, the hybridi...

We analyse the morphological, structural and luminescence properties of self-assembled ZnO nanowires grown by chemical vapour transport on Si(001). The examination of nanowire ensembles by scanning electron microscopy reveals that a non-negligible fraction of nanowires merge together forming coalesced aggregates during growth. We show that the coal...

We study the nanopatterning of silicon surfaces under near-normal 40-keV Ar+ sputtering with simultaneous Fe oblique codeposition. The ion-beam incidence was kept at 15°, for which no pattern is produced in the absence of metal incorporation. Morphological and compositional analyses were performed by atomic force microscopy, in its morphological an...

We analyse the morphological, structural and luminescence properties of self-assembled ZnO nanowires grown by chemical vapour transport on Si(001). The examination of nanowire ensembles by scanning electron microscopy reveals that a non-negligible fraction of nanowires merge together forming coalesced aggregates during growth. We show that the coal...

In this work, the electrical stability of zinc nitride (Zn3N2) Thin-film Transistors (TFTs) under negative bias stress (NBS) and positive bias stress (PBS) is presented. The Zn3N2 TFTs were fabricated on plastic substrates. Spin-on glass was used as gate dielectric. The threshold voltage shift (ΔVT) and its recovery are analyzed during a long stres...

Plasmonic gallium (Ga) nanoparticles (NPs) are well known to exhibit good performance in numerous applications such as surface enhanced fluorescence and Raman spectroscopy or biosensing. However, to reach the optimal optical performance, the strength of the localized surface plasmon resonances (LSPRs) must be enhanced particularly by suitable narro...

A rapid fluorometric method is described for the determination of lactate and cholesterol by using ZnO nanowires (ZnO NWs). The assay is based on the detection of the hydrogen peroxide generated during the enzymatic reactions of the oxidation of lactate or cholesterol. Taking advantage of the electrostatic interactions between the enzymes and the Z...

Graphene Oxide (GO) is considered an ideal candidate for the fabrication of hydrogen gas (H2 (g)) sensors due to its excellent capabilities for direct wiring, thanks to the presence of functional groups, which provide an opportunity to modify its chemical functionalities. In this study, we have fabricated a H2 (g) sensor based on the precise positi...

In this work, we use Joule-effect thermal evaporation to produce hybrid structures made of Ga and In NPs on Si (100) substrates. Taking advantage of the protective oxide shell, In NPs can be used as a template for a second deposition step without structural changes, enabling the hybridization of NPs of materials. These complex structures of mixed N...

Here, we report on the production of nanoripples on the surface of ZnO bulk substrates by ion beam erosion with 20 keV Ar+ ions at an oblique incidence (60°). The ripple patterns, analyzed by atomic force microscopy, follow a power law dependence for both the roughness and the wavelength. At high fluences these ripples show coarsening and asymmetri...

The physics of collective optical response of molecular assemblies, pioneered by Dicke in 1954, has long been at the center of theoretical and experimental scrutiny. The influence of the environment on such phenomena is also of great interest due to various important applications in e.g. energy conversion devices. In this manuscript we demonstrate...

The physics of collective optical response of molecular assemblies, pioneered by Dicke in 1954, has long been at the center of theoretical and experimental scrutiny. The influence of the environment on such phenomena is also of great interest due to various important applications in e.g. energy conversion devices. In this manuscript we demonstrate...

The physics of collective optical response of molecular assemblies, pioneered by Dicke in 1954, has long been at the center of theoretical and experimental scrutiny. The influence of the environment on such phenomena is also of great interest due to various important applications in e.g. energy conversion devices. In this manuscript we demonstrate...

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 p...

In this work, the comparison of source/drain electrodes in thin film transistors (TFTs) based on room temperature deposited Zinc Nitride (Zn3N2) films is presented. Aluminum and aluminum doped zinc oxide (AZO) f ilms are used as electrodes. Both devices exhibit an on/off-current ratio of 104 and a subthreshold slope close to 1V/Dec. The extracted f...

In this work, high mobility TFTs based on zinc nitride (Zn3N2) sputtered at room temperature using spin-on glass (SOG) as gate dielectric are presented. The inverted coplanar structure is used for the Zn3N2 TFTs. The devices exhibit an on/off-current ratio of 106 and a subthreshold slope of 0.88 V/decade. The extracted field-effect mobility was 15....

2D monolayer molybdenum disulphide (MoS2) has been the focus of an intense research due to its direct bandgap compared with the indirect bandgap of its bulk counterpart, however its photoluminescence (PL) intensity is limited due to its low absorption efficiency. Herein, we use gallium hemispherical nanoparticles (Ga NPs) deposited by thermal evapo...

Scalable nanostructuring of surfaces using ion beam sputtering (IBS) is a versatile alternative to traditional lithography. Semiconductors, metals or compounds are amenable for IBS where different patterns can be obtained by tuning the experimental setup. This special issue addresses this problem in a wide range of topics, from a basic understandin...

Ordered porous anodic alumina has become a popular template for the nanopatterning of different materials due to its ease for manufacturing. However, an aluminium nanopatterned template obtained after removing the alumina has not been widely used despite it maintains its hexagonal periodicity. In this work, we use that nanopatterned aluminium to de...

Core-shell gallium nanoparticles (Ga NPs) have recently been proposed as an ultraviolet plasmonic material for different applications but only at room temperature. Here, the thermal stability as a function of the size of the NPs is reported over a wide range of temperatures. We analyse the chemical and structural properties of the oxide shell by x-...

We have bombarded crystalline silicon targets with a 40 keV Fe+ ion beam at different incidence angles. The resulting surfaces have been characterized by atomic force, current-sensing and magnetic force microscopies, scanning electron microscopy, and x-ray photoelectron spectroscopy. We have found that there is a threshold angle smaller than 40° fo...

Zinc oxynitride layers are becoming popular as semiconductor materials for thin film transistors. However, the formation of these ternary phases with high N content is challenging because of the different crystalline structures and stability of the binaries involved. In this work we study both the formation and stability of ternary ZnOxNy phases gr...

In this paper, zinc nitride (Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )-based flexible thin-film transistors (TFTs) are presented. The zinc nitride thin film is deposited by magnet...

Strain is a critical parameter affecting the growth and the performance of many semiconductor systems but, at the same time, the accurate determination of strain profiles in heterostructures can be challenging, especially at the nanoscale. Ion channelling/blocking is a powerful technique for the detection of the strain state of thin films, normally...

The effect of the oxidation of gallium nanoparticles (Ga NPs) on their plasmonic properties is investigated. Discrete dipole approximation has been used to study the wavelength of the out-of-plane localized surface plasmon resonance (LSPR) in hemispherical Ga NPs, deposited on silicon substrates, with oxide shell (Ga2O3) of different thickness. The...

AlGaN/GaN HEMTs and MOS-HEMTs using Gd2O3 as gate dielectric were irradiated with 2 MeV protons up to fluence of 1 × 1015 cm-2. Results showed that proton irradiation causes a strong degradation in the Schottky gate devices, featured by more than three orders of magnitude increase in reverse leakage current, a 30% decrease in maximum drain current...

Zinc nitride films can be deposited by radio frequency magnetron sputtering using a Zn target at substrate temperatures lower than 250°C. This low deposition temperature makes the material compatible with flexible substrates. The asgrown layers present a black color, polycrystalline structures, large conductivities, and large visible light absorpti...

Epitaxial GaN layers with a-, c- and m-plane surface orientations were implanted with 300 keV Ar-ions at 15 K with fluences ranging from 2 × 10¹² to 4 × 10¹⁶ at/cm². Damage build-up proceeds in three steps separated by wide fluence regions where the maximum damage level, measured by in situ Rutherford Backscattering Spectrometry/Channelling, satura...

Zinc nitride (Zn3N2) is a metastable material in ambient conditions due to its high reactivity with water molecules. In this work we perform a systematic analysis of the oxidation of Zn3N2 layers grown by RF magnetron sputtering at room temperature. The aging and transformation of the layers towards a ZnO film is explored by means of spectroscopic...

We have produced self-organised silicide nanodot patterns by medium-energy ion beam sputtering (IBS) of silicon targets with a simultaneous and isotropic molybdenum supply. Atomic force microscopy (AFM) studies show that these patterns are qualitatively similar to those produced thus far at low ion energies. We have determined the relevance of the...

In this article, ion-beam induced effects in multi-layered III–V semiconductor structures are reviewed. Besides doping, important effects occurring during ion irradiation are defect formation and diffusion, amorphisation and intermixing. It is shown that these processes are closely related to each other. In layered systems consisting of group III-p...

The built-in piezoelectric fields in group III-nitrides can act as road blocks on the way to maximizing the efficiency of opto-electronic devices. In order to overcome this limitation, a proper characterization of these fields is necessary. In this work nano-beam electron diffraction in scanning transmission electron microscopy mode has been used t...

Almost all, if not all, general purpose codes for analysis of Ion Beam Analysis data have been originally developed to handle laterally homogeneous samples only. This is the case of RUMP, NDF, SIMNRA, and even of the Monte Carlo code Corteo. General-purpose codes usually include only limited support for lateral inhomogeneity. In this work, we show...

Compositional grading of InGaN/GaN multi quantum wells (QWs) was proposed to mitigate polarization effects and Auger losses in InGaN-based light emitting diodes [K. P. O'Donnell et al., Phys. Status Solidi RRL 6 (2012) 49]. In this paper we are reviewing our recent attempts on achieving such gradient via quantum well intermixing. Annealing up to 12...

Chromium oxide (CrOx) thin films were grown by pulsed-DC reactive magnetron sputter deposition in an Ar/O2 discharge as a function of the O2 fraction in the gas mixture (ƒ) and for substrate temperatures, Ts, up to 450ºC. The samples were analysed by Rutherford backscattering spectrometry (RBS), spectroscopic ellipsometry (SE), atomic force microsc...

The built-in piezoelectric fields in group III-nitrides can act as road blocks on the way to maximizing the efficiency of opto-electronic devices. In order to overcome this limitation, a proper characterization of these fields is necessary. In this work nano-beam electron diffraction in scanning transmission electron microscopy mode has been used t...

Ion-induced damage and intermixing was evaluated in InGaN/GaN multi-quantum wells (MQWs) using 35 keV N(+) implantation at room temperature. In situ ion channeling measurements show that damage builds up with a similar trend for In and Ga atoms, with a high threshold for amorphization. The extended defects induced during the implantation, basal and...

We present a simple and robust method to acquire quantitative maps of compositional fluctuations in nanostructures from low magnification high-angle annular dark field (HAADF) micrographs calibrated by energy-dispersive X-ray (EDX) spectroscopy in scanning transmission electron microscopy (STEM) mode. We show that a nonuniform background in HAADF-S...

We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the densities, energy levels, and spatial distributions of zinc/magnesium cation and oxygen vacancies in isostructural, single-phase, non-polar Mg x Zn 1−xO alloys over a wide (0 ≤ x ≤ 0.56) range. Within this wide range, both defect types exhib...

With the rise of MgZnO alloys as UV optoelectronic components, deep level defects in these materials have assumed added importance due to their impact on free carrier recombination, heterojunction band offsets, and Schottky barriers. Yet their dependence on alloy content and lattice structure is relatively unexplored. We have used depth-resolved ca...

We studied the optical properties of metalorganic chemical vapour deposited (MOCVD) InGaN/GaN multiple quantum wells (MQW) subjected to nitrogen (N) implantation and post-growth annealing treatments. The optical characterization was carried out by means of temperature and excitation density-dependent steady state photoluminescence (PL) spectroscopy...

A lack of universality with respect to ion species has been recently established in nanostructuring of semiconductor surfaces by low-energy ion-beam bombardment. This variability affects basic properties of the pattern formation process, like the critical incidence angle for pattern formation, and has remained unaccounted for. Here, we show that no...

Using an ion microprobe, a comprehensive lateral and in-depth characterization of a single GaN-based high electron mobility transistor is carried out by means of Rutherford backscattering spectrometry (RBS) in combination with particle induced X-ray emission (PIXE). Elemental distribution was obtained for every individual section of the device (waf...

We investigate the role of the initial structural condition in silicon surface nanopatterning by low-energy ion beam sputtering. Specifically, we address the influence of the target atomic structure in ripple formation under oblique irradiation by 500 eV &$\text{Ar}^+$ ; ions. To this end, we compare results obtained on single-crystal, amorphous, a...

We address the impact of metal co-deposition in the nanodot patterning dynamics of Si(100) surfaces under normal-incidence 1 keV Ar(+) ion-beam sputtering (IBS). In particular, the effect of both the metal nature (Fe or Mo) and flux has been studied. Morphological and compositional evolution were followed by atomic force microscopy (AFM) and Ruther...