A green chemistry procedure for a green chemistry catalyst
A 3D-aromatic and photoredox catalyst, can be readily synthesized in high yield by a fast and clean solvent-free reaction. This innovative approach yields the desired molecules by simply heating the solid compounds to high temperature for a very short time
3,2,1 and stop! An innovative, straightforward and clean route for the flash synthesis of metallacarboranes
Ines Bennour, Ana M. Cioran, Francesc Teixidor, Clara Viñas
Green Chemistry 21, 1925, 2019
Figure: Schematic view of the valuable 3,2,1 and stop! synthetic procedure to achieve 3D shaped metallacarborane [Co(C2B9H11)2]− derivatives.
As a target,Green Chemistry is the whole process aiming at producing chemical products that reduce or eliminate the use or generation of hazardous substances. Green chemistry goes beyond the synthesis and applies across the life cycle of a chemical product, including its use, and ultimate disposal.
By the judicious study of a desired compound, in our case a metallacarborane with a characteristic 3D shape, and with the formula [3,3’-Co(1,2-C2B9H11)2]− has been possible by applying the concepts of green chemistry to create an alternative procedure to avoid hazardous substances. The process was designed to achieve the targeted metallacarborane at the shortest time while reducing waste and demand on energy.
In the paper cited below, a new, fast and environmentally-friendly solid state reaction for the syntheses of cobaltabis(dicarbollide) derivatives, [3,3’-Co(1,2-R2-1,2-C2B9H9)2]− (R and R’= H, alkyl, aryl) is presented. Our approach is a significant improvement on the traditional syntheses in solution in both speed of reaction and generated yield. We demonstrate that the [3,3’-Co(1,2-C2B9H11)2]− building reaction works well with starting plain, single or double Ccluster-substituted nido [7,8-C2B9H12]- clusters. However, care has to be taken when β-hydride elimination may take place because in this case the resulting [Co(C2B9H11)2]− derivative may be different to the expected one based on the precursor nido cluster due to the β-hydride elimination, as commonly occurs in organometallic chemistry. The presence of substituents bearing a free pair of electrons also influences the complex formation. Meta-isomers also give rise to the corresponding cobaltabis(dicarbollide), [3,3’-Co(1,7-C2B9H11)2]−, but in this case, the reaction time needs to be increased. A suggested mechanism of the complexation reaction is proposed, based on identifying the chemical nature of the evolved gas, the pH of the mixture, the crystal structure of the target complex and the absence of Co2+ dismutation.
The fact that metallacarboranes can find many applications in materials, energy, catalysis, sensors/biosensors and medicine, among others makes this innovative, straightforward and clean route for their flash synthesis very valuable.
Ambipolar solution processed organic field-effect transistors (OFETs) and water-gated OFET with carbon-composite gate contact
Unconventional solution processed organic field-effect transistors (OFETs): charge transfer complex as ambipolar semiconductor and carbon composite gate in electrolyte-gated OFET
Carbon-paste nanocomposites as unconventional gate electrodes for electrolyte-gated organic field-effect transistors: electrical modulation and bio-sensing
Jose Muñoz, Francesca Leonardi, Tayfun Özmen, Marta Riba-Moliner, Arantzazu González-Campo, Mireia Baeza, Marta Mas-Torrent
J. Mater. Chem. C 2019, 7, 14993
Solution-processed thin films of a charge transfer complex for ambipolar field-effect transistors
Tommaso Salzillo, Antonio Campos, Marta Mas-Torrent
J. Mater. Chem. C 2019, 7, 1025
Figure: (Left) Crystalline thin film of a charge transfer complex prepared from a solution of a donor and acceptor molecules blended with polystyrene as a binding polymer. (Right) Electrolyte-gated field-effect transistor in which the gate contact is a composite carbon based electrode composed of carbon-nanotubes functionalised with β-cyclodextrines.
Solution processed organic field-effect transistors (OFETs) are raising great interest for the development of low-cost electronics. Despite the impressive progress achieved in the last years, there is still plenty of room in terms of material engineering. Here, we highlight two recent works where we have used an unconventional material as active ambipolar semiconductor and another one where an alternative carbon-based electrode has been exploited as gate contact.
1) Charge transfer (CT) complexes are composed of a donor and acceptor molecule that crystallize together either in segregated or alternated stacks. They have been studied for a long time as organic conductors and, recently have also been attracting great interest as potential candidates for ambipolar semiconductors. However, their application in OFETs has been limited to ideal single crystals or to evaporated films, hindering their potential for real applications. Here, we report the preparation of thin films of a CT complex using a simple solution shearing technique and blending the precursors with a binding polymer. The resulting OFET devices exhibited ambipolar field-effect in environmental conditions. Thus, this work opens new perspectives for the application of CT complexes in electronic devices.
2) Nanocomposite paste electrodes using carbon nanotubes (CNTs) have been investigated for the first time in electrolyte-gated organic field-effect transistors (EGOFETs) as a replacement of conventional metal gate electrodes. The potential of using such non-conventional gate electrodes for sensing purposes has also been evaluated by investigating, as a proof of concept, the formation of a supramolecular complex between a CNT functionalised with β-cyclodextrin (β-CD) as a bio-recognition element and tryptophan, giving detection limits at picomolar levels. Accordingly, carbon-composite electrodes have been demonstrated to be a potential alternative to metal gate electrodes for the development of a new generation of highly sensitive carbon-based EGOFET bio-sensors.
Bacteria grown thermoelectrics for heat and solar energy harvesting
This two studies represent our baby-step contributions towards engineering advanced functional materials based on circular economy approaches
Farming thermoelectric paper
Deyaa Abol-Fotouh, Bernhard Dörling, Osnat Zapata-Arteaga, Xabier Rodríguez-Martínez, Andrés Gómez, J. Sebastian Reparaz, Anna Laromaine, Anna Roig, Mariano Campoy-Quiles
Energy & Environmental Science 12, 716-719, 2019
Solar Harvesting: a Unique Opportunity for Organic Thermoelectrics?
José P. Jurado, Bernhard Dörling, Osnat Zapata-Arteaga, Anna Roig, Agustín Mihi, Mariano Campoy-Quiles
Advanced Energy Materials 9, 1902385, 2019
Figure: Bacterials enable the concept of farming thermoelectric materials by growing free standing films of carbon nanotubes embedded within a bacterial cellulose matrix.
Thermoelectric materials allow to directly convert waste heat into electricity without requiring any moving parts. Abundant and non-toxic organic materials present an opportunity towards cheaper renewable energy generation because they can be solution-processed at low temperatures.
Bacterial cellulose patches for plant healing
Antibacterial patches of bacterial cellulose and silver nanoparticles protect and heal plant wounds: joint publication between ICMAB and CRAG
Enhancing Localized Pesticide Action through Plant Foliage by Silver-Cellulose Hybrid Patches Alejandro Alonso-Díaz, Jordi Floriach-Clark, Judit Fuentes, Montserrat Capellades, Núria S. Coll, Anna Laromaine
ACS Biomater. Sci. Eng. 5 (2), pp 413–419, 2019
Figure: (Left) Tomato plant leaves covered with bacterial cellulose (left), plant cellulose (top) and the silver nanoparticles-bacterial cellulose hybrid patch (bottom) at the site of infection with the bacterial pathogen Pseudomonas syringae pv tomato, causing agent of bacterial speck. (Right) Schematics of the placing of the antibacterial patch on the infected leaves.
Plants, like humans, can also get wounded. These wounds can be caused by several agents and are a breach of the outer protective layers (the skin) of plants, giving open access to many microbial pathogens that can cause severe diseases, resulting in dramatic crop losses for farmers.
Herein we present a material to avoid contamination and heal plant wounds. This solution is based on the use of an environmentally friendly nanocomposite patch made of bacterial cellulose and silver nanoparticles.
Currently, the efficacy and efficiency of the pesticides used to fight crop infections still face many challenges. Seeking to improve them, we have anchored antipathogenic silver nanoparticles, to the bacterial cellulose structure. An advantage of this biopolymer is that its molecular structure is similar to plant cellulose, one of the plant’s main structural components. Moreover, due to its high-water holding capacity, bacterial cellulose has a hydrogel-like consistency, which increases its adherence to the plant leaves. The wound healing properties of bacterial cellulose have already been patented. The hybrid patch avoids runoff loss and rolling down of the nanoparticles, providing a slow and effective release of the pesticide effects from the bacterial cellulose and safety to our environment.
We have demonstrated the positive antibacterial and antifungal properties of these hybrid patches in in vitro assays against Escherichia coli and two agro-economically relevant pathogens: the bacterium Pseudomonas syringae and the fungus Botrytis cinerea. In addition, in vivo infection inhibition was proved in two different plants (Nicotiana benthamiana and tomato plant leaves).
Biofunctionalized substrates for high-throughput cell motility studies
High-throughput cell motility studies on substrates biofunctionalized with protein nanoparticles with eighty areas presenting diferent structural and compositional characteristics
High-Throughput Cell Motility Studies on Surface-Bound Protein Nanoparticles with Diverse Structural and Compositional Characteristics
Witold I. Tatkiewicz, Joaquin Seras-Franzoso, Elena Garcia-Fruitos, Esther Vazquez, Adriana R. Kyvik, Nora Ventosa, Judith Guasch, Antonio Villaverde, Jaume Veciana, Imma Ratera
ACS Biomaterials Science & Engineering 5, 5470-5480, 2019
Figure: Scheme of 9 different areas ilustrating the inputs used for the high-throughput and the resulting cell motiliy outputs studied
Surface-bound gradients of protein nanoparticles (pNPs) consisting of the green fluorescence protein (GFP) have been recently shown to influence cell motility (ACS Appl. Mater. Interfaces, 10,25779, 2018). Encouraged by the latter results, which were based only on physical cues (i.e., topography, geometry, and roughness), here we have studied the effects of fibroblast growth factor (FGF) based pNPs that introduce a biochemical activity to the substrate for promoting cell migration.
Eighty areas with different structural and compositional characteristics made of pNPs formed by FGF-pNPs were simultaneously patterned on a glass surface using a recently reported device based on an evaporation-assisted method that relies on the coffee-drop effect. The resulting surface enabled to perform a high-throughput study of the motility of NIH-3T3 fibroblasts under the different conditions including gradient steepness, particle concentrations, and area widths of patterned FGF-pNPs, in a fast way reducing the time and resources needed, as well as the batch to- batch variability that sometimes occurs in the pNP production. With the resulting patterned surface, we studied in the same experiment the influence of the following factors: (A) constant vs gradient concentrations of pNPs, (B) the steepness of pNP gradients, (C) the different absolute concentrations of pNPs, and (D) the impact of broad vs narrow paths (i.e., cell movement constraining on cell motility).
For the data analysis we have used a methodology that includes “heat maps”. From this analysis, we observed that gradients of concentrations of surface-bound FGF-pNPs stimulate the total cell movement but do not affect the total net distances traveled by cells. Moreover, cells tend to move toward an optimal intermediate FGF-pNP concentration. Additionally, a higher motility was obtained when cells were deposited on narrow and highly concentrated areas with pNPs demonstrating that FGF-pNPs can be therefore used to enhance and guide cell migration, confirming that the decoration of surfaces with such pNPs is a promising platform for regenerative medicine and tissue engineering.
Combining magnetic nanoparticles and icosahedral boron clusters in biocompatible inorganic nanohybrids for cancer therapy
Combining magnetic nanoparticles and icosahedral boron clusters in biocompatible inorganic nanohybrids for cancer therapy
Oleshkevich, Elena; Morancho, Anna; Saha, Arpita; Galenkamp, Koen M. O.; Grayston, Alba; Crich, Simonetta Geninatti; Alberti, Diego; Protti, Nicoletta; Comella, Joan X.; Teixidor, Francesc; Rosell, Anna; Vinas, Clara
Nanomedicine: Nanotechnology, Biology, and Medicine 20 (2019) 101986
Figure: Schematic representation of the bifunctional magnetic nanoparticles (1-MNPs) and a TEM image of a A172 glioblastoma cell showing the presence of 1-MNPs into the cytoplasm with a larger load.
Cancer is among the leading causes of death worldwide. According to International Agency for Research on Cancer, cancer burden rises to 18.1 million new cases and 9.6 million deaths in 2018. Most of the FDA approved anticancer drugs are purely organic molecules. The successful introduction of cisplatin as an anticancer drug in the early 1980’s opened the possibility to investigate the potential applications of organometallic complexes in medicine. Boron and carbon are the elements that have the property to build molecules of unlimited size by covalent self-bonding. Largely, the white solid twelve-vertex C2B10H12 carboranes, rank among the most chemical and biological stable molecular compounds known, which display many particular characteristics that do not find a parallel in their organic counterparts. Current chemotherapy cancer treatments not only kill both cancer and healthy cells but also frequently produces drug resistance in human patients that makes treatment failure. In order to overcome this situation, more effective and selective treatments are necessary. Boron Neutron Capture Therapy (BNCT), based on the large capture neutrons surface of 10B atoms, is a promising binary therapy for the treatment of cancer, because malignant cells can be selectively targeted and destroyed.
Following our research based on the development of a new hybrid compounds’ families that offering the possibility of dual action (chemiotherapy + radiotherapy) may result into significant clinical benefits. The reported bifunctional nanoparticles (1-MNPs) combine magnetic core and icosahedral boron-clusters to develop new bimodal cancer treatment (thermoterapy + BNCT) with the aim to obtain the best therapeutic effect using the lowest doses and therefore avoiding unwanted organism toxicity and side effects suffered by the patient. The cellular uptake and toxicity profile of 1-MNPs from culture media by human brain endothelial cells (hCMEC/D3) and glioblastoma multiform A172 cell line were demonstrated as well as colloidal stability studies in different culture media and temperatures. Importantly, thermal neutrons irradiation in BNCT reduced by 2.5 the number of cultured glioblastoma cells after 1-MNP treatment, and the systemic administration of 1-MNPs in mice was well tolerated with no major signs of toxicity.
Combining old and modern tools to predict how materials respond to external stimuli
Combining the “long-wave method”—a mainstay of condensed-matter theory since the 1950s—with modern electronic-structure techniques allows for highly accurate predictions of physical responses of crystals to nonhomogenous external perturbations.
First-principles theory of spatial dispersion: Dynamical quadrupoles and flexoelectricity
Miquel Royo and Massimiliano Stengel
Physical Review X 9, 2, 021050-22, 2019.
Figure: Charge density response to the displacement of the two dissimilar atoms in the silicon lattice. The density distribution clearly shows a quadrupolar, i.e. induced by spatial-dispersion effects, character.
In materials science and engineering, scientists often assume that crystals respond locally to an externally applied perturbation such as a strain or an electromagnetic field. Microscopically, however, the effects of the perturbation always propagate over a neighborhood around the point of application. At the macroscopic level, this means that the material response depends on gradients of the applied field, which is known as spatial dispersion. While these effects are generally small, they have attracted increasing interest in the past few years. Notable examples are flexoelectricity, the electrical voltage generated by a flexural deformation, and natural optical activity, the rotation of transmitted light polarization by some crystals. Here, we establish a general and efficient quantum-mechanical formalism to address this broad class of problems.
Density-functional perturbation theory (DFPT) is nowadays the state-of-the-art method to accurately calculate from first principles how materials respond to external stimuli. Our new approach consists of incorporating the long-wave method, a mainstay of condensed-matter theory since the early days of quantum mechanics, into the modern tools of DFPT. This allows one to access a broad range of spatial-dispersion properties at a surprisingly small computational cost and with unprecedented accuracy. We demonstrate our method, which we have implemented in a publicly distributed package (abinit), by calculating the flexoelectric tensor and the “dynamical quadrupoles” (i.e., the quadrupolar moment of the charge-density response to an atomic displacement) of several materials. We obtain excellent agreement with earlier studies, whenever available.
Our “long-wave DFPT” significantly extends the scopes and capabilities of perturbative electronic-structure approaches and opens the door to the systematic exploration of a vast range of gradient-related physical properties.
Control of nanosized defects in solution deposited YBa2Cu3O7 films by accelerated growth processing
Accelerated growth and the incorporation of preformed nanoparticles enable the preparation of high performance solution-derived YBa2Cu3O7 superconducting films upon understanding of the transformation pathway from intermediate phases to epitaxial films
Control of nanostructure and pinning properties in solution deposited YBa2Cu3O7−x nanocomposites with preformed perovskite nanoparticles
Ziliang Li, Mariona Coll, Bernat Mundet, Natalia Chamorro, Ferran Vallès, Anna Palau, Jaume Gazquez, Susagna Ricart, Teresa Puig, Xavier Obradors
Scientific Reports 9, 5828, 1-14, 2019
Accelerated growth by flash heating of high critical current trifluoroacetate solution derived epitaxial superconducting YBa2Cu3O7 films
Ziliang Li, Mariona Coll, Bernat Mundet, Anna Palau, Teresa Puig, Xavier Obradors
Journal of Materials Chemistry C 4748-4759, 2019
Figure: High performance YBCO thin films by solution deposition strongly depends on the presence of nanosized defects (nanoparticles, structural defects) which can be tuned by the processing conditions
Solution processing of YBa2Cu3O7 from the trifluoroacetates route has been proved successful to prepare cost-effective superconducting films with high critical currents. Importantly, this approach offers many new opportunities to continue improving the film performance upon tight control of the molecular precursors transformation to the intermediate nanocrystalline phases formation, the generation of nanoscale defects, and the conversion to crystalline, epitaxial films. Here we have explored two of these aspects, first, the influence of the kinetics on the transformation of the intermediate phases to the epitaxial YBa2Cu3O7 by designing a phase diagram of the intermediate phase evolution and second, the control of artificial secondary phases (size, composition, concentration) on the generation of microstructural defects and vortex pinning.
We demonstrate that a fast kinetic transformation of the intermediate polycrystalline phases, Ba1-xYxF2+x and CuO, through a heating rate 30 times faster than the conventional route boosts the nucleation, minimizes the coarsening of the intermediates and generates nanometric structural defects named intergrowths. This cascade of phenomena contributes to decreasing the overall processing temperature and enhance the performance at high magnetic fields. This fast processing route has been adopted to subsequently explore the effect of incorporating artificial nanosized secondary phases in the YBCO to prepare epitaxial and superconducting nanocomposites. Pre-formed BaHfO3 and BaZrO3nanoparticles with a size ranging from 5 nm to 10 nm has been added ( 0-25 % mol) in the YBCO precursor solution and fast converted to epitaxial nanocomposite films. 7 nm nanoparticles generate high density of intergrowth both contributing to enhance the artificial vortex pinning. Additionally, the preparation of a YBCO seed layer prior to nanocomposite deposition ensures a well-dispersed distribution of the nanoparticles within the YBCO matrix throughout the film thickness maximizing the pinning efficiency. These studies allowed us to overcome important synthetic challenges in YBCO preparation and better understand the role of kinetics and nanosized defects in the superconducting film putting forward a cost-effective route to further disentangle the underlying physics of high temperature superconductors for power applications.
Enhanced current density in high-temperature superconducting nanowires
This work provides a novel avenue toward achieving unprecedentedly high values of currents, at high magnetic field and temperatures, in high-temperature superconducting nanowires with tailored geometry
Depairing Current at High Magnetic Fields in Vortex-Free High-Temperature Superconducting Nanowires
Víctor Rouco, Carles Navau, Núria Del-Valle, Davide Massarotti, Gian Paolo Papari, Daniela Stornaiuolo, Xavier Obradors, Teresa Puig, Francesco Tafuri, Álvaro Sanchez, Anna Palau
NanoLetters 19, 4174-4179, 2019
Figure: (a) False colour top-view (top) and cross-sectional (bottom) SEM image of 80 nm-wide, 150 nm-thick nanowire. (b) First penetration field, Hc1, as a function of the nanowire width, W. Inset figures depict the aspect ratio of different nanowires
Practical applications of superconductors, both in large-scale devices or highly sensitive superconducting electronics is limited by the presence of vortices (quantized magnetic flux lines), whose movements result in losses, internal noise, and reduced performances. The conventional strategy to overcome the flow of vortices within a superconducting material is to pin them along artificial defects.
This research provides a novel avenue toward achieving unprecedentedly high values of the critical current density at high field and temperatures, in high temperature superconducting nanowires by tailoring the material geometry, preventing vortex penetration. We have theoretically and experimentally demonstrated that by reducing the width, W, of nanowire-patterned high temperature superconducting films, the first penetration field, Hc1, below which no vortices are present, is extended up to very large applied field values, on the order of∼1 T. Tailored nanowires show a basically temperature-independent critical current density values, approaching the superconducting depairing limit, well above the values achieved using conventional flux pinning strategies.
Our results may have important consequences in practical applications. On the one hand, the fact that no vortices are present in the nanowires makes them excellent candidates to be used in noise-sensitive sensors or quantum systems. On the other hand, the very large values of current density achieved at high applied fields and temperatures may be also relevant at large scale, with potential to improve the performance of actual thin strips.
Halide perovskites are not ferroelectric
Lead halide perovskites are ferroelectricity-free, whereas domains observed in PFM measurements are likely due to twinning driven by strain compensation
Ferroelectricity-free lead halide perovskites
Andrés Gómez, Qiong Wang, Alejandro R. Goñi, Mariano Campoy-Quiles, Antonio Abate
Energy and Environment Science 12, 2537−2547, 2019
Figure: (a) Scheme of the DPFM measurement on a ferroelectric sample with antiparallel domain configuration. The current signal recorded in DPFM should reverse its sign when the tip crosses different domains, depending upon scan direction. (b) DPFM images obtained for periodically poled lithium niobate (PPLN), for which the current sign is reversed as the scan direction changes, exactly as expected for conventional ferroelectric materials. (c) DPFM images of the CsFAMA tri-cation perovskite scanned under similar conditions to those of PPLN. The CsFAMA perovskite does not show any sign reversal, resembling typical current-sensing AFM mappings.
Ferroelectric materials are characterized by a switchable macroscopic polarization. A wide number of perovskite oxides have ferroelectric behavior. In contrast, the existence of ferroelectricity in organic-inorganic perovskite thin films has been matter of intense debate over the past few years.
Improved resistive switching memory devices
A non-volatile memory element in which data is stored in a single high resistance state is built based on back-to-back series connection of two ferroelectric tunnel devices.
Complementary resistive switching using metal-ferroelectric-metal tunnel junctions
Mengdi Qian, Ignasi Fina, Milena C. Sulzbach, Florencio Sánchez, Josep Fontcuberta
Small 15, 1805042, 2019
Figure: Intensity-Voltage (I-V) characteristics of back-to-back series connection of ferroelectric resistive switching device. Top-left: sketch of the used back-to-back series connection. The device resistance at remanence is always high, but the two ferroelectric devices connected show different polarization up-down or down-up states corresponding to different logic states.
Resistive switching elements are attracting a lot of interest, because these are building blocks for artificial intelligence computing. In resistive switching devices a switch from a high resistance to a low resistance and vice versa is produced depending on the prepoling applied voltage. Intermediate resistance states can be also set while sweeping prepoling applied voltage. Ferroelectric tunnel junctions are resistive switching devices, where resistance is modulated by ferroelectric polarization. Ferroelectric tunnel junctions are interesting because they can show improved power consumption, retention and reliability. In a resistive switching memory device, arrays of resistive switching elements are fabricated. However, these arrays present the sneak current problem. The sneak problem results from the fact that reading currents addressed to a high resistance state leak through memory elements in the low resistance state. If the resistive switching memory device is fabricated based on a ferroelectric material the same problem holds. In the highlighted work, it is shown that two different logic states can be stored in a series back-to-back connection of ferroelectric tunnel junctions performing the same high resistance. The two logic states correspond to up-down or down-up polarization state of the two ferroelectric junctions. Therefore, as all the junctions are in high resistance state, the sneak currents are avoided and the device scale-up is possible. Moreover, authors demonstrate that the engineered device shows less power consumption than resistive switching elements based on single ferroelectric tunnel junction.
Is manganese really inert in Manganese-rich Lithium batteries?
Synchrotron light provides an insight on the supposedly inert manganese in the durability of lithium and manganese-rich high energy battery materials
Role of Manganese in Lithium- and Manganese-Rich Layered Oxides Cathodes
Laura Simonelli, Andrea Sorrentino, Carlo Marini, Ramanan, Nitya; Heinis, Dominique; Olszewski, Wojciech; Mullaliu, Angelo; Birrozzi, Agnese; Laszczynski, Nina; Giorgetti, Marco; Passerini, Stefano; Tonti, Dino
Journal of Physical Chemistry Letters 10, (12), 3359–3368, 2019
Figure: Semiquantitative molar fractions for different oxidation states obtained from intensities of O and Mn K-edge absorption spectra from bare and coated samples at different charge states along charge (yellow background) and discharge (green) cycles: Ni4+ (a), Mn4+ (b) and Mn4+ vs. Ni 4+.
The environmental challenges issued by the current development of our societies urge a redesign of the whole energy cycle. The intermittence of renewable energies requires storage, and their use in most transport needs a vector with high energy density.
Magnetic properties of oxide thin films deposited by Polymer-Assisted-Deposition
High microstructural quality of La0.92MnO3 thin films grown by Polymer-Assisted-Deposition technique, suitable or spintronic applications
Dynamic magnetic properties and spin pumping in polymer-assisted-deposited La0.92MnO3 thin films
Hailin Wang, Alberto Pomar, Sergi Martín-Rio, Carlos Frontera, Narcis Mestres, Benjamín Martıínez
J. Mater. Chem. C 7, 12633-12640, 2019
Figure: Magnetic damping is enhanced in La0.92MnO3 thin films grown by Polymer-Assisted Deposition by spin pumping in a Pt capping layer. Inset: Ferromagnetic resonance spectra as a function of applied field for the two main in-plane orientations taken at 100K and 9GHz.
The growth of thin films by chemical methods has been a hot topic in the recent years as they offer appealing advantages over vacuum techniques as stoichiometric versatility and low-cost scalability. Among them, Polymer-Assisted-Deposition (PAD) is particularly attractive as it relies in environmentally friendly water-based solutions. However, serious concerns have been raised on the control of their interfacial quality limiting their use in emergent applications relaying in flat sharp interfaces, for example, for spintronics.
It is shown that La0.92MnO3 (LMO) thin films grown by PAD are of high microstructural quality with low magnetic damping, thus suitable for spintronic applications. Ferromagnetic resonance measurements in LMO/Pt bilayers gives clear indications of injection of pure spin currents into the Pt layer by spin pumping. This transfer of spin angular momentum through the interface between the ferromagnetic layer (LMO) and Pt layer is evidenced by an increase of magnetic damping. These results are of strong interest since they demonstrate that PAD technique allows obtaining complex oxide thin films of high microstructural quality suitable for spintronic applications.
We also present a deep study of the temperature dependence of the magnetodynamic properties of LMO thin films prepared by PAD showing that microstructural strain release from rhombohedral bulk phase results in an in-plane four-fold anisotropy with  as easy axis.
Our results demonstrate that LMO films grown by PAD may be used as efficient spin source systems in heterostructures for spintronic devices.
Multifunctional molecular switches based on radical dendrimers
New radical dendrimers based on polyphosphorhydrazone (PPH) dendrimers fully functionalized with perchlorotriphenylmethyl (PTM) radicals as electrochemical molecular switches with optical (absorption and fluorescence) and magnetic responses.
Redox active PTM radical dendrimers as promising multifunctional molecular switches
Vega Lloveras, Flonja Liko, José L. Muñoz-Gómez, Jaume Veciana, José Vidal-Gancedo
Chem. Mater. 31, 22, 9400-9412, 2019
Figure: Representation of the electrochemical switch (on/off) of PTM radical dendrimers (Gn(PTM·)x, n=0, 1, 2; x=6, 12, 24). The PTM molecule has two redox states, the radical (left) and anion (right) forms, which can be electrochemically interconverted. Radical dendrimers Gn(PTM·)x exhibit spin S=x.½ (EPR active), an absorbance band at 386 nm (yellow-brownish colour) and red fluorescence emission, and their corresponding anionic forms Gn(PTM-)x are diamagnetic species with S=0 (EPR silent), with a maximum absorbance band at ca. 520 nm (deep wine or purple colour) and are not fluorescent.
Nowadays, there is a great interest in using individual molecules as nanometer-scale switches and logic devices, with the aim of reaching higher power and smaller size. Demonstrating that one molecular switch can be turned on and off at room temperature, simply by applying a current to a neighboring molecule has interesting implications.
In this work, we report the synthesis and characterization of three generations of polyphosphorhydrazone (PPH) dendrimers, fully functionalized with 6, 12 and 24 redox active perchlorotriphenylmethyl (PTM) radicals in the periphery, capable of undergoing an electrochemical reversible switching (on/off) by multi-electron reduction and oxidation, for many cycles. An electrical input is used to trigger the physical properties of these radical dendrimers in a reversible way, modifying their optical and magnetic properties. Gn(PTM•)x radical dendrimers are paramagnetic, exhibit an absorbance band at 386 nm and red fluorescence emission, if in radical state (on). When they are switched to their anion state, these dendrimers convert to diamagnetic species with a maximum absorbance band at ca. 520 nm and no fluorescence emission (off). Furthermore, in this work we open the perspective of controlling the exact number of electrons transferred during the switching process, that could lead not only to a two-state (on/off) but also to a multi-state switch in the near future.
In addition, the high electron accepting capacity of these radical dendrimers able to accept and donate up to 24 electrons per molecule at the same time at very accessible potentials and in a reversible way makes them good electron-reservoir molecules.
Undoubtedly, the high control over the synthesis, stability and reversibility of systems like the ones reported in this work, further supports the perspective of using macromolecules as scaffolds in the electronic devices of the future.
Nonpolar/polar magnetic switch in a strong ferromagnet
We unveil a nonpolar/polar transition in a strong ferromagnetic perovskite associated to the concurrence of two non-polar magnetic distortions. Several switching mechanisms are proposed based on magnetic trilinear coupling.
Magnetic inversion symmetry breaking and spin reorientation in Tb2MnNiO6: a polar strong ferromagnet
Jose Luis García-Muñoz, Javier Blasco, Xiaodong Zhang, Oscar Fabelo
Physical Review B 99, 184444, 9pp, 2019
Figure: (left) Magnetic irreps and isotropy subgroups: successive activation of nonpolar magnetic modes at the A and B sites that produce the P21' polar phase, allowing a trilinear coupling with the polarization in the free energy. (right) Changes in the magnetic order at A and B sites during the FM3 (P21'/c') « FM4 (P21') transformation showing the ferromagnetic spin reorientation. Electric and magnetic mechanisms to switch the polar/non-polar (FE/anti-FE) transformation between P21'/c' and P21' states.
Unlike proper ferroelectrics, in improper ferroelectrics the polarization does not arises from the condensation of a polar lattice distortion associated to a zone-center instability. Understanding the interplay between magnetism and ferroelectricity in improper multiferroics is of interest in fundamental and applied research. At present, there is a good number of examples of improper ferroelectrics induced by antiferromagnetic order. This order is compatible with antitranslations that can suppress inversion centers or screw axis and favor symmetry breaks into polar symmetries.
Generally, cooperative distortions at the point k=0 (zone center) are more favorable to ferromagnetic configurations. In practice, ferromagnetic improper multiferroics are much more rare than antiferromagnets, and in most cases are simply weak-ferromagnets. However strong ferromagnetic multiferroics can have important advantages in magnetoelectric devices.
We completed a comprehensive study on four successive magnetic phases driven by zone-center modes in Tb2MnNiO6 ferromagnet. The interactions between A (Tb) and B (metals) spin subsystems stabilizes a ferromagnetic ground state with polar symmetry which makes this oxide potentially multiferroic with polarization by magnetic trilinear coupling. Its macroscopic magnetization is large and not related to a weak-ferromagnetic component from Dzyaloshinskii–Moriya terms.
Symmetry analysis of neutron data (ILL, Grenoble) unveils that the nonpolar/polar transition occurs due to the concurrence of two different non-polar magnetic distortions. The concurrence of these non-polar distortions produces an overall polar symmetry, in which the loss of inversion center splits the orbits of Tb and O sites. In addition, thanks to a severe spin reorientation of the ferromagnetic axis across the polar/non polar transition we anticipate that in this material the direction of the magnetization can be used as a lever to switch the polar/non-polar (ferroelectric/antiferroelectric) transformation. Likewise, the control of the magnetization direction would be possible by electrical fields.
Organic free radicals: a new trend in optoelectronics and spintronics
New perspectives in organic free radical molecules: when luminescence, chirality and magnetic activity result in a winning combination.
Organic Free Radicals as Circularly Polarized Luminescence Emitters
Paula Mayorga-Burrezo, Vicente G. Jiménez, Davide Blasi, Imma Ratera, Araceli G. Campaña, Jaume Veciana
Angew. Chem. Int. Ed. 58, 16282 –16288, 2019
Figure: Molecular structures of optically and magnetically active enantiomers of one studied organic free radical
Over the past decades, increasing attention has been devoted to circularly polarized luminescence (CPL) up to becoming one of the most powerful and reliable spectroscopic tool for the analysis of a great variety of chemical systems. Resulting from the influence that chirality has over luminescent properties, the course of this technique is nowadays leaded by inorganic CPL emitters. However, it is known that pure organic samples with CPL activity may provide additional advantages (i.e. processability, lightness, transparency, etc.) and represent a hugely desirable option in several hot applications where toxicity factors are crucial (i.e., bioimaging). As a result, great efforts are currently being made for the development of these promising organic-based alternatives.
In this work, the study of CPL activity in organic free radicals emitters has been addressed for the first time, encouraged by the enhanced performance proved for magnetically active compounds in optics and optoelectronics. To this end, two triphenylmethyl (trityl) radical-based chlorinated derivatives, with propeller chirality, were considered, achieving an efficient chiral emission after the resolution of the racemic compounds.
Consequently, the pioneering approach here developed aims at laying the foundations for a new trend in optoelectronics and spintronics, where chiral, magnetic and luminescent properties can be used interchangeably in a single device. Thus, taking full advantage of the versatile nature of organic compounds will place us a step further in the miniaturization race of multifunctional nanomaterials.
Perovskite gaps ruled by thermal expansion and electron-phonon interaction
In lead halide perovskites, the variation of the fundamental gap with temperature is equally determined by thermal expansion and electron-phonon interaction effects
Equal Footing of Thermal Expansion and Electron-Phonon Interaction in the Temperature Dependence of Lead Halide Perovskite Band Gaps
Adrián Francisco-López, Bethan Charles, M. Isabel Alonso, Miquel Garriga, Mariano Campoy-Quiles, Mark T. Weller, Alejandro Goñi
J. Phys. Chem. Lett. 10, 2971−2977, 2019
Figure: Sketch illustrating the contribution from thermal expansion (TE) and electron-phonon interaction (EP) to the temperature-induced renormalization of the perovskite band gap with temperature (data points).
For all the spectacular developments in lead-halide perovskite-based photovoltaics, there are still several fundamental physical questions that remain a matter of debate. In particular, this is the case of the atypical temperature dependence of the fundamental optical gap of most halide perovskites, for which the gap increases with increasing temperature.
Photoluminescent boron-based materials for bioimaging and cancer treatment
We have developed a set of photoluminescence boron-containing molecular materials that exhibit blue light emission with extraordinary high quantum efficiency (around 100 %), making them excellent candidates for optical devices and bioimaging probes. Moreover, due to the high boron content of these materials, they could be useful for BNCT cancer therapy.
Efficient blue light emitting materials based on m-carborane-anthracene dyads. Structure, photophysics and bioimaging studies
Mahdi Chaari, Zsolt Kelemen, Duane Choquesillo-Lazarte, Nerea Gaztelumendi, Francesc Teixidor, Clara Viñas, Carme Nogués,* Rosario Núñez*. Biomaterials Science, 7, 5324, 2019
Figure: Fluorescence intensity emitted by cells incubated for 4 h with 10 µM of diiodinated antracene-m-carborane. Image obtained with the confocal laser scanning microscope.
The development of photoluminescent boron cluster-based organic p-conjugated systems has attracted huge interest as active materials in (opto)electronic devices, solar cells, biological sensors and fluorescence bioimaging. Anthracene derivatives are molecules with excellent luminescence properties, whereas carborane clusters (C2B10H12) are fascinating chemical species with unique structural and electronic properties, as well as low toxicity in biological systmes. In carborane-containing fluorophores, the fluorescence efficiency can be tailored by the cluster isomer and the substituent at the cluster atom (Cc).
We have synthesized three m-carborane-anthracenyl dyads, containing 0, 1 or 2 iodo groups at Bc atoms. They exhibit exceptional blue emission properties with high quantum yields (around 100 %) in solution, confirming that linking m-carborane to a fluorophore produces a significant enhancement of the emission efficiency in the target compounds. Notably, these dyads exhibit moderate fluorescence in aggregate state (between 19–23 %), pointing out that they are extremely good emitters in solution, while maintaining the emission properties in solid state. None of them shows cytotoxicity for HeLa cells. Confocal microscopy studies confirm that all compounds are internalised by cells via endocytosis, being the di-iodinated compound the best-internalised by cells. This suggest that the presence of iodo lead to a higher lipophilicity facilitating an efficient transport across the plasma membrane and a better cellular uptake. This di-iodinated dyad is an excellent fluorescent dye for bioimaging studies in fixed cells, and due to the high boron content and exceptional cellular uptake, a potential anticancer agent for Boron Neutron Cancer Therapy (BNCT).
Probing time correlations with quantum wells
The photoresponse of LaAlO3/SrTiO3 quantum wells is sensitive to time order of optical pulses and replicates the synaptic plasticity observed in neurobiological systems.
Plasticity of Persistent Photoconductance of Amorphous LaAlO3/SrTiO3 Interfaces under Varying Illumination Conditions
Yu Chen, Blai Casals, Gervasi Herranz
ACS Appl. Electron. Mater. 2019, 1, 6, 810–816, 2019
Solid-State Synapses Modulated by Wavelength-Sensitive Temporal Correlations in Optic Sensory Inputs
Yu Chen, Blai Casals, Florencio Sanchez, Gervasi Herranz
ACS Appl. Electron. Mater. 2019, 1, 7, 1189–1197, 2019
Figure: Probing time correlations with quantum wells. We have uncovered photoresponsive quantum wells that mimic spike-timing dependent plasticity using optical pulses as stimuli. The conductance is sensitive to the time order of optical inputs of different wavelengths (see bottom panel, where blue and red arrows indicate different sequences of blue and red pulses). Therefore, these quantum wells can be used as optical synapses in neuromorphic devices.
Spike-timing dependent plasticity (STDP) is a fundamental concept in neurobiology. Briefly, the relative timing of two neuron spikes reinforces or weakens the synapse between them, so that events caused by another should trigger spikes in a particular time order. A reversal of this order causes the weakening of the synapse, so it penalizes the correlation. This process allows the brain to establish causal correlations from the environment and it is widely used in computational neuroscience. Recently, Yu Chen et al. (ACS Appl. Electron. Mater. 2019, 1, 6, 810–816 (2019)) have found that the photoconductive properties of quantum wells at the LaAlO3/SrTiO3 interface mimic STDP, using time correlations in optical pulses. More specifically, the conductance of the quantum well is increased or decreased depending on the relative timing of optical pulses of short- (blue) and long- (red) wavelengths (Figure). Remarkably, the conductance changes plastically in proportion to the intensity of the optical stimulus, in a way that is reminiscent of synaptic plasticity found in neurobiological systems (Yu Chen, ACS Appl. Electron. Mater. 2019, 1, 6, 810–816 (2019)). The sensitivity of the conductance to these correlations opens up fascinating perspectives on the use of optical synapses for neuromorphic devices based on these photoconductive systems.
Resistive switching in semimetallic thin films
The study of different thickness SrIO3 thin films shows different behaviors, from insulating to semimetallic, in resistive switching memory devices
Resistive Switching in Semimetallic SrIrO3 Thin Films
Víctor Fuentes, Borislav Vasić, Zorica Konstantinović, Benjamín Martínez, Lluís Balcells, Alberto Pomar
ACS Appl. Electron. Mater. 1, 1981−1988, 2019
Figure: Left: Disorder and spatial localization due to thickness reduction allow generating a metal-insulator transition in semimetallic SrIrO3 thin films. Below about 3nm films are insulating with hysteretic I-V curves indicative of resistive switching behavior at room temperature. Right: Current maps (a and c) allow demonstrating the writing/erasing processes required for the implementation of Re-RAMs. Corresponding topography images (b, d).
Iridates are of strong interest because large spin-orbit coupling (SOC) is expected in these materials, thus the interplay between magnetic and electronic properties will be strongly reinforced opening the access to new magneto-electronic devices.
In the search for a new generation of faster and more energy efficient electronic devices, the use of reversible resistive switching (RS) phenomena has been proposed as a very appealing solution for the development of non-volatile memory devices. Here we address the analysis of resistive switching processes in SrIrO3 thin films by means of local Intensity-Voltage (I-V) curve measurements and current mapping, by using conductive atomic force microscopy (C-AFM).
While SrIrO3 exhibits semimetallic character, in thin films, an Anderson-type metal-insulator transition (MIT) triggered by disorder and spatial localization due to film thickness reduction is observed, and their influence on the resistive switching behaviour is analysed. For thin enough films (below ~3nm) samples are insulating with hysteretic I-V curves indicative of reversible resistive switching behaviour between two states of clearly different resistance at room temperature. A sharp transition into a low resistance state (LRS), i.e an abrupt increase of the current intensity, is detected above a well-defined threshold voltage indicative of localization of charge carriers. On the other hand, thicker samples exhibit a semimetallic character and I-V curves show progressive changes of the local resistance without a clearly defined threshold voltage, thus evidencing the absence of a MI transition with a well-defined resistance jump between the different resistance states.
Reversible switching of gold surface energy
Reversible switching of gold surface energy by near infrared irradiation using bistable Self Assembly Monolayers (SAMs) based on radical molecules
Effect of the Molecular Polarizability of SAMs on the Work Function Modification of Gold: Closed- versus Open-Shell Donor–Acceptor SAMs
Valentin Diez-Cabanes, Deyana Morales, Manuel Souto, Markos Paradinas, Francesca Delchiaro, Anna Painelli, Carmen Ocal, David Cornil, Jérôme Cornil, Jaume Veciana, Imma Ratera
Advanced Materials Technologies 4, 1800152, 2019
Reversible switching of the Au(111) work function by near infrared irradiation with a bistable SAM based on a radical donor-acceptor dyad
Valentin Diez-Cabanes, Andrés Gomez, Manuel Souto, Nerea Gonzalez-Pato, Jérôme Cornil, Jaume Veciana, Imma Ratera
Journal of Materials Chemistry C 7, 7418, 2019
Figure: Reversible switching of gold WF by NIR irradiation using SAMs of D-A radicals.
In organic electronic devices, charge injection barriers at metal-organic interfaces can be tuned by modifying the work function (WF) of metallic electrodes using self-assembled monolayers (SAMs) of polar molecules. An interesting example of polar molecule is offered by donor–acceptor (D–A) dyads based on ferrocene (Fc) as electron-donor unit and a polychlorotriphenylmethyl radical as electron-acceptor unit, connected by a π-conjugated vinylene bridge. The magnitude of the shift in the charge injection barriers for this D–A systems is estimated by means of surface potential measurements performed by Kelvin probe force microscopy (KPFM). The experimental data has been rationalized by density functional theory calculations, which evidence the importance of presenting not only high molecular dipole moments but also low polarizabilities along the direction normal to the substrate to achieve high work function (WF) shifts of metals upon SAM formation.
Based on these findings, we have described the modification of the WF of Au(111) upon deposition of self-assembled monolayers (SAMs) of the two donor–acceptor (D–A) systems, the radical (Fc–PTM) dyad and its non-radical analogue. Interestingly, the WF of the radical SAM is significantly shifted by +250 when irradiated with NIR light recovering their original values when the irradiation is suppressed. This phenomena, is attributed to the bistable nature of this SAM in which neutral radical dyad molecules are excited into a zwitterionic state following a light driven intramolecular charge transfer (ICT) from the Fc unit to the PTM radical unit. Remarkable is the large WF shift attained, one of the highest values reported in the literature, and the unprecedented fact that it is achieved under irradiation in the IR region due to an intramolecular electronic reorganization. In contrast, the WF of the non-radical SAM does not change upon NIR irradiation since this SAM does not display bistability.
Small pores in the surface of feldspar minerals are responsible of ice formation in the atmosphere
Environmental scanning electron microscopy images of ice-nucleation on feldspar surfaces, known to be the most efficient ice-nucleation agents present in the atmosphere, showed that nucleation is triggered at pores of the surface
Pores Dominate Ice Nucleation on Feldspars
Elzbieta Pach, Albert Verdaguer
Journal of Physical Chemistry C 123, 34, 20998–21004, 2019
Figure: Sequence of enviromental SEM images showing ice nucleation occuring in a surface pore of a k-Feldspar mineral.
The formation of ice, when and how water freezes, is still poorly understood, even though this is essential for understanding Earth’s climate. Knowing more about the molecular mechanisms underlying these processes can help to build atmospheric and climate models with higher confidence.
Superconductors substituting copper for the future circular collider beam screen (FCC-hh) at CERN
The FCC-hh considers a novel utilization of coated conductors reliant on the high frequency response of high-temperature superconductors under extremely challenging working conditions
Coated Conductor technology for the beamscreen chamber of future high energy circular colliders
Teresa Puig, Patrick Krkotic, Artur Romanov, Joan O'Callaghan, Danilo Andrea Zanin, Holger Neupert, Pedro Costa Pinto, Pierre Demolon, Ângelo Rafael Granadeiro Costa, Mauro Taborelli, Francis Perez, Montse Pont, Joffre Gutierrez, Sergio Calatroni
Superconductor Science and Technology 32, 094006 (8pp), 2019
Figure: Left pannel: Experimental values of the surface resistance of coated conductors are lower than that of copper at working conditions close to those found in the FCC-hh. Right pannel: The theoretical predicions based on our experimental values show that coated conductors have a 40 times lower surface resistance at the FCC-hh working conditions (16T and 1 GHz) as compared to copper. Insert to right pannel: Sketch of the cross section of the FCC-hh beam screen chamber coated with stripes of REBa2Cu3O7-x coated conductos (black regions).
The FCC-hh is the most ambitious scenario for a post Large Hadron Collider (LHC) machine proposed by CERN. It will operate as a 80-100 km acceleration ring where 16-18 T magnets will steer 1011 protons in 8 cm bunches with revolution period of 0.3 ms. In this machine, collision energies of 100 TeV are expected to be reached. The 35.4 W/m/beam synchrotron radiation emitted by the protons will be absorbed by a stainless steel tube, the so called beam screen, held at a temperature window of 40-60 K. The beam screen chamber is located in the beam-steering superconducting magnetic dipoles to thermally shield them. Given the prospected beam parameters, mirror charges will be induced into the beam screen that peak at magnitudes of 25 A and wiggle with frequency spectrum 0-1 GHz. Governed by the necessity to maintain a stable beam during acceleration of hadrons, highly conductive coatings will have to cover the interior of the beam screen chamber.
Scientists from the Superconducting Materials and Large Scale Nanostructures (SUMAN) at ICMAB have proposed a solution to this challenge: coating the beam screen chamber with a high-temperature superconductor (HTS) instead of copper. Compared to copper, which is already used in CERN’s LHC, HTS promise with their lower surface resistance and thus, bigger beam stability margins at operation temperature. HTS of the type REBa2Cu3O7-x (where RE is a rare earth metal, such as Y, Gd or Eu), are produced worldwide as flexible materials in hundreds of km length and could be ideal candidates. In this work, scientists within a consortium made by SUMAN-ICMAB, ALBA, IFAE and UPC have demonstrated that REBa2Cu3O7-x HTS are capable of outperforming copper’s surface resistance by a factor of 40 or more under the extreme working conditions to be found in the FCC-hh.
The atomistic origin of the peculiar amphiphilic behavior of cellulose
Molecular insight into the wetting behavior and amphiphilic character of cellulose nanocrystals
David C. Malaspina and Jordi Faraudo
Advances in Colloid and Interface Science 267, 15–25, 2019
Figure: Summary of the systems studied by atomistic MD simulations. Center: scheme of the cellolose crystal structures considered in this work. Top: snapshots from the simulations of celloluse surfaces in contact with different molecules in water (carbonate ion, EGF protein and tetraphenil borate ion). Bottom: snapshots from the wetting simulations of cellulose with droplets of different solvents (water and organic solvent (tetradecane)). Movies of the simulations can be seen in the SoftMatter Youtube channel: https://www.youtube.com/playlist?list=PLWhDHF4i-Is0c407wNLOEhH4aiEHFPLOb
Cellulose (the most abundant biopolymer in Earth) shows a puzzling behavior in its interaction with solvents. It has a strong H-bonding capacity, typical of hydrophilic molecules, but it is insoluble in water. There are also controvertial claims of the presence of hydrophobic interactions in cellulose and possible amphiphilic behavior. This question was clarified using extensive atomistic molecular dynamics simulations of different crystal surfaces of cellulose and different solvents (water and organic solvents) and different molecules (small hydrophilic or hydrophobic solutes, proteins with exposed aminoacids of hydrophilic and hydrophobic character).
Our results show that crystalline cellulose have the remarkable property of being simultaneously hydrophilic and lipophilic. In our work this behavior is directly linked to both the molecular structure and the supramolecular organization of crystalline cellulose.
Thermal conductivity à la carte for phononic applications
We propose strategies to engineer materials with thermal properties on demand, which pave the way to the design of thermal devices and signal processing with phonons
Phonon Engineering in Twinning Superlattice Nanowires
Marta De Luca, Claudia Fasolato, Marcel A. Verheijen, Yizhen Ren, Milo Y. Swinkels, Sebastian Kölling, Erik P. A. M. Bakkers, Riccardo Rurali, Xavier Cartoixà, Ilaria Zardo
Nano Letters 19 (7), 4702, 2019
Giant Electrophononic Response in PbTiO3 by Strain Engineering
Pol Torres, Jorge Íñiguez, Riccardo Rurali
Rev. Lett. 123, 185901, 2019
Figure: TEM image of the atomic arrangement of a twin superlattice. The change in the stacking of the different layers can be appreciated and is also in the cartoon that displays the atomic arrangement around the twin inversion plane. The right-hand side panel displays the Raman signature of the twin superlattice.
In electronics, information is transferred with charge carriers, whose motion can be easily controlled with external fields. This is not the case of phononics, where the manipulation of phonons is intrinsically more challenging: this is why we live in a world of electronic devices and heat is normally regarded as a source of loss.
Transparent and highly conducting metallic oxides
Metals are known to be bright by reflecting light. Many applications however, require transparent rather than reflecting metals. Transition metal oxides offer a solution to this dilemma
High Carrier Mobility, Electrical Conductivity, and Optical Transmittance in Epitaxial SrVO3 Thin Films
Mathieu Mirjolet, Florencio Sánchez, Josep Fontcuberta
Adv. Funct. Mater. 29, 1808432, 2019
Independent Tuning of Optical Transparency Window and Electrical Properties of Epitaxial SrVO3 Thin Films by Substrate Mismatch
Mathieu Mirjolet, Hari Babu Vasili, LLuís López-Conesa, Sònia Estradé, Francesca Peiró, José Santiso, Florencio Sánchez, Pamela Machado, Pierluigi Gargiani, Manuel Valvidares, Josep Fontcuberta
Adv. Funct. Mater. 29, 1904238, 2019
Figure: Plasma energy of SrVO3 thin films (left axis) and room-temperature electrical resistivity (right axis) grown on different substrates, imposing tensile or compressive stress on SrVO3, as indicated.
Information technologies require new materials with high electrical conductivity and optical transparency to face scarcity of critical materials and improve performances. Oxide thin films based on early transition metals (e.g. V, Nb, Mo, etc.), the partially occupation of ndxorbitals (i.e. nd1, nd2...) gives rise to metallic conductivity. Transparency at visible range requires that the plasm edge to be at red or infrared. The narrow conducting 3d band of SrVO3 is expected to enhance the carrier effective mass, thus lowering the plasma frequency below the visible as required. However, growing thin films of these oxides typically requires an extremely low oxygen pressure, that compromises point defect concentration in the film and thus challenges obtaining high conducting materials as required. Using pulsed laser deposition (PLD) as a tool to grow epitaxial thin films of SrVO3, we have discovered that the use of a non-reactive gas controls the ablation plume expansion and allows to obtain SrVO3 films with low room-temperature resistivity (r ≈ 31 mW cm) and large carrier mobility (m ≈ 8.3 cm2 V-1 s-1) and residual resistivity ratio (RRR ≈ 11.5), which are record figures of merit for PLD grown films, while preserving the plasma frequency at infrared and improving optical transparency in the visible range.
Moreover, we show that by exploiting the strain caused by the substrates on the structure and microstructure of the films, the carrier concentration and the effective mass of carriers can be modulated while preserving the optical transmittance window. As indicated by linear X-ray dichroism experiments performed at Boreas Beamline at ALBA synchrotron, the electronic bandwidth and orbital occupation appear to rule the observed effects.
Why the interface matters in perovskites solar cell performances
The reported data for diverse hole-transporting-material (HTM) deposited on a perovskite layer help understanding the limitations when designing new organic semiconductor molecules to improve the perovskite solar cell efficiency.
Energy Alignment and Recombination in Perovskite Solar Cells: Weighted Influence on the Open Circuit Voltage
Ilario Gelmettia, Núria F. Montcada, Ana Pérez-Rodríguez, Esther Barrena, Carmen Ocal, Inés García-Benito, Agustín Molina-Ontoria, Nazario Martín, Anton Vidal-Ferrana, Emilio Palomares
Energy and Environment Science 12, 1309-1316, 2019
Figure: (Top) Kelvin Probe Force Microscopy measurements for surfaces of pristine CsFAMAPbIBr and the different HTM devices (spiro-OMeTAD, TAE-1, TAE-3 and TAE-4). The vacuum level shifts are obtained by extracting the diverse work function from the parabolic data. (Bottom) Molecular representation of the HTM devices.
Organic-inorganic lead halide perovskites have become the focus of intense research due to their outstanding performance in hybrid photovoltaic devices. One essential component for attaining stable and high efficient solar cell is the employed hole transporting material (HTM).