Charging of highly resistive granular metal films

We have used the Scanning Kelvin probe microscopy technique to monitor the charging process of highly resistive granular thin films. The sample is connected to two leads and is separated by an insulator layer from a gate electrode. When a gate voltage is applied, charges enter from the leads and rearrange across the sample. We find very slow processes with characteristic charging times exponentially distributed over a wide range of values, resulting in a logarithmic relaxation to equilibrium. After the gate voltage has been switched off, the system again relaxes logarithmically slowly to the new equilibrium. The results cannot be explained with diffusion models, but most of them can be understood with a hopping percolation model, in which the localization length is shorter than the typical site separation. The technique is very promising for the study of slow phenomena in highly resistive systems and will be able to estimate the conductance of these systems when direct macroscopic measurement techniques are not sensitive enough.Comment: 8 pages, 7 figure

Increasing environmental sciences students' awareness of the link between soil and Sustainable Development Goals

[EN] Education must prepare students to find solutions for the global and local challenges of today and the future, by conferring students the knowledge, skills and attitudes to address them, including environmental degradation. Soils perform a number of key environmental, social and economic functions (e.g. production of food and biomass, nutrient cycling, water filter, climate control). Various Sustainable Development Goals (SDGs) are connected with soil. Sustainable soil use is crucial for many SDGs. Target 2.4 of SDG 2 (Zero Hunger) mentions the implementation of resilient agricultural practices to improve land and soil quality. Target 3.9 of the SDG 3 (Good Health and Wellbeing) indicates that the number of deaths and illnesses from soil pollution and contamination must be substantially reduced. Target 12.4 of SDG 12 (Responsible Consumption and Production) mentions reducing the release of chemicals to soil to minimize their adverse impacts on human health and the environment. Target 15.3 of SDG 15 (Life on Land) includes the restoration of degraded soil. Although soil is not mentioned in other SDG targets, it is related to other SDGs. We present the results of the analysis of the activity performed by the students related to soil and SDGs and the transversal competence ¿knowledge of contemporary problems¿. In the activity, the students were asked to write down with reasons the SDGs that soil is related to. Afterward, they were asked to write down soil degradation processes and their consequences for people lives and the environment. Next the students worked in groups on the link between soil functions and soil degradation processes using communication material designed by the Food and Agriculture Organization. Finally, they answered a questionnaire, and five open questions to explain the link between soil and the SDGs 2, 3, 6, 13 and 15. The students gave a value of 9.1 out of 10 to the importance of knowledge toward an integrated approach to the environment. The students rated the importance of studying Soil Science to increase their ability to perceive and realize the existence and uniqueness of soils with 8.7 out of 10. The need to raise awareness about soils among people who are not in direct contact with soils was rated with 9.2 out of 10. The students who knew that the SDGs have 169 targets were 85%. The students related the statement ¿Women remain a minority in soil science¿ to SDGs 5 (Gender Equality) and 10 (Reduced inequalities). Ninety-five percent of the students stated that "zero hunger" is not only a question of crop production, but it is also related to the quality of education, malnutrition, etc. All the students stated that there is now scientific evidence that healthy soils support nutritious and healthy food and, therefore, contribute to people's health. When students were asked about the origin of toxicity in the soil that can affect human health, 50% named heavy metals, 35% radioactive elements, 35% organic chemicals, and 15% diseases due to exposure to soil organisms. The students were asked if they knew that zinc deficiency is the fifth leading cause of death and disease in the developing world; only 52% said that they did. Soil science has important links to several SDGs and students must know them to advance in their achievement.Lull, C.; Llinares Palacios, JV.; Bautista, I.; Lidón, A. (2022). Increasing environmental sciences students' awareness of the link between soil and Sustainable Development Goals. IATED. 5708-5717. https://doi.org/10.21125/edulearn.2022.1344S5708571

Growth and formation of inverse GaP and InP opals

Opals consist of an ordered array of SiO2 spheres. This leads to a modulation of the refractive index and hence photonic stop bands behaviour over the visible/IR range of the electro-magnetic spectrum. The exact position of the stop bands depends on the size of the silica spheres. However, the refractive index contrast between the SiO2 spheres and air spaces is not great enough to open up a full photonic band gap (PBG), only the pseudogap. To increase the contrast the air spaces are filled with a material of high refractive index such as InP or GaP. To further increase the contrast the SiO2 is removed leaving a III-V framework as the inverse opal structure. By use of MOCVD we have been able to infill opals with InP and GaP to such a level that has supported the inversion of the composite forming a structure of air holes within a III-V lattice. XRD and Raman confirmed the quality of the III-V infill, while the extent of the infill was studied by SEM and reflectance measurements

Nanoscale Charge Density and Dynamics in Graphene Oxide

Graphene oxide (GO) is widely used as a component in thin film optoelectronic device structures for practical reasons because its electronic and optical properties can be controlled. Progress critically depends on elucidating the nanoscale electronic structure of GO. However, direct experimental access is challenging because of its disordered and nonconductive character. Here, we quantitatively mapped the nanoscopic charge distribution and charge dynamics of an individual GO sheet by using Kelvin probe force microscopy (KPFM). Charge domains are identified, presenting important charge interactions below distances of 20 nm. Charge dynamics with very long relaxation times of at least several hours and a logarithmic decay of the time correlation function are in excellent agreement with Monte Carlo simulations, revealing an universal hopping transport mechanism best described by Efros-Shklovskii''s law. © 2021 The Authors. Published by American Chemical Society

Broadening of band-gap in photonic crystals with optically saturated media

Due to strong absorption of the incident light, the media with high refractive index are considered restrictive for applications in photonic crystals (PhCs). The possibility to resolve this problem by optical saturation effectively minimizing the absorption of the PhC medium is discussed. Such approach might be promising for the significant broadening of the photonic band-gap.Comment: 10 page

Graphene oxide: key to efficient charge extraction and suppression of polaronic transport in hybrids with poly (3-hexylthiophene) nanoparticles

Nanoparticles (NPs) of conjugated polymers in intimate contact with sheets of graphene oxide (GO) constitute a promising class of water-dispersible nanohybrid materials of increased interest for the design of sustainable and improved optoelectronic thin-film devices, revealing properties exclusively pre-established upon their liquid-phase synthesis. In this context, we report for the first time the preparation of a P3HTNPs–GO nanohybrid employing a miniemulsion synthesis approach, whereby GO sheets dispersed in the aqueous phase serve as a surfactant. We show that this process uniquely favors a quinoid-like conformation of the P3HT chains of the resulting NPs well located onto individual GO sheets. The accompanied change in the electronic behavior of these P3HTNPs, consistently confirmed by the photoluminescence and Raman response of the hybrid in the liquid and solid states, respectively, as well as by the properties of the surface potential of isolated individual P3HTNPs–GO nano-objects, facilitates unprecedented charge transfer interactions between the two constituents. While the electrochemical performance of nanohybrid films is featured by fast charge transfer processes, compared to those taking place in pure P3HTNPs films, the loss of electrochromic effects in P3HTNPs–GO films additionally indicates the unusual suppression of polaronic charge transport processes typically encountered in P3HT. Thus, the established interface interactions in the P3HTNPs–GO hybrid enable a direct and highly efficient charge extraction channel via GO sheets. These findings are of relevance for the sustainable design of novel high-performance optoelectronic device structures based on water-dispersible conjugated polymer nanoparticles

Inclusión de los ODS en la enseñanza-aprendizaje de la Ciencia del Suelo

[EN] Soil management plays a key role in achieving the Sustainable Development Goals (SDGs). This is due to the fact that soils perform functions and provide essential services for human activities and the sustainability of ecosystems, such as: food production and other biomass production; the storage, filtering and transformation of nutrients, water, and carbon; habitat and biodiversity reserve; platform of human activities and element of the landscape; carbon sequestration. SDGs related to soil are SDG 2 (zero hunger), SDG 6 (clean water and sanitation), SDG 13 (climate action) and SDG 15 (life of terrestrial ecosystems). Universities must play a key role in achieving the SDGs by providing students with knowledge and skills to face environmental challenges from a sustainable development perspective. In the subject of Soil Science, the students were proposed to carry out an activity about the relationship of soil organic matter management with the SDGs. Students learning about soil functions, soil organic matter and their relationships with the SDGs was verified through the answers to various questions in the final exam.[ES] El manejo del suelo juega un papel clave en la consecución de los Objetivos de Desarrollo Sostenible (ODS). Esto se debe a que los suelos realizan funciones y prestan servicios esenciales para las actividades humanas y la sostenibilidad de los ecosistemas, como son: producción de alimentos y demás producción de biomasa; el almacenamiento, filtrado y la transformación de nutrientes, agua, y carbono; hábitat y reserva de la biodiversidad; plataforma de actividades humanas y elemento del paisaje; secuestro de carbono. ODS relacionados con el suelo son el ODS 2 (hambre cero), ODS 6 (agua limpia y saneamiento), ODS 13 (acción por el clima) y ODS 15 (vida de ecosistemas terrestres). Las universidades deben jugar un papel primordial en la consecución de los ODS proporcionando conocimiento y habilidades a los estudiantes para afrontar los desafíos medioambientales desde una perspectiva de desarrollo sostenible. En la materia de Edafología (Ciencia del suelo) se propuso a los estudiantes trabajar la relación del manejo de la materia orgánica del suelo con los ODS. El aprendizaje de los estudiantes de las funciones del suelo, la materia orgánica del suelo y su relación con los ODS fue verificado a través de las respuestas a varias preguntas en el examen final.La publicación de este trabajo ha sido parcialmente financiada por el proyecto de innovación educativa (PIME 20-21/224) concedido por el Vicerrectorado de Estudios, Calidad y Acreditación de la Universitat Politècncia de València (UPV).Lull Noguera, C.; Bautista Carrascosa, MI.; Lidón Cerezuela, AL.; Llinares Palacios, JV.; Soriano Soto, MD. (2021). Inclusión de los ODS en la enseñanza-aprendizaje de la Ciencia del Suelo. En IN-RED 2021: VII Congreso de Innovación Edicativa y Docencia en Red. Editorial Universitat Politècnica de València. 1133-1143. https://doi.org/10.4995/INRED2021.2021.13802OCS1133114

Graphene oxide: key to efficient charge extraction and suppression of polaronic transport in hybrids with poly (3-hexylthiophene) nanoparticles

Nanoparticles (NPs) of conjugated polymers in intimate contact with sheets of graphene oxide (GO) constitute a promising class of water-dispersible nanohybrid materials of increased interest for the design of sustainable and improved optoelectronic thin-film devices, revealing properties exclusively pre-established upon their liquid-phase synthesis. In this context, we report for the first time the preparation of a P3HTNPs-GO nanohybrid employing a miniemulsion synthesis approach, whereby GO sheets dispersed in the aqueous phase serve as a surfactant. We show that this process uniquely favors a quinoid-like conformation of the P3HT chains of the resulting NPs well located onto individual GO sheets. The accompanied change in the electronic behavior of these P3HTNPs, consistently confirmed by the photoluminescence and Raman response of the hybrid in the liquid and solid states, respectively, as well as by the properties of the surface potential of isolated individual P3HTNPs-GO nano-objects, facilitates unprecedented charge transfer interactions between the two constituents. While the electrochemical performance of nanohybrid films is featured by fast charge transfer processes, compared to those taking place in pure P3HTNPs films, the loss of electrochromic effects in P3HTNPs-GO films additionally indicates the unusual suppression of polaronic charge transport processes typically encountered in P3HT. Thus, the established interface interactions in the P3HTNPs-GO hybrid enable a direct and highly efficient charge extraction channel via GO sheets. These findings are of relevance for the sustainable design of novel high-performance optoelectronic device structures based on water-dispersible conjugated polymer nanoparticles.This work was funded by Spanish MCIN/AEI/10.13039/501100011033 under projects PID2019-104272RB-C51, PID2019-104272RB-C52, PID2019-104272RB-C55, and PID2019-104739GB-100. Financial support from Gobierno de Aragon (DGA) under project “Grupos Consolidados” T03_20R is acknowledged. E.C. is grateful for PhD grant BES2017-080020 funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investingin your future”. M.N.R.’s work was financed by grant PID2019-104272RB-C52/PRE2020-094503 funded by MCIN/AEI/10.13039/501100011033 and by “‘ESF Investingin your future”’. R.A. acknowledge ssupport from EU H2020“ESTEEM3”(Grant number 823717)and Graphene Flagship (881603)

Responses to environmental stress in plants adapted to Mediterranean gypsum habitats

[EN] Gypsum areas are stressful environments inhabited by gypsophytes, plants that are exclusive for such habitats, and by plants that grow on gypsum but also on other soil types, the so-called gypsovags. To investigate possible differences between gypsovags and gypsophytes with respect to basic stress response mechanisms, two common osmolytes, glycine betaine and total soluble sugars, as well as monovalent (Na+ and K+) and bivalent (Ca2+ and Mg2+) cations, were quantified, under field conditions, in two Iberian endemic gypsophytes (Gypsophila struthium subsp. hispanica and Ononis tridentata) and two common Mediterranean gypsovags (Rosmarinus officinalis and Helianthemum syriacum). Their spatial variation according to a topographic gradient and their temporal variation over a period of three successive seasons were correlated with climatic data and soil characteristics. This analysis confirmed that water stress is the main environmental stress factor in gypsum habitats, whereas the percentage of gypsum in the soil does not seem to play any relevant role in the activation of stress responses in plants. Glycine betaine may contribute to stress tolerance in the gypsophytes, but not in the gypsovags, according to the close correlation found between the level of this osmolyte and the gypsophily of the investigated taxa. Cation contents in the plants did not correlate with those present in the soil, but the gypsophytes have higher levels of Ca2+ and Mg2+ than the gypsovags, under all environmental conditions, which may represent an adaptation mechanism to their specific habitat,This work has been supported by the Spanish Ministry of Science and Innovation (Project CGL2008-00438/BOS), with contribution from the European Regional Development Fund.Llinares Palacios, JV.; Bautista Carrascosa, I.; Donat-Torres, MP.; Lidón, A.; Lull Noguera, C.; Mayoral García-Berlanga, O.; Wankhade, SD.... (2015). Responses to environmental stress in plants adapted to Mediterranean gypsum habitats. Notulae Scientia Biologicae. 7(1):37-44. https://doi.org/10.15835/nsb.7.1.9537S37447

Seasonal variation of Glycine Betaine in Plants from a Littoral Salt-Marsh in SE Spain

Supported by the Spanish Ministry of Science and Innovation (project CGL2008-00438/BOS), with contribution from the European Regional Development Fund.Boscaiu Neagu, MT.; Tifrea, M.; Donat-Torres, MP.; Mayoral García-Berlanga, O.; Llinares Palacios, JV.; Bautista Carrascosa, I.; Lidón Cerezuela, AL.... (2011). Seasonal variation of Glycine Betaine in Plants from a Littoral Salt-Marsh in SE Spain. Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca : Horticulture. 68(1):543-544. http://hdl.handle.net/10251/62931S54354468