Organic ambipolar semiconductors for TFT applications

In the last years we have devoted some effort to the search of new high-mobility semiconductors with ambipolar performances, good processability and environmental stability. Our approach, which is one of the most widely used, consists in the combination of donor and acceptor moieties in the conjugated skeleton, which allows fine tuning of the frontier molecular orbitals. For OTFT applications, low-lying HOMOs are essential to resist air oxidation and thus increase device stability. However, if the HOMO energy is too low, the resulting barrier to hole injection may compromise the transistor performance. Thus, a delicate balance between these two effects is needed. In particular, we have combined naphthaleneimide-derived moieties as electron accepting groups with electron-rich oligothiophene fragments. In these materials, we have found that the presence of ambipolar transport in these planar molecules can be understood on the basis of three interrelated properties: (i) the absence of skeletal distortions allows closer intermolecular pi-pi stacking and enhanced intramolecular pi-conjugation, (ii) increased pi-conjugation raises the HOMO energy, which approaches the Fermi level of common used electrodes; and (iii) more planar structures translate into lower Marcus reorganization energies. However, one of the limitations of these types of semiconductors is the presence of a molecular dipole moment, which forces the molecules to pack with pairwise intermolecular interactions orienting the naphthaleneimide cores in opposite directions, decreasing in some cases molecular orbitals overlapping. In recent contributions, we have devoted our efforts to analyze the effect of molecular interactions, through chemical modifications in order to induce parallel and antiparallel molecular packing, on the electronic properties of ambipolar semiconductors.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Understanding organic materials performance in field-effect transistors

Comunicación oralIn the last years, much of our effort has been devoted to the search and study of new high-mobility semiconductors for organic thin film transistors. The approach used for the materials design has been two-fold: (i) the combination of donor and acceptor moieties in the pi-conjugated skeleton, which allows fine tuning of the frontier molecular orbitals, being this necessary for achieving electron/hole or ambipolar transport and ambient stability; and (ii) rational selection of the type and positioning of specific solubilizing substituents ensuring processability, which is essential to make these materials scalable to industry. However, material processability should be attained minimizing a negative effect on charge transport. Therefore, proper energy levels, planar molecular conformations, close intermolecular pi-pi stacking and adequate thin film crystallinity need to be maintained upon alkyl substitution. In this communication, several examples of molecular and polymeric materials are shown. A rational design, guided by experimental and theoretical evidences, has prompted modifications on their conjugated skeletons, donor/acceptor subunits ratio and/or selection of proper alkyl solubilizing chains, which induce noticeable changes in their electronic performances. The main aim of these studies is the basic understanding of charge transport in organic materials. For this end, we will use Raman spectroscopy and DFT quantum-chemical calculations as important tools for materials characterization.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

A financial analysis of born-global firms: evidence from Spain

From the beginning of the 1970s to the present day, significant changes have taken place in the competitive and organizational behavior of small and medium-sized companies (SMEs). Recently, some of these factors have applied more intensively, and this has given rise to growth in the number of new companies that undertake overseas operations almost immediately (known as born globals). The phenomenon of early internationalization is relatively recent, so there are still many aspects that need to be studied. The objective of this study is to contribute to the scarce empirical literature existing in Spain on this topic, by providing evidence on the possible differences in character of the born-global firms compared with the rest of exporting companies. To this end, the focus of the study is on the analysis of variables such as the size and sector of activity of these companies, and their principal economic and financial magnitudes. A sample of 1,324 Spanish SMEs that were exporting in 2007 was surveyed; of this total approximately 12% identified themselves as having adopted early internationalization. The results obtained indicate that the born-global firms are, on average, smaller; they are classified mostly to the services sector; and they are much more leveraged than the rest of Spanish SMEs that export

CaloriNet: From silhouettes to calorie estimation in private environments

We propose a novel deep fusion architecture, CaloriNet, for the online estimation of energy expenditure for free living monitoring in private environments, where RGB data is discarded and replaced by silhouettes. Our fused convolutional neural network architecture is trainable end-to-end, to estimate calorie expenditure, using temporal foreground silhouettes alongside accelerometer data. The network is trained and cross-validated on a publicly available dataset, SPHERE_RGBD + Inertial_calorie. Results show state-of-the-art minimum error on the estimation of energy expenditure (calories per minute), outperforming alternative, standard and single-modal techniques.Comment: 11 pages, 7 figure

Social Media Behaviour Analysis in Disaster-Response Messages of Floods and Heat Waves via Artificial Intelligence

This paper analyses social media data in multiple disaster-related collections of floods and heat waves in the UK. The proposed method uses machine learning classifiers based on deep bidirectional neural networks trained on benchmark datasets of disaster responses and extreme events. The resulting models are applied to perform a qualitative analysis via topic inference in text data. We further analyse a set of behavioural indicators and match them with climate variables via decoding synoptical records to analyse thermal comfort. We highlight the advantages of aligning behavioural indicators along with climate variables to provide with 7 additional valuable information to be considered especially in different phases of a disaster and applicable to extreme weather periods. The positiveness of messages is around 8% for disaster, 1% for disaster and medical response, 7% for disaster and humanitarian related messages. This shows the reliability of such data for our case studies. We show the transferability of this approach to be applied to any social media data collection

Edema mamario ante y post parto en vacas lecheras en la Finca San José de las Ramplas, Mateare, Managua, mayo – agosto 2013

Con el objeto de evaluar la prevalencia del edema mamario bovino, se desarrolló el presente estudio de caso en la Finca San José de las Ramplas, municipio de Mateare, Managua. Se analizaron 4 casos positivos a edema de la glándula mamaria ante y post parto, de un total de 34 vacas lactantes en el periodo de mayo-agosto del 2013. El edema mamario consiste en la acumulación excesiva de fluidos en el espacio intercelular que puede generar efectos negativos en el animal, tales como: estrés, dolor, aumento en la susceptibilidad por heridas a causa de la tensión de la piel, mayor probabilidad de sufrir mastitis, daño al pezón, ruptura del ligamento suspensorio de la ubre, disminución de la producción de leche e inconvenientes en el ordeño. El diagnóstico de la alteración se realizó a partir de la inspección de los casos positivos detectados mediante examen clínico y el análisis comparativo con las tablas 1 y 2 de calificación de presencia de edema mamario; se realizaron pruebas complementarias para diagnóstico de mastitis, la anamnesis y conjuntamente el llenado de la hoja clínica; recolectando los datos para analizar las causas y factores predisponentes que conllevaron a esta patología en las vacas; obteniendo una prevalencia de 11.76 % con respecto a la población de la categoría lactante. Esta patología se presenta comúnmente en vaquillas y vacas en el preparto, post parto y primigestas, causada por el cambio brusco en la alimentación, escaso consumo de agua, y primer parto a mayor edad. Para prevenir esta patología, se recomienda conocer el manejo del hato bovino, indagar sobre la correcta alimentación e implementar los programas nutricionales de acuerdo con los recursos que existen en la finca y que suplan las necesidades de cada categoría, implementar un plan sanitario que incluya la suplementación con vitaminas y minerales de acuerdo a su estado productivo y reproductivo para el correcto funcionamiento del bovino según sus necesidades y capacitar al personal de la finca en cuanto a las normas de bioseguridad y manejo adecuado de cada categoría del hato

Organic semiconductors: The effect of small modifications on device performance

Invited oral presentationIn the search on new high-mobiliity semiconductors with ambipolar performances, good processability and excellent environmental stability, diverse synthetic strategies have been approached. One of the most widely used consists in the alternation of donor and acceptor moieties in the conjugated skeleton, which allows fine tuning of the frontier molecular orbitals. For OTFT applications,low-lying HOMOs are essential to resist air oxidation and thus increase device stability. However, if the HOMO energy is too low, the resulting barrier to hole injection may compromise the transistor performance. Thus, a delicate balance between these two effects is needed. Furthermore, high performance solution-processable materials require the correct selection and positioning of the specific solubilizing substituents in order to achieve proper HOMO and LUMO energy levels, planar molecular conformations, close intermolecular pi-pi stacking, and proper thin film crystallinity. In this communication, several examples of molecular and polymeric materials where modifications on their conjugated skeletons, donor/acceptor subunits ratio and/or the selection of proper alkyl solubilizing chains induce noticeable changes in their electronic performances.Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tec

Understanding the structure-property correlations of n-type organic semiconductors in OFETs

In the organic electronic research field, the development of high-performance unipolar n-type semiconductors is still challenging. Here we present an in-depth study of a series of ladder-type semiconductors, which due to their all-acceptor backbones, exhibit unipolar n-type transport in OTFTs. It is well know that the performance of organic semiconductors is governed not only by their molecular structures but also by their intermolecular assembly in the solid state. Thus, highly planar backbones are beneficial for a good molecular packing and film ordering leading to good charge transport characteristics. In this contribution, we study a series of BTI small molecules and polymers, both from a molecular and from a supramolecular point of view, in order to establish useful structure-property relationships that may guide the rational synthesis of new and improved materials. To carry out this study, we make use of different spectroscopic techniques, supported by quantum theoretical calculations at the DFT level.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Understanding polymer orientation at the interface by SERS

In the organic electronic research field, it is well known that the largest contribution to charge transport occurs within the first few nanometers of the semiconductor near the dielectric interface. Surface Enhanced Raman spectroscopy (SERS) appears as an easy and straightforward technique to analyze this buried interface and to provide useful information on molecular orientation at the device active layer. Here we present the study of the molecular orientation of the widely studied P(NDI2OD-T2) polymer at the semiconductor/dielectric and semiconductor/metal interfaces using SERS and DFT calculations. Our first SERS results show a relative intensification of selected normal modes, which indicates that the orientation of the polymer changes from a face-on (before annealing treatment) to and edge-on disposition after melt annealing, being this in good agreement with the previous results gathered from other techniques (Figure 1).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech