Threshold voltage and space charge in organic transistors

We investigate rubrene single-crystal field-effect transistors, whose stability and reproducibility are sufficient to measure systematically the shift in threshold voltage as a function of channel length and source-drain voltage. The shift is due to space-charge transferred from the contacts, and can be modeled quantitatively without free fitting parameters, using Poisson's equation, and by assuming that the density of states in rubrene is that of a conventional inorganic semiconductor. Our results demonstrate the consistency, at the quantitative level, of a variety of recent experiments on rubrene crystals, and show how the use of FET measurements can enable the determination of microscopic parameters (e.g., the effective mass of charge carriers).Comment: 4 pages, 4 figure

Ambipolar Light-Emitting Transistors on Chemical Vapor Deposited Monolayer MoS2

We realize and investigate ionic liquid gated field-effect transistors (FETs) on large-area MoS2 monolayers grown by chemical vapor deposition (CVD). Under electron accumulation, the performance of these devices is comparable to that of FETs based on exfoliated flakes. FETs on CVD-grown material, however, exhibit clear ambipolar transport, which for MoS2 monolayers had not been reported previously. We exploit this property to estimate the bandgap {\Delta} of monolayer MoS2 directly from the device transfer curves and find {\Delta} $\approx$ 2.4-2.7 eV. In the ambipolar injection regime, we observe electroluminescence due to exciton recombination in MoS2, originating from the region close to the hole-injecting contact. Both the observed transport properties and the behavior of the electroluminescence can be consistently understood as due to the presence of defect states at an energy of 250-300 meV above the top of the valence band, acting as deep traps for holes. Our results are of technological relevance, as they show that devices with useful optoelectronic functionality can be realized on large-area MoS2 monolayers produced by controllable and scalable techniques

Progress in organic single-crystal field-effect transistors

Research on organic thin-film transistors tends to focus on improvements in device performance, but very little is understood about the ultimate limits of these devices, the microscopic physical mechanisms responsible for their limitations, and, more generally, the intrinsic transport properties of organic semiconductors. These topics are now being investigated through the study of transport in organic transistors realized using molecular single crystals of unprecedented chemical purity and structural quality. These studies are elucidating detailed microscopic aspects of the physics of organic semiconductors and corresponding devices and have also led to unforeseen high values for carrier mobility in these materials. Here, we discuss developments in this area and present a brief outlook on future goals that have come into experimental reac

Profitability and social performance of microfinance institutions : empirical evidence of relations between different types of variables

Las Instituciones Microfinancieras se contemplan como organizaciones que deben atender a objetivos económico-financieros, al tiempo que atienden a una finalidad social. Desde una perspectiva optimista, se ha considerado a los programas de microfinanzas como una nueva clave para el desarrollo, suponiendo que tienen por su propia naturaleza un importante valor añadido social. Este artículo contribuye, a partir de una amplia base de datos, al estudio de las variables asociadas a los objetivos sociales y financieros de las Instituciones Microfinancieras. En el conjunto de los datos, que reflejan grandes diferencias entre las entidades, no se observan relaciones entre el tamaño de las mismas, su rentabilidad y desempeño social.________________________________________________Microfinance is often considered a “double bottom line” sector, which refers to organizations that take care of their financial side and their social responsibility, trying to give minimum coverage to both. An optimistic vision of microfinance programs as a new key for development considered that they had, in themselves, an important social value. This paper contributes to the study of the relations between variables linked to social and financial purposes of a wide database of Microfinance Institutions. The data reflect large differences between the entities, but no relation is found between the size, profitability and social performance of institutions

Finanzas : Valoración de la importancia de las decisiones de financiación y costo de financiación de la empresa Electronic,S.A. para el periodo finalizado 2014-2015

El trabajo realizado se basó en la recopilación de información documental en cuanto a la parte teórica y aplicación de conocimientos en cuanto a la parte práctica. Abordamos el tema de finanzas como: generalidades de las finanzas, finanzas a largo plazo decisiones de financiación y el costo de financiación, nuestro trabajo se enfocó en el análisis de las decisiones de financiación esto debido a la importancia que tiene para los directivos de la empresa realizar decisiones más acertadas que aportaran más ganancia en el futuro de la empresa ELECTRONIC, S.A. en el periodo 2014-2015. Investigamos y explicamos diversas formas para calcular los costos de las fuentes específicas del capital por ejemplo el costo capital promedio ponderado el cual es la tasa de rendimiento interno que nuestra empresa deberá pagar a los inversores para incitarles a arriesgar su dinero en la compra de los títulos emitidos. Ejemplo: (acciones ordinarias, acciones preferentes, obligaciones, préstamos, etc.). Se realizó un caso práctico ficticio de la empresa ELECTRONIC, S.A. con el objetivo de poner en práctica los conocimientos que hemos adquirido en clases como en el presente trabajo. En nuestro caso práctico valoramos 4 proyectos los cuales denominamos A,B,C Y D, de los cuales aceptamos el proyecto C, lo hemos aceptado porque su TIR respectiva excede al CCMP esto significa que dicho proyecto nos generara mayor ganancia, y hemos rechazado los proyectos A,B, porque el rendimiento esperado es menor al del proyecto C, rechazamos el proyecto D porque su TIR está por debajo del CCMP esto significa que este proyecto no es viable ya que su rendimiento esperado es menor a nuestro costo de capital por ende no se obtendría ningún beneficio de dicha inversión

Tuning the charge transfer in Fx-TCNQ/rubrene single-crystal interfaces

Interfaces formed by two different organic semiconductors often exhibit a large conductivity, originating from transfer of charge between the constituent materials. The precise mechanisms driving charge transfer and determining its magnitude remain vastly unexplored, and are not understood microscopically. To start addressing this issue, we have performed a systematic study of highly reproducible single-crystal interfaces based on rubrene and Fx-TCNQ, a family of molecules whose electron affinity can be tuned by increasing the fluorine content. The combined analysis of transport and scanning Kelvin probe measurements reveals that the interfacial charge carrier density, resistivity, and activation energy correlate with the electron affinity of Fx-TCNQ crystals, with a higher affinity resulting in larger charge transfer. Although the transport properties can be described consistently and quantitatively using a mobility-edge model, we find that a quantitative analysis of charge transfer in terms of single-particle band diagrams reveals a discrepancy ~ 100 meV in the interfacial energy level alignment. We attribute the discrepancy to phenomena known to affect the energetics of organic semiconductors, which are neglected by a single-particle description, such as molecular relaxation and band-gap renormalization due to screening. The systematic behavior of the Fx-TCNQ/rubrene interfaces opens the possibility to investigate these phenomena experimentally, under controlled conditions

Análisis en los rotulados sobre productos alimenticios frente a la publicidad engañosa en puente piedra

En la presente investigación se ha tenido como objetivo analizar si los rotulados de productos alimenticios con publicidad engañosa afectan a los consumidores del distrito de Puente Piedra del presente año 2018, Además la presente tesis tiene un enfoque cualitativo, estudio de técnica de contrastación por cuanto es orientado a la compresión, el fin que persigue es de básica o pura y con diseño de estudio teoría fundamentada y un nivel o alcance de investigación descriptiva. También se utilizó la técnica de recolección de datos que comprende en 20 encuestados que se realizaron de forma anónima en el distrito de Puente Piedra, 10 entrevistas a abogados especialistas, y el análisis documental referente al tema de investigación. Los instrumentos de recolección de datos fueron el cuestionario, guía de entrevistas y la ficha de análisis documental. Por tanto la conclusión que se llegó en la presente tesis de investigación fue que el Instituto Nacional de Defensa de la Competencia y de la Protección de la Propiedad Intelectual (Indecopi), no fiscaliza de manera eficaz en los proveedores del distrito de Puente Piedra con respecto a la publicidad engañosa de productos alimenticios y los consumidores del distrito de Puente Piedra consideran que se ve afectados por la publicidad engañosa

Single-Crystal Organic Charge-Transfer Interfaces probed using Schottky-Gated Heterostructures

Organic semiconductors based on small conjugated molecules generally behave as insulators when undoped, but the hetero-interfaces of two such materials can show electrical conductivity as large as in a metal. Although charge transfer is commonly invoked to explain the phenomenon, the details of the process and the nature of the interfacial charge carriers remain largely unexplored. Here we use Schottky-gated heterostructures to probe the conducting layer at the interface between rubrene and PDIF-CN2 single crystals. Gate-modulated conductivity measurements demonstrate that interfacial transport is due to electrons, whose mobility exhibits band-like behavior from room temperature to ~ 150 K, and remains as high as ~ 1 cm2V-1s-1 at 30 K for the best devices. The electron density decreases linearly with decreasing temperature, an observation that can be explained quantitatively based on the heterostructure band diagram. These results elucidate the electronic structure of rubrene-PDIF-CN2 interfaces and show the potential of Schottky-gated organic heterostructures for the investigation of transport in molecular semiconductors.Comment: 37 pages, 9 Figures (including supplementary information

Lithium-ion conducting glass ceramics for electrostatic gating

We explore solid electrolytes for electrostatic gating using field-effect transistors (FETs) in which thin WSe$_2$ crystals are exfoliated and transferred onto a lithium-ion conducting glass ceramic substrate. For negative gate voltages ($V_G < 0$) the devices work equally well as ionic liquid gated FETs while offering specific advantages, whereas no transistor action is seen for $V_G>0$. For $V_G <0$ the devices can nevertheless be driven into the ambipolar injection regime by applying a large source-drain bias, and strong electroluminescence is observed when direct band-gap WSe$_2$ monolayers are used. Detecting and imaging the emitted light is much simpler in these FETs as compared to ionic liquid gated transistors, because the semiconductor surface is exposed (i.e., not covered by another material). Our results show that solid electrolytes are complementary to existing liquid gates, as they enable experiments not possible when the semiconductor is buried under the liquid itself