We fabricate and characterize vertical molecular junctions consisting of self-assembled monolayers of diarylethene (DAE) contacted by a multilayer graphene (MLG) electrode on the top and gold on the bottom. The DAE molecular junctions show two stable electrical states, a closed state (high conductance) or an open state (low conductance), which are created upon illumination with UV or visible light, respectively. For the Au-DAE-MLG junction structure, we observe that the current levels between the two conductance states are separated by 2 orders of magnitude. However, in a real-time measurement, we observe only unidirectional switching behavior from the open to the closed state.
SummaryWe report the development of a novel method to determine the thermopower of atomic-sized gold contacts at low temperature. For these measurements a mechanically controllable break junction (MCBJ) system is used and a laser source generates a temperature difference of a few kelvins across the junction to create a thermo-voltage. Since the temperature difference enters directly into the Seebeck coefficient S = −ΔV/ΔT, the determination of the temperature plays an important role. We present a method for the determination of the temperature difference using a combination of a finite element simulation, which reveals the temperature distribution of the sample, and the measurement of the resistance change due to laser heating of sensor leads on both sides next to the junction. Our results for the measured thermopower are in agreement with recent reports in the literature.
La gran cantidad de coque de petróleo producido en Venezuela, conllevó a su uso como controlador de filtrado en fluidos base aceite. Inicialmente el coque se sometió a un proceso de extracción de aceite mediante el método Soxhlet y extracción de azufre mediante microondas. Seguidamente se le realizó una Espectroscopia de Infrarrojo (IR) y se comparó con otra espectroscopia del coque de petróleo natural, donde quedó evidenciado la efectividad del proceso aplicado. Se formularon cuatro (4) fluidos de perforación (12 lpg) con coque como controlador de filtrado, variando su concentración en 6, 8, 10 y 12 lb/bl y después de un envejecimiento dinámico (300°F, 100 lpcm) se estudiaron las propiedades físicas de viscosidad plástica, punto cedente, gel 10 s, gel 10 min y filtrado, obteniéndose rango de valores de 25,3-26,3; 5,7-6,3; 4-5; 7-10 y 10,3-10,9 respectivamente. Un estudio estadístico de parcelas divididas demostró que existieron diferencias estadísticas significativas entre las propiedades físicas de los fluidos formulados y las propiedades físicas de un fluido patrón con lignito como controlador de filtrado. Se concluyó que a pesar de las diferencias estadísticas presentadas es posible el uso de coque de petróleo como controlador de filtrado para las condiciones en estudio.
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