Exploratory Investigation of Viscoelastic Nanoindentation on Polyvinyl Acetate

Nanoindentation load-displacement data of polyvinyl acetate (PVAc) was obtained at different temperatures ranging from ~20 oC to 42 oC using two novel equipments, Hysitron Triboindenter and Interfacial Force Microscopy (IFM). Load-displacement data was analyzed using viscoelastic contact theory and JKR contact mechanics theory. Load-displacement data obtained by Hysitron Triboindenter was analyzed using viscoelastic theory and shear creep compliance curves were obtained at different temperatures. Load-displacement data obtained by IFM was analyzed using viscoelastic theory and JKR contact mechanics theory and shear creep compliance curves were obtained at different temperatures. Small drift rate in load-displacement data obtained by Hysitron Triboindenter resulted in big error in shear creep compliance curves so that master shear creep compliance curve could not be formed. Glass transition temperature of PVAc was found at ~34 oC using shear creep compliance curves and it showed that glass transition temperature of PVAc is not unique. Adhesion forces between PVAc and tip was observed by IFM and invalidity of JKR method for PVAc was shown.Mechanical & Aerospace Engineerin

Indium antimonide photovoltaic cells for near-field thermophotovoltaics

International audienceIndium antimonide photovoltaic cells are specifically designed and fabricated for use in a near-field thermophotovoltaic device demonstrator. The optimum conditions for growing the p-n junction stack of the cell by means of solid-source molecular beam epitaxy are investigated. Then processing of circular micron-sized mesa structures, including passivation of the side walls, is described. The resulting photovoltaic cells, cooled down to around 77 K in order to operate optimally, exhibit excellent performances in the dark and under far-field illumination by thermal sources in the [600-1000] °C temperature range. A short-circuit current beyond 10 µA, open-circuit voltage reaching almost 85 mV, fill factor of 0.64 and electrical power at the maximum power point larger than 0.5 W are measured for the cell with the largest mesa diameter under the highest illumination. These results demonstrate that these photovoltaic cells will be suitable for measuring a near-field enhancement of the generated electrical power

Optimization of CVD parameters on 3D graphene foam structures with response surface methodology (RSM)

###EgeUn###Chemical vapour deposition (CVD) is one of the common methods to obtain high quality graphene structures with micro/macro pore sizes and large surface area. Finding the optimum growth parameters to produce high quality graphene structures is often difficult and time consuming. In this study, foam like three dimensional (F-3D) graphene structures were obtained by CVD to find the optimum growth parameters and the effects of the these parameters on the specific surface area of the F-3D graphene structures were analysed in details using response surface methodology (RSM) approach based on the central composite design. Additionally, surface characterization of 3D graphene structures were performed with Raman spectroscopy and scanning electron microscope (SEM) and the specific surface area of graphene foam measured with BET technique was found 870 m(2) g(-1), under the optimum growth parameters. The analysis of variance (ANOVA) results showed that the applied model was statistically significant to obtain high F (88.46) and very low P (<0.0001) values. Mathematical equation was created for the optimized growth parameters after reviewing the results of ANOVA.Sabanci University Nanotechnology Research and Applications Center (SUNUM)Sabanci University; Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [115Y344]The equipment and characterization support provided by the Sabanci University Nanotechnology Research and Applications Center (SUNUM). The Scientific and Technological Research Council of Turkey (TUBITAK) funded this study under the grant No: 115Y344. The authors are grateful toSUNUMand TUBITAK for their valuable supports

Electrochemical Glucose Sensor using Single-Wall Carbon Nanotube Field Effect Transistor

In this paper, we present a simple yet sensitive method for glucose sensing using carbon nanotube field-effect transistor (CNTFET) based biosensor. The CNTs were well-dispersed to form CNT networks and maintain functional connectivity among CNTs, which increases the electron transfer through the network and thus, the electronic readout. Moreover, glucose oxidase (GOx) molecules are immobilized by CNT functionalization to form effective and sensitive CNT networks as FET channel. The CNTs are functionalized with linkers (1-pyrenebutanoic acid succinimidyl ester) to immobilize GOx on CNTs, where GOx serves as a mediator between CNTs and glucose for electron transfer. The liquid analyte glucose is adsorbed on CNTs via GOx and linkers by releasing additional electrons in the CNTFET channel and thus, increasing the CNTFET readout current. The binding of the target glucose molecules and GOx emulates the gate potential of FET channel and the electronic response of the sensor is recorded in real-time. Moreover, the variations in electronic readout of CNTFET biosensor are observed and is stipulated due to variation in CNT dispersion on each device. Overall, this work presents a simple, fast, sensitive, low-cost, and low concentration (0.01 mM) detection of glucose using CNTFET sensors

Mesures expérimentales du transfert radiatif en champ proche et de la conversion thermophotovoltaïque

National audienc

Design of Pt-Supported 1D and 3D Multilayer Graphene-Based Structural Composite Electrodes with Controlled Morphology by Core–Shell Electrospinning/Electrospraying

Platinum (Pt)-decorated graphene-based carbon composite electrodes with controlled dimensionality were successfully fabricated via core–shell electrospinning/electrospraying techniques. In this process, multilayer graphene sheets were converted into the three different forms, fiber, sphere, and foam, by tailoring the polymer concentration, molecular weight of polymer, and applied voltage. As polymer concentration increased, continuous fibers were produced, whereas decreasing polymer concentration caused the formation of graphene-based foam. In addition, the reduction in polymer molecular weight in electrospun solution led to the creation of three-dimensional (3D) spherical structures. In this work, graphene-based foam was produced for the first time by utilizing core–shell electrospraying technology instead of available chemical vapor deposition techniques. The effect of morphologies and dimensions of carbonized graphene-based carbon electrodes on its electrochemical behavior was investigated by cyclic voltammetry and galvanostatic charge–discharge methods. Among the three different electrodes, Pt-supported 3D graphene-based spheres showed the highest specific capacitance of 118 F/g at a scan rate of 1 mV/s owing to the homogeneous decoration of Pt particles with a small diameter of 4 nm on the surface. After 1000 cycles of charging–discharging, Pt-decorated graphene-based structures showed high cyclic stability and retention of capacitance, indicating their potential as high-performance electrodes for energy storage devices

Near-field radiative heat transfer experiments for thermophotovoltaic conversion

International audienc

Near-field radiative heat transfer experiments and thermophotovoltaic conversion

International audienc