This work reports a facile and cost-effective method for synthesizing photoactive α-Fe(2)O(3) films as well as their performances when used as photoanodes for water oxidation. Transparent α-Fe(2)O(3) mesoporous films were fabricated by template-directed sol-gel chemistry coupled with the dip-coating approach, followed by annealing at various temperatures from 350 °C to 750 °C in air. α-Fe(2)O(3) films were characterized by X-ray diffraction, XPS, FE-SEM and electrochemical measurements. The photoelectrochemical performance of α-Fe(2)O(3) photoanodes was characterized and optimized through the deposition of Co-based co-catalysts via different methods (impregnation, electro-deposition and photo-electro-deposition). Interestingly, the resulting hematite films heat-treated at relatively low temperature (500 °C), and therefore devoid of any extrinsic dopant, achieve light-driven water oxidation under near-to-neutral (pH = 8) aqueous conditions after decoration with a Co catalyst. The onset potential is 0.75 V vs. the reversible hydrogen electrode (RHE), thus corresponding to 450 mV light-induced underpotential, although modest photocurrent density values (40 μA cm(-2)) are obtained below 1.23 V vs. RHE. These new materials with a very large interfacial area in contact with the electrolyte and allowing for a high loading of water oxidation catalysts open new avenues for the optimization of photo-electrochemical water splitting.
SummaryThe hypersensitive response has been mostly studied by molecular and biochemical methods after sample destruction. The development of imaging techniques allows the monitoring of physiological changes before any signs of cell death. Here, we follow the early steps of a hypersensitive-like response induced by the bacterial elicitor harpin in Nicotiana sp. We describe cytological modifications after inoculation of the harpin protein, using confocal fluorescence microscopy (CFM) and optical coherence tomography (OCT), an interferometric-based microscopy. The changes detected by CFM occurred 5 h after harpin infiltration and corresponded to a redistribution of the chloroplasts from the upper to the inner regions of the palisade mesophyll cells which could be related to a perturbation in the microtubule network. Using OCT, we were able to detect a decrease in chloroplast backscattered signal as early as 30 min after harpin infiltration. A simple physical model, which accounted for the structure and distribution of thylakoid membranes, suggested that this loss of scattering could be associated with a modification in the refractive index of the thylakoid membranes. Our OCT observations were correlated with a decrease in photosynthesis, emphasizing changes in chloroplast structure as one of the earliest hallmarks of plant hypersensitive cell death.
Nanoelectromechanical Systems (NEMS) are among the best candidates to measure interactions at nanoscale [1,2,3,4,5,6], especially when resonating oscillators are used with high quality factor [7,8]. Despite many efforts [9,10], efficient and easy actuation in NEMS remains an issue [11]. The mechanism that we propose, thermally mediated Center Of Mass (COM) displacements, represents a new actuation scheme for NEMS and MEMS. To demonstrate this scheme efficiency we show how mechanical nanodisplacements of a MEMS is triggered using modulated X-ray microbeams. The MEMS is a microswing constituted by a Ge microcrystal attached to a Si microcantilever. The interaction is mediated by the Ge absorption of the intensity modulated X-ray microbeam impinging on the microcrystal. The small but finite thermal expansion of the Ge microcrystal is large enough to force a nanodisplacement of the Ge microcrystal COM glued on a Si microlever. The inverse mechanism can be envisaged: MEMS can be used to shape X-ray beams. A Si microlever can be a high frequency X-ray beam chopper for time studies in biology and chemistry. Previous studies of light mechanical effects on MEMS and NEMS have shown radiation pressure [12] or thermal switch effect in the lever [13] as actuation mechanism for mechanical systems. We show that these effects are not effective enough to induce the observed oscillation amplitude in our experiments. The experimental set-up is presented in fig.
We report on the imaging of biological cells including living neurons by a dedicated fibered interferometric scanning optical microscope. The topography and surface roughness of mouse fibroblasts and hippocampal neurons are clearly revealed. This straightforward far-field technique allows fast, high resolution observation of samples in liquids without lengthy alignment procedures or costly components.
An oxide isolated complementary SiGe base bipolar technology is presented that incorporates JFETs, poly-and thin-film resistors, capacitors and Schottky Barrier diodes for high-precision, high-voltage, high speed, low-noise analog applications at significantly reduced package size.
Concentrator photovoltaic (CPV) systems are one of the most promising technologies for future energy supply. Several studies reported the interest of using a Fresnel lens coupled with a secondary optical element in such a system. For high concentration factor, the optimization of the optical configuration plays a key role regarding electrical performances. On the other hand, the thermal management of the solar cell is also critical to ensure a better module efficiency. This paper presents a study of a Â1024 CPV system performances and a methodology for estimating the optical chain efficiency, the cell temperature impact and the alignment requirements. Module efficiencies were then measured as a function of the cell temperature and correlated to optical performances through current-tension characterizations under real solar illumination conditions and the estimation of the power density received by the solar cell. The system yield was up to 27% for a cell temperature around 30 C, confirming that high concentration ratio should be of great interest in the near future. A 1D model was also developed in order to quantify the possible improvements of this CPV system. Using a solar cell with an efficiency of 36.7% at Â600, we then demonstrated that the Â1024 CPV system could reach up to 30% in standard test conditions.
Time-resolved x-ray experiments require intensity modulation at high frequencies (advanced rotating choppers have nowadays reached the kHz range). We here demonstrate that a silicon microlever oscillating at 13 kHz with nanometric amplitude can be used as a high frequency x-ray chopper. We claim that using micro-and nanoelectromechanical systems (MEMS and NEMS), it will be possible to achieve higher frequencies in excess of hundreds of megahertz. Working at such a frequency can open a wealth of possibilities in chemistry, biology and physics time-resolved experiments.
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