The dependence of the wettability of graphene on the nature of the underlying substrate remains only partially understood. Here, we systematically investigate the role of liquid-substrate interactions on the wettability of graphene by varying the area fraction of suspended graphene from 0 to 95% by means of nanotextured substrates. We find that completely suspended graphene exhibits the highest water contact angle (85° ± 5°) compared to partially suspended or supported graphene, regardless of the hydrophobicity (hydrophilicity) of the substrate. Further, 80% of the long-range water-substrate interactions are screened by the graphene monolayer, the wettability of which is primarily determined by short-range graphene-liquid interactions. By its well-defined chemical and geometrical properties, supported graphene therefore provides a model system to elucidate the relative contribution of short and long range interactions to the macroscopic contact angle.
Silver metal nanoparticles are among the most widely studied nanoparticles. They are widely used heterogeneous catalysts used for many purposes such as antisepsis, hydrogenation, and carboxylation but also for the trapping of xenon in nuclear test and detection facilities. The catalytic activity and adsorption capacity of silver nanoparticles, which depend on their size distribution and dispersion on the support, generally decrease with time because of agglomeration of the metal into larger particles. In this study, we quantified the sintering process of silver nanoparticles supported in Zeolite Socony Mobil 5 (ZSM-5) zeolite. It was found that 85% of the sintering process of the silver nanoparticles was driven by Ostwald ripening. We found that silver nanoparticles are trapped in porous cavities that are meso- or macroporous defects in the zeolite. Although this phenomenon limits the amount of silver that diffuses to the zeolite external surface, it does not prevent the formation of large particles by atom migration. The presence of chloride reactants facilitates the sintering phenomenon by lowering the energy barrier. This finding provides a rational basis for the design of silver-containing zeolite-based heterogeneous catalysts.
In systems with multiple radiation detectors, time synchronization of the data collected from different detectors is essential to reconstruct multi-detector events such as scattering and coincidences. In cases where the number of detectors exceeds the readout channels in a single data acquisition electronics module, multiple modules have to be synchronized, which is traditionally accomplished by distributing clocks and triggers via dedicated connections.To eliminate this added cabling complexity in the case of a new radioactive gas detection system prototype under development at the French Atomic Energy Commission, we implemented time synchronization between multiple XIA Pixie-Net detector readout modules through the existing Ethernet network, based on the IEEE 1588 precision time protocol. The detector system is dedicated to the measurement of radioactive gases at low activity and consists of eight large silicon pixels and two NaI(Tl) detectors, instrumented with a total of three 4-channel Pixie-Net modules. Detecting NaI(Tl)/silicon coincidences will make it possible to identify each radioisotope present in the sample. To allow these identifications at low activities, the Pixie-Net modules must be synchronized to a precision well below the targeted coincidence window of 500-1000 ns. Being equipped with an Ethernet PHY compatible with IEEE 1588 and synchronous Ethernet that outputs a locally generated but system-wide synchronized clock, the Pixie-Net can operate its analog to digital converters and digital processing circuitry with that clock and match time stamps for captured data across the three modules. Depending on the network configuration and synchronization method, the implementation is capable to achieve timing precisions between 300 ns and 200 ps. Index Terms-Radioxenon, network time synchronization, precision time protocol, coincidence detection. W. Hennig (whennig@xia.com) and S. Hoover are with XIA LLC, Hayward, CA 94544 USA. V. Thomas and O. Delaune are with CEA, DAM,
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