Optical properties of colloidal II-VI semiconductor CdSe cores with ZnS and CdS multishell quantum dots (QDs) have been studied by experimental characterization and theoretical analysis. Due to the large number of energy states densely compacted in both conduction and valence bands of the quantum dots, strong interband and intraband optical couplings are induced by the multiphoton excitation, implicating an efficient fluorescence of such II-VI-based core-multishell CdSe QDs. This fact in combination with the advantage of the size tolerance of II-VI QDs with respect to the narrow fluorescence bandwidth make these systems excellent candidates for applications using fluorescence induced by multiphoton excitation.
MgNi-carbon nanotube composites were prepared by ballmilling the MgNi alloy and multiwalled carbon nanotubes ͑CNTs, 10 wt %͒ at various periods of time. It was confirmed by scanning electron microscope images that the MgNi alloy surface was modified by shorter and broken CNTs. The MgNi-CNT composites prepared by ballmilling after 60 min were found to show improved electrochemical properties with respect to the original MgNi alloy. In particular, the discharge capacity of the composite electrode increased from 400 to 480 mAh/g by surface modification with CNTs. The electrochemical reaction activity of the composite electrode was improved as confirmed by cyclic voltammogram. The analysis of the electrochemical impedance spectra showed that the double layer capacitance of the composite electrode increased under steady-state condition, which related to surface area of the particles. On the contrary, however, the improvement of the electrode cycle life was unsatisfactory, which probably attributed to the further generation of a new MgNi-CNT interface.Mg-based hydrogen storage alloys have attracted great attention as metal hydride ͑MH͒ electrode materials for Ni/MH battery and potential hydrogen storage materials for fuel cell vehicles because of their extremely high hydrogen storage capacity. 1 Recently, carbon nanotubes ͑CNTs͒ have been demonstrated to be new hydrogen storage materials in gas/solid reactions and electrochemical reactions, 2-4 although the hydrogen storage capacity of CNTs and graphite nanofibers have been reported to be greatly different compared to previous experimental results. [5][6][7] In particular, CNTs have a high stability in 6 N KOH electrolyte. Is it possible to prepare a composite material using Mg-based alloys and CNTs to improve electrochemical performance? It is well known that CNTs are formed by a rolled graphite sheet with a hemisphere closed on both sides. The chemical characteristics of CNTs and graphite are very close to each other. Inoue et al. 8 reported that two-step surface modifications for crystalline Mg 2 Ni alloy were tried to improve the charge/discharge characteristics. In particular, the subsequent surface modification with graphite led to a further increase in discharge capacity due to the improvement of electrocatalytic activity. It was also reported by the same group 9 that the electrochemical characteristics of the MgNi-graphite composites prepared by ballmilling were greatly enhanced with respect to the original MgNi alloy. The discharge capacity of 510 mAh/g of the MgNi-graphite composites with 20 wt % graphite was obtained after ballmilling for 10 min, higher than that of original MgNi alloy, 370 mAh/g. Therefore, it is possible to modify the MgNi alloy with CNTs for the improvement of electrochemical properties.In this work, an attempt is made to prepare the MgNi-CNT composites by ballmilling and to investigate their electrochemical properties in terms of initial discharge capacity and electrochemical activity.
ExperimentalCNTs were synthesized by the catalytic d...
We propose a highly sensitive bending sensor based on the intermodal interference properties of a strongly coupled two-dimentional waveguide array fiber (WAF). The interference resonance peaks formed by the SMF-WAF-SMF Mach-Zehnder interferometer are intrinsically the result of interference between the LP(01)-like supermode and other higher order supermodes, displaying supernormal sensitivity to bending in a wide curvature range. The bending sensitivity of the intermodal MZI is a quadratic function of curvature, and the resonance wavelength shift is up to 100 nm within a curvature range 0-10 m(-1). The fabrication reveals briefness, and temperature response shows little impact on the bend sensing precision. The high bending sensitivity and wide sensing range can make this device a candidate for bending discrimination and measurement in widespread areas.
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