Reconfigurable,graphene-coated,chalcogenide nanowires with a sub-10-nm enantioselective sorting capability

Chiral surface plasmon polaritons(SPPs)produced by plasmonic nanowires can be used to enhance molecular spectroscopy for biosensing applications.Nevertheless,the switchable stereoselectivity and detection of various analytes are limited by a lack of switchable,chiral SPPs.Using both finite-element method simulations and analytic calculations,we present a graphene-coated chalcogenide(GCC)nanowire that produces mid-infrared,chiral SPPs.The chiral SPPs can be reversibly switched between“on”(transparent)and“off”(opaque)by non-volatile structural state transitions in the dielectric constants of the chalcogenide glass Ge2Sb2Te5.Furthermore,by controlling the Fermi energy of the graphene-coating layer,the nanowire can output either non-chiral or chiral SPPs.A thermal-electric model was built to illustrate the possibility of ultrafast on/off switching of the SPPs at the terminus of the nanowire.Finally,we show that a selective,lateral sorting of sub-10-nm enantiomers can be achieved via the GCC nanowire.Chiral nanoparticles with opposite handedness experience transverse forces that differ in both their sign and magnitude.Our design may pave the way for plasmonic nanowire networks and tunable nanophotonic devices,which require the ultrafast switching of SPPs,and provide a possible approach for a compact,enantiopure synthesis.

Three-dimensional flow field simulation of steady flow in the serrated diffusers and nozzles of valveless micro-pumps

This paper presents a three-dimensional flow field simulation of the steady flows through diffusers and nozzles with straight or serrated-sided walls to analyze the effect of the channel structure on the flow characteristics.The pressure and velocity profiles in the diffusers and the nozzles as well as the net volumetric flow rate are determined.Our simulation demonstrates that the pressure and velocity profiles in the serrated diffuser/nozzles are more complicated than those with the straight-sided wall,while the net steady flow rate with the straight-sided wall increases monotonically with the increase of the pressure difference,the steady flow rate with serrated sided walls increases gradually to reach a maximum and then decreases with the increase of the pressure difference.The results suggest that the number of the sawteeth plays a significant role in optimizing the design of serrated diffusers and nozzles for improving the transport efficiency of valveless micro-pumps.