Superconductivity at 44.4 K achieved by intercalating EMIM^(+) into FeSe

Superconductivity with transition temperature Tc above 40 K was observed in protonated FeSe(Hy-FeSe)previously with the ionic liquid EMIM-BF4 used in the electrochemical process.However,the real superconducting phase is not clear until now.And detailed structural,magnetization,and electrical transport measurements are lacking.By using similar protonating technique on FeSe single crystals,we obtain superconducting samples with Tc above 40 K.We show that the obtained superconducting phase is not Hy-FeSe but actually an organic-ion(C6H11N+2 referred to as EMIM^(+))-intercalated phase(EMIM)xFeSe.By using x-ray diffraction technique,two sets of index peaks corresponding to different c-axis lattice constants are detected in the obtained samples,which belong to the newly formed phase of intercalated(EMIM)xFeSe and the residual FeSe,respectively.The superconductivity of(EMIM)xFeSe with Tc of 44.4 K is confirmed by resistivity and magnetic susceptibility measurements.Temperature dependence of resistivity with different applied magnetic fields reveals that the upper critical field Hc2 is quite high,while the irreversibility field Hirr is suppressed quickly with increasing temperature till about 20 K.This indicates that the resultant compound has a high anisotropy with a large spacing between the FeSe layers.

Molecule-based vertical transistor via intermolecular charge transport throughπ-πstacking

Theπ-πstacking is a well-recognized intermolecular interaction that is responsible for the construction of electron hopping channels in numerous conducting frameworks/aggregates.However,the exact role ofπ-to-πchannels within typical single crystalline organic semiconductors remains unclear as the orientations of these molecules are diverse,and their control usually requires additional side chain groups that misrepresent the intrinsic properties of the original semiconducting molecules.Therefore,the construction of conduction channels with intrinsicπ-πstacking in the molecule-based device is crucial for the utilization of their unique transport characteristics and understanding of the transport mechanism.To this end,we present a molecular intercalation strategy that integrates two-dimensional layered materials with functional organic semiconductor molecules for functional molecule-based electronics.Various organic semiconductor molecules can be effectively intercalated into the van der Waals gaps of semi-metallic TaS_(2) withπ-πstacking configuration and controlled intercalant content.Our results show that the vertical charge transport in the stacking direction shows a tunneling-dominated mechanism that strongly depends on the molecular structures.Furthermore,we demonstrated a new type of molecule-based vertical transistor in which TaS_(2) andπ-πstacked organic molecules function as the electrical contact and the active channel,respectively.On/off ratios as high as 447 are achieved under electrostatic modulation in ionic liquid,comparable to the current state-of-the-art molecular transistors.Our study provides an ideal platform for probing intrinsic charge transport acrossπ-πstacked conjugated molecules and also a feasible approach for the construction of high-performance molecule-based electronic devices.

Intercalation and hybrid heterostructure integration of two-dimensional atomic crystals with functional organic semiconductor molecules

Van der Waals(vdW)integration affords semiconductor heterostructures without constrains of lattice matching and opens up a new realm of functional devices by design.A particularly interesting approach is the electrochemical intercalation of two-dimensional(2D)atomic crystal and formation of superlattices,which can provide scalable production of novel vdW heterostructures.However,this approach has been limited to the use of organic cations with non-functional aliphatic chains,therefore failed to take the advantage of the vast potentials in molecular functionalities(electronic,photonic,magnetic,etc.).Here we report the integration of 2D crystal(MoS_(2),WS_(2),highly oriented pyrolytic graphite(HOPG),WSe_(2) as model systems)with electrochemically inert organic molecules that possess semiconducting characteristics(including perylene-3,4,9,10-tetracarboxylic dianhydride(PTCDA),pentacene and fullerene),through on-chip electrochemical intercalation.An unprecedented long-range spatial feature of intercalation has been achieved,which allowed facile assembly of a vertical MoS_(2)-PTCDA-Si junction.The intercalated heterostructure shows significant modulation of the lateral transport,and leads to a molecular tunneling characteristic at the vertical direction.The general intercalation of charge neutral and functional molecules defines a versatile platform of inorganic/organic hybrid vdW heterostructures with significantly extended molecular functional building blocks,holding great promise in future design of nano/quantum devices.

Intercalation-deintercalation design in MXenes for high-performance supercapacitors

MXene is a new intercalation pseudocapacitive electrode material for supercapacitor application.Intensifying fast ion diffusion is significantly essential for MXene to achieve excellent electrochemical performance.The expansion of interlayer void by traditional spontaneous species intercalation always leads to a slight increase in capacitance due to the existence of species sacrificing the smooth diffusion of electrolyte ions.Herein,an effective intercalation-deintercalation interlayer design strategy is proposed to help MXene achieve higher capacitance.Electrochemical cation intercalation leads to the expansion of interlayer space.After electrochemical cation extraction,intercalated cations are deintercalated mostly,leaving a small number of cations trapped in the interlayer silt and serving as pillars to maintain the interlayer space,offering an open,unobstructed interlayer space for better ion migration and storage.Also,a preferred surface with more-O terminations for redox reaction is created due to the reaction between cations and-OH terminations.As a result,the processed MXene delivers a much improved capacitance compared to that of the original Ti_(3)C_(2)T_(x)electrode(T stands for the surface termination groups,such as-OH,-F,and-O).This study demonstrates an improvement of electrochemical performance of MXene electrodes by controlling the interlayer structure and surface chemistry.