Research Of 2D Material-based Memories And Hybrid Nanogenerators

The new generation of electronic devices have already become one of the most important technology-driving-force for the development of modern societies during the last half-a-century.Among all of them,electronic memories are essential elements of most modern integrated circuits,as they allow storing information in an easy,cheap and fast way.The use of two dimensional(2D)materials to improve the capabilities of electronic devices is a promising strategy that has recently gained much interest in both academe and industry.However,and while the research in 2D metallic and semiconducting materials is well established,detailed knowledge and applications of 2D insulators are still scarce.In this report we study the presence of resistive switching(RS)in multilayer hexagonal boron nitride(h-BN)using different electrode materials,and we engineer a family of h-BN-based resistive random access memories with tuneable capabilities.The devices show the coexistence of forming-free bipolar and threshold type RS with low operation voltages down to 0.4 V,high current on/off ratio up to 106,long retention times above 10 hours,and low variability.The RS is driven by the grain boundaries(GBs)in the polycrystalline h-BN stack,which allow the penetration of metallic ions from adjacent electrodes.This reaction can be boosted by the generation of B vacancies,which are more abundant at the GBs.To the best of our knowledge,h-BN is the first 2D material showing the coexistence of bipolar and threshold RS,which may open the door to additional functionalities and applications.In order to realize the fabrication of self-powered nanoscale electronic devices in the future,we also presented one piezoelelcric nanogenerator in this work by using ZnO nanowire arrays.In energy harvesters using arrays of nanowires(NWs),a larger density of NWs should imply higher performance,but in reality the efficiency of the cells is always deteriorated due to NW collision.Impeding the formation of NW clusters in highly populated arrays is essential to ensure effective NW movement and provide a high surface area.Here we present a cost-effective methodology to avoid NW clustering in highly populated arrays of nanowires.First,a flexible polymer is intercalated between the NWs by spin coating,and then its height is tuned by controlled oxygen plasma etching.The resulting optimized energy harvesters show an enhancement in the piezoelectric effect by a factor of 80,as well as a notable improvement in the photoelectric response.The relationship between the height of the intercalated polymer and the piezo potential produced by the nanowires is simulated by the finite element method calculations,which support the experimental observations.