In Situ Study Of Interfaces Characteristics Of Advanced Materials And Devices

As device characteristic dimension continues to scale down,the performance and stability of advanced nano-materials and nano-devices are increasingly affected by the interface.As the interfaces dominate the properities of materials and performance of devices,the interface is the device.Therefore,it is very important to apply straightforward in situ characterization to study the influence of interface characteristics on the properties of advanced materials and the performance of advanced devices at the macro and micro scales.In this paper,the interfaces are the core research problem.The in situ characterization methods such as high-resolution Raman spectroscopy and atomic-level transmission electron microscopy are applied.The research route is in accordance with interface complexity increasing from materials,single interface to multiple interfaces.The effects of interface defects on the properties of advanced materials,the effects of single interface on the performance of advanced devices,and the influences of multiple interfaces on resisitvie switching performance of resistive random access memory?RRAM?with metal/dielectric layer/metal structure are respectively investigated for research on two dimensional materials interface,two dimensional materials/metal interface,and the metal/dielectric layer/metal interfaces.The main research contents and results of this article are listed as follows:1.In situ study of the effects of interface defects of two dimensional materials on its properties,taking tungsten disulfide?WS₂?as an example.Defects modulate the band structure of WS₂,which in turn affects the photoluminescence?PL?characteristics of materials.There is a phenomenon of heterogeneous intensity distribution in the PL mapping of monolayer hexagonal WS₂.Low-magnitude transmission electron microscopy?TEM?and scanning transmission electron microscopy?STEM?were used to perform in situ characterization on the WS₂ interface.Combined with the contrast analysis of the atoms in the STEM image,it was found that the heterogeneous intensity distribution of the PL of the WS₂ is caused by the heterogeneous distribution of antisite defects where sulfur substitutes tungsten.The relationship between the luminescence characteristics of advanced materials and point defects is revealed at atomic scale.2.In situ study of the effects of two dimensional material/metal single interface on the electrical performance of advanced devices,taking graphene/metal contact interface as an example.The graphene/metal interface is a typical two dimensional and three dimensional materials contact issue.Since the thickness of graphene is only a few nanometers,the graphene/metal interface determines the device resistance of advanced devices composed of graphene and metals,which determines the performance of advanced devices.Generally speaking,according to the interaction between metals and graphene at the graphene/metal interface,metals can be classified into two types,the physical adsorption and the chemical adsorption.Characterization of the graphene/metal interface by in situ electrical testing and Raman spectroscopy showed that the chemically adsorbed metals forms a chemical contact interface with graphene.The graphene/metal interface contact resistance is reduced effectively.On the other hand,the phonon vibration mode and the Raman characteristic peaks of graphene have also been changed.Thus,high resolution Raman spectroscopy can be used to quickly distinguish the contact types of graphene/metal interface in situ,which reduces the contact resistance of two dimensional materials and provides new ideas for improving device performance.3.In situ TEM study of the effects of metal/dielectric layer/metal interfaces on resistive switching performance of RRAM.The traditional RRAM W/HfO₂/Al₂O₃/Al and novel organometal halide perovskite based RRAM Ag/CH₃NH₃PbI₃/W are taken as examples.The formation or rupture of conductive filaments occurs at the metal/dielectric layer/metal interfaces.Therefore,the metal/dielectric layer/metal interfaces have an important influence on the resistance switching characteristics of RRAM.?1?The in situ electrical transmission electron microscope was used to dynamically observe the resistance switching process of the W/HfO₂/Al₂O₃/Al interface under an extra electric field.When a positive voltage is applied to the Al electrode,Al atoms migrate toward the W electrode by electrochemical migration;when a negative voltage is applied,Al atoms also migrate toward the W electrode by electromigration.However,the amorphous and uneven W/HfO₂/Al₂O₃interface can hardly block the migration of Al atoms.Eventually,leading to irreversible resistance switching of the device.Therefore,we believe that a post annealing process will help to improve the crystallinity and stability of the interface,thereby effectively improving the reliability of advanced devices.?2?The resistive switching process of Ag/CH₃NH₃PbI₃/W was studied by in situ transmission electron microscopy under an extra electric field,which reveals the resistive swithcing mechanism of the device based on the migration of Ag ions and I ions.This discovery is helpful for understanding the resistance switching mechanism of advanced devices based on organometallic halide perovskite nanowires,and provides a scientific basis for the future application of advanced devices.In situ characterization methods such as transmission electron microscopy and Raman spectroscopy are used to study the interfaces characteristics of advanced materials and devices.Revealing the influence of the interfaces on the properties of advanced materials and the performance of advanced devices.It provides new ideas for adjusting the properties of advanced materials and device performance in the future.