The Study Of New Two-dimensional C_xN_y Structure Prediction And Its Electronic Properties

Since the successful preparation of graphene in experiments in 2004,low-dimensional materials,especially two-dimensional materials,have attracted great attention due to their excellent physical and chemical properties,and have quickly become the focus of research.In many fields,two-dimensional materials have great theoretical research value and practical application value.Compared with bulk materials,two-dimensional materials have the advantages of high specific surface area,ultra-thin thickness,rich surface functional groups and easy porosity.In recent years,two-dimensional have attracted wide attention from researchers due to their extremely excellent properties.Two-dimensional carbon-nitrogen materials are environmentally friendly and highly stable,and are popular in electronic information,new energy,and environmental protection.Therefore,the design and research of new two-dimensional carbon-nitrogen materials have very important theoretical value and application prospects.This paper mainly uses the first-principles calculation to predict the structure and physical properties of several types of two-dimensional carbon-nitrogen compounds.The main research contents are as follows:1.Structural prediction and performance simulation of two-dimensional C_xN_y materials.Based on g-C₂N and C₃N??-C₃N?,we successfully predicted five graphene-like two-dimensional honeycomb grid structures.The simplest molecular formula can be recorded as:C₃N??-C₃N?,C₄N,C₅N₂,C₇N₂ and C₇N₃.We analyzed the stability of these five structures by combining energy,phonon spectra,and molecular dynamics simulations at room temperature.The calculations show that there are no virtual frequencies in the phonon spectrum,indicating that these structures are likely to exist.Further,molecular dynamics simulations show that these structures remain intact at room temperature.In addition,we explored the electronic properties of these structures.The calculations show that C₇N₃,?-C₃N and C₄N exhibit no band gap metality,while C₅N₂ and C₇N₂ are indirect bandgap semiconductors with band gaps of 0.594 eV and1.155 eV respectively.It is particularly interesting that C₄N and C₇N₂ are magnetic.2.Study on the electronic properties of h-BN/g-C₂N van der Waals?vdW?heterojunction.The heterojunction formed by hexagonal boron nitride?h-BN?and g-C₂N stacking is a typical type II heterojunction,and the interlayer interaction is van der Waals interaction,thus h-BN/g-C₂N is a typical van der Waals heterojunction.We found that h-BN and g-C₂N exist in three different stacking modes,and their formation energy is between 0.24⁰.28 J/m²,and the interaction is larger than that of double-layer graphene.The h-BN/g-C₂N heterojunctions of the three stacking methods are direct band gaps,and the band gap width does not change with the stacking mode,which is about 0.80 eV.The atomic projection density and charge density distributions indicate that the valence band top?VBM?and the conduction band bottom?CBM?of the h-BN/g-C₂N heterojunction are provided by h-BN and g-C₂N,respectively.In addition,we found that for the h-BN/g-C₂N heterojunction,the change in bandgap with the increase of the vertical interlayer distance is very small.