Theoretical Study On Electronic Properties And Modulation Of GeP₃ And CrI₃ Nanoribbons For Two Typical Two-dimentional Materials

Two-dimensional?2D?materials have attracted considerable attention owing to their unique properties and potential applications in future nanodevices.Though the study of the ground properties of2D materials have been investigated rapidly.The study on electrical and magnetic properties of two-dimensional materials and the modulation of the properties are still the hot topics.The size of materials are finite when they are used in devices,so it is a meaningful issue to study the properties of materials with finite size.As a simple mean,nanoribbons not only can be used to study the effect of size on the properties of 2D materials,but also can make up some shortcomings of their monolayer counterparts.For example,the armchair graphene nanoribbons are semiconductors which making up the defect of zero band gap of graphene.In addition,the electronic properties of materials can be effectively modulated by changing the size of nanoribbons and modulating their edges.The GeP₃ and CrI₃ have typical electrical and magnetic properties,so we use the first-principles to study the electronic properties of their nanoribbons.Besides,we investigated the effect of size and edges on these properties.The main contents and results are in the following:Firstly,2D GeP₃ is an indirect nonmagnetic semiconductor,and according to its structural characteristics,the nanoribbons are divided into armchair type and zigzag type.The results show that both armchair and zigzag nanoribbons are inderect semiconductors,and the band gaps increase after the dangling bonds are passivated by hydrogens.Compared to the unpassivated armchair nanoribbons,the decorated ones exhibit a direct gap when the width N is odd.It makes these nanoribbons potential for optoelectronic applications.Besides,duing to the geometric symmetry,the band gaps exhibit even-odd oscillations with the width increasing.Based on the strong band gap oscillating nature of GeP₃ nanoribbons,we designed a lateral homogenous heterojunction which constructed by nanoribbons with different widths.For the zigzag GeP₃ nanoribbons,when the nanoribbons are un-passivated,the band gaps trend to be a constant as the width increasing.When the nanoribbons are passivated by hydrogens,the gaps of nanoribbons decrease oscillationally and tend to be a constant when the size is large enough.Moreover,the gaps of the nanoribbons are larger when the width is 3p+1?p is an integer?.The results provide theoretical support for experimental study of GeP₃ nanoribbons.Secondly,CrI₃ is an intrinsic ferromagnet material with only one configuration of nanoribbon.The electronic structure of CrI₃ nanoribbon shows that both the valence band maximum?VBM?and conduction band minimum?CBM?are contributed by the p orbital of I atoms.The VBM is provided by the spin-up state,while the CBM is provided by the spin-down state.This is different from the monolayer which both the VBM and CBM are provided by the spin-up states.The reason for this phenomenon is that the edge state of spin-down is introduced by the I atoms at the edges.Then,we investigated the size effect of the nanoribbons on the band gap and magnetic moment.The results show that the band gap trend to be a constant with the increasing of size.As the size increases,the magnetic moment of each Cr atom in the nanoribbons gradually approaches to the value of Cr in the 2D CrI₃.This results enlarge the scale of magnetic material research and provide theoretical data for the future study of magnetic nanoribbons.