Fouces On Preparation And Piezoelectric Properties Of Two Dimension Nanotwinned Boron Nitride Nanoribbons

In recent years,two-dimensional（2D）nanotwinned materials have been exhibited with some novel properties and further applicated in the fields of nanoelectronics,new thermoelectric devices,new ferroelectric function devices,and microwave devices.2D wide bandgap hexagonal Boron-Nitride Nanoribbon（h-BNNR）has good chemical and thermal stability,symmetrical polar covalent bonding,Van-Der-Waals interlayer stacking structure and other properties.More interestingly,the altered crystal configuration of the BNNR has been shown excellent piezoelectric properties.Nowadays,conventional BNNR preparation methods have been not used to the successfully achieve the end of nanotwinning substrate-free BNNRs;the theoretical model of research on the piezoelectric properties of 2D-BNNRs have been not supported;and there is no literature reports on the effects of nanotwins on the piezoelectric properties of BNNRs.In view of the above issues,this paper focuses on the preparing and nano-twinning method of high-purity controllable morphology substrate-free BNNR;the establishment and verification of the theoretical model of crystal configuration and piezoelectric properties of BNNR;The influences of nanotwins on the piezoelectric properties of BNNR,etc.In this paper,based on the principle of solid-state surface diffusion at high temperature,it has been investigated the mechanism of iron-based nanoparticle-catalyzed growth of BN crystals and the directional exfoliation of BN nanotube（Nanotube）walls by alkali metal catalysts;accordingly,it was revealed that BNNR alkali metal catalyst high-temperature wall decomposition growth method,and it was proposed that catalyst size,concentration and reaction temperature are the key influencing factors for for the controllable preparation of BNNR.In the method,BNNR with 15-200 nm width,high crystallization,controlled aspect ratio and thickness were obtained,and the controllable preparation of highly crystallized substrate-free BNNR was completed.In this paper,we have successfully obtained multi-periodic nanotwinning structures on BNNR by incorporating high-gradient deformation into the BNNR crystal plane with a high aspect ratio,based on the BNNR crystal conformation changes under high strain.The experimental study of the electrical properties of BNNR under strain has shown that the new crystal configuration induced by strain in BNNR can significantly enhance the electrical conductivity of BNNR from 10^-8level（no strain）to 10-⁶level（nano-twinning）,and the introduction of the new crystal configuration also leads to a change in the main carrier transport mode of BNNR.It also confirms the existence of piezoelectric properties and ferroelectricity in nanotwinned BNNR,which strongly supports the theoretical study and modelling of the piezoelectric properties of BNNR.In this paper,a theoretical model of the piezoelectric properties of BNNR is constructed based on the relationship between strain and BNNR crystal configuration,a hexagonal lattice discretization iterative calculation method is proposed,the relationship between the piezoelectric properties of BNNR and the crystal strain is calculated,and the power function relationship between the piezoelectric constants of BNNR and the crystal strain is experimentally verified,pointing out a new direction to improve the piezoelectric properties of BNNR.The paper establishes a model for the piezoelectric properties of BNNR,calculates the effect of nanotwin structure on the piezoelectric properties of BNNR,and finds that nanotwin structure can significantly improve the piezoelectric properties of BNNR,and make its piezoelectric properties have surface non-uniformity and boundary characteristics.The highest value of the piezoelectric constant d₃₃ is-276.875 pm·V^-1,which is at least two orders of magnitude higher than that of thin-film h-BN nanosheets,monolayer h-BN and 2D WSe₂ materials.This paper proposes a controllable high-temperature wall stripping preparation methods of BNNR and a high-strain induced nanotwinning structure method in BNNR,which sustain the related properties study of the new crystal configuration BNNR.The piezoelectric properties model and experimental research’s results of nanotwinned BNNR reveals that the nanotwinning can significantly imporve its piezoelectric properties,expanding its application prospects in new flexible sensing devices,nano piezoelectric functional devices and other fields.In the meantime,paper reveals anther purely physical means through nanotwinning to induce the ferroelectric conversion of 2D nanotwinned BNNR,precise studies on the piezoelectric and ferroelectric properties of the nanotwinning in other asymmetric Van Der Waals layered 2D materials is also worthy of future investigation.