Research On The Fabrication And Characterizations Of Hexagonal Boron Nitride Nanostructures

Following the rise of graphene in 2004,the atomically thin two-dimensional(2D)layered material,hexagonal boron nitride(h-BN),became one of the world’s most popular nanomaterials.As a 2D layered material consisting of alternating sp~2-bonded boron and nitrogen atoms,h-BN has a lattice structure that is highly similar to graphene,and the lattice constant difference is only～1.5%.However,unlike graphene,which is semi-metallic,h-BN is the only insulator in all known two-dimensional materials.Besides,it’s atomically smooth surface free of dangling bonds and charge traps are also considered to be an ideal substrate and tunneling barrier for graphene devices.h-BN even performs better in thermal and chemical stability than graphene,which enables it to function as an anti-oxidation layer,even at temperatures as high as 1100℃.In addition,monolayer h-BN sheets remains stable up to800℃in air.Other properties like ultra-thin,high flexibility and mechanical strength of the monolayer h-BN also make it extremely promising in selective film applications.Three different nanostructures of h-BN are realized and characterized in this work,which lays a good foundation for their potential applications.Firstly,we studied the etching of nano trench on the surface of h-BN.Monolayer-deep trenches were obtained by catalytic metal nanoparticles at high temperatures.The width,length and density of these trenches could be controlled by adjusting experimental conditions including the density of metal nanoparticles,etching duration and temperature.Characterizations of atomic force microscope(AFM)shew that the length of trench could be up to～4μm,while the width could be minimized to～5nm.The etched h-BN substrates could serve as a high-quality template for the next growth of graphene nanoribbons.Especially,elements such as Ni,Fe,Zn and Au could only etch trenches along zigzag orientation on the surface of h-BN,while Pt could etch the nano trenches of armchair-type boundaries under the same conditions,which made the trench etching of h-BN selective in boundary orientation.Moreover,our work continues to study the experiment of treating h-BN with hydrogen plasma based on the AA’stacking order between its layers.It was shown that protons would be recombined into hydrogen molecules internally after penetrating the h-BN lattice,which could not escape from the multi-layer h-BN afterwards and finally formed the bubble structure.The hydrogen containing bubble nanostructure was demonstrated by AFM,transmission electron microscope(TEM),energy dispersion X-ray spectrum(EDX)and other characterization means.More importantly,the study also shew that hydrogen bubbles could be formed on multilayer h-BN surface after a plasma treatment with gases such as methane,acetylene and argon/hydrogen mixture,making this work of more far-reaching research value.Furthermore,our work studied how to fabricate high-quality boron nitride nanotube(BNNT)crystals on the periphery of carbon nanotubes(CNTs),which was known as the one-dimensional van der Waals coaxial heterostructures.Ammonium deoxycholic acid(ADC)was firstly used as the surfactant to dissolve CNTs into the aqueous solution.These CNTs were then transferred to the sample preparation grid of the TEM for special process of the surfactant annealing,and finally covered by BNNT crystals along the suspended CNT template by copper vapor catalytic method in chemical vapor deposition system.TEM and electron energy loss spectrum were carried out to structurally and chemically demonstrate the CNT/BNNT van der Waals heterostructures.For the first work,we provid a selective growth template for graphene nanoribbons with two different boundary(zigzag or armchair)orientations.Graphene nanoribbons filled in the zigzag trenches with a bandgap of 0.5 e V was measured after the growth,opening up a new way for the bandgap engineering research of graphene.For the second work of proton penetration of h-BN,we firstly demonstrated the AA’stacking order of h-BN,then explored for the first time of separating,extracting and storing hydrogen energy by combining h-BN with a plasma equipment.Finally,by successfully fabricating the CNT/BNNT van der Waals heterostructures,this paper provides a solution of high-quality outer protective crystal shell for the inner semiconducting CNT in the application of CNT based nanoelectronics.