Oxidation Resistance And Electrical Properties Of Hexagonal Boron Nitride Grown By Chemical Vapor Deposition

Hexagonal boron nitride(h-BN)is a two dimensional insulating layered material.The atoms in every layer are connected by covalent bonds and the atoms between two layers interact by Van der Waal forces.This unique structures provide h-BN with several superior physical properties.Furthermore,h-BN interacts very well with graphene.For all these reasons,h-BN has attracted a lot of attention in the academia and the industry.In this thesis,we studied the performance of h-BN for two different applications:i)Oxidation resistance of h-BN in aqueous and atmospheric oxidative environment.In this section,firstly,monolayer h-BN/Cu and 5-7 layers h-BN/Cu were immersed into 30 % H2O2 for the same time(11 hours)to analyze the oxidation resistance of h-BN in aqueous medium.The samples were analyzed by optical microscopy(OM)and scanning electron microscopy(SEM).The results show that the surface of the copper protected by monolayer h-BN was oxidized severely;on the contrary,the surface of the copper protected by 5-7 layers h-BN did not oxidize,indicating that 5-7 layers thick h-BN has good oxidation resistance in aqueous medium.Then,10-15 layers h-BN/Ni-doped Cu samples were exposed to atmospheric environment for 230 days(the humidity in our laboratory is ~80 %),and the oxidation resistance of h-BN under atmospheric environment was analyzed by SEM,auger electron spectroscopy(AES)and nano-scale secondary ion mass spectroscopy(nano-SIMS).The results show that oxygen can infiltrate through the grain boundaries of the 10-15 layers h-BN stack,reaching the substrate and oxidizing it.Note that,here we used nano-SIMS to analyze the chemical composition of samples,which can detect the chemical composition of the samples at depths of tens of nanometers.This is an advantage compared to X-ray photoelectron spectroscopy(XPS),which can only detect the chemical composition of the samples within depths of 5-10 nm.ii)Dielectric strength and dielectric breakdown(BD)of h-BN when used as dielectric.In this section,the surfaces of monolayer h-BN/Cu Ni and multilayer h-BN/Cu Ni before and after ramp voltage stress(RVS)test were scanned by conductive atomic force microscopy(C-AFM),the results show that the surface has no changes after the stress,which is surprising and different from what happen in traditional dielectrics.Probably the excellent thermal conductivity of monolayer h-BN could reduce the effect of the breakdown.For multilayer h-BN,some hillocks induced by BD appeared on the surface after RVS,similar to what happened in traditional dielectrics Si O2,high-k materials Hf O2 and Al2O3.It is worth noting that topographic,adhesion and deformation maps of one of the hillocks were obtained by atomic force microscopy(AFM)using the Peak Force TUNA mode,which allowed analyzing the charge distribution of the BD spot.These results are helpful to understand charge flow direction inside the h-BN dielectric,as well as the entire BD process.