Defects In Layered Black Phosphorus And The Fabrication Of Novel Nanostructures Assisted By E-beam Irradiation

Since the discovery of graphene,two-dimensional(2D)materials have attracted extensive attention owing to their intriguing properties.Black phosphorus(BP)is a newly rediscovered graphene-like material except for transition metal dichalcogenide(TMDs)and hexagonal boron nitride(h-BN).As a direct band gap semiconductor,black phosphorus has been emerged as a promising candicate for many potential applications in nanoelectronics and optoelectronics.The nanostructures including edge reconstruction and defects in black phosphorus would dramatically influence its electrical and mechanical properties.In this work,we perform the fundamental research on its nanostructures using the aberration-corrected transmission electron microscope(TEM).An all-dry method was adopted to transfer to the exfoliated few-layer BP flakes onto a heating chip and then load it into a Cs-corrected TEM.With a combination of electron irradiation and in-situ annealing process,the amorphous residual introduced during the exfoliation and transfer process would be partly removed and expose the ultra clean BP surface for atomic scale characterization.The few-layer BP would be thinning down to monolayer phosphorene through a layer-by-layer sublimation process.During the layer-by-layer thing process,the growth and dynamics i.e.,rupture and edge migration of one-dimensional phosphorus chains are experimentally captured for the first time.Furthermore,the dynamic behaviors and associated energetics of the as-formed phosphorus chains are further investigated by density functional theory(DFT)calculations.The atomic structure of the suspended phosphorus atomic chain was resolved,and a possible transformation from pristine BP lattice to atomic chain was proposed.The BP nanoribbons along different directions were fabricated through a top-down method via electron beam sculpturing.The migration of phosphorus atom along the zigzag(ZZ)edge in black phosphorene was directly observed.Different types of ZZ edge reconstruction were characterized at the atomic scale,and the dimerization of the dangling phosphorus atoms in Klein edge was revealed.The energetics of different edge types were revealed by DFT calculations.The formation and migration of 585-A divacancy was investigated via in-situ TEM.A possible migration pathway was proposed by DFT calculations.The diffusion barrier is 2.1 eV along the ZZ direction and 1.6 eV along the diagonal direction.The vacancies in black phosphorene prefer to be arranged in line along the ZZ direction and form a chain vacancy.The chain vacancies can be continuously extended along the ZZ direction and reach a dozens of nanometers.The chain vacancy can migrate along the armchair or diagonal direction when its legth is relatively short.Finaly,I summarized the thesis on the nanostructures in black phosphorus and it is hoped that these special structures will serve as a novel platform and inspire further exploration of the versatile properties of BP.