On-demand Construction Of Nanomaterials Surface At The Atomic Scale

With the rapid development of semiconductor industry,the development of nanodevices is imperative.How to achieve controllable manufacture in sub-nanometer or even atomic-scale precision is an important challenge for the miniaturization of devices.Due to the development of electron microscopy,transmission electron microscopy?TEM?is not only a tool of material characterization;but can also be used to observe the dynamic processes of materials'structural evolution under the external fields in real time.In this thesis,high-energy TEM electron beam is used as an effective tool to realize the etching and repair of materials in atomic scale,achieving high-precision addition and subtraction of nanomaterials.The in situ observation of microstructural evolution behavior of the material surface under electron beam irradiation revealed its evolution mechanism,providing theoretical basis and experimental guidance for high-precision controlled fabrication.In addition,based on the exploration of electron beam induced regulation of surface structure of nanomaterials,this thesis also attempted to regulate the surface of polycyclic aromatic hydrocarbons?PAHs?with different amounts of benzene rings under macroscopic conditions,which could be converted into nanodiamonds through low temperature hydrothermal method.The main results are summarized as follows:1.Atomic scale precision etching of calcium oxide surface under electron beam irradiation has been studied.Through detailed analysis of the dynamic evolution behavior of the atomic structure during the etching process,a electron beam etching mechanism has been investigated in-depth:?1?The surface facets with defects would be preferentially etched;while the undamaged facets had a certain stability,the atoms would not be easily sputtered until a defect appears.At the same time,the adsorbed atoms on the materials surface diffused to the etching position and repair partial defects.?2?During the whole etching process,the sputtering was preferable at{200}facet and led to notches.As the etching proceeds,pits gradually appeared on the close-packed{111}facet as well.The etching rate of the{200}facet was higher than that of{111}facet.The change of surface morphology during etching also explained what caused the surface roughness of materials,which was of great significance for understanding the traditional etching and surface roughening.2.In situ repair of two-dimensional?2D?chalcogenides including molybdenum disulfide?MoS₂?and bismuth telluride?Bi₂Te₃?under electron beam irradiation has been investigated.Through analyzing the evolution of atomic structures,the repair mechanism of 2D chalcogenides has been explored in-depth.?1?Electron beam irradiation could repair small defects on monolayer MoS₂.?2?Under electron beam irradiation(beam density?10⁵ A·m^-2),the nanopores on the multi-layered MoS₂ and Bi₂Te₃ gradually shrank and eventually disappeared.Geometric phase analysis?GPA?revealed that the repaired material had high quality crystallinity with few defects.?3?From the computer calculations and statistical analysis,it can be concluded that atoms preferentially occupied the sites with more surrounding atom columns?channels?.The materials were repaired columns by columns along the direction perpendicular to the plane rather than layer by layer parallel to the plane.3.Sub-4 nm diamonds have been successfully synthesized using low-temperature hydrothermal method and nitrification treatment of various types of PAHs.?1?Nitrification was performed on the surfaces of PAHs?naphthalene,anthracene,phenanthrene,and pyrene?with two,three,and four benzene rings.Due to the large specific surface area of nanomaterials,the nitrated PAHs were transformed into nanodiamonds using hydrothermal method at a low temperature of 150°C rather than high temperature and high pressure?HTHP?method.The synthesized nanodiamonds were high-crystalline with an average diameter of2³ nm.?2?The chemical composition of the synthesized nanoparticles was analyzed by using energy dispersive X-ray spectrometry?EDS?and electron energy loss spectrometry?EELS?,confirming that it was carbon and excluding possible metal particles.?3?High-resolution TEM?HRTEM?images of highly crystalline nanoparticles have been acquired,and their interplanar spacings and angles were measured and compared with those of nanodiamonds.It can be finally confirmed that the synthesized nanoparticles are sub-4 nm diamonds.