Electron Diffraction And Microscopy Study Of Binary Sulfide Nanotubes

One-dimensional nanotubes have attracted a great deal of attention ever since the discovery of graphitic carbon nanotubes.Numerous papers have been published on their synthesis,structure,properties,and applications.Among these,the synthetic methods and determination of atomic structure are two major research topics of the field.In this thesis,we will develop new approaches to synthesize the nanotubes and conduct accurate measurement of the chirality of nanotubes.The main contents of this thesis are as follows:1.Simulations of electron micrographs of WS₂ nanotubes.The formation of high-resolution transmission electron microscopy?HRTEM?images of WS₂ nanotubes supported by an amorphous carbon?AC?film were studied.In the case where the nanotube diameter is smaller 1 nm,it is difficult to identify the nanotube in the HRTEM images.In the case where the nanotube diameter is greater than 1 nm and the thickness of the AC film is small?² nm?,the nanotube can be identified and the nanotube diameter can be measured accurately.However,if the thickness of AC film is large?>10 nm?,the measurement of diameter is difficult.2.Accurate measurement of the chirality of WS₂ nanotubes.We describe the structural parameters and the atomic positions of a single-walled WS₂ nanotube using both Cartesian and cylindrical coordinates.The structure factor is calculated in detail using analytic expressions for both single-walled and multiwalled WS₂ nanotubes.A zoning scheme has been developed to obtain the ratio of chiral indices m/n from the electron diffraction patterns.The procedure for determination of the chiral indices of both single-walled and multiwalled WS₂ nanotubes and the tilt angle are illustrated in detail for both normal and inclined incidence.As an example of application,the determination of the chiral indices of a quintuple-walled WS₂ nanotube is carried out and the tilt angle is obtained as 17.7°.This method can be extended to the analysis chiral indices of other kinds of nanotubes,such as MoS₂,TiO₂,and SnS₂ nanotubes.3.Synthesis of thin WS₂ nanotubes from ultrathin W₁₈O₄₉ nanowires.WS₂ nanotubes of small diameter?<10 nm?and few layers?<4?are synthesized by heating ultrathin W₁₈O₄₉ nanowires and S powders in an H2/Ar atmosphere at 840 °C.The morphology and structure of these nanotubes,examined by electron diffraction and high-resolution electron microscopy,reveal that single-and double-walled WS₂ nanotubes usually have a structure close to either the zigzag or the armchair type,while multiwalled WS₂ nanotubes often have a dispersed distribution of chiral angles.The growth mechanism of WS₂ nanotubes was studied via investigation of one incipient nanotube.It is suggested that,in the process of formation and growth of a WS₂ nanotube,the W₁₈O₄₉ phase transformed first into an amorphous WS₃ structure via the absorption and diffusion of sulfur atoms to substitute the oxygen atoms,and followed by a phase transition from amorphous WS₃ to 2H-WS₂ by losing sulfur atoms to form the shels of the WS₂ nanotubes.4.Synthesis of SnS₂ or SnS₂/SnS nanotubes and fullerene-like nanoparticles catalyzed by Bi nanoparticles.Bi nanoparticles are prepared by thermal decomposition of Bi[N?SiMe₃?₂]₃.SnS₂ nanoflakes,which are produced by heating aqueous solutions of Sn Cl₄?H₂O and HCl with thioacetamide,are used as the precursors for the growth of nanotubes.SnS₂ or SnS₂/SnS nanotubes and fullerene-like?IF?nanoparticles are synthesized by the vapor-liquid-solid?VLS?transformation utilizing Bi nanoparticles as a liquid catalyst.The growth mechanism for SnS₂ nanotubes is proposed as follows: The liquid Bi nanoparticles absorb the SnS molecules from the atmosphere to form a hybrid structure.SnS will eventually separate out of the hybrid structure when it is supersaturated and form the shells of SnS₂ or SnS nanotubes.