Several Peculiar-Shaped Micro-and Nanostructures Fabricated By Two Different Chemical Deposition Methods

Peculiar-shaped micro-and nanostructures,such as various types of superstructures constructed by assembled nanoparticles,differnet types of complex and hierarchical microarchitectures,serpentine interconnects for stretchable electronics,tin dioxide zigzag nanobelt for humidity sensing and detection of organic vapours,etc.have attracted widespread interests in materals science,chemistry,physics,electronics and related interdisciplinary areas.This can be attributed to the unique properties that originate from the peculiar shapes of such micro-and nanostructures which are different from the common forms of micro-and nanostructures like nanoparticles,hollow structures,micro-and nanowires/rods and nanostructured thin films.Then,the unique properties of these peculiar-shaped micro-and nanostructures make them irreplaceable components for stretchable electronics,catalysis,sensing and other practical applications.In contrast to the top-down approaches,bottom-up nanofabrication offers several favorasble advantages for complex micro-and nanostrcutures which are as follows:the crystal growth habit of the targeted materials could be supported which leads to the chemically stable forms of the micro-and nanostructures enclosed by low energy facets while process few dangling bonds;considerably large numbers of the bottom-up approaches like electrochemical deposition and chemical vapor deposition employed in this thesis only need the simple available apparatus;the formation of nanoscale twins could be achieved by some bottom-up approaches like pulsed electrodeposition and magnetron sputtering,and then these twins can be helpful for the achievement of good mechanical properties;controllable doping for tunable properties could also be realized in the bottom-up synthesis of semiconducting micro-and nanostructures,which means that both intrinsic and doped semiconductors could be achieved in these strategies.This thesis is mainly focused on the the study of bottom-up sythesis of peculiar-shaped micro-and nanostructures using electrochemical deposition or vapor chemical deposition.Based on the different characteristics of both solution-based electrodeposition and chemical vapor deposition methods,the former is suitable for synthesis of dispersed nanoparticles and the latter is always employed for preparing high-quality one-dimensional single-crystal micro-and nanostructures,we develop several strategies for preparing micro-and nanostructure with peculiar shapes.Such strategies include self-templated growth and directed assembly of Cu2O cubic nanoparticles,electrodeposition of ultralong Cu wavy microstructures,and the preparation of SnO2 zigzag nanobelts.The details are list as follows:(I)Conjunctional method involveing lithography patterning and electrodeposition is employed for achieving the self-templated growth and directed assembly of Cu2O ionic crystal cubic nanoparticles(NPs),and groove edge guided assembly of Cu2O cubic NPs.We discussed the reaction kinetics and mechanisms for the electrode process.The results can be summarized as:1)Self-templated growth and directed assembly of Cu2O cubic NPs can be achieved on ultrathin film electrode with Au NPs and specific groove array pattern.Self-template-directed assembly on the basis of the good cohesion between ultrathin film electrode and the supporting Si substrate with groove array pattern,together with the well-defined structure of the dispersed Au NPs in the film electrode.2)The shielding effect of the groove array pattern will help to attain different thicknesses of the sputtered Au NPs layer on each edge-line of the groove.Thence,guided assembly nanowires with Cu2O NPs as building blocks can be obtained on the edge-line with relatively thin Au NPs layer.(II)Conjunctional method involving lithography patterning and electrodeposition was employed for achieving large-scale production of ultralong Cu WMSs on lithographically patterned and NOL-passivated p Si electrode constructed by dry-overetching.The as-deposited Cu WMS consists of an interconnected network of nanoparticles with randomly oriented grain boundaries at the crystallite interfaces,and its length as well as aspect ratio can reach centimeter-scale and up to 104.The electrical resistivity of Cu WMSs is estimated to range from 8.36 ??·cm to 16.72??·cm,slightly worse than that of bulk Cu but obviously superior to those of Cu oxides.Moreover,the plausible forming mechanism of WMSs is proposed based on two-stage tunneling:(i)local electric field enhancement-induced tunneling makes electrochemical nucleation at the sharp ridges of surface microscopic structures;(ii)high surface diffusion coefficient of Cu nuclei and electrochemical potential drive nuclei to diffuse along the curved surfaces and tunneling inside the MIS junction facilitates the crystallization of metal nanoparticles.(?)SnO2 zigzag nanostructures were successfully prepared by a kinetically controlled thermal chemical vapor deposition(CVD)method.Based on the microstructure characterization,the morphology evolution of the SnO2 zigzag nanostructures is studied.In the early stage of the crystal growth,the zigzag nanostructures are enclosed by a mix of(010)and {101} facets with the nearly same exposed areas.It is worthy noting that a distinct junction shape of the zigzag structures looks like the Chinese character "?" can be observed in this stage.The 68° and 112°junction corners could continuously serve atomic steps for the building blocks from the vapor phase as lattice sites for new surface forming.And at the final stage,the zigzag nanobelts will finally evolve a belt shape with plain sidewalls.The SnO2 nanostructures evolve to their thermodynamically stable forms enclosed by a mix of large(010)and relatively small(100)facets.The formation mechanism of the single crystal SnO2 is further confirmed to be the vapor-solid(VS)growth mechanism.