Growth, structure and applications of nanorods by glancing angle deposition.

摘要

Glancing angle deposition (GLAD) is a thin-film deposition technique where the deposition flux, consisting of atoms and molecules from gas phase, impinges on substrate at oblique angles, resulting in highly under-dense, columnar microstructures which are purposely engineering to achieve novel desired properties. GLAD is a simple, one-step process to obtain many novel nanostructures of current interest.; The primary objective of this thesis is to extend the current capabilities of the GLAD technique for the creation of multi-component nanostructures. It is aimed to study the growth dynamics of nanostructures during GLAD. This work also aims to demonstrate, both theoretically and experimentally, the capabilities and limitations of a novel simultaneously opposing GLAD (SOGLAD) technique by creating branched Cu nanostructures. Two of the potential applications of the nanostructures have been investigated.; It is shown for Cr, Si, and Ta single-component, and Cr-Si multi-component nanorods that growth on flat and patterned substrates results in strikingly different morphologies. This observation was explained on the basis of a competitive growth mode which occurs during the growth process favoring the larger rods to grow at the expense of smaller ones. Substrate patterning, achieved by colloid self-assembly and electron beam lithography, prior to GLAD delays or completely prevents intercolumnar competition.; Intrinsic crystal properties such as stacking faults and three dimensional EhrlichSchwoebel barriers can result in the formation of branched nanostructures during glancing angle deposition. This is demonstrated using a combination of molecular dynamics simulations and GLAD experiments on Cu nanorod arrays. SOGLAD on to a stationery substrate results in the anisotropic broadening in Cu nanorods. A numerical model provides a qualitative understanding of the lateral growth in the nanorods when the deposition is switched from continuous substrate rotation to stationery deposition from opposite sides.; Finally, two practical applications for GLAD nanostructures are presented. GLAD nanosprings and nanorods exhibit a reversible change in resistivity upon loading and unloading, indicating their potential as pressure sensors. It is shown that Si-Au nanorods can be controllably assembled (end-to-end) using biological connector molecules, in particular biotin and streptavidin, which are selectively attached to the Au portion at the end of the nanorods. This new hybrid physical-vapor-deposition/wet-chemistry approach will be useful for assembling complex hierarchical nanoarchitectures including nanohoneycombs, nano-ladders, and 3D nanorod networks, comprised of controlled materials combinations.