Ph.D Thesis


Ph.D StudentShirly Borukhin
SubjectThe Surface Structure of Template Stripped Thin Films of
Gold
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Pokroy Boaz
Full Thesis textFull thesis text - English Version


Abstract

Ultra-flat metal surfaces can be formed by Template Stripping (TS), which is a method for obtaining a thin metal film with an average surface roughness in the order of < 1nm. Such surfaces are important in plasmonics, for the support of high quality Self Assembled Monolayer (SAM) surfaces and numerous other applications.  By means of HR-XRD, HRSTM , and HR-TEM we show for the first time that TS introduces a very high density of surface nano-defects (twins and stacking faults), which can strongly hinder surface-induced properties such as SAM ordering and plasmonic phenomena, despite the seeming overall ultra-high flatness. We also demonstrate how these nano-defects can be completely eliminated.

Additionally, we present the self-formation of periodic atomic and nano steps at the interface between the thin metal film and the underlying supporting substrate, revealed by the TS method. Such atomic stepped surfaces of metals and semiconductors exhibit well-arranged, periodic atomic steps and have numerous applications in microelectronics, catalysis, directed growth of nanowire arrays, patterning of quantum dots and magnetic domains, and many more. In contrast to classical vicinal surfaces, which are produced by the expensive and tedious procedure in which single crystals of a desired material are cut at a small angle to the low surface energy plane followed by surface sputtering and annealing under ultra-high vacuum (UHV), these surfaces form on polycrystalline materials, at almost room temperature, and at atmospheric environments and have no need of any further preparation procedure in order to be imaged. We also demonstrate how the step periodicity can be easily controlled.

In addition to the self-formation of steps, we also show a new surface reconstruction that is spontaneously formed on large terraces of the {111} plane of gold, and demonstrates an extremely periodic ordering that is well defined with an atomic precision. The structure comprises equal strips of 2.5 nm each, separated by straight defect lines of a sub-nanometric gap. We derived an atomistic model, and explained this phenomenon in the framework of crystallographic defects formed under the tendency of reducing surface energy and surface stress. We believe that this is a meta-stable structure, which is preserved by the non-destructive surface fabrication method.