טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKovalenko Oleg
SubjectMorphology and Nano-Mechanics of Iron Particles on
Sapphire Produced by Solid State Dewetting
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Eugen Rabkin
Full Thesis textFull thesis text - English Version


Abstract

Solid state dewetting of thin metal films on ceramic substrates is a well-known phenomenon which results in agglomeration of the film and formation of an array of particles. The resulting particles are mostly perfect single crystals of different sizes in the sub-micrometer range. These crystals can be used to investigate the size dependence of mechanical properties and, in contrast to nanopillars machined by focused ion beam (FIB), they are free of defects that can affect the mechanical behavior of the samples.

  We studied the initial stages of solid-state dewetting of 25 nm-thick Fe films on basal plane-oriented sapphire substrates, and the mechanical response of the submicron particles formed at the late stages of dewetting, by the nanoindenting atomic force microscopy (AFM) technique. The particles were strongly faceted, with the {011} top facet parallel to the substrate, and a strong in-plane texture. These crystals were indented by a sharp diamond tip in the AFM and exhibited elastic behavior up to very high stresses, followed by an abrupt massive displacement burst (pop-in). The hardness of the particles was calculated using a method based on the work of indentation, and the resulting values were compared with the hardness of polycrystalline coarse grain bulk Fe. The majority of the particles showed significantly higher values of hardness than the bulk, and analysis of the data revealed that particles become harder as their aspect ratio decreases.