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Abstract

Ion beam sputtering induces morphological as well as compositional changes on the
surfaces of ion-sputtered substrates. The surface undergoes kinetic processes, which
lead to different morphological details: periodic ripples, substrate-defined etch pits or
protuberant structures, roughening and smoothing are some possibilities for surface
evolution.
The aim of my doctoral dissertation was to explore Ar+ ion beam-induced patterns
formed on three different classes of metallic substrates: thin polycrystalline films, polycrystalline
alloy and single crystal materials. The substrates were sputtered by Ar+ ions
of 0.8 - 10 keV at different ion fluences, and the resulting morphological features were
characterized adopting a multi-technique approach: Atomic force microscopy (AFM)
for determination of surface roughness and resulting structure morphology; Scanning
electron microscopy (FE-SEM) for visualization of surfaces at a larger scale, Electron
backscatter diffraction (EBSD) technique was used for the determination of texture and
individual crystal properties.
Thin films were prepared by different methods to achieve different starting roughness
and grain sizes. After off-normal grazing incidence sputtering the films exhibit elongated
ripples with wavelengths comparable to grain sizes in the order of 100 nm; and
after prolonged sputtering the ripples become more regular. The initial wavelength
selection process is governed by the so-called shadowing effect of the larger and taller
grains, resulting in initial wavelengths comparable to grain sizes.
As a polycrystalline alloy, FeSiAl steel (silicon steel; electrical steel) was used. The sputtering
was performed at normal and off-normal incidences. The results show a grainorientation
dependent behavior that is concise with formation of chemically induced
etch pits on the surface of alloys of similar composition at normal incidence sputtering.
At off-normal incidence, the surface undergoes changes that result in ripples, facets or
smoother surfaces; depending on the individual crystal grain orientation.
Electron backscatter diffraction along with scanning electron microscopy was employed
to correlate the individual crystal orientation to the pattern formed inside that individual
grain. To compare the results obtained from polycrystalline alloys, single crystal
substrates of well-defined orientations were used. The sputtering at normal incidence
again results in the formation of etch pits with crystal symmetry.