| Abstract |
Biomimetics offer the possibility of biological systems simulation on artificial
surfaces, with desired properties. There are many attempts to fabricate artificially
these surfaces.
The present thesis comprises three parts. The first one is the fabrication of
micropatterned silicon substrates via ultra-short pulsed laser irradiation under
different experimental parameters, including laser fluence. The second part is the
fabrication of hierarchical micro-nano-patterned substrates. These comprise micropatterned
silicon substrates which have been thermally oxidized and nano-decorated
with spherical and rod shaped gold nanoparticles of various functionalities and sizes.
Gold nanoparticles have been attached via silane chemistry. Both types of substrates
have been characterized with respect to their morphological, wetting and optical
properties. The third part is the fabrication of micropatterned steel substrates via ultrashort
pulsed laser irradiation under different experimental parameters, including
irradiation medium. Steel samples fabricated, for constant laser fluence, in air and
ammonia gaseous environments.
Regarding the micropatterned substrates, the morphological characterization
showed that as the laser fluence increased, the roughness of the surface increased as
well. Micropatterned substrates comprised microcones of varying height and density.
Specifically, the density and the height of the micro-features (i.e. microcones)
decreased and increased respectively, with increasing laser fluence. Optical
characterization showed that as the surface roughness appears, the absorbance
increased, across the range of wavelength (250-2000nm). The layer of silicon oxide
on flat silicon substrates lead to reduction of the reflectance, in contrast with the case
of micro-structured substrates, where silicon oxide layer increased the reflectivity, in
near infrared spectrum. This leads to absorbance reduction in near IR range but very
high absorbance efficiency in UV/Vis range (~97%).
Regarding the hierarchical micro-nano substrates, SEM analysis confirmed the
successful deposition of the gold nanoparticles on the micropattenred silicon
substrates. Deposition gave a homogenous distribution of single nanoparticles and
some regions of small clusters. All types of the gold nanoparticles (NPs) being tested,
which carried diverse functionalities (e.g. oligopeptides, including the CALNN-RGD and organic moieties, including the DMAP) have been successfully attached on the
surfaces of the micropatterned silicon substrates. Rod shaped AuNPs do not carry any
ligands. Remarkably, the NPs covered the whole 3D surface of the micropatterned
substrates giving a distribution that was comparable to that on the flat silicon
substrates. Optical characterization showed that gold nanoparticles caused increment
of absorbance of the oxidized micro-patterned silicon substrates in near IR range.
Finally, steel micro-patterned substrates have been characterized for their
morphological and wetting properties. Morphological characterization showed that in
presence of reactive gas (ammonia), during the irradiation procedure, steel
microcones were smaller and shorter than the air-structured ones. As for the wetting
characterization, in the case of air-structured surfaces there was non stable wetting
behavior, in contrast with the ammonia-structured steel surfaces which remained
hydrophilic for over 100 contact angle measurement days. Also, the ammoniastructured
surfaces appeared anti-corrosive behavior.
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