| Abstract |
Silicon (Si) is a material widely used in electronic and optoelectronic applications. Its
properties combined with its abundance and low-cost, have constituted Si as the basis of
the integrated circuit (IC) technology and made its use possible in a number of
applications in everyday life. Compatibility to this technology as a means of avoiding
multilevel interconnects, thus increasing reliability and minimizing manufacturing costs,
is very important for commercial viability. But despite the advantages of Si, as in any
other material, there are limitations for its use in certain types of applications. In order to
overcome these limitations and extend the use of Si based devices in interdisciplinary
applications, extensive research has been directed in finding ways to improve silicon’s
properties
Bottom-up and top-down fabrication approaches have been implemented for
addressing this problem. In many cases, the key engineering challenges are related to the
application of this technology beyond the laboratory environment. To this end, a
significant amount of research effort has been devoted in quest of fabrication techniques
with limited processing steps which can optimize and/or extend the properties of Si, in
low vacuum and cleanliness conditions.
This thesis describes a method which exploits a number of phenomena taking
place under the action of intense pulsed laser irradiation of crystalline Si in the presence
of a reactive gas, in order to induce morphological, structural and compositional
modifications on its surface. The resulting structures, apart from their unique (conical)
morphology, also exhibit improved optical, electronic and wetting response. In particular,
proper tuning of the laser and reactive gas parameters can lead to the formation of
structures which exhibit:
a) Increased absorptance of more than 90% even for below-bandgap wavelengths
and throughout a wide spectral range (250 nm<λ<2.5 μm).
b) Low-threshold field-electron emission, with a threshold as low as 2.5 V/μm,
comparable to that observed in some of the best field emitters to date (e.g.
carbon nanotubes).
c) Hydrophobic, or even superhydrophobic and highly water repellent behavior
equivalent to that of the “model” superhydrophobic and water repellent natural
surface (lotus leaf).
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Study of electron and ion emission mechanisms from micro/nano-structured Si surfaces using ultrashort laser pulses
