It is of paramount importance for our society that the
environment, life style, science and amusement flourish together in a
balance way. Some trends in this direction are the increased utilization
of renewable energy, like solar photovoltaics; better diagnostic tools,
for example advanced biosensors; high definition TV or high-resolution
cameras; and novel scientific tools for better understanding of scientific
observations. Advancement of micro and nanotechnology has directly and
positively impacted our stance in these application domains. One such
example is that of vertical periodic or aperiodic nano or micro pillar
assemblies which have attracted significant research and industrial
interest in recent years. In particular, Si pillars are very attractive
due to the versatility of silicon. There are many potential applications
of Si nanopillar/nanowire assemblies ranging from light emission, solar
cells, antireflection, sensing, and nonlinear optical effects. Compared to
bulk, Si pillars or their assemblies have several unique properties, such
as high surface to volume ratios, light localization, efficient light
guiding, better light absorption, selective band of light propagation etc.
The focuses here are on the fabrication of Si pillar assemblies and
hierarchical ZnO nanowires on Si micro structures in top-down and
bottom-up approaches; their optical properties and different
applications. Here, we have investigated periodic and aperiodic Si
nano and micro structure assemblies and their properties, such as
light propagation, localization, selective guiding and light-matter
interaction. These properties are exploited in a few important
optoelectronic/photonic applications, such as for optical biosensor,
broad-band anti-reflection of light, radial-junction solar cells,
second harmonic generation and color filter.
Some highlights are:
• We have achieved a low average reflectivity of ~ 2.5 % with the periodic Si micro-pyramid-ZnO NWs hierarchical arrays.
• A convenient top-down fabrication of radial junction nanopillar solar cell using spin-on doping and rapid thermal annealing (RTA) process is presented. Broad band suppressed reflection, on average 5%, in 300- 850 nm wavelength range and an un-optimized cell efficiency of 6.2 % are achieved.
• Silicon dioxide (SiO2) coated silicon nanopillar (NP) arrays are demonstrated for surface sensitive optical biosensing. Bovine serum albumin (BSA)/anti-BSA model system is used for biosensing trials by photo-spectrometry in reflection mode. Best sensitivity in terms of limit of detection of 5.2 ng/ml for Bovine serum albumin (BSA)/anti-BSA model system is determined for our nanopillar biosensor.
• Aperiodic Si nanopillar assemblies in PDMS matrix are demonstrated for efficient color filtering in transmission mode. These assemblies are designed using the ‘‘molecular dynamics-collision between hard sphere’’ algorithm. The developed color filter is applicable as a stand-alone filter for visible color in its present form and can be adapted for display, image senor (monolithic integration) and aesthetic applications.