27 research outputs found
Opposite effects of NO on electrical injection in porous silicon gas sensors
The electrical conductance of porous silicon fabricated with heavily doped
p-type silicon is very sensitive to NO. A concentration of 10 ppb can be
detected by monitoring the current injection at fixed voltage. However, we show
that the sign of the injection variations depends on the porous layer
thickness. If the thickness is sufficiently low -- of the order of few
\micro\meter{} -- the injection decreases instead of increasing. We discuss the
effect in terms of an already proposed twofold action of NO, according to
which the free carrier density increases, and simultaneously the energy bands
are bent at the porous silicon surface.Comment: 3 pages, 3 figures, requires SIunits packag
Photon energy lifter
We propose a time-dependent photonic structure, in which the carrier
frequency of an optical pulse is shifted without changing its shape. The
efficiency of the device takes advantage of slow group velocities of light
attainable in periodic photonic structures. The frequency shifting effect is
quantitatively studied by means of Finite Difference Time Domain simulations
for realistic systems with optical parameters of conventional silicon
technology.Comment: 4 pages 5 figure
Role of microstructure in porous silicon gas sensors for NO
Electrical conductivity of porous silicon fabricated form heavily doped
p-type silicon is very sensitive to NO, even at concentrations below 100
ppb. However, sensitivity strongly depends on the porous microstructure. The
structural difference between sensitive and insensitive samples is
independently confirmed by microscopy images and by light scattering behavior.
A way to change the structure is by modifying the composition of the
electrochemical solution. We have found that best results are achieved using
ethanoic solutions with HF concentration levels between 13% and 15%.Comment: 3 pages, 4 figures, package SIunits require
Aberration-free ultra-thin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces
The concept of optical phase discontinuities is applied to the design and
demonstration of aberration-free planar lenses and axicons, comprising a phased
array of ultrathin subwavelength spaced optical antennas. The lenses and
axicons consist of radial distributions of V-shaped nanoantennas that generate
respectively spherical wavefronts and non-diffracting Bessel beams at telecom
wavelengths. Simulations are also presented to show that our aberration-free
designs are applicable to high numerical aperture lenses such as flat
microscope objectives
Light modulation with porous silicon.
Light modulation with porous silicon
Frontiers in Surface Nanophotonics: Principles and Applications
With the rapid technical advancement of nanoscale fabrication, the science of optics has recently undergone a renaissance with the characterization of new and distinctive kinds of photonic interaction. Beyond the well-known plasmonic processes, many of these effects also arise from intricate local field effects associated with surfaces, where the surface morphology determines the detailed electromagnetic behavior. As such interactions move into practical device applications across the globe, this book presents an overview of some cutting edge developments, contributed by members of several highly renowned research groups. Copiously illustrated and with extensive references to original literature, Frontiers in Surface Nanophotonics will appeal to a wide readership with interests in optics, materials science and nanotechnology
Tuning of resonant Zener tunneling by vapor diffusion and condensation in porous optical superlattices
We study a vapor-controlled optical superlattice realized with a silicon-based dielectric mesoporous material. By flowing organic vapors through the nanometer-sized pores, the position dependent refractive index can be continuously tuned, resulting in a tilted photonic band structure. A careful design of pore size distribution, close to the critical radius of capillary condensation of vapor, makes the superlattice sensitive to the flow direction. We drive the optical superlattice to the resonant Zener tunneling condition, introducing an enhanced transmission channel through the photonic crystal. Our results show that vapor capillary condensation can be used to modify the properties of optical superlattices allowing, e.g., to realize fast gas sensing devices due to their advantage to respond to vapor flow fronts