Periodic silicon nanostructures can be used for different kinds of gas sensors depending on the analyte concentration.
First we present an optical gas sensor based on the classical non-dispersive infrared technique for ppm-concentration
using ultra-compact photonic crystal gas cells. It is conceptually based on low group velocities inside a photonic crystal
gas cell and anti-reflection layers coupling light into the device. Experimentally, an enhancement of the CO2 infrared
absorption by a factor of 2.6 to 3.5 as compared to an empty cell, due to slow light inside a 2D silicon photonic crystal
gas cell, was observed; this is in excellent agreement with numerical simulations. In addition we report on silicon nanotip
arrays, suitable for gas ionization in ion mobility microspectrometers (micro-IMS) having detection ranges in principle
down to the ppt-range. Such instruments allow the detection of explosives, chemical warfare agents, and illicit drugs, e.g., at airports. We describe the fabrication process of large-scale-ordered nanotips with different tip shapes. Both silicon microstructures have been fabricated by photoelectrochemical etching of silicon.
We present a new high-index-contrast material system to realize ridge waveguides and PhC waveguides made
of a thin silicon slab embedded in two silica layers. Hence fully symmetrical structures can be etched and two
important conditions for low-loss guiding of light can be matched: The symmetry properties of the material
avoid polarization mixing and the high index contrast leads to strong confinement of light. Because of operating
completely below the lightcone the PhC waveguides allow theoretically lossless guiding of light.
The bandstructure of photonic crystals offers intriguing possibilities for the manipulation of electromagnetic waves. During the last years, research has mainly focussed on the application of these photonic crystal properties in the telecom area. We suggest utilization of photonic crystals for sensor applications such as qualitative and quantitative gas and liquid analysis. Taking advantage of the low group velocity and certain mode distributions for some ~k-points in the bandstructure of a photonic crystal should enable the realization of very compact sensor devices. We show different device configurations of a photonic crystal based on macroporous silicon that fulfill the demands to serve as a compact gas sensor.
The bandstructure of photonic crystals offers intriguing
possibilities for the manipulation of electromagnetic waves.
During the last years, research has mainly focussed on the
application of these photonic crystal properties in the telecom
area. We suggest utilization of photonic crystals for sensor
applications such as qualitative and quantitative gas and liquid
analysis. Taking advantage of the low group velocity and certain
mode distributions for some k-points in the bandstructure
of a photonic crystal should enable the realization of very
compact sensor devices. We show different device configurations of
a photonic crystal based on macroporous silicon that fulfill the
demands to serve as a compact gas sensor.
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