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 CO<sub>2</sub> 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 measurements of the thermal emission properties of 2D and 3D silicon photonic crystals using either
localized integrated emission sources or resistively heating the entire photonic crystals with and without substrate.
The in-plane as well as out-of-plane emission properties were recorded and compared to numerical simulation.