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Porous silicon free-standing microcavity structures, with different layer designs, have been fabricated. Single microcavities show transmission resonances in the technologically relevant wavelength region of 1.55 μm with quality factors up to 3380. High-order cavities show sub-nm transmission peaks over the whole stop band. Coupled microcavity structures, where splitting of the degenerate cavity mode occurs, lead to multiple transmission peaks in a limited region of the stop band. We also report incident angle-dependent measurements, where transmission peak blueshift and splitting of transverse electric and transverse magnetic polarized modes due to porous silicon birefringence were observed. [ABSTRACT FROM AUTHOR]

Presents a study which examined thermally based light modulation of a large laser through free-standing porous silicon film. Details on the experiment; Conclusion.

Near-field optical spectroscopy has been used to investigate photoluminescence features of porous silicon microcavity samples with a subwavelength space resolution. The emission is found to be markedly dependent on the lateral position, with the presence of relatively narrow spectral features peaked at different wavelengths in the range 610–690 nm. Furthermore, the spectrum obtained by summing up spectra taken at different sampling points (relative displacement ∼100 nm) recovers the standard (macroscopic) photoluminescence spectrum of porous silicon, except for the presence of a dip around the resonance wavelength of the microcavity resonator. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the experimental characterization of porous silicon free-standing coupled microcavities. We have grown free-standing structures of up to 109 stacked layers. Free-standing structures are interesting because reflectance spectra can be measured on both sides of the samples. The comparison of reflectance spectra from the front and back side indicates that the porous silicon anodization process has a natural drift along the growth direction. However, we demonstrate that this drift can be compensated, showing a homogeneous structure of ten coupled microcavities, in which all ten resonance peaks are resolved in both transmission and reflection measurements. [ABSTRACT FROM AUTHOR]

We report the observation of strongly anisotropic scattering of laser light at oblique incidence on a (100)-oriented porous silicon layer. The scattered light forms cones tangent to the incident and reflected beams. The conical pattern is caused by scattering on the vertical walls of pores, which are straight along the layer thickness. The light cone defines structured light rings onto a screen normal to the cone axis. We explain the various structures by optical anisotropy of porous silicon. For the sample under analysis, we directly measure from the ring patterns a value of δn/n[sub ord] = 8% of positive birefringence. [ABSTRACT FROM AUTHOR]

Porous silicon (PS) conductometric gas sensors can exhibit large sensitivity to gases, due to the large surface versus volume ratio of porous silicon. A possible application is the detection of traces of nitrogen dioxide (NO2), an air pollutant. ΔG/G signals in excess of 10 in the presence of concentrations as low as 50 ppb in dry air can be demonstrated. Unfortunately, such high sensitivity to NO2 is achieved, in fresh samples, with poor reversibility. Another problem is the interference of water vapor, which also affects the porous silicon conductivity. However, we show that reversibility is complete in aged samples, and sensitivity to water vapor is lowered. Although in aged samples large ΔG/G signals are harder to achieve, we show that concentration levels of NO2 at few tens of ppb are still detectable. [Copyright &y& Elsevier]

We report a nitrogen dioxide sensor suitable for environmental control, based on the change in conductivity of a single meso-porous silicon (PS) layer with about 80% porosity. We present the characterization of the sensor in the presence of low concentrations of NO2 in dry air and study the influence of humidity on sensor behaviour. The sensor shows a sensitivity to 12 ppb of NO2 in dry air and a good response to 50 ppb in humid air. [Copyright &y& Elsevier]