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Schematic for fabrication of samples for PLM transmission and PBG reflectance measurements. Ordered PBG silicon structures were formed by interference lithography and electrochemical etching. For out of plane transmission measurements, the substrate was removed by chemical etching. For reflectance measurement in plane of the PBG structure, the sample was cleaved. In both cases, aluminum contacts were formed on the top and bottom of a sample by evaporation.
Electron micrograph of an attached porous silicon membrane (a) and detailed photograph showing the structure of the electrical contact (b).
(Color online) Transmitted light intensity vs applied voltage for a -thick porous silicon membrane. Triangles—light transmitted through the crossed polarizers. Diamonds—transmission of unpolarized light. The lines are guides for the eye. The figure also shows a schematic LC orientation before and after the phase transition. The PLM measurement setup is shown on the right. LCs undergo a Frederiks transition into axial orientation, reducing the LC birefringence and thus the transmitted polarized light intensity. At the same time, the phase transition reduces scattering, thus increasing the transmission of unpolarized light.
(Color online) Redshift of the higher energy TM band edge as a function of applied voltage for a -thick PBG layer. The solid line is a guide for the eye. The inset shows the schematic of PBG reflectance measurements.
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