Vacuum evaporated porous silicon photonic interference filters

Abstract

Porous materials with nanometer-scale structure are important in a wide variety of applications including electronics, photonics, biomedicine, and chemistry. Recent interest focuses on understanding and controlling the properties of these materials. Here we demonstrate porous silicon interference filters, deposited in vacuum with a technique that enables continuous variation of the refractive index between that of bulk silicon and that of the ambient (n approximately 3.5 to 1). Nanometer-scale oscillations in porosity were introduced with glancing angle deposition, a technique that combines oblique deposition onto a flat substrate of glass or silicon in a high vacuum with computer control of substrate tilt and rotation. Complex refractive index profiles were achieved including apodized filters, with Gaussian amplitude modulations of a sinusoidal index variation, as well as filters with index matching antireflection regions. A novel quintic antireflection coating is demonstrated where the refractive index is smoothly decreased to that of the ambient, reducing reflection over a broad range of the infrared spectrum. Optical transmission characterstics of the filters were accurately predicted with effective medium modeling coupled with a calibration performed with spectroscopic ellipsometry.

Optical and Structural Properties of Bilayer Circular Filter Prepared by Glancing Angle Deposition

“…By exploiting various rotation schemes for the substrate, a wide variety of thin-film morphologies including slanted columns, helices, S-shapes, C-shapes and zigzag/chevron structures can be fabricated [5][6][7][8]. Because of controlled porosity and microstructure, GLAD films have a wide range of suggested applications, such as three-dimensional photonic crystals [9][10][11], birefrigent omnidirectional reflectors [12], graded index optical filters [13,14], broadband antireflection coatings [15,16], linear polarizers [17], and fluid concentration sensors [18,19].…”

Porous silicon-based rugate filters

“…20 Also, vacuum-evaporated PS permits a periodic smooth variation of porosity. 21 In this paper, we report a detailed study of PSbased rugate filters, focusing on design, fabrication, and discussion of results. Section 2 is a theoretical introduction that describes some features of rugate filters and techniques for improving the filter response.…”

Understanding Nickel Thin Film crystallization using X-Ray Diffractometry

“…Some already feasible usages include magnetic media high density information storage (Hsieh et al, 1997), liquid crystal display technology (Robbie et al, 1999), photonic crystal (Kennedy et al, 2003), optical rotators, polarization beam splitters (Azzam, 1992), optical filters (Hodgkinson et al, 2000;Hodgkinson et al, 2000a;Kaminska et al, 2003). The technique is being explored for applications in the bioluminescence sensors, electroluminescent devices, optical transparent conducting films from pure metals, multistate electronic switches based on filamentary conduction, optical sensors that can detect and quantify various chemical and biological fluids, microsieves for entrapment of viruses, porous materials for growing biological tissues, chemical sensors, catalytic reaction surfaces, optical coatings, thermoelectric materials, quantum effect devices, field emitters, and solar cells.…”