Photoluminescent nanostructured thin films have been fabricated using physical vapour deposition and the glancing angle deposition (GLAD) technique. Precision controlled substrate motion and oblique incidence (>75o) enable the fabrication of a variety of 3-D morphologies including vertical posts, helical (chiral) columns and chevrons. Scanning electron microscopy and X-ray diffraction were used to characterize the film nanostructure. These experiments focussed on the chiral morphology which exhibits intriguing polarization behaviour such as selective transmission of circularly
polarized light and circularly polarized photoluminescence. Helical films of Y2O3:Eu and Alq3 were fabricated with thicknesses in excess of 2 μm and densities nominally 60% of bulk. Transmission spectroscopic ellipsometry measurements were used to determine the degree of selective transmission of polarized light through the samples. The degree of circular polarization for the photoluminescent light emitted from helical films was measured with the use of a quarter waveplate and linear polarizer. Polarized photoluminescence efficiencies were consistent with the observed selective transmission of circularly polarized light through the films. The use of GLAD to control the nanoscale morphology of the films allows for the spectral location and strength of these polarization effects to be easily and accurately selected.
Chiral thin films have been demonstrated to have significant optical activity and device applications for gratings, filters, retarders and optical switches. These helically nanostructured films may be microfabricated onto silicon or other substrates utilizing the Glancing Angle Deposition (GLAD) technique with various nanostructures such as helices, chevrons, or polygonal spirals. GLAD is a simple one-step process that enables ready integration of these structures onto optical chips. As proposed by Toader and John, the GLAD technique can be used to fabricate large bandwidth photonic crystals based on the diamond lattice. This structure yields a predicted photonic bandgap as much as 15% of the gap center frequency. Moreover, the corresponding inverse square spiral structure is predicted to have a photonic bandgap as much as 24% of the gap center frequency. We report the details of basic chiral thin film fabrication and calibration. We will also discuss optical characteristics of the chiral films such as the optical rotatory power. Finally, we present the results of our efforts to fabricate square spiral and inverse square spiral structures.