Peter C. P. Hrudey

Strong circular Bragg phenomena in self-ordered porous helical nanorod arrays of Alq3

Porous chiral thin films composed of a nearly hexagonal-close-packed array of helical nanorods of tris-(8-hydroxyquinoline) aluminum (Alq3) are fabricated using glancing angle deposition and exhibit a one-dimensional polarization-dependent photonic stop band. These chiral thin films transmit only one handedness of circularly polarized light and emit highly circularly polarized photoluminescence. The strong circular Bragg phenomena exhibited by these films suggest potential for use of these films in low-threshold mirrorless lasing and circularly polarized emission applications, while the porosity of the films allows for infiltration by dyes or liquid crystals to enable the formation of unique hybrid materials.

Optical properties of porous nanostructured Y2O3:Eu thin films

Nanostructured photoluminescent thin films of europium-doped yttrium oxide (Y2O3:Eu), a well-known luminescent material, were grown using electron-beam evaporation in combination with the glancing-angle deposition technique. GLAD makes use of controlled substrate motion during extremely oblique physical vapor deposition of a thin film resulting in a high degree of control over the nanostructure of the film. Scanning electron microscopy and x-ray diffraction were used to characterize film nanostructure, while the light emission properties of these films were characterized by photoluminescence measurements. Transmission ellipsometry measurements were used to determine the degree of selective transmission of polarized light through the samples. The polarization of the emission from chevronic and helical films was determined through the measurement of the Stokes parameters of the emitted light for each sample. Comparison of the degree of polarization during the emission experiments to the degree of selective ...

Photoluminescence emission profiles of Y 2 O 3 :Eu films composed of high-low density stacks produced by glancing angle deposition

Periodic high-/low-index film stacks composed of Y(2)O(3) : Eu were grown by glancing angle deposition on silicon and fused silica substrates. Postdeposition annealing at temperatures from 600 to 1000 degrees C for 1 h in air was performed to activate photoluminescence. Absolute photoluminescence spectra were obtained as a function of observation angle. The angular emission distribution was non-Lambertian, with peak emission at angles of 50 to 60 degrees with respect to substrate normal. Spectroscopic transmittance and ellipsometry measurements were performed to characterize the films. Using this description, we were able to reproduce the angular photoluminescence patterns of the films.

Obliquely deposited tris(8-hydroxyquinoline) aluminium (Alq3) biaxial thin films with negative in-plane birefringence

Tilted columnar biaxial thin films were fabricated by thermally evaporating tris(8-hydroxyquinoline) aluminium (Alq3) at oblique angles of incidence α≥65° measured from the substrate normal. Variable angle spectroscopic ellipsometry and Bruggeman effective medium approximations were used to characterize the structure and the optical anisotropy of the films. The structural characteristics were also examined using scanning electron microscopy, revealing a lack of column broadening and a predominantly circular column cross-section. The films also exhibited larger column tilt angles than those typical of inorganic tilted columnar films. These structural properties gave rise to optical anisotropy leading to negative values of in-plane birefringence of the films that increased in magnitude with deposition angle. The observed negative in-plane birefringence contrasts with the typical behaviour of inorganic biaxial columnar thin films which exhibit positive values of in-plane birefringence, with peak values obtained for films grown at angles of 60°<α<70°. The maximum in-plane birefringence obtained with Alq3 films was −0.073 ± 0.002 and was observed for films grown at α = 85°.

Effects of film structure on photoluminescent emission properties of nanostructured Y2O3:Eu thin films

Nanostructured europium-doped yttrium oxide (Y2O3:Eu) films were fabricated using electron beam evaporation, in combination with the Glancing Angle Deposition (GLAD) technique. GLAD makes use of controlled substrate motion during physical vapour deposition (PVD) of a thin film resulting in a high degree of control over the nanostructure of the film. Films were deposited using pre-doped Y2O3:Eu source material. Scanning electron microscopy was used to characterize film nanostructure, while the light emission properties of these films were characterized by photoluminescence measurements. Films of four different nanostructures were used in this study: chevrons, pillars, helices, and normally-deposited solid thin films. For each film nanostructure, measurements of the angular dependence of the intensity of the emitted light, as well as absolute brightness, were obtained and compared. The polarization of the light emitted from the chevron film was also examined using a linear polarizer to analyze the polarization state. Measurements of the selective transmission of circularly polarized light through the helical samples were obtained using variable angle spectroscopic ellipsometry.

Photonic device applications of nano-engineered thin film materials

Optical studies of porous nano-engineered thin film materials fabricated using Glancing Angle Deposition (GLAD) have been a focal point of research since the inception of the GLAD technique over ten years ago. As the sophistication of porous nano-engineered thin film designs has increased over the years, photonic device applications of these materials have been explored. We will review some of our recent advancements in the study and fabrication of porous nano-engineered thin films for optical applications including our groups work with helical films and devices, square spiral photonic crystal films, and graded-index (GRIN) films and devices. Initial optical studies of helical films focused upon the circular Bragg effects and optical rotatory dispersion exhibited by such structures. In recent years, the exploration of different materials and the fabrication of liquid crystal (LC) cells using these films have brought the prospect of using such film-LC hybrids in display applications much closer. Helical films made from luminescent materials have also been investigated and were found to emit partially circularly-polarized light. Our work with square spiral structures focuses upon the fabrication of periodic arrays of such structures in order to yield a three-dimensional photonic bandgap. Our techniques also enable the formation of designed defects in the array with relative ease, opening the door to a myriad of potential applications. Finally, we will discuss graded-index structures which are made by varying the porosity of the film structure during film growth. Films of this nature have been designed and fabricated for use as wide-band antireflection coatings, rugate filters, spectral-hole filters, and optical humidity sensors.

Luminescence of nanostructured Y2O3:Eu thin films fabricated using glancing angle deposition techniques

Thin films of europium-doped yttrium oxide (Y2O3:Eu), a well-known luminescent material, were grown using electron beam evaporation, in combination with the Glancing Angle Deposition (GLAD) technique. GLAD makes use of controlled substrate motion during physical vapour deposition (PVD), resulting in a high degree of control over the nanostructure of the film. Until recently GLAD had not been used with luminescent materials. Films were deposited using pre-doped Y2O3:Eu source material, with either 4.0% (wt) Eu doping or 5.6% (wt) Eu doping. The nanostructure of these films was characterized through scanning electron microscopy, while the light emission properties of these films was characterized by photoluminescence measurements. In order to optimize the light emission properties of the films the partial pressure of oxygen during the deposition of the films was varied. Films were deposited on both silicon and sapphire substrates, in order to compare how different substrates affect the growth and light emission of the films.

Circularly polarized luminescence from chiral thin films

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.

Fabrication and Characterization of Self-Organized Alq 2 Chiral Thin Film Nanostructures

Chiral thin films of Alq3are fabricated and characterized. The films, deposited via the Glancing Angle Deposition (GLAD) process, display high structural precision and a highly self-organized structure. The selective transmission of left versus right-handed circularly polarized light is measured to reach ~62%.

Evaporated nanostructured Y/sub 2/O/sub 3/:Eu thin films

Europium-doped yttrium oxide (Y/sub 2/O/sub 3/:Eu) is a well-known luminescent material that has been experimented with in recent years in thin film form. However, to date there has not been a great effort put into altering the nanostructure of these films. A thin film deposition technique called glancing angle deposition (GLAD) allows for a high degree of control over the nanostructure of the thin film, resulting in thin films with nanostructures ranging from chevrons and posts to helices. GLAD was used here to make europium-doped yttrium oxide thin films with different nanostructures. Scanning electron microscopy was then used to characterize the nanostructures of the films, while UV excitation was used to characterize the photoluminescence properties of the films.