(Color online) A schematic illustration of thin film column growth at oblique deposition angles. The deposition angle is measured from the substrate normal.
(a) A chevron thin film is produced by rotating the substrate 180° prior to forming each arm of the zigzag microstructure; (b) using SBD, the length of each arm is less than the column diameter so that the zigzag microstructure is reduced to a vertically aligned column.
(Color online) The in-plane birefringence of SBD thin films over a range of deposition angles and wavelengths. The degree of anisotropy in obliquely deposited thin films depends on the deposition angle and reaches a maximum at approximately 70°.
(Color online) Shown here is the in-plane birefringence of a SBD thin film, before and after applying a heat treatment for . A simplified Sellmeier formula was fit to the spectra using the form given in Eq. (5). Crystallization of the has caused the birefringence to double in magnitude across the optical wavelength range.
(Color online) Annealing of thin films formed by SBD at indicates that the largest increases in birefringence can be obtained by annealing for or longer. The dotted line represents the birefringence of the as-deposited sample. The fitted line in each case is a guide to the eyes.
The normal incidence birefringence of annealed thin films at a wavelength of for deposition angles of (a) 60°, (b) 65°, (c) 70°, and (d) 75°. The largest increases in birefringence occur at annealing temperatures in the range of and .
XRD patterns of thin films, before and after annealing. The characteristic diffraction peaks of anatase (A) and rutile (R) are labeled. The inset shows the growth of anatase grains with annealing temperature based on the width of the (101) and (004) diffraction peaks.
Transmittance of the annealed films remains high until the annealing temperature exceeds approximately . The inset shows the transmittance as a function of temperature at a wavelength of .
(Color online) Atomic force microscopy of a thin film surface deposited by SBD at : (a) as deposited and (b) annealed at . Both the surface roughness and structural anisotropy increase after annealing.
Top-down SEM images shown here were taken from SBD thin films formed at and annealed at the following temperatures: (a) as deposited, (b) , (c) , and (d) .
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