Ribbon structures on the submicrometer scale are of interest for the development of nanodevices in various fields. We fabricate periodic arrays of silicon ribbons using electron beam lithography and thin film deposition at highly oblique incident angles. A periodicity of 1 µm and a line width less than 100 nm is used for the lithographically prepatterned substrate seed layers to ensure that the planar fill factor was less than the equilibrium volume fill factor of the thin film. Individual ribbons exhibit a width of approximately 1.8 µm, controlled by the length of deposition, and a thickness of approximately 100 nm. The ribbons fabricated for this experiment have a length of 4 mm, and exhibit an amorphous structure with scattered crystallites throughout the matrix.
In this paper, we present the growth and optical characterization of the preliminary stages of amorphous silicon square spiral growth on pre-patterned and unpatterned sections of silicon substrates. The periodicity of the seeding was set to 1 μm using electron beam lithography, and a seed enhancement layer was deposited on top of the seeds, followed by a quarter-turn square spiral on top of that. It was found that the optical constants in the wavelength region of 1000 nm to 1700 nm for the film materials were higher for the patterned sections of the film as compared with the unpatterned sections of the film.
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.