Fabrication of Perforated Film Nanostructures
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H8.5.1
Fabrication of Perforated Film Nanostructures
A. L. Elias, K. D. Harris and M. J. Brett Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB, Canada T6G 2V4, [email protected] ABSTRACT We have demonstrated the fabrication of perforated thin films (PTFs), comprised of thin coatings perforated with unusual pore shapes such as helices or chevrons. PTFs are fabricated using a template of nanohelices or nanochevrons produced using the Glancing Angle Deposition (GLAD) technique. PTFs can be produced by filling GLAD films with a variety of substances, etching back the coating to reveal the tips of the helices or chevrons, and etching out the template film. A process for fabricating nickel PTFs has been developed, and a nickel PTF of helical pores with nominal diameters of 100nm has been produced. INTRODUCTION There are a number of techniques that may be used to produce thin films perforated by ordered and randomly arranged pores. A two-step anodization process can be used to produce straight pores 100µm deep in alumina with aspect ratios of around 500 [1]. These pores may be randomly organized, self-organized or grown from a lithographically produced pre-pattern. Similarly, ordered arrangements of pores may be produced in silicon by electrochemically etching an illuminated, pre-patterned wafer in hydrofluoric acid [2]. Etching occurs along the [100] direction of the silicon, resulting in the formation of straight pores. Electrochemically etched pores are typically cylindrically symmetric and extend straight through the film in a direction perpendicular to the surface. We have previously demonstrated the fabrication of photoresist and spin-on-glass films consisting of thin (1µm – 2µm) films perforated by unusually shaped pores such as helices and chevrons [3]. These films have been produced in a four-step process using SiO and SiO2 GLAD films as templates. Periodic arrays of helices have been demonstrated by using a template film deposited on a lithographically pre-patterned substrate. These films have a variety of potential applications. Both helical template and perforated films exhibit circular birefringence – linearly polarized light incident on these films experiences strong rotation. The optical rotatory power of photoresist PTFs has been shown to be two to three times as high as the SiO2 template films from which they were cast [4]. The large surface area of template and perforated thin films also makes them useful for applications such as sensors. SiO template films and photoresist perforated films have been demonstrated as high speed humidity sensors [5]. Other potential applications for perforated thin films include photonic bandgap crystals [6] or chirally selective filters.
H8.5.2
FABRICATION We will now discuss the 4-step fabrication process used to produce nickel films perforated with helical pores. Each of the four steps is illustrated by scanning electron micrograph (SEM) images of side and top views. These images were taken at every step in the processing of a
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