Large-Area Subwavelength Hole Arrays

Hole arrays are generally produced by focused ion beam (FIB) milling a serial low throughput process. Free-standing suspended films can be fabricated by FIB and reactive ion etching but generation of multi-layered films has been limited to a few metals. No technique has been developed for producing optical quality hole arrays in a parallel fashion from multiple materials and in areas larger than hundreds of square microns. The present process employs a combination of phase-shifting photolithography wet-chemical etching and electron-beam deposition to generate single or multiple material films of desired thickness. Removal of the substrate affords defect free large-area (> 1 in²) hole array films on glass. Single metal or multiple material layered structures including 50 100 nm thick Au films with 250 nm holes 50/50 nm thick Au/Ni films 40/20/40 nm Au/Ni/Au films and 20/70/20 nm Au/SiOx/Au films have been fabricated The process enables construction of anisotropic hole arrays of varying size shape configuration curvature and pitch. The optical quality of these films has been demonstrated by transmission near-field scanning optical microscopy (NSOM). Under 633 nm illumination a 100‑nm thick Au film produced enhanced transmission at the holes generated by the localized surface plasmon resonance with the holes and standing wave patterns between adjacent holes. Use of polarized light exhibits dramatic changes in emission properties as hole material shape and configuration are altered. Process variables permit fine control of the hole array spectral response. Nanoholes and nanoparticles appear to provide complementary structures which should be facilitated by the present invention. This technology provides a flexible strategy to create subwavelength films whose properties are tunable for applications in microscopy sensors magneto-optic data storage and solar cells. Status: Issued U.S. Patents 7999353 and 8415240