Fabrication of High-Aspect Metal Nanostructure Using Anodic Porous Alumina and Its Optical Property

High-aspect nanostructure, such as a nanohole and a coaxial nanocable, are considered as a powerful candidate for a light waveguide. Especially, a coaxial nanocable can efficiently propagate the incident light because the coaxial nanocable does not have cut-off wavelength as seen in a nanohole. In addition, by reducing the opening size of the coaxial nanocable, the coaxial nanocable can propagate the light to an area less than a wavelength of the incident light beyond the diffraction limit. Therefore, the coaxial nanocable is expected to be applied to fabricate various types of functional optical devices, such as nanoimaging device and high-density optical recording device. However, it is still difficult to fabricate the high-aspect nanostructure with complicated geometrical features such as the coaxial nanocable because of fabrication difficulties. Until now, our group had been reported fabrication process of the high-aspect metal nanostructures using an anodic porous alumina and its optical property [1-3]. Anodic porous alumina has an ordered array of straight nanoholes having high aspect ratio. Due to this unique geometrical character, anodic porous alumina is commonly used as a starting material to fabricate nanostructures having high aspect feature. In our previous work, we reported fabrication of the coaxial nanocables having high aspect ratio using anodic porous alumna [3]. In addition, it was observed that the coaxial nanocable could efficiently propagate the visible light. In the present work, with the aim of improving the performance of the functional devices based on the coaxial nanocable, reduction of opening size of the coaxial nanocable and evaluation of the optical property were demonstrated. This fabrication process is expected to be applied to fabricate various types of functional optical devices requiring the fine coaxial nanocable.

1. K. Nishio, M. Nakao, A. Yokoo, H. Masuda, Jpn. J. Appl. Phys., 42, L83 (2003).

2. T. Kondo, N. Kitagishi, T. Yanagishita, H. Masuda, Appl. Phys. Express, 8, 06200 (2015).

3. T. Kondo, R. Ichinose, M. Kurosawa, T. Yanagishita, H. Masuda, The 87^th ECSJ Spring Meeting, 1C06 (2020).