Functional Optical Devices Based on Highly Ordered Metal Nanostructures Obtained Using Anodic Porous Alumina

There has been increasing interests in the fabrication process of ordered metal nanostructures due to its applicability to the enhancement of the electric field of the incident light based on the localized surface plasmon resonance (LSPR).  Various functional optical devices based on LSPR have been proposed, such as sensing devices, nonlinear optics, photovoltaic cells, and so on.  The performance of the optical devices is dependent on the shapes and arrangement of metals because the efficiency of the enhancement of the electric field by LSPR is determined by the geometrical structures of metals.  However, the fabrication process of geometrically controlled metal nanostructures with large sample area has not been established so far because of the difficulties in the precise fabrication of nanostructures.  We have reported the fabrication of highly ordered metal nanostructures using anodic porous alumina and its application to the functional optical devices based on LSPR [1,2].  Anodic porous alumina, which is formed by anodization of Al in acidic solutions, is a typical self-ordered mesoporous material.  The ordered metal nanostructures could be obtained using the anodic porous alumina as a template for the fabrication.  One of advantageous points of the process using the anodic porous alumina is the precise controllability of the geometrical structures.  In the report, the fabrication of various types of the metal nanostructures and its application to the substrate for the measurements of surface-enhanced Raman scattering (SERS) will be presented.  The highly ordered metal nanostructures (dots or wires) were fabricated using anodic porous alumina templates.  The obtained structures were applied to the substrates for the SERS measurements.  The SERS activity was optimized by controlling the shape and arrangement of the metal nanostructures.  The present process can be used not only for the fabrication of the SERS substrates but also for the fabrication of functional optical devices requiring the highly ordered metal nanostructures.

[1] T. Kondo, K. Nishio, H. Masuda, Appl. Phys. Express, 6, 102401 (2013).

[2] T. Kondo, H. Masuda, K. Nishio, J. Phys. Chem. C, 117, 2531 (2013).