Abstract
Porous films of anodic aluminum oxide are widely used as templates for the electrochemical preparation of functional nanocomposites containing ordered arrays of anisotropic nanostructures. In these structures, the volume fraction of the inclusion phase, which strongly determines the functional properties of the nanocomposite, is equal to the porosity of the initial template. For the range of systems, the most pronounced effects and the best functional properties are expected when the volume fraction of metal is less than 10%, whereas the porosity of anodic aluminum oxide typically exceeds this value. In the present work, the possibility of the application of anodic aluminum oxide for obtaining hyperbolic metamaterials in the form of nanocomposites with the metal volume fraction smaller than the template porosity is demonstrated for the first time. A decrease in the fraction of the pores accessible for electrodeposition is achieved by controlled blocking of the portion of pores during anodization when the template is formed. The effectiveness of the proposed approach has been shown in the example of obtaining nanocomposites containing Au nanorods arrays. The possibility for the control over the position of the resonance absorption band corresponding to the excitation of collective longitudinal oscillations of the electron gas in the nanorods in a wide range of wavelengths by controlled decreasing of the metal volume fraction, is shown.
Highlights
Nanocomposites, owing to the synergy of matrix and inclusion phase properties, have found wide applications in many areas of science and technology [1,2,3]
The possibility of the application of anodic aluminum oxide for obtaining hyperbolic metamaterials in the form of nanocomposites with the metal volume fraction smaller than the template porosity is demonstrated for the first time
To obtain hyperbolic metamaterials based on an array of metallic nanorods in a dielectric matrix as a template, porous films of anodic aluminum oxide (AAO) containing an array of highly ordered pores and possessing high transmission in the visible spectral range are frequently used [11]
Summary
Nanocomposites, owing to the synergy of matrix and inclusion phase properties, have found wide applications in many areas of science and technology [1,2,3]. To obtain hyperbolic metamaterials based on an array of metallic nanorods in a dielectric matrix as a template, porous films of anodic aluminum oxide (AAO) containing an array of highly ordered pores and possessing high transmission in the visible spectral range are frequently used [11]. To reduce the porosity of AAO templates, the post-treatment of the films after anodization using the atomic layer deposition technique can be applied [16] This method allows one to cover the pore walls by the layer of desired material with uniform thickness, it is an extremely time- and resource-consuming process. The efficiency of the developed technique is demonstrated in the example of the controlled variation of the optical properties of the hyperbolic metamaterials based on the arrays of Au nanorods in the anodic aluminum matrix
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