Identifying low-loss plasmonic materials

Abstract

Plasmonics is a research area that merges optics and nanoelectronics by confining light to the nanoscale, thereby enabling a family of novel devices.1–6 Plasmonics is also a building block for metamaterials, which are artificial materials designed and engineered to exhibit properties beyond those found in nature.7–11 Both plasmonics and metamaterials pave the way to many applications with unprecedented functionalities, ranging from subwavelength waveguides and optical nanoantennas to hyperlenses and light concentrators.9–11 However, at telecommunication and visible frequencies, plasmonic devices face significant challenges because of losses related to the constituent metals that seriously limit their practical use. The plasmon phenomenon typically originates from the collective oscillations of free charges in a material released by an applied electromagnetic field. Consequently, plasmonic devices generally require metallic components, which have an abundance of free electrons. These electrons provide the negative real permittivity () that is an essential property of any plasmonic material. However, metals are plagued by large losses associated with the imaginary part of permittivity (), especially in the visible and UV spectral ranges, arising primarily from interband electronic transitions. Even metals with the highest conductivities suffer from large losses at optical frequencies that are detrimental to the performance of plasmonic devices.12 To mitigate material losses, optical gain materials can be combined with metallic structures. However, even the best gain materials available offer little compensation.13 One approach to this problem involves alloying two or more metals to create plasmonic materials with unique band structures that can be tuned for applications at specific frequencies. For instance, by n-doping noble metals with transition metals, absorption peaks can be shifted to a region of the spectrum Figure 1. Experimentally measured (a) real () and (b) imaginary () parts of permittivity for indium tin oxide annealed under various conditions. Ag: Silver. N: Nitrogen. O: Oxygen.