Single Crystalline Silver Films for Plasmonics: From Monolayer to Optically Thick Film

TL;DR

This paper presents a universal method for growing atomically smooth, precisely controlled single crystalline silver films from monolayers to thick layers, enhancing plasmonic device performance and protection with an in-situ aluminum oxide capping layer.

Contribution

It introduces a new growth approach that combines the advantages of existing methods, enabling precise thickness control and high-quality epitaxial silver films across a wide thickness range.

Findings

Successful growth of atomically smooth epitaxial Ag films from monolayer to thick regimes.

Demonstrated improved surface plasmon polariton propagation lengths.

Enhanced device performance in waveguide plasmonic nanolasers.

Abstract

Epitaxial growth of single crystalline noble metals on dielectric substrates has received tremendous attention recently due to their technological potentials as low loss plasmonic materials. Currently there are two different growth approaches, each with its strengths and weaknesses. One adopts a sophisticated molecular beam epitaxial procedure to grow atomically smooth epitaxial Ag films. However, the procedure is rather slow and becomes impractical to grow films with thickness > 50 nm. Another approach adopts a growth process using rapid e-beam deposition which is capable of growing single crystalline Ag films in the thick regime (> 300 nm). However, the rapid growth procedure makes it difficult to control film thickness precisely, i.e., the method is not applicable to growing thin epitaxial films. Here we report a universal approach to grow atomically smooth epitaxial Ag films with precise thickness control from a few monolayers to the optically thick regime, overcoming the limitations of the two aforementioned methods. In addition, we develop an in-situ growth of aluminum oxide as the capping layer which exhibits excellent properties protecting the epitaxial Ag films. The performance of the epitaxial Ag films as a function of the film thickness is investigated by directly measuring the propagation length of the surface plasmon polaritons (SPPs) as well as their device performance to support a waveguide plasmonic nanolaser in infrared incorporating an InGaAsP quantum well as the gain media.