The ability to guide and localize photons on features much smaller than the wavelength of light is critical for the development of new photonic chips, enhanced energy conversion schemes, and biosensors. Plasmonics leverages the strong light-matter interactions between materials with large free-electron densities and electromagnetic waves to confine light in subwavelength features and generate enhanced EM fields near the surface of the material. Most plasmonic materials are based on noble metals such as gold and silver which have plasmon resonances in the visible. However, there is growing demand for plasmonic activity in the infrared (IR) which eliminates the use of noble metals since their losses are extremely high at these wavelengths. Alternate materials for IR plasmonics are highly-doped semiconductors such as ZnO, GaAs, indium tin oxide (ITO), and silicon. We are interested in developing materials that not only have low loss in the IR, but also have highly tunable plasmonic resonances and can be fabricated with techniques that are compatible with complementary metal-oxide-semiconductor (CMOS) processing. For example, we have demonstrated that aluminum doped ZnO (AZO) can be deposited via atomic layer deposition (ALD) onto nanostructures with excellent conformality and with tunable plasmon resonances from the mid-IR to near IR. Ongoing work is focused on optimizing the properties of these materials and integrating them into energy conversion and other optoelectronic devices.
(left) Electron micrograph of a silicon nanopillar array coated (via ALD) with AZO. (middle) Optical density of ALD AZO thin films deposited at different temperatures. (right) Tunable plasmon resonances of AZO by altering the amount of aluminum.
Related references
1. C.T. Riley, T.A. Kieu, J.S.T. Smalley, S.H.A. Pan, S.J. Kim, K.W. Post, A. Kargar, D.N. Basov, X. Pan, Y. Fainman, D. Wang, and D.J. Sirbuly "Plasmonic tuning of aluminum doped zinc oxide nanostructures by atomic layer deposition" Phys. Status Solidi RRL, DOI: 10.1002/pssr.201409359 (2014).
Awards:Our work on 3D optical printing of piezoelectric nanoparticle-polymer composites was chosen for the 2015 SPIE Best Paper Award in 3D printing, fabrication, and manufacturing.