Localized Surface Plasmon Resonance Nanosensor: A High-Resolution Distance-Dependence Study Using Atomic Layer Deposition

Abstract

Atomic layer deposition (ALD) is used to deposit 1−600 monolayers of Al₂O₃ on Ag nanotriangles fabricated by nanosphere lithography (NSL). Each monolayer of Al₂O₃ has a thickness of 1.1 Å. It is demonstrated that the localized surface plasmon resonance (LSPR) nanosensor can detect Al₂O₃ film growth with atomic spatial resolution normal to the nanoparticle surface. This is approximately 10 times greater spatial resolution than that in our previous long-range distance-dependence study using multilayer self-assembled monolayer shells. The use of ALD enables the study of both the long- and short-range distance dependence of the LSPR nanosensor in a single unified experiment. Ag nanoparticles with fixed in-plane widths and decreasing heights yield larger sensing distances. X-ray photoelectron spectroscopy, variable angle spectroscopic ellipsometry, and quartz crystal microbalance measurements are used to study the growth mechanism. It is proposed that the growth of Al₂O₃ is initiated by the decomposition of trimethylaluminum on Ag. Semiquantitative theoretical calculations were compared with the experimental results and yield excellent agreement.