The scattering of electromagnetic waves by periodic layered media plays a crucial role in many applications in optics and photonics, in particular in nanoplasmonics for topics as diverse as extraordinary optical transmission, photonic crystals, metamaterials, and surface plasmon resonance biosensing. With these applications in mind, we focus on surface plasmon resonances excited in the context of insulator-metal structures with a periodic, corrugated interface. The object of this contribution is to study the geometric limits required to generate these fundamentally important phenomena. For this we use the robust, rapid, and highly accurate field expansions method to investigate these delicate phenomena and demonstrate how very small perturbations (e.g., a 5 nm deviation on a 530 nm period grating) can generate strong (in this instance 20%) plasmonic absorption, and vanishingly small perturbations (e.g., a 1 nm deviation on a 530 nm period grating) can generate nontrivial (in this instance 1%) plasmonic absorption. (C) 2016 Optical Society of America