4 May 2018 Quantum spill-out in few-nanometer metal gaps: Effect on gap plasmons and reflectance from ultrasharp groove arrays in silver
Author Affiliations +
A gap plasmon is an electromagnetic wave propagating in a gap between two noble metal surfaces. Such gap plasmons have previously been studied using only a classical description of the noble metals, but this model fails and shows unphysical behavior for sub-nanometer gaps. To overcome this problem quantum spill-out is included in this paper by applying Density-Functional Theory (DFT), such that the electron density is smooth across the interfaces between metal and air. The mode index of a gap plasmon propagating in the gap between the two metal surfaces is calculated from the smooth electron density, and in the limit of vanishing gap width the mode index is found to converge properly to the refractive index of bulk metal. When neglecting quantum spill out in this limit the mode index shows unphysical behavior and diverges instead. The mode index is applied to calculate the reflectance of an ultrasharp groove array in silver, as gaps of a few nm are found in the bottom of such grooves. At these positions the gap plasmon field is highly delocalized implying that it mostly exists in the bulk silver region where absorption takes place. Surprisingly, when the bottom width is a few nm and the effect of spill out at a first glance seems to be negligible, strong absorption is found to take place 1-2 Å from the groove walls as a consequence of the dielectric function being almost zero at these positions. Hence quantum spill out is found to significantly lower the reflectance of such groove arrays in silver.
© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Enok J. H. Skjølstrup, Enok J. H. Skjølstrup, Thomas Søndergaard, Thomas Søndergaard, Thomas G. Pedersen, Thomas G. Pedersen, } "Quantum spill-out in few-nanometer metal gaps: Effect on gap plasmons and reflectance from ultrasharp groove arrays in silver", Proc. SPIE 10672, Nanophotonics VII, 1067205 (4 May 2018); doi: 10.1117/12.2306750; https://doi.org/10.1117/12.2306750


Plasmonics for THz frequency applications
Proceedings of SPIE (February 21 2011)
Plasmonic enhancement using core-shell nanoparticles
Proceedings of SPIE (June 01 2005)
Surface Plasmon Scanning Microscopy
Proceedings of SPIE (July 11 1988)

Back to Top