Highly Efficient and Tailorable On-Chip Metal–Insulator–Metal Plasmonic Nanofocusing Cavity

Simulation techniques were used to investigate the properties of a deep subwavelength-scale on-chip optical cavity composed of a highly efficient metal–insulator–metal 3D-tapered plasmonic nanofocusing waveguide and easily tailorable metal–insulator–metal plasmonic crystals. The configuration described here significantly enhanced the highly efficient field localization in the plasmonic nanofocusing waveguide at the center of the cavity due to the impedance tuning capabilities of the plasmonic crystals. The plasmonic crystals served as nanoscale input and output couplers with designable reflectivities and a clear band-stop regime around the telecommunication wavelength, λ₀ = 1.55 μm. Simulation studies indicated that this configuration could efficiently confine electromagnetic waves on the nanometer length scale through a field intensity enhancement of 7 × 10³ and a Purcell enhancement of 8 × 10³ within a volume of 1.4 × 10^–5 λ₀³. To evaluate the performance of the highly efficient metal–insulator–metal 3D-tapered plasmonic nanofocusing waveguide structure itself, the overall focusing efficiency, that is, the transmission rate from the wavelength-scale input side to the deep subwavelength-scale focusing core in the tapered waveguide, was calculated to be around 85%

Harnessing Chemical Raman Enhancement for Understanding Organic Adsorbate Binding on Metal Surfaces

Surface-enhanced Raman spectroscopy (SERS) is a known approach for detecting trace amounts of molecular species. Whereas SERS measurements have focused on enhancing the signal for sensing trace amounts of a chemical moiety, understanding how the substrate alters molecular Raman spectra can enable optical probing of analyte binding chemistry. Here we examine binding of trans-1,2-two­(4-pyridyl) ethylene (BPE) to Au surfaces and understand variations in experimental data that arise from differences in how the molecule binds to the substrate. Monitoring differences in the SERS as a function of incubation time, a period of several hours in our case, reveals that the number of BPE molecules that chemically binds with the Au substrate increases with time. In addition, we introduce a direct method of accessing relative chemical enhancement from experiments that is in quantitative agreement with theory. The ability to probe optically specific details of metal/molecule interfaces opens up possibilities for using SERS in chemical analysis