We have observed the direct light emission from the slow mode of surface plasmon polaritons (SPP) of metal-insulator-metal (MIM) tunnel junctions formed on a ultra-fine grating. The grating (period=100 nm, groove depth=12 nm, area=200 µm×200 µm) was created on a Si(100) wafer, using a direct electron beam lithography technique and wet etching of SiO2 The MIM junction was formed by evaporation of Al and Au films on this grating. The emission peak for the Al-Oxide-Au junction was observed at 1.55 eV that is expected from the dispersion curve of the slow mode. The spectral width is appreciably narrower than the emission due to the natural residual micro-roughness of the junction.
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