Ultra-small light sources which can be controlled electrically or optically are of great interest to nano-photonics. Electroluminescence induced by inelastic tunneling from an STM-junction is such an example, however hampered due to a small quantum efficiency. We observe enhanced emission of photons from such a tunneling junction by almost three orders of magnitudes by additionally exciting a gap-plasmon oscillation with laser irradiation. Either a pristine Au-substrate/Au-tip tunneling junction or a junction (Au-substrate/self-assembled molecular monolayer/Au-tip) with molecules chemically bound to the Au substrate is used. Analyzing the emission spectra from the junction recorded as a function of bias voltage for the Au-Au junction we conclude that the enhanced intensity is induced by laser illumination and originates from the radiative decay of hot electrons closely above the Fermi level via inelastic tunneling into the plasmon modes formed by the tip-substrate gap. In the presence of molecules in the gap, we observe a bias dependent spectral narrowing characteristic for superluminescence. The optically pumped molecular junction behaves as a bias-driven point source, operating at ambient conditions and providing almost three orders of magnitude higher electron-to-photon conversion efficiency than electroluminescence induced by inelastic tunneling without optical pumping. The enhanced emission can be modeled by rate equations taking into account the hole-injection from the tip (anode) into the highest occupied orbital of the closest substrate bound molecule (lower level) and radiative recombination with an electron from above the Fermi-level (upper level), hence feeding photons back by stimulated emission resonant with the gap mode.
Alfred J. Meixner, Kai Braun, and Frank Wackenhut, "Plasmon-enhanced light emission from an optically pumped bias-controlled tunneling junction (Conference Presentation)," Proc. SPIE 10540, Quantum Sensing and Nano Electronics and Photonics XV, 1054010 (Presented at SPIE OPTO: January 30, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289179.5751529256001.
Conference Presentations are recordings of oral presentations given at SPIE conferences and published as part of the conference proceedings. They include the speaker's narration along with a video recording of the presentation slides and animations. Many conference presentations also include full-text papers. Search and browse our growing collection of more than 14,000 conference presentations, including many plenary and keynote presentations.