1. Date of download: 9/19/2016 Copyright © 2016 SPIE. All rights reserved. (a) Schematic of the microscope head with the tip runner on top of the base plate for adjusting the tip into the focus of the PM. (b) The tuning fork and an attached gold tip (left prong), which is used for STM-feedback. (c) Photograph of the tip runner with the electrical connections for (i) bias voltage, (ii) coarse positioning, (iii) tuning fork, and (iv) piezo-tube for scanning and fine positioning. Figure Legend: From: Hot-electron-induced light amplification J. Photon. Energy. 2016;6(4):042506. doi:10.1117/1.JPE.6.042506

2. Date of download: 9/19/2016 Copyright © 2016 SPIE. All rights reserved. (a) Sketch of the laser-illuminated Au–Au tunneling junction which consists of an Au tip and an Au substrate. (b) PL spectra of the laser (170 μW) illuminated Au–Au junction recorded as a function of bias voltage. (c) and (d) PL spectra and the fitting curves at bias voltages of −4 and −0.1 V, respectively. The PL spectrum at −0.1 V is fitted by a single Lorentzian curve, while the spectrum at −4 V is fitted by four Lorentzian curves. (e) Peak positions of the Lorentzian curves fitted to the PL. The circles represent the peak- maxima related to the local plasmon modes, and the squares represent the peak maxima due to laser excited electron–hole combination. (f) Illustration of the radiative decay processes related to electron–hole recombination and local plasmon modes in the junction. Figure Legend: From: Hot-electron-induced light amplification J. Photon. Energy. 2016;6(4):042506. doi:10.1117/1.JPE.6.042506

3. Date of download: 9/19/2016 Copyright © 2016 SPIE. All rights reserved. (a) Sketch of in the laser-illuminated Au/Cl-MBT/Au tunneling junction consisting of an Au tip, a monolayer of Cl-MBT molecules, and the Au substrate. (b) Emission spectra of the laser-illuminated molecular junction as a function of the bias voltage. (c) Comparison of the spectra recorded at bias voltages of +1.6 V and −1.5 V. The inset shows the spectrally integrated intensity trajectory as a function of the bias voltage and demonstrates the dependence on the polarity of the bias voltages. (d) Illustration of the energy level diagram of the molecule/gap hybrid system and the processes involved in the molecular tunneling junction. Figure Legend: From: Hot-electron-induced light amplification J. Photon. Energy. 2016;6(4):042506. doi:10.1117/1.JPE.6.042506

4. Date of download: 9/19/2016 Copyright © 2016 SPIE. All rights reserved. PL spectra recorded from the junction as a function of pump laser power for a bias voltage of 1.8 V and under pulsed excitation. (a2) Comparison of the FWHMs of two spectra taken from the junction with a low-pump (blue) and a high-pump (gray) power, respectively. (a3) PL intensities and the FWHM as a function of the pump power. (b1–b3) PL spectra recorded as a function of pump power under the same conditions (1.8 V) as in (a1–a3) but with cw excitation. (c1–c3) The spectra recorded as a function of the incident cw laser power at a bias voltage of 0.2 V. Figure Legend: From: Hot-electron-induced light amplification J. Photon. Energy. 2016;6(4):042506. doi:10.1117/1.JPE.6.042506

5. Date of download: 9/19/2016 Copyright © 2016 SPIE. All rights reserved. (a) The spectrally integrated EL (black) and PL (blue) intensities as a function of the bias voltages. The experimental data are shown as open squares (EL) and circles (PL). The calculated intensity-bias dependences using the dynamics models are plotted as the solid lines. (b) The experimental (open circle) and calculated spectral intensity (solid line) using the dynamics models as a function of the pump laser power. A constant bias of 1.8 V is applied. Both the experimental and the calculated results demonstrate a low gain, high gain, and close-to saturation regime. Figure Legend: From: Hot-electron-induced light amplification J. Photon. Energy. 2016;6(4):042506. doi:10.1117/1.JPE.6.042506