Abstract
Electron injection from the tip of a scanning tunnelling microscope (STM) has been used to stimulate local photon emission from the surface of a thin MgO film grown on Mo(001). Depending on the excitation energy, several emission regimes have been identified on the basis of the energy and the spatial distribution of the emitted photons. At low excitation bias, tip-induced plasmons are excited in the tip–sample gap, carrying little information on the oxide film. With increasing tip bias, radiative electron transitions between field-emission resonances dominate the photon response from the MgO surface. Intrinsic optical modes of the oxide material, such as radiative decays of electron–hole pairs, are only observed when operating the STM in the field emission regime, where the direct correlation between the photon signal and the local surface morphology gets partially lost due to the increased tip–sample distance.
Highlights
Light emission spectroscopy with the scanning tunneling microscope (STM) has evolved into a powerful tool to measure optical properties of a sample surface with nanometre spatial resolution [1]
To verify this assignment on a purely experimental base, local structural and optical information has to be acquired from the insulator surface, which is in principle feasible using light emission spectroscopy with the scanning tunnelling microscope (STM)
We have demonstrated that electron injection from an STM tip can be used to stimulate photon emission from an MgO surface [11]
Summary
Light emission spectroscopy with the scanning tunneling microscope (STM) has evolved into a powerful tool to measure optical properties of a sample surface with nanometre spatial resolution [1]. Based on its distinct blue-shift and intensity decrease with increasing sample bias, the emission is assigned to coupled plasmon modes excited in the STM cavity, so called TIPs [1].
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