Abstract
Electron tunneling is associated with light emission. In order to elucidate its generating mechanism, we provide a novel experimental ansatz that employs fixed-distance epitaxial graphene as metallic electrodes. In contrast to previous experiments, this permits an unobscured light spread from the tunnel junction, enabling both a reliable calibration of the visible to infrared emission spectrum and a detailed analysis of the dependence of the parameters involved. In an open, non-resonant geometry, the emitted light is perfectly characterized by a Planck spectrum. In an electromagnetically resonant environment, resonant radiation is added to the thermal spectrum, both being strictly proportional in intensity. In full agreement with a simple heat conduction model, we provide evidence that in both cases the light emission stems from a hot electronic subsystem in interaction with its linear electromagnetic environment. These very clear results should resolve any ambiguity about the mechanism of light emission in nano contacts.
Highlights
In full agreement with a simple heat conduction model, we provide evidence that in both cases the light emission stems from a hot electronic subsystem in interaction with its linear electromagnetic environment
It has been known since the early days of scanning tunneling microscopy (STM), and even before, that electron tunneling from a metallic tip to a metallic surface is associated with light emission [1,2,3]
While earlier experiments on metal-insulator-metal stacks [4,5] and point contacts [6] favored a thermal light emission due to hot electrons, in STM another physical explanation took over, referring to the discrete nature of charge: The tunneling current consists of a sequence of single-electron bursts obeying Poisson statistics, which generates shot noise, but is capable of triggering electromagnetic modes, in particular resonant surface plasmons [2,7,8,9,10,11,12,13,14]
Summary
It has been known since the early days of scanning tunneling microscopy (STM), and even before, that electron tunneling from a metallic tip to a metallic surface is associated with light emission [1,2,3]. In full agreement with a simple heat conduction model, we provide evidence that in both cases the light emission stems from a hot electronic subsystem in interaction with its linear electromagnetic environment. While earlier experiments on metal-insulator-metal stacks [4,5] and point contacts [6] favored a thermal light emission due to hot electrons, in STM another physical explanation took over, referring to the discrete nature of charge: The tunneling current consists of a sequence of single-electron bursts obeying Poisson statistics, which generates shot noise, but is capable of triggering electromagnetic modes, in particular resonant surface plasmons [2,7,8,9,10,11,12,13,14].
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