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STM & photons

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In a scanning tunneling microscope (STM), the biased tunneling junction between a metallic tip and a metallic or semiconducting sample surface can be the source of light emission. This very local light source allows the study of the inelastic tunneling process at a nanometric scale.

Contact (SINanO): roland.coratger[at]cemes.fr
Contact (GNS): olivier.guillermet[at]cemes.fr
Contact (NeO): renaud.pechou[at]cemes.fr

The experimental study of this phenomenon is now possible at ambient conditions in the CEMES clean room. An original experimental setup based on a modified hybrid near-field microscope (cf. figure) has been developed. The photons emitted by the tunneling junction are collected by high NA optical fibers and are driven to (i) a cooled PM tube working in photon counting mode in the 185-900 nm range to draw photon cartographies (number of photons emitted at each point of the surface) and (ii) a LN2 spectrometer to record spectra of the light emitted in the 300-1050 nm range. These experimental data are correlated with the STM images recorded simultaneously.

Figure 1: STM/AFM Dimension 3000 and light emission spectra recorded on an Au/Au tunneling junction. © CEMES-CNRS


The fundamental physical mechanisms leading to light emission depend on the type of sample surface: radiative decay of localized plasmon modes excited by inelastic tunneling electrons in the case of metal-metal tunneling junction, and radiative recombination of electron-hole pairs in the case of metal-semiconductor junction.

Light emission stimulated by STM is part of a lot of more common near-field experimental techniques available at CEMES. It allows the study of fundamental physical properties (e.g. the plasmonic density of states) of nanostructures or nanostructures assemblies (rods, prisms, sub-wavelength waveguides). It can also be used to study the effects of the coupling between nano-objects giving birth to hybrid modes, or to study the luminescence of 2D semiconductors (e.g. transition metal dichalcogenides TMDs) locally excited by tunneling electrons.

Experimental material : STM Dimension 3000, cooled PM Hamamatsu, LN2-cooled Princeton Spectrometer, photon counting unit.

Collaborations : Rice University (Pr. J. Lou), Mechanics team of the Pole Ingénierie.


[1] A. Carladous et al., Phys. Rev. B 66, 045401 (2002).

[2] R. Péchou et al., Appl. Phys. Lett. 72, 671 (1998).

[3] C. Maurel et al., Surf. Sci. 600, 442 (2006).