A light detection system for a STM

Several processes in a scanning tunneling microscope (STM) may induce light emission by the sample. Among others, such light can be emitted by plasmonic nanoparticles, direct band-gap semiconductors and color centers.[1,2] The... [ view full abstract ]

Several processes in a scanning tunneling microscope (STM) may induce light emission by the sample. Among others, such light can be emitted by plasmonic nanoparticles, direct band-gap semiconductors and color centers.[1,2] The spectroscopy of such emitted light can be very rich and provide insightful information about the electronic structures of semiconductors or about the plasmon resonances of metallic nanoparticles. Moreover, in the STM, luminescence mapping can be coupled with usual STM imaging and even with spectroscopy information such as scanning tunneling spectroscopy (STS).

Efficient detection of light emitted inside an STM can be challenging due the several restrictions imposed by the STM and even more so in the case of UHV and Low Temperature devices. In this project, we are striving to build a high efficiency light detection system that provides high collection efficiency while preserving good energy resolution of the emitted light for a LT UHV STM. This light detection system applies patented solutions and tries to solve specific problems in the context of the STM.[3,4] The solution uses a mirror collector with high numerical aperture which is positioned with sub-micrometric precision to ensure an accurate alignment. Numerical simulations predict a solid angle above 70% of a hemisphere. Light is then couple by optical fibers into an optical spectrometer. A software is under development to allow the acquisition of luminescence maps (hyper spectral imaging) automatically and simultaneously with regular images, similarly to cathodoluminesnce in a Scanning Transmission Electron Microsocpe (CL-STEM).[5]

Once operational, we plan on applying our LT UHV STM with the custom built high efficiency light detection system to the study of nano-sctructured luminescent materials such as semiconducting nanoparticles and 2D materials as WSe₂. [6]

[1] Klaus Kuhnke et al. Chem. Rev. 2017, 117, 5174−5222.

[2] D. Frank Ogletree et al. Adv. Mater. 2015, 27, 5693–5719.

[3] M. Kociak, et al.  WO Patent 2011/148072, 2011.

[4] M. Kociak, et al. WO Patent 2011/148073, 2011.

[5] L. F. Zagonel et al. Nanotechnology 23 (2012) 455205.

[6] Acknowledgements: FAPESP funding 2014/23399-9.