Project is organized along three workpackages : (i) better material, (ii) deeper material understanding and (iii) better devices. Results include
*Development of the first THz absorbing nanocrystals : Over the pas decade there was a challenge to push the absorption of nanocrystals toward longer wavelength as it enable new type of application (thermal imaging). We have developed a new synthetic procedure to grow large HgTe nanocrystals. Thanks to this procedure absorption of HgTe nanocystal film reaches up to 60 µm peak and up to 200 µm for the cut-off wavelength. This is by far the reddest values reported. This result has lead to a patent application (Far infrared and THz nanocrystals and uses of thereof, FR 17 59276 (2017), E. Lhuillier, N. Goubet, Y.-P. Lin, FR 17 59276) and to a publication N. Goubet, et al J. Am. Chem. Soc. 140, 5053 (2018).
*Development of new synthetic process compatible with mass scale production : Current best performing nanocrystals for IR sensing are based on lead and mercury chalcogenides which raises some obvious toxicity issue. The synthetic procedure needs to minimize work foce exposure to heavy metal. Current synthesis were actually very dilute which generate cost (solvent and facilities) and increase the number of synthesis to conduct to obtain a given amount of material. We have work on a new procedure, where the precursor of Hg is liquid Hg. This synthesis is 10-100 times more concentrated than any previous procedure. This result has led to a patent application Method of preparation of nanoparticles using mercury thiolate compounds, E. Lhuillier, et al EP 19 306 130.6. and to a publication Near to Long Wave Infrared Mercury Chalcogenide Nanocrystals from Liquid Mercury, N. Goubet, et al J Phys Chem C 124, 8423 (2020)
*Development of new surface chemistry to enable the formation of thick strongly photoconductive film. The conventional way to prepare film of nanocrystal relies on the deposition of a film which is then followed a liogand exchange step. Her ewe have develloped an ink which ease the formation of thick film (up to 600 nm) while being compatible with large thin film mobilty . This result has been publised in HgTe Nanocrystal Inks for Extended Short Wave Infrared Detection, B. Martinez, et al Adv Opt Mat 7, 1900348 (2019)
*Regarding the electronic structure of the material, we have systematically characterize the band alignment of HgTe and HgSe as a function of size and surface chemistry. Most of these measurements have been conducted using photoemission beamline on Soleil synchrotron. These results have led to several publications Nano Lett 17, 4067 (2017), ACS Appl. Mater. Interfaces 9, 36173 (2017), J. Phys. Chem. C 122, 859–865 (2018), ACS Phot. 5, 4569 (2018), ACS Appl. Mater. Interfaces 11, 33116 (2019), Nanoscale 11, 3905 (2019)
*Regarding the transport properties I has identified the control of carrier density as a key parameter. As a result, i wanted to develop new strategies to gate nanocrystal film. We have investigated in particular the potential of ionic glass to obtain high capacitance gating. These results have led to several publications Nano Lett 19, 3981 (2019), Adv Func Mat 29, 1902723 (2019), ACS Nano 14, 4567 (2020)
*Finally on the device side, we have explored new device geometries by proposing new layers for the design of photovoltaic devise based on interband (ACS Phot. 5, 4569 (2018)) or intraband transition (Nature Comm 10, 2125 (2019)). We have also tested the potential of the coupling of the HgTe nanocrystals to 2D material such as graphene used as infrared transparent electrodes leading to enhanced charge dissociation once coupled with an ionic glass gate (ACS Nano 14, 4567 (2020)).
development on the device side also include effort to push the fabrication of full imaging setup in close collaboration with SME compagnies New Imaging technologies (Nanoscale 14, 9359 (2022) and Appl. Phys. Lett. 123, 051108 (2023)
*Based on development relative to photodetection we also start to interest to infrared electroluminescence using the same material platform (Nature Photonics 16, 38 (2022),Nano Letters 20, 6185 (2020)
the output of the project has been above 80 publications; it has generated multiple new collaborations very valuable for the next step of the PI career
