Thin Films of Mercury Selenide Colloidal Quantum Dots: Insights in Surface Chemistry

Mercury selenide (HgSe) colloidal quantum dot (CQD)-based thin films are prospective materials for manufacturing the new generation of photodetectors for mid-infrared (IR) range. The efficiency of devices depends on the compositions of nanocrystal ligand shells in thin films. Herein, we report on the new approach to follow up ligand exchange by Fourier transform infrared (FT-IR) spectroscopy in thin films of HgSe CQDs by applying a FT-IR horizontal attenuated total reflectance accessory. Several inorganic and organic ligands were tested in the ligand exchange of oleate shells in alcohols and acetonitrile. The newly developed method compares efficiency of ligand exchange as well as exchange reaction rate. The highest oleate replacement ratio of 95% was observed with 1,4-benzedithiol. Many ligand-solvent systems do not induce conversion over 50% even after 30 min. We found that the position of intraband absorption peak maximum depends on the ligand and is correlated with the ratio of substitution in the ligand shell. The developed method and obtained results provide important chemical insights into the processes of HgSe CQD thin films.