Reversible Electrochemistry of Mercury Chalcogenide Colloidal Quantum Dot Films

Abstract

The absolute positions of the energy levels of colloidal quantum dots of Hg(S, Se, Te), which are of interest as mid-infrared materials, are determined by electrochemistry. The bulk valence bands are at -5.85, -5.50, and -4.77 eV (±0.05 eV) for zinc-blend HgS, HgSe, HgTe, respectively, in the same order as the anions p-orbital energies. The conduction bands are conversely at -5.20, -5.50, and -4.77 eV. The stable ambient n-doping of Hg(S, Se) quantum dots compared to HgTe arises because the conduction band is sufficiently lower than the measured environment Fermi level of ∼ -4.7 eV to allow for n-doping for HgS and HgSe quantum dots even with significant electron confinement. The position of the Fermi level and the quantum dots states are reported for a specific surface treatment with ethanedithiol and electrolyte environment. The positions are however sensitive to different surface treatments, providing an avenue to control doping. Electrochemical gating is further used to determine the carrier mobility in the films of the three different systems as a function of CQD size. HgSe and HgS show increasing mobility with increasing particle sizes while HgTe shows a nonmonotonous behavior, which is attributed to some degree of aggregation of HgTe QDs.

Effect of Pressure on Interband and Intraband Transition of Mercury Chalcogenide Quantum Dots

“…The effect of the size (ie the quantum confinement) on the band alignment of HgSe 22 and HgTe 4 has already been reported. 23 Similarly, the change of the band alignment with the surface grafting of molecule has been reported by Robin et al 21 , Martinez et al 22,24 Pressure contributions still needs, on the other hand, to be quantified.…”

Investigation of the Self‐Doping Process in HgSe Nanocrystals

“…For larger CQD, the narrower band gap nature makes that the reduction by the environment is even more important . It has been shown in the case of HgS that higher order states get filled and that little by little the transition switches from its intraband behavior to a plasmonic behavior …”

Direct Imprinting of Quasi‐3D Nanophotonic Structures into Colloidal Quantum‐Dot Devices

“…The measurement setup and calculation of mobility can be found in a previous report. [37] Electrochemistry measurements show that hole/electron mobility and doping level are preserved after imprinting. Therefore, the imprinting technique is not only a method that creates high-resolution quasi-3D nanostructures, but also a method that preserves the original properties of colloidal nanomaterials.…”

“…Besides resistance and PL, the carrier mobility and doping level of the CQD were also characterized before and after imprinting (Figure g). The measurement setup and calculation of mobility can be found in a previous report . Electrochemistry measurements show that hole/electron mobility and doping level are preserved after imprinting.…”