Chiral 2D Colloidal Semiconductor Quantum Wells

Abstract

Induced chirality in colloidal semiconductor nanoparticles has raised significant attention in the past few years as an extremely sensitive spectroscopic tool and due to the promising applications of chiral quantum dots in sensing, quantum optics, and spintronics. Yet, the origin of the induced chiroptical effects in semiconductor nanoparticles is still not fully understood, partly because almost all the theoretical and experimental studies to date are based on the simple model system of a spherical nanocrystal. Here, the realization of induced chirality in atomically flat 2D colloidal quantum wells is shown. A strong circular dichroism (CD) response as well as an absorptive-like CD line shape is observed in chiral CdSe nanoplatelets (NPLs), significantly differing from that previously observed in spherical dots. Furthermore, this intense CD signal almost completely disappears after coating with a very thin CdS shell. In contrast, CdSe-CdS core-crown NPLs exhibit a spectral response which seems to originate independently from the core and the crown regions of the NPL. This work on the one hand further advances the understanding of the fundamental origin of induced chiroptical effects in semiconductor nanoparticles, and on the other opens a pathway toward applications using chiroptical materials.

Chiral CdSe nanoplatelets as an ultrasensitive probe for lead ion sensing

“…The red-shift originates from the partial delocalization of the carrier wave function from the NPLs to the ligands. 27 Besides, the evident broadening of the two excitonic peaks demonstrates the change of ligand density, as well as the dipole-dipole coupling after ligand exchange and the new aqueous dispersion. Electronic CD measurements were then performed to investigate the chiroptical response of the cysteine functionalized CdSe NPLs.…”

“…The observed absorption peaks indicate the thickness of NPLs herein is around four monolayers according to previous studies. 27,49 After the preparation and characterization of OA-capped NPLs, the subsequent ligand exchange reaction was performed using either the L-or D-form of the chiral cysteine ( Please do not adjust margins…”

“…As a result, the intriguing circular dichroism (CD) peaks occur in the vicinity of the absorption bands of the colloidal NPs. 21 Recently, chiral ligand capped semiconductor nanodots, [22][23][24][25] nanorods 10,26 and NPLs [27][28][29][30] as well as their core-shell nanostructures have been extensively studied. Like in the case of metallic plasmonic NPs such as Au or Ag, the strong coupling between chiral ligand and achiral semiconductor can induce subsequent chirality transfer from molecules to semiconductor core with an anisotropic factor close to 10 -4 .…”

Multi‐Dimensional Quantum Nanostructures with Polarization Properties for Display Applications

“…[35] Soon after that, Yang and co-workers presented a detailed study of the induced chirality in atomically flat 2D colloidal quantum wells or NPLs and various CdSe/CdS NPLs heterostructures using CD spectroscopy. [36] A strong CD response as well as an absorptive-like CD line shape were observed in chiral CdSe NPLs, significantly differing from that previously observed in spherical dots, which was because of the larger surface to volume ratio and zinc-blende structure of the NPLs. These effects were well established through size (lateral size and thickness) dependent CD spectra (Figure 8a).…”

“…Recently, chiral optical properties of tapered 2D semiconductor nanoscrolls and screw‐dislocated nanodisks were discussed . Soon after that, Yang and co‐workers presented a detailed study of the induced chirality in atomically flat 2D colloidal quantum wells or NPLs and various CdSe/CdS NPLs heterostructures using CD spectroscopy . A strong CD response as well as an absorptive‐like CD line shape were observed in chiral CdSe NPLs, significantly differing from that previously observed in spherical dots, which was because of the larger surface to volume ratio and zinc‐blende structure of the NPLs.…”