Dielectric Confinement and Excitonic Effects in Two-Dimensional Nanoplatelets
- 25 June 2020
- journal article
- research article
- Published by American Chemical Society (ACS) in ACS Nano
- Vol. 14 (7), 8257-8265
- https://doi.org/10.1021/acsnano.0c01950
Abstract
Quasi-two-dimensional (2D) semiconductor nanoplatelets manifest strong quantum confinement with exceptional optical characteristics of narrow photoluminescence peaks with energies tunable by thickness with monolayer precision. We employed scanning tunneling spectroscopy (STS) in conjunction with optical measurements to probe the thickness-dependent band gap and density of excited states in a series of CdSe nanoplatelets. The tunneling spectra, measured in the double-barrier tunnel junction configuration, reveal the effect of quantum confinement on the band gap taking place mainly through a blue-shift of the conduction band edge, along with a signature of 2D electronic structure intermixed with finite lateral-size and/or defects effects. The STS fundamental band gaps are larger than the optical gaps as expected from the contributions of exciton binding in the absorption, as confirmed by theoretical calculations. The calculations also point to strong valence band mixing between the light- and split-off hole levels. Strikingly, the energy difference between the heavy-hole and light-hole levels in the tunneling spectra are significantly larger than the corresponding values extracted from the absorption spectra. Possible explanations for this, including an interplay of nanoplatelet charging, dielectric confinement, and difference in exciton binding energy for light and heavy holes, are analyzed and discussed.Keywords
Funding Information
- Israel Science Foundation (2495/17, 661/16)
- Office of Naval Research
- University of California (LFR-17-477237)
- U.S. Department of Defense
- National Natural Science Foundation of China (2495/17)
- Division of Materials Research (DMR-1629361)
- Harry de Jur Foundation
This publication has 46 references indexed in Scilit:
- Negatively Charged Excitons in CdSe NanoplateletsNano Letters, 2020
- Hot-Carrier Relaxation in CdSe/CdS Core/Shell NanoplateletsThe Journal of Physical Chemistry C, 2020
- Doping as a Strategy to Tune Color of 2D Colloidal NanoplateletsACS Applied Materials & Interfaces, 2019
- Two-Dimensional Colloidal Metal Chalcogenides Semiconductors: Synthesis, Spectroscopy, and ApplicationsAccounts of Chemical Research, 2015
- Colloidal nanoplatelets with two-dimensional electronic structureNature Materials, 2011
- Lamellar Assembly of Cadmium Selenide Nanoclusters into Quantum BeltsJournal of the American Chemical Society, 2011
- Large‐Scale Soft Colloidal Template Synthesis of 1.4 nm Thick CdSe NanosheetsAngewandte Chemie-International Edition, 2009
- Quasi 2D Colloidal CdSe Platelets with Thicknesses Controlled at the Atomic LevelJournal of the American Chemical Society, 2008
- Quantum Well Optical Devices and MaterialsAnnual Review of Materials Science, 1993
- Applications of Quantum Semiconductor StructuresPublished by Elsevier BV ,1991