journal article·2020-07-28

Dielectric Confinement and Excitonic Effects in Two-Dimensional Nanoplatelets

Botao Ji, Eran Rabani, Alexander L. Efros, Roman Vaxenburg, Or Ashkenazi, Doron Azulay, Uri Banin, Oded Millo

ACS Nano· Volume 14· Issue 7
Publisher page

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.
Source: openalex_inverted_index · Quality: baseline

Research context

OpenAlex topics: Quantum Dots Synthesis And Properties · Chalcogenide Semiconductor Thin Films · 2D Materials and Applications

SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.

Affiliations

Department of Chemistry and the Hebrew University Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

Key Laboratory of 3D Micro/Nano Fabrication and Characterization of Zhejiang Province, School of Engineering, Westlake University and Institute of Advanced Technology, Westlake Institute for Advanced Study, Hangzhou 310024, China

Department of Chemistry, University of California Berkeley, Berkeley, California 94720, United States

Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

The Raymond and Beverly Sackler Center of Computational Molecular and Materials Science, Tel Aviv University, Tel Aviv 69978, Israel

Center for Computational Material Science, Naval Research Laboratory, Washington, D.C. 20375, United States

Howard Hughes Medical Institute, Janelia Research Campus, 19700 Helix Drive, Ashburn, Virginia 20147, United States

Racah Institute of Physics and the Hebrew University Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

Azrieli, Jerusalem College of Engineering, Jerusalem 9103501, Israel

Funding

Israel Science Foundation · Office of Naval Research · University of California · U.S. Department of Defense · National Natural Science Foundation of China · Division of Materials Research · Harry de Jur Foundation

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