Nature of the Positron State in CdSe Quantum Dots

Nature of the Positron State in CdSe Quantum Dots

Shi, W. (TU Delft RST/Fundamental Aspects of Materials and Energy)
Callewaert, Vincent (Universiteit Antwerpen)
Barbiellini, Bernardo (Northeastern University; Lappeenranta University of Technology)
Saniz, Rolando (Universiteit Antwerpen)
Butterling, M. (TU Delft RST/Fundamental Aspects of Materials and Energy)
Egger, Werner (University of the Federal Armed Forces Munich)
Dickmann, Marcel (University of the Federal Armed Forces Munich)
Hugenschmidt, Christoph (Technische Universität München)
Shakeri, Behtash (University of Maine)
Brück, E.H. (TU Delft RST/Fundamental Aspects of Materials and Energy)
Eijt, S.W.H. (TU Delft RST/Fundamental Aspects of Materials and Energy)

2018

Previous studies have shown that positron-annihilation spectroscopy is a highly sensitive probe of the electronic structure and surface composition of ligand-capped semiconductor quantum dots (QDs) embedded in thin films. The nature of the associated positron state, however, whether the positron is confined inside the QDs or localized at their surfaces, has so far remained unresolved. Our positron-annihilation lifetime spectroscopy studies of CdSe QDs reveal the presence of a strong lifetime component in the narrow range of 358-371 ps, indicating abundant trapping and annihilation of positrons at the surfaces of the QDs. Furthermore, our ab initio calculations of the positron wave function and lifetime employing a recent formulation of the weighted density approximation demonstrate the presence of a positron surface state and predict positron lifetimes close to experimental values. Our study thus resolves the long-standing question regarding the nature of the positron state in semiconductor QDs and opens the way to extract quantitative information on surface composition and ligand-surface interactions of colloidal semiconductor QDs through highly sensitive positron-annihilation techniques.

http://resolver.tudelft.nl/uuid:f90a4d48-8538-42f6-905e-b33227abb90c

https://doi.org/10.1103/PhysRevLett.121.057401

0031-9007

Physical Review Letters, 121 (5)

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journal article

© 2018 W. Shi, Vincent Callewaert, Bernardo Barbiellini, Rolando Saniz, M. Butterling, Werner Egger, Marcel Dickmann, Christoph Hugenschmidt, Behtash Shakeri, E.H. Brück, S.W.H. Eijt, More Authors