Project title: Probing surface and vacancies of zinc oxysulfide (Zn(O,S)) quantum dots using high-field NMR and DNP-enhanced NMR
A three-year PhD position on NMR of Zn(O,S) quantum dots using high-fields, ultra-low temperature MAS and Dynamic Nuclear Polarization is available. This will be a joint PhD between the CNRS/university of Lille and CEA / Univ. Grenoble Alpes.
Starting date between September and December 2023.
Background and motivation: Semiconductor nanocrystals, also known as quantum dots (QDs), are exciting materials for a wide range of applications, including optoelectronics (display devices), optical bioimaging, solar cells and photocatalysis. Most existing quantum dots contain cadmium, which is toxic and weakly abundant. As a result, ZnO and ZnS QDs appear as key alternatives, with non-toxic and abundant elements. Nevertheless, their application is limited by their wide band energy gap (3.4-3.9 eV), which only leads to absorption of UV light. To circumvent this issue and reduce the energy band gap, defects engineering (i.e. oxygen or sulfur vacancies) and the development of zinc oxysulfide (Zn(O,S)) nanocrystals appear a promising approach. However, the rational improvement of the optoelectronic properties of these Zn(O,S) nanocrystals is limited by the lack of information about the defects and their mechanism of formation.
Approach: In this project, the structure of these defects, including vacancies and O/S substitution, will be characterized using advanced solid-state NMR experiments. Since the isotopes found in Zn(O,S) nanocrystals (17O, 67Zn and 33S) are quadrupolar nuclei with low gyromagnetic ratio and low natural abundance, which are extremely challenging to detect by NMR, we will develop an innovative approach relying on ultra-high-field NMR (up to 28 T), dynamic nuclear polarization (DNP), ultra-low temperature MAS (down to 30 K) and spin labelling strategies. The obtained NMR data will provide unique insights into the structure of Zn(O,S) quantum dots, paving the way to improve their optoelectronic properties.
Hosts and research infrastructure: This project is funded by ANR, French research funding agency. The PhD student will be supervised by Gaël De Paëpe at CEA / Univ. Grenoble Alpes (https://nmr-dnp-grenoble.net/), and Olivier Lafon at the University of Lille (https://uccs.univ-lille.fr/index.php/en/solid-state-chemistry/rm2i) and hence, will have the opportunity to be trained in two leading groups at international level in complementary advanced solid-state NMR techniques: High-field DNP and NMR at low temperature in Grenoble and ultra-high-field NMR of quadrupolar nuclei in Lille. This project will benefit from the unique NMR instruments available in these research groups: DNP-NMR spectrometers with temperature down to 30 K in Grenoble and high-field NMR magnets (800, 900 MHz and 1.2 GHz) in Lille. This project will be carried out in collaboration with the Coordination Chemistry Laboratory (Yannick Coppel, Myrtil L. Kahn) in Toulouse for the preparation of Zn(O,S) nanocrystals.
The candidate: We seek application from national and international students who have graduated in chemistry, physics or materials science, preferably with a background in NMR spectroscopy.
Contact: Applications (cover letter, CV, transcripts of grades and names for recommendation) and informal queries about the lab and research projects should be directed by email to olivier.lafon@univ-lille.fr and gael.depaepe@cea.fr
Recent selected publications:
- Observation of low-γ quadrupolar nuclei by surface-enhanced NMR spectroscopy, H. Nagashima, J. Trébosc, Y. Kon, K. Sato, O. Lafon, and J.-P. Amoureux Journal of American Chemical Society 2020, 142, 10659-10672. Revealing Brønsted Acidic Bridging SiOHAl Groups on Amorphous Silica-Alumina by Ultrahigh Field Solid-State NMR, Z. Wang, K. Chen, Y. Jiang, J. Trébosc, W. Yang, J.-P. Amoureux, I. Hung, Z. Gan, A. Baiker, O. Lafon, and J. Huang Journal of Physical Chemistry Letters 2021, 47, 11563–11572.
- Disclosing Interfaces of ZnO Nanocrystals Using Dynamic Nuclear Polarization: Sol‐Gel versus Organometallic Approach, D. Lee, M. Wolska‐Pietkiewicz, S. Badoni, A. Grala, J. Lewiński, G. De Paëpe, Angewandte Chemie International Edition, 2019, 58 (48), 17163-17168. ZnO Nanoplatelets with controlled Thickness: Atomic insight into Facet-Specific Bimodal Ligand Binding Using DNP NMR, M. Terlecki, S. Badoni, M. K. Leszczynski, S. Gierlotka, I. Justyniak, H. Okuno, M. Wolska-Pietkiewicz, D. Lee, G. De Paëpe, J. Lewinski, Advanced Functional Materials, 2021, 31, 2105318.
- Evidence for core oxygen dynamics and exchange in metal oxide nanocrystals from in situ 17O MAS-NMR, Y. Champouret, Y. Coppel, M. L. Kahn, J. Am. Chem. Soc., 2016, 138, 16322-16328. Highly Efficient Polarizing Agents for MAS-DNP of Proton-dense Molecular Solids, R. Harrabi, T. Halbritter, F. Aussenac, O. Dakhlaoui, J. van Tol, K. Damodaran, D. Lee, S. Paul, S. Hediger, F. Mentink-Vigier, S. Sigurdsson, G. De Paëpe, Angewandte Chemie International Edition, 2022, 61, e202114103.
Keywords:
solid-state NMR, DNP, high-fields, quantum dots, Zn(O,S)
Contact:
Professor Olivier Lafon
Univ. of Lille, CNRS,
UCCS UMR 8181
F-59000 Lille, France
olivier.lafon@univ-lille.fr
Dr. Gaël De Paëpe
Univ. Grenoble Alpes, CEA
IRIG/MEM/RM
CEA Grenoble, France
gael.depaepe@cea.fr