seminars

Spin-doped colloidal semiconductor nanostructures: Design, synthesis, and investigation of their magnetic and magneto-optical properties

Physical and Analytical Chemistry Seminar

Lecturer: Joanna Dehnel

Date:
17-17 Nov 2020 @ 15:30

Location: Join Zoom Meeting at https://technion.zoom.us/j/98640529463

Spin-doped colloidal semiconductor nanostructures: Design, synthesis, and investigation of their magnetic and magneto-optical properties

 

The incorporation of diluted concentrations of magnetic impurities in bulk or epitaxially grown semiconductors has been of great interest in the past, for the regulation of magneto-optical properties. The topic received a renewed interest in recent times in colloidal nanostructures, in which a giant enhancement of carrier-to-dopant spin interactions led to new physical phenomena, like giant magnetization and spin-polarized emission. Magnetic doping was implemented extensively in colloidal quantum dots, but with limited way in anisotropic structures.  Here, we will discuss works1,2 deals with the control and characterization of spin degrees of freedom of photo-generated carriers in colloidal seeded nanorods (sNRs) and nanoplatelets (NPLs) upon implementation of magnetic doping. The material under consideration is CdSe/CdS:Mn core-shell nanostructures, including a diluted concentration of Mn2+ ions across the shell.

The spin degrees of freedom in the mentioned materials were monitored by an optically detected magnetic resonance (ODMR) spectroscopy, providing significant information on the exact location of host carriers and dopants, as well as examine the interaction between them. The extracted physical parameters from the ODMR experiments included: g-factors and their anisotropy, spin-exchange interactions, angular momentum, carrier-dopant coupling constants, radiative, and spin-lattice relaxation times.

The temporary resolved ODMR measurements of sNRs deconvoluted a few recombination events: band-to-band, trap-to-band, and trap-to-trap processes, where carriers’ trapping occurred at the seed/rod interface.  Those trapped carriers already possess unpaired spins, endowing selective magneto-optical properties along with relatively long radiative and spin-relaxation times. The dominant interaction with the magnetic dopant takes place along the seed/rod interface, leading to further enhancement of spin helicity and bestows an order of magnitude extension of spin-lattice relaxation time.

The main observations for NPLs indicate the formation of a giant magnetization and a large g-factor of an exciton. Furthermore, the data convincingly presents the interaction between a carrier and nuclear spins of magnetic ions located at neighboring surrounding, with consequent influence on the carrier’s spin coherence time. The spin-properties in confined systems as mentioned here undoubtedly can play an important role in the development of new spin-based technologies.

Moreover, the additional project will be discussed where we implemented the ODMR technique for investigation of the defect sites in inorganic halide perovskite nanostructures.

(1)      Dehnel, J.; Barak, Y.; Meir, I.; Budniak, A. K.; Nagvenkar, A. P.; Gamelin, D. R.; Lifshitz, E. Insight into the Spin Properties in Undoped and Mn-Doped CdSe/CdS Seeded Nanorods by Optically Detected Magnetic Resonance. ACS Nano 2020, 10, 13478–13490.

(2)      Strassberg, R.; Delikanli, S.; Barak, Y.; Dehnel, J.; Kostadinov, A.; Maikov, G.; Hernandez-Martinez, P. L.; Sharma, M.; Demir, H. V.; Lifshitz, E. Persuasive Evidence for Electron-Nuclear Coupling in Diluted Magnetic Colloidal Nanoplatelets Using Optically Detected Magnetic Resonance Spectroscopy. J. Phys. Chem. Lett. 2019, 10 (15), 4437–4447.