1
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Jiang M, Men Y, Zhang Y, Cheng L, Wang Y, Jia T, Sun Z, Feng D. Anomalous Laser-Fluence Dependence of Electron Spin Excitation in CdS Colloidal Quantum Dots: Surface Effects. J Phys Chem Lett 2023; 14:9069-9074. [PMID: 37787500 DOI: 10.1021/acs.jpclett.3c02285] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
Electron spin dynamics in CdS quantum dots (QDs) with hole acceptor 1-octanethiol organic molecules are investigated by time-resolved ellipticity spectroscopy. An anomalous dependence of laser fluences on electron spin excitation for the first time is reported. Increasing the laser fluence, the electron spin is switched from one direction to an antiparallel direction (spin direction switching, SDS) when adding enough 1-octanethiol hole acceptors in an air atmosphere. The analysis shows that the electron spin direction changes from heavy hole excitation defined to spin-orbit split hole excitation defined. In as-grown CdS QDs with native ligands, laser-fluence-dependent SDS phenomena are absent. Electron wave function spread into 1-octanethiol molecules is demonstrated to be important for the presence of SDS phenomena. The finding here thus reveals the importance of surface conditions on electron spin excitation processes in semiconductor QDs and that the surface can be used as an important factor to manipulate the spin.
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Affiliation(s)
- Meizhen Jiang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Yumeng Men
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Yuanyuan Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Lin Cheng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Yang Wang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Tianqing Jia
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Zhenrong Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Donghai Feng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
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2
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Jiang M, Zhang Y, Hu R, Men Y, Cheng L, Liang P, Jia T, Sun Z, Feng D. Methods for Obtaining One Single Larmor Frequency, Either v1 or v2, in the Coherent Spin Dynamics of Colloidal Quantum Dots. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:2006. [PMID: 37446521 DOI: 10.3390/nano13132006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2023] [Revised: 07/02/2023] [Accepted: 07/03/2023] [Indexed: 07/15/2023]
Abstract
The coexistence of two spin components with different Larmor frequencies in colloidal CdSe and CdS quantum dots (QDs) leads to the entanglement of spin signals, complicating the analysis of dynamic processes and hampering practical applications. Here, we explored several methods, including varying the types of hole acceptors, air or anaerobic atmosphere and laser repetition rates, in order to facilitate the obtention of one single Larmor frequency in the coherent spin dynamics using time-resolved ellipticity spectroscopy at room temperature. In an air or nitrogen atmosphere, manipulating the photocharging processes by applying different types of hole acceptors, e.g., Li[Et3BH] and 1-octanethiol (OT), can lead to pure spin components with one single Larmor frequency. For as-grown QDs, low laser repetition rates favor the generation of the higher Larmor frequency spin component individually, while the lower Larmor frequency spin component can be enhanced by increasing the laser repetition rates. We hope that the explored methods can inspire further investigations of spin dynamics and related photophysical processes in colloidal nanostructures.
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Affiliation(s)
- Meizhen Jiang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Yuanyuan Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Rongrong Hu
- College of Sciences, Shanghai Institute of Technology, Shanghai 201418, China
| | - Yumeng Men
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Lin Cheng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Pan Liang
- College of Arts and Sciences, Shanghai Dianji University, Shanghai 201306, China
| | - Tianqing Jia
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Zhenrong Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Donghai Feng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
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3
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Qiang G, Zhukov EA, Evers E, Yakovlev DR, Golovatenko AA, Rodina AV, Onushchenko AA, Bayer M. Electron Spin Coherence in CdSe Nanocrystals in a Glass Matrix. ACS NANO 2022; 16:18838-18848. [PMID: 36317947 DOI: 10.1021/acsnano.2c07645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The coherent spin dynamics of electrons in CdSe nanocrystals embedded in a glass matrix with diameters from 3.3 up to 6.1 nm are investigated by time-resolved Faraday ellipticity at room and cryogenic temperatures. Only one Larmor precession frequency is detected, which corresponds to the larger of the two precession frequencies and thus g-factor values found in the typical signal from solution-grown colloidal CdSe nanocrystals. We identify this frequency accordingly as associated with the spin precession of resident electrons localized in the nanocrystals in the vicinity of the surface. We provide a detailed theoretical analysis of the exciton level spin structure in the magnetic field and model the spin dynamics in CdSe nanocrystals of different symmetries. This allows us to exclude the exciton as the origin of the experimentally observed oscillating signal. At a cryogenic temperature of 6 K, an additional nonoscillating component emerges in the spin dynamics. We consider several possible origins of this signal and conclude that it is related to the hole spin polarization.
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Affiliation(s)
- Gang Qiang
- Experimentelle Physik 2, Technische Universität Dortmund, 44221Dortmund, Germany
| | - Evgeny A Zhukov
- Ioffe Institute, Russian Academy of Sciences, 194021St. Petersburg, Russia
| | - Eiko Evers
- Experimentelle Physik 2, Technische Universität Dortmund, 44221Dortmund, Germany
| | - Dmitri R Yakovlev
- Experimentelle Physik 2, Technische Universität Dortmund, 44221Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences, 194021St. Petersburg, Russia
| | | | - Anna V Rodina
- Ioffe Institute, Russian Academy of Sciences, 194021St. Petersburg, Russia
| | | | - Manfred Bayer
- Experimentelle Physik 2, Technische Universität Dortmund, 44221Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences, 194021St. Petersburg, Russia
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4
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Zhang Y, Jiang M, Wu Z, Yang Q, Men Y, Cheng L, Liang P, Hu R, Jia T, Sun Z, Feng D. Hyperfine-Induced Electron-Spin Dephasing in Negatively Charged Colloidal Quantum Dots: A Survey of Size Dependence. J Phys Chem Lett 2021; 12:9481-9487. [PMID: 34559541 DOI: 10.1021/acs.jpclett.1c02754] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The electron spin relaxation processes are complicated in semiconductor quantum dots. Different spin relaxation mechanisms may result in an increased or decreased spin relaxation rate with the size. The information on size-dependent spin dynamics helps to clarify and better understand the underlying spin relaxation processes. We investigate the size dependence of the electron spin dynamics in negatively photocharged CdSe and CdS colloidal quantum dots by time-resolved ellipticity spectroscopy. It is revealed that the electron spin dephasings of photodoped electron in zero or weak magnetic fields are dominated by the electron-nuclear hyperfine interaction for all measured samples. The hyperfine-induced electron spin dephasing time is ∼1-2 ns at room temperature and decreases with decreasing the size D. In addition to a size-dependent dephasing time that is directly proportional to D3/2, our measurements also show a size-independent time component, likely due to the laser-induced nuclear spin ordering.
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Affiliation(s)
- Yuanyuan Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Meizhen Jiang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Zhen Wu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Qing Yang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Yumeng Men
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Lin Cheng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Pan Liang
- College of Arts and Sciences, Shanghai Dianji University, Shanghai 201306, China
| | - Rongrong Hu
- College of Sciences, Shanghai Institute of Technology, Shanghai 201418, China
| | - Tianqing Jia
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Zhenrong Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Donghai Feng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
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5
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Wu Z, Zhang Y, Hu R, Jiang M, Liang P, Yang Q, Deng L, Jia T, Sun Z, Feng D. Hole-Acceptor-Manipulated Electron Spin Dynamics in CdSe Colloidal Quantum Dots. J Phys Chem Lett 2021; 12:2126-2132. [PMID: 33625852 DOI: 10.1021/acs.jpclett.0c03669] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Electron spin dynamics in CdSe quantum dots with hole acceptors are investigated by time-resolved ellipticity spectroscopy. Two types of hole acceptors, Li[Et3BH] and 1-octanethiol, result in distinctly different electron spin dynamics. The differences include electron g factors, spin dephasing/relaxation times, and mechanisms. In CdSe quantum dots with Li[Et3BH], the electron spin dephasing and relaxation are dominated by electron-nuclear hyperfine interactions in zero and weak magnetic fields. In contrast, hyperfine interactions, electron carrier lifetimes, and exchange interactions between electrons and holes or surface dangling bond spins control the electron spin dynamics in CdSe quantum dots with 1-octanethiol. Inhomogeneous dephasing limits the spin coherence time in larger transverse magnetic fields for both hole acceptor cases, but with distinct different g-factor inhomogeneity. These findings manifest that surface conditions play an important role in the spin dynamics and that thereby the surface and its surroundings can be exploited to control the spin in colloidal nanostructures.
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Affiliation(s)
- Zhen Wu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Yuanyuan Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Rongrong Hu
- College of Sciences, Shanghai Institute of Technology, Shanghai 201418, China
| | - Meizhen Jiang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Pan Liang
- College of Arts and Sciences, Shanghai Dianji University, Shanghai 201306, China
| | - Qing Yang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Li Deng
- School of Physics & Electronic Science, East China Normal University, Shanghai 200241, China
| | - Tianqing Jia
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Zhenrong Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
| | - Donghai Feng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China
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6
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Xiang D, Li Y, Wang L, Ding T, Wang J, Wu K. Electron and Hole Spin Relaxation in CdSe Colloidal Nanoplatelets. J Phys Chem Lett 2021; 12:86-93. [PMID: 33306386 DOI: 10.1021/acs.jpclett.0c03257] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Solution-processed quantum-confined nanocrystals are important building blocks for scalable implementation of quantum information science. Extensive studies on colloidal quantum dots (QDs) have revealed subpicosecond hole spin relaxation, whereas the electron spin dynamics remains difficult to probe. Here we study electron and hole spin dynamics in CdSe colloidal nanoplatelets (also called quantum wells) of varying thicknesses using circularly polarized transient absorption spectroscopy at room temperature. The clear spectroscopic features of transition bands associated with heavy, light, and spin-orbit split-off holes enabled separate probes of electron and hole dynamics. The hole spin-flip occurred within ∼200 fs, arising from strong spin-orbit coupling in the valence band. The electron spin lifetime decreased from 6.2 to 2.2 ps as the platelet thickness is reduced from 6 to 4 monolayers, reflecting an exchange interaction between the electron and the hole and/or surface dangling bond spins enhanced by quantum confinement.
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Affiliation(s)
- Dongmei Xiang
- State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Yulu Li
- State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Lifeng Wang
- State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
- University of the Chinese Academy of Sciences, Beijing 100049, China
| | - Tao Ding
- State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Junhui Wang
- State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
| | - Kaifeng Wu
- State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China
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7
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Feng D, Yakovlev DR, Dubertret B, Bayer M. Charge Separation Dynamics in CdSe/CdS Core/Shell Nanoplatelets Addressed by Coherent Electron Spin Precession. ACS NANO 2020; 14:7237-7244. [PMID: 32453553 DOI: 10.1021/acsnano.0c02402] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We investigate the charge separation dynamics provided by carrier surface trapping in CdSe/CdS core/shell nanoplatelets by means of a three-laser-beam pump-orientation-probe technique, detecting the electron spin coherence at room temperature. Signals with two Larmor precession frequencies are found, which strongly differ in their dynamical characteristics and dependencies on pump power and shell thickness. The electron trapping process occurs on a time scale of about 10 ns, and the charge separation induced thereby has a long lifetime of up to hundreds of microseconds. On the other hand, the hole trapping requires times from subpicoseconds to hundreds of picoseconds, and the induced charge separation has a lifetime of a few nanoseconds. With increasing CdS shell thickness the hole trapping vanishes, while the electron trapping is still detectable. These findings have important implications for understanding the photophysical processes of nanoplatelets and other colloidal nanostructures.
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Affiliation(s)
- Donghai Feng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Dmitri R Yakovlev
- Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
| | - Benoit Dubertret
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI, CNRS, 75231 Paris, France
| | - Manfred Bayer
- Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
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8
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Hu R, Wu Z, Zhang Y, Yakovlev DR, Liang P, Qiang G, Guo J, Jia T, Sun Z, Bayer M, Feng D. Long-Lived Negative Photocharging in Colloidal CdSe Quantum Dots Revealed by Coherent Electron Spin Precession. J Phys Chem Lett 2019; 10:4994-4999. [PMID: 31408346 DOI: 10.1021/acs.jpclett.9b02341] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Photoinduced charging in CdSe colloidal quantum dots (QDs) is investigated by time-resolved pump-probe spectroscopy that is sensitive to electron spin polarization. This technique monitors the coherent spin dynamics of optically oriented electrons precessing around an external magnetic field. By addition of 1-octanethiol to the CdSe QD solution in toluene, an extremely long-lived negative photocharging is detected that lives up to 1 month in an N2 atmosphere and hours in an air atmosphere at room temperature. 1-Octanethiol not only acts as a hole acceptor but also results in a reduction of the oxygen-induced photo-oxidation in CdSe QDs, allowing air-stable negative photocharging. Two types of negative photocharging states with different spin precession frequencies and very different lifetimes are identified. These findings have important implications for understanding the photophysical processes in colloidal nanostructures.
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Affiliation(s)
- Rongrong Hu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Zhen Wu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Yuanyuan Zhang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Dmitri R Yakovlev
- Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
| | - Pan Liang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Gang Qiang
- Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany
| | - Jiaxing Guo
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Tianqing Jia
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Zhenrong Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - Manfred Bayer
- Experimentelle Physik 2, Technische Universität Dortmund, 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences, 194021 St. Petersburg, Russia
| | - Donghai Feng
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
- Collaborative Innovation Center of Extreme Optics, Shanxi University, Shanxi 030006, China
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9
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Hu R, Yakovlev DR, Liang P, Qiang G, Chen C, Jia T, Sun Z, Bayer M, Feng D. Origin of Two Larmor Frequencies in the Coherent Spin Dynamics of Colloidal CdSe Quantum Dots Revealed by Controlled Charging. J Phys Chem Lett 2019; 10:3681-3687. [PMID: 31244276 DOI: 10.1021/acs.jpclett.9b01534] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Coherent spin dynamics in colloidal CdSe quantum dots (QDs) typically show two spin components with different Larmor frequencies, whose origin is an open question. We exploit the photocharging approach to identify their origin and find that surface states play a key role in the appearance of the spin signals. By controlling the photocharging with electron or hole acceptors, we show that the specific spin component can be enhanced by the choice of acceptor type. In core/shell CdSe/ZnS QDs, the spin signals are significantly weaker. Our results exclude the neutral exciton as the spin origin and suggest that both Larmor frequencies are related to the coherent spin precession of electrons in photocharged QDs. The lower frequency is due to the electron confined in the middle of the QD, and the higher frequency to the electron additionally localized in the vicinity of the surface.
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Affiliation(s)
- Rongrong Hu
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Dmitri R Yakovlev
- Experimentelle Physik 2 , Technische Universität Dortmund , 44221 Dortmund , Germany
- Ioffe Institute , Russian Academy of Sciences , 194021 St. Petersburg , Russia
| | - Pan Liang
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Gang Qiang
- Experimentelle Physik 2 , Technische Universität Dortmund , 44221 Dortmund , Germany
| | - Cong Chen
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Tianqing Jia
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Zhenrong Sun
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
| | - Manfred Bayer
- Experimentelle Physik 2 , Technische Universität Dortmund , 44221 Dortmund , Germany
- Ioffe Institute , Russian Academy of Sciences , 194021 St. Petersburg , Russia
| | - Donghai Feng
- State Key Laboratory of Precision Spectroscopy , East China Normal University , Shanghai 200062 , China
- Collaborative Innovation Center of Extreme Optics , Shanxi University , Shanxi 030006 , China
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10
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Shornikova EV, Biadala L, Yakovlev DR, Feng D, Sapega VF, Flipo N, Golovatenko AA, Semina MA, Rodina AV, Mitioglu AA, Ballottin MV, Christianen PCM, Kusrayev YG, Nasilowski M, Dubertret B, Bayer M. Electron and Hole g-Factors and Spin Dynamics of Negatively Charged Excitons in CdSe/CdS Colloidal Nanoplatelets with Thick Shells. NANO LETTERS 2018; 18:373-380. [PMID: 29160075 DOI: 10.1021/acs.nanolett.7b04203] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We address spin properties and spin dynamics of carriers and charged excitons in CdSe/CdS colloidal nanoplatelets with thick shells. Magneto-optical studies are performed by time-resolved and polarization-resolved photoluminescence, spin-flip Raman scattering and picosecond pump-probe Faraday rotation in magnetic fields up to 30 T. We show that at low temperatures the nanoplatelets are negatively charged so that their photoluminescence is dominated by radiative recombination of negatively charged excitons (trions). Electron g-factor of 1.68 is measured, and heavy-hole g-factor varying with increasing magnetic field from -0.4 to -0.7 is evaluated. Hole g-factors for two-dimensional structures are calculated for various hole confining potentials for cubic- and wurtzite lattice in CdSe core. These calculations are extended for various quantum dots and nanoplatelets based on II-VI semiconductors. We developed a magneto-optical technique for the quantitative evaluation of the nanoplatelets orientation in ensemble.
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Affiliation(s)
- Elena V Shornikova
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
- Rzhanov Institute of Semiconductor Physics, Siberian Branch of Russian Academy of Sciences , 630090 Novosibirsk, Russia
| | - Louis Biadala
- Institut d'Electronique, de Microélectronique et de Nanotechnologie, CNRS , 59652 Villeneuve-d'Ascq, France
| | - Dmitri R Yakovlev
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences , 194021 St. Petersburg, Russia
| | - Donghai Feng
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
- State Key Laboratory of Precision Spectroscopy, East China Normal University , 200062 Shanghai, China
| | - Victor F Sapega
- Ioffe Institute, Russian Academy of Sciences , 194021 St. Petersburg, Russia
| | - Nathan Flipo
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
| | | | - Marina A Semina
- Ioffe Institute, Russian Academy of Sciences , 194021 St. Petersburg, Russia
| | - Anna V Rodina
- Ioffe Institute, Russian Academy of Sciences , 194021 St. Petersburg, Russia
| | - Anatolie A Mitioglu
- High Field Magnet Laboratory (HFML-EMFL), Radboud University , 6525 ED Nijmegen, The Netherlands
| | - Mariana V Ballottin
- High Field Magnet Laboratory (HFML-EMFL), Radboud University , 6525 ED Nijmegen, The Netherlands
| | - Peter C M Christianen
- High Field Magnet Laboratory (HFML-EMFL), Radboud University , 6525 ED Nijmegen, The Netherlands
| | - Yuri G Kusrayev
- Ioffe Institute, Russian Academy of Sciences , 194021 St. Petersburg, Russia
| | - Michel Nasilowski
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI, CNRS , 75231 Paris, France
| | - Benoit Dubertret
- Laboratoire de Physique et d'Etude des Matériaux, ESPCI, CNRS , 75231 Paris, France
| | - Manfred Bayer
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences , 194021 St. Petersburg, Russia
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11
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Feng D, Yakovlev DR, Pavlov VV, Rodina AV, Shornikova EV, Mund J, Bayer M. Dynamic Evolution from Negative to Positive Photocharging in Colloidal CdS Quantum Dots. NANO LETTERS 2017; 17:2844-2851. [PMID: 28367630 DOI: 10.1021/acs.nanolett.6b05305] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The optical properties of colloidal semiconductor nanocrystals are largely influenced by the trapping of charge carriers on the nanocrystal surface. Different concentrations of electron and hole traps and different rates of their capture to the traps provide dynamical charging of otherwise neutral nanocrystals. We study the photocharging formation and evolution dynamics in CdS colloidal quantum dots with native oleic acid surface ligands. A time-resolved technique with three laser pulses (pump, orientation, and probe) is developed to monitor the photocharging dynamics with picosecond resolution on wide time scales ranging from picoseconds to milliseconds. The detection is based on measuring the coherent spin dynamics of electrons, allowing us to distinguish the type of carrier in the QD core (electron or hole). We find that although initially negative photocharging happens because of fast hole trapping, it eventually evolves to positive photocharging due to electron trapping and hole detrapping. The positive photocharging lasts up to hundreds of microseconds at room temperature. These findings give insight into the photocharging process and provide valuable information for understanding the mechanisms responsible for the emission blinking in colloidal nanostructures.
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Affiliation(s)
- Donghai Feng
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
- State Key Laboratory of Precision Spectroscopy, East China Normal University , Shanghai 200062, China
| | - Dmitri R Yakovlev
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences , 194021 Saint Petersburg, Russia
| | - Victor V Pavlov
- Ioffe Institute, Russian Academy of Sciences , 194021 Saint Petersburg, Russia
| | - Anna V Rodina
- Ioffe Institute, Russian Academy of Sciences , 194021 Saint Petersburg, Russia
| | - Elena V Shornikova
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
| | - Johannes Mund
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
| | - Manfred Bayer
- Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany
- Ioffe Institute, Russian Academy of Sciences , 194021 Saint Petersburg, Russia
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Mondal PC, Fontanesi C, Waldeck DH, Naaman R. Spin-Dependent Transport through Chiral Molecules Studied by Spin-Dependent Electrochemistry. Acc Chem Res 2016; 49:2560-2568. [PMID: 27797176 PMCID: PMC5112609 DOI: 10.1021/acs.accounts.6b00446] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
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Molecular spintronics (spin + electronics), which aims to exploit
both the spin degree of freedom and the electron charge in molecular
devices, has recently received massive attention. Our recent experiments
on molecular spintronics employ chiral molecules which have the unexpected
property of acting as spin filters, by way of an effect we call “chiral-induced spin selectivity” (CISS). In this
Account, we discuss new types of spin-dependent electrochemistry measurements
and their use to probe the spin-dependent charge transport properties
of nonmagnetic chiral conductive polymers and biomolecules, such as
oligopeptides, L/D cysteine, cytochrome c, bacteriorhodopsin
(bR), and oligopeptide-CdSe nanoparticles (NPs) hybrid structures.
Spin-dependent electrochemical measurements were carried out by employing
ferromagnetic electrodes modified with chiral molecules used as the
working electrode. Redox probes were used either in solution or when
directly attached to the ferromagnetic electrodes. During the electrochemical
measurements, the ferromagnetic electrode was magnetized either with
its magnetic moment pointing “UP” or “DOWN”
using a permanent magnet (H = 0.5 T), placed underneath
the chemically modified ferromagnetic electrodes. The spin polarization
of the current was found to be in the range of 5–30%, even
in the case of small chiral molecules. Chiral films of the l- and d-cysteine tethered with a redox-active dye, toludin
blue O, show spin polarizarion that depends on the chirality. Because
the nickel electrodes are susceptible to corrosion, we explored the
effect of coating them with a thin gold overlayer. The effect of the
gold layer on the spin polarization of the electrons ejected from
the electrode was investigated. In addition, the role of the structure
of the protein on the spin selective transport was also studied as
a function of bias voltage and the effect of protein denaturation
was revealed. In addition to “dark” measurements, we
also describe photoelectrochemical measurements in which light is
used to affect the spin selective electron transport through the chiral
molecules. We describe how the excitation of a chromophore (such as
CdSe nanoparticles), which is attached to a chiral working electrode,
can flip the preferred spin orientation of the photocurrent, when
measured under the identical conditions. Thus, chirality-induced spin
polarization, when combined with light and magnetic field effects,
opens new avenues for the study of the spin transport properties of
chiral molecules and biomolecules and for creating new types of spintronic
devices in which light and molecular chirality provide new functions
and properties.
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Affiliation(s)
| | - Claudio Fontanesi
- Department
of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
- Department
of Engineering, University of Modena and Reggio Emilia, Via Vivarelli
10, 41125 Modena, Italy
| | - David H. Waldeck
- Department
of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Ron Naaman
- Department
of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel
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