Category Archives: Quantum Dots

Resolving the Core and the Surface of CdSe Quantum Dots and Nanoplatelets Using Dynamic Nuclear Polarization Enhanced PASS–PIETA NMR Spectroscopy #DNPNMR

Piveteau, Laura, Ta-Chung Ong, Brennan J. Walder, Dmitry N. Dirin, Daniele Moscheni, Barbara Schneider, Janine Bär, et al. “Resolving the Core and the Surface of CdSe Quantum Dots and Nanoplatelets Using Dynamic Nuclear Polarization Enhanced PASS–PIETA NMR Spectroscopy.” ACS Central Science 4, no. 9 (September 26, 2018): 1113–25.

https://doi.org/10.1021/acscentsci.8b00196.

Understanding the surface of semiconductor nanocrystals (NCs) prepared using colloidal methods is a longstanding goal of paramount importance for all their potential optoelectronic applications, which remains unsolved largely because of the lack of site-specific physical techniques. Here, we show that multidimensional 113Cd dynamic nuclear polarization (DNP) enhanced NMR spectroscopy allows the resolution of signals originating from different atomic and magnetic surroundings in the NC cores and at the surfaces. This enables the determination of the structural perfection, and differentiation between the surface and core atoms in all major forms of size- and shape-engineered CdSe NCs: irregularly faceted quantum dots (QDs) and atomically flat nanoplatelets, including both dominant polymorphs (zinc-blende and wurtzite) and their epitaxial nanoheterostructures (CdSe/CdS core/shell quantum dots and CdSe/CdS core/crown nanoplatelets), as well as magic-sized CdSe clusters. Assignments of the NMR signals to specific crystal facets of oleate-terminated ZB structured CdSe NCs are proposed. Significantly, we discover far greater atomistic complexity of the surface structure and the species distribution in wurtzite as compared to zinc-blende CdSe QDs, despite an apparently identical optical quality of both QD polymorphs.

Dynamic nuclear polarization and Hanle effect in (In,Ga)As/GaAs quantum dots. Role of nuclear spin fluctuations

Gerlovin, I.Y., et al., Dynamic nuclear polarization and Hanle effect in (In,Ga)As/GaAs quantum dots. Role of nuclear spin fluctuations. AIP Conference Proceedings, 2013. 1566(1): p. 319-320.

http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4848414

The degree of circular polarization of photoluminescence of (In,Ga)As quantum dots as a function of magnetic field applied perpendicular to the optical axis (Hanle effect) is experimentally studied. The measurements have been performed at various regimes of the optical excitation modulation. The analysis of experimental data has been performed in the framework of a vector model of regular nuclear spin polarization and its fluctuations. The analysis allowed us to evaluate the magnitude of nuclear polarization and its dynamics at the experimental conditions used.

Dynamic nuclear polarization and Hanle effect in (In,Ga)As/GaAs quantum dots. Role of nuclear spin fluctuations

Gerlovin, I.Y., et al., Dynamic nuclear polarization and Hanle effect in (In,Ga)As/GaAs quantum dots. Role of nuclear spin fluctuations. AIP Conference Proceedings, 2013. 1566(1): p. 319-320.

http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4848414

The degree of circular polarization of photoluminescence of (In,Ga)As quantum dots as a function of magnetic field applied perpendicular to the optical axis (Hanle effect) is experimentally studied. The measurements have been performed at various regimes of the optical excitation modulation. The analysis of experimental data has been performed in the framework of a vector model of regular nuclear spin polarization and its fluctuations. The analysis allowed us to evaluate the magnitude of nuclear polarization and its dynamics at the experimental conditions used.

Dynamical nuclear polarization and confinement effects in ZnO quantum dots

P. G. Baranov et al., Dynamical nuclear polarization and confinement effects in ZnO quantum dots, Phys. Status Solidi B., 2010, 247, 1476-1479

http://dx.doi.org/10.1002/pssb.200983218

The spatial distribution of the electronic wave function of a  shallow donor (SD) in a ZnO semiconductor quantum dots (QD’s) has been determined in the regime of quantum confinement by using the nuclear spins as probes. Hyperfine (HF) interactions as monitored by electron nuclear double resonance spectroscopy quantitatively reveal the transition from semiconductor to molecular properties upon reduction of the size of the nanoparticles. Influence of confinement effect on g-factor value of SD’s in ZnOand CdS QD’s was displayed. The almost complete dynamic nuclear polarization (DNP) of nuclear spins has been demonstrated can be achieved in ZnO QD’s by saturating the EPR transition of the SD present in the QD’s with using high-frequency at low temperatures. Polarization of 67Zn nuclear spins inZnO core and of 1Hnuclear spins in the Zn(OH)2 capping layer have been obtained which manifests itself via the creation of a hole and an antihole in the EPR absorption line of the SD in QD’s and a shift of the hole (antihole). The enhancement of the nuclear polarization opens the possibility to study semiconductor nanostructures with NMR techniques

Dynamical nuclear polarization and confinement effects in ZnO quantum dots

P. G. Baranov et al., Dynamical nuclear polarization and confinement effects in ZnO quantum dots, Phys. Status Solidi B., 2010, 247, 1476-1479

http://dx.doi.org/10.1002/pssb.200983218

The spatial distribution of the electronic wave function of a  shallow donor (SD) in a ZnO semiconductor quantum dots (QD’s) has been determined in the regime of quantum confinement by using the nuclear spins as probes. Hyperfine (HF) interactions as monitored by electron nuclear double resonance spectroscopy quantitatively reveal the transition from semiconductor to molecular properties upon reduction of the size of the nanoparticles. Influence of confinement effect on g-factor value of SD’s in ZnOand CdS QD’s was displayed. The almost complete dynamic nuclear polarization (DNP) of nuclear spins has been demonstrated can be achieved in ZnO QD’s by saturating the EPR transition of the SD present in the QD’s with using high-frequency at low temperatures. Polarization of 67Zn nuclear spins inZnO core and of 1Hnuclear spins in the Zn(OH)2 capping layer have been obtained which manifests itself via the creation of a hole and an antihole in the EPR absorption line of the SD in QD’s and a shift of the hole (antihole). The enhancement of the nuclear polarization opens the possibility to study semiconductor nanostructures with NMR techniques

Have a question?

If you have questions about our instrumentation or how we can help you, please contact us.