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Your search keyword '"Pietryga, Jeffrey M."' showing total 190 results
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190 results on '"Pietryga, Jeffrey M."'

2. Influence of the Core/Shell Interface on Biexciton Auger Recombination in Individual Nanocrystal Quantum Dots

Author

Park, Young-Shin, Bae, Wan Ki, Padilha, Lazaro A., Pietryga, Jeffrey M., and Klimov, Victor I.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Previous single-particle spectroscopic studies of colloidal quantum dots have indicated a significant spread in biexciton lifetimes across an ensemble of nominally identical nanocrystals. It has been speculated that in addition to dot-to-dot variation in physical dimensions, this spread is contributed to by variations in the structure of the quantum dot interface, which controls the shape of the confinement potential. Here we directly evaluate the effect of the composition of the core-shell interface on single- and multi-exciton dynamics via side-by-side measurements of individual core-shell CdSe-CdS nanocrystals with a sharp vs. smooth (graded) interface. To realize the latter type of structures, we incorporate a CdSexS1-x alloy layer of controlled composition and thickness between the CdSe core and the CdS shell. We observe that while having essentially no effect on single-exciton decay, the interfacial alloy layer leads to a systematic increase in biexciton lifetimes. This observation provides direct experimental evidence that in addition to the size of the quantum dot, its interfacial properties also significantly affect the rate of Auger recombination, which governs biexciton decay. These findings help rationalize previous observations of a significant heterogeneity in the biexciton lifetimes across similarly sized quantum dots and should facilitate the development of Auger-recombination-free colloidal nanostructures for a range of applications from lasers and light-emitting diodes to photodetectors and solar cells., Comment: This paper has been withdrawn by the author due to insufficient experimental data

Published
2013

3. The influence of Auger recombination on the performance of quantum-dot light-emitting diodes

Author

Bae, Wan Ki, Park, Young-Shin, Lim, Jaehoon, Lee, Donggu, Padilha, Lazaro A., McDaniel, Hunter, Robel, Istvan, Lee, Changhee, Pietryga, Jeffrey M., and Klimov, Victor I.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

A growing interest in colloidal quantum dot (QD) based light-emitting diodes (QD-LEDs) has been motivated by the exceptional color purity and spectral tunability of QD emission as well as the amenability of QD materials to highly scalable and inexpensive solution processing. One current challenge in the QD-LED field has been a still incomplete understanding of the role of extrinsic factors (e.g., recombination via QD surface defects) versus intrinsic processes such as multicarrier Auger recombination or electron-hole separation due to applied electric field in defining device efficiency. Here, we address this problem with a study of excited-state dynamics in a series of structurally engineered QDs, which is performed in parallel with characterization of their performance upon incorporation into LEDs. The results of this study indicate that under both zero and forward bias, a significant fraction of the QDs within the active emitting layer is negatively charged and therefore, Auger recombination represents an important factor limiting the efficiency of these devices. We further observe that the onset of the LED efficiency roll-off is also controlled by Auger recombination and can be shifted to higher currents by using newly developed QDs with an intermediate alloy layer at the core-shell interface introduced for suppression of Auger decay. Our findings suggest that further improvement in the performance of QD-LEDs can be achieved by developing effective approaches for controlling Auger recombination and/or minimizing the effects of QD charging via improved balancing of electron and hole injection currents., Comment: This paper has been withdrawn by the author due to a crucial sign error in equation 1

Published
2013
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4. Utilizing the lability of lead selenide to produce heterstructured nanocrystals with bright, stable infrared emission

Author

Pietryga, Jeffrey M., Werder, Donald J., Williams, Darrick J., Casson, Joanna L., Schaller, Richard D., Klimov, Victor I., and Hollingsworth, Jennifer A.

Subjects
Ion exchange -- Research, Lead alloys -- Chemical properties, Quantum electrodynamics -- Research, Chemistry
Abstract

A partial cation-exchange method is described in which the lability is considered for synthesizing PbSe/CdSe core/shell nanocrystal quantum dots (NQDs). The NQDs have undergone additional shell growth in order to produce PbSe/CdSe/ZnS core/shell NQDs that have represented initial steps toward bright, biocompatible near-infrared optical labels.

Published
2008

8. Perspectives on Designer Photocathodes for X-ray Free-Electron Lasers: Influencing Emission Properties with Heterostructures and Nanoengineered Electronic States

Author

Moody, Nathan A., primary, Jensen, Kevin L., additional, Shabaev, Andrew, additional, Lambrakos, Samuel G., additional, Smedley, John, additional, Finkenstadt, Daniel, additional, Pietryga, Jeffrey M., additional, Anisimov, Petr M., additional, Pavlenko, Vitaly, additional, Batista, Enrique R., additional, Lewellen, John W., additional, Liu, Fangze, additional, Gupta, Gautam, additional, Mohite, Aditya, additional, Yamaguchi, Hisato, additional, Hoffbauer, Mark A., additional, and Robel, István, additional

Published
2018
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9. Infrared-active heterostructured nanocrystals with ultralong carrier lifetimes

Author

Lee, Doh C., Robel, Istvan, Pietryga, Jeffrey M., and Klimov, Victor I.

Subjects
Infrared radiation -- Usage, Lead compounds -- Structure, Lead compounds -- Chemical properties, Nanotechnology -- Research, Photocatalysis -- Analysis, Chemistry
Abstract

The synthesis of compositePbSe/CdS nanocrystals with two distinct geometries, core/shell/shell structures and tetrapods, is described. The ultralong carrier lifetimes and controlled geometry have made the nanocrystals attractive for a variety of applications from lasing to photocatalysis and photovoltaics.

Published
2010

10. A reduction pathway in the synthesis of PbSe nanocrystal quantum dots

Author

Joo, Jin, Pietryga, Jeffrey M., McGuire, John A., Jeon, Sea-Ho, Williams, Darrick J., Hsing-Lin Wang, and Klimov, Victor I.

Subjects
Lead alloys -- Chemical properties, Lead alloys -- Electric properties, Lead alloys -- Optical properties, Quantum electrodynamics -- Analysis, Selenium -- Chemical properties, Selenium -- Electric properties, Selenium -- Optical properties, Chemistry
Abstract

The effects of diphenylphosphine and 1,2-hexadecanediol, as surrogates for putative trioctylphosphine-based reducing impurities for synthesis of PbSe nanocrystal quantum dots (NQDs) were examined to compare their influence on NQD size, chemical yield, and photoluminescence quantum yield. Both additives which substantially increased the chemical yield of the synthesis demonstrated markedly different effects on emission quantum yield of the product NQDs.

Published
2009

11. Colloidal synthesis of infrared-emitting germanium nanocrystals

Author

Doh C. Lee, Pietryga, Jeffrey M., Robel, Istvan, Werder, Donald J., Schaller, Richard D., and Klimov, Victor I.

Subjects
Germanium -- Chemical properties, Germanium -- Optical properties, Infrared radiation -- Analysis, Nanocrystals -- Structure, Nanocrystals -- Chemical properties, Nanocrystals -- Optical properties, Oxidation-reduction reaction -- Analysis, Transmission electron microscopes -- Usage, Chemistry
Abstract

Ge nanocrystals are prepared and the effects of variables such as solvents, reducing agents, reaction temperature and capping ligands are studied. The nanocrystals have shown infrared photoluminescence and enhanced resistance to oxidation and the size dependence of the emission is consistent with the effects of quantum confinement.

Published
2009

12. New aspects of carrier multiplication in semiconductor nanocrystal

Author

McGuire, John A., Jin Joo, Pietryga, Jeffrey M., Schaller, Richard D., and Klimov, Victor I.

Subjects
Electrostatic interactions -- Analysis, Nanocrystals -- Electric properties, Nanocrystals -- Structure, Photons -- Evaluation, Semiconductors -- Electric properties, Semiconductors -- Optical properties, Chemistry, Science and technology
Published
2008

13. Unraveling internal structures of highly luminescent PbSe nanocrystallites using variable-energy synchrotron radiation photoelectron spectroscopy

Author

Sapra, Sameer, Nanda, J., Pietryga, Jeffrey M., Hollingsworth, Jennifer A., and Sarma, D.D.

Subjects
Photoelectron spectroscopy -- Usage, Lead compounds -- Structure, Lead compounds -- Chemical properties, Selenium compounds -- Structure, Selenium compounds -- Chemical properties, Chemicals, plastics and rubber industries
Abstract

The internal structure of PbSe nanocrystals is deduced using synchrotron X-ray photoemission spectroscopy for three different sizes of nanocrystals. The photoemission data reveals the layered structure of PbSe nanocrystals with the crystalline PbSe core surrounded by a nonstoichiometric [Pb.sub.1-x]Se shell, finally passivated by a capping agent in the outermost layer.

Published
2006

21. Charge-Transport Mechanisms in CuInSexS2–xQuantum-Dot Films

Author

Yun, Hyeong Jin, Lim, Jaehoon, Fuhr, Addis S., Makarov, Nikolay S., Keene, Sam, Law, Matt, Pietryga, Jeffrey M., and Klimov, Victor I.

Abstract

Colloidal quantum dots (QDs) have attracted considerable attention as promising materials for solution-processable electronic and optoelectronic devices. Copper indium selenium sulfide (CuInSexS2–xor CISeS) QDs are particularly attractive as an environmentally benign alternative to the much more extensively studied QDs containing toxic metals such as Cd and Pb. Carrier transport properties of CISeS-QD films, however, are still poorly understood. Here, we aim to elucidate the factors that control charge conductance in CISeS QD solids and, based on this knowledge, develop practical approaches for controlling the polarity of charge transport and carrier mobilities. To this end, we incorporate CISeS QDs into field-effect transistors (FETs) and perform detailed characterization of these devices as a function of the Se/(Se+S) ratio, surface treatment, thermal annealing, and the identity of source and drain electrodes. We observe that as-synthesized CuInSexS2–xQDs exhibit degenerate p-type transport, likely due to metal vacancies and CuIn’’anti-site defects (Cu1+on an In3+site) that act as acceptor states. Moderate-temperature annealing of the films in the presence of indium source and drain electrodes leads to switching of the transport polarity to nondegenerate n-type, which can be attributed to the formation of In-related defects such as InCu••(an In3+cation on a Cu1+site) or Ini•••(interstitial In3+) acting as donors. We observe that the carrier mobilities increase dramatically (by 3 orders of magnitude) with increasing Se/(Se+S) ratio in both n- and p-type devices. To explain this observation, we propose a two-state conductance model, which invokes a high-mobility intrinsic band-edge state and a low-mobility defect-related intragap state. These states are thermally coupled, and their relative occupancies depend on both QD composition and temperature. Our observations suggest that the increase in the relative fraction of Se moves conduction- and valence band edges closer to low-mobility intragap levels. This results in increased relative occupancy of the intrinsic band-edge states and a corresponding growth of the measured mobility. Further improvement in charge-transport characteristics of the CISeS QD samples as well as their stability is obtained by infilling the QD films with amorphous Al2O3using atomic layer deposition.

Published
2018
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26. Pushing the band gap envelope: Mid-infrared emitting colloidal PbSe quantum dots

Author

Pietryga, Jeffrey M., Schaller, Richard D., Stewart, Michael H., Klimov, Victor I., Holingsworth, Jennifer A., and Werder, Donald

Subjects
Transmission electron microscopes -- Usage, Photoluminescence -- Research, Lead -- Chemical properties, Chemistry
Abstract

The synthesis of the first colloidal quantum dots (QDs) with efficient, particle-size-tunable, narrow-bandwidth mid-IR photoluminescence (PL) at energies as low as 0.30 eV is described. All QDs were characterized by PL and absorption spectroscopy, as well as by transmission electron microscopy TEM).

Published
2004

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