Electronic and Impurity Doping in Colloidal Semiconductor Nanocrystals PDF Download
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Author: Alina Marie Schimpf
Publisher:
ISBN:
Category :
Languages : en
Pages : 229
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Book Description
This thesis presents investigations of semiconductor nanocrystals doped with impurity ions, excess charge carriers, or both. The introduction of excess charge carriers into colloidal semiconductor nanocrystals constitutes a longstanding challenge in the development of nanocrystal building blocks for various technologies including solar cells, photovoltaic devices and electroluminescent devices. Chapter 1 discusses methods for electronic doping in semiconductor nanocrystals, focusing on photodoping and aliovent doping strategies. Of the various successful strategies for electronic doping, photodoping is particularly useful as a post-synthetic method for reversible and quantifiable tuning of carrier density. Alternatively, aliovalently doped nanocrystals are attractive due to the great stability of charge carriers. Chapter 2 presents a comparative study of conduction-band electrons in colloidal ZnO nanocrystals added via photodoping or aliovalent doping. The studies show that, although they have very similar spectroscopic properties, the reactivites of the electrons are vastly different, owing to the relative mobilities of their charge-compensating cations. Chapters 3, 4 and 5 present investigations of the ability to add excess electrons to a variety of systems via photodoping. The study in Chapter 3 shows that the maximum number of elecrons that may be added photochemically is dependent on the nanocrystal volume, such that all nanocrystals may be photodoped to the same electron density. Furthermore, the identities of the sacrifical reductant and the charge-compensating cation determine the maximum photodoping density. For the first time, alkyl borohydrides were used as sacrificial reductants to photodope ZnO, leading to much larger carrier densities than previously observed. These findings informed the first demonstration of photodoping in CdE (E= S, Se, Te) nanocrystals, presented in Chapter 4. Chapter 5 presents a combination of photodoping and aliovalent doping in In2O3 nanocrystals to investigate the redox chemistries in In2O3 and ITO nanocrystals. The study shows that all nanocrystals have the same Fermi level, and Sn4[superscript +] stabilizes that conduction band to allow accumulation of excess delocalized electrons. Moreover, regardless of Sn4[superscript +] doping and therefore of initial carrier density, all nanocrystals have the same number of electrons that may be added photochemically. These results, in conjunction with those presented in Chapters 3 and 4, suggest maximum photodoping density is thermodynamically limited, and is not an intrinsic property of the nanocrystal, nor a result of competition between productive hole-quenching and non-productive Auger recombination in the photoexcited nanocrystals. The ability to reversibly tune the carrier densities in colloidal semiconductor nanocrystals via photodoping allows new photophsyical investigations of electronically doped systems. Chapters 5 and 6 use photodoping to investigate the properties of plasmon resonances in ZnO and In2O3 nanocrystals. Chapter 5 shows that the plasmon energy is affected by both carrier density and Sn4[superscript +] doping. Chapter 6 shows that plasmons in ZnO nanocrystals are subject to quantum confinement and therefore may not be understood with a classical Drude picture. The large magnetic exchange interaction between charge carriers and magnetic dopants make diluted magnetic semiconductors (DMSs) particularly attractive for spin-based information processing. Chapter 7 uses pulsed electron paramagnetic resonance (pEPR) spectroscopy to investigate the affect of excess electrons on the Mn2[superscript +] spin dynamics in doped ZnO nancorystals, showing that Mn2[superscript +] spin relaxation is greatly accelerated by the presence of even one conduction-band electron. Chapter 8 uses pEPR to investigate the intrinsic spin dynamics of Mn2[superscript] in a variety of II-VI colloidal semiconductor nanocrystals. Finally, Chapter 9 shows the ability to tune the effective g value in DMSs at low fields using temperature.
Author: Alina Marie Schimpf
Publisher:
ISBN:
Category :
Languages : en
Pages : 229
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Book Description
This thesis presents investigations of semiconductor nanocrystals doped with impurity ions, excess charge carriers, or both. The introduction of excess charge carriers into colloidal semiconductor nanocrystals constitutes a longstanding challenge in the development of nanocrystal building blocks for various technologies including solar cells, photovoltaic devices and electroluminescent devices. Chapter 1 discusses methods for electronic doping in semiconductor nanocrystals, focusing on photodoping and aliovent doping strategies. Of the various successful strategies for electronic doping, photodoping is particularly useful as a post-synthetic method for reversible and quantifiable tuning of carrier density. Alternatively, aliovalently doped nanocrystals are attractive due to the great stability of charge carriers. Chapter 2 presents a comparative study of conduction-band electrons in colloidal ZnO nanocrystals added via photodoping or aliovalent doping. The studies show that, although they have very similar spectroscopic properties, the reactivites of the electrons are vastly different, owing to the relative mobilities of their charge-compensating cations. Chapters 3, 4 and 5 present investigations of the ability to add excess electrons to a variety of systems via photodoping. The study in Chapter 3 shows that the maximum number of elecrons that may be added photochemically is dependent on the nanocrystal volume, such that all nanocrystals may be photodoped to the same electron density. Furthermore, the identities of the sacrifical reductant and the charge-compensating cation determine the maximum photodoping density. For the first time, alkyl borohydrides were used as sacrificial reductants to photodope ZnO, leading to much larger carrier densities than previously observed. These findings informed the first demonstration of photodoping in CdE (E= S, Se, Te) nanocrystals, presented in Chapter 4. Chapter 5 presents a combination of photodoping and aliovalent doping in In2O3 nanocrystals to investigate the redox chemistries in In2O3 and ITO nanocrystals. The study shows that all nanocrystals have the same Fermi level, and Sn4[superscript +] stabilizes that conduction band to allow accumulation of excess delocalized electrons. Moreover, regardless of Sn4[superscript +] doping and therefore of initial carrier density, all nanocrystals have the same number of electrons that may be added photochemically. These results, in conjunction with those presented in Chapters 3 and 4, suggest maximum photodoping density is thermodynamically limited, and is not an intrinsic property of the nanocrystal, nor a result of competition between productive hole-quenching and non-productive Auger recombination in the photoexcited nanocrystals. The ability to reversibly tune the carrier densities in colloidal semiconductor nanocrystals via photodoping allows new photophsyical investigations of electronically doped systems. Chapters 5 and 6 use photodoping to investigate the properties of plasmon resonances in ZnO and In2O3 nanocrystals. Chapter 5 shows that the plasmon energy is affected by both carrier density and Sn4[superscript +] doping. Chapter 6 shows that plasmons in ZnO nanocrystals are subject to quantum confinement and therefore may not be understood with a classical Drude picture. The large magnetic exchange interaction between charge carriers and magnetic dopants make diluted magnetic semiconductors (DMSs) particularly attractive for spin-based information processing. Chapter 7 uses pulsed electron paramagnetic resonance (pEPR) spectroscopy to investigate the affect of excess electrons on the Mn2[superscript +] spin dynamics in doped ZnO nancorystals, showing that Mn2[superscript +] spin relaxation is greatly accelerated by the presence of even one conduction-band electron. Chapter 8 uses pEPR to investigate the intrinsic spin dynamics of Mn2[superscript] in a variety of II-VI colloidal semiconductor nanocrystals. Finally, Chapter 9 shows the ability to tune the effective g value in DMSs at low fields using temperature.
Author: Lijun Zu
Publisher:
ISBN:
Category :
Languages : en
Pages : 352
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Book Description
Author: Swamy Pittala
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Spin-based electronics use the spins of electrons in addition to their charges and have potential applications to create a next generation of quantum computers, capable of storing vast amounts of data in an energy-efficient way. Diluted magnetic semiconductor quantum dots (DMS-QDs) have shown great promise as ideal materials for application in spin-based electronics. However, doping impurities into quantum confined colloidal nanocrystals (NCs) has been a great challenge due to the lack of control over the dopant reactivity during the specific stages of nucleation and growth. The mechanism of dopant incorporation into nanocrystals is complex and well-defined and atomically precise molecular clusters can provide detailed knowledge and novel insights into the doping process. This work focuses on the synthesis of Co2+ substituted CdS and ZnS based molecular clusters and understanding doping mechanism at the molecular level and use these clusters as precursors to make doped nanocrystals. The cation exchange rates and thermodynamic stability of dopants in the smallest tetrameric clusters is found to depend mainly on the identity of the host cation in the cluster. The surface ligand dynamics of clusters directly control the rate of dopant ion exchange into molecular clusters. As the size of molecular clusters increases the ligand dynamics decreases and dopant exchange into these larger clusters becomes less feasible. We developed a method to synthesize doped NCs using these pre-doped magnetic molecular chalcogenide clusters, as single-source precursors. We obtained very high concentration of cobalt impurities into CdS nanocrystals without undergoing spinodal decomposition. This high doping level is attributed to the growth mechanism that involves formation of dopant substituted metastable magic-sized nuclei (CdS)34 before the critical nuclei during the synthesis. Furthermore, the particular growth mechanism of doped nanocrystals can be controlled by the size of diluted magnetic molecular precursors. The synthetic strategy demonstrated here utilizes magnetic inorganic clusters as true single-source precursors and provides an effective and tunable route to synthesize doped nanocrystals with high dopant concentrations.
Author: Victor I. Klimov
Publisher: CRC Press
ISBN: 1420079271
Category : Technology & Engineering
Languages : en
Pages : 485
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Book Description
A review of recent advancements in colloidal nanocrystals and quantum-confined nanostructures, Nanocrystal Quantum Dots is the second edition of Semiconductor and Metal Nanocrystals: Synthesis and Electronic and Optical Properties, originally published in 2003. This new title reflects the book’s altered focus on semiconductor nanocrystals. Gathering contributions from leading researchers, this book contains new chapters on carrier multiplication (generation of multiexcitons by single photons), doping of semiconductor nanocrystals, and applications of nanocrystals in biology. Other updates include: New insights regarding the underlying mechanisms supporting colloidal nanocrystal growth A revised general overview of multiexciton phenomena, including spectral and dynamical signatures of multiexcitons in transient absorption and photoluminescence Analysis of nanocrystal-specific features of multiexciton recombination A review of the status of new field of carrier multiplication Expanded coverage of theory, covering the regime of high-charge densities New results on quantum dots of lead chalcogenides, with a focus studies of carrier multiplication and the latest results regarding Schottky junction solar cells Presents useful examples to illustrate applications of nanocrystals in biological labeling, imaging, and diagnostics The book also includes a review of recent progress made in biological applications of colloidal nanocrystals, as well as a comparative analysis of the advantages and limitations of techniques for preparing biocompatible quantum dots. The authors summarize the latest developments in the synthesis and understanding of magnetically doped semiconductor nanocrystals, and they present a detailed discussion of issues related to the synthesis, magneto-optics, and photoluminescence of doped colloidal nanocrystals as well. A valuable addition to the pantheon of literature in the field of nanoscience, this book presents pioneering research from experts whose work has led to the numerous advances of the past several years.
Author: Earl D. Goodwin
Publisher:
ISBN:
Category :
Languages : en
Pages : 306
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Book Description
Colloidal semiconductor nanocrystals have emerged as fascinating new materials and gained interest in the last 30 years because of their size, shape, and compositionally tunable electronic and optical properties as well as their potential to serve as artificial atoms. Challenges and opportunities have arisen when assembling nanocrystals into nanocrystal solids for electronic and optoelectronic applications, largely because of the significant influence of nanocrystal surface chemistry on the electronic, optical, and structural properties of nanocrystal solids. In order to assemble nanocrystal solids for high performance devices, we must understand and be able to control the effects of nanocrystal surface organic capping ligands, non-stoichiometry, and impurity doping on the electronic and optoelectronic properties of the nanocrystal solids.
Author: Vladimir Lesnyak
Publisher: Frontiers Media SA
ISBN: 2889632695
Category :
Languages : en
Pages : 110
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Book Description
Author: Wesley Chiang
Publisher: American Chemical Society
ISBN: 0841299854
Category : Science
Languages : en
Pages : 163
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Book Description
Today, the fascinating story of colloidal quantum dots has no series finale yet. Instead, there continue to be advancements in our understanding of the fundamental properties of these nanocrystals, each of these advancements catalyzing a spin-off into a new journey toward potential applications. These remarkable advancements include improving the synthesis techniques, characterizing nanocrystals at the single-particle level, and tailoring their properties for specific applications. The quantum-confined colloidal semiconductor nanocrystals field has witnessed a remarkable convergence of nanoscience, materials chemistry, and spectroscopy, resulting in unprecedented control over their properties. With ongoing research efforts, the potential of semiconductor nanocrystals continues to unfold. Scientists are exploring new materials, developing scalable synthesis methods, and pushing the boundaries of their applications in fields such as quantum computing, energy storage, and biological sensing. The authors take the reader into quantum confinement and quantum dots. While the contents of this primer are rather expansive, they merely scratch the surface of the complex voyage that quantum dot sciences have undergone. The authors have identified vital terminology, valuable concepts, techniques, and applications.
Author: Andrey Rogach
Publisher: Springer Science & Business Media
ISBN: 3211752374
Category : Technology & Engineering
Languages : en
Pages : 374
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Book Description
This is the first book to specifically focus on semiconductor nanocrystals, and address their synthesis and assembly, optical properties and spectroscopy, and potential areas of nanocrystal-based devices. The enormous potential of nanoscience to impact on industrial output is now clear. Over the next two decades, much of the science will transfer into new products and processes. One emerging area where this challenge will be very successfully met is the field of semiconductor nanocrystals. Also known as colloidal quantum dots, their unique properties have attracted much attention in the last twenty years.
Author: E. Fred Schubert
Publisher: E. Fred Schubert
ISBN: 0986382639
Category : Science
Languages : en
Pages : 624
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Book Description
This is the first book to describe thoroughly the many facets of doping in compound semiconductors. Equal emphasis is given to the fundamental materials physics and to the technological aspects of doping. The author describes various doping techniques, including doping during epitaxial growth, doping by implantation, and doping by diffusion. The key characteristics of all dopants that have been employed in III-V semiconductors are discussed. In addition, general characteristics of dopants are analyzed, including the electrical activity, saturation, amphotericity, autocompensation, and maximum attainable dopant concentration. Redistribution effects are important in semiconductor microstructures. Linear and non-linear diffusion, different microscopic diffusion mechanisms, surface segregation, surface drift, surface migration, impurity-induced disordering, and the respective physical driving mechanisms are illustrated. Topics related to basic impurity theory include the hydrogenic model for shallow impurities, linear screening, density of states, classical and quantum statistics, the law of mass action, as well as many analytic approximations for the Fermi-Dirac integral for three-, two- and one dimensional systems. The timely topic of highly doped semiconductors, including band tails, impurity bands, bandgap renormalization, the Mott transition, and the Burstein-Moss shift, is discussed as well. Doping is essential in many semiconductor heterostructures including high-mobility selectively doped heterostructures, quantum well and quantum barrier structures, doping superlattice structures and d-doping structures. Technologically important deep levels are summarized, including Fe, Cr, and the DX-center, the EL2 defect, and rare-earth impurities. The properties of deep levels are presented phenomenologically, including emission, capture, Shockley-Read recombination, the Poole-Frenkel effect, lattice relaxation, and other effects. The final chapter is dedicated to the experimental characterization of impurities. This book will be of interest to graduate students, researchers and development engineers in the fields of electrical engineering, materials science, physics, and chemistry working on semiconductors. The book may also be used as a text for graduate courses in electrical engineering and materials science.
Author: Hankyeol Jung
Publisher:
ISBN:
Category :
Languages : en
Pages : 111
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Book Description
Modulation of chemical, photophysical, and electronic properties by controlling the type and concentration of carriers is an essential ability that enables semiconductor applications in a wide range of technologies. Colloidal semiconductor nanocrystals are an attractive class of solution processable and tunable semiconductor materials. Several doping strategies have been successfully applied to semiconductor nanocrystals, making them promising components of emerging technologies. Photochemical doping has emerged as a particularly attractive strategy for post-synthetic electronic doping of colloidal semiconductor nanocrystals because it is reversible, nondestructive and solution-stable. This dissertation focuses on the photochemical manipulation of nanoscale materials, including colloidal nanocrystals and cluster-based frameworks.Chapter 1 provides an introductory overview of electronic doping strategies. Furthermore, background on the classes of materials studied within, colloidal nanocrystals and cluster-based frameworks, is provided. Chapter 2 presents the photochemical reduction of colloidal maghemite nanocrystals as a means to access high-quality magnetite nanocrystals. The phase-transformation of iron oxide nanocrystal via introduction of excess carriers is analyzed by X-ray, optical, and magnetic characterization methods. Furthermore, the factors limiting photochemical reduction are discussed. Chapter 3 details the UV irradiation of colloidal 2H tungsten diselenide nanocrystals using lithium triethylborohydride. This phototreatment leads to a bleach of the band-edge absorption and an enhancement and blue-shift of the C-exciton absorption. Powder X-ray diffraction suggests that these changes are primarily due to lithium-ion intercalation into these two-dimensional materials. Chapter 4 extends the methods for electron-quantification in photochemically doped semiconductor nanocrystals do photochemically reduced cluster-based frameworks. The synthesis of cluster-based frameworks allows for in situ photodoping to access highly crystalline, reduced cluster-based frameworks. The results are used to demonstrates the unique stability of reduced Zn-bridged frameworks based on Mo-doped Preyssler clusters.
