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Full-Text Articles in Nanoscience and Nanotechnology

Excited-State Dynamics Of Semiconductor Nanocrystals: Trapped-Hole Diffusion And Electron-Transfer Kinetics In Cds And Cdse Nanorods, James Keller Utterback Jan 2018

Excited-State Dynamics Of Semiconductor Nanocrystals: Trapped-Hole Diffusion And Electron-Transfer Kinetics In Cds And Cdse Nanorods, James Keller Utterback

Chemistry & Biochemistry Graduate Theses & Dissertations (1986-2018)

Colloidal semiconductor nanocrystals have many remarkable properties—such as exceptionally tunable excited states and surface chemistry—that have led to an enthusiastic interest in using them for optoelectronic applications such as solar-energy conversion. Such technologies require control over the generation, separation, and extraction of photoexcited electrons and holes. However, the interpretation of experimentally measured excited-state decay curves is challenging because they typically exhibit complicated shapes that are elusive to simple kinetic models. To understand the principles that govern electron and hole relaxation dynamics in these complex systems, models rooted in fundamental physical phenomena are needed. This dissertation describes efforts to ...


Using Semiconductor Nanocrystals To Drive Redox Enzymes With Light, Hayden Tyler Hamby Jan 2018

Using Semiconductor Nanocrystals To Drive Redox Enzymes With Light, Hayden Tyler Hamby

Chemistry & Biochemistry Graduate Theses & Dissertations (1986-2018)

Nanocrystals are an emergent strategy for providing electrons to redox enzymes for catalysis. In this dissertation I present my work on the investigation of how nanocrystals can be used to drive active site chemistry of two different enzymes. In the first project I present for the first time the direct coupling of cadmium sulfide nanorods (CdS NRs) to a CO2 reduction enzyme for the creation of new carbon-carbon bonds using light. Under optimal conditions, the maximum turnover frequency (TOFmax) for CO2 reduction is similar to that obtained in the native system where the native electron donor ferredoxin ...


Magnetic And Catalytic Properties Of Transition Metal Doped Mos2 Nanocrystals, Luis Martinez Jan 2018

Magnetic And Catalytic Properties Of Transition Metal Doped Mos2 Nanocrystals, Luis Martinez

Open Access Theses & Dissertations

Magnetism and catalytic activity of nanoscale layered two-dimensional (2D) transition metal dichalcogenides (TMDs) have gained an increasing research interest in the recent past. To broaden the current knowledge and understanding on this subject, in this work, together with my collaborators, I study the magnetic and electrocatalytic properties of hydrothermally grown pristine and transition metal doped (10% of Co, Ni, Fe and Mn) 2H-MoS2 nanosheets/nanocrystals (NCs), with the particle size of 25-30 nm. A broad range of experimental measurements such as x-ray diffraction, transmission electron microscopy, x-ray photo absorption spectroscopy, Raman spectroscopy, magnetic, catalytic and electron spin resonance have been ...


Photophysics And Electron Transfer Dynamics Of Type-Ii And Quasi Type-Ii Heterostructure Nanocrystals, Amanda Norell Grennell Jan 2017

Photophysics And Electron Transfer Dynamics Of Type-Ii And Quasi Type-Ii Heterostructure Nanocrystals, Amanda Norell Grennell

Chemistry & Biochemistry Graduate Theses & Dissertations (1986-2018)

Type-II and quasi type-II heterostructure nanocrystals are known to exhibit extended excited-state lifetimes compared to their single material counterparts because of reduced wavefunction overlap between the electron and hole. Thus, type-II heterostructures are promising materials for solar-to-fuel conversion, as extended excited-state lifetimes make transfer of charges to a catalyst more competitive with intrinsic nanocrystal decay processes. However, due to fast and efficient hole trapping and non-uniform morphologies, the photophysics of dot-in-rod heterostructures are more rich and complex than this simple picture. Using transient absorption spectroscopy, we observe that the behavior of electrons in the CdS “rod” or “bulb” regions of ...


Photophysics And Electron Transfer Dynamics Of Type-Ii And Quasi Type-Ii Heterostructure Nanocrystals, Amanda N. Grennell Jan 2017

Photophysics And Electron Transfer Dynamics Of Type-Ii And Quasi Type-Ii Heterostructure Nanocrystals, Amanda N. Grennell

Chemistry & Biochemistry Graduate Theses & Dissertations (1986-2018)

Type-II and quasi type-II heterostructure nanocrystals are known to exhibit extended excited-state lifetimes compared to their single material counterparts because of reduced wavefunction overlap between the electron and hole. Thus, type-II heterostructures are promising materials for solar-to-fuel conversion, as extended excited-state lifetimes make transfer of charges to a catalyst more competitive with intrinsic nanocrystal decay processes. However, due to fast and efficient hole trapping and non-uniform morphologies, the photophysics of dot-in-rod heterostructures are more rich and complex than this simple picture. Using transient absorption spectroscopy, we observe that the behavior of electrons in the CdS “rod” or “bulb” regions of ...


The Dawn Of New Quantum Dots: Synthesis And Characterization Of Ge1-Xsnx Nanocrystals For Tunable Bandgaps., Richard J. Esteves Jan 2016

The Dawn Of New Quantum Dots: Synthesis And Characterization Of Ge1-Xsnx Nanocrystals For Tunable Bandgaps., Richard J. Esteves

Theses and Dissertations

Ge1-xSnx alloys are among a small class of benign semiconductors with composition tunable bandgaps in the near-infrared spectrum. As the amount of Sn is increased the band energy decreases and a transition from indirect to direct band structure occurs. Hence, they are prime candidates for fabrication of Si-compatible electronic and photonic devices, field effect transistors, and novel charge storage device applications. Success has been achieved with the growth of Ge1-xSnx thin film alloys with Sn compositions up to 34%. However, the synthesis of nanocrystalline alloys has proven difficult due to larger discrepancies (~14%) in ...


The Optoelectronic Properties Of Surface-Modified Semiconductor Nanocrystal Solids, Earl D. Goodwin Jan 2015

The Optoelectronic Properties Of Surface-Modified Semiconductor Nanocrystal Solids, Earl D. Goodwin

Publicly Accessible Penn Dissertations

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 ...


Designing Nanomaterials For Electronic And Optoelectronic Devices Through Charge Carrier Control, Soong Ju Oh Jan 2014

Designing Nanomaterials For Electronic And Optoelectronic Devices Through Charge Carrier Control, Soong Ju Oh

Publicly Accessible Penn Dissertations

Colloidal semiconductor nanocrystals (NCs) have been shown to be promising materials for electronic and optoelectronic device applications because of their unique size-dependent properties and low-cost solution processability. However, the integration of these materials into devices has been challenging due to a lack of available methods to: 1) accurately control charge carrier statistics, such as majority carrier type and concentration, and carrier mobilities, and 2) efficiently passivate surface defects inherent in NC materials arising from their high surface-volume ratio.

In this thesis, we study the fundamental physics of charge carriers paramount for device application. Then, we introduce several measurement techniques to ...


Directed Synthesis And Doping Of Wide Bandgap Semiconducting Oxide Nanocrystals, Thomas Ross Gordon Jan 2013

Directed Synthesis And Doping Of Wide Bandgap Semiconducting Oxide Nanocrystals, Thomas Ross Gordon

Publicly Accessible Penn Dissertations

Wide bandgap semiconducting oxide nanocrystals are a useful class of materials with high stability and numerous useful properties. In the field of catalysis, high surface area oxides are commonly used as catalytic supports and have been found to be photocatalytically active for the production of renewable fuels. Ultra high vacuum studies of single crystals indicate that the surface structure and faceting of oxides dramatically influence their catalytic properties. For plasmonics applications, degenerately doped oxide nanocrystals may act as low-loss substitutes for metals, but little is known regarding the influence of particle shape or assembly on their optical response. With the ...


Semiconductor Nanocrystals: From Quantum Dots To Quantum Disks, Zheng Li Aug 2012

Semiconductor Nanocrystals: From Quantum Dots To Quantum Disks, Zheng Li

Theses and Dissertations

The bottom-up colloidal synthesis opened up the possibility of finely tuning and tailoring the semiconductor nanocrystals. Numerous recipes were developed for the preparation of colloidal semiconductor nanocrystals, especially the traditional quantum dots. However, due to the lack of thorough understanding to those systems, the synthesis chemistry is still on the empirical level. CdS quantum dots synthesis in non-coordinating solvent were taken as a model system to investigate its molecular mechanism and formation process, ODE was identified as the reducing agent for the preparation of CdS nanocrystals, non-injection and low-temperature synthesis methods developed. In this model system, we not only proved ...


Nanocrystals Of Chemotherapeutic Agents For Cancer Theranostics: Development And In Vitro And In Vivo Evaluation, Christin P. Hollis Jan 2012

Nanocrystals Of Chemotherapeutic Agents For Cancer Theranostics: Development And In Vitro And In Vivo Evaluation, Christin P. Hollis

Theses and Dissertations--Pharmacy

The majority of pharmacologically active chemotherapeutics are poorly water soluble. Solubilization enhancement by the utilization of organic solvents often leads to adverse side effects. Nanoparticle-based cancer therapy, which is passively targeted to the tumor tissue via the enhanced permeation and retention effect, has been vastly developed in recent years. Nanocrystals, which exist as crystalline and carry nearly 100% drug loading, has been explored for delivering antineoplastic agents. Additionally, the hybrid nanocrystal concept offers a novel and simple way to integrate imaging agents into the drug crystals, enabling the achievement of theranostics. The overall objective of this dissertation is to formulate ...


Understanding Molecular Chemistry Of Nanocrystals And Nanostructures: Precursor, Ligand, And Surface Chemistry, Weon-Kyu Koh Aug 2011

Understanding Molecular Chemistry Of Nanocrystals And Nanostructures: Precursor, Ligand, And Surface Chemistry, Weon-Kyu Koh

Publicly Accessible Penn Dissertations

The aim of this dissertation is to understand the molecular chemistry of nanomaterials and to correlate their structures to their functions. The first part of this dissertation explores how we can use precursor chemistry to develop a synthetic approach to novel structures of nanomaterials. There will be a demonstration of morphology control in lead chalcogenide nanocrystals following an investigation of the precursor chemistry which gives valuable information on precursor decomposition during the crystal growth. At the same time, there will be a discussion about how we can understand structure-dependent properties of nanomaterials using advanced spectroscopic techniques. Well-established synthetic approaches discussed ...