Tin-doped Indium Oxide (ITO) Nanocrystal Superlattices (Surface Chemistry, Charge Transport, and Sensing Applications) PDF Download

Author: Mahdi Samadi Khoshkhoo
Publisher:
ISBN:
Category : Indium
Languages : en
Pages :

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Author: Sebastien Dahmane Lounis
Publisher:
ISBN:
Category :
Languages : en
Pages : 126

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Colloidally prepared nanocrystals of transparent conducting oxide (TCO) semiconductors have emerged in the past decade as an exciting new class of plasmonic materials. In recent years, there has been tremendous progress in developing synthetic methods for the growth of these nanocrystals, basic characterization of their properties, and their successful integration into optoelectronic and electrochemical devices. However, many fundamental questions remain about the physics of localized surface plasmon resonance (LSPR) in these materials, and how their optoelectronic properties derive from their underlying structural properties. In particular, the influence of the concentration and distribution of dopant ions and compensating defects on the optoelectronic properties of TCO nanocrystals has seen little investigation. Indium tin oxide (ITO) is the most widely studied and commercially deployed TCO. Herein we investigate the role of the distribution of tin dopants on the optoelectronic properties of colloidally prepared ITO nanocrystals. Owing to a high free electron density, ITO nanocrystals display strong LSPR absorption in the near infrared. Depending on the particular organic ligands used, they are soluble in various solvents and can readily be integrated into densely packed nanocrystal films with high conductivities. Using a combination of spectroscopic techniques, modeling and simulation of the optical properties of the nanocrystals using the Drude model, and transport measurements, it is demonstrated herein that the radial distribution of tin dopants has a strong effect on the optoelectronic properties of ITO nanocrystals. ITO nanocrystals were synthesized in both surface-segregated and uniformly distributed dopant profiles. Temperature dependent measurements of optical absorbance were first combined with Drude modeling to extract the internal electrical properties of the ITO nanocrystals, demonstrating that they are well-behaved degenerately doped semiconductors displaying finite conductivity at low temperature and room temperature conductivity reduced by one order of magnitude from that of high-quality thin film ITO. Synchrotron based x-ray photoelectron spectroscopy (XPS) was then employed to perform detailed depth profiling of the elemental composition of ITO nanocrystals, confirming the degree of dopant surface-segregation. Based on free carrier concentrations extracted from Drude fitting of LSPR absorbance, an inverse correlation was found between surface segregation of tin and overall dopant activation. Furthermore, radial distribution of dopants was found to significantly affect the lineshape and quality factor of the LSPR absorbance. ITO nanocrystals with highly surface segregated dopants displayed symmetric LSPRs with high quality factors, while uniformly doped ITO nanocrystals displayed asymmetric LSPRs with reduced quality factors. These effects are attributed to damping of the plasmon by Coulombic scattering off ionized dopant impurities. Finally, the distribution of dopants is also found to influence the conductivity of ITO nanocrystal films. Films made from nanocrystals with a high degree of surface segregation demonstrated one order of magnitude higher conductivity than those based on uniformly doped crystals. However, no evidence was found for differences in the surface electronic structure from one type of crystal to the other based on XPS and the exact mechanism for this difference is still not understood. Several future studies to further illuminate the influence of dopant distribution on ITO nanocrystals are suggested. Using synchrotron radiation, detailed photoelectron spectroscopy on clean ITO nanocrystal surfaces, single-nanoparticle optical measurements, and hard x-ray structural studies will all be instructive in elucidating the interaction between oscillating free electrons and defect scattering centers when a plasmon is excited. In addition, measurements of temperature and surface treatment-dependent conductivity with carefully controlled atmosphere and surface chemistry will be needed in order to better understand the transport properties of ITO nanocrystal films. Each of these studies will enable better fundamental knowledge of the plasmonic properties of nanostructures and improve the development of nanocrystal based plasmonic devices.

Author: Chet Carter
Publisher:
ISBN:
Category :
Languages : en
Pages : 648

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This dissertation has focused on the study of the ITO/organic heterojunction and the chemistries therein, it proposes appropriate strategies that enhance the interfacial physical and electronic properties for charge injection with application to organic thin-layer devices. We focused on four major aspects of this work: i) To characterize the ITO surface and chemistries that may be pertinent to interaction with adjacent organic layers in a device configuration. This developed a working model of surface and provided a foundation for modification strategies. Characterization of the electronic properties of the surface indicate less than 5% of the geometrical surface is responsible for the bulk of current flow while the rest is electrically inactive. ii) To determine the extent to which these chemistries are variable and propose circumstances where compositional changes can occur. It is shown that the surface chemistry of ITO is heterogeneous and possible very dynamic with respect to the surrounding environment. iii) To propose a strategy for modification of the interface. Modification of ITO surfaces by small molecules containing carboxylic acid functionalities is investigated. Enhancements in the electron transfer rate coefficient were realized after modification of the ITO electrode. The enhancements are found to stem from a light etching mechanism. Additionally, an elecro-catalytic effect was observed with some of the modifiers. iv) Apply these modifications to organic light emitting diodes (OLEDs) and organic photovoltaic devices (OPVs). Enhancements seen in solution electrochemical experiments are indicative of the enhancements seen for solid state devices. Modifications resulted in substantially lower leakage currents (3 orders of magnitude in some cases) as well as nearly doubling the efficiency. An additional chapter describesthe creation and characterization of electrochemically grown polymer nano-structures based on blazed angle diffraction gratings. The discussion details the micro-contact printing process and the electro-catalytic growth of the conductive polymers PANI and PEDOT to form diffraction grating structures in their own right. The resulting diffraction efficiency of these structures is shown to be sensitive to environmental conditions outlining possible uses as chemical sensors. This is demonstrated by utilizing these structures as working pH and potentiometric sensors based on the changing diffraction efficiency.

Author: Hui Che
Publisher:
ISBN:
Category : Indium tin oxide
Languages : en
Pages : 136

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In this study, we used UV-ozone Ar sputtering, X-ray photoelectron and ultra-violet photoelectron spectroscopies and sputtering based depositions of RuO2 and Se nano-layers on indium tin oxides (ITOs). We elucidated the effect of Ar sputtering on the composition and chemistry of Sn rich ITO surface. We demonstrated that while a combination of UV-ozone radiation and Ar sputtering removes most of the hydrocarbons responsible for degrading the work function of ITO, it also removes significant amount of the segregated SN at the ITO surface that's responsible for its reasonable work function of 4.7eV. We also demonstrated for the first time that sputtering cleaning ITO surface leads to the reduction of the charge state of Sn from Sn4+ to Sn2+ that adds to the degradation of the work function. For the nano-layers coverage of ITO studies, we evaluated both RuO2 and Se. For RuO2 coated ITO, XPS showed the formation of a Ru-Sn-O ternary oxide. The RuO2 nano-layer reduced the oxidation state of Sn in the Sn-rich surface of ITO from +4 to +2. The best work function obtained for this system is 4.98eV, raising the effective work function of ITO by more than 0.5 eV. For the Se coated ITO studies, a systematic study of the dependence of the effective work function on the thickness of Se overage and its chemistry at the Se/ITO interface was undertaken. XPS showed that Se reacts with Sn at the Sn-rich surface of ITO determined the presence of both negative and positive oxidation state of Se at the Se/ITO interface. The Se also reduced the oxidation state of Sn from Sn4+ to Sn2+ in the Sn-rich ITO surface. The highest effective work function obtained for this system is 5.06eV. A combination of RuO2/Se nanoscale coating of optimally cleaned ITO would be a good alternative for device applications that would provide work function tuning in addition to their potential ability to act as interface stabilizers and a barrier to reaction and inter-diffusion at ITO/active layers interfaces responsible for long term stability of devices and especially organic solar cells and organic light emitting diodes.

Author: James Sylvester Grundy
Publisher:
ISBN:
Category :
Languages : en
Pages : 254

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Novel engineered nanomaterials (ENMs) continue to be synthesized and adopted for commercial and industrial applications. Currently, the classes of ENMs utilized most in consumer products are metal oxides, metals, and carbonaceous materials. An emerging subset of metal oxide ENMs with potential in many applications are doped metal oxides, which are binary metal oxides (MO [subscript x] ) with some amount of another element, metal or non metal, inserted into the crystal lattice. This research focused on the environmental fate and transport of a major doped metal oxide, indium tin oxide (ITO), that is currently widely produced for applications in electronics. Specifically, this dissertation investigated the particle stability, solubility, and production of reactive oxygen species (ROS) by ITO nanoparticles in aqueous systems. The stability of ITO particles in electrolyte solutions and the effect of Sn level was investigated in a series of homoaggregation studies. In order to better compare colloidal stability, a novel method, called the TAA-logistic method, for estimating the critical coagulation concentration (CCC) from dynamic light scattering data was developed and tested with experimental and literature data. Using the new method, particle aggregation kinetics were compared for a range of solution conditions including pH, electrolyte valency, ionic strength, and presence of natural organic matter (NOM). Aggregation kinetics were determined for a set of synthesized particles coated with PAA-PEO polymer and for a set of bare, commercially-obtained particles. Aggregation experiments indicated inclusion of Sn in In2O3 decreased the aqueous stability of the nanoparticle, largely due to decreases in the magnitude of surface charge. However, the surface charge and aqueous stability did not always trend linearly with Sn content, indicating other factors, such as the distribution of Sn within the ITO crystal, were also important. Lastly, Suwannee River aquatic natural organic matter (NOM) significantly increased the aqueous stability of ITO nanoparticles through charge reversal and electrostatic stabilization. Dissolution of ITO in dilute, inert electrolyte was studied in batch and flowthrough experiments. Slow dissolution kinetics were shown in both experimental con- figurations. Sn was not appreciably leached from ITO at either pH = 4 or pH = 6. Inclusion of Sn appeared to reduce In solubility relative to In2O3 at pH = 6 but increased In leaching at pH = 4. The discrepancy between dissolution behavior at the two pH values relative to the In2O3 end-member indicated more complex solubility than explained by simple ideal solid solution aqueous solution behavior. Lastly, the electronic band structure of ITO was determined for multiple levels of Sn using ultraviolet photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. Inclusion of tin resulted in an increase of the optical band gap and a shift of the conduction band minimum, Fermi level, and valence band maximum to more oxidizing potentials relative to un-doped In2O3. From these findings, ITO would thermodynamically be able to produce hydroxyl radicals from water by photocatalysis under UVB irradiation, regardless of the level of Sn doping. However, the ITO with the highest doping level investigated, which is the ITO currently produced commercially, was able to produce hydroxyl radicals under UVB illumination at a significantly faster rate than lesser- and un-doped ITO. This study showed that numerous characteristics related to the transport, transformation, and toxicity of ITO nanoparticles in aqueous environmental matrices were affected by the amount of Sn in ITO. However, the behaviors exhibited by ITO were not easily predicted by simply considering ITO as a mixture of varying amounts of the In2O3 and SnO2 end-members. Therefore, further study of the environmental fate and transport of a more extensive set of doped metal oxides is needed to develop more complex models for assessing the environmental fate and transport of doped metal oxides.

Author: Man-Kin Fung
Publisher: Open Dissertation Press
ISBN: 9781361291016
Category :
Languages : en
Pages :

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This dissertation, "Fabrications of Tin-doped Indium Oxide Nanostructures and Their Applications" by Man-kin, Fung, 馮文健, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Tin-doped indium oxide (ITO) has been widely used for various optoelectronic devices such as display panels, light-emitting diodes and solar cells due to its unique optical and electrical properties. Thin ITO films can be fabricated by a number of methods such as molecular beam epitaxy (MBE), laser ablation, dc sputtering, e-beam deposition, vapor phase deposition, electrochemical deposition and hydrothermal method. Apart from the conventional thin film form, one dimensional ITO nanorods or nanowires are attracting much research interest due to their high aspect ratio and large surface to volume ratio. For instance, a network made of ITO nanowires can exhibit high transparency (over 95 %) and high flexibility without losing its conducting property as reported recently. This network can be potentially used for flexible photovoltaic devices. In this study, ITO nanorods or nanowires were fabricated using the vapor deposition, dc sputtering and e-beam deposition. The use of short ITO nanorods (100 nm) on glass and commercial ITO substrates as bottom electrodes improving the charge collection of bulk heterojunction organic solar cells had been demonstrated. The morphology of the ITO nanostructures was studied by scanning electron microscope (SEM) and transmission electron microscope (TEM). The crystal structure and growth direction were studied by x-ray diffraction (XRD) and selected area electron diffraction (SAED), respectively. Optical properties were examined using transmission and photoluminescence measurements. The performance of the organic solar cells was examined using the I-V characteristics and external quantum efficiency (EQE) measurements. The growth mechanism of the ITO nanowires using different fabrication methods was discussed. The effects of the substrate temperature, oxygen content, choice of substrate and evaporation rate on the morphology, transmittance and sheet resistivity were investigated. When short ITO nanorods were incorporated into the bulk heterojunction organic solar cells, a significant improvement of the power conversion efficiency (PCE) was observed. The higher efficiency of the studied solar cells was attributed to the improved charge collection. DOI: 10.5353/th_b4784945 Subjects: Nanostructured materials Indium compounds Tin compounds Metallic oxides

Author: Richard Allen Gilstrap (Jr)
Publisher:
ISBN:
Category : Colloids
Languages : en
Pages :

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A logical progression from the maturing field of colloidal semiconductor quantum dots to the emerging subclass of impurity-doped colloidal semiconductor nanoparticles is underway. To this end, the present work describes the formation and analysis of a new form of Tin-doped Indium Oxide (ITO). The form is that of a colloidal dispersion comprised of pure-phase, 4-6 nanometer ITO particles possessing an essentially single crystalline character. This system forms a non-agglomerated, optically clear solution in a variety of non-polar solvents and can remain in this state, at room temperature, for months and potentially, years. ITO is the most widely used member of the exotic materials family known as Transparent Conductive Oxides (TCOs) and is the primary enabling material behind a wide variety of opto-electronic device technologies. Material synthesis was achieved by initiating a series of interrelated nucleophilic substitution reactions that provided sufficient intensity to promote doping efficiencies greater than 90% for a wide range of tin concentrations. The optical clarity of this colloidal system allowed the intrinsic properties of single crystalline ITO particles to be evaluated prior to their use in thin-films or composite structures. Monitoring the temporal progression of n-type degeneracy by its effects on the optical properties of colloidal dispersions shed light on the fundamental issues of particle formation, band filling (Burstein-Moss) dynamics, and the very origin of n-type degeneracy in ITO. Central to these studies was the issue of excess electron character. The two limiting cases of entirely free and entirely confined electron motion were evaluated by application of bulk-like band dispersion analysis and the effective mass approximation, respectively. This provided a means to estimate the number of excess conduction band electrons present within an individual particle boundary. The ability to control and optimize the level of n-type degeneracy within the colloidal ITO nanoparticle form by compositional variation was also demonstrated. A key to the widespread adoption of a new material by industry is an ability to produce multi-gram and perhaps, kilogram quantities with no significant sacrifice in quality. Accordingly, a modified synthesis process was developed to allow for the mass production of high-quality colloidal ITO nanocrystals.

Author:
Publisher: Elsevier
ISBN: 0128133589
Category : Technology & Engineering
Languages : en
Pages : 608

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Colloidal Metal Oxide Nanoparticles: Synthesis, Characterization and Applications is a one-stop reference for anyone with an interest in the fundamentals, synthesis and applications of this interesting materials system. The book presents a simple, effective and detailed discussion on colloidal metal oxide nanoparticles. It begins with a general introduction of colloidal metal oxide nanoparticles, then delves into the most relevant synthesis pathways, stabilization procedures, and synthesis and characterization techniques. Final sections discuss promising applications, including bioimaging, biosensing, diagnostic, and energy applications—i.e., solar cells, supercapacitors and environment applications—i.e., the treatment of contaminated soil, water purification and waste remediation. Provides the most comprehensive resource on the topic, from fundamentals, to synthesis and characterization techniques Presents key applications, including biomedical, energy, electronic and environmental Discusses the most relevant techniques for synthesis, patterning and characterization

Author: Sivashankar Krishnamoorthy
Publisher: CRC Press
ISBN: 1466591269
Category : Technology & Engineering
Languages : en
Pages : 292

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Nanomaterials are being incorporated into products all around us, having an incredible impact on durability, strength, functionality, and other material properties. There are a vast number of nanomaterials presently available, and new formulations and chemistries are being announced daily. Nanomaterials: A Guide to Fabrication and Applications provides product developers, researchers, and materials scientists with a handy resource for understanding the range of options and materials currently available. Covering a variety of nanomaterials and their applications, this practical reference: Discusses the scale of nanomaterials and nanomachines, focusing on integrated circuits (ICs) and microelectromechanical systems (MEMS) Offers insight into different nanomaterials’ interactions with chemical reactions, biological processes, and the environment Examines the mechanical properties of nanomaterials and potential treatments to enhance the nanomaterials’ performance Details recent accomplishments in the use of nanomaterials to create new forms of electronic devices Explores the optical properties of certain nanomaterials and the nanomaterials’ use in optimizing lasers and optical absorbers Describes an energy storage application as well as how nanomaterials from waste products may be used to improve capacitors Featuring contributions from experts around the globe, Nanomaterials: A Guide to Fabrication and Applications serves as a springboard for the discovery of new applications of nanomaterials.

Author: Markus Niederberger
Publisher: Springer Science & Business Media
ISBN: 1848826710
Category : Science
Languages : en
Pages : 223

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Metal Oxide Nanoparticles in Organic Solvents discusses recent advances in the chemistry involved for the controlled synthesis and assembly of metal oxide nanoparticles, the characterizations required by such nanoobjects, and their size and shape depending properties. In the last few years, a valuable alternative to the well-known aqueous sol-gel processes was developed in the form of nonaqueous solution routes. Metal Oxide Nanoparticles in Organic Solvents reviews and compares surfactant- and solvent-controlled routes, as well as providing an overview of techniques for the characterization of metal oxide nanoparticles, crystallization pathways, the physical properties of metal oxide nanoparticles, their applications in diverse fields of technology, and their assembly into larger nano- and mesostructures. Researchers and postgraduates in the fields of nanomaterials and sol-gel chemistry will appreciate this book’s informative approach to chemical formation mechanisms in relation to metal oxides.