Author:
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Category :
Languages : en
Pages : 0
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The objective of the contract was the investigation of hot electron transport on a microscopic scale in metal oxide semiconductor (MOS) structures in order to assess intrinsic transport properties in SiO2 and defect generation processes that lead to oxide failure. The technique used to achieve microscopic resolution was Ballistic Electron Emission Microscopy (BEEM), a variant of the Scanning Tunneling Microscope (STM). In BEEM, use is made of the nearly monochromatic and highly forward focused electron beam of the STM to inject hot electrons through the thin metal 'gate' and into the conduction band of the SiO2. The measured minimum electron energy required to achieve injection and subsequent detection in the Si defines the oxide barrier potential. A research highlight was the demonstration of image force effects in electron transport through MOS structures. The observation was made that the oxide barrier potential decreased with the application of an oxide field. This effect was attributed to screening by metal electrons and was described by classical image force powering, an often-ignored concept by the MOS science and engineering community. The results led to a new 'dynamic' value for the dielectric constant of SiO2, which was confirmed by theoretical modeling of the MOS transport process. Monte Carlo simulations were made of the spreading of the beam as it traverses the oxide. The inclusion of image force effects was necessary for agreement with experiment.
Author: Hamid Bentarzi
Publisher: Springer Science & Business Media
ISBN: 3642163041
Category : Technology & Engineering
Languages : en
Pages : 115
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Book Description
This book focuses on the importance of mobile ions presented in oxide structures, what significantly affects the metal-oxide-semiconductor (MOS) properties. The reading starts with the definition of the MOS structure, its various aspects and different types of charges presented in their structure. A review on ionic transport mechanisms and techniques for measuring the mobile ions concentration in the oxides is given, special attention being attempted to the Charge Pumping (CP) technique associated with the Bias Thermal Stress (BTS) method. Theoretical approaches to determine the density of mobile ions as well as their distribution along the oxide thickness are also discussed. The content varies from general to very specific examples, helping the reader to learn more about transport in MOS structures.
Author: Amish B. Shah
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The ability to grow ultrathin films layer-by-layer with well-defined epitaxial relationships has allowed research groups worldwide to grow a range of artificial films and superlattices, first for semiconductors, and now with oxides. In the oxides thin film research community, there have been concerted efforts recently to develop a number of epitaxial oxide systems grown on single crystal oxide substrates that display a wide variety of novel interfacial functionality, such as enhanced ferromagnetic ordering, increased charge carrier density, increased optical absorption, etc, at interfaces. The magnitude of these novel properties is dependent upon the structure of thin films, especially interface sharpness, intermixing, defects, and strain, layering sequence in the case of superlattices and the density of interfaces relative to the film thicknesses. To understand the relationship between the interfacial thin film oxide atomic structure and its properties, atomic scale characterization is required. Transmission electron microscopy (TEM) offers the ability to study interfaces of films at high resolution. Scanning transmission electron microscopy (STEM) allows for real space imaging of materials with directly interpretable atomic number contrast. Electron energy loss spectroscopy (EELS), together with STEM, can probe the local chemical composition as well as local electronic states of transition metals and oxygen. Both techniques have been significantly improved by aberration correctors, which reduce the probe size to 1 ©5, or less. Aberration correctors have thus made it possible to resolve individual atomic columns, and possibly probe the electronic structure at atomic scales. Separately, using electron probe forming lenses, structural information such as the crystal structure, strain, lattice mismatches, and superlattice ordering can be measured by nanoarea electron diffraction (NED). The combination of STEM, EELS, and NED techniques allows us to gain a fundamental understanding of the properties of oxide superlattices and ultrathin films and their relationship with the corresponding atomic and electronic structure. In this dissertation, I use the aforementioned electron microscopy techniques to investigate several oxide superlattice and ultrathin film systems. The major findings are summarized below. These results were obtained with stringent specimen preparation methods that I developed for high resolution studies, which are described in Chapter 2. The essential materials background and description of electron microscopy techniques are given in Chapter 1 and 2. In a LaMnO3-SrMnO3 superlattice, we demonstrate the interface of LaMnO3-SrMnO3 is sharper than the SrMnO3-LaMnO3 interface. Extra spectral weights in EELS are confined to the sharp interface, whereas at the rougher interface, the extra states are either not present or are not confined to the interface. Both the structural and electronic asymmetries correspond to asymmetric magnetic ordering at low temperature. In a short period LaMnO3-SrTiO3 superlattice for optical applications, we discovered a modified band structure in SrTiO3 ultrathin films relative to thick films and a SrTiO3 substrate, due to charge leakage from LaMnO3 in SrTiO3. This was measured by chemical shifts of the Ti L and O K edges using atomic scale EELS. The interfacial sharpness of LaAlO3 films grown on SrTiO3 was investigated by the STEM/EELS technique together with electron diffraction. This interface, when prepared under specific conditions, is conductive with high carrier mobility. Several suggestions for the conductive interface have been proposed, including a polar catastrophe model, where a large built-in electric field in LaAlO3 films results in electron charge transfer into the SrTiO3 substrate. Other suggested possibilities include oxygen vacancies at the interface and/or oxygen vacancies in the substrate. The abruptness of the interface as well as extent of intermixing has not been thoroughly investigated at high resolution, even though this can strongly influence the electrical transport properties. We found clear evidence for cation intermixing through the LaAlO3-SrTiO3 interface with high spatial resolution EELS and STEM, which contributes to the conduction at the interface. We also found structural defects, such as misfit dislocations, which leads to increased intermixing over coherent interfaces.
Author: Heinz Frei
Publisher: Royal Society of Chemistry
ISBN: 1839163712
Category : Technology & Engineering
Languages : en
Pages : 379
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Book Description
Ultrathin metal oxide layers have emerged in recent years as a powerful approach for substantially enhancing the performance of photo, electro, or thermal catalytic systems for energy, in some cases even enabling the use of highly attractive materials previously found unsuitable. This development is due to the confluence of new synthetic preparation methods for ultrathin oxide layers and a more advanced understanding of interfacial phenomena on the nano and atomic scale. This book brings together the fundamentals and applications of ultrathin oxide layers while highlighting connections and future opportunities with the intent of accelerating the use of these materials and techniques for new and emerging applications of catalysis for energy. It comprehensively covers the state-of-the-art synthetic methods of ultrathin oxide layers, their structural and functional characterization, and the broad range of applications in the field of catalysis for energy. Edited by leaders in the field, and with contributions from global experts, this title will be of interest to graduate students and researchers across materials science and chemistry who are interested in ultrathin oxide layers and their applications in solar energy conversion, renewable energy, photocatalysis, electrocatalysis and protective coatings.
Author: Electrochemical Society. Meeting
Publisher:
ISBN:
Category : Electrochemistry
Languages : en
Pages : 1700
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Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 2540
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Author:
Publisher:
ISBN:
Category : Electrical engineering
Languages : en
Pages : 2240
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Author:
Publisher:
ISBN:
Category : Engineering
Languages : en
Pages : 1688
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Author: New Brunswick. Department of Transportation
Publisher:
ISBN: 9781550483925
Category :
Languages : en
Pages : 1272
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Book Description
General activity review of associated branches and agencies to the Department which includes corporate securities registrations, a list of tenders received, and general financial data. Branches and agencies reviewed are responsible for motor vehicle activity, highway construction, traffic engineering, telecommunications and public utilities.
Author: Huan Pang
Publisher: Springer Nature
ISBN: 9811373728
Category : Science
Languages : en
Pages : 224
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Book Description
This book provides a comprehensive review of functional nanomaterials for electrochemical applications, presenting interesting examples of nanomaterials with different dimensions and their applications in electrochemical energy storage. It also discusses the synthesis of functional nanomaterials, including quantum dots; one-dimensional, two-dimensional and three-dimensional nanostructures; and advanced nanocomposites. Highlighting recent advances in current electrochemical energy storage hotpots: lithium batteries, lithium-ion batteries, sodium-ion batteries, other metal-ion batteries, halogen ion batteries, and metal–gas batteries, this book will appeal to readers in the various fields of chemistry, material science and engineering.
