Download or read book Investigating Photoinduced Structural Changes in Si Using Femtosecond Electron Diffraction written by Maher Harb and published by . This book was released on 2009 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis reports on developing a femtosecond electron diffraction technique and its application in following the structural changes associated with photoexcited Si. Time resolved electron diffraction is capable in principle of capturing transient structures of photoinduced phenomena with femtosecond time resolution. In practice, however, the time resolution is severely limited by the broadening of electron pulses due to space-charge forces. Another technical difficulty lies in that diffraction in transmission geometry requires samples that are semi-transparent to electrons. These experimental challenges were dealt with using innovative engineering and software development, and novel nanofabrication methods. Subsequently, a robust highly automated experimental setup was established, and 50 nm free-standing membranes of polycrystalline Si were nanofabricated. These membranes were first excited below damage threshold with 387 nm light, at an absorbed fluence of 5.6 mJ/cm2. The observed loss of intensity and associated dynamics under these conditions are related to the Debye-Waller effect as the lattice heats up through electron-phonon processes. At high excitation levels, greater than ∼6% of the valence electron density, the crystalline structure of the lattice was lost in 500 fs. This observed time scale is indicative of an electronically driven order-to-disorder phase transition due to an abrupt change in the potential-energy landscape of the lattice. In addition, it was discovered that the high sensitivity of the electron diffraction process to shear-type deformation in single crystals makes the technique ideal to the generation and detection of coherent acoustic phonons. Longitudinal and shear acoustic phonons were subsequently resolved in (001)-oriented Si crystals. This study constitutes the first direct observation of shear phonons in symmetrically cut crystals, in sharp in contrast to the all-optical methods that rely on crystals asymmetrically cut at 20° to enhance the amplitude of the shear mode in order to detect its displacements.
Download or read book Investigating Photoinduced Structural Changes in Silicon Using Femtosecond Electron Diffraction written by Maher Harb and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Chemistry in Action Making Molecular Movies with Ultrafast Electron Diffraction and Data Science written by Lai Chung Liu and published by Springer Nature. This book was released on 2020-09-10 with total page 249 pages. Available in PDF, EPUB and Kindle. Book excerpt: The thesis provides the necessary experimental and analytical tools to unambiguously observe the atomically resolved chemical reactions. A great challenge of modern science has been to directly observe atomic motions during structural transitions, and while this was first achieved through a major advance in electron source brightness, the information content was still limited and new methods for image reconstruction using femtosecond electron diffraction methods were needed. One particular challenge lay in reconciling the innumerable possible nuclear configurations with the observation of chemical reaction mechanisms that reproducibly give the same kind of chemistry for large classes of molecules. The author shows that there is a simple solution that occurs during barrier crossing in which the highly anharmonic potential at that point in nuclear rearrangements couples high- and low-frequency vibrational modes to give highly localized nuclear motions, reducing hundreds of potential degrees of freedom to just a few key modes. Specific examples are given in this thesis, including two photoinduced phase transitions in an organic system, a ring closure reaction, and two direct observations of nuclear reorganization driven by spin transitions. The emerging field of structural dynamics promises to change the way we think about the physics of chemistry and this thesis provides tools to make it happen.
Download or read book Femtosecond Electron Diffraction and Spectroscopic Studies of a Solid State Organic Chemical Reaction written by Hubert Jean-ruel and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Femtosecond Electron Diffraction Studies of Strongly driven Structural Phase Transitions microform written by Bradley John Siwick and published by National Library of Canada = Bibliothèque nationale du Canada. This book was released on 2004 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt: The new technique of femtosecond electron diffraction is developed and applied to the study of an ultrafast structural phase transition. A combination of numerical and analytical modeling is used to obtain a comprehensive understanding of the space-charge dominated propagation dynamics of high number density femtosecond electron pulses and to design a novel photoactivated electron gun. This electron source, capable of producing sub-500 femtosecond electron pulses with sufficient brightness to allow the study of even irreversible structural dynamics, is employed to investigate the strongly driven, laser-induced solid-to-liquid phase transition in polycrystalline aluminum. We are able to see, in real time, the loss of the long-range order present in the crystalline phase and the emergence of the liquid structure where only short-range atomic correlations are present; this transition occurs in 3.5 ps for thin-film aluminum with an excitation fluence of 70 mJ/cm2. The sensitivity and temporal resolution was sufficient to capture the time-dependent atomic pair correlation function as the material evolved from the solid to liquid state. These observations provide an atomic level description of the melting process in which the dynamics are best understood as a thermal phase transition under strongly driven conditions.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 602 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 974 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2692 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Physics Briefs written by and published by . This book was released on 1994 with total page 1248 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Optics Letters written by and published by . This book was released on 2004 with total page 808 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Memoirs of the Institute of Scientific and Industrial Research Osaka University written by Ōsaka Daigaku. Sangyō Kagaku Kenkyūjo and published by . This book was released on 2010 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Science written by John Michels (Journalist) and published by . This book was released on 2003 with total page 1236 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2001 with total page 818 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Visualizing Chemistry written by National Research Council and published by National Academies Press. This book was released on 2006-06-01 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Scientists and engineers have long relied on the power of imaging techniques to help see objects invisible to the naked eye, and thus, to advance scientific knowledge. These experts are constantly pushing the limits of technology in pursuit of chemical imagingâ€"the ability to visualize molecular structures and chemical composition in time and space as actual events unfoldâ€"from the smallest dimension of a biological system to the widest expanse of a distant galaxy. Chemical imaging has a variety of applications for almost every facet of our daily lives, ranging from medical diagnosis and treatment to the study and design of material properties in new products. In addition to highlighting advances in chemical imaging that could have the greatest impact on critical problems in science and technology, Visualizing Chemistry reviews the current state of chemical imaging technology, identifies promising future developments and their applications, and suggests a research and educational agenda to enable breakthrough improvements.
Download or read book American Doctoral Dissertations written by and published by . This book was released on 1991 with total page 724 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Macromolecular Syntheses written by Charles Gilbert Overberger and published by . This book was released on 2002 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is an up-to-date collection of presentations and posters given at a tutorial and workshop sponsored by the Polymer Division of the American Chemical Society. The material included encompasses recent research results, overviews of critical areas and short presentations in the form of posters and preprints. The book is targeted at established workers in the field of fluoropolymers as well as those wishing to develop a quick understanding of current knowledge and trends in this important field.
Download or read book Electrical Electronics Abstracts written by and published by . This book was released on 1997 with total page 2304 pages. Available in PDF, EPUB and Kindle. Book excerpt:
