Browsing by Author "Liu, Yu"

Now showing 1 - 7 of 7
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    A study of the Meissner effect in type I superconductors
    (1966) Liu, Yu; Houston, William V.
    This report includes an analysis of the flux penetration and expulsion from a normal conducting cylinder and then an account of the observed results of a superconducting ellipsoid. The penetration and expulsion of magnetic flux during the normal to superconducting transition was governed principally by the eddy current shielding. There was au initial rapid penetration and expulsion of flux as the external magnetic field became equal to the critical field.
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    Chemistry of novel nanoscale carbon materials: Nanodiamond and carbon nano-onions
    (2006) Liu, Yu; Halas, Naomi J.
    Nanoscience is the area of science concerning materials on the level of nanometer scale. Currently much of the discussion of nanoscience is focused on carbon-based nanostructures. Tremendous studies have been carried out on fullerenes and carbon nanotubes in the past a couple of decade due to their unique chemical and physical properties. This thesis studies the chemistry of the other two novel nanostructures in the carbon family: nanodiamond and carbon nano-onions. Nanodiamond is relatively a new engineering material with particular applications for fabrication of wear-resistant surface coatings, lubricating films and prototypes field emission displays. These materials are also of interest for studies of chemical reactivity stemming from their nanoscale particle sizes. The surface fluorination of nanodiamond at various temperatures yields a fluoro-nanodiamond with up to 8.6 at. % fluorine content. The fluoro-nanodiamond was used as a precursor for preparation of the series of functionalized nanodiamonds by subsequent reactions with alkyllithium reagents, diamines, and amino acids. The fluoro-nanodiamond and all derivatives were characterized by SEM, TEM, XRD, TG-MS, FTIR, XPS, and Raman measurements. In comparison with the pristine nanodiamond, all functionalized nanodiamonds show an improved solubility in polar organic solvents, e.g., alcohols and THF, and a reduced particle agglomeration. The fluoro-nanodiamond powder was also used as a precursor for diamond coating on solid substrate surface e.g. glass. This novel approach is based on the wet chemistry process (solution reaction) occurring at low temperature and resulting in a covalent bonding of tiny nanodiamond crystals to substrate through a molecular linker, 3-aminopropyltriethoxysilane (APTES). SEM, AFM and XPS were used for evaluation of surface morphology and elemental analysis to confirm the presence of diamond particles on surface. Carbon nano-onion studied in this thesis is another new material synthesized by our collaborators. The layer-by-layer structures make it a potential candidate as lubricant materials. The nano-onions were fluorinated at various temperatures resulting in fluoro-onions with different fluorine content. The inside layered structures are damaged due to fluorination, which was characterized by Raman, XRD, TEM et al. Defluorination treatment was also performed. All the samples show improved lubricating properties according to the test carried out by our collaborators.
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    Fluorinated nanodiamond as a precursor for solid substrate surface coating using wet chemistry
    (2011-08-23) Khabashesku, Valery N.; Liu, Yu; Halas, Nancy J.; Rice University; United States Patent and Trademark Office
    The present invention is directed to nanodiamond (ND) surface coatings and methods of making same. Such coatings are formed by a covalent linkage of ND crystals to a particular surface via linker species. The methods described herein overcome many of the limitations of the prior art in that they can be performed with standard wet chemistry (i.e., solution-based) methods, thereby permitting low temperature processing. Additionally, such coatings can potentially be applied on a large scale and for coating large areas of a variety of different substrates.
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    Fluorinated nanodiamond as a precursor for solid substrate surface coating using wet chemistry
    (2010-12-28) Khabashesku, Valery N.; Liu, Yu; Halas, Nancy J.; Rice University; United States Patent and Trademark Office
    The present invention is directed to nanodiamond (ND) surface coatings and methods of making same. Such coatings are formed by a covalent linkage of ND crystals to a particular surface via linker species. The methods described herein overcome many of the limitations of the prior art in that they can be performed with standard wet chemistry (i.e., solution-based) methods, thereby permitting low temperature processing. Additionally, such coatings can potentially be applied on a large scale and for coating large areas of a variety of different substrates.
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    Functionalization of nanodiamond powder through fluorination and subsequent derivatization reactions
    (2010-10-26) Khabashesku, Valery N.; Liu, Yu; Margrave, John L.; Margrave, Mary Lou; Rice University; United States Patent and Trademark Office
    The present invention is directed to functionalized nanoscale diamond powders, methods for making such powders, applications for using such powders, and articles of manufacture comprising such powders. Methods for making such functionalized nanodiamond powders generally comprise a fluorination of nanodiamond powder. In some embodiments, such methods comprise reacting fluorinated nanodiamond powder with a subsequent derivatization agent, such as a strong nucleophile.
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    High fidelity numerical study of nonlinear impact wave propagation: methods, analysis, and applications
    (2014-11-06) Liu, Yu; Dick, Andrew J; Akin, John E; Stanciulescu, Ilinca
    Various systems and structures are subjected to impact loading in industrial and military applications. Many of these impact loads have very high magnitudes and very short durations, resulting in high frequency content. Under some conditions, the response to these loading conditions can be significantly influenced by nonlinearities. The goal of this thesis is to develop new tools for studying the nonlinear wave propagation which can result from this extreme impact loading and provide an in-depth understanding of the underlying physical process. It consists of analytical, numerical, and experimental studies. Two new numerical methods are developed for high fidelity simulation of nonlinear wave propagations: the alternating frequency-time finite element method (AFT-FEM) and the alternating wavelet-time finite element method (AWT-FEM). A perturbation based approach is developed to derive analytical formula of the wavenumber for one-dimensional rod model. By employing these numerical and analytical methods, numerical simulations of wave propagations in both infinite and finite domains for one-dimensional and two-dimensional structures are conducted to explore nonlinear behaviors in the responses. Experimental efforts are also made to verify numerical results of impact wave propagation. Through comparison with other existing numerical approaches, the advantages of AWT-FEM in computational efficiency and high fidelity are demonstrated and the method is employed for applications of nonlinear force identification and drill-string stability monitoring.
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    The Magnetic Genome of Two-Dimensional van der Waals Materials
    (American Chemical Society, 2022) Wang, Qing Hua; Bedoya-Pinto, Amilcar; Blei, Mark; Dismukes, Avalon H.; Hamo, Assaf; Jenkins, Sarah; Koperski, Maciej; Liu, Yu; Sun, Qi-Chao; Telford, Evan J.; Kim, Hyun Ho; Augustin, Mathias; Vool, Uri; Yin, Jia-Xin; Li, Lu Hua; Falin, Alexey; Dean, Cory R.; Casanova, Fèlix; Evans, Richard F.L.; Chshiev, Mairbek; Mishchenko, Artem; Petrovic, Cedomir; He, Rui; Zhao, Liuyan; Tsen, Adam W.; Gerardot, Brian D.; Brotons-Gisbert, Mauro; Guguchia, Zurab; Roy, Xavier; Tongay, Sefaattin; Wang, Ziwei; Hasan, M. Zahid; Wrachtrup, Joerg; Yacoby, Amir; Fert, Albert; Parkin, Stuart; Novoselov, Kostya S.; Dai, Pengcheng; Balicas, Luis; Santos, Elton J.G.
    Magnetism in two-dimensional (2D) van der Waals (vdW) materials has recently emerged as one of the most promising areas in condensed matter research, with many exciting emerging properties and significant potential for applications ranging from topological magnonics to low-power spintronics, quantum computing, and optical communications. In the brief time after their discovery, 2D magnets have blossomed into a rich area for investigation, where fundamental concepts in magnetism are challenged by the behavior of spins that can develop at the single layer limit. However, much effort is still needed in multiple fronts before 2D magnets can be routinely used for practical implementations. In this comprehensive review, prominent authors with expertise in complementary fields of 2D magnetism (i.e., synthesis, device engineering, magneto-optics, imaging, transport, mechanics, spin excitations, and theory and simulations) have joined together to provide a genome of current knowledge and a guideline for future developments in 2D magnetic materials research.