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You searched for +publisher:"Cornell University" +contributor:("Ast, Dieter G."). Showing records 1 – 3 of 3 total matches.

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Cornell University

1. Smith, Eva Helena. Structure prediction, growth, and characterization of perovskites.

Degree: PhD, Materials Science and Engineering, 2017, Cornell University

The heart of materials science is understanding the relationship between structure (how molecules are connected at the atomic level, as well as in hierarchical building blocks) and properties. Historically this has been achieved by studying the properties of materials in hand, either found in nature or synthesized in the laboratory. As the understanding of the relationship between structure and properties has grown, and our ability to calculate and in particular to solve Schrödinger’s equation for solids has improved, so too has our desire and ability to predict structures with enhanced properties through computation. In this thesis I do each of those three tasks – prediction, synthesis, and characterization – on a system that is of interest in its own right and which I hope may yield results that can be applied to other materials systems as well. All of these systems are materials in the highly-versatile perovskite structure, which can accommodate most of the elements of the periodic table. Perovskites have been the object of much study in the laboratory as well as being used extensively in industrial applications, with such properties as ferroelectricity, piezoelectricity, ferromagnetism, and superconductivity. First, I delineate the chemical factors that determine the ground-state structure of CsPbF3. I use CsPbF3 as a guide to search for rules to rationally design from first principles new polar fluoride and halide perovskites with stoichiometry ABX3 and as a model compound to study the interactions of lone pair electrons, antipolar structural distortions, and the different coordination requirements of A and B cations. I show that the coordination requirements of the A-site cation Cs+ and the stereoactivity of the B-site lone pair cation Pb2+ compete or cooperate via the anionic displacements that accompany polar distortions, and consider the generalizability of my findings to other halide and oxide perovskites. Next, I describe the chemical reactions that govern growth of PbTiO3 and BiFeO3 by molecular-beam epitaxy. PbTiO3 and BiFeO3 are among two dozen complex oxides that are grown by MBE using thermodynamic composition control. I show that kinetics are also critical to growing phase-pure materials by this method, and that oxidation of lead or bismuth can be the rate-limiting step in the synthesis of PbTiO3 or BiFeO3, respectively, from component elements. I establish a simple kinetic model for the growth of these materials that complements the existing thermodynamic theories and delineate the factors controlling the range of temperatures and pressures in which kinetics permit these materials to be grown by thermodynamic control. Finally, I detail how to predict and verify the presence of hybrid reflections in x-ray diffraction patterns of phase-pure epitaxial oxide thin films grown on single-crystal substrates. I present symmetric θ-2θ scans of such films of PbTiO3, BaxSr1−xTiO3, and layered perovskite-relative La2NiO4, in which there occur peaks (reflections) that correspond to neither the film nor the… Advisors/Committee Members: Schlom, Darrell (chair), Ast, Dieter G. (committee member), Disalvo, Francis J. (committee member).

Subjects/Keywords: density functional theory; molecular-beam epitaxy; perovskite; Materials Science; Crystal Growth; Inorganic chemistry; science; Engineering

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APA (6th Edition):

Smith, E. H. (2017). Structure prediction, growth, and characterization of perovskites. (Doctoral Dissertation). Cornell University. Retrieved from http://hdl.handle.net/1813/56777

Chicago Manual of Style (16th Edition):

Smith, Eva Helena. “Structure prediction, growth, and characterization of perovskites.” 2017. Doctoral Dissertation, Cornell University. Accessed September 20, 2020. http://hdl.handle.net/1813/56777.

MLA Handbook (7th Edition):

Smith, Eva Helena. “Structure prediction, growth, and characterization of perovskites.” 2017. Web. 20 Sep 2020.

Vancouver:

Smith EH. Structure prediction, growth, and characterization of perovskites. [Internet] [Doctoral dissertation]. Cornell University; 2017. [cited 2020 Sep 20]. Available from: http://hdl.handle.net/1813/56777.

Council of Science Editors:

Smith EH. Structure prediction, growth, and characterization of perovskites. [Doctoral Dissertation]. Cornell University; 2017. Available from: http://hdl.handle.net/1813/56777


Cornell University

2. Lynch, David Michael. Indium Gallium Zinc Oxide: Phase Formation and Crystallization Kinetics During Millisecond Laser Spike Annealing.

Degree: PhD, Materials Science and Engineering, 2017, Cornell University

Flat panel displays have become ubiquitous, enabling products from highresolution cell phones to ultra-large television panels. Amorphous silicon (a- Si) has been the industry workhorse as the active semiconductor in pixeladdressing transistors due to its uniformity and low production costs. However, a-Si can no longer support larger and higher-resolution displays, and new materials with higher electron mobilities are required. Amorphous indium gallium zinc oxide (a-IGZO), which retains the uniformity and low cost of amorphous films, has emerged as a viable candidate due to its enhanced transport properties. However, a-IGZO devices suffer from long-term instabilities—the origins of which are not yet fully understood—causing a drift in switching characteristics over time and affecting product lifetime. More recently, devices fabricated from textured nanocrystalline IGZO, termed c-axis aligned crystalline (CAAC), have demonstrated superior stability. Unfortunately, little is known regarding the phase formation and crystallization kinetics of either the CAAC structure or in the broader ternary IGZO system. Crystallinity and texture of CAAC IGZO films deposited by RF reactive sputtering were studied and characterized over a wide range of deposition conditions. The characteristic CAAC (0 0 9) peak at 2 = 30 was observed by X-ray diffraction, and nanocrystalline domain texture was determined using a general area detector diffraction system (GADDS). Highly ordered CAAC films were obtained near the InGaZnO4 composition at a substrate temperature of 310C and in a 10%O2/90% Ar sputtering ambient. High-resolution transmission electron microscopy (HRTEM) confirmed the formation of CAAC and identified 2– 3 nm domains coherently aligned over large ranges extending beyond the field of view (15 nm 15 nm). Cross-section HRTEM of the CAAC/substrate interface shows formation of an initially disordered IGZO layer prior to CAAC formation, suggesting a nucleation mechanism similar to ZnO thin films. A classical nucleation and growth model is proposed and compared to alternative models proposed in literature. Extending this study of CAAC IGZO, the formation and growth of crystalline IGZO over a wide composition range and processing conditions were explored. IGZO itself is one composition of a class of homologous structures in the pseudo-binary InGaO3(ZnO)m system. For integer m, the equilibrium structure is known and well-characterized; however, for non-integer m, disorder must exist and the kinetics of the structural development remain almost completely unknown. A high-throughput (combinatorial) approach utilizing co-sputter deposition, millisecond timescale thermal gradient laser annealing, and spatially-resolved characterization using microbeam wide-angle X-ray scattering was used to probe the structural evolution as a function of temperature, time, and composition. As-deposited films were amorphous in the InGaO3- rich composition range, becoming crystalline (wurtzite) with increasing ZnO content. Under millisecond heating, films… Advisors/Committee Members: Thompson, Michael Olgar (chair), Shealy, James Richard (committee member), Ast, Dieter G. (committee member), Greene, Raymond G (committee member).

Subjects/Keywords: Electrical engineering; Crystallization Kinetics; Homologous Compounds; IGZO; Millisecond Annealing; TFTs; Laser Spike Annealing; Materials Science

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Lynch, D. M. (2017). Indium Gallium Zinc Oxide: Phase Formation and Crystallization Kinetics During Millisecond Laser Spike Annealing. (Doctoral Dissertation). Cornell University. Retrieved from http://hdl.handle.net/1813/59108

Chicago Manual of Style (16th Edition):

Lynch, David Michael. “Indium Gallium Zinc Oxide: Phase Formation and Crystallization Kinetics During Millisecond Laser Spike Annealing.” 2017. Doctoral Dissertation, Cornell University. Accessed September 20, 2020. http://hdl.handle.net/1813/59108.

MLA Handbook (7th Edition):

Lynch, David Michael. “Indium Gallium Zinc Oxide: Phase Formation and Crystallization Kinetics During Millisecond Laser Spike Annealing.” 2017. Web. 20 Sep 2020.

Vancouver:

Lynch DM. Indium Gallium Zinc Oxide: Phase Formation and Crystallization Kinetics During Millisecond Laser Spike Annealing. [Internet] [Doctoral dissertation]. Cornell University; 2017. [cited 2020 Sep 20]. Available from: http://hdl.handle.net/1813/59108.

Council of Science Editors:

Lynch DM. Indium Gallium Zinc Oxide: Phase Formation and Crystallization Kinetics During Millisecond Laser Spike Annealing. [Doctoral Dissertation]. Cornell University; 2017. Available from: http://hdl.handle.net/1813/59108

3. Tabassum, Tasnuva. CORRELATING THERMAL PROPERTIES OF SPUTTERED TANTALUM AND TANTALUM NITRIDE THIN FILMS OF VARYING N2 CONTENT WITH MECHANICAL, ELECTRICAL AND STRUCTURAL PROPERTIES.

Degree: M.S., Materials Science and Engineering, Materials Science and Engineering, 2017, Cornell University

With rapid growth in the semiconductor industry, the need for optimization of nanofabrication processes is ever increasing. In such processes, TaN films are of great interest as they create effective diffusion barriers against Cu interconnects in integrated circuits. These circuits may be subjected to elevated temperatures during processing and it is important to study the changes in properties of materials involved. Surprisingly, limited data on the constant pressure specific heat capacity (cp) of Ta and TaN thin films exist. This thesis studies the changes in cp from room temperature to 400°C of sputter-deposited Ta and TaN thin films with varied N2 partial pressure. Parallel studies of mechanical, electrical and structural changes are conducted on as-deposited and annealed samples to correlate to changes in cp. The cp of films increases with temperature, as seen in bulk forms of Ta and TaN. Low temperature resistivity measurements are performed to study the effect of lattice vibrations decreasing. The electrical properties of TaN, deposited in greater than 23% N2 content, are found to be insulating. Annealing decreases the resistivity of Ta films which is attributed to defect healing. The hardness and Young’s modulus increase up to 27% N2 content of TaN films. The residual stress in these films range from highly tensile Ta to increasingly compressive TaN with increased N2 content. The TaN film with the lowest inducing stress was 18% N2 with a compressive stress of -5.82 MPa. Advisors/Committee Members: Van Dover, Robert B. (chair), Ast, Dieter G. (committee member), Phoenix, Stuart Leigh (committee member).

Subjects/Keywords: Thermal; electrical; semiconductor; Nanoindentation; thin films; Materials Science; Nanotechnology; Engineering; tantalum nitride

…so far. Finally, thank you Cornell University for accepting me. You are the reason I am… …Materials Science and Engineering department at Cornell University, who works with Professor… …Shefford Baker. A Hysitron “TriboIndenter” (TI-900) in Bard Hall, Cornell University is… …in Bard Hall at Cornell University, uses a poly-cap focusing system to focus a very intense… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Tabassum, T. (2017). CORRELATING THERMAL PROPERTIES OF SPUTTERED TANTALUM AND TANTALUM NITRIDE THIN FILMS OF VARYING N2 CONTENT WITH MECHANICAL, ELECTRICAL AND STRUCTURAL PROPERTIES. (Masters Thesis). Cornell University. Retrieved from http://hdl.handle.net/1813/56807

Chicago Manual of Style (16th Edition):

Tabassum, Tasnuva. “CORRELATING THERMAL PROPERTIES OF SPUTTERED TANTALUM AND TANTALUM NITRIDE THIN FILMS OF VARYING N2 CONTENT WITH MECHANICAL, ELECTRICAL AND STRUCTURAL PROPERTIES.” 2017. Masters Thesis, Cornell University. Accessed September 20, 2020. http://hdl.handle.net/1813/56807.

MLA Handbook (7th Edition):

Tabassum, Tasnuva. “CORRELATING THERMAL PROPERTIES OF SPUTTERED TANTALUM AND TANTALUM NITRIDE THIN FILMS OF VARYING N2 CONTENT WITH MECHANICAL, ELECTRICAL AND STRUCTURAL PROPERTIES.” 2017. Web. 20 Sep 2020.

Vancouver:

Tabassum T. CORRELATING THERMAL PROPERTIES OF SPUTTERED TANTALUM AND TANTALUM NITRIDE THIN FILMS OF VARYING N2 CONTENT WITH MECHANICAL, ELECTRICAL AND STRUCTURAL PROPERTIES. [Internet] [Masters thesis]. Cornell University; 2017. [cited 2020 Sep 20]. Available from: http://hdl.handle.net/1813/56807.

Council of Science Editors:

Tabassum T. CORRELATING THERMAL PROPERTIES OF SPUTTERED TANTALUM AND TANTALUM NITRIDE THIN FILMS OF VARYING N2 CONTENT WITH MECHANICAL, ELECTRICAL AND STRUCTURAL PROPERTIES. [Masters Thesis]. Cornell University; 2017. Available from: http://hdl.handle.net/1813/56807

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