Phase Selective Synthesis of Tl-Ba-Ca-Cu-O Thin Films and Multilayer Structures by Metal-organic Chemical Vapor Deposition PDF Download
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Author: Richard Joseph McNeely
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Languages : en
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Metal-organic chemical vapor deposition (MOCVD), utilizing volatile metalorganic sources Ba(hfa)2·mep, Ca(hfa)2·tet, and Cu(dpm)2 (hfa hexafluoroacetylacetonate, mep = methylethylpentaglyme, tet = tetraglyme, dpm dipivaloylmethanate) characterized by thermogravimetric analysis (TGA), is employed to grow BaCaCuO(F) thin films on crystalline (110) LaAlO3. An ex situ, bulk pellet equilibrium anneal incorporates thallium to form epitaxial, superconducting Tl2Ba 2CaCu2O8 (Tl-2212) and TlBa2Ca 2Cu3O9+x (Tl-1223) thin films. The film electrical properties are determined by transport and magnetic measurements, and the film microstructures are characterized by x-ray diffraction, electron microscopy, and profilometry. The Tl-2212 films, formed via a Tl2O3/Tl 2O anneal at temperatures of 720--890°C in flowing O2 /Ar (0--100%), exhibit Tc ∼ 105 K, Jc = 1.2 x 105 A/cm2 (77 K), and microwave surface resistance, Rs , as low as 400 muO (40 K; 10 GHz). These Tl-2212 films are also incorporated into an MOCVD process utilizing Mg(dPM)2 to form Tl-2212/MgO/Tl-2212 trilayer structures. However, rough surface morphology is found to affect the quality of the resulting trilayer structures by allowing pinhole defects that permit interlayer shorting. The Tl-1223 films are formed via a novel TlF annealing process that affords phase-selective nucleation under a wide range of conditions that produce multiple-phase samples when Tl2O3/Tl2O is employed as the thallium source. The microstructure and electrical properties of these TIF-annealed films are fully characterized, with typical values of Tc ∼ 103 K and Jc ∼ 2 x 105 A/cm2 (5 K). Calculated flux pinning activation energies of MOCVD-derived, TlF-annealed Bi- and Sr-substituted Tl-1223 analogs are found to agree with literature values. On unsubstituted TlF-annealed Tl-1223 thin films, a quenching study is undertaken to elucidate the function of fluoride in the TlF annealing process. X-ray diffraction and electron microscopy of thin films quenched at various stages in an optimized annealing schedule reveal the phase evolution and microstructural development of the resulting Tl-1223 thin films. It is proposed that TIF reacts with BaO in the bulk pellet and forms Tl2O early in the annealing process to thereby afford a higher Tl2O partial pressure during initial stages in superconducting phase formation.
Author: Richard Joseph McNeely
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Languages : en
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Metal-organic chemical vapor deposition (MOCVD), utilizing volatile metalorganic sources Ba(hfa)2·mep, Ca(hfa)2·tet, and Cu(dpm)2 (hfa hexafluoroacetylacetonate, mep = methylethylpentaglyme, tet = tetraglyme, dpm dipivaloylmethanate) characterized by thermogravimetric analysis (TGA), is employed to grow BaCaCuO(F) thin films on crystalline (110) LaAlO3. An ex situ, bulk pellet equilibrium anneal incorporates thallium to form epitaxial, superconducting Tl2Ba 2CaCu2O8 (Tl-2212) and TlBa2Ca 2Cu3O9+x (Tl-1223) thin films. The film electrical properties are determined by transport and magnetic measurements, and the film microstructures are characterized by x-ray diffraction, electron microscopy, and profilometry. The Tl-2212 films, formed via a Tl2O3/Tl 2O anneal at temperatures of 720--890°C in flowing O2 /Ar (0--100%), exhibit Tc ∼ 105 K, Jc = 1.2 x 105 A/cm2 (77 K), and microwave surface resistance, Rs , as low as 400 muO (40 K; 10 GHz). These Tl-2212 films are also incorporated into an MOCVD process utilizing Mg(dPM)2 to form Tl-2212/MgO/Tl-2212 trilayer structures. However, rough surface morphology is found to affect the quality of the resulting trilayer structures by allowing pinhole defects that permit interlayer shorting. The Tl-1223 films are formed via a novel TlF annealing process that affords phase-selective nucleation under a wide range of conditions that produce multiple-phase samples when Tl2O3/Tl2O is employed as the thallium source. The microstructure and electrical properties of these TIF-annealed films are fully characterized, with typical values of Tc ∼ 103 K and Jc ∼ 2 x 105 A/cm2 (5 K). Calculated flux pinning activation energies of MOCVD-derived, TlF-annealed Bi- and Sr-substituted Tl-1223 analogs are found to agree with literature values. On unsubstituted TlF-annealed Tl-1223 thin films, a quenching study is undertaken to elucidate the function of fluoride in the TlF annealing process. X-ray diffraction and electron microscopy of thin films quenched at various stages in an optimized annealing schedule reveal the phase evolution and microstructural development of the resulting Tl-1223 thin films. It is proposed that TIF reacts with BaO in the bulk pellet and forms Tl2O early in the annealing process to thereby afford a higher Tl2O partial pressure during initial stages in superconducting phase formation.
Author: Bruce Jackson Hinds
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Languages : en
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Category : Dissertations, Academic
Languages : en
Pages : 898
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Category : Chemistry
Languages : en
Pages : 1850
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Faculties, publications and doctoral theses in departments or divisions of chemistry, chemical engineering, biochemistry and pharmaceutical and/or medicinal chemistry at universities in the United States and Canada.
Author: Chyi Shyuan Chern
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Languages : en
Pages : 390
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Category : Physics
Languages : en
Pages : 914
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Author: Deborah Ann Neumayer
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Languages : en
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Author: Stuart Irvine
Publisher: John Wiley & Sons
ISBN: 1119313015
Category : Technology & Engineering
Languages : en
Pages : 582
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Systematically discusses the growth method, material properties, and applications for key semiconductor materials MOVPE is a chemical vapor deposition technique that produces single or polycrystalline thin films. As one of the key epitaxial growth technologies, it produces layers that form the basis of many optoelectronic components including mobile phone components (GaAs), semiconductor lasers and LEDs (III-Vs, nitrides), optical communications (oxides), infrared detectors, photovoltaics (II-IV materials), etc. Featuring contributions by an international group of academics and industrialists, this book looks at the fundamentals of MOVPE and the key areas of equipment/safety, precursor chemicals, and growth monitoring. It covers the most important materials from III-V and II-VI compounds to quantum dots and nanowires, including sulfides and selenides and oxides/ceramics. Sections in every chapter of Metalorganic Vapor Phase Epitaxy (MOVPE): Growth, Materials Properties and Applications cover the growth of the particular materials system, the properties of the resultant material, and its applications. The book offers information on arsenides, phosphides, and antimonides; nitrides; lattice-mismatched growth; CdTe, MCT (mercury cadmium telluride); ZnO and related materials; equipment and safety; and more. It also offers a chapter that looks at the future of the technique. Covers, in order, the growth method, material properties, and applications for each material Includes chapters on the fundamentals of MOVPE and the key areas of equipment/safety, precursor chemicals, and growth monitoring Looks at important materials such as III-V and II-VI compounds, quantum dots, and nanowires Provides topical and wide-ranging coverage from well-known authors in the field Part of the Materials for Electronic and Optoelectronic Applications series Metalorganic Vapor Phase Epitaxy (MOVPE): Growth, Materials Properties and Applications is an excellent book for graduate students, researchers in academia and industry, as well as specialist courses at undergraduate/postgraduate level in the area of epitaxial growth (MOVPE/ MOCVD/ MBE).
Author: Shrikant Prabhakar Lohokare
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Languages : en
Pages : 574
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Chemical vapor deposition (CVD) is becoming an increasingly important manufacturing process for the fabrication of VLSI and ULSI devices. A major challenge in optimizing a CVD process is developing an understanding of the complex mechanistic pathways followed. The first section in this thesis reports studies on the thermal and dynamical activation of surface bound alkyl species which play a vital role in the form of intermediates in metal-organic chemical vapor deposition. The particular systems of interest are those of aluminum CVD precursors. Models of these intermediates are obtained by thermal decomposition of alkyl iodides. The results provide an insight into the complex reaction patterns involved in the thermal reactions and rate-structure sensitivities of the alkyl species in the presence of the coadsorbed halogen atom. Multiple reaction pathways including metal etching processes which bear direct implications to the synthesis of organometallics and metal etching, are identified. It is becoming apparent that chemistry at surfaces, whether it be heterogeneous catalysis, semiconductor etching, or chemical vapor deposition, is controlled by much more than the nature and structure of the surface. Also, nonthermal activation of autocatalytic reactions is often required for the nucleation and growth of thin films in devices so that the stability of the device structure is maintained. Dynamical pathways followed in these high pressure and energy processes have to be well understood. The second part of these studies describe an investigation of collision-induced reaction of alkyl intermediates using supersonic inert gas atomic beams. Selective activation of a thermodynamically favored unimolecular decomposition reaction is initiated by hyperthermal collisions. Quantitative estimations of the reaction cross sections are made using straightforward hard sphere energy transfer dynamics. This successful demonstration of collision-induced activation of large, multiatomic moieties has paved the way for proposed studies (now underway in our group) on actual CVD precursors with known barriers to nucleation and growth. In the second section, the reaction mechanisms and kinetics of competitive dissociation, disproportionation, and thin film growth processes involved in the chemical vapor deposition of metal-silicide thin films are investigated. Metal-silicides are widely used as interconnect and gate materials in devices and also as corrosion resistant materials. Reactivity of silane and disilane with copper is studied in detail using temperature programmed reaction, Auger electron, Fourier transform infrared reflection absorption spectroscopies and low energy electron diffraction. For both the precursors, the structural chemistry and product distributions of adsorbed intermediates found at low temperatures are quite rich but significantly differ at the mechanistic level. It is shown quantitatively that disilane is almost 2-3 orders of magnitude more reactive than silane due to its facile Si-Si bond dissociation. However, in both cases, kinetics of silicon deposition and silicide formation are limited by the site-blocking effect of surface bound hydrogen generated by the decomposition of the silyl fragments. An ordered silicide overlayer is readily formed at higher coverages effected above dihydrogen desorption temperatures. This bimolecular process has to compete with an associative reaction which leads to the formation of silane. The results obtained from the different spectroscopic data show that the growth process involves an intriguing set of coupled reactions in which deposition, island growth, and Si etching effectively compete in a complex manner. Understanding of these parameters and the reaction mechanisms involved, enables the application of this process for the vapor phase growth of silicide thin films.
Author: Dong-Wook Noh
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Languages : en
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