Scientific and Technical Aerospace Reports
Scientific and Technical Aerospace Reports

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Published: 1994

Total Pages: 652

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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.

Thin Film Growth and Characterization of the Electron-doped Superconductor Sm2̳-̳x̳Ce̳x̳CuO4̳-̳y̳
Thin Film Growth and Characterization of the Electron-doped Superconductor Sm2̳-̳x̳Ce̳x̳CuO4̳-̳y̳

Author: Daniel Joseph Scanderbeg

Publisher:

Published: 2007

Total Pages: 101

ISBN-13:

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Sm2̳-̳x̳Ce̳x̳CuO4̳-̳y̳ belongs to a class of materials known as electron-doped superconductors (Ln2̳-̳x̳Mx̳CuO4̳-̳y̳;Ln = Pr, Nd, Sm, Eu; M = Ce, Th) and has a moderately high superconducting critical temperature, Tc̳, of ~ 20 K at optimal doping (x = 0.15). The trivalent rare earth site is doped with tetravalent Ce or Th; hence the name "electron-doped". Sm2̳-̳x̳Ce̳x̳CuO4̳-̳y̳ also exhibits a unique magnetic structure at low temperatures (T 6 K) due to the antiferromagnetic ordering of the Sm3 ions. In this study, thin films of the electron-doped superconductor Sm2̳-̳x̳Ce̳x̳CuO4̳-̳y̳ (SCCO) have been grown by pulsed laser deposition (PLD) for a cerium concentration range of x = 0.13 to x = 0.19. The films have been characterized through x-ray diffraction, electrical transport, and thermal transport measurements. A temperature versus cerium content (T-x) phase diagram has been constructed from the electrical transport measurements and yields a superconducting region similar to that of two of the other electron-doped superconductors Nd2̳-̳x̳Ce̳x̳CuO4̳-̳y̳ and Pr2̳-̳x̳Ce̳x̳CuO4̳-̳y̳. Thermopower measurements were also performed on the samples and show a dramatic change from the underdoped region (x

Growth and Characterization of Thermoelectric Ba[sub]8[/sub]Ga[sub]16[/sub]Ge[sub]30[/sub] Type-I Clathrate Thin-Films Deposited by Pulsed Dual-Laser Ablation
Growth and Characterization of Thermoelectric Ba[sub]8[/sub]Ga[sub]16[/sub]Ge[sub]30[/sub] Type-I Clathrate Thin-Films Deposited by Pulsed Dual-Laser Ablation

Author: Robert Harry Hyde

Publisher:

Published: 2011

Total Pages:

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The on-going interest in thermoelectric (TE) materials, in the form of bulk and films, motivates investigation of materials that exhibit low thermal conductivity and good electrical conductivity. Such materials are phonon-glass electron-crystals (PGEC), and the multi-component type-I clathrate Ba8Ga16Ge30 is in this category. This work reports the first investigation of Ba8Ga16Ge30 films grown by pulsed laser deposition (PLD). This dissertation details the in-situ growth of polycrystalline type-I clathrate Ba8Ga16Ge30 thin-films by pulsed laser ablation. Films deposited using conventional laser ablation produced films that contained a high density of particulates and exhibited weak crystallinity. In order to produce high quality, polycrystalline, particulate-free films, a dual-laser ablation process was used that combines the pulses of (UV) KrF excimer and (IR) CO2 lasers that are temporally synchronized and spatially overlapped on the target surface. The effect of the laser energy on stoichiometric removal of material and morphology of the target has been investigated. In addition, in-situ time-gated emission spectroscopy and imaging techniques were used to monitor expansion of components in the ablated plumes. Through these investigations, the growth parameters were optimized not only to significantly reduce the particulate density but also to produce large area stoichiometric films. Structure and electrical transport properties of the resultant films were also evaluated. This work provides new insight toward the in-situ growth of complex multi-component structures in thin-film form for potential TE applications.

Film Synthesis and Growth Using Energetic Beams: Volume 388
Film Synthesis and Growth Using Energetic Beams: Volume 388

Author: H. A. Atwater

Publisher:

Published: 1995-10-10

Total Pages: 472

ISBN-13:

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With over 16 countries represented, this book represents international developments in the field of film synthesis and growth using energetic beams. It focuses on pulsed-laser deposition. Fundamental issues pertaining to the generation of laser ablation plumes, temperature distributions and collisional effects are described. Ion-assisted pulsed-laser deposition, pulsed-ion deposition, applications of hyperthermal beams and aspects of surface dynamics are discussed. The inclusion of an ion beam with the ablation process leads to some unique modifications in the thin-film growth mechanisms, and hence, film properties. Likewise, the collision of high-mass metal cluster ions with substrates shows promise for growth of novel structures. Also featured are new developments of optoelectronic materials, nitrides and carbon films using a variety of techniques. The effects of beam-induced defects on growth and surface morphology, chemical effects during growth, and characterization of film growth and film properties are addressed.

Functional Complex Oxide Thin Films and Related Superlattices Grown Via Pulsed Laser Deposition
Functional Complex Oxide Thin Films and Related Superlattices Grown Via Pulsed Laser Deposition

Author: Joseph A. Cianfrone

Publisher:

Published: 2011

Total Pages:

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ABSTRACT: Oxide electronics offer a wide array of interesting properties, including ferromagnetism, ferroelectricity and superconductivity. This dissertation investigates the transport, magnetic, and structural properties of several perovskite and spinel material systems, with particular interest in their manipulation at the nanoscale through the growth of functional heterostructures. Spinel phase ZnCo2O4 is investigated as a ferromagnetic semiconductor whose carrier type changes with oxygen concentration. The perovskite system of K(Ta, Nb)O3 is investigated for its interesting properties as a solid solution which exhibits a ferroelectric transition dependent on composition. Its thin film epitaxial growth modes are investigated via reflection high energy electron diffraction, with particular attention paid to the volatile potassium ion. Superlattices of K(Ta, Nb)O3 and SrTiO3 are also investigated for the possibility of dielectric enhancement and conductive interfaces. The multiferroic properties of BaFeO3 K(Ta, Nb)O3 superlattices are investigated, with particular attention paid to the role of magnetoelectric coupling and strain as stabilizing mechanisms.