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Al2O3 Substrate (al2o3 + substrate)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Thermoelectric Performance of Epitaxial Thin Films of Layered Cobalt Oxides Grown by Reactive Solid-Phase Epitaxy with Topotactic Ion-Exchange Methods

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2007
Kenji Sugiura
This article reviews high-quality epitaxial film growth of layered cobalt oxides by reactive solid-phase epitaxy (R-SPE) with topotactic ion-exchange methods. Epitaxial film of Na0.8CoO2 was grown on a (0001)-oriented ,-Al2O3 substrate by R-SPE using CoO film as the starting material. The Na0.8CoO2 epitaxial films were converted into high-quality epitaxial films of Sr0.32Na0.21CoO2 and [Ca2CoO3]xCoO2 by topotactic ion-exchange methods. The Sr0.32Na0.21CoO2 film exhibited better stability against moisture than that of the Na0.8CoO2 film, while it retained the good thermoelectric properties of Na0.8CoO2. The [Ca2CoO3]xCoO2 film exhibited a high electrical conductivity of 2.95 × 102 S/cm and a large Seebeck coefficient of +125 ,V/K at 300 K. [source]

Comparison of ECR plasma pretreatment techniques for ZnO atomic layer epitaxy on the sapphire substrate

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2004
Kyoungchul Shin
Abstract ZnO films were grown on sapphire substrates treated with ECR plasma by the atomic layer epitaxy (ALE) technique. ZnO nucleation enhancing effects of oxygen, hydrogen, and argon plasma treatments were compared. The incubation period for ZnO nucleation was measured by using scanning electron microscopy (SEM) and Auger electron emission spectrometric (AES) analysis. The incubation period for ZnO nucleation on the Al2O3 substrate not treated with plasma was more than 40 ALE cycles. The incubation period was shortened down to less than 35 cycles by argon or hydrogen ECR plasma pretreatment and to less than 30 cycles by oxygen ECR plasma pretreatment. It was found that a microwave power of 300W and a plasma exposure times of 10 min were appropriate for oxygen ECR plasma treatment of sapphire substrate surfaces to enhance ZnO nucleation. Higher power and longer exposure time would not be effective or would rather aggravate than enhance ZnO nucleation. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ferromagnetism in epitaxial Zn0.95Co0.05O films grown on ZnO and Al2O3

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 14 2006
K. Nielsen
Abstract In this article, the possible mechanisms resulting in strong ferromagnetic coupling in transition metal(TM)-doped ZnO and other diluted magnetic semiconductors (DMS) are reviewed and the prerequisites for the observation of room temperature ferromagnetism in TM-doped ZnO are defined. In order to study the ferromagnetic behavior we have grown epitaxial Zn0.95Co0.05O films simultaneously on (0001) ZnO and Al2O3 substrates by laser molecular beam epitaxy at different deposition temperatures. A systematic study of the structural and magnetic properties has been performed to reveal their interdependence. Room temperature ferromagnetism has been found in Zn0.95Co0.05O films grown on ZnO, whereas for films deposited on sapphire only weak ferromagnetic signals have been detected which could not unambiguously be separated from those of the substrate. The different behavior is explained by different structural properties and defect densities in both films. Our experimental findings are in good agreement with a spin split impurity band model, where strong ferromagnetic exchange in ZnO:Co2+ is obtained by a strong hybridization between the magnetic Co2+ ion states and the donor states due to a large density of native defects. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Hot carrier energy losses in conducting layers of AlGaN/GaN heterostructures grown on SiC and Al2O3 substrates

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2006
B. A. Danilchenko
Abstract The energy relaxation rate for hot electrons in AlGaN/GaN heterostructures was measured over the temperature range 4.2,300 K. Samples grown on sapphire and 4H-SiC substrates were studied. The most important result is that the hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. In the case of sapphire substrate, the dissipation can be described by the emission of optical phonons with an energy of 90 meV and relaxation time of 25 fs. In the case of SiC substrate, both activation energy and relaxation time exceed the values characteristic of the electron-LO-phonon dissipation process. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]