Epitaxial growth of Co films and Co/Cu superlattices on sapphire substrates with and without buffer layers

Bröhl, K.; Bödeker, P.; Metoki, Naoto; Stierle, Andreas; Zabel, H.

doi:10.1016/0022-0248(93)90710-e

Cited by 30 publications

(6 citation statements)

References 5 publications

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“…The procedure for growing Nb films of high structural quality is well established, and has been reported in several places. 11,12 The sapphire substrates had a miscut of less than 1°, and were of high crystalline quality with mosaicities between 0.002°and 0.006°. The Nb deposition was carried out in a Riber EVA 32 MBE machine under ultrahigh vacuum ͑UHV͒ conditions ͑base pressure better than 2ϫ10 Ϫ9 Pa͒ working pressure 10 Ϫ8 Pa. After chemically etching and rinsing in acetone and isopropanol, the substrates were transferred into the UHV system.…”

Section: Sample Preparation and Experimental Proceduresmentioning

confidence: 99%

“…More recently, Weidinger and his group reported a solubility study of H in epitaxial Nb͑110͒ films of different thickness. 5 The H concentration was determined in situ by the resonant nuclear reaction 1 H( 15 N,␣␥) 12 C method. From these measurements they concluded that the metal-hydrogen interaction is essentially the same as in the bulk, and that the H-H interaction is reduced by at least a factor of 2.…”

Section: Introductionmentioning

confidence: 99%

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Solubility isotherms of hydrogen in epitaxial Nb(110) films

et al. 1996

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The solubility isotherms of hydrogen in epitaxial Nb͑110͒ films have been determined via in situ x-ray lattice-parameter measurements. The Nb films were grown by molecular-beam epitaxial techniques on Al 2 O 3 (1120) substrates with thicknesses ranging from 32 to 527 nm. All isotherms can be well described by the standard expression for the solubility of a monatomic lattice gas. Aside from the metal-hydrogen interaction, which appears to be bulklike, all other properties exhibit a strong thickness dependence, including the hydrogen-hydrogen interaction, the critical temperature for the ␣-␣Ј transition, and the maximum latticeparameter change that can be reached in saturation. For the critical temperature we find a scaling with the film thickness, which most likely is due to the elastic boundary condition provided by the rigid substrate. The clamping of the epitaxial film to the substrate hinders critical fluctuations of macroscopic hydrogen density modes from developing, thereby lowering the critical temperature for the ␣-␣Ј transition.

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Section: Sample Preparation and Experimental Proceduresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Solubility isotherms of hydrogen in epitaxial Nb(110) films

et al. 1996

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“…[23] In addition, the crystal structure can be stable initially as the fcc phase and transform to the hcp phase with increasing thickness. [24] The layers grown by MOCVD in the present study were analyzed by X-ray diffraction and a typical X-ray diffrac- Table 1. Summary of the precursors used for MOCVD of cobalt/cobalt silicide.…”

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Metal Organic CVD of Cobalt Thin Films Using Cobalt Tricarbonyl Nitrosyl

Lane¹,

Oliver²,

Wright³

et al. 1998

Chem. Vap. Deposition

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“…The procedure for growing Nb films of high structural quality is well established and has been reported at several places [7,17,18]. Nb was evaporated with an electron beam gun at a substrate temperature of 900 ± C. In situ reflection high energy electron diffraction (RHEED) confirmed a very smooth growth of the Nb films [17]. Subsequently, a Pd film with [111] orientation and about 2 nm thickness was deposited on the Nb surface.…”

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Extraordinary Adhesion of Niobium on Sapphire Substrates

et al. 1997

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We have investigated the adhesion between a metal and a ceramic interface, in particular between Nb(110) films and Al 2 O 3 ͑1120͒ substrates. We have tested the adhesion properties by hydrogen loading of the metal film. The resulting strains were measured by in-and out-of-plane lattice parameter measurements. In contrast to the bulk behavior, we find for hydrogen in thin Nb films a highly anisotropic in plane strain. Comparing the in-plane expansion with the free case, we observe a tensile stress exceeding the yield stress of bulk Nb by at least a factor of 10. This unusually large resistance against expansion is due to giant adhesive forces at the metal/ceramic interface.[S0031-9007(97)04843-6] PACS numbers: 68.60.Bs, Understanding adhesion properties of metals on ceramic substrates is one of the most intriguing and important topics of current materials research [1]. High temperature composite materials, corrosion resistant coatings, and electronic packaging rely on the adhesive strength of metal/ ceramic interfaces. Two different models have been brought forth to describe the interfacial bond energy. In one of them the electrostatic image charges between the oxide ions and the metallic surface are made responsible for the bonding [2,3]. Other models favor a hybridization effect between the oxygen p-and the metal d-orbitals, which may lead to a slightly covalent or ionic bond at the interface [4,5]. The latter model requires a well-defined epitaxial relationship at the metal/ceramic interface, whereas the former is independent of specific atomic coordinations. In practice, good adhesion has been observed at both, heteroepitaxial pseudomorphic, as well as amorphous metal/ceramic interfaces. Therefore, a decision in favor of one or the other model is difficult to make.Niobium thin films on sapphire substrates can be considered as a model system for studying adhesion properties between metals and ceramics. The growth of Nb on sapphire has been studied in much detail recently and the epitaxial relation is well understood [6][7][8][9][10][11]. The Nb͞Al 2 O 3 interface can be described by a unique threedimensional epitaxy characterized the following orientational relationships [7-10]:Nb grows on the sapphire substrate almost strain free and forms a highly ordered crystal structure with large structural coherence lengths [12,13]. The residual epitaxial strain which depends on the film thickness is usually less than 0.05%. Small amounts of hydrogen may help to release residual stresses and the crystal structure becomes even more perfect due to a "cold" annealing effect [14]. Furthermore, Nb and sapphire have nearly the same thermal expansion coefficients [15]. Therefore thermal strains are not confused with epitaxial or applied strains.Measuring the adhesion of an epitaxial film is not an easy task. Usually the films are bent together with the substrate and the critical radius of curvature is determined before the film lifts off [16]. We have probed the adhesion properties of the metal/oxide interface in a different ...

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Epitaxial growth of Co films and Co/Cu superlattices on sapphire substrates with and without buffer layers

Cited by 30 publications

References 5 publications

Solubility isotherms of hydrogen in epitaxial Nb(110) films

Solubility isotherms of hydrogen in epitaxial Nb(110) films

Metal Organic CVD of Cobalt Thin Films Using Cobalt Tricarbonyl Nitrosyl

Extraordinary Adhesion of Niobium on Sapphire Substrates

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