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Non-equilibrium Surfaces of Metallic Thin Films
Linköping University, Department of Physics, Measurement Technology, Biology and Chemistry. Linköping University, The Institute of Technology.
1998 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Growth and structural characterization of metallic multilayers have been performed on the Mo/W, Mo/V and Ag/Ni systems utilizing magnetron sputtering under ultra-high-vacuum deposition conditions. Structural characterization has been performed both in situ and ex situ with several electron beam probing techniques as well as x-ray diffraction. The investigations have focused primarily on the relationship between the deposition process and the resulting layer quality including studies of the initial conditions for the layers, as induced by the substrate and its interaction with the initial metal layer. For the Mo/W system, I have established by x-ray diffraction that magnetron sputtering creates asymmetric interfaces in single-crystal superlattices, and that this asymmetry is caused by the difference in energies of the energetic neutrals impinging on the surface during growth. With existing knowledge of the Mo/V system, a technique for assessing the relationship between surface microstructure and growth conditions was evaluated. The methodology employed in situ reflection high energy electron diffraction (RHEED) analysis during magnetron sputtering; a technique not widely used due to the difficulties of incorporating a RHEED system into a sputtering chamber with its high gas pressures during the deposition process. This work makes it possible to determine the effect of changed process parameters directly, even though post-processing of the data provided both additional information and better statistics. For both the Mo/W and Mo/V material systems, the substrate was MgO and the initial metal layer was Mo. To fully assess the initial conditions that will determine the growth of the metallic superlattices on the ceramic substrate, in situ scanning tunnelling microscopy was employed in conjunction with electron beam techniques. I have shown independently by both in situ low energy electron diffraction (LEED) and time-resolved in situ RHEED measurements that oxygen is present on the Mo surface during the initial stages, up to ~300Å, of Mo deposition, and that it originates from the oxygen within the MgO substrate. The oxygen causes the growing Mo surface to continuously reconstruct with the (×), p(2x2) and c(2x2) structures and, for the first time, scanning tunnelling microscope images of the p(2x2) and c(2x2) reconstructions are shown. The measurements also reveal a surface which is typically interspersed with random 2x2 holes, only visible by techniques such as scanning tunnelling microscopy. Their non-periodic nature prevents observation with diffraction based techniques. In pre-studies of the Ag/Ni system, the growth temperature dependence of dc-magnetron sputter deposited Ni films on MgO substrateswas determined by x-ray diffraction. In the interval of 20°C to 700° C, three temperature ranges were observed: (1) CD at room temperature, the texture of the Ni film was <0 2 2> coexistingwith <1 -4 1> and traces of <0 0 2> texture; (2) from 100°C to 200°C, a singleNi domain of <0 0 2> texture was formed; and (3) @ from 300°C to 700°C, the texture was <7 5 -1> which at higher temperatures gradually became better defined. The most useful Ni films are likely to be the smooth single-crystal films grown at 100-200°C . The reason for these textural changes is the increased Ni atom mobility with temperature. In one example, the change from single crystallinity to <7 5 -1> texture at around 250°C, this change accommodates both the strong Ni metal-metal bonds as well as placing each interfacial Ni atom in the preferred position, directly on top of an O atom in the MgO, with a minimal mismatch between the two crystal lattices. These atomic rearrangements have a higher degree of probability at the elevated temperature above ~250°C. All the depositions within this thesis are done far from equilibrium conditions, where the knowledge of growth behaviour is still incomplete. Hopefully this work will take that knowledge one small step further.

Place, publisher, year, edition, pages
Linköping: Linköping University , 1998. , p. 57
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 549
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-181134Libris ID: 7624173ISBN: 9172193174 (print)OAI: oai:DiVA.org:liu-181134DiVA, id: diva2:1612268
Public defence
1998-12-18, Planck, Fysikhuset, Linköpings universitet, Linköping, 09:15
Opponent
Note

All or some of the partial works included in the dissertation are not registered in DIVA and therefore not linked in this post.

Available from: 2021-11-17 Created: 2021-11-17 Last updated: 2021-11-17Bibliographically approved
List of papers
1. Asymmetric interface broadening in epitaxial Mo/W (001) superlattices grown by magnetron sputtering
Open this publication in new window or tab >>Asymmetric interface broadening in epitaxial Mo/W (001) superlattices grown by magnetron sputtering
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1998 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 16, no 2, p. 633-638Article in journal (Refereed) Published
Abstract [en]

The interfacial structure in epitaxial Mo/W(001) superlattices, grown by magnetron sputtering on MgO(001) substrates has been studied. The films were grown in Ar and Kr discharges at a substrate temperature of 700 degrees C, and the as-deposited samples were analyzed by x-ray diffraction and found to be epitaxial with no high-angle grain boundaries. The degree of interfacial intermixing, caused by fluxes of different energetic species impinging on the growth surface, was estimated using a combination of Monte Carlo binary collision computer codes and a gas scattering computational model. In the Ar discharge case, large asymmetries in the Mo/W and W/Mo interfaces were found, with the W/Mo interface being more than a factor of 2 broader than the Mo/W interface. Simulations of x-ray reflectivity curves using the calculated interface profiles as input parameters without any additional fitting parameters agreed very well with measured data. The overall good fit between the calculated and measured reflectivity curves using the calculated compositional profiles is an indicator that the growth simulations using TRIM based codes provides interface profiles that are reasonably accurate, which can be used as a starting point for further refinements of the details of the interface structures. (C) 1998 American Vacuum Society.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 1998
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-105978 (URN)10.1116/1.581080 (DOI)
Available from: 2014-04-16 Created: 2014-04-15 Last updated: 2021-12-29Bibliographically approved

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