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Energy distributions of positive and negative ions during magnetron sputtering of an Al target in Ar/O2 mixtures
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-1744-7322
2006 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, no 3, Art. No. 033305 AUG 1 2006- p.Article in journal (Refereed) Published
Abstract [en]

The ion flux obtained during reactive magnetron sputtering of an Al target in Ar/O2 gas mixtures was studied by energy-resolved mass spectrometry, as a function of the total and O2 partial pressures. The positive ions of film-forming species exhibited bimodal energy distributions, both for direct current and radio frequency discharges, with the higher energy ions most likely originating from sputtered neutrals. For the negative oxygen ions a high-energy peak was observed, corresponding to ions formed at the target surface and accelerated towards the substrate over the sheath potential. As the total pressure was increased the high-energy peaks diminished due to gas-phase scattering. Based on these results, the role of energetic bombardment for the phase constituent of alumina thin films are discussed.

Place, publisher, year, edition, pages
College Park, MD, United States: American Institute of Physics (AIP), 2006. Vol. 100, no 3, Art. No. 033305 AUG 1 2006- p.
Keyword [en]
aluminium, sputter deposition, diffusion, mass spectra, high-frequency discharges, plasma materials processing
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-10472DOI: 10.1063/1.2219163ISI: 000239764100014OAI: oai:DiVA.org:liu-10472DiVA: diva2:17222
Note

Original publication: Jon M. Andersson, E. Wallin, E. P. Münger & U. Helmersson, Energy distributions of positive and negative ions during magnetron sputtering of an Al target in Ar/O2 mixtures, 2006, Journal of Applied Physics, (100), 033305. http://dx.doi.org/10.1063/1.2219163. Copyright: American Institute of Physics, http://jap.aip.org/jap/top.jsp

Available from: 2007-12-19 Created: 2007-12-19 Last updated: 2017-12-14
In thesis
1. Controlling the Formation and Stability of Alumina Phases
Open this publication in new window or tab >>Controlling the Formation and Stability of Alumina Phases
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work, physical phenomena related to the growth and phase formation of alumina, Al2O3, are investigated by experiments and computer calculations. Alumina finds applications in a wide variety of areas, due to many beneficial properties and several existing crystalline phases. For example, the α and κ phases are widely used as wear-resistant coatings due to their hardness and thermal stability, while, e.g., the metastable γ and θ phases find applications as catalysts or catalyst supports, since their surface energies are low and, hence, they have large surface areas available for catalytic reactions.

The metastable phases are involved in transition sequences, which all irreversibly end in the transformation to the stable α phase at about 1050 °C. As a consequence, the metastable aluminas, which can be grown at low temperatures, cannot be used in high temperature applications, since they are destroyed by the transformation into α. In contrast, α-alumina, which is the only thermodynamically stable phase, typically require high growth temperatures (~1000 °C), prohibiting the use of temperature sensitive substrates. Thus, there is a need for increasing the thermal stability of metastable alumina and decreasing the growth temperature of the α phase.

In the experimental part of this work, hard and single-phased α-alumina thin films were grown by magnetron sputtering at temperatures down to 280 °C. This dramaticdecrease in growth temperature was achieved by two main factors. Firstly, the nucleation stage of growth was controlled by pre-depositing a chromia “template” layer, which is demonstrated to promote nucleation of α-alumina. Secondly, it is shown that energetic bombardment was needed to sustain growth of the α phase. Energy-resolved mass spectrometry measurements demonstrate that the likely source of energetic bombardment, in the present case, was oxygen ions/atoms originating from the target surface. Overall, these results demonstrate that low-temperature α-alumina growth is possible by controlling both the nucleation step of growth as well as the energetic bombardment of the growing film. In addition, the mass spectrometry studies showed that a large fraction of the deposition flux consisted of AlO molecules, which were sputtered from the target. Since the film is formed by chemical bonding between the depositing species, this observation is important for the fundamental understanding of alumina thin film growth.

In the computational part of the work, the effect of additives on the phase stability of α- and θ-alumina was investigated by density functional theory calculations. A systematic study was performed of a large number of substitutional dopants in the alumina lattices. Most tested dopants tended to reverse the stability between α- and θ-alumina; so that, e.g., Modoping made the θ phase energetically favored. Thus, it is possible to stabilize the metastable phases by additives. An important reason for this is the physical size of the dopant ions with respect to the space available within the alumina lattices. For example, large ions induced θ stabilization, while ions only slightly larger than Al, e.g., Co and Cu, gave a slight increase in the relative stability of the α phase. We also studied the stability of some of these compounds with respect to pure alumina and other phases, containing the dopants, with the result that phase separations are energetically favored and will most likely occur at elevated temperatures.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2005
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 987
Keyword
thin films, alumina, magnetron sputtering, phase stability, density functional theory
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:liu:diva-5038 (URN)91-85457-71-X (ISBN)
Public defence
2005-12-15, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2005-12-13 Created: 2005-12-13 Last updated: 2013-10-30

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Andersson, Jon M.Wallin, ErikMünger, PeterHelmersson, Ulf

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