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Wallin, Erik
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Wallin, E., Münger, P., Chirita, V. & Helmersson, U. (2009). Low-temperature alpha-alumina thin film growth: ab initio studies of Al adatom surface migration. JOURNAL OF PHYSICS D-APPLIED PHYSICS, 42(12), 125302
Öppna denna publikation i ny flik eller fönster >>Low-temperature alpha-alumina thin film growth: ab initio studies of Al adatom surface migration
2009 (Engelska)Ingår i: JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN 0022-3727, Vol. 42, nr 12, s. 125302-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Investigations of activation energy barriers for Al surface hopping on alpha-Al2O3 (0 0 0 1) surfaces have been carried out by means of first-principles density functional theory calculations and the nudged elastic band method. Results show that surface diffusion on the (most stable) Al-terminated surface is relatively fast with an energy barrier of 0.75 eV, whereas Al hopping on the O-terminated surface is slower, with barriers for jumps from the two metastable positions existing on this surface to the stable site of 0.31 and 0.99 eV. Based on this study and on the literature, the governing mechanisms during low-temperature alpha-alumina thin film growth are summarized and discussed. Our results support suggestions made in some previous experimental studies, pointing out that limited surface diffusivity is not the main obstacle for alpha-alumina growth at low-to-moderate temperatures, and that other effects should primarily be considered when designing novel processes for low-temperature alpha-alumina deposition.

Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-19393 (URN)10.1088/0022-3727/42/12/125302 (DOI)
Anmärkning
Original Publication: Erik Wallin, Peter Münger, Valeriu Chirita and Ulf Helmersson, Low-temperature alpha-alumina thin film growth: ab initio studies of Al adatom surface migration, 2009, JOURNAL OF PHYSICS D-APPLIED PHYSICS, (42), 12, 125302. http://dx.doi.org/10.1088/0022-3727/42/12/125302 Copyright: Iop Publishing Ltd http://www.iop.org/ Tillgänglig från: 2009-06-29 Skapad: 2009-06-22 Senast uppdaterad: 2013-10-30Bibliografiskt granskad
Lundin, D., Brenning, N., Jädernäs, D., Larsson, P., Wallin, E., Lattemann, M., . . . Helmersson, U. (2009). Transition between the discharge regimes of high power impulse magnetron sputtering and conventional direct current magnetron sputtering. PLASMA SOURCES SCIENCE and TECHNOLOGY, 18(4), 045008
Öppna denna publikation i ny flik eller fönster >>Transition between the discharge regimes of high power impulse magnetron sputtering and conventional direct current magnetron sputtering
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2009 (Engelska)Ingår i: PLASMA SOURCES SCIENCE and TECHNOLOGY, ISSN 0963-0252, Vol. 18, nr 4, s. 045008-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Current and voltage have been measured in a pulsed high power impulse magnetron sputtering (HiPIMS) system for discharge pulses longer than 100 mu s. Two different current regimes could clearly be distinguished during the pulses: (1) a high-current transient followed by (2) a plateau at lower currents. These results provide a link between the HiPIMS and the direct current magnetron sputtering (DCMS) discharge regimes. At high applied negative voltages the high-current transient had the characteristics of HiPIMS pulses, while at lower voltages the plateau values agreed with currents in DCMS using the same applied voltage. The current behavior was found to be strongly correlated with the chamber gas pressure, where increasing gas pressure resulted in increasing peak current and plateau current. Based on these experiments it is suggested here that the high-current transients cause a depletion of the working gas in the area in front of the target, and thereby a transition to a DCMS-like high-voltage, lower current regime.

Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-51382 (URN)10.1088/0963-0252/18/4/045008 (DOI)
Tillgänglig från: 2009-10-30 Skapad: 2009-10-30 Senast uppdaterad: 2015-05-28
Selinder, T., Coronel, E., Wallin, E. & Helmersson, U. (2009). α-alumina coatings on WC/Co substrates by physical vapor deposition. International journal of refractory metals & hard materials, 27(2), 507-512
Öppna denna publikation i ny flik eller fönster >>α-alumina coatings on WC/Co substrates by physical vapor deposition
2009 (Engelska)Ingår i: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 27, nr 2, s. 507-512Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Physical vapor deposition coatings for cutting tools may be deposited by, e.g. reactive magnetron sputtering. Alumina growth in Ar/O2 gas mixtures gives rise to problems due to insulating layers on targets, and hysteresis effects with respect to oxygen gas flow. In this paper is described a technology for the deposition of crystalline alumina: reactive high power impulse magnetron sputtering. Pure Al was used as target material, and the cemented carbide (WC/Co) substrates were kept at 500-650 ºC. Hysteresis effects with respect to oxygen gas flow were alleviated, which enabled stable growth at a high deposition rate. The high power impulses were helpful in obtaining a crystalline oxide coating. X-ray diffraction and crosssection transmission electron microscopy showed that α-alumina films were formed. Technological testing of these PVD alumina coatings, with state-of-the-art AlTiN as benchmark, showed significantly improved crater wear resistance in steel turning.

Nyckelord
HiPIMS, HPPMS, ionized-PVD, alumina, corundum
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-15359 (URN)10.1016/j.ijrmhm.2008.10.007 (DOI)
Anmärkning
On the day of defence date the status of article VII was: Accepted. Original Publication: T.I. Selinder, E. Coronel, Erik Wallin and Ulf Helmersson, α-alumina coatings on WC/Co substrates by physical vapor deposition, 2009, International journal of refractory metals & hard materials, (27), 2, 507-512. http://dx.doi.org/10.1016/j.ijrmhm.2008.10.007 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Tillgänglig från: 2009-02-23 Skapad: 2008-11-05 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
Wallin, E. (2008). Alumina Thin Films: From Computer Calculations to Cutting Tools. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Öppna denna publikation i ny flik eller fönster >>Alumina Thin Films: From Computer Calculations to Cutting Tools
2008 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The work presented in this thesis deals with experimental and theoretical studies related to alumina thin films. Alumina, Al2O3, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. However, controlling thin film growth of this material, in particular at low substrate temperatures, is not straightforward. The aim of this work is to increase the understanding of the basic mechanisms governing alumina growth and to investigate novel ways of synthesizing alumina coatings. The thesis can be divided into two main parts, where the first part deals with fundamental studies of mechanisms affecting alumina growth and the second part with more application-oriented studies of high power impulse magnetron sputter (HiPIMS) deposition of the material.

In the first part, it was shown that the thermodynamically stable α phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of merely 500 °C by controlling the nucleation surface. This was done by predepositing a Cr2O3 nucleation layer. Moreover, it was found that an additional requirement for the formation of the α phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of α-alumina (in addition to the effect of the chromia nucleation layer). Moreover, the effects of residual water on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline α-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1*10-5 Torr was introduced, the columnar α-alumina growth was disrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the γ-alumina content was found to increase with increasing film thickness.

To gain a better understanding of the atomistic processes occurring on the surface, density functional theory based computational studies of adsorption and diffusion of Al, O, AlO, and O2 on different α-alumina (0001) surfaces were also performed. The results give possible reasons for the difficulties in growing the α phase at low temperatures through the identification of several metastable adsorption sites and also show how adsorbed hydrogen might inhibit further growth of α-alumina crystallites. In addition, it was shown that the Al surface diffusion activation energies are unexpectedly low, suggesting that limited surface diffusivity is not the main obstacle for low-temperature α-alumina growth. Instead, it is suggested to be more important to find ways of reducing the amount of impurities, especially hydrogen, in the process and to facilitate α-alumina nucleation when designing new processes for low-temperature deposition of α-alumina.

In the second part of the thesis, reactive HiPIMS deposition of alumina was studied. In HiPIMS, a high-density plasma is created by applying very high power to the sputtering magnetron at a low duty cycle. It was found, both from experiments and modeling, that the use of HiPIMS drastically influences the characteristics of the reactive sputtering process, causing reduced target poisoning and thereby reduced or eliminated hysteresis effects and relatively high deposition rates of stoichiometric alumina films. This is not only of importance for alumina growth, but for reactive sputter deposition in general, where hysteresis effects and loss of deposition rate pose a substantial problem. Moreover, it was found that the energetic and ionized deposition flux in the HiPIMS discharge can be used to lower the deposition temperature of α-alumina. Coatings predominantly consisting of the α phase were grown at temperatures as low as 650 °C directly onto cemented carbide substrates without the use of nucleation layers. Such coatings were also deposited onto cutting inserts and were tested in a steel turning application. The coatings were found to increase the crater wear resistance compared to a benchmark TiAlN coating, and the process consequently shows great potential for further development towards industrial applications.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2008. s. 59
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1221
Nyckelord
Alumina, thin films, coatings, sputtering, density functional theory, high power impulse magnetron sputtering, HIPIMS
Nationell ämneskategori
Övrig annan teknik Bearbetnings-, yt- och fogningsteknik Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-15360 (URN)978-91-7393-769-6 (ISBN)
Disputation
2008-11-27, Planck, Physics building, Campus Valla, Linköping University, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2008-11-05 Skapad: 2008-11-05 Senast uppdaterad: 2013-10-30Bibliografiskt granskad
Lundin, D., Larsson, P., Wallin, E., Lattemann, M., Brenning, N. & Helmersson, U. (2008). Cross-field ion transport during high power impulse magnetron sputtering. Plasma Sources Science and Technology, 17(035021)
Öppna denna publikation i ny flik eller fönster >>Cross-field ion transport during high power impulse magnetron sputtering
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2008 (Engelska)Ingår i: Plasma Sources Science and Technology, ISSN 0963-0252, Vol. 17, nr 035021Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In this study, the effect on thin film growth due to an anomalous electron transport, found in high power impulse magnetron sputtering (HiPIMS), has been investigated for the case of a planar circular magnetron. An important consequence of this type of transport is that it affects the way ions are being transported in the plasma. It was found that a significant fraction of ions are transported radially outwards in the vicinity of the cathode, across the magnetic field lines, leading to increased deposition rates directly at the side of the cathode (perpendicular to the target surface). Furthermore, this mass transport parallel to the target surface leads to that the fraction of sputtered material reaching a substrate placed directly in front of the target is substantially lower in HiPIMS compared with conventional direct current magnetron sputtering (dcMS). This would help to explain the lower deposition rates generally observed for HiPIMS compared with dcMS. Moreover, time-averaged mass spectrometry measurements of the energy distribution of the cross-field transported ions were carried out. The measured distributions show a direction-dependent high-energy tail, in agreement with predictions of the anomalous transport mechanism.

Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-13209 (URN)10.1088/0963-0252/17/3/035021 (DOI)
Anmärkning
Original Publication: Daniel Lundin, Petter Larsson, Erik Wallin, Martina Lattemann, Nils Brenning and Ulf Helmersson, Cross-field ion transport during high power impulse magnetron sputtering, 2008, Plasma Sources Science and Technology, (17), 035021. http://dx.doi.org/10.1088/0963-0252/17/3/035021 Copyright: Iop Publishing http://www.iop.org/ Tillgänglig från: 2009-02-26 Skapad: 2009-02-26 Senast uppdaterad: 2013-10-30Bibliografiskt granskad
Wallin, E. (2008). Deposition of Crystalline Alumina Coatings using Reactive High Power Impulse Magnetron Sputtering - Process and Film Properties. In: The 11:th International Conference on Plasma Surface Engineering,2008.
Öppna denna publikation i ny flik eller fönster >>Deposition of Crystalline Alumina Coatings using Reactive High Power Impulse Magnetron Sputtering - Process and Film Properties
2008 (Engelska)Ingår i: The 11:th International Conference on Plasma Surface Engineering,2008, 2008Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-43325 (URN)73522 (Lokalt ID)73522 (Arkivnummer)73522 (OAI)
Tillgänglig från: 2009-10-10 Skapad: 2009-10-10
Wallin, E. (2008). Deposition of Metal Oxide Coatings using Reactive High Power Impulse Magnetron Sputtering. In: AVS 55th International Symposium,2008.
Öppna denna publikation i ny flik eller fönster >>Deposition of Metal Oxide Coatings using Reactive High Power Impulse Magnetron Sputtering
2008 (Engelska)Ingår i: AVS 55th International Symposium,2008, 2008Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
Abstract [en]

  

Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-43329 (URN)73527 (Lokalt ID)73527 (Arkivnummer)73527 (OAI)
Tillgänglig från: 2009-10-10 Skapad: 2009-10-10
Wallin, E. & Helmersson, U. (2008). Hysteresis-free reactive high power impulse magnetron sputtering. Thin Solid Films, 516(18), 6398-6401
Öppna denna publikation i ny flik eller fönster >>Hysteresis-free reactive high power impulse magnetron sputtering
2008 (Engelska)Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, nr 18, s. 6398-6401Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

High power impulse magnetron sputtering (HIPIMS) of an Al target in Ar/O2 mixtures has been studied. The use of HIPIMS is shown to drastically influence the process characteristics compared to conventional sputtering. Under suitable conditions, oxide formation on the target as the reactive gas flow is increased is suppressed, and the hysteresis effect commonly observed as the gas flow is varied during conventional sputtering can be reduced, or even completely eliminated, using HIPIMS. Consequently, stoichiometric alumina can be deposited under stable process conditions at high rates. Possible explanations for this behavior as well as a model qualitatively describing the process are presented.

Nyckelord
Reactive Sputtering, High Power Impulse Magnetron Sputtering, Alumina, Process modeling
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-15028 (URN)10.1016/j.tsf.2007.08.123 (DOI)
Anmärkning
Original publication: E. Wallin and U. Helmersson, Hysteresis-free reactive high power impulse magnetron sputtering, 2008, Thin Solid Films, (516), 18, 6398-6401.http://dx.doi.org/10.1016/j.tsf.2007.08.123. Copyright: Elsevier B.V., http://www.elsevier.com/Tillgänglig från: 2008-10-10 Skapad: 2008-10-10 Senast uppdaterad: 2017-12-11Bibliografiskt granskad
Wallin, E., Andersson, J. M., Lattemann, M. & Helmersson, U. (2008). Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films. Thin Solid Films, 516(12), 3877-3883
Öppna denna publikation i ny flik eller fönster >>Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films
2008 (Engelska)Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, nr 12, s. 3877-3883Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The effects of residual water on the phase formation, composition, and microstructure evolution of magnetron sputter deposited crystalline alumina thin films have been investigated. To mimic different vacuum conditions, depositions have been carried out with varying partial pressures of H2O. Films have been grown both with and without chromia nucleation layers. It is shown that films deposited onto chromia nucleation layers at relatively low temperatures (500 °C) consists of crystalline alpha-alumina if deposited at a low enough total pressure under ultra high vacuum (UHV) conditions. However, as water was introduced a gradual increase of the gamma phase content in the film with increasing film thickness was observed. At the same time, the microstructure changed drastically from a dense columnar structure to a structure with small, equiaxed grains. Based on mass spectrometry measurements and previous ab initio calculations, we suggest that either bombardment of energetic negative (or later neutralized) species being accelerated over the target sheath voltage, adsorbed hydrogen on growth surfaces, or a combination of these effects, is responsible for the change in structure. For films containing the metastable gamma phase under UHV conditions, no influence of residual water on the phase content was observed. The amounts of hydrogen incorporated into the films, as determined by elastic recoil detection analysis, were shown to be low. Overall, the results demonstrate that residual water present during film growth drastically affects film properties, also in cases where the hydrogen incorporation is found to be low.

Ort, förlag, år, upplaga, sidor
ScienceDirect, 2008
Nyckelord
Aluminum oxide, Phase formation, Sputtering, Water
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-11476 (URN)10.1016/j.tsf.2007.07.135 (DOI)
Anmärkning
Original publication: E. Wallin, J.M. Andersson, M. Lattemann, and U. Helmersson, Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films, 2008, Thin Solid Films, (516), 12, 3877-3883. http://dx.doi.org/10.1016/j.tsf.2007.07.135. Copyright: Elsevier B.V., http://www.elsevier.com/Tillgänglig från: 2008-04-03 Skapad: 2008-04-03 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
Wallin, E. (2008). Low-temperature Hysteresis-free Reactive Deposition of Alpha-alumina. In: 51st SVC Annual Technical Conference,2008.
Öppna denna publikation i ny flik eller fönster >>Low-temperature Hysteresis-free Reactive Deposition of Alpha-alumina
2008 (Engelska)Ingår i: 51st SVC Annual Technical Conference,2008, 2008Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
Abstract [en]

   

Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-42811 (URN)69020 (Lokalt ID)69020 (Arkivnummer)69020 (OAI)
Tillgänglig från: 2009-10-10 Skapad: 2009-10-10
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