liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Alumina Thin Films: From Computer Calculations to Cutting Tools
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2008. , 59 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1221
Keyword [en]
Alumina, thin films, coatings, sputtering, density functional theory, high power impulse magnetron sputtering, HIPIMS
National Category
Other Engineering and Technologies not elsewhere specified Manufacturing, Surface and Joining Technology Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-15360ISBN: 978-91-7393-769-6 (print)OAI: oai:DiVA.org:liu-15360DiVA: diva2:114053
Public defence
2008-11-27, Planck, Physics building, Campus Valla, Linköping University, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-11-05 Created: 2008-11-05 Last updated: 2013-10-30Bibliographically approved
List of papers
1. Phase control of Al2O3 thin films grown at low temperatures
Open this publication in new window or tab >>Phase control of Al2O3 thin films grown at low temperatures
Show others...
2006 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 513, no 1-2, 57-59 p.Article in journal (Refereed) Published
Abstract [en]

Low-temperature growth (500 °C) of α-Al2O3 thin films by reactive magnetron sputtering was achieved for the first time. The films were grown onto Cr2O3 nucleation layers and the effects of the total and O2 partial pressures were investigated. At 0.33 Pa total pressure and ≥ 16 mPa O2 partial pressure α-Al2O3 films formed, while at lower O2 pressure or higher total pressure (0.67 Pa), only γ phase was detected in the films (which were all stoichiometric). Based on these results we suggest that α phase formation was promoted by a high energetic bombardment of the growth surface. This implies that the phase content of Al2O3 films can be controlled by controlling the energy of the depositing species. The effect of residual H2O (10− 4 Pa) on the films was also studied, showing no change in phase content and no incorporated H (< 0.1%). Overall, these results are of fundamental importance in the further development of low-temperature Al2O3 growth processes.

Place, publisher, year, edition, pages
Elsevier, 2006
Keyword
Aluminum oxide, Chromium oxide, Sputtering, Ion bombardment, X-ray diffraction
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-14318 (URN)10.1016/j.tsf.2006.01.016 (DOI)
Note
Original publication: Andersson, J.M., Wallin, E., Helmersson, U., Kreissig, U. and Münger, E.P., Phase control of Al2O3 thin films grown at low temperatures, 2006, Thin Solid Films, (513), 1-2, 57-59. http://dx.doi.org/10.1016/j.tsf.2006.01.016. Copyright: Elsevier B.V., http://www.elsevier.com/ Available from: 2007-03-02 Created: 2007-03-02 Last updated: 2017-12-13Bibliographically approved
2. Ab initio studies of Al, O, and O2 adsorption on α-Al2O3 (0001) surfaces
Open this publication in new window or tab >>Ab initio studies of Al, O, and O2 adsorption on α-Al2O3 (0001) surfaces
Show others...
2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 12, 125409-1-125409-9 p.Article in journal (Refereed) Published
Abstract [en]

The interactions of Al, O, and O2 with different α- Al2O3 (0001) surfaces have been studied using ab initio density functional theory methods. All three surface terminations obtainable by cleaving the bulk structure [single Al-layer (AlO), double Al-layer (AlAl), and O terminations] have been considered, as well as a completely hydrogenated O-terminated surface. Adsorbed Al shows strong ioniclike interaction with the AlO - and O-terminated surfaces, and several metastable adsorption sites are identified on the O-terminated surface. On the completely hydrogenated surface, however, Al adsorption in the bulk position is found to be unstable or very weak for the studied configurations of surface H atoms. Atomic O is found to interact strongly with the AlAl -terminated surface, where also O2 dissociative adsorption without any appreciable barrier is observed. In contrast, O adsorption on the AlO -terminated surface is metastable relative to molecular O2. On the O-terminated surface, we find the creation of O surface vacancies to be plausible, especially upon exposure to atomic O at elevated temperatures. The results are mainly discussed in the context of alumina thin film growth and provide insight into phenomena related to, e.g., preferred adsorption sites and effects of hydrogen on the growth.

Place, publisher, year, edition, pages
College Park, MD, United States: American Physical Society, 2006
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-10427 (URN)10.1103/PhysRevB.74.125409 (DOI)000240872500080 ()
Note

Original publication: E. Wallin, J.M. Andersson, E.P. Münger, V. Chirita & U. Helmersson, Ab initio studies of Al, O, and O2 adsorption on α- Al2 O3 (0001) surfaces, 2006, Physical Review B, (74), 125409. http://dx.doi.org/10.1103/PhysRevB.74.125409. Copyright: The America Physical Society, http://prb.aps.org/

Available from: 2007-12-12 Created: 2007-12-12 Last updated: 2017-12-14Bibliographically approved
3. Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films
Open this publication in new window or tab >>Influence of residual water on magnetron sputter deposited crystalline Al2O3 thin films
2008 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 12, 3877-3883 p.Article in journal (Refereed) 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.

Place, publisher, year, edition, pages
ScienceDirect, 2008
Keyword
Aluminum oxide, Phase formation, Sputtering, Water
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-11476 (URN)10.1016/j.tsf.2007.07.135 (DOI)
Note
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/Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2017-12-13Bibliographically approved
4. Low-temperature alpha-alumina thin film growth: ab initio studies of Al adatom surface migration
Open this publication in new window or tab >>Low-temperature alpha-alumina thin film growth: ab initio studies of Al adatom surface migration
2009 (English)In: JOURNAL OF PHYSICS D-APPLIED PHYSICS, ISSN 0022-3727, Vol. 42, no 12, 125302- p.Article in journal (Refereed) 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.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-19393 (URN)10.1088/0022-3727/42/12/125302 (DOI)
Note
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/ Available from: 2009-06-29 Created: 2009-06-22 Last updated: 2013-10-30Bibliographically approved
5. Hysteresis-free reactive high power impulse magnetron sputtering
Open this publication in new window or tab >>Hysteresis-free reactive high power impulse magnetron sputtering
2008 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 516, no 18, 6398-6401 p.Article in journal (Refereed) 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.

Keyword
Reactive Sputtering, High Power Impulse Magnetron Sputtering, Alumina, Process modeling
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-15028 (URN)10.1016/j.tsf.2007.08.123 (DOI)
Note
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/Available from: 2008-10-10 Created: 2008-10-10 Last updated: 2017-12-11Bibliographically approved
6. Synthesis of α-Al2O3 thin films using reactive high power impulse magnetron sputtering
Open this publication in new window or tab >>Synthesis of α-Al2O3 thin films using reactive high power impulse magnetron sputtering
2008 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 82, no 3, 36002- p.Article in journal (Refereed) Published
Abstract [en]

α-alumina coatings have been deposited directly onto cemented-carbide and Mo substrates at a temperature as low as 650 °C using reactive high-power impulse magnetron sputtering (HiPIMS) of Al in an Ar/O2 gas mixture. The coatings consisted of plate-like crystallites, as revealed by scanning electron microscopy. α phase growth was retained over the studied range of substrate bias voltages (from floating potential up to -100 V), with films exhibiting a slightly denser microstructure at higher bias voltages. X-ray diffraction indicated that the α-alumina grains had a preferred orientation of (0001)-planes perpendicular to the substrate surface. X-ray analysis of films deposited at 575 °C indicated the presence of γ-alumina, whereas films grown at 500 °C or lower were X-ray amorphous.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-15354 (URN)10.1209/0295-5075/82/36002 (DOI)
Note
Original Publication: Erik Wallin, T. I. Selinder, M. Elfwing and Ulf Helmersson, Synthesis of α-Al2O3 thin films using reactive high power impulse magnetron sputtering, 2008, Europhysics letters, (82), 36002. http://dx.doi.org/10.1209/0295-5075/82/36002 Copyright: EDP Sciences. http://publications.edpsciences.org/ Available from: 2009-02-22 Created: 2008-11-05 Last updated: 2017-12-14Bibliographically approved
7. α-alumina coatings on WC/Co substrates by physical vapor deposition
Open this publication in new window or tab >>α-alumina coatings on WC/Co substrates by physical vapor deposition
2009 (English)In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 27, no 2, 507-512 p.Article in journal (Refereed) 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.

Keyword
HiPIMS, HPPMS, ionized-PVD, alumina, corundum
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-15359 (URN)10.1016/j.ijrmhm.2008.10.007 (DOI)
Note
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/ Available from: 2009-02-23 Created: 2008-11-05 Last updated: 2017-12-14Bibliographically approved

Open Access in DiVA

fulltext(1098 kB)12546 downloads
File information
File name FULLTEXT01.pdfFile size 1098 kBChecksum SHA-512
f1d9800b67440c733da80a7ed0639d2d2848f86a92649d5f7483d0270a1e2178f8f37d507a536421f3ad2deb00ebf21cbf4471a2364f529e381e0b9915ae7f17
Type fulltextMimetype application/pdf
cover(1605 kB)120 downloads
File information
File name COVER01.pdfFile size 1605 kBChecksum SHA-512
72e33d07166644a25558cd86b48d3ee5971d246ab7560e4f34dfeefcfbb3b654d18e16a679d742251f8c823704841cb56f9c975f117de600658e06e0dbb9ff43
Type coverMimetype application/pdf

Other links

Link to Licentiate Thesis

Authority records BETA

Wallin, Erik

Search in DiVA

By author/editor
Wallin, Erik
By organisation
Plasma and Coating Physics The Institute of Technology
Other Engineering and Technologies not elsewhere specifiedManufacturing, Surface and Joining TechnologyCondensed Matter Physics

Search outside of DiVA

GoogleGoogle Scholar
Total: 12548 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 5950 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf