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Growth and Phase Stability Studies of Epitaxial Sc-Al-N and Ti-Al-N Thin Films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

¨This Thesis treats the growth and characterization of ternary transition metal nitride thin films. The aim is to probe deep into the Ti-Al-N system and to explore novel Sc-Al-N compounds. Thin films were epitaxially grown by reactive dual magnetron sputtering from elemental targets onto single-crystal substrates. Ion beam analyses were used for compositional analysis and depth profiling. Different X-ray diffraction techniques were employed, ex situ using Cu radiation and in situ during deposition using synchrotron radiation, to achieve information about phases, texture, and thickness of films, and to follow roughness evolution of layers during and after growth. Transmission electron microscopy was used for overview and lattice imaging, and to obtain lattice structure information by electron diffraction.

In the Sc-Al-N system, the perovskite Sc3AlN was for the first time synthesized as a thin film and in single phase, with a unit cell of 4.40 Å. The hardness was found to be 14.2 GPa, the elastic modulus 21 GPa, and the room temperature resistivity 41.2 μΩcm. Cubic solid solutions of Sc1-xAlxN can be synthesized with AlN molar fraction up to ~60%. Higher AlN contents yield three different epitaxial relations to ScN(111), namely, #1 Sc1-xAlxN(0001) || ScN(111) with Sc1-xAlxN[11210] || ScN[110], #2 Sc1-xAlxN(1011) || ScN(110) with Sc1-xAlxN[1210] || ScN[110], and #3 Sc1-xAlxN(1011) || ScN(113). An in situ deposition and annealing study of cubic Sc0.57Al0.43N films showed volume induced phase separation into ScN and wurtzite structure AlN, via nucleation and growth at the domain boundaries. The first indications for phase separation are visible at 1000 °C, and the topotaxial relationship between the binaries after phase separation is AlN(0001) || ScN(001) and AlN<01ɸ10> || ScN <1ɸ10>. This is compared with Ti1-xAlxN, for which an electronic structure driving force leads to spinodal decomposition into isostructural TiN and AlN already at 800 °C. First principles calculations explain the results on a fundamental physics level. Up to ~22% ScN can under the employed deposition conditions be dissolved into wurtzite Sc1-xAlxN films, while retaining a single-crystal structure and with lattice parameters matching calculated values.

In the Ti-Al-N system, the Ti2AlN phase was synthesized epitaxially by solid state reaction during interdiffusion between sequentially deposited layers of AlN(0001) and Ti(0001). When annealing the sample, N and Al diffused into the Ti layer, forming Ti3AlN(111) at 400 ºC and Ti2AlN(0001) at 500 ºC. The Ti2AlN formation temperature is 175 ºC lower than earlier reported results. Another way of forming Ti2AlN phase is by depositing understoichiometric TiNx at 800 °C onto Al2O3(0001). An epitaxial Ti2Al(O,N) (0001) oxynitride forms close to the interface between film and substrate through a solid state reaction. Ti4AlN3 was, however, not possible to synthesize when depositing films with a Ti:Al:N ratio of 4:1:3 due to competing reactions. A substrate temperature of 600 ºC yielded an irregularly stacked Tin+1AlNn layered structure because of the low mobility of Al ad-atoms. An increased temperature led to Al deficiency due to outdiffusion of Al atoms, and formation of the Ti2AlN phase and a Ti1-xAlxN cubic solid solution.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. , 98 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1314
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-56274ISBN: 978-91-7393-391-9 (print)OAI: oai:DiVA.org:liu-56274DiVA: diva2:318057
Public defence
2010-05-28, Visionen, Hus B, ingång 27, Campus Valla, Linköpings universitet, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2010-05-06 Created: 2010-05-06 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Sc3AlN: A New Perovskite
Open this publication in new window or tab >>Sc3AlN: A New Perovskite
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2008 (English)In: European Journal of Inorganic Chemistry, ISSN 1434-1948, Vol. 2008, no 8, 1193-1195 p.Article in journal (Refereed) Published
Abstract [en]

Sc3AlN with perovskite structure has been synthesized as the first ternary phase in the Sc–Al–N system. Magnetron sputter epitaxy at 650 °C was used to grow single-crystal, stoichiometric Sc3AlN(111) thin films onto MgO(111) substrates with ScN(111) seed layers as shown by elastic recoil detection analysis, X-ray diffraction, and transmission electron microscopy. The Sc3AlN phase has a lattice parameter of 4.40 Å, which is in good agreement with the theoretically predicted 4.42 Å. Comparisons of total formation energies show that Sc3AlN is thermodynamically stable with respect to all known binary compounds. Sc3AlN(111) films of 1.75 μm thickness exhibit a nanoindentation hardness of 14.2 GPa, an elastic modulus of 249 GPa, and a roomtemperature electrical resistivity of 41.2 μΩ cm.

Keyword
Crystal growth, Density functional theory, Electron microscopy, Perovskite nitride phases, Thin films
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17106 (URN)10.1002/ejic.200701356 (DOI)
Available from: 2009-04-14 Created: 2009-03-06 Last updated: 2016-08-31Bibliographically approved
2. Cubic Sc1-xAlxN solid solution thin films deposited by reactive magnetron sputter epitaxy onto ScN(111)
Open this publication in new window or tab >>Cubic Sc1-xAlxN solid solution thin films deposited by reactive magnetron sputter epitaxy onto ScN(111)
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2009 (English)In: JOURNAL OF APPLIED PHYSICS, ISSN 0021-8979, Vol. 105, no 11, 132862- p.Article in journal (Refereed) Published
Abstract [en]

Reactive magnetron sputter epitaxy was used to deposit thin solid films of Sc1-xAlxN (0 andlt;= x andlt;= 1) onto MgO(111) substrates with ScN(111) seed layers. Stoichiometric films were deposited from elemental Sc and Al targets at substrate temperatures of 600 S C. The films were analyzed by Rutherford backscattering spectroscopy, elastic recoil detection analysis, x-ray diffraction, and transmission electron microscopy. Results show that rocksalt structure (c)-Sc1-xAlxN solid solutions with AlN molar fractions up to similar to 60% can be synthesized. For higher AlN contents, the system phase separates into c- and wurtzite structure (w)-Sc1-xAlxN domains. The w-domains are present in three different orientations relative to the seed layer, namely, Sc1-xAlxN(0001)parallel to ScN(111) with Sc1-xAlxN[(1) over bar2 (1) over bar0]parallel to ScN[1 (1) over bar0], Sc1-xAlxN(10 (1) over bar1)parallel to ScN(111) with Sc1-xAlxN[(1) over bar2 (1) over bar0]parallel to ScN[1 (1) over bar0], and Sc1-xAlxN(10 (1) over bar1)parallel to ScN(113). The results are compared to first-principles density functional theory calculations for the mixing enthalpies of c-, w-, and zinc blende Sc0.50Al0.50N solid solutions, yielding metastability with respect to phase separation for all temperatures below the melting points of AlN and ScN.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-19664 (URN)10.1063/1.3132862 (DOI)
Note
Original Publication: Carina Höglund, Javier Bareno, Jens Birch, Björn Alling, Zsolt Czigany and Lars Hultman, Cubic Sc1-xAlxN solid solution thin films deposited by reactive magnetron sputter epitaxy onto ScN(111), 2009, JOURNAL OF APPLIED PHYSICS, (105), 11, 132862. http://dx.doi.org/10.1063/1.3132862 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2009-07-10 Created: 2009-07-10 Last updated: 2016-08-31
3. Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions
Open this publication in new window or tab >>Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 22, 224101- p.Article in journal (Refereed) Published
Abstract [en]

Thin solid films of metastable rocksalt structure (c-) Sc1-xAlxN and Ti1-xAlxN were employed as model systems to investigate the relative influence of volume mismatch and electronic structure driving forces for phase separation. Reactive dual magnetron sputtering was used to deposit stoichiometric Sc0.57Al0.43N(111) and Ti0.51Al0.49N(111) thin films, at 675 °C and 600 °C, respectively, followed by stepwise annealing to a maximum temperature of 1100 °C. Phase transformations during growth and annealing were followed in situ using X-ray scattering. The results show that the as-deposited Sc0.57Al0.43N films phase separate at 1000 °C – 1100 °C into non-isostructural c-ScN and wurtzite-structure (w-) AlN, via nucleation and growth at domain boundaries. Ti0.51Al0.49N, however, exhibits spinodal decomposition into isostructural coherent c-TiN and c-AlN, in the temperature interval of 800 °C – 1000 °C. X-ray pole figures show the coherency between c-ScN and w-AlN, with AlN(0001) || ScN(001) and AlN<01ɸ10> || ScN<1ɸ10>. First principles calculations of mixing energy-lattice spacing curves explain the results on a fundamental physics level and open a route for design of novel metastable pseudobinary phases for hard coatings and electronic materials.

Keyword
TiAlN, ScAlN, spinodal decomposition, nitrides, TiN, ScN, AlN, XRD, TEM, first-principles, phase separation, meta stable
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-56270 (URN)10.1103/PhysRevB.81.224101 (DOI)000278300900004 ()
Note
Original Publication: Carina Höglund, Björn Alling, Jens Birch, Manfred Beckers, Per O. Å. Persson, Carsten Baehtz, Zsolt Czigány, Jens Jensen and Lars Hultman, Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions, 2010, Physical Review B. Condensed Matter and Materials Physics, (81), 22, 224101. http://dx.doi.org/10.1103/PhysRevB.81.224101 Copyright: American Physical Society http://www.aps.org/ Available from: 2010-05-06 Created: 2010-05-06 Last updated: 2017-12-12
4. Wurtzite-structure Sc1-xAlxN solid solution films grown by reactive magnetron sputter epitaxy: structural characterization and first-principles calculations
Open this publication in new window or tab >>Wurtzite-structure Sc1-xAlxN solid solution films grown by reactive magnetron sputter epitaxy: structural characterization and first-principles calculations
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2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 107, no 12, 123515- p.Article in journal (Refereed) Published
Abstract [en]

AlN(0001) was alloyed with ScN with molar fractions up to ~22%, while retaining a singlecrystal wurtzite (w-) structure and with lattice parameters matching calculated values. Material synthesis was realized by magnetron sputter epitaxy of thin films starting from optimal conditions for the formation of w-AlN onto lattice-matched w-AlN seed layers on Al2O3(0001) and MgO(111) substrates. Films with ScN contents between 23% and ~50% exhibit phase separation into nanocrystalline ScN and AlN, while ScN-rich growth conditions yield a transformation to rocksalt-structure Sc1-xAlxN(111) films. The experimental results are analyzed with ion beam analysis, X-ray diffraction, and transmission electron microscopy, together with ab-initio calculations of mixing enthalpies and lattice parameters of solid solutions in wurtzite, rocksalt, and layered hexagonal phases.

Place, publisher, year, edition, pages
American Institute of Physics, 2010
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-56272 (URN)10.1063/1.3448235 (DOI)000279993900042 ()
Note
Original Publication: Carina Höglund, Jens Birch, Björn Alling, Javier Bareño, Zsolt Czigány, Per O. Å. Persson, Gunilla Wingqvist, Agne Zukauskaite and Lars Hultman, Wurtzite-structure Sc1-xAlxN solid solution films grown by reactive magnetron sputter epitaxy: structural characterization and first-principles calculations, 2010, Journal of Applied Physics, (107), 12, 123515. http://dx.doi.org/10.1063/1.3448235 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2010-05-06 Created: 2010-05-06 Last updated: 2017-12-12Bibliographically approved
5. Topotaxial growth of Ti2AlN by solid state reaction in AlN/Ti(0001) multilayer thin films
Open this publication in new window or tab >>Topotaxial growth of Ti2AlN by solid state reaction in AlN/Ti(0001) multilayer thin films
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2007 (English)In: Applied Physics Letters, ISSN 0003-6951, Vol. 90, no 174106Article in journal (Refereed) Published
Abstract [en]

The formation of Ti2AlN by solid state reaction between layers of wurtzite-AlN and α-Ti was characterized by in situ x-ray scattering. The sequential deposition of these layers by dual magnetron sputtering onto Al2O3(0001) at 200 °C yielded smooth, heteroepitaxial (0001) oriented films, with abrupt AlN/Ti interfaces as shown by x-ray reflectivity and Rutherford backscattering spectroscopy. Annealing at 400 °C led to AlN decomposition and diffusion of released Al and N into the Ti layers, with formation of Ti3AlN. Further annealing at 500 °C resulted in a phase transformation into Ti2AlN(0001) after only 5 min.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17105 (URN)10.1063/1.2731520 (DOI)
Available from: 2009-04-14 Created: 2009-03-06 Last updated: 2016-08-31Bibliographically approved
6. Ti2Al(O,N) formation by solid state reaction between substoichiometric TiN thin films and Al2O3(0001) substrates
Open this publication in new window or tab >>Ti2Al(O,N) formation by solid state reaction between substoichiometric TiN thin films and Al2O3(0001) substrates
2011 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 8, 2421-2425 p.Article in journal (Refereed) Published
Abstract [en]

Titanium nitride TiNx (0.1 ≤ x ≤ 1) thin films were deposited onto Al2O3(0001) substrates using reactive magnetron sputtering at substrate temperatures (Ts) ranging from 800 ºC to 1000 ºC and N2 partial pressures (pN2) between 0.1 and 1.0 mTorr. It is found that Al and O from the substrates diffuse into the substoichiometric TiNx films during deposition. Solid state reactions between the film and substrate result in the formation of Ti2O and Ti3Al domains at low N2 partial pressures, while for increasing pN2, the Ti2AlN MAX phase nucleates and grows together with TiNx. Depositions at increasingly stoichiometric conditions result in a decreasing incorporation of the substrate species into the growing film. Eventually, a stoichiometric deposition gives a stable TiN(111) || Al2O3(0001) structure without the incorporation of substrate species. Growth at Ts 1000 ºC yields Ti2AlN(0001), leading to a reduced incorporation of substrate species compared to films grown at 900 ºC, but contains also Ti2AlN(101ɸ3) grains. Finally, the Ti2AlN domains incorporate O, likely on the N site, such that a MAX phase oxynitride Ti2Al(O,N) is formed. The results were obtained by a combination of structural methods, including X-ray diffraction (XRD) and (scanning) transmission electron microscopy ((S)TEM), together with spectroscopy methods, which comprise elastic recoil detection analysis (ERDA), energy dispersive X-ray spectroscopy (EDX), and electron energy loss spectroscopy (EELS).

Place, publisher, year, edition, pages
Elsevier, 2011
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-56273 (URN)10.1016/j.tsf.2010.12.002 (DOI)000287631500007 ()
Note
Original Publication: P. O. Å. Persson, Carina Höglund, Jens Birch and Lars Hultman, Ti2Al(O,N) formation by solid state reaction between substoichiometric TiN thin films and Al2O3(0001) substrates, 2011, Thin Solid Films, (519), 2421-2425. http://dx.doi.org/10.1016/j.tsf.2010.12.002 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-05-06 Created: 2010-05-06 Last updated: 2017-12-12
7. The influence of substrate temperature and Al mobility on the microstructural evolution of magnetron sputtered ternary Ti-Al-N thin films
Open this publication in new window or tab >>The influence of substrate temperature and Al mobility on the microstructural evolution of magnetron sputtered ternary Ti-Al-N thin films
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2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 6, 064915- p.Article in journal (Refereed) Published
Abstract [en]

Ternary Ti-Al-N films were deposited onto Al2O3 (0001) substrates by reactive co‑sputtering from elemental Ti and Al targets and analyzed by in situ and ex situ x-ray scattering, Rutherford backscattering spectroscopy, transmission electron microscopy and x-ray photoemission spectroscopy. The deposition parameters were set to values that yield Ti:Al:N ratios of 2:1:1 and 4:1:3 at room temperature. 2TiAlN depositions at 675 °C result in epitaxial Ti2AlN growth with basal planes parallel to the substrate surface. Nominal 4TiAl3N depositions at 675 °C and above, however, yield TiN and Ti2AlN domains due to Al loss to the vacuum. Depositions at a lower temperature of 600 °C yield films with correct 4:1:3 stoichiometry, but Ti4AlN3 formation is supposedly prevented by insufficient adatom mobility. Instead, an incoherent Tin+1AlNn structure with random twinned stacking sequences n is obtained, that exhibits both basal plane orientations parallel as well as nearly perpendicular to the substrate interface. X‑ray photoemission spectroscopy shows that in contrast to stoichiometric nitrides the Al is metallically bonded and hence acts as twinning plane within the Tin+1AlNn stackings. Domains with perpendicular basal plane orientation overgrowth those with parallel ones in a competitive growth mode. The resulting morphology is a combination of smooth‑surfaced parallel basal plane orientation domains interrupted by repeated facetted hillock-like features with perpendicular basal plane orientation.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17107 (URN)10.1063/1.3208065 (DOI)
Available from: 2009-04-14 Created: 2009-03-06 Last updated: 2016-08-31Bibliographically approved

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