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MAX phase thin films: unique multifunctional ceramics with the elements Ti, Si, Ge, Sn, and C
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mn+1AXn phases are ternary carbides or nitrides (X) consisting of an early transition metal (M), and (A)- group element (group III-V). They combine ceramic and metallic properties with high oxidation and thermal shock resistance as well as low resistivity. Depending on stoichiometry, they can be classified as 211 (n=1), 312 (n=2), and 413 (n=3) phases. The main purpose of this Thesis is to present the synthesis by epitaxial growth of Tin+1ACn (A: Si, Ge, Sn; n=1-3) thin solid films and to report on the material’s intrinsic mechanical and electrical properties. DC magnetron sputtering of MAX-phase carbides from three individual elemental targets is presented as an original and successful deposition method. The emphasis is on the archetypical Ti3SiC2, but I also demonstrate growth of a wide range of other single-crystal Tin+1ACn thin films, including Ti2GeC, Ti3GeC2, Ti2SnC, previously available only in bulk form, as well as completely new phases of Ti4SiC3, Ti4GeC3, and Ti3SnC2, together with some intergrown 523 (211+312) and 725 (312+413) structures.

A combination of x-ray diffraction (XRD), transmission electron micrcoscopy (TEM) analysis, x-ray photoelectron spectroscopy, elastic recoil detection analysis, and Rutherford backscattering spectrometry of the films reveal single-phase and epitaxial growth of Tin+1SiCn(0001) (n = 2, 3) and Ti2GeC MAX phases at substrate temperatures (TS) above 700 to 1000 °C. For TS = 500 – 700 °C, Si is accommodated at twin boundaries between TiC(111) planes. Depositions at TS = RT – 350 °C yield nc-TiC/SiC nanocomposite films or TiC growth with substitutionally incorporated Si due to kinetic constraints. Vacuum-annealing with in situ XRD measurements of the films between 800 – 1400 °C revealed a thermal stability of up to ~1000 °C. A MAX-phase decomposition model is presented within this Thesis. It starts by Si out-diffusion and evaporation from the surface between ~1000 – 1100 °C and is accompanied by any O uptake and SiO evaporation. Subsequently, the free Ti3C2 slabs relax and undergo detwinning. The decomposition process is ended by TiC0.67 formation by C redistribution and recrystallization with void formation.

The mechanical response to deformation was tested on Ti3SiC2(0001) films using nanoindentation. Small applied normal forces yielding a minimum on plastic deformation reveal hardness values of up to 24 GPa, which decrease with larger indentation depths. Young’s moduli between 320 and 343 GPa were measured. Atomic force microscopy (AFM) surface imaging and Focused Ion Beam cross-sectional TEM studies confirm that mechanical deformation in this ductile ceramic takes place by kink formation and delamination along basal planes, due to edge dislocation pile-ups forming the kink boundaries resulting in local deformation-energy dissipation. Friction measurements yield a friction coefficient (μ) of 0.1 for normal loads of FN = 100-200 μN. μ increases to 0.8 with increased FN up to 0.24 N, as delamination and kinking are introduced accompanied by third-body abrasion as shown by scanning electron microscopy. By comparing electrical resistivity values obtained by four-point probe measurements, it is found that all studied MAX-phase thin film systems exhibit good conduction properties.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2006. , 48 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1024
Keyword [en]
Thin solid films, Single-crystal
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-7449ISBN: 91-85523-64-X (print)OAI: oai:DiVA.org:liu-7449DiVA: diva2:22446
Public defence
2006-06-16, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Available from: 2006-09-27 Created: 2006-09-27 Last updated: 2012-11-19
List of papers
1. Growth of Ti3SiC2 thin films by elemental target magnetron sputtering
Open this publication in new window or tab >>Growth of Ti3SiC2 thin films by elemental target magnetron sputtering
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2004 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 9, 4817-4826 p.Article in journal (Refereed) Published
Abstract [en]

Epitaxial Ti3SiC2(0001) thin films have been deposited by dc magnetron sputtering from three elemental targets of Ti, C, and Si onto MgO(111) and Al2O3(0001) substrates at temperatures of 800–900 °C. This process allows composition control to synthesize Mn+1AXn (MAX) phases (M: early transition metal; A: A-group element; X: C and∕or N; n=1–3) including Ti4SiC3. Depositions on MgO(100) substrates yielding the Ti–Si–C MAX phases with (105), as the preferred orientation. Samples grown at different substrate temperatures, studied by means of transmission electron microscopy and x-ray diffraction investigations, revealed the constraints of Ti3SiC2 nucleation due to kinetic limitations at substrate temperatures below 700 °C. Instead, there is a competitive TiCx growth with Si segregation to form twin boundaries or Si substitutional incorporation in TiCx. Physical properties of the as-deposited single-crystal Ti3SiC2 films were determined. A low resistivity of 25 μΩ cm was measured. The Young’s modulus, ascertained by nanoindentation, yielded a value of 343–370 GPa. For the mechanical deformation response of the material, probing with cube corner and Berkovich indenters showed an initial high hardness of almost 30 GPa. With increased maximum indentation loads, the hardness was observed to decrease toward bulk values as the characteristic kink formation sets in with dislocation ordering and delamination at basal planes.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-29682 (URN)10.1063/1.1790571 (DOI)15069 (Local ID)15069 (Archive number)15069 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
2. Mn+1AXn phases in the Ti-Si-C system studied by thin-film synthesis and ab initio calculations
Open this publication in new window or tab >>Mn+1AXn phases in the Ti-Si-C system studied by thin-film synthesis and ab initio calculations
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2004 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 16, 165401- p.Article in journal (Refereed) Published
Abstract [en]

Thin films of Mn+1AXn layered compounds in the Ti-Si-C system were deposited on MgO(111) and Al2O3(0001) substrates held at 900°C using dc magnetron sputtering from elemental targets of Ti, Si, and C. We report on single-crystal and epitaxial deposition of Ti3SiC2 (the previously reported MAX phase in the Ti-Si-C system), a previously unknown MAX phase Ti4SiC3 and another type of structure having the stoichiometry of Ti5Si2C3 and Ti7Si2C5. The latter two structures can be viewed as an intergrowth of 2 and 3 or 3 and 4 M layers between each A layer. In addition, epitaxial films of Ti5Si3Cx were deposited and Ti5Si4 is also observed. First-principles calculations, based on density functional theory (DFT) of Tin+1SiCn for n=1,2,3,4 and the observed intergrown Ti5Si2C3 and Ti7Si2C5 structures show that the calculated difference in cohesive energy between the MAX phases reported here and competing phases (TiC, Ti3SiC2, TiSi2, and Ti5Si3) are very small. This suggests that the observed Ti5Si2C3 and Ti7Si2C5 structures at least should be considered as metastable phases. The calculations show that the energy required for insertion of a Si layer in the TiC matrix is independent of how close the Si layers are stacked. Hardness and electrical properties can be related to the number of Si layers per Ti layer. This opens up for designed thin film structures the possibility to tune properties.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-29680 (URN)10.1103/PhysRevB.70.165401 (DOI)15067 (Local ID)15067 (Archive number)15067 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
3. Kink formation around indents in laminated Ti3SiC2 thin films studied in the nanoscale
Open this publication in new window or tab >>Kink formation around indents in laminated Ti3SiC2 thin films studied in the nanoscale
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2003 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 49, no 2, 155-160 p.Article in journal (Refereed) Published
Abstract [en]

The deformation mechanisms in ductile Ti3SiC2(0 0 0 1) single-crystal films have been analysed by nanoindentation and cross-sectional transmission electron microscopy. Permanent deformation includes formation of kink bands, as the nanolaminated material buckles out at the perimeter of the contact area, and delamination cracks. Evidence is presented for incipient kink-band formation.

Keyword
Carbides, Nanoindentation, Nanolaminated MAX phases, Thin films, Transmission electron microscopy
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46574 (URN)10.1016/S1359-6462(03)00214-8 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
4. Thermal stability of Ti3SiC2 thin films
Open this publication in new window or tab >>Thermal stability of Ti3SiC2 thin films
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2007 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 55, no 4, 1479-1488 p.Article in journal (Refereed) Published
Abstract [en]

The thermal stability of Ti3SiC2(0 0 0 1) thin films is studied by in situ X-ray diffraction analysis during vacuum furnace annealing in combination with X-ray photoelectron spectroscopy, transmission electron microscopy and scanning transmission electron microscopy with energy dispersive X-ray analysis. The films are found to be stable during annealing at temperatures up to ∼1000 °C for 25 h. Annealing at 1100–1200 °C results in the rapid decomposition of Ti3SiC2 by Si out-diffusion along the basal planes via domain boundaries to the free surface with subsequent evaporation. As a consequence, the material shrinks by the relaxation of the Ti3C2 slabs and, it is proposed, by an in-diffusion of O into the empty Si-mirror planes. The phase transformation process is followed by the detwinning of the as-relaxed Ti3C2 slabs into (1 1 1)-oriented TiC0.67 layers, which begin recrystallizing at 1300 °C. Ab initio calculations are provided supporting the presented decomposition mechanisms.

Keyword
Ti3SiC2 thin films, Phase transformations, X-ray diffraction, Transmission electron microscopy, Ab initio electron theory
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-14478 (URN)10.1016/j.actamat.2006.10.010 (DOI)
Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2017-12-13
5. Micro and macroscale tribological behavior of epitaxial Ti3SiC2 thin films
Open this publication in new window or tab >>Micro and macroscale tribological behavior of epitaxial Ti3SiC2 thin films
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2008 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 264, no 11-12, 914-919 p.Article in journal (Refereed) Published
Abstract [en]

Ti3SiC2(0 0 0 1) thin films prepared by magnetron sputtering were investigated for their response to tribomechanical strain induced during ball-on-disk experiments with 6 mm alumina balls and scratch tests with a 1 μm cono-spherical diamond tip. Normal loads of 100 μN to 0.24 N were applied resulting in a friction coefficient of 0.1 for the low loads. With higher applied normal loads, the friction coefficient increased up to 0.8. Analysis of the wear tracks using atomic force microscopy, scanning electron microscopy, and Raman spectroscopy revealed excessive debris resulting in third-body abrasion and fast wear. The formation of the debris can be explained by the generation of subsurface delamination cracks on basal planes. Subsequent kink formation obstructs the ball movement which results in the removal of the kinked film parts.

Place, publisher, year, edition, pages
Amsterdam, Netherlands: Elsevier, 2008
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-39728 (URN)10.1016/j.wear.2007.06.013 (DOI)000254766900002 ()50916 (Local ID)50916 (Archive number)50916 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13Bibliographically approved
6. Growth and characterization of MAX-phase thin films
Open this publication in new window or tab >>Growth and characterization of MAX-phase thin films
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2005 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 193, no 1-3, 6-10 p.Article in journal (Refereed) Published
Abstract [en]

We report that magnetron sputtering can be applied to synthesize MAX-phase films of several systems including Ti–Si–C, Ti–Ge–C, Ti–Al–C, and Ti–Al–N. In particular, epitaxial films of the known phases Ti3SiC2, Ti3GeC2, Ti2GeC, Ti3AlC2, Ti2AlC, and Ti2AlN as well as the newly discovered thin film phases Ti4SiC3, Ti4GeC3 and intergrown structures can be deposited at 900–1000 °C on Al2O3(0001) and MgO(111) pre-seeded with TiC or Ti(Al)N. From XTEM and AFM we suggest a growth and nucleation model where MAX-phase nucleation is initiated at surface steps or facets on the seed layer and followed by lateral growth. Differences between the growth behavior of the systems with respect to phase distribution and phase stabilities are discussed. Characterization of mechanical properties for Tin+1Si–Cn films with nanoindentation show decreased hardness from about 25 to 15 GPa upon penetration of the basal planes with characteristic large plastic deformation with pile up dependent on the choice of MAX material. This is explained by cohesive delamination of the basal planes and kink band formation, in agreement with the observations made for bulk material. Measurements of the electrical resistivity for Ti–Si–C and Ti–Al–N films with four-point probe technique show values of 30 and 39 μΩ cm, respectively, comparable to bulk materials.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-24507 (URN)10.1016/j.surfcoat.2004.08.174 (DOI)6636 (Local ID)6636 (Archive number)6636 (OAI)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13
7. Electrical resistivity of Tin+1ACn (A = Si, Ge, Sn, n = 1–3) thin films
Open this publication in new window or tab >>Electrical resistivity of Tin+1ACn (A = Si, Ge, Sn, n = 1–3) thin films
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2007 (English)In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 22, no 8, 2279-2287 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated the electrical resistivity of (0001)-oriented Tin+1ACn (A = Si, Ge, Sn, n = 1–3) thin films deposited by magnetron sputtering onto Al2O3(0001) substrates at temperatures ranging from 500 to 950 °C. Four-point-probe measurements show that all films are good conductors with resistivity values of ∼21–51 μΩ cm for Ti–Si–C films, ∼15–50 μΩ cm for Ti–Ge–C films, and ∼46 μΩ cm for Ti2SnC. We find a general trend of decreasing resistivity with decreasing n for the Ti–Si–C and Ti–Ge–C systems due to the increased metallicity obtained with increasing density of A-element layers. We also show that crystalline quality and competitive growth of impurity phases affect the measured resistivity values. The effect of a given impurity phase largely depends on its location in the sample. Specifically, a TiCx layer in the center of the film constricts the current flow and results in an increased measured resistivity value. However, TiCx transition or seed layers at the substrate–film interface as well as surface segregation of Ge and Ti5Ge3Cx (for Ti–Ge–C) have only little effect on the measured resistivity values. For the Ti–Sn–C system, the resistivity is mainly influenced by the segregation of metallic Sn, yielding a wide spread in the measured values ranging from 20–46 μΩ cm, in the order of increased film purity.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-14476 (URN)10.1557/jmr.2007.0284 (DOI)
Available from: 2007-05-14 Created: 2007-05-14 Last updated: 2017-12-13

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