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Synthesis and Characterization of Amorphous Carbide-based Thin Films
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, research on synthesis, structure and characterization of amorphous carbide-based thin films is presented. Crystalline and nanocomposite carbide films can exhibit properties such as high electrical conductivity, high hardness and low friction and wear. These properties are in many cases structure-related, and thus, within this thesis a special focus is put on how the amorphous structure influences the material properties.

Thin films within the Zr-Si-C and Cr-C-based systems have been synthesized by magnetron sputtering from elemental targets. For the Zr-Si-C system, completely amorphous films were obtained for silicon contents of 20 at.% or higher. Modeling of these films, as well as experimental results suggest that the films exhibit a network-type structure where the bond types influence the material properties. Higher hardness and resistivity were observed with high amounts of covalent Si-C bonds.

Several studies were performed in the Cr-C-based systems. Cr-C films deposited in a wide composition range and with substrate temperatures of up to 500 °C were found to be amorphous nanocomposites, consisting of amorphous chromium carbide (a-CrCx) and amorphous carbon (a-C) phases. The carbon content in the carbidic phase was determined to about 30-35 at.% for most films. The properties of the Cr-C films were very dependent of the amount of a-C phase, and both hardness and electrical resistivity decreased with increasing a-C contents. However, electrochemical analysis showed that Cr-C films deposited at higher substrate temperature and with high carbon content exhibited very high oxidation resistance. In addition, nanocomposite films containing Ag nanoparticles within an amorphous Cr-C matrix were studied in an attempt to improve the tribological properties. No such improvements were observed but the films exhibited a better contact resistance than the corresponding binary Cr-C films. Furthermore, electrochemical analyses showed that Ag nanoparticles on the surface affected the formation of a stable passive film, which would make the Cr-C/Ag films less resilient to oxidation than the pure Cr-C films.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 63 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1239
Keyword [en]
Amorphous, coating, thin film, nanocomposite, sputter deposition, PVD, XPS, SEM, TEM, electrical properties, mechanical properties
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-247282ISBN: 978-91-554-9198-7 (print)OAI: oai:DiVA.org:uu-247282DiVA: diva2:795631
Public defence
2015-05-08, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2015-04-16 Created: 2015-03-16 Last updated: 2015-07-07
List of papers
1. Magnetron sputtering of Zr-Si-C thin films
Open this publication in new window or tab >>Magnetron sputtering of Zr-Si-C thin films
2012 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 520, no 20, 6375-6381 p.Article in journal (Refereed) Published
Abstract [en]

The phase composition and chemical bonding of Zr-C and Zr-Si-C films deposited by magnetron sputtering has been studied. The results show that the binary Zr-C films at higher carbon contents form nanocrystallites of ZrC in an amorphous carbon matrix. The addition of Si induces a complete amorphization of the films above a critical concentration of about 15 at.%. X-ray diffraction and transmission electron microscopy confirm that the amorphous films contain no nanocrystallites and therefore can be described as truly amorphous carbides. The amorphous films are thermally stable but start to crystallize above 500 degrees C. Analysis of the chemical bonding with X-ray photoelectron spectroscopy suggests that the amorphous films exhibit a mixture of different chemical bonds such as Zr-C, Zr-Si and Si-C and that the electrical and mechanical properties are dependent on the distribution of these bonds. For higher carbon contents, strong Si-C bonds are formed in the amorphous Zr-Si-C films making them harder than the corresponding binary Zr-C films.

Keyword
Sputtering, Amorphous materials, Carbides, Zr-Si-C, Thin films, Physical vapor deposition, X-ray diffraction, Transmission electron microscopy, X-ray photoelectron spectroscopy
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-179567 (URN)10.1016/j.tsf.2012.06.044 (DOI)000306476400005 ()
Available from: 2012-08-20 Created: 2012-08-20 Last updated: 2017-12-07Bibliographically approved
2. Structural properties of amorphous metal carbides: Theory and experiment
Open this publication in new window or tab >>Structural properties of amorphous metal carbides: Theory and experiment
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2012 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 12, 4720-4728 p.Article in journal (Refereed) Published
Abstract [en]

By means of theoretical modeling and experimental synthesis and characterization, we investigate the structural properties of amorphous Zr-Si-C. Two chemical compositions are selected: Zr0.31Si0.29C0.40 and Zr0.60Si0.33C0.07. Amorphous structures are generated in the theoretical part of our work by the stochastic quenching (SQ) method, and detailed comparison is made regarding the structure and density of the experimentally synthesized films. These films are analyzed experimentally using X-ray absorption spectroscopy, transmission electron microscopy and X-ray diffraction. Our results demonstrate a remarkable agreement between theory and experiment concerning bond distances and atomic coordination of this complex amorphous metal carbide. The demonstrated power of the SQ method opens up avenues for theoretical predictions of amorphous materials in general.

Keyword
Amorphous materials, Ab initio calculations, X-ray absorption spectroscopy, Metal carbide glasses, Atomic structure
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-181138 (URN)10.1016/j.actamat.2012.04.044 (DOI)000307415200006 ()
Available from: 2012-09-18 Created: 2012-09-17 Last updated: 2017-12-07Bibliographically approved
3. Beam-induced crystallization of amorphous Me-Si-C (Me = Nb or Zr) thin films during transmission electron microscopy
Open this publication in new window or tab >>Beam-induced crystallization of amorphous Me-Si-C (Me = Nb or Zr) thin films during transmission electron microscopy
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2013 (English)In: MRS Communications, ISSN 2159-6859, Vol. 3, no 3, 151-155 p.Article in journal (Refereed) Published
Abstract [en]

We report that an electron beam focused for high-resolution imaging rapidly initiates observable crystallization of amorphous Me-Si-C films. For 200-keV electron irradiation of Nb-Si-C and Zr-Si-C films, crystallization is observed at doses of similar to 2.8 x 10(9) and similar to 4.7 x 10(9) e(-)/nm(2), respectively. The crystallization process is driven by atomic displacement events, rather than heating from the electron beam as in situ annealing (400-600 degrees C) retains the amorphous state. Our findings demand a critical analysis of alleged amorphous and nanocrystalline ceramics including reassessing previous reports on nanocrystalline Me-Si-C films for possible electron-beam-induced crystallization effects.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-210740 (URN)10.1557/mrc.2013.31 (DOI)000325095100007 ()
Available from: 2013-11-14 Created: 2013-11-14 Last updated: 2015-07-07Bibliographically approved
4. Deposition and characterization of magnetron sputtered amorphous Cr-C films
Open this publication in new window or tab >>Deposition and characterization of magnetron sputtered amorphous Cr-C films
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2012 (English)In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 86, no 9, 1408-1416 p.Article in journal (Refereed) Published
Abstract [en]

Thin films in the Cr-C system with carbon content of 25-85 at.% have been deposited using non-reactive DC magnetron sputtering from elemental targets. Analyses with X-ray diffraction and transmission electron microscopy confirm that the films are completely amorphous. Also, annealing experiment show that the films had not crystallized at 500 degrees C. Furthermore, X-ray spectroscopy and Raman spectroscopy show that the films consist of two phases, an amorphous CrCx phase and an amorphous carbon (a-C) phase. The presence of two amorphous phases is also supported by the electrochemical analysis, which shows that oxidation of both chromium and carbon contributes to the total current in the passive region. The relative amounts of these amorphous phases influence the film properties. Typically, lower carbon content with less a-C phase leads to harder films with higher Young's modulus and lower resistivity. The results also show that both films have lower currents in the passive region compared to the uncoated 316L steel substrate. Finally, our results were compared with literature data from both reactively and non-reactively sputtered chromium carbide films. The comparison reveals that non-reactive sputtering tend to favour the formation of amorphous films and also influence e.g. the sp(2)/sp(3) ratio of the a-C phase. 

Keyword
Amorphous, Chromium carbide, Magnetron sputtering, Electrochemical, Nanoindentation
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-174582 (URN)10.1016/j.vacuum.2012.01.021 (DOI)000302839400037 ()
Available from: 2012-05-29 Created: 2012-05-22 Last updated: 2017-12-07Bibliographically approved
5. Influence of deposition temperature and amorphous carbon on microstructure and oxidation resistance of magnetron sputtered nanocomposite Cr-C films
Open this publication in new window or tab >>Influence of deposition temperature and amorphous carbon on microstructure and oxidation resistance of magnetron sputtered nanocomposite Cr-C films
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2014 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 305, 143-153 p.Article in journal (Refereed) Published
Abstract [en]

It is known that mechanical and tribological properties of transition metal carbide films can be tailored by adding an amorphous carbon (a-C) phase, thus making them nanocomposites. This paper addresses deposition, microstructure, and for the first time oxidation resistance of magnetron sputtered nanocomposite Cr C/a-C films with emphasis on studies of both phases. By varying the deposition temperature between 20 and 700 C and alternating the film composition, it was possible to deposit amorphous, nanocomposite, and crystalline Cr C films containing about 70% C and 30% Cr, or 40% C and 60% Cr. The films deposited at temperatures below 300 degrees C were X-ray amorphous and 500 C was required to grow crystalline phases. Chronoamperometric polarization at +0.6 V vs. Ag/AgCl(sat. KG) in hot 1 mM H-2 SO4 resulted in oxidation of Cr C, yielding Cr203 and C, as well as oxidation of C. The oxidation resistance is shown to depend on the deposition temperature and the presence of the a-C phase. Physical characterization of film surfaces show that very thin C/Cr2O3/Cr C layers develop on the present material, which can be used to improve the oxidation resistance of, e.g. stainless steel electrodes. (C) 2014 Elsevier B.V. All rights reserved.

Keyword
Chromium carbide, Magnetron sputtering, Nanocomposite, Deposition temperature, Carbon oxidation
National Category
Physical Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-227992 (URN)10.1016/j.apsusc.2014.03.014 (DOI)000336525400020 ()
Available from: 2014-07-04 Created: 2014-07-02 Last updated: 2017-12-05
6. Electronic structure and chemical bonding of amorphous chromium carbide thin films
Open this publication in new window or tab >>Electronic structure and chemical bonding of amorphous chromium carbide thin films
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2012 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, no 22, 225004- p.Article in journal (Refereed) Published
Abstract [en]

The microstructure, electronic structure and chemical bonding of chromium carbide thin films with different carbon contents have been investigated with high-resolution transmission electron microscopy, electron energy loss spectroscopy and soft x-ray absorption-emission spectroscopies. Most of the films can be described as amorphous nanocomposites with non-crystalline CrCx in an amorphous carbon matrix. At high carbon contents, graphene-like structures are formed in the amorphous carbon matrix. At 47 at.% carbon content, randomly oriented nanocrystallites are formed creating a complex microstructure of three components. The soft x-ray absorption-emission study shows additional peak structures exhibiting non-octahedral coordination and bonding.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-177220 (URN)10.1088/0953-8984/24/22/225004 (DOI)000304873300006 ()
Available from: 2012-07-12 Created: 2012-07-04 Last updated: 2017-12-07Bibliographically approved
7. Structure and properties of Cr-C/Ag films deposited by magnetron sputtering
Open this publication in new window or tab >>Structure and properties of Cr-C/Ag films deposited by magnetron sputtering
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2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 281, 184-192 p.Article in journal (Refereed) Published
Abstract [en]

Cr-C/Ag thin films with 0-14 at% Ag have been deposited by magnetron sputtering from elemental targets. The samples were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to study their structure and chemical bonding. A complex nanocomposite structure consisting of three phases; nanocrystalline Ag, amorphous CrCx and amorphous carbon is reported. The carbon content in the amorphous carbide phase was determined to be 32-33 at% C, independent of Ag content Furthermore, SEM and XPS results showed higher amounts of Ag on the surface compared to the bulk. The hardness and Young's modulus were reduced from 12 to 8 GPa and from 270 to 170 GPa, respectively, with increasing Ag content. The contact resistance was found to decrease with Ag addition, with the most Ag rich sample approaching the values of an Ag reference sample. Initial tribological tests gave friction coefficients in the range of 0.3 to 0.5, with no clear trends. Annealing tests show that the material is stable after annealing at 500 degrees C for 1 h, but not after annealing at 800 degrees C for 1 h. In combination, these results suggest that sputtered Cr-C/Ag films could be potentially applicable for electric contact applications.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-247276 (URN)10.1016/j.surfcoat.2015.09.054 (DOI)000366072200024 ()
Funder
Swedish Foundation for Strategic Research , RMA11-0029Swedish Research Council, 621-2011-3492
Available from: 2015-03-16 Created: 2015-03-16 Last updated: 2017-12-04Bibliographically approved
8. Electrochemical studies of Cr-C/Ag nanocomposite thin films containing surface Ag nanoparticles
Open this publication in new window or tab >>Electrochemical studies of Cr-C/Ag nanocomposite thin films containing surface Ag nanoparticles
(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-247277 (URN)
Available from: 2015-03-16 Created: 2015-03-16 Last updated: 2015-07-07

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