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Sputter-cleaned Epitaxial VxMo(1-x)Ny/MgO(001)Thin Films Analyzed by X-ray PhotoelectronSpectroscopy: 1. Single-crystal V0.48Mo0.52N0.64
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.ORCID-id: 0000-0002-4898-5115
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. Department of Materials Science and the Fredrick Seitz Materials Research Laboratory, University of Illinois, Urbana, USA.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan. Department of Materials Science and the Fredrick Seitz Materials Research Laboratory, University of Illinois, Urbana, USA.
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2013 (Engelska)Ingår i: Surface Science Spectra, ISSN 1055-5269, E-ISSN 1520-8575, Vol. 20, nr 1, s. 68-73Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Epitaxial VxMo(1-x)Ny thin films grown by ultrahigh vacuum reactive magnetron sputter deposition on Mg(001) substrates are analyzed by x-ray photoelectron spectroscopy (XPS). This contribution presents analytical results for 300-nm-thick single-crystal V0.48Mo0.52N0.64 films deposited by reactive cosputtering from V (99.95 % purity) and Mo (99.95 % purity) targets. Film growth is carried out at 900 °C in mixed Ar/N2 atmospheres at a total pressure of 5 mTorr, with a N2 partial pressure of 3.2 mTorr; a bias of −30 V is applied to the substrate. Films composition is determined by Rutherford backscattering spectrometry (RBS). XPS measurements employ monochromatic Al K α radiation (hν = 1486.6 eV) to analyze V0.48Mo0.52N0.64(001) surfaces sputter-cleaned in-situ with 4 keV Ar+ ions incident at an angle of 70° with respect to the surface normal. XPS results show that the ion-etched sample surfaces have no measurable oxygen or carbon contamination; film composition, obtained using XPS sensitivity factors, is V0.33Mo0.67N0.64. All core level peaks, including the nearby Mo 3p3/2 (binding energy of 394.0 eV) and N 1s (at 397.6 eV) peaks, are well-resolved.

Ort, förlag, år, upplaga, sidor
2013. Vol. 20, nr 1, s. 68-73
Nationell ämneskategori
Naturvetenskap
Identifikatorer
URN: urn:nbn:se:liu:diva-106357DOI: 10.1116/11.20130301OAI: oai:DiVA.org:liu-106357DiVA, id: diva2:715585
Tillgänglig från: 2014-05-05 Skapad: 2014-05-05 Senast uppdaterad: 2017-12-05
Ingår i avhandling
1. Toughness Enhancement in Hard Single-Crystal Transition-Metal Nitrides: V-Mo-N and V-W-N Alloys
Öppna denna publikation i ny flik eller fönster >>Toughness Enhancement in Hard Single-Crystal Transition-Metal Nitrides: V-Mo-N and V-W-N Alloys
2014 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Transition-metal nitrides are known for their high hardness, good wear resistance, high-temperature stability, and chemical inertness. Because of these properties, they are extensively used in many industrial applications, notably as protective wear, erosion, and scratch resistant coatings, which are often subjected to high thermo-mechanical stresses. While high hardness is essential, most applications also require high ductility, to avoid brittle failure due to cracking. However, transitionmetal nitrides, as most ceramics, generally exhibit low ductility and hence poor toughness.

Improving toughness, the combination of hardness and ductility, of ceramic materials requires suppression of crack initiation and/or propagation, both of which depend on the microstructure, electronic structure, and bonding nature of the coating material. This, however, is an extremely challenging task that requires a fundamental understanding of the mechanical behavior of materials. Theoretical studies, for example, ab initio calculations and simulations are therefore useful in the design of “unbreakable” materials by providing information about the electronic origins of hardness and ductility. Recent density functional theory calculations predicted that alloying can increase toughness in a certain family of transition-metal nitrides such as V-Mo-N and V-W-N alloys. Toughness enhancement in these alloys arises from a near optimal filling of the metallic d-t2g states, due to their high valence electron concentrations, leading to an orbital overlap which favors ductility during shearing.

This thesis focuses on the growth and characterization of V1-xMoxNy (0 ≤ x ≤ 0.7, 0.55 ≤ y ≤ 1.03) and V1-xWxNy (0 ≤ x ≤ 0.83, 0.75 ≤ y ≤ 1.13) cubic alloy thin films. I show that alloying VN with WN increases the alloy hardness and reduces the elastic modulus, an indication of enhanced toughness. I investigated the growth, nanostructure, and atomic ordering of as-deposited V1-xWxNy(001)/MgO(001) thin films. In addition, I studied the growth, structural and mechanical properties,  and electronic structure of V1-xMoxNy(001)/MgO(001) and V0.5Mo0.5Ny(111)/Al2O3(0001) thin films. I demonstrate that these alloys exhibit not only higher hardness than the parent binary compound, VN, but also dramatically increased ductility. V0.5Mo0.5N hardness is more than 25% higher than that of VN. Using nanoindentation I show that while VN and TiN reference samples undergo severe cracking typical of brittle ceramics, V0.5Mo0.5N films do not crack. Instead, they exhibit material pile-up around nanoindents, characteristic of plastic flow in ductile materials. Furthermore, the wear resistance of V0.5Mo0.5N is significantly higher than that of VN. I also show, for the first time, anion-vacancyinduced toughening of single-crystal V0.5Mo0.5Ny/MgO(001) films. Nanoindentation hardness of these alloys increases with the introduction of N-vacancies, while the elastic modulus remains essentially constant. In addition, typical scanning electron micrographs of nanoindents show no cracks, which demonstrate that N-vacancies lead to toughness enhancement in these alloys. Valence band x-ray photoelectron spectroscopy analyses show that vacancy-induced toughening is due to a higher electron density of d-t2g(Metal) – d-t2g(Metal) orbitals with increasing N-vacancy concentration, and essentially equally dense p(N) – d-eg(Metal) first neighbor bonds.

Overall, I demonstrate that it is possible to design and deposit hard and ductile transition-metal nitride coatings. My research results thus provide a pathway toward the development of new tough materials.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2014. s. 69
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1578
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-106472 (URN)10.3384/diss.diva-106472 (DOI)978-91-7519-392-2 (ISBN)
Disputation
2014-06-02, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2014-05-08 Skapad: 2014-05-08 Senast uppdaterad: 2019-11-19Bibliografiskt granskad

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