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Atom Probe Tomography of TiSiN Thin Films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
##### Abstract [en]

This thesis concerns the wear resistant coating TiSiN and the development of the analysis technique atom probe tomography (APT) applied to this materials system. The technique delivers compositional information through time-of-flight mass spectrometry, with sub-nanometer precision in 3D for a small volume of the sample. It is thus a powerful technique for imaging the local distribution of elements in micro and nanostructures. To gain the full benefits of the technique for the materials system in question, I have developed a method that combines APT with isotopic substitution, here demonstrated by substitution of natN with 15N. This alters the time-of-flight of ions with of one or more N and will thereby enable the differentiation of the otherwise inseparable isotopes 14N and 28Si. Signs of small-scale fluctuations in the data led the development of an algorithm needed to properly visualize these fluctuations. A method to identify the best sampling parameter for visualization of small-scale compositional fluctuations was added to an algorithm originally designed to find the best sampling parameters for measuring and visualizing strong compositional variations. With the identified sampling parameters, the nano-scale compositional fluctuations of Si in the metal/metalloid sub-lattice could be visualized. The existence and size of these fluctuations were corroborated by radial distribution functions, a technique independent of the previously determined sampling parameter. The radial distribution function algorithm was also developed further to ease in the interpretation. The number of curves could thereby be reduced by showing elements, rather than single and molecular ions (of which there were several different kinds). The improvement of the algorithm also allowed interpretation of signs regarding the stoichiometry of SiNy. With a combination of analytical transmission electron microscopy and APT we show Si segregation on the nanometer scale in arc-deposited Ti0.92Si0.0815N and Ti0.81Si0.1915N thin films. APT composition maps and proximity histograms generated from Ti-rich domains show that the TiN contain at least ~2 at. % Si for Ti0.92Si0.08N and ~5 at. % Si for Ti0.81Si0.19N, thus confirming the formation of solid solutions. The formation of relatively pure SiNy domains in the Ti0.81Si0.19N films is tied to pockets between microstructured, columnar features in the film. Finer SiNy enrichments seen in APT possibly correspond to tissue layers around TiN crystallites, thus effectively hindering growth of TiN crystallites, causing TiN renucleation and thus explaining the featherlike nanostructure within the columns of these films.

##### Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1733
##### National Category
Physical Sciences
##### Identifiers
ISBN: 978-91-7685-901-8 (print)OAI: oai:DiVA.org:liu-122724DiVA: diva2:872201
##### Supervisors
Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2016-08-31Bibliographically approved
##### List of papers
1. Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
Open this publication in new window or tab >>Resolving Mass Spectral Overlaps in Atom Probe Tomography by Isotopic Substitutions: Case of TiSi15N
##### Abstract [en]

Mass spectral overlaps in atom probe tomography (APT) analyses of complex compounds typically limit the identification of elements and microstructural analysis of a material. This study concerns the TiSiN system, chosen because of severe mass-to-charge-state ratio overlaps of the 14N+ and 28Si2+ peaks as well as the 14N$\tiny\frac{+}{2}$ and 28Si2+ peaks. By substituting 14N with 15N, mass spectrum peaks generated by ions composed of one or more N atoms will be shifted toward higher mass-to-charge-state ratios, thereby enabling the separation of N from the predominant Si isotope. We thus resolve thermodynamically driven Si segregation on the nanometer scale in cubic phase Ti1-xSix15N thin films for Si contents 0.08 ≤ x ≤ 0.19 by APT, as corroborated by transmission electron microscopy. The APT analysis yields a composition determination that is in good agreement with energy dispersive X-ray spectroscopy and elastic recoil detection analyses. Additionally, a method for determining good voxel sizes for visualizing small-scale fluctuations is presented and demonstrated for the TiSiN system.

##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-122721 (URN)
Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2016-08-31Bibliographically approved
2. Solid Solution and Segregation Effects in Arc-Deposited Ti1-xSixN Thin Films Resolved on the nanometer scale by 15N Isotopic Substitution in AtomP robe Tomography
Open this publication in new window or tab >>Solid Solution and Segregation Effects in Arc-Deposited Ti1-xSixN Thin Films Resolved on the nanometer scale by 15N Isotopic Substitution in AtomP robe Tomography
##### Abstract [en]

Nanostructured TiSiN is an important material in wear--‐resistant coatings for extending the lifetime of cutting tools. Yet, the understanding regarding the structure, phase composition, and bonding on the detailed nanometer scale, which determines the properties of TiSiN, is lacking. This limits our understanding of the growth phenomena and eventually a larger exploitation of the material. By substituting natN2 with 15N2 during reactive arc deposition of TiSiN thin films, atom probe tomography (APT) gives elemental sensitivity and sub-nanometer resolution, a finer scale than what can be obtained by commonly employed energy dispersive electron spectroscopy in scanning transmission electron microscopy. Using a combination of analytical transmission electron microscopy and APT we show that arc-deposited Ti0.92Si0.0815N and Ti0.81Si0.1915N exhibit Si segregation on the nanometer scale in the alloy films. APT composition maps and proximity histograms from domains with higher than average Ti content show that the TiN domains contain at least ~2 at. % Si for Ti0.92Si0.08N and ~5 at. % Si for Ti0.81Si0.19N, thus confirming the formation of solid solutions. The formation of relatively pure SiNy domains in the Ti0.81Si0.19N films is tied to pockets between microstructured, columnar features in the film. Finer SiNy enrichments seen in APT possibly correspond to tissue layers around TiN crystallites, thus effectively hindering growth of TiN crystallites, causing TiN renucleation and thus explaining the featherlike nanostructure within the columns of these films. For the stoichiometry of the TiN phase, we establish a global under stoichiometry, in accordance with the tendency for SiNy films to have tetrahedral bonding coordination towards a nominal Si3N4 composition.

##### National Category
Physical Sciences
##### Identifiers
urn:nbn:se:liu:diva-122722 (URN)
Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2016-08-31Bibliographically approved

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