Change search
ReferencesLink to record
Permanent link

Direct link
Growth and Mechanical Properties of Transition Metal Nitrides and Carbides
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The atomic-scale dynamical processes at play during film growth cannot be resolved by even the most advanced experimental methods. As such, computational methods, and chiefly classical molecular dynamics, are the only available research tools to study these processes. The investigation of key dynamical processes during thin film growth yields a deeper understanding of the film growth evolution, ultimately allowing for the optimization of experimental parameters and tailoring of film properties. This thesis details the study of fundamental surface dynamics processes, and the role played by primary diffusing species, during TiN film growth, here employed as a model system for transition metal nitrides in general. It is found that Ti adatoms and TiN2 admolecules are the fastest diffusing species, and the species which most rapidly descend from islands onto the growing film. Thus, they are the main contributors and players in driving the layer-by-layer growth mode. TiN3 admolecules, in contrast, are essentially stationary and thereby promote multilayer growth. Large-scale growth simulations reveal that tailoring the incident N/Ti ratio and N kinetic energy significantly affects the growth mode and film microstructure.

The mechanical properties of ternary transition metal nitride and carbide alloys, investigated using density functional theory, are also discussed herein, in comparison to recent experimental results. By optimizing the valence electron concentration in these compounds, the occupation of shear-compliant d‑t2g electronic states can be maximized. The investigation of M1M2N alloys, where M1 = Ti or V and M2 = W or Mo, with different structures demonstrates that this optimization leads to enhanced ductility, and thereby toughness, in transition metal nitride alloys regardless of the degree of ordering on the metal sublattice. Estimations based on the calculation of the mechanical properties of the corresponding M1M2C transition metal carbide alloys indicate that these materials remain brittle. However, charge density analysis and calculations of stress/strain curves reveal features commonly associated with ductile materials.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. , 48 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1791
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-132272DOI: 10.3384/diss.diva-132272ISBN: 9789176856840 (Print)OAI: oai:DiVA.org:liu-132272DiVA: diva2:1044857
Public defence
2016-11-30, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2016-11-11 Created: 2016-10-25 Last updated: 2016-11-11Bibliographically approved
List of papers
1. Dynamics of Ti, N, and TiNx (x=1-3) admolecule transport on TiN(001) surfaces
Open this publication in new window or tab >>Dynamics of Ti, N, and TiNx (x=1-3) admolecule transport on TiN(001) surfaces
Show others...
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 15, 155443- p.Article in journal (Refereed) Published
Abstract [en]

We use classical molecular dynamics and the modified embedded atom method formalism to investigate the dynamics of atomic-scale transport on a low-index model compound surface, TiN(001). Our simulations, totaling 0.25 mu s for each case study, follow the pathways and migration kinetics of Ti and N adatoms, as well as TiNx complexes with x = 1-3, which are known to contribute to the growth of TiN thin films by reactive deposition from Ti, N-2, and N precursors. The simulations are carried out at 1000 K, within the optimal range for TiN(001) epitaxial growth. We find Ti adatoms to be the highest-mobility species on TiN(001), with the primary migration path involving jumps of one nearest-neighbor distance d(NN) between adjacent fourfold hollow sites along in-plane andlt; 100 andgt; channels. Long jumps, 2d(NN), are also observed, but at much lower frequency. N adatoms, which exhibit significantly lower migration rates than Ti, diffuse along in-plane andlt; 110 andgt; directions and, when they intersect other N atoms, associatively form N-2 molecules, which desorb at kinetic rates. As expected, TiN and TiN3 complexes migrate at even lower rates with complex diffusion pathways involving rotations, translations, and rototranslations. TiN2 trimers, however, are shown to have surprisingly high diffusion rates, above that of N adatoms and almost half that of Ti adatoms. TiN3 motion is dominated by in-place rotation with negligible diffusion.

Place, publisher, year, edition, pages
American Physical Society, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-86129 (URN)10.1103/PhysRevB.86.155443 (DOI)000310130800008 ()
Note

Funding Agencies|Swedish Research Council (VR)|2008-6572|Swedish Government Strategic Research Area Grant in Materials Science|Mat-LiU 2009-00971|

Available from: 2012-12-07 Created: 2012-12-07 Last updated: 2016-11-07
2. Ti and N adatom descent pathways to the terrace from atop two-dimensional TiN/TiN(001) islands
Open this publication in new window or tab >>Ti and N adatom descent pathways to the terrace from atop two-dimensional TiN/TiN(001) islands
Show others...
2014 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 558, 37-46 p.Article in journal (Refereed) Published
Abstract [en]

We use classical molecular dynamics and the modified embedded atom method to determine residence times and descent pathways of Ti and N adatoms on square, single-atom-high, TiN islands on TiN(001). Simulations are carried out at 1000 K, which is within the optimal range for TiN(001) epitaxial growth. Results show that the frequency of descent events, and overall adatom residence times, depend strongly on both the TiN(001) diffusion barrier for each species as well as the adatom island-edge location immediately prior to descent. Ti adatoms, with a low diffusion barrier, rapidly move toward the island periphery, via funneling, where they diffuse along upper island edges. The primary descent mechanism for Ti adatoms is via push-out/exchange with Ti island-edge atoms, a process in which the adatom replaces an island edge atom by moving down while pushing the edge atom out onto the terrace to occupy an epitaxial position along the island edge. Double push-out events are also observed for Ti adatoms descending at N corner positions. N adatoms, with a considerably higher diffusion barrier on TiN(001), require much longer times to reach island edges and, consequently, have significantly longer residence times. N adatoms are found to descend onto the terrace by direct hopping over island edges and corner atoms, as well as by concerted push-out/exchange with N atoms adjacent to Ti corners. For both adspecies, we also observe several complex adatom/island interactions, before and after descent onto the terrace, including two instances of Ti islandatom ascent onto the island surface.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-91377 (URN)10.1016/j.tsf.2014.02.053 (DOI)000334314100006 ()
Available from: 2013-04-23 Created: 2013-04-23 Last updated: 2016-11-07Bibliographically approved
3. Effects of atomic ordering on the elastic properties of TiN- and VN-based ternary alloys
Open this publication in new window or tab >>Effects of atomic ordering on the elastic properties of TiN- and VN-based ternary alloys
2014 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 571, no Part 1, 145-153 p.Article in journal (Refereed) Published
Abstract [en]

Improved toughness is one of the central goals in the development of wear-resistant coatings. Previous studies of toughness in transition metal nitride alloys have addressed the effects of chemical composition in these compounds. Herein, we use density functional theory to study the effects of various metal sublattice configurations, ranging from fully ordered to fully disordered, on the mechanical properties of VM2N and TiM2N (M2 = W, Mo) ternary alloys. Results show that all alloys display high incompressibility, indicating strong M-N bonds. Disordered atomic arrangements yield lower values of bulk moduli and C11 elastic constants, as well as higher values of C44 elastic constants, compared to ordered structures. We attribute the low C44 values of ordered structures to the formation of fully-bonding states perpendicular to the applied stress. We find that the ductility of these compounds is primarily an effect of the increased valence electron concentration induced upon alloying.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Nitrides, Density functional theory, Elastic properties, Ductility, Toughness
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-111949 (URN)10.1016/j.tsf.2014.09.048 (DOI)000346053900024 ()
Available from: 2014-11-11 Created: 2014-11-11 Last updated: 2016-11-07Bibliographically approved
4. The dynamics of TiNx (x = 1 – 3) admolecule interlayer and intralayer transport on TiN/TiN(001) islands
Open this publication in new window or tab >>The dynamics of TiNx (x = 1 – 3) admolecule interlayer and intralayer transport on TiN/TiN(001) islands
Show others...
2015 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 589, 133-144 p.Article in journal (Refereed) Published
Abstract [en]

It has been shown both experimentally and by density functional theory calculations that the primary diffusing species during the epitaxial growth of TiN/TiN(001) are Ti and N adatoms together with TiNx complexes (x = 1, 2, 3), in which the dominant N-containing admolecule species depends upon the incident N/Ti flux ratio. Here, we employ classical molecular dynamics (CMD) simulations to probe the dynamics of TiNx (x = 1–3) admolecules on 8 × 8 atom square, single-atom-high TiN islands on TiN(001), as well as pathways for descent over island edges. The simulations are carried out at 1000 K, a reasonable epitaxial growth temperature. We find that despite their lower mobility on infinite TiN(001) terraces, both TiN and TiN2 admolecules funnel toward descending steps and are incorporated into island edges more rapidly than Ti adatoms. On islands, TiN diffuses primarily via concerted translations, but rotation is the preferred diffusion mechanism on infinite terraces. TiN2 migration is initiated primarily by rotation about one of the N admolecule atoms anchored at an epitaxial site. TiN admolecules descend from islands by direct hopping over edges and by edge exchange reactions, while TiN2 trimers descend exclusively by hopping. In contrast, TiN3 admolecules are essentially stationary and serve as initiators for local island growth. Ti adatoms are the fastest diffusing species on infinite TiN(001) terraces, but on small TiN/TiN(001) islands, TiN dimers provide more efficient mass transport. The overall results reveal the effect of the N/Ti precursor flux ratio on TiN(001) surface morphological evolution and growth modes.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Titanium nitride; Molecular dynamics; Film growth simulations; TiNx admolecule diffusion on TiN/TiN(001) islands; TiNx admolecule descent from TiN/TiN(001) islands
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-111948 (URN)10.1016/j.tsf.2015.05.013 (DOI)000360320000023 ()
Available from: 2014-11-11 Created: 2014-11-11 Last updated: 2016-11-07
5. Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth
Open this publication in new window or tab >>Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth
Show others...
2016 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 34, no 4, 041509-1-041509-9 p.Article in journal (Refereed) Published
Abstract [en]

Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200K are carried out using incident flux ratios N/Ti -1, 2, and 4. The films are analyzed as a function of composition, island size distribution, island edge orientation, and vacancy formation. Results show that N/Ti-1 films are globally understoichiometric with dispersed Ti-rich surface regions which serve as traps to nucleate 111-oriented islands, leading to local epitaxial breakdown. Films grown with N/Ti=2 are approximately stoichiometric and the growth mode is closer to layer-by-layer, while N/Ti-4 films are stoichiometric with N-rich surfaces. As N/Ti is increased from 1 to 4, island edges are increasingly polar, i. e., 110-oriented, and N-terminated to accommodate the excess N flux, some of which is lost by reflection of incident N atoms. N vacancies are produced in the surface layer during film deposition with N/Ti-1 due to the formation and subsequent desorption of N-2 molecules composed of a N adatom and a N surface atom, as well as itinerant Ti adatoms pulling up N surface atoms. The N vacancy concentration is significantly reduced as N/Ti is increased to 2; with N/Ti-4, Ti vacancies dominate. Overall, our results show that an insufficient N/Ti ratio leads to surface roughening via nucleation of small dispersed 111 islands, whereas high N/Ti ratios result in surface roughening due to more rapid upper-layer nucleation and mound formation. The growth mode of N/Ti-2 films, which have smoother surfaces, is closer to layer-by-layer. (C) 2016 American Vacuum Society.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2016
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-130405 (URN)10.1116/1.4953404 (DOI)000379588000027 ()
Note

Funding Agencies|Swedish Research Council (VR) Linkoping Linnaeus Initiative LiLi-NFM [2008-6572, 2009-00971, 2013-4018, 2014-5790]; Swedish Government Strategic Research Area Grant in Materials Science on Advanced Functional Materials; Knut and Alice Wallenberg Foundation (Isotope Project)

Available from: 2016-08-15 Created: 2016-08-05 Last updated: 2016-11-07

Open Access in DiVA

Growth and Mechanical Properties of Transition Metal Nitrides and Carbides(986 kB)41 downloads
File information
File name FULLTEXT02.pdfFile size 986 kBChecksum SHA-512
ccd265d367c11f00bcfdded6c26b90ac3f699cb338984238dbe7a87fe98a054b250ef298f5bbe797ab3b7a6813eb4fb20cbb1dfe018a50ad7787153001066c2c
Type fulltextMimetype application/pdf
omslag(5199 kB)22 downloads
File information
File name COVER01.pdfFile size 5199 kBChecksum SHA-512
12d5c7ccc6c6eb03b28588ca98ae304d62f93793caf483fdf25b32030532b2e79285e215b9ed251f7a279c171e4b5c93da70df59b4efb512d83227e8071ba514
Type coverMimetype application/pdf

Other links

Publisher's full text

Search in DiVA

By author/editor
Edström, Daniel
By organisation
Thin Film PhysicsFaculty of Science & Engineering
Condensed Matter Physics

Search outside of DiVA

GoogleGoogle Scholar
Total: 41 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 810 hits
ReferencesLink to record
Permanent link

Direct link