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The dynamics of TiNx (x = 1 – 3) admolecule interlayer and intralayer transport on TiN/TiN(001) islands
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.ORCID-id: 0000-0002-1379-6656
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska högskolan.ORCID-id: 0000-0002-2837-3656
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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2015 (Engelska)Ingår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 589, s. 133-144Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
Elsevier, 2015. Vol. 589, s. 133-144
Nyckelord [en]
Titanium nitride; Molecular dynamics; Film growth simulations; TiNx admolecule diffusion on TiN/TiN(001) islands; TiNx admolecule descent from TiN/TiN(001) islands
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:liu:diva-111948DOI: 10.1016/j.tsf.2015.05.013ISI: 000360320000023OAI: oai:DiVA.org:liu-111948DiVA, id: diva2:762287
Tillgänglig från: 2014-11-11 Skapad: 2014-11-11 Senast uppdaterad: 2019-06-28
Ingår i avhandling
1. A theoretical study of mass transport processes on TiN(001) and mechanical properties of TiN- and VN-based ternaries
Öppna denna publikation i ny flik eller fönster >>A theoretical study of mass transport processes on TiN(001) and mechanical properties of TiN- and VN-based ternaries
2014 (Engelska)Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis concerns computer simulations, using classical molecular dynamics, of transport processes related to TiN(001) growth. It is motivated from the challenge to understand transport processes at the atomic scale responsible for crystal and film growth and their different growth modes. Not even the most advanced experimental techniques are capable of resolving the sub ps time and sub-Ångström length-scales required. TiN belongs to an important class of transition metal nitrides, and is chosen here as a model system for such fundamental studies of surface transport. The simulations show that on terraces, Ti adatoms exhibit much higher migration rates than N adatoms. For TiNx complexes, as x increases from 1 to 3, rotation becomes increasingly more prevalent than translation. This leads to surprisingly high mobilities of TiN2 trimers, higher than that of N adatoms. On islands, Ti adatoms experience a significant funneling effect, resulting in short residence times. TiN dimers and TiN2 trimers exhibit surprisingly high diffusivities and residence times even shorter than Ti adatoms. TiN3 trimers, however, are essentially stationary on both terraces and islands and serve as nucleation clusters. Overall, Ti adatoms and TiN2 trimers are the most efficient carriers of Ti and N atoms with and between TiN(001) surface layers. These results indicate that Ti/N flux ratios close to one promote layer-by-layer TiN(001) growth, whereas lower ratios result in surface roughening. Understanding of these phenomena enables experimentalists to tune  the growth processes to optimize material properties.

In this thesis I also carry out theoretical calculations to investigate the role of configurational order on the metallic sublattice in relation to toughness enhancement. My studies set out from the recent understanding that the toughness of transition metal nitrides can be enhanced by tuning the valence electron concentration. My results show that ordered alloys exhibit lower resistance to shear deformations than disordered alloys, and higher resistance to tensile deformation. The lower resistance to shear deformations is explained by the formation of fully bonding electronic states perpendicular to the applied stress. Using the Pugh-Pettifor criterion, it is shown that while configurational order has an effect on the ductility of the material, this is primarily governed by the valence electron concentration.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2014. s. 22
Serie
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1686
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-111950 (URN)10.3384/lic.diva-111950 (DOI)978-91-7519-197-3 (ISBN)
Handledare
Tillgänglig från: 2014-11-11 Skapad: 2014-11-11 Senast uppdaterad: 2016-08-31Bibliografiskt granskad
2. Growth and Mechanical Properties of Transition Metal Nitrides and Carbides
Öppna denna publikation i ny flik eller fönster >>Growth and Mechanical Properties of Transition Metal Nitrides and Carbides
2016 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2016. s. 48
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1791
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:liu:diva-132272 (URN)10.3384/diss.diva-132272 (DOI)9789176856840 (ISBN)
Disputation
2016-11-30, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (Engelska)
Opponent
Handledare
Forskningsfinansiär
VetenskapsrådetKnut och Alice Wallenbergs Stiftelse
Tillgänglig från: 2016-11-11 Skapad: 2016-10-25 Senast uppdaterad: 2019-10-29Bibliografiskt granskad

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