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Configurational disorder effects on adatom mobilities on Ti1-xAlxN(001) surfaces from first principles
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-6914-9354
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
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2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 24, 245422- p.Article in journal (Refereed) Published
Abstract [en]

We use metastable NaCl-structure Ti0.5Al0.5N alloys to probe effects of configurational disorder on adatom surface diffusion dynamics which control phase stability and nanostructural evolution during film growth. First-principles calculations were employed to obtain energy potential maps of Ti and Al adsorption on an ordered TiN(001) reference surface and a disordered Ti0.5Al0.5N(001) solid-solution surface. The energetics of adatom migration on these surfaces are determined and compared to isolate effects of configurational disorder. The results show that alloy surface disorder dramatically reduces Ti adatom mobilities. Al adatoms, in sharp contrast, experience only small disorder-induced differences in migration dynamics.

Place, publisher, year, edition, pages
american physical society , 2012. Vol. 85, no 24, 245422- p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-78822DOI: 10.1103/PhysRevB.85.245422ISI: 000305089700007OAI: oai:DiVA.org:liu-78822DiVA: diva2:536055
Available from: 2012-06-21 Created: 2012-06-21 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Development of molecular dynamics methodology for simulations of hard materials
Open this publication in new window or tab >>Development of molecular dynamics methodology for simulations of hard materials
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on molecular dynamics simulations, both classical and ab initio. It is devoted to development of new methods and applications of molecular dynamics based techniques to a series of materials, all of which have the common property of being hard.

I first study grain boundaries in diamond and apply a novel method to better explore the configurational phase space. Using this method several new grain boundary structures are found. The lowest energy grain boundary structure has 20% lower energy then the one obtained with a conventional approach.

Another area is the development of efficient methods for first principles Born-Oppenheimer molecular dynamics. Here a fundamental shortcoming of the method that limits efficiency and introduces drift in the total energy of the system, is addressed and a solution to the problem is presented. Special attention is directed towards methods based on plane waves. The new molecular dynamics simulation method is shown to be more efficient and conserves the total energy orders of magnitude better then previous methods.

The calculation of properties for paramagnetic materials at elevated temperature is a complex task. Here a new method is presented that combines the disordered local moments model and ab initio molecular dynamics. The method is applied to calculate the equation of state for CrN were the connection between magnetic state and atomic structure is very strong. The bulk modulus is found to be very similar for the paramagnetic cubic and the antiferromagnetic orthorhombic phase.

TiN has many applications as a hard material. The effects of temperature on the elastic constants of TiN are studied using ab initio molecular dynamics. A significant dependence on temperature is seen for all elastic constants, which decrease linearly with temperature.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 69 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1454
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-78823 (URN)978-91-7519-883-5 (ISBN)
Public defence
2012-06-08, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Available from: 2012-06-21 Created: 2012-06-21 Last updated: 2012-06-21Bibliographically approved
2. A Theoretical Study of Piezoelectricity, Phase Stability, and Surface Diffusion in Disordered Multicomponent Nitrides
Open this publication in new window or tab >>A Theoretical Study of Piezoelectricity, Phase Stability, and Surface Diffusion in Disordered Multicomponent Nitrides
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Disordered multicomponent nitride thin film can be used for various applications. The focus of this Licentiate Thesis lies on the theoretical study of piezoelectric properties, phase stability and surface diffusion in multifunctional hard coating nitrides using density functional theory (DFT).

Piezoelectric thin films show great promise for microelectromechanical systems (MEMS), such as surface acoustic wave resonators or energy harvesters. One of the main benefits of nitride based piezoelectric devices is the much higher thermal stability compared to the commonly used lead zirconate titanate (PZT) based materials. This makes the nitride based material more suitable for application in, e.g., jet engines.

The discovery that alloying AlN with ScN can increase the piezoelectric response more than 500% due to a phase competition between the wurtzite phase in AlN and the hexagonal phase in ScN, provides a fundamental basis for constructing highly responsive piezoelectric thin films. This approach was utilized on the neighboring nitride binaries, where ScN or YN was alloyed with AlN, GaN, or InN. It established the general role of volume matching the binaries to easily achieve a structural instability in order to obtain a maximum increase of the piezoelectric response. For Sc0.5Ga0.5N this increase is more than 900%, compared to GaN. Y1-xInxN is, however, the most promising alloy with the highest resulting piezoelectric response seconded only by Sc0.5Al0.5N.

Phase stability and lattice parameters (stress-strain states) of the Y1-xAlxN alloy have been calculated in combination with experimental synthesis.

Hard protective coatings based on nitride thin films have been used in industrial applications for a long time. Two of the most successful coatings are TiN and the metastable Ti1-xAlxN. Although these two materials have been extensively investigated both experimentally and theoretically, at the atomic level little is known about Ti1-xAlxN diffusion properties. This is in large part due to problems with configurational disorder in the alloy, because Ti and Al atoms are placed randomly at cation positions in the lattice, considerably increasing the complexity of the problem. To deal with this issues, we have used special quasi-random structure (SQS) models, as well as studying dilute concentrations of Al.

One of the most important mechanisms related to the growth of Ti1-xAlxN is surface diffusion. Because Ti1-xAlxN is a metastable material it has to be grown as a thin film with methods such as physical vapor deposition (PVD), in which surface diffusion plays a pivotal role in determining the microstructure evolution of the film.

In this work, the surface energetics and mobility of Ti and Al adatoms on a disordered Ti0.5Al0.5N(001) surface are studied. Also the effects on the adatom energetics of Ti, Al, and N by the substitution of one Ti with an Al surface atom in TiN(001), TiN(011), and TiN(111) surfaces is studied. This provides an indepth atomistic understanding of how the energetics behind surface diffusion changes as TiN transitions into Ti0.5Al0.5N.

The investigations revealed many interesting results. i) That Ti adatom mobilities are dramatically reduced on the TiN and Ti0.5Al0.5N(001) surfaces while Al adatoms are largely unaffected. ii) The reverse effect is found on the TiN(111) surface, Al adatom migration is reduced while Ti adatom migration is unaffected. iii) The magnetic spin polarization of Ti adatoms is shown to have an important effect on binding energies and diffusion path, e.g., the adsorption energy at bulk sites is increased by 0.14 eV.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 48 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1675
Keyword
Piezoelectricity, phase stability, surface diffusion, disordered multicomponent nitrides
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-110363 (URN)10.3384/lic.diva-110363 (DOI)978-91-7519-253-6 (ISBN)
Presentation
2014-10-03, Plank Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-09-11 Created: 2014-09-09 Last updated: 2016-08-31Bibliographically approved
3. Piezoelectricity, Phase Stability, and Surface Diffusion in Multicomponent Nitrides
Open this publication in new window or tab >>Piezoelectricity, Phase Stability, and Surface Diffusion in Multicomponent Nitrides
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The last hundred years have been full of scientific discoveries leading to technological advances, such as, computers, smart phones, etc. Most of the advances would not have been possible without new discoveries within the vast field of materials science. The specific area within materials science covered in this thesis is multicomponent nitride alloys, which are commonly used as thin films in industrial applications, e.g., as hard wear-resistant coatings for cutting-tools or as part of intricate electronic components in mobile telecommunication devices. The core of this thesis is towards the fundamental understanding of existing, and the discovery of new, nitride alloys using theoretical tools. Knowledge about the quantum mechanics of the alloys was gained using density functional theory, alloy theory, and thermodynamics investigating piezoelectricity, phase stability, and surface diffusion.

The focus of the piezoelectricity research is on piezoelectric properties of both ordered and disordered nitrides. The exploration of disordered wurtzite nitrides revealed important aspects of the nitride alloying physics and the implications for their piezoelectric response, in addition to the discovery of interesting alloy candidates and their synthesis, e.g., YxIn1-xN. For the ordered nitrides, novel TMZnN2 (TM = Ti, Zr, Hf) structures with high piezoelectric responses have been predicted as stable.

The focus of the piezoelectricity research is on piezoelectric properties of both ordered and disordered nitrides. The exploration of disordered wurtzite nitrides revealed important aspects of the nitride alloying physics and the implications for their piezoelectric response, in addition to the discovery of interesting alloy candidates and their synthesis, e.g., YxIn1-xN. For the ordered nitrides, novel TMZnN2 (TM = Ti, Zr, Hf) structures with high piezoelectric responses have been predicted as stable.

The thermodynamic stability of novel alloys with interesting properties is investigated in order to determine if equilibrium or non-equilibrium synthesis is feasible. The studies consist of ternary phase diagrams of TM-Zn-N, mixing enthalpies for disordered YxAl1-xN and YxIn1-xN that can be used to predict possible synthesis routes and guide experiments. In addition, mixing enthalpies for strained ScxAl1-xN/InyAl1-yN superlattices show that the stability of certain phases and, therefore, the crystalline quality can be improved by modifying in-plane lattice parameters through higher indium content in the InAlN layers.

Surface diffusion is studied because it is an important factor during thin film growth with, for example, physical vapor deposition. It is the main atomic transport mechanism and, thus, governs the structure development of thin films. Specifically, the research is focused on diffusion on the surfaces of disordered alloys, and in particular Ti, Al, and N adatom diffusion on TiN and TiAlN surfaces. The investigations revealed that Ti adatom mobilities are dramatically reduced in the presence of Al in the surface layer on the TiN and Ti0.5Al0.5N(0 0 1) surfaces, while Al adatoms are largely unaffected. Furthermore, the reverse effect is found on the TiN(1 1 1) surface, Al adatom migration is reduced while Ti adatom migration is unaffected. In addition, it is shown that neglecting the magnetic spin polarization of Ti adatoms will locally underestimate the binding energies and the diffusion path, e.g., underestimating the stability of TiN(0 0 1) bulk sites.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 104 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1741
National Category
Condensed Matter Physics Other Materials Engineering Manufacturing, Surface and Joining Technology Other Physics Topics Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-125919 (URN)10.3384/diss.diva-125919 (DOI)978-91-7685-836-3 (ISBN)
Public defence
2016-04-01, Plank, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Available from: 2016-03-08 Created: 2016-03-08 Last updated: 2016-08-31Bibliographically approved

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