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Piezoelectricity, Phase Stability, and Surface Diffusion in Multicomponent Nitrides
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0001-6914-9354
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: urn:nbn:se:liu:diva-125919DOI: 10.3384/diss.diva-125919ISBN: 978-91-7685-836-3 (print)OAI: oai:DiVA.org:liu-125919DiVA: diva2:910116
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
List of papers
1. Volume matching condition to establish the enhanced piezoelectricity in ternary (Sc,Y)0.5(Al,Ga,In)0.5N alloys
Open this publication in new window or tab >>Volume matching condition to establish the enhanced piezoelectricity in ternary (Sc,Y)0.5(Al,Ga,In)0.5N alloys
2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 9Article in journal (Refereed) Published
Abstract [en]

Recently, ScAlN alloys attracted attention for their giant piezoelectric moduli. In this study the piezoelectric response of the wurtzite group-III nitrides AlN, GaN, and InN mixed with 50 mol% of ScN or YN is investigated using ab initio calculations. We confirm that the energy flattening phenomenon gives rise to the simultaneous appearance of elastic softening and local structural instability, and explains the enhanced piezoelectricity of the alloys. Furthermore, we present a volume matching condition for an efficient search of new piezoelectric materials. It states that alloys in which the parent components show close volume matching exhibit a flatter potential-energy landscape and higher increase of piezoelectric moduli. We suggest YInN, beyond ScAlN, as a promising material for piezoelectric energy harvesting with its enhanced ≈400% piezoelectric moduli.

Place, publisher, year, edition, pages
American Physical Society, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-91013 (URN)10.1103/PhysRevB.87.094107 (DOI)000316098600002 ()
Note

Funding Agencies|Swedish Research Council Linneaus Environment LiLi-NFM||Knut and Alice Wallenberg Scholar LH Grant||Swedish Research Council|621-2011-4426|Swedish Foundation for Strategic Research (SSF)|10-0026|

Available from: 2013-04-11 Created: 2013-04-11 Last updated: 2017-12-06Bibliographically approved
2. YxAl1-xN Thin Films
Open this publication in new window or tab >>YxAl1-xN Thin Films
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2012 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 45, no 42, 422001- p.Article in journal (Refereed) Published
Abstract [en]

Reactive magnetron sputtering was used to deposit YxAl1-xN thin films, 0≤x≤0.22, onto Al2O3(0001) and Si(100) substrates. X-ray diffraction and analytical electron microscopy show that the films are solid solutions. Lattice constants are increasing with Y concentration, in agreement with ab initio calculations. Spectroscopic ellipsometry measurements reveal a band gap decrease from 6.2 eV (x=0) down to 4.9 eV (x=0.22). Theoretical investigations within the special quasirandom structure approach show that the wurtzite structure has the lowest mixingenthalpy for 0≤x≤0.75.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-76472 (URN)10.1088/0022-3727/45/42/422001 (DOI)000309766700001 ()
Note

funding agencies|Linkoping Linnaeus Initiative on Nanoscale Functional Materials (LiLiNFM)||Swedish Research Council (VR)|349-2008-6582|FCT Portugal|SFRH/BPD/66818/2009|VR|2010-3848|Swedish Governmental Agency for Innovation Systems (VINNOVA)|2011-03486|

Available from: 2012-04-10 Created: 2012-04-10 Last updated: 2017-12-07Bibliographically approved
3. Ab initio calculations and experimental study of piezoelectric YxIn1-xN thin films deposited using reactive magnetron sputter epitaxy
Open this publication in new window or tab >>Ab initio calculations and experimental study of piezoelectric YxIn1-xN thin films deposited using reactive magnetron sputter epitaxy
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2016 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 105, 199-206 p.Article in journal (Refereed) Published
Abstract [en]

By combining theoretical prediction and experimental verification we investigate the piezoelectric properties of yttrium indium nitride (YxIn1-xN). Ab initio calculations show that the YxIn1-xN wurtzite phase is lowest in energy among relevant alloy structures for 0≤x≤0.5. Reactive magnetron sputter epitaxy was used to prepare thin films with Y content up to x=0.51. The composition dependence of the lattice parameters observed in the grown films is in agreement with that predicted by the theoretical calculations confirming the possibility to synthesize a wurtzite solid solution. An AlN buffer layer greatly improves the crystalline quality and surface morphology of subsequently grown YxIn1-xN films. The piezoelectric response in films with x=0.09 and x=0.14 is observed using piezoresponse force microscopy. Theoretical calculations of the piezoelectric properties predict YxIn1−xN to have comparable piezoelectric properties to ScxAl1-xN.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
YInN, Thin films, Sputter deposition, Piezoelectricity, Ab initio calculations
National Category
Condensed Matter Physics Materials Chemistry Inorganic Chemistry Other Materials Engineering Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:liu:diva-125918 (URN)10.1016/j.actamat.2015.11.050 (DOI)000370086500023 ()
Available from: 2016-03-08 Created: 2016-03-08 Last updated: 2017-11-30Bibliographically approved
4. Stabilization of Wurtzite Sc0.4Al0.6N in Pseudomorphic Epitaxial ScxAl1-xN/InyAl1-yN Superlattices
Open this publication in new window or tab >>Stabilization of Wurtzite Sc0.4Al0.6N in Pseudomorphic Epitaxial ScxAl1-xN/InyAl1-yN Superlattices
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2015 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 94, 101-110 p.Article in journal (Refereed) Published
Abstract [en]

Pseudomorphic stabilization in wurtzite ScxAl1-xN/AlN and ScxAl1-xN/InyAl1-yN superlattices (x=0.2, 0.3, and 0.4; y=0.2-0.72), grown by reactive magnetron sputter epitaxy was investigated. X-ray diffraction and transmission electron microscopy show that in ScxAl1-xN/AlN superlattices the compressive biaxial stresses due to positive lattice mismatch in Sc0.3Al0.7N and Sc0.4Al0.6N lead to loss of epitaxy, although the structure remains layered. For the negative lattice mismatched In-rich ScxAl1-xN/InyAl1-yN superlattices a tensile biaxial stress promotes the stabilization of wurtzite ScxAl1-xN even for the highest investigated concentration x=0.4. Ab initio calculations with fixed in-plane lattice parameters show a reduction in mixing energy for wurtzite ScxAl1-xN under tensile stress when x≥0.375 and support the experimental results.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-103831 (URN)10.1016/j.actamat.2015.04.033 (DOI)000357143500010 ()
Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2017-12-06Bibliographically approved
5. Large piezoelectric response of quarternary wurtzite nitride alloys and its physical origin from first principles
Open this publication in new window or tab >>Large piezoelectric response of quarternary wurtzite nitride alloys and its physical origin from first principles
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2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 17, 174119- p.Article in journal (Refereed) Published
Abstract [en]

The potential of quarternary wurtzite TMx/2Mx/2Al1-xN (TM = Ti, Zr, Hf; M = Mg, Ca, Zn) alloys for piezoelectric applications is investigated using first-principles calculations. All considered alloys show increased piezoelectric response compared to pure AlN, and competing with the best ternary system proven to date: ScAlN. (Zr, Hf)(x/2)(Mg, Ca)(x/2)Al1-xN alloys are particularly promising. Calculations reveal positive mixing enthalpies indicative for phase separating systems; their values are smaller compared to related nitride alloys, which still can be grown as metastable thin films. The wurtzite phase of the alloys is lowest in energy at least up to x = 0.5 and for Tix/2Znx/2Al1-xN in the full composition range. Moreover, calculations reveal that wurtzite TM0.5Zn0.5N (TM = Ti, Zr, Hf) are piezoelectric alloys with d(33,f) = 19.95, 29.89, and 24.65 pC/N respectively, up to six times that of AlN. Finally, we discuss the physical origin behind the increased piezoelectric response and show that the energy difference between tetrahedrally coordinated zinc-blende (B3) and the layered hexagonal (B-k) phases of the TM0.5M0.5N alloy can be used as a descriptor in a high-throughput search for complex wurtzite alloys with high piezoelectric response.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-123799 (URN)10.1103/PhysRevB.92.174119 (DOI)000365506400001 ()
Note

Funding Agencies|Knut and Alice Wallenberg Foundation Scholar Grant; Swedish Research Council (VR) Linkoping Linnaeus Initiative LiLi-NFM [2008-6572]; Swedish Government Strategic Research Area Grant in Materials Science on Advanced Functional Materials [MatLiU 2009-00971]; Swedish Research Council [621-2011-4417, 330-2014-6336]; Swedish Foundation for Strategic Research (SSF) Programme SRL [10-0026]; Swedish Research Council (VR) [621-2011-4426]

Available from: 2016-01-11 Created: 2016-01-11 Last updated: 2017-11-30
6. Configurational disorder effects on adatom mobilities on Ti1-xAlxN(001) surfaces from first principles
Open this publication in new window or tab >>Configurational disorder effects on adatom mobilities on Ti1-xAlxN(001) surfaces from first principles
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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
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-78822 (URN)10.1103/PhysRevB.85.245422 (DOI)000305089700007 ()
Available from: 2012-06-21 Created: 2012-06-21 Last updated: 2017-12-07Bibliographically approved
7. Effect of Al substitution on Ti, Al, and N adatom dynamics on TiN(001), (011), and (111) surfaces
Open this publication in new window or tab >>Effect of Al substitution on Ti, Al, and N adatom dynamics on TiN(001), (011), and (111) surfaces
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2014 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 630, 28-40 p.Article in journal (Refereed) Published
Abstract [en]

Substituting Al for Ti in TiN(001), TiN(011), and N- and Ti-terminated TiN(111) surfaces has significant effects on adatom surface energetics which vary strongly with the adatom species and surface orientation. Here, we investigate Ti, Al, and N adatom surface dynamics using density functional methods. We calculate adatom binding and diffusion energies with both a nudged elastic band and grid-probing techniques. The adatom diffusivities are analyzed within a transition-state theory approximation. We determine the stable and metastable Ti, Al, and N binding sites on all three surfaces as well as the lowest energy migration paths. In general, adatom mobilities are fastest on TiN(001), slower on TiN(111), and slowest on TiN(011). The introduction of Al has two major effects on the surface diffusivity of Ti and Al adatoms. First, Ti adatom diffusivity on TiN(001) is significantly reduced near substituted Al surface atoms; we observe a 200% increase in Ti adatom diffusion barriers out of fourfold hollow sites adjacent to Al surface atoms, while Al adatom diffusivity between bulk sites is largely unaffected. Secondly, on TiN(111), the effect is opposite; Al adatoms are slowed near the substituted Al surface atom, while Ti adatom diffusivity is largely unaffected. In addition, we note the importance of magnetic spin polarization on Ti adatom binding energies and diffusion path. These results are of relevance for the atomistic understanding of Ti1-xAlxN alloy and Ti1-xAlxN/TiN multilayer thin-film growth processes.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Diffusion, First principles, Surface diffusion, TiAlN, Titanium nitrides
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-110351 (URN)10.1016/j.susc.2014.06.010 (DOI)000344435900005 ()
Available from: 2014-09-08 Created: 2014-09-08 Last updated: 2017-12-05Bibliographically approved

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