Phase field crystal modeling of two-dimensional materials

Petri Hirvonen

Phase field crystal modeling of two-dimensional materials

Julkaisun otsikon käännös: Kaksiulotteisten materiaalien faasikenttäkidemallintaminen

Petri Hirvonen

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Virheettömillä kaksiulotteisilla (2D) materiaaleilla esiintyy monia poikkeuksellisia ominaisuuksia, joita ei havaita tavallisilla materiaaleilla. Valmistusmenetelmät, jotka ovat skaalattavissa suuren mittakaavan tuotantoon, kuitenkin johtavat monikiteisiin mikrorakenteisiin, joissa on rakeita eri orientaatioissa ja viivamaisia raeraja-kidevirheitä niiden välissä. Raerajat saattavat heikentää näiden materiaalien ainutlaatuisia ominaisuuksia. Kasvuprosessin ohjausta on parannettava, jotta kidevirheet voitaisiin välttää tai ainakin niiden jakaumaa hallita. Valitettavasti 2D-mikrorakentei-den muodostuminen tunnetaan huonosti, johtuen tässä vaikuttavien pituus- ja aikaskaalojen suurista vaihteluväleistä.Faasikenttäkidemallit (PFC) ovat tuore lähestymistapa kidevirheellisten materiaalien moniskaala-mallintamiseen. PFC on lupaava tutkittaessa monimutkaisia suuren mittakaavan mikrorakenteita ja niiden hidasta kehitystä pitkien diffuusiivisten aikaskaalojen yli. Tässä väitöskirjassa esitetyssä työssä laajensimme PFC-viitekehyksen oikeiden 2D-materiaalien kvantitatiiviseen mallintamiseen. Arvioimme ensin PFC:n soveltuvuuden 2D-materiaalien raerajojen ja näiden kolmoispisteiden mallintamiseen. Vertailtuamme tuloksiamme kokeellisten havaintojen ja atomipohjaisiin malleihin perustuvien laskelmien kanssa havaitsimme toden-mukaisia kidevirherakenteita ja muodostumis-energioita. Tutkimme lopulta erilaisten kiteisten ja kvasikiteisten mikrorakenteiden piirteitä ja karkenemista PFC:n avulla. Havaitsimme monet mikrorakenteiden ominaisuudet universaaleiksi ja riippumattomiksi taustalla olevan kiderakenteen symmetrioista. Tunnistettuamme todenmukaisia grafeenirakenteita tuottavan PFC-mallin, hyödynsimme sitä mallisysteemien tuottamisessa molekyylidynamiikkasimulaatioihin perustuvia lämmönsiirto-tutkimuksia varten. Nämä todenmukaiset ja hyvin relaksoidut systeemit mahdollistivat monta uutta tieteellistä löytöä. Osoitimme esimerkiksi, että raerajat grafeenissa sirottavat atomitason sisäisiä ja sitä vastaan kohtisuoria fononimoodeja hyvin eri tavoin. Toistimme nämä analyysit kuusikulmaisen boorinitridille ja havaitsimme kvalitatiivisesti samanlaista käyttäytymistä. Kehitimme myös erinäisiä laskennallisia menetelmiä tutkimuksemme helpottamiseksi. Nämä menetelmät liittyvät matalaenergisten kidevirhemuodostelmien löytämiseen, PFC-tiheyskenttien muuntamiseen erillisiksi atomikoordinaateiksi ja mikrorakenteiden analysointiin. Kehitimme esimerkiksi menetelmän paikallisen kideorientaation ja kidevirheiden tunnistamiseksi kiteisissä ja kvasikiteisissä mikrorakenteissa sekä niiden raerakenteen erottamiseksi. Tämä oli ensimmäinen kvasikiteille soveltuva kaltaisensa menetelmä. Tässä väitöskirjassa tehty työ luo vakaan perustan PFC-menetelmien soveltamiseksi tutkittaessa muita 2D-materiaaleja tai niiden muita fysikaalisia ominaisuuksia, kuten mekaanisia tai sähkövarausten siirtoon liittyviä ominaisuuksia.

Julkaisun otsikon käännös	Kaksiulotteisten materiaalien faasikenttäkidemallintaminen
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Ala-Nissilä, Tapio, Vastuuprofessori Ala-Nissilä, Tapio, Ohjaaja Elder, Ken, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-8607-1
Sähköinen ISBN	978-952-60-8608-8
Tila	Julkaistu - 2019
OKM-julkaisutyyppi	G5 Tohtorinväitöskirja (artikkeli)

Tutkimusalat

faasikenttäkide
kaksiulotteiset materiaalit
grafeeni
kuusikulmainen boorinitridi
kvasikiteet
mikrorakenne
hilavirherakenteet
muodostumisenergia
lämmönsiirto

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http://urn.fi/URN:ISBN:978-952-60-8608-8

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@phdthesis{b99da15c38894294ab649789506258a3,

title = "Phase field crystal modeling of two-dimensional materials",

abstract = "Pristine two-dimensional (2D) materials display many exceptional properties unseen in conventional bulk materials. However, techniques scalable to large-scale production yield polycrystalline microstructures with grains in different orientations and grain boundary line defects between them. Grain boundaries can impair the unique properties of these materials. Better control of the growth process is needed to avoid defects or at least to control their distribution. Unfortunately, the formation of 2D microstructures is poorly understood due to the large span of length and time scales involved. Phase field crystal (PFC) models are a recent approach to multiscale modeling of defected materials. PFC holds great promise for studying complex large-scale microstructures and their slow evolution over long, diffusive time scales. In the work reported in this thesis, we have extended the PFC framework to quantitative modeling of real 2D materials. We first assessed the suitability of PFC for modeling the grain boundaries and triple junctions found in polycrystalline graphene. After detailed comparisons with experimental evidence and atomistic calculations, we found realistic defect structures and formation energies. Finally, we studied the coarsening and characteristics of different crystalline and quasicrystalline microstructures using PFC. We observed that many microstructural properties are universal and independent of the underlying lattice symmetry. Having identified a PFC model capable of yielding realistic graphene structures, we exploited it in a multiscale approach to produce sample model systems for heat transport molecular dynamics studies. These realistic, highly-relaxed samples allowed multiple new discoveries. For example, we showed that the in- and out-of-plane phonon modes in graphene are scattered very differently by grain boundaries. We repeated these analyses for PFC samples of hexagonal boron nitride and observed qualitatively similar behavior. In addition to new knowledge about 2D microstructures and heat transport through them, we developed various computational techniques to facilitate our research. These methods are related to sampling low-energy defect configurations, converting PFC density fields to discrete atomic coordinates and analyzing microstructures. As an example, we developed a method for detecting the local lattice orientation and defects in crystalline and quasicrystalline microstructures, and for extracting the grain structures in them. This was the first method of this kind applicable to quasicrystals. The work in this thesis has laid a solid foundation for application of the PCF methodology to study other 2D materials or further physical properties of them, such as their mechanical or electronic transport properties.",

keywords = "phase field crystal, two-dimensional materials, graphene, hexagonal boron nitride, quasicrystals, microstructure, defect structures, formation energy, heat transport, faasikentt{\"a}kide, kaksiulotteiset materiaalit, grafeeni, kuusikulmainen boorinitridi, kvasikiteet, mikrorakenne, hilavirherakenteet, muodostumisenergia, l{\"a}mm{\"o}nsiirto, phase field crystal, two-dimensional materials, graphene, hexagonal boron nitride, quasicrystals, microstructure, defect structures, formation energy, heat transport",

author = "Petri Hirvonen",

year = "2019",

language = "English",

isbn = "978-952-60-8607-1",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "116",

address = "Finland",

school = "Aalto University",

}

TY - THES

T1 - Phase field crystal modeling of two-dimensional materials

AU - Hirvonen, Petri

PY - 2019

Y1 - 2019

N2 - Pristine two-dimensional (2D) materials display many exceptional properties unseen in conventional bulk materials. However, techniques scalable to large-scale production yield polycrystalline microstructures with grains in different orientations and grain boundary line defects between them. Grain boundaries can impair the unique properties of these materials. Better control of the growth process is needed to avoid defects or at least to control their distribution. Unfortunately, the formation of 2D microstructures is poorly understood due to the large span of length and time scales involved. Phase field crystal (PFC) models are a recent approach to multiscale modeling of defected materials. PFC holds great promise for studying complex large-scale microstructures and their slow evolution over long, diffusive time scales. In the work reported in this thesis, we have extended the PFC framework to quantitative modeling of real 2D materials. We first assessed the suitability of PFC for modeling the grain boundaries and triple junctions found in polycrystalline graphene. After detailed comparisons with experimental evidence and atomistic calculations, we found realistic defect structures and formation energies. Finally, we studied the coarsening and characteristics of different crystalline and quasicrystalline microstructures using PFC. We observed that many microstructural properties are universal and independent of the underlying lattice symmetry. Having identified a PFC model capable of yielding realistic graphene structures, we exploited it in a multiscale approach to produce sample model systems for heat transport molecular dynamics studies. These realistic, highly-relaxed samples allowed multiple new discoveries. For example, we showed that the in- and out-of-plane phonon modes in graphene are scattered very differently by grain boundaries. We repeated these analyses for PFC samples of hexagonal boron nitride and observed qualitatively similar behavior. In addition to new knowledge about 2D microstructures and heat transport through them, we developed various computational techniques to facilitate our research. These methods are related to sampling low-energy defect configurations, converting PFC density fields to discrete atomic coordinates and analyzing microstructures. As an example, we developed a method for detecting the local lattice orientation and defects in crystalline and quasicrystalline microstructures, and for extracting the grain structures in them. This was the first method of this kind applicable to quasicrystals. The work in this thesis has laid a solid foundation for application of the PCF methodology to study other 2D materials or further physical properties of them, such as their mechanical or electronic transport properties.

AB - Pristine two-dimensional (2D) materials display many exceptional properties unseen in conventional bulk materials. However, techniques scalable to large-scale production yield polycrystalline microstructures with grains in different orientations and grain boundary line defects between them. Grain boundaries can impair the unique properties of these materials. Better control of the growth process is needed to avoid defects or at least to control their distribution. Unfortunately, the formation of 2D microstructures is poorly understood due to the large span of length and time scales involved. Phase field crystal (PFC) models are a recent approach to multiscale modeling of defected materials. PFC holds great promise for studying complex large-scale microstructures and their slow evolution over long, diffusive time scales. In the work reported in this thesis, we have extended the PFC framework to quantitative modeling of real 2D materials. We first assessed the suitability of PFC for modeling the grain boundaries and triple junctions found in polycrystalline graphene. After detailed comparisons with experimental evidence and atomistic calculations, we found realistic defect structures and formation energies. Finally, we studied the coarsening and characteristics of different crystalline and quasicrystalline microstructures using PFC. We observed that many microstructural properties are universal and independent of the underlying lattice symmetry. Having identified a PFC model capable of yielding realistic graphene structures, we exploited it in a multiscale approach to produce sample model systems for heat transport molecular dynamics studies. These realistic, highly-relaxed samples allowed multiple new discoveries. For example, we showed that the in- and out-of-plane phonon modes in graphene are scattered very differently by grain boundaries. We repeated these analyses for PFC samples of hexagonal boron nitride and observed qualitatively similar behavior. In addition to new knowledge about 2D microstructures and heat transport through them, we developed various computational techniques to facilitate our research. These methods are related to sampling low-energy defect configurations, converting PFC density fields to discrete atomic coordinates and analyzing microstructures. As an example, we developed a method for detecting the local lattice orientation and defects in crystalline and quasicrystalline microstructures, and for extracting the grain structures in them. This was the first method of this kind applicable to quasicrystals. The work in this thesis has laid a solid foundation for application of the PCF methodology to study other 2D materials or further physical properties of them, such as their mechanical or electronic transport properties.

KW - phase field crystal

KW - two-dimensional materials

KW - graphene

KW - hexagonal boron nitride

KW - quasicrystals

KW - microstructure

KW - defect structures

KW - formation energy

KW - heat transport

KW - faasikenttäkide

KW - kaksiulotteiset materiaalit

KW - grafeeni

KW - kuusikulmainen boorinitridi

KW - kvasikiteet

KW - mikrorakenne

KW - hilavirherakenteet

KW - muodostumisenergia

KW - lämmönsiirto

KW - phase field crystal

KW - two-dimensional materials

KW - graphene

KW - hexagonal boron nitride

KW - quasicrystals

KW - microstructure

KW - defect structures

KW - formation energy

KW - heat transport

M3 - Doctoral Thesis

SN - 978-952-60-8607-1

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Phase field crystal modeling of two-dimensional materials

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