The control of low dimensional materials holds potential for revolutionizing the electronic, thermal, and thermoelectric materials engineering. Through strategic manipulation and optimization of these materials, unique properties can be uncover which enable more efficient and effective materials development. Towards the determination of nanoscale strategies to improve the electronic and phononic devices, computational simulations of modified low dimensional materials have been carried in this research. First, the electronic properties of chemically func tionalized phosphorene monolayers are evaluated with spin-polarized Density Functional Theory, as a potential method to tune their electronic properties.
The functionalization not only leads to formation of additional states within the semiconducting gap, but also to the emergence of local magnetism. The magnetic ground state and electronic structure are investigated in dependence of molecular coverage, lattice direction of the molecular adsorption and molecule type functionalization. Furthermore, the physical and transport properties of phosphorene grain boundaries under uniaxial strain are evaluated by the use of Density Functional based Tight Binding method in combination with Landauer theory. In both grain boundary types, the electronic bandgap decreases under strain, however, the respective thermal conductance is only weakly affected, despite rather strong changes in the frequency-resolved phonon transmission. The combination of both effects results in an enhancement in the thermoelectric figure of merit in the phosphorene grain boundary systems. Finally, the thermoelectric properties of carbon nanotubes peapod heterostructures are studied and compared to pristine nanotubes using also the Density Functional based Tight Binding method and Landauer theory. It is found that the fullerene encapsulation modifies the electron and phonon transport properties, causing the formation of electronic channels and the suppression of vibrational modes that lead to an improvement of the thermoelectric figure of merit. The results of this thesis highlight the potential of strategic manipulation and optimization of low dimensional materials in improving their unique electronic and thermal properties, revealing promising avenues for improving electronic and phononic devices.:ABSTRACT i
ZUSAMMENFASSUNG ii
ACKNOWLEDGEMENT iv
LIST OF FIGURES ix
LIST OF TERMS AND ABBREVIATIONS xviii
1 Introduction 1
1.1 Motivation 1
1.2 Objectives and outline 6
2 Computational Methods 8
2.1 Density Functional Theory 8
2.1.1 The Many-Body System Hamiltonian and the Born-Oppenheimer approximation 9
2.1.2 Thomas-Fermi-Dirac approximation model 10
2.1.3 The Hohenberg-Kohn theorems 12
2.1.4 The Kohn-Sham orbitals equations 13
2.1.5 Exchange-correlation functionals 15
2.2 Density Functional Based Tight Binding method 16
2.2.1 Tight-binding formalism 17
2.2.2 From DFT to DFTB 20
2.2.3 Parametrization 22
2.3 Atomistic Green’s functions 23
2.3.1 Non-Equilibrium Green’s functions for modeling electronic transmission 23
2.3.2 Non-equilibrium Green’s function for modeling thermal transmission 27
3 Tuning the electronic and magnetic properties through chemical functionalization
3.1 Introduction 33
3.1.1 Black phosphorus as a 2D material 33
3.1.2 Chemical Functionalization of low dimensional systems 35
3.1.3 Bipolar Magnetic Semiconductors 36
3.2 Computational approach 38
3.3 Interface effects in phosphorene by OH functionalization 39
3.3.1 Single molecule functionalization 39
3.3.2 Lattice selection 43
3.3.3 Coverage 45
3.4 Chiral functionalization effect in phosphorene 48
3.5 Functionalizing phosphorene towards BMS 51
3.6 Summary 53
4 Tuning transport properties through strain and grain bound-aries
4.1 Introduction 54
4.1.1 Strain in low dimensional materials 54
4.1.2 Grain boundaries 56
4.2 Computational approach 58
4.2.1 Molecular systems 58
4.2.2 Electron and phonon transport and thermoelectric figure of merit 58
4.3 Structural modification by strain in GB systems 60
4.4 Electronic structure modification by strain in GB systems 63
4.5 Thermal transport modification by strain in GB systems 65
4.6 Thermoelectric figure of merit of strained GB systems 68
4.7 Summary 71
5 Tuning transport properties through hybrid nanomaterials: CNT peapods 73
5.1 Introduction 73
5.1.1 Carbon-based nanostructures 73
5.1.2 CNT peapods as hybrid nanomaterials 76
5.2. Computational details 77
5.2.1 CNT peapod model 77
5.2.2 Quantum transport methodology 78
5.3 Structural properties of CNT peapods 79
5.4 Electronic properties of CNT peapods 80
5.5 Thermal properties of CNT peapods 83
5.6 Thermoelectronic properties of CNT peapods 85
5.7 Summary 88
6 Conclusions and outlook 91
Appendices
Appendix A Supplementary information to phosphorene functionalization
A.1 Spin resolved density of states of 1-OH system 96
A.2 Spin valve model 97
Appendix B Supplementary information to phosphorene grain boundaries 98
B.1 Projected Phonon Density of States in GB1 98
B.2 Thermoelectric transport properties of GB2 99
Appendix C Supplementary information to CNT peapods 101
C.1 Geometry optimization of CNT peapods with larger CNT diameter 101
C.2 Additional analysis of electron transport properties 102
C.3 Phonon band structure of different CNT structures 104
C.4 Additional analysis of thermoelectric performance 105
REFERENCES 105
LIST OF PUBLICATIONS 131
PRESENTATIONS 132 / Die Kontrolle niedrigdimensionaler Materialien birgt das Potenzial für eine Revolutionierung der elektronischen, thermischen und thermoelektrischen Technologien. Durch strategische Manipulation und Optimierung dieser Materialien können einzigartige Eigenschaften aufgedeckt werden, die eine effizientere und effektivere Materialentwicklung ermöglichen. Um Strategien im Nanobereich zur Verbesserung elektronischer und phononischer Bauelemente zu ermitteln, wurden in dieser Forschungsarbeit rechnerische Simulationen modifizierter niedrigdimensionaler Materialien durchgeführt. Zunächst werden die elektronischen Eigenschaften von chemisch funktionalisierten Phosphoren-Monoschichten mit Hilfe der spinpolarisierten Dichtefunktionaltheorie als potenzielle Methode zur Abstimmung ihrer elektronischen Eigenschaften bewertet. Die Funktionalisierung führt nicht nur zur Bildung zusätzlicher Zustände innerhalb der halbleitenden Lücke, sondern auch zum Auftreten von lokalem Magnetismus. Der magnetische Grundzustand und die elektronische Struktur werden in Abhängigkeit von der molekularen Bedeckung, der Gitterrichtung der molekularen Adsorption und der Funktionalisierung des Moleküls untersucht. Darüber hinaus werden die Transporteigenschaften von Phosphoren-Korngrenzen unter uniaxialer Belastung
mit Hilfe der auf Dichtefunktionen basierenden Tight-Binding-Methode in Kombination mit der Landauer-Theorie untersucht. In beiden Korngrenzentypen nimmt die elektronische Bandlücke unter Dehnung ab, die jeweilige Wärmeleitfähigkeit wird jedoch nur schwach beeinflusst, trotz ziemlich starker Änderungen in der frequenzaufgelösten Phononentransmission. Die Kombination bei der Effekte führt zu einer Erhöhung der thermoelektrischen Leistungszahl in den Phosphorkorngrenzensystemen. Schließlich werden die thermoelektrischen Eigenschaften von Kohlenstoffnanoröhren-Peapod-Heterostrukturen untersucht und mit denen von reinen Nanoröhren verglichen, wobei auch die auf Dichtefunktionen basierende Tight-Binding-Methode und die Landauer-Theorie verwendet werden. Es wird festgestellt, dass die Fullereneinkapselung die Elektronen- und Phononentransporteigenschaften modifiziert und die Bildung von elektronischen Kanälen und die Unterdrückung von Schwingungsmoden bewirkt, was zu einer Verbesserung der thermoelektrischen Leistungszahl führt. Die Ergebnisse dieser Arbeit verdeutlichen das Potenzial der strategischen Manipulation und Optimierung niedrigdimensionaler Materialien zur Verbesserung ihrer einzigartigen elektronischen und thermischen Eigenschaften und zeigen vielversprechende Wege zur Verbesserung elektronischer und phononischer Bauteile auf.:ABSTRACT i
ZUSAMMENFASSUNG ii
ACKNOWLEDGEMENT iv
LIST OF FIGURES ix
LIST OF TERMS AND ABBREVIATIONS xviii
1 Introduction 1
1.1 Motivation 1
1.2 Objectives and outline 6
2 Computational Methods 8
2.1 Density Functional Theory 8
2.1.1 The Many-Body System Hamiltonian and the Born-Oppenheimer approximation 9
2.1.2 Thomas-Fermi-Dirac approximation model 10
2.1.3 The Hohenberg-Kohn theorems 12
2.1.4 The Kohn-Sham orbitals equations 13
2.1.5 Exchange-correlation functionals 15
2.2 Density Functional Based Tight Binding method 16
2.2.1 Tight-binding formalism 17
2.2.2 From DFT to DFTB 20
2.2.3 Parametrization 22
2.3 Atomistic Green’s functions 23
2.3.1 Non-Equilibrium Green’s functions for modeling electronic transmission 23
2.3.2 Non-equilibrium Green’s function for modeling thermal transmission 27
3 Tuning the electronic and magnetic properties through chemical functionalization
3.1 Introduction 33
3.1.1 Black phosphorus as a 2D material 33
3.1.2 Chemical Functionalization of low dimensional systems 35
3.1.3 Bipolar Magnetic Semiconductors 36
3.2 Computational approach 38
3.3 Interface effects in phosphorene by OH functionalization 39
3.3.1 Single molecule functionalization 39
3.3.2 Lattice selection 43
3.3.3 Coverage 45
3.4 Chiral functionalization effect in phosphorene 48
3.5 Functionalizing phosphorene towards BMS 51
3.6 Summary 53
4 Tuning transport properties through strain and grain bound-aries
4.1 Introduction 54
4.1.1 Strain in low dimensional materials 54
4.1.2 Grain boundaries 56
4.2 Computational approach 58
4.2.1 Molecular systems 58
4.2.2 Electron and phonon transport and thermoelectric figure of merit 58
4.3 Structural modification by strain in GB systems 60
4.4 Electronic structure modification by strain in GB systems 63
4.5 Thermal transport modification by strain in GB systems 65
4.6 Thermoelectric figure of merit of strained GB systems 68
4.7 Summary 71
5 Tuning transport properties through hybrid nanomaterials: CNT peapods 73
5.1 Introduction 73
5.1.1 Carbon-based nanostructures 73
5.1.2 CNT peapods as hybrid nanomaterials 76
5.2. Computational details 77
5.2.1 CNT peapod model 77
5.2.2 Quantum transport methodology 78
5.3 Structural properties of CNT peapods 79
5.4 Electronic properties of CNT peapods 80
5.5 Thermal properties of CNT peapods 83
5.6 Thermoelectronic properties of CNT peapods 85
5.7 Summary 88
6 Conclusions and outlook 91
Appendices
Appendix A Supplementary information to phosphorene functionalization
A.1 Spin resolved density of states of 1-OH system 96
A.2 Spin valve model 97
Appendix B Supplementary information to phosphorene grain boundaries 98
B.1 Projected Phonon Density of States in GB1 98
B.2 Thermoelectric transport properties of GB2 99
Appendix C Supplementary information to CNT peapods 101
C.1 Geometry optimization of CNT peapods with larger CNT diameter 101
C.2 Additional analysis of electron transport properties 102
C.3 Phonon band structure of different CNT structures 104
C.4 Additional analysis of thermoelectric performance 105
REFERENCES 105
LIST OF PUBLICATIONS 131
PRESENTATIONS 132
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:87656 |
| Date | 25 October 2023 |
| Creators | Rodriguez Mendez, Alvaro Gaspar |
| Contributors | Cuniberti, Gianaurelio, Breitkopf, Cornelia, Mujica, Vladimiro, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/updatedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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