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First principle-based Research on properties of twisted bilayer of Graphene and GaN / XIANG CAI

Swansea University Author: XIANG CAI

DOI (Published version): 10.23889/SUthesis.58747

Abstract

Since quantum theory was founded in 1920s, it has developed quite rapidly and led people to a new field that totally different from the classical ones. As the size of an object decrease to a certain level, the classical physical law would be invalid and quantum mechanics would become the ruler of ob...

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Published: Swansea 2021
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
Supervisor: Li, Lijie
URI: https://cronfa.swan.ac.uk/Record/cronfa58747
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first_indexed 2021-11-22T14:13:33Z
last_indexed 2021-11-23T04:24:21Z
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spelling 2021-11-22T14:54:59.6647220 v2 58747 2021-11-22 First principle-based Research on properties of twisted bilayer of Graphene and GaN 938ad1333be734797afc721407afc9f1 XIANG CAI XIANG CAI true false 2021-11-22 Since quantum theory was founded in 1920s, it has developed quite rapidly and led people to a new field that totally different from the classical ones. As the size of an object decrease to a certain level, the classical physical law would be invalid and quantum mechanics would become the ruler of object behaviors. The property under quantum mechanics achieves functions that never been seen before. So, scientist would invent new materials and devices with properties that never found before. This is the reason that new materials and devices have been emerging due to vast developments in nanotechnologies. The project of my PHD research in four years is to research and analysis the property of nano semiconductor materials. In this thesis, there are mainly four parts. The first part is Introduction. In this part the basic concepts and related information would be listed. The second part is the first project that guide me to the further study. This project is set to simulate the electronic transport in quantum region based on the Schrodinger equation for random shaped energy barriers, which is very basic to quantum mechanics. The method of simulation is matlab coding. The simulation will help in understanding the concept of quantum field and applications in design and analysis of nanometer scale devices and systems. The third part is my first paper. In this paper I cooperate with my workmate Shuo Deng and we investigate the electron transport and thermoelectric property of twisted bilayer graphene nanoribbon junction (TBGNRJ) in 0o, 21.8o, 38.2o and 60o rotation angles by first principles calculation with Landauer-Buttiker and Boltzmann theories. It is found that TBGNRJs exhibit a strong reduction of thermal conductance compared with the single graphene nanoribbon (GNR) and negative differential resistance (NDR) in 21.8 o and 38.2 o rotation angles under ±0.2 V bias voltage. More importantly, three peak ZT values of 2.0, 2.7 and 6.1 can be achieved in the 21.8o rotation angle at 300K. The outstanding ZT values of TBGNRJs are interpreted as the combination of the reduced thermal conductivity and enhanced electrical conductivity at optimized angles. The fourth part is my second paper. In this paper I report electronic and optical properties of the GaN bilayer structures that are rotated in plane at several optimized rotation angles by using the density functional theory method. For the aim of maintaining the structural stability and using a small cell size, the twisting angles of the GaN bilayer structures are optimized to be 27.8°, 38.2° and 46.8° using the crystal matching theory. The last part is conclusion, possible further study and acknowledgement. E-Thesis Swansea 22 11 2021 2021-11-22 10.23889/SUthesis.58747 COLLEGE NANME COLLEGE CODE Swansea University Li, Lijie Doctoral Ph.D 2021-11-22T14:54:59.6647220 2021-11-22T14:10:19.0912371 Faculty of Science and Engineering School of Engineering and Applied Sciences - Uncategorised XIANG CAI 1 58747__21630__60e37e7f586b45048ebb8bdcd9363a22.pdf Cai_Xiang_PhD_Thesis_Final_Redacted_Signature.pdf 2021-11-22T14:46:21.8757092 Output 5370625 application/pdf E-Thesis – open access true Copyright: The author, Xiang Cai, 2021. true eng
title First principle-based Research on properties of twisted bilayer of Graphene and GaN
spellingShingle First principle-based Research on properties of twisted bilayer of Graphene and GaN
XIANG CAI
title_short First principle-based Research on properties of twisted bilayer of Graphene and GaN
title_full First principle-based Research on properties of twisted bilayer of Graphene and GaN
title_fullStr First principle-based Research on properties of twisted bilayer of Graphene and GaN
title_full_unstemmed First principle-based Research on properties of twisted bilayer of Graphene and GaN
title_sort First principle-based Research on properties of twisted bilayer of Graphene and GaN
author_id_str_mv 938ad1333be734797afc721407afc9f1
author_id_fullname_str_mv 938ad1333be734797afc721407afc9f1_***_XIANG CAI
author XIANG CAI
author2 XIANG CAI
format E-Thesis
publishDate 2021
institution Swansea University
doi_str_mv 10.23889/SUthesis.58747
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Engineering and Applied Sciences - Uncategorised{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Uncategorised
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description Since quantum theory was founded in 1920s, it has developed quite rapidly and led people to a new field that totally different from the classical ones. As the size of an object decrease to a certain level, the classical physical law would be invalid and quantum mechanics would become the ruler of object behaviors. The property under quantum mechanics achieves functions that never been seen before. So, scientist would invent new materials and devices with properties that never found before. This is the reason that new materials and devices have been emerging due to vast developments in nanotechnologies. The project of my PHD research in four years is to research and analysis the property of nano semiconductor materials. In this thesis, there are mainly four parts. The first part is Introduction. In this part the basic concepts and related information would be listed. The second part is the first project that guide me to the further study. This project is set to simulate the electronic transport in quantum region based on the Schrodinger equation for random shaped energy barriers, which is very basic to quantum mechanics. The method of simulation is matlab coding. The simulation will help in understanding the concept of quantum field and applications in design and analysis of nanometer scale devices and systems. The third part is my first paper. In this paper I cooperate with my workmate Shuo Deng and we investigate the electron transport and thermoelectric property of twisted bilayer graphene nanoribbon junction (TBGNRJ) in 0o, 21.8o, 38.2o and 60o rotation angles by first principles calculation with Landauer-Buttiker and Boltzmann theories. It is found that TBGNRJs exhibit a strong reduction of thermal conductance compared with the single graphene nanoribbon (GNR) and negative differential resistance (NDR) in 21.8 o and 38.2 o rotation angles under ±0.2 V bias voltage. More importantly, three peak ZT values of 2.0, 2.7 and 6.1 can be achieved in the 21.8o rotation angle at 300K. The outstanding ZT values of TBGNRJs are interpreted as the combination of the reduced thermal conductivity and enhanced electrical conductivity at optimized angles. The fourth part is my second paper. In this paper I report electronic and optical properties of the GaN bilayer structures that are rotated in plane at several optimized rotation angles by using the density functional theory method. For the aim of maintaining the structural stability and using a small cell size, the twisting angles of the GaN bilayer structures are optimized to be 27.8°, 38.2° and 46.8° using the crystal matching theory. The last part is conclusion, possible further study and acknowledgement.
published_date 2021-11-22T04:15:31Z
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score 11.012678

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