Twist Angle-Dependent Transport Properties and applications of Twisted Bilayer Graphene = Twisted bilayer graphene의 twist angle에 따른 전하 수송 특성 및 그 응용

다국어 초록 (Multilingual Abstract)

Two-dimensional (2D) materials research is advancing through the development of more complex heterostructures with tailored functions. Lattice constant and crystal orientation within these structures play a critical role in determining their electronic and chemical properties. Twisted bilayer graphene (tBLG), with its tunable electronic and chemical characteristics arising from the relative twist angle between its two graphene layers, offers valuable insights in this context.
This dissertation investigates the optimization and applicability of tBLG using excimer UV treatment. We systematically studied the influence of twist angle (0°-30°) on the electrical transport properties of tBLG and tBLG field-effect transistors (FETs). Notably, tBLG with a high twist angle (9°-30°) exhibited enhanced conductivity and mobility compared to its low twist angle counterpart (0°-9°) Additionally Scanning Kelvin Probe Microscopy (SKPM) confirmed work function values consistent with theoretical calculations, validating the observed trends. These finding provide a foundation for understanding how twist angle influences the functionality of tBLG devices.
Furthermore, we investigated the complex interplay between various fabrication techniques and subsequent UV treatment on tBLG. Our findings reveal a multifaceted relationship between twist angle, interlayer interaction, stacking configuration, surface oxidation, and ultimately, electronic transport properties. Notably, UV treatment offers a promising avenue for engineering surface properties, potentially leading to tailored functionalities in future tBLG-based devices.
This comprehensive understanding of the relationship between fabrication methods, UV treatment, and resulting properties provides opportunities for designing and optimizing tBLG-based devices with tailored functionalities for future electronic applications.

국문 초록 (Abstract)

2차원 (2D) 물질 연구는 점점 더 다양하고 복잡한 기능성 물질의 이종 구조 (heterostructure)의 탐구를 통해 빠르게 발전하고 있다. 이러한 이종 구조에서 격자 상수 (lattice constant)와 결정방향 (crystal orientation)은 전자 및 화학적 특성을 결정하는 중요한 역할을 한다. Twisted Bilayer Graphene (tBLG)의 연구는 이러한 구조에서 동일한 격자구조를 가지지만 두 그래핀 층 사이의 twist angle에 따른 조절가능한 전자 및 화학적 특성을 제공한다.
이 학위논문에서는 엑시머 UV처리를 사용하여 tBLG의 최적화 및 응용 가능성을 확인하였다. 우리는 0º ~ 30º 범위에서 twist angle이 tBLG의 전하수송특성에 미치는 영향을 체계적으로 조사하였다. 또한 Moiré pattern의 영향을 받는 tBLG 전계효과 트랜지스터 (FET)의 전기적 특성을 조사했다. 주목할만한 점으로는 높은 twist angle (9º ~ 30º)의 tBLG는 낮은 twist angle (0º ~ 9º)의 tBLG에 비해 향상된 전기전도도 및 전하 이동성을 나타냈다. 또한 Scanning Kelvin Probe Microscopy (SKPM)을 통해 얻은 일함수와 이론적계산을 통해 얻은 일함수를 비교하여 동일한 경향을 확인했다. 이러한 연구결과는 twist angle이 tBLG FET 소자의 기능에 어떤 영향을 미치는지 이해하는 기초가 될 것이다.
표면 기능화 연구는 Bilayer graphene (BLG)의 계층 상호작용 연구에 중요하다. 이 연구는 다양한 BLG 제작 기술과 이후 UV 처리 사이의 복합적인 상호작용을 제시하였다. 이 발견은 twist angle, 계층간 상호작용, 적층 구성, 표면 산화 및 전자전달 특성 사이의 다면적인 관계를 보여준다. 특히, UV 처리는 표면 특성 엔지니어링을 위한 방법을 제공하여 잠재적으로 향후 tBLG 기반 장치의 맞춤형 기능으로 이어질 수 있다. 이러한 tBLG 제조방법, UV 처리 및 결과들은 미래 전자응용 분야를 위한 맞춤형 기능을 갖춘 tBLG 기반 소자를 최적화 하기위한 가능성을 시사한다.

목차 (Table of Contents)

• List of Figures ⅲ
• ABSTRACT ⅴ
• Chapter 1. Introduction 1
• 1.1. Two-dimensional (2D) materials and heterostructure 1
• 1.2. Twisted Bilayer Graphene (tBLG) 4
• 1.3. UV assisted surface oxidation of graphene 7
• Chapter 2. Experimental methods 10
• 2.1. Fabrication methods twisted bilayer graphene (tLBG) 10
• 2.1.1. Mechanical exfoliation 10
• 2.1.2. Chemical Vapor Deposition (CVD) growth of graphene 13
• 2.1.3. vertical stacking method 17
• 2.2. Characterization 19
• 2.2.1. Raman spectroscopy 19
• 2.2.2. 2-probe measurement 21
• 2.2.3. scanning kelvin probe microscopy (SKPM) 23
• Chapter 3. Twist angle-dependent transport properties of twisted bilayer
• graphene 25
• 3.1. Introduction 25
• 3.2. tBLG preparation and field effect transistor(FET) device fabrication 27
• 3.2.1. sample preparation 27
• 3.2.2. Field effect transistor (FET) fabrication 30
• 3.3. Raman spectra feature-induced twist angle classification 34
• 3.3.1. Raman spectroscopy measurement 34
• 3.3.2. twist angle characterization by Raman information 37
• 3.4. Twist-angle dependent electrical properties 43
• 3.4.1. Gate dependence of I-V properties 43
• 3.4.2. Twist angle dependency of transport characteristics of tBLG 46
• 3.5. Twist-angle dependent work function characteristics 49
• 3.5.1. Surface potential properties of tBLG 49
• 3.5.2. Surface potential analysis and work function calculation 52
• 3.5.3. Work function and fermi level modulations 55
• 3.6. Summary 58
• Chapter 4. Surface oxidation effects of twisted bilayer graphene 59
• 4.1. Introduction 59
• 4.2. Sample preparation 61
• 4.3. Surface oxidation by UV treatment 64
• 4.3.1. BLG produced by mechanical exfoliation 65
• 4.3.2. tBLG produced by CVD method 67
• 4.3.3. tBLG produced by vertical stacking 70
• 4.4. Prolonged UV oxidation and laser reduction 72
• 4.5. Electronic transport characteristics in UV oxidized tBLG 76
• 4.6. Summary 78
• Chapter 5. Conclusion 79
• References 81
• Appendix(option) 93
• Abstract (in Korean) 95

참고문헌 (Reference)

1. Van der Waals heterostructures, Geim, A. K., Grigorieva, I. V., 499, 419-425 DOI: https://doi. org/10.1038/nature12385, , 2013

2. The work function of few-layer graphene, Van Haesendonck, C., Leenaerts, O., Peeters, F. M., Volodin, A., Partoens, B., 29, 035003 Doi: https://doi. org/10.1088/0953-8984/29/3/035003, , 2017

3. Van der Waals heterostructures and devices, Huang, Yu, H., Liu, Y., Weiss, N. O., Duan, X, Duan, X., Cheng, H.-C., 1, 16042 DOI: https://doi. org/10.1038/natrevmats.2016.42, , 2016

4. Moiré bands in twisted double-layer graphene, MacDonald, A. H., Bistritzer, R., 108, 12233-12237. DOI: https://doi. org/10.1073/pnas.1108174108, , 2011

5. Raman Spectroscopy in Graphene Related Systems, Dresselhaus, G., Saito, R., Jorio, A., Dresselhaus, M. S., Wiley-VCH Verlag GmbH Berlin DOI https://doi. org/10.1002/9783527632695, , 2011

6. 2D materials and van der Waals heterostructures, Novoselov, K. S., Castro Neto, A. H., Carvalho, A., Geim, A. K., 353, aac9439 DOI: https://doi. org/10.1126/science. aac9439, , 2016

7. Synthesis of Large-Area Single-Crystal Graphene, Luo, D., Wang, B., Wang, M., Ruoff, R. S., 3, 15-33 DOI: https://doi. org/10.1016/j. trechm.2020.10.009, , 2021

8. Doping effect in graphene-graphene oxide interlayer, Park, M., Choi, J. S., Kim, J. H., Haidari, M. M., Lee, H., Kim, H., 10, 8258 DOI: https://doi. org/10.1038/s41598-020-65263-y, , 2020

9. Effect of strain on the reactivity of graphene films, Kropp, T., Mavrikakis, M., J. Catal. 390, 67-71 DOI: https://doi. org/10.1016/j. jcat.2020.07.030, , 2020

10. Moiré Flat Bands in Twisted Double Bilayer Graphene, Wu, Q., Yazyev, O. V., Kruchkov, A. J., Haddadi, F., 20, 2410-2415 DOI https://doi. org/10.1021/acs. nanolett.9b05117, , 2020

11. Twistronics: a turning point in 2D quantum materials, Hennighausen, Z., Kar, S., Electron. Struct. 3, 014004 DOI https://doi. org/10.1088/2516-1075/abd957, , 2021

12. Electric Field Effect in Atomically Thin Carbon Films, Dubonos, S. V., Novoselov, K. S., Morozov, S. V., Firsov, A. A., Zhang, Y., Geim, A. K., Grigorieva, I. V., Science 306, 666-669 DOI: https://doi. org/10.1126/science.1102896, , 2004

13. Efficient pseudopotentials for plane-wave calculations, Troullier, N., Martins, J. L., 43 DOI: https://doi. org/10.1103/PhysRevB.43.1993, , 1993

14. Facile Dry Surface Cleaning of Graphene by UV Treatment, Kim, J. H., Yu, Y.-J., Kim, H., Haidari, M. M., Park, J., Choi, J. S., 72, 1045-1051 DOI: https://doi. org/10.3938/jkps.72.1045, , 2018

15. Ground State of the Electron Gas by a Stochastic Method, Ceperley, D. M., Alder, B. J., 45, 566 DOI: https://doi. org/10.1103/PhysRevLett.45.566, , 1980

16. Electronic properties of bilayer and multilayer graphene, Castro Neto, A. H., Guinea, F., Nilsson, J., Peres, N. M. R., 78, 045405 DOI: https://doi. org/10.1103/PhysRevB.78.045405, , 2008

17. Fractal Landau-Level Spectra in Twisted Bilayer Graphene, Liu, F., Chou, M. Y., Wang, Z. F., 12, 3833-3838 DOI https://doi. org/10.1021/nl301794t, , 2012

18. Nature of Interaction between Epoxides in Graphene Oxide, Pancharatna, P. D., Jhaa, G., Balakrishnarajan, M. M., 124, 1695-1703 DOI: https://doi. org/10.1021/acs. jpcc.9b10262, , 2020

19. Disorder in van der Waals heterostructures of 2D materials, Hone, J., Rhodes, D., Chae, S. H., Ribeiro-Palau, R., 18, 541-549 DOI https://doi. org/10.1038/s41563-019-0366-8, , 2019

20. Tuning the Graphene Work Function by Electric Field Effect, Yu, Y.-J., Kim, K. S., Zhao, Y., Ryu, S., Brus, L. E., Kim, P., 9, 3430-3434 DOI: https://doi. org/10.1021/nl901572a, , 2009

21. Localization of Dirac Electrons in Rotated Graphene Bilayer, Laissardière, G. T., Magaud, L., Mayou, D., 10, 804-808 DOI: https://doi. org/10.5772/intechopen.106058, , 2010

22. Facile fabrication of properties-controllable graphene sheet, Kim, J. S., Cho, H., Jeong, H. Y., Choi, C.-G., Choi, J. S., Choi, H., Kim, K.-C., Yu, Y.-J., Kim, J. T., 6, 24525 DOI: https://doi. org/10.1038/srep24525, , 2016

23. Electronic Hybridization of Large-Area Stacked Graphene Films, Robinson, J. T., Long, J. P., Culbertson, J. C., Beechem, T. E., Diaconescu, C. B., Ohta, T., Schmucker, S. W., Friedman, A. L., 7, 637-644 DOI: https://doi. org/10.1021/nn304834p, , 2013

24. High-Precision Twist-Controlled Bilayer and Trilayer Graphene, Chen, Y., Xin, W., Chen, X.-D., Tian, J.-G., Jiang, W.-S., 28, 2563-2570 DOI: https://doi. org/10.1002/adma.201505129, , 2016

25. Boron nitride substrates for high-quality graphene electronics, Kim, P., Young, A. F., Wang, Sorgenfrei, S., Hone, J., Taniguchi, T., Lee, C., Dean, C. R., Watanabe, K., Shepard, K. L., Meric, I., 5, 722-726, , 2010

26. Kelvin probe force microscopy of semiconductor surface defects, Sadewasser, S., Rosenwaks, Y., Glatzel, Th., Shikler, R., 70, 085320 DOI: https://doi. org/10.1103/PhysRevB.70.085320, , 2004

27. Chemical Vapor Deposition Synthesis of Graphene on Copper Foils, Campos-Delgado, J., Hernández, A. R. R., Cruz, A. G., In Graphene-A Wonder Material for Scientists and Engineers; IntechOpen London United Kingdom, DOI: https://doi. org/10.5772/intechopen.106058, , 2022

28. Observation of Van Hove singularities in twisted graphene layers, Andrei, E. Y., Kong, J., Renina, A., Luican, A., Li, G., Lopes dos Santos, J, M. B., Castro Neto, A. H., 6, 109-113 DOI:https://doi. org/10.1038/nphys1463, , 2010

29. Developing Graphene-Based Moiré Heterostructures for Twistronics, Wang, L., Liu, M., Yu, G., 9, 2103170 DOI: https://doi. org/10.1002/advs.202103170, , 2022

30. Density-Functional method for very large system with LCAO basis sets, Soler, J. M., Sánchez-Portal, D., Ordejón, Artacho, E., 65, 453-461 DOI: https://doi. org/10.1002/(SICI)1097-461X(1997)65:5<453::AID-QUA9>3.0. CO;2-V, , 1997

31. A review on mechanical exfoliation for scalable production of graphene, Shen, Z., Yi, M., A 3, 11700-11715 DOI https://doi. org/10.1039/C5TA00252D, , 2015

32. Unconventional superconductivity in magic-angle graphene superlattices, Watanabe, K., Jarillo-Herrero, P., Fatemi, V., Taniguchi, T., Kaxiras, E., Cao, Y., Nature 556, 43-50 DOI: https://doi. org/10.1038/nature26160, , 2018

33. Band gap of reduced graphene oxide tuned by controlling functional groups, Podkolzin, S. G., Lee, W., Jin, Y., Zhen, Y., C 8, 4885-4894 DOI: https://doi. org/10.1039/C9TC07063J, , 2020

34. Flat bands in slightly twisted bilayer graphene: Tight-binding calculations, Correa, J. D., Pacheco, V. M., Barticevic, Z., Morell, E. S., 82, 121407(R) DOI: https://doi. org/10.1103/PhysRevB.82.121407, , 2010

35. Chapter 1 – Two-Dimensional Nanomaterials: Crystal Structure and Synthesis, Parvez, K., In Biomedical Applications of Graphene and 2D Nanomaterials; Micro and Nano Technologies; Elsevier Amsterdam The Netherlands pp 1-25. DOI: https://doi. org/10.1016/B978-0-12-815889-0.00001-5, , 2019

36. Functionalization of graphene layers and advancements in device applications, Lee, S., Mudusu, D., Nandanapalli K. R., carbon 152, 954-985 DOI: https://doi. org/10.1016/j. carbon.2019.06.081, , 2019

37. Angle-Dependent van Hove Singularities in a Slightly Twisted Graphene Bilayer, He, L., Chu, Z,-D., Meng, L., Liu, M., Dou, R.-F., Zhang, Y., Yan, W., Feng, L., Liu, Z., Nie, J.-C., 109 126801 (2012). DOI: https://doi. org/10.1103/PhysRevLett.109.126801, , 2012

38. Two-dimensional heterostructures: fabrication, characterization, and application, Fang, Z., Liu, F., Fu, W., Zhou, W., Liu, Z., Wang, H., Naoscale 6, 12250-12272 DOI: https://doi. org/10.1039/C4NR03435J, , 2014

39. Role of Hydrogen in Graphene Chemical Vapor Deposition Growth on a Copper Surface, Ding, F., Zhang, X., Wang, Lu, Xin, J., Yakobson, B. I., 136, 3040-3047 DOI: https://doi. org/10.1021/ja405499x, , 2014

40. Twisted Bilayer Graphene: Interlayer Configuration and Magnetotransport Signatures, Haug, R. J., Schmidt, H., Smirnov, D., Rode, J. C., Belke, C., 529, 1700025 DOI https://doi. org/10.1002/andp.201700025, , 2017

41. Layer number identification of CVD-grown multilayer graphene using Si peak analysis, Kim, H., Choi, J. S., Yu, Y.-J., No, Y.-S., Choi, H. K., Kim, J.-S., Choi, C.-G., 8, 571 DOI: https://doi. org/10.1038/s41598-017-19084-1, , 2018

42. Two-dimensional crystals-based heterostructures: materials with tailored properties, Novoselov, K. S., Castro Neto, A. H., 2012 014006 DOI: https://doi. org/10.1088/0031-8949/2012/T146/014006, , 2012

43. Layer-by-layer assembly of two-dimensional materials into wafer-scale heterostructure, Lee, K.-H., Muller, D. A., Han, Y., Gao, H., Kang, K., Park, J., Xie. S., Nature 550, 229-122 DOI https://doi. org/10.1038/nature23905, , 2017

44. Chemical Vapor Deposition of Graphene on Cu-Ni Alloys: The Impact of Carbon Solubility, Derby, B., Kinloch, I. A., Al-Hilfi, S. H., Coatings 11, 892. DOI: https://doi. org/10.3390/coatings11080892, , 2021

45. Direct Measurement of the Fermi Energy in Graphene Using a Double-Layer Heterostructure, Banerjee, S. K., Fallahazad, B., Yao, Z., Jo, I., Tutuc, E., Kim, S., Ferrer, D. A., Dillen, D. C., 108, 116404 DOI: https://doi. org/10.1103/PhysRevLett.108.116404, , 2012

46. Comparison of mobility extraction methods based on filed-effect measurements for graphene, Peng, L.-M., Zhong, H., Zhang, Z., Xu, H., Qiu, C., AIP Adv. 5, 057136. DOI: https://doi. org/10.1063/1.4921400, , 2015

47. Thermal reversibility in electrical characteristics of ultraviolet/ozone-treated graphene, Mulyana, Y., Koh, S., Horita, M., Uraoka, Y., Ishikawa, Y., 103, 063107 DOI: https://doi. org/10.1063/1.4818329, , 2013

48. Specific stacking angles of bilayer graphene grown on atomic flat and -stepped Cu surfaces, Park, Y., Choi, H. C., Cho, H., Kim, S., Kim, T.-H., Ahn, T., Npj 2D Mater. Appl. 4, 35 DOI: https://doi. org/10.1021/nn402830f, , 2020

49. Relaxation of moiré pattern for slightly misaligned identical lattice: graphene on graphite, Schuring, A., van Wijk, M. M., Katsnelson, M. I., Fasolino, A., 2D Mater. 2, 034010 DOI: https://doi. org/10.1088/2053-1583/2/3/034010, , 2015

50. Atomic corrugation and electron localization due to Moiré patterns in twisted bilayer graphenes, Oshiyama, A., Furuya, S., Iwata, J.-I., Uchida, K., 90, 155451 DOI: https://doi. org/10.1103/PhysRevB.90.155451, , 2014

51. Orbital diamagnetism in multilayer graphene: Systematic stucdy with the effective mass approximation, Koshino, M., Ando, T., 76, 085425 DOI: https://doi. org/10.1103/PhysRevB.76.085425, , 2007

52. DC conductivity of twisted bilayer graphene: Angle-dependent transport properties and effects of disorder, Anđelković, M., Peeters, F. M., Covaci, L., Phys. Rev. Materials 2, 034004 DOI: https://doi. org/10.1103/PhysRevMaterials.2.034004, , 2018

53. Quasicrystalline 30º twisted bilayer graphene as incommensurate supper lattice with strong interlayer coupling, Zhou, S., Wang, E., Bao, C., Yao, W., 115, 6928-6933 DOI https://doi. org/10.1073/pnas.1720865115, , 2018

54. Twistronics Manupulating the electronic properties of two-dimensional layered structures through their twist angle, Cazeaux, P., Carr, S., Fang, S., Luskin, M., Massatt, D., Kaxiras, E., 95, 075420 DOI https://doi. org/10.1103/PhysRevB.95.075420, , 2017

55. Theory of double resonant Raman spectra in graphene: Intensity and line shape of defect induced and two- phonon bands, Venezuela, P., Lazzeri, M., Mauri, F., 84, 035433 DOI: https://doi. org/10.1103/PhysRevB.84.035433, , 2011

56. Experimental evidence for orbital magnetic momonts generated by moiré-scale current loops in twisted bilayer graphene, Liu, J., Zhang, Y., He, L., Li, S.-Y., Ren, Y.-N., Dai, X., 102, 121406(R) DOI: https://doi. org/10.1103/PhysRevB.102.121406, , 2020

57. A Primer on twistronics: a massless Dirac fermions journey to moiré patterns and flat bands in twisted bilayer graphene, Aggarwal, D., Narula, R., Ghosh, S., 35, 143001 DOI: https://doi. org/10.1088/1361-648X/acb984, , 2022

58. Reversible Oxidation of Graphene Through Ultraviolet/Ozone Treatment and Its Nonthermal Reduction through Ultraviolet Irradiation, Uraoka, Y., Mulyana, Y., Uenuma, M., Ishikawa, Y., 118, 27372-27381 DOI: https://doi. org/10.1021/jp508026g, , 2014

59. Machine Learning Determination of the Twist Angle of Bilayer Graphene by Raman Spectroscopy: Implications for van der Waals Heterostructures, Solís-Ferenández, P., Ago, H., 5, 1356-1366 DOI: https://doi. org/10.1021/acsanm.1c03928, , 2022

60. Variations in the work function of doped single- and few-layer graphene assessed by Kelvin probe force microscopy and density functional theory, Gava, P., Güttinger, F., Saitta, A. M., Stemmer, A., Mauri, F., Ziegler, D., Lazzeri, M., Wirtz, L., Stampfer, C., 83, 235434 (2011). DOI: https://doi. org/10.1103/PhysRevB.83.235434, , 2011

61. The effects of hydroxide and epoxide functional groups on the mechanical properties of graphene oxide and its failure mechanism by molecular dynamics simulations, Sun, Y., Bao, H., Yang, Z., Tang, X., Ma, F., RCS Adv. 10, 29610-29617 DOI: https://doi. org/10.1039/D0RA04881J, , 2020