Local electrical characterizations of nanomaterials with scanning probe microscopy
Local electrical characterizations of nanomaterials with scanning probe microscopy
- 주제(키워드) single-walled carbon nanotube , zinc oxide nanowire , graphene oxide , electrostatic force microscopy , scanning gate microscopy
- 발행기관 아주대학교
- 지도교수 박지용
- 발행년도 2016
- 학위수여년월 2016. 2
- 학위명 박사
- 학과 및 전공 일반대학원 에너지시스템학과
- 실제URI http://www.dcollection.net/handler/ajou/000000022137
- 본문언어 영어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
In this thesis, local electrical characterizations of nanomaterials and nanomaterial-based devices were carried out using scanning-probe-microscopy (SPM)-based techniques. For the experiments, various nanomaterials and nanodevices were synthesized and fabricated. Electrostatic force microscopy (EFM) and scanning gate microscopy (SGM) with a conventional electrical measurement, like IV characteristics, were employed to analyze the nanomaterials and the nanodevices. Firstly, operation of single-walled carbon nanotube (SWCNT) network FET devices was investigated using ac-EFM and SGM measurements. The device in this experiment has the apparent on-off ratio of 104, which is expected to be a FET based on semiconducting SWCNTs. However, SGM measurements show that localized segments of ~600 nm determines semiconducting characteristics of the whole device, and ac-EFM reveal that resistances are composed of resistances of electrode-SWCNT, SWCNT-SWCNT, and SWCNT segments with a kinked defect. Therefore, ac-EFM and SGM demonstrated the transfer characteristics of 1D network devices in nanoscale. Taking advantage of ac-EFM and SGM in nanoscale, we investigated the effects of nitric acid vapor treatment, as a doping method, through SWCNT-network FET devices. From SGM measurements before and after exposure of nitric acid vapor, p-type doping of the treatment is confirmed in nanoscale. Furthermore, additional current paths in metallic SWCNT network region after nitric acid vapor treatment are seen in ac-EFM images. As a result, nitric acid treatment can affect p-type doping and reduction of SWCNT-SWCNT resistances in the SWNCT networks. In dielectrophoretically-deposited CNT devices, SGM measurements with IV characteristics confirm metallic CNTs are well-separated from SWCNT dispersion because there are no gate responses in both IV and SGM measurements. Also, resistance of these DEP-deposited CNT devices is affected by connection among CNTs rather than at electrode-CNT junctions. Although EFM measurement provide relative differences of voltage in nanomaterials and nanodevices, quantitative analysis is, basically, difficult due to the local capacitive term in the EFM signal. Thus, we demonstrate a calibration procedure to obtain quantitative local voltage distributions of 1D-nanodevices. As voltage profiles are compared to IV characteristics, local resistances of electrode-SWCNT, electrode-ZnO nanowire, and defect in a SWCNT in the nanodevices are calculated. Moreover, photo-induced carrier concentrations of ZnO nanowires are also extracted from these results. Finally, 2D conductance mapping was carried out using EFM phase measurements. Graphene oxide is intrinsically an insulator. However, its conductivity can be recovered by reduction process. We find homogeneous electrical state of reduced graphene oxide is related to higher conductivity from EFM measurements in thermal and chemical reduction, and this result is confirmed again by combining EFM measurements and IV characteristics. In conclusion, EFM and SGM measurements can visualize electrical informations, such as electric potential differences, local perturbations’, and local conductivities, of the nanomaterials and the nanodevices, and these local measurements with nanoscale informations can compensate conventional characterizing tools for bulk samples. In addition, quantitative analysis through calibration of EFM images provides much detailed informations in nanoscale of the nanodevies. In even 2D nanomaterials, local conductance mapping is successfully carried out. Therefore, EFM and SGM techniques will be actively applied to various fields related to nanoscience and nanotechnology.
more목차
Chapter 1 Introduction 1
Chapter 2 Theoretical background 3
2.1 Field-effect transistors and nanomaterials 3
2.2 1D- and 2D-nanomaterials 9
2.2.1 Single-walled carbon nanotube 9
2.2.2 Zinc oxide nanowire 14
2.2.3 Graphene oxide and its reduction 17
2.3 Atomic force microscopy 19
2.3.1 Brief history of atomic force microscopy 19
2.3.2 Electrical characterizations using AFM 20
2.3.3 Principles of AFM 21
2.3.4 Setup and operation modes of AFM 21
2.3.5 Principle of electrostatic force microscopy (EFM) 28
2.3.6 Principle of scanning gate microscopy (SGM) 30
Chapter 3 Local investigations of SWCNT-network devices using EFM and SGM 32
3.1 Introduction 32
3.2 Sample preparation 33
3.3 Experimental results and discussion 34
3.3.1 Investigating operation of SWCNT-network FETs 34
3.3.2 Local investigation of nitric acid vapor treatments on SWCNT networks 42
3.4 Conclusion 50
Chapter 4 Local characterizations of dielectrophoretically deposited CNTs 52
4.1 Introduction 52
4.2 Sample preparation 53
4.3 Experimental results and discussion 53
4.4 Conclusion 60
Chapter 5 Quantitative voltage profile inside 1D-nanomaterial devices 61
5.1 Introduction 61
5.2 Sample preparation 62
5.3 Experimental results and discussion 62
5.4 Conclusion 72
Chapter 6 Local conductance mapping of graphene oxide and reduced-graphene oxide during reduction process 74
6.1 Introduction 74
6.2 Sample preparation 75
6.3 Experimental results and discussion 75
6.4 Conclusion 94
Chapter 7 Conclusion 95
Bibliography/Reference 97
Publication list 107
