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Investigation of light-induced carrier behaviors in monolayer MoS₂ with Kelvin probe force microscopy
- Author(s)
- 임웅빈
- Advisor
- 박지용
- Department
- 일반대학원 에너지시스템학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2021-08
- Language
- eng
- Keyword
- KPFM; MoS; Photogating
- Alternative Abstract
- In this thesis, we analyzed the properties of 1D and 2D nanomaterials using Kelvin Probe Force Microscopy (KPFM) and Atomic Force Microscopy (AFM), which are based on Scanning Probe Microscopy (SPM). And also, various nanomaterials and nanodevices required for the research were synthesized and fabricated. First, the surface potential distribution of monolayer Molybdenum disulfide (MoS₂) flake was mapped by KPFM measurement. Typically, the photoresponsivity of monolayer MoS₂ increases under light illumination. By applying these properties to a photonic device, the distribution of charges in monolayer MoS₂ flake due to illumination was investigated. When light is irradiated on monolayer MoS₂, the work function increase, and the observed change in the surface potential distribution may be related to charge carrier generation, diffusion, and recombination in MoS₂ under light illumination. The polarity of surface potential changes points to the trapping of photogenerated holes at the interface between MoS₂ and the substrate as a major mechanism for the photoresponse in monolayer MoS₂. The temporal response of the surface potential changes is compatible with the time constant of monolayer MoS₂ photodetectors. We also investigate spatial inhomogeneity in the surface potential changes at the low light intensity that is related to the defect distribution in MoS₂. In addition, we observed that the effects of MoS₂/SiO₂ interfacial separation, passivation and P-doping were enhanced by chemical treatment. Finally, we measured the photoresponse of MoS₂ in a nitrogen environment to confirm the effects of adsorption and photodesorption of water or oxygen molecules. Next, single-walled carbon nanotube (SWCNTs) and multi-walled carbon nanotube (MWCNTs) devices embedding a polymer matrix were measured using Atomic Force Microscopy (AFM). We investigate the interaction of SWCNTs and MWCNTs embedded in a polymer matrix [Poly(methyl methacrylate) (PMMA)] with Ar plasma, which results in the formation of PMMA nanostructures as CNTs act as an etching mask. Due to the difference in the Ar ion sputtering yields between the CNTs and PMMA, PMMA lines with a width similar to that of the CNTs (for SWCNTs) or as high as 80 nm (for MWCNTs) could be obtained. After repeatedly exposing the CNT/PMMA film to Ar plasma, IV characteristics and Raman spectrum changes were investigated to confirm the etching mechanism. We follow the etching process by investigating changes in IV characteristics and Raman spectra of CNTs after each exposure to Ar plasma, which shows progressive defect generations in CNTs while they maintain structural integrity long enough to act as an etching mask for PMMA underneath. The PMMA nanostructured patterns can be transferred to other polymer substrates, such as nanoimprinting.
- Fulltext
- Appears in Collections:
- Graduate School of Ajou University > Department of Energy Systems > 4. Theses(Ph.D)
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