Title Page
Contents
ABSTRACT 11
Ⅰ. Introduction 14
Ⅱ. Theoretical background 15
1. The properties of molybdenum disulfide (MoS₂) 15
2. Metal-organic polyhedra (MOP) 17
3. Gas-sensing mechanism for 2D MoS₂ 19
4. Gas sensitivity 20
5. Mobility and Carrier concentrations 21
5.1. Mobility 21
5.2. Carrier concentrations 22
Ⅲ. Experimental method 23
1. Mechanical exfoliation 23
2. Raman Spectrometer 25
2.1. Raman Spectroscopy 26
2.2. Photoluminescence (PL) Spectroscopy 30
3. E-Beam Lithography (EBL) 34
4. Atomic Force Microscope (AFM) 36
5. Wire Bonding 38
6. Electrical Measurements 40
6.1. ID - VG Measurement[이미지참조] 40
6.2. ID - VDS Measurement[이미지참조] 41
6.3. ID - t (real-time) Measurement[이미지참조] 41
Ⅳ. Result and discussion 43
1. Optical & Surface analyses 43
1.1. Optical microscopy 43
1.2. Atomic-force microscopy 45
1.3. Raman spectroscopy & Photoluminescence spectroscopy 47
2. Electrical result 49
2.1. ID - VG results[이미지참조] 49
2.2. ID - VDS results[이미지참조] 54
2.3. ID - t (real-time) results[이미지참조] 57
3. Mobility & Carrier concentration 59
4. Comparison of gas sensitivity 61
Ⅴ. Summary and Conclusion 66
Ⅵ. References 67
국문초록 70
Table 1. E₂g¹ and A₁g peak frequencies with various laser line[이미지참조] 29
Table 2. Mobility of a 3-layer MoS₂ FET 60
Table 3. Carrier concentration of a 3-layer MoS₂ FET 60
Figure 1. Structure of MoS₂. 16
Figure 2. Structure of MOP. 18
Figure 3. Mechanical exfoliation process. 24
Figure 4. Raman Scattering. 27
Figure 5. Raman spectra of thin (nL) and bulk MoS₂ films. 29
Figure 6. Principle of Photoluminescence: Electronic band structure and optical transitions. 31
Figure 7. Reflection and photoluminescence spectra of ultrathin MoS₂ layers. 33
Figure 8. E-beam lithography process. 35
Figure 9. Force and distance relation of atomic force microscopy. 37
Figure 10. Wire bonding process. 39
Figure 11. Schematic diagram of a 2D MoS₂ FET-based gas sensor 42
Figure 12. Optical microscope image of 2D MoS₂ FET (a) without MOP, (b) with MOP 44
Figure 13. AFM height image of 3-layer MoS₂ 46
Figure 14. Raman spectrometer spectrum of 3-layrer MoS₂ (a) Raman spectroscopy, (b) Photoluminescence spectroscopy 48
Figure 15. ID - VG of 2D MoS₂ FET devices without MOP under various environmental conditions[이미지참조] 50
Figure 16. ID - VG of 2D MoS₂ FET devices with MOP under various environmental conditions[이미지참조] 51
Figure 17. ID - VG graphs at 500 Torr for each gas (a) without MOP, (b) with MOP[이미지참조] 53
Figure 18. ID - VDS of 2D MoS₂ FET devices without MOP under various environmental conditions[이미지참조] 55
Figure 19. ID - VDS of 2D MoS₂ FET devices with MOP under various environmental conditions[이미지참조] 56
Figure 20. ID-t cycle[이미지참조] 58
Figure 21. Gas sensitivity of a 3-layer MoS₂ FET 62
Figure 22. Gas sensitivity of a 3-layer MoS₂ FET 63
Figure 23. Gas sensitivity of MoS₂ FETs as a function of the number of layers 65