臺灣博碩士論文加值系統

石墨烯由於其特殊的能帶結構是一種攸關電子科技之前瞻性材料。化學官能基修飾可以改變石墨烯的電子性質，藉形成共價鍵使表面sp2混成的碳轉變為sp3，配合修飾反應的可逆來調控石墨烯能帶的開關。本研究中選用化學氣相沉積製作的單層石墨烯與五元雜環為反應物種，在超高真空系統下運用程溫脫附質譜(TPD)分辨鍵結強度，由反射式吸收紅外光譜(RAIR)判別表面物種的吸附形式及位向，而在腔體內反應後取出之樣品作拉曼檢定，由D(1350cm-1)、 G(1500cm-1)、 2D(2700cm-1) band的相對比例檢驗石墨烯是否因官能基化發生結構改變，最後透過密度泛函理論(DFT)計算構型、吸附能進而對照出合理的表面鍵結形式。
由Haddon等人報告指出，石墨烯擁有親二烯(dienophile)與二烯(diene)雙重性質使其可藉由Diels-Alder環加成反應修飾石墨烯。本篇將先用順丁烯二酸酐(Maleic anhydride)為示範實驗，在420 K左右TPD有測量到可能來自Retro-DA的脫附訊號，而在日本製石墨烯樣品的RAIR光譜經過背景干擾去除與基線校正後發現ν(Csp2-H)位移至ν(Csp3-H)有疑似化學修飾的痕跡，而在拉曼與計算結果皆暗示有化學官能基修飾的可能。
由上述示範實驗架構我們將嘗試用五元雜環:呋喃、吡咯與呋喃衍生物修飾石墨烯表面，其中我們將探討環電性對環加成的影響，推拉電子基增強呋喃為親二烯(dienophile)或二烯(diene)的性質，雙取代位置異構物造成的立體障礙是否影響環加成的路徑，但是由於石墨烯樣品的問題使我們在TPD與RAIR部分的結果並不一致，不過RAIR指出在所有五元雜環樣品脫附前的光譜依然保持分子特徵峰暗示化學反應並無發生，而在拉曼鑑定的D-band可能非化學修飾造成的結果，此外在DFT計算中僅有少數的吸附能是負值，統整上述實驗結果可以了解五元雜環分子在石墨烯上的交互作用。

Graphene, a prospective material with novel band structure makes it pertinent to the future electronic technology. Chemical functionalization is effective to modulate the electronic properties of graphene. Forming covalent bonds can change the carbon hybridization from sp2 to sp3 state, in collaboration with its reaction reversibility, to the graphene band gap of graphene can be switched. In my research, the cycloaddition reactions of CVD-grown single-layer graphene with a series of π-conjugated 5-membered heterocycles were investigated.. Under ultrahigh vacuum conditions, temperature-programmed desorption (TPD) was utilized to characterize the bonding strengths and the desorbing species, and reflection-absorption infrared spectroscopy (RAIRS) measurements assisted to identify the adsorption geometry of the corresponding adsorbates. After cycloaddition with heterocycles in vacuum, the graphene samples were removed out for ex-situ Raman inspection. The relative intensities of D and G to 2D band are indicative of the functionalized graphene. Finally, density functional theory calculations were conducted to predict the bonding geometry and adsorption energies which help to interpret the experimental data.
According to Haddon’s report, graphene can be functionalized via Diels-Alder reactions attributed to its dual roles as diene or dienophile. In this study, maleic anhydride (MA) was selected as a dienophile to demonstrate the feasibility of the DA reaction. The TPD spectra show desorption peak at 420 K, reasonably attributable to the temperature for retro-DA reaction. The RAIR spectra acquired from a graphene sample reveal a transition from the sp2-CH stretch to sp3-CH stretch after background subtraction and baseline correction, a definitive evidence for graphene functionalization. In addition, the DFT and Raman spectra results of the MA-graphene system strongly suggest the possibility of surface modification.
We also tested the DA reactivity of graphene with several other 5-membered heterocycles, such as furan, pyrrole and substituted furan derivatives. The issues about the aromaticity, the electronic effects of substituted groups and the steric effects were thoroughly investigated. However, the TPD and RAIR results from sample to sample are not quite correlated, and the RAIR spectra indicated that the 5-membered heterocycles are unreactive towards the cycloaddition reactions. Graphene functionalization is not adequate to account for the observed D-band emergence in the Raman spectra. DFT calculations revealed that noncovalent interaction is dominant on the graphene surface.

目錄
論文審定書 i
謝誌 ii
摘要 iv
Abstract v
Table of Content vii
List of Figures ix
List of table xvi
Chapter 1. Introduction 1
Chapter 2 Experimental section 9
2.1 Ultrahigh Vacuum System 9
2.2 Temperature-programmed desorption spectroscopy(TPD) 12
2.3 Reflection-absorption infrared spectroscopy (RAIRS) 14
2.4 Raman spectroscopy 18
2.5 Density functional theory (DFT) calculations 19
2.6 Reagents and materials 20
Chapter 3 Results 22
3.1 Maleic anhydride (MA) 22
3.2 Furan-graphene experiment 35
3.3 Pyrrole 50
3.4 2-Furonitrile and furfurylamine 53
3.5 2,3-Dihydrofuran and 2,5-dihydrofuran 57
3.6 2, 3-Dimethylfuran and 2, 5-dimethylfuran 60
Chapter 4 Discussion 63
4.1 Functionalization of graphene with maleic anhydride via Diels-Alder reaction under UHV conditions: a dry process 63
4.2 Interactions of graphene with 5-membered heterocycles are dominated by noncovalent π-bonding. 66
4.3 Experimental results were not reproducible on various commercial graphene samples and the perspective of graphene grown on Cu(111). 69
Chapter 5. Conclusions 72
References 74
Appendix 78

List of Figures
Figure 1.1. Different dimensionalities of carbon materials: 0D buckyball, 1D nanotube, 2D graphene and 3D graphite1. 2
Figure 1.2. Band structure of graphene and zero bandgap at the Dirac points. 2
Figure 1.3. Various types of reactions for graphene functionlization10. 3
Figure 1.4. (Left) Raman spectra of graphene before and after hydrogenation12. (Right) Raman spectra of fluorinated single-layer graphene before and after annealing. It is noted that the defect peaks are suppressed, indicating that the functionalization is reversible 22. 4
Figure 1.5. The resonance forms of graphene19. 5
Figure 1.6. Dual nature of reactivity of graphene in Diels-Alder chemistry19. 5
Figure 1.7. Two types of graphene models terminated with hydrogen atoms. Graphene can be either considered as a 2π or 4π system with different types of cycloadditions23. 6
Figure 1.8. Graphene models with various types of defects24. 7
Figure 1.9. (Left) The intensity ratio of I2D/IG can be used to determine the number of graphene layers29. (Right) The intensity ratio ID/IG is widely used for characterizing the defect quantity in graphene26. 8
Figure 2.2.1 Experimental setup for performing a TPD experiment. The form of a TPD spectrum is also depicted. 13
Figure 2.3.1 The phase shift for light reflection from metal surface as calculated for light polarized both parallel to (p) and perpendicular to (s) the plane of incidence. 15
Figure 2.3.2. Schematic of the Reflection-adsorption infrared spectroscopy apparatus. 16
Figure 2.5.1 Furan-graphene cycloaddition. (left) Furan as diene react at site a-c (Right) furan as dienophile react at site 1-3. 19
Figure 2.6.1. Graphene purchased from different companies. (Left) Graphenea copper foil thickness 18μm (Right) Platform copper foil thickness 35 μm. 20
Figure 2.6.2. Due to the different thickness Platform (Japan) graphene installation is easier than Graphenea (Spain) graphene. 20
Figure 3.1.1. TPD spectrum after adsorption of 400 L MA on graphene/Cu at 95 K. 23
Figure 3.1.2. The ATR spectra of (a) exfoliated graphene (b) maleic anhydride (MA), and (c) MA-graphene (adopted from ref 18). 24
Figure 3.1.3. Coverage-dependent RAIR spectra after exposing graphene/Cu to MA at 95 K. 25
Figure 3.1.4. Temperature-dependent RAIR spectra after adsorption of 1800 L MA on graphene/Cu at 95 K. 25
Figure 3.1.5. Temperature-dependent RAIR spectra after the adsorption of 1500 L MA on graphene/Cu at 300 K. 27
Figure 3.1.6. Difference spectrum after substracting the 600 K spectrum from the 450 K RAIR spectrum. 27
Figure 3.1.7. Temperature-dependent RAIR spectra after the adsorption of 1.5 L MA on graphene/Cu at 200 K. 28
Figure 3.1.8. Coverage-dependent TPD spectra obtained after the adsorption of MA on graphene/Cu supplied from Graphene Platform (JP) at 95 K. 30
Figure 3.1.9. Temperature-dependent RAIR spectra after the adsorption of 10 L MA on graphene/Cu (JP) at 95 K. 30
Figure 3.1.10. Maleic anhydride RAIR spectrum after subtraction and baseline correction. 31
Figure 3.1.11. Raman spectra of graphene as-received (Right) and graphene after reaction (Left). Insets show the optical micro-images of the surface. 33
Figure 3.2.1. The guiding concepts for furan-based experiments. 34
Figure 3.2.2. Coverage-dependent TPD spectra after dosing furan on graphene/Cu (ESP) at 95 K. 36
Figure 3.2.3. TPD spectra from 200 to 800 K to highlight the chemisorbed species. 36
Figure 3.2.4. RAIR spectrum obtained after exposing on graphene/Cu to 30 L furan at 95 K. 38
Figure 3.2.5. Temperature-dependent RAIR spectra after adsorption of 20 L furan on graphene/Cu at 95 K. 38
Figure 3.2.6. Temperature-dependent RAIR spectra after adsorption of 2 L furan on graphene/Cu at 95 K. 39
Figure 3.2.7. Coverage-dependent RAIR spectra after the furan adsorption from 0.1 to 2 L on graphene/Cu at 95 K. 40
Figure 3.2.8. Coverage-dependent TPD spectra after exposing graphene/Cu (JP) to furan at 95 K. The inset highlights the desorption features in the 200 to 600 K range. 42
Figure 3.2.9. Temperature-dependent RAIR spectra after the adsorption of 20 L furan on graphene/Cu (JP) at 95 K. 42
Figure 3.2.10. Coverage-dependent TPD spectra after dosing furan on Cu foil at 95 K. 44
Figure 3.2.11. Temperature-dependent RAIR spectra after dosing furan on Cu foil at 95 K. 44
Figure 3.2.12. (a) the delocalized MO indicating the π-interaction (b) furan(4π)-graphene(2π) at site C (c) furan(2π)-gaphene(4π) at site 3. 46
Figure 3.2.3. The optical images (a) graphene (Graphenea, ESP) /Cu foil As-received (b) graphene transferred to SiO2 (c) after the interaction with furan. The Raman spectra (left) measured (a), (b) and (c), and the right shows graphene (Graphene Platform, JP) /Cu foil As-received. 48
Figure 3.2.14. Raman spectra of furan-graphene (ESP) obtained by 633 nm Laser excitation. 49
Figure 3.2.15. Raman spectra of furan-graphene (JP) obtained by 633 nm Laser excitation. 49
Figure 3.3.1 Multiple-ion TPD spectra after the adsorption of 1 L pyrrole on different graphene samples at 95 K. 51
Figure 3.3.2. Temperature-dependent RAIR spectra after exposing pyrrole to samples from Graphenea (left) and Graphene Platform (Right), respectively, at 95 K. 51
Figure 3.3.3 (Left) (2+2) and (Right) (4+2) pyrrole cycloadducts at site a on graphene where graphene functions as the dienophile. 52
Figure 3.4.1. Temperature-dependent RAIR spectra after the adsorption of 10 L 2-furonitrile on graphene (Spain) at 95 K. 55
Figure 3.4.2. Temperature-dependent RAIR spectra after exposing on graphene (Spain) to 5 L furfurylamine at 95 K. 55
Figure 3.4.3. Coverage-dependent TPD spectra after dosing furfurylamine on graphene (Spain) at 95 K. 56
Figure 3.5.1. Coverage-dependent TPD spectra after exposing 2,3-dihydrofuran (Left) and 2,5-dihydrofuran (Right) on graphene (Japan) at 95 K. 58
Figure 3.5.2. Temperature-dependent RAIR spectra after the adsorption of 2.5 L 2,3-dihydrofuran (Left) and 10 L 2,5-dihydrofuran (Right) on graphene (JP) at 95 K. 59
Figure 3.6.1. Coverage-dependent TPD spectra after exposing graphene (Spain) to 1 L 2, 3-dimethylfuran (Left) and 2, 5-dimethylfuran (Right) at 95 K. 61
Figure 3.6.2. Temperature-dependent RAIR spectra after dosing 2,3-dimethylfuran (Left) and 2,5-dimethylfuran (Right) on graphene (Japan) at 95 K. 62
Figure 4.1.1 Comparison of Haddon’s IR spectra to our results. (Left) ATR spectra from exfoliated graphene, the red trace shows the ν(Csp3-H) at 2850 and 2925 cm-1. (adopted from ref 15) (Right) Our RAIR spectra show the ν(Csp3-H) at 2925 and 2863 cm-1. 65
Figure 4.1.2 Raman spectra from epitaxial graphene (Left) and CVD-grown graphene. The epitaxial graphene (EG) films, grown on the C-face of SiC substrates was measured with 532 nm laser excitation. 65
Figure 4.2. Different stages correspond to the amount of furan adsorption on the surface. 68
Figure 4.3.1 TPD spectra after adsorption of 0.1 L (left) and 2.5 L (right) on different samples at 95 K. 70
Figure 4.3.2 Comparison of commercial and home-made graphene samples. The inset shows serious oxidation occurred on the commercial graphene surface and the Raman spectra indicate the home-made graphene is closer to a single-layered graphene state. 71
Figure A.1. Time dependence of Cu (111) pretreatment parameters: temperature and composition/flow rate. 79
Figure A.2. Time dependence of graphene growth parameters: temperature and composition/flow rate. 79

List of Table
Table 2.6 List of reagents used in experiment. 21
Table 3.1.1. Comparisons of DFT calculation results of Houk (M06-2X/6-31G(d))23 with ours (M06L/6-31G(d)). The adsorption energies are given in kcal/mol. 32
Table 3.2. DFT results for furan-graphene interactions and the adsorption energies are given in kcal/mol. 46
Table 3.3. DFT energetic results from furan-graphene and pyrrole-graphene systems where graphene was set as dienophile. The adsorption energies are given in kcal/mol. 52
Table 3.4. Substituted furan DFT calculation results where graphene was set as dienophile. The adsorption energies are given in kcal/mol. 56
Table 3.5. Dihydrofuran DFT calculation results where graphene was set as either dienophile or diene. The adsorption energies are given in kcal/mol. 59
Table 3.6. Dimethylfuran DFT calculation results, where graphene wasset as dienophile. The adsorption energies are given in kcal/mol. 62
Table 4.2. Summarized TPD results obtained after exposing graphene/Cu to diverse 5-membered heterocyclic reactants at 95 K. 68

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