Supplementary Material for
Spectral change of simulated X-ray photoelectron spectroscopy from graphene to fullerene
Jungpil Kim, Yasuhiro Yamada*, Miki Kawai, Takehiro Tanabe, Satoshi Sato
Graduate School of Engineering, Chiba University, 1-33Yayoi, Inage, Chiba 263-8522, Japan
*Corresponding author. Tel/Fax: +81-43-290-3376. E-mail address: (Y. Yamada).
S1. Results and Discussion
S1.1Comparison of graphene with different molecular weight
Figure S1 shows peak positions and FWHMs of simulated C1s spectra of graphene with different molecular weight such as C62H20, C100H26, and C146H32. Peak positions were shifted to high binding energies as the molecular weight increased. The peak position of C1s spectrum of graphene (C100H26) was 284.0 eV, which was sufficiently close to that of graphene with large molecular weight such as C146H32 (284.2 eV).It indicates that the peak position of C100H26is close tothat of graphene with infinite molecular weight.FWHMs were almost constant, even thoughthe molecular weight increased.Thus, C100H26 was selected as the basic structure for lowcalculation cost.
S1.2 Simulated C1s XPS spectra of structures before applying asymmetric Voigt function.
FigureS2 shows simulated C1s spectra of structures shown in Fig. 2before applying asymmetric Voigt function.The number of orbitals was countedevery 0.05 eV to draw simulated C1s. C1 indicates carbon atoms on hexagons which bonded with carbon atoms. C2 indicates carbon atoms bondedwith hydrogen atoms. C3 indicates carbon atoms on pentagons.
S1.3 Ratio of Lorentzian function to Gaussian function (m) and asymmetry factor (α)
Figure S3a and b showsactual and simulated C1s spectra of graphite and C60. For the simulation, asymmetric Voigt-typelineshape with different values of ratioof Lorentzian function to Gaussian function (m) and asymmetry factor (α) was applied.The shapeofsimulated C1s spectrum of graphenewas well-matched with that of actual C1s spectrum of graphite, whereas the shape of simulated C1s spectrum of C60was relatively matched with that of actual C1s spectrum of C60. The slight shift of simulated spectrum of C60 from actual spectrum will be adjusted at the end of this work (Fig. 6).Figure S3c shows the proposed values of m and α, which wereapplied to simulated C1s spectra(Fig. 3).
S1.4 Mulliken charge distribution
Figure S4 shows the Mulliken charges of each carbon atom in graphene terminated hydrogen atoms (Fig. 2a).Numbers of electrons of carbon atoms on C2 were much larger than those on C1 because hydrogen atoms donate electrons to C2.Thus, aC1s peak of graphene was divided into two types of peaks originating from C1 (thin line in Fig. 3a) and C2 (dashed line in Fig. 3a) at 284.0 and 283.7 eV, respectively [22].
Figure S5 shows an optimized structure and the Mulliken charge distribution of graphene with two pentagons (Fig. 2b). These two pentagons in graphene are identical in structures.The increment of the electron in pentagons is caused by the electron-withdrawing nature of pentagons.The averaged charge distribution of one carbon atom on one pentagon is -0.066 which was calcualted by averaging the sum of all charges on carbon atoms in one pentagon: (-0.074 + -0.069 + -0.063 + -0.040 + -0.082) / 5. It means that an averaged number of electrons of one carbon atom on one pentagon is 6.066.
Figure S6 shows Mulliken charge distributions of isolated and connected pentagons.The averaged charge distribution of one carbon atom on one pentagon in two isolated pentagons (Fig. S6a) is -0.068which is calcualted by averaging the sum of all charges on carbon atoms in one pentagon: (-0.093 × 2 + -0.062 × 2 + -0.032) / 5.It means that an averaged number of electrons of one carbon atom on one pentagon is 6.068. The averaged number of electrons of one carbon atom decreased because of the presence of two connetected pentagons.The averaged charges of one carbon atom on one pentagon in two connected pentagons (Fig. S6b) was -0.046,which was calcualted as (-0.051 × 2 + -0.053 × 2 + -0.022) / 5. Thus, the number of electrons of carbon atoms on pentagon decreased because of thepresence of connected pentagons (Fig. 4b and Fig. S6b and c).
Figure S7 shows the optimized structure (a) and simulated XPS spectrum (b) of graphene with one Stone-Thrower-Wales (STW) defect. C4 indicates the carbon atoms on heptagons (Fig. S7). The calculated data for the peak shifts, FWHMs, and work function were also shown in Table S1. The peak top of normal graphene (284.0 eV) (Table 1) increased to 284.2 eV in graphene with one STW defect (Table S1) because of the decrement of the work function (Table S1). The FWHM of normal graphene (1.25) (Table 1) increased to 1.40 eV (Table S1) because of the increment of different states of C-C bondings by introduction of the STW defect. FWHM of whole C1s spectrum using large graphene molecule in this work was the same as our previous work using relatively small graphene molecule [21].
Table S1Calculated peak shifts and FWHMs of C1s spectra and work function of graphene with one STW defect.
Ratio of the number of carbon atoms (C1:C2:C3:C4) / 32:26:10:6 / C2 (C-H) / Peak top / eV / 283.9FWHM / eV / 1.20
Whole C1s spectrum
(C1 + C2 + C3 + C4) / Peak top / eV / 284.2 / C3 (Pentagon) / Peak top / eV / 284.1
FWHM / eV / 1.40 / FWHM / eV / 1.75
C1 + C3 + C4
(Hexagon + Pentagon + Heptagon) / Peak top / eV / 284.2 / C4 (Heptagon) / Peak top / eV / 284.8
FWHM / eV / 1.40 / FWHM / eV / 1.25
C1 (Hexagon) / Peak top / eV / 284.2 / Work function / eV / 3.79
FWHM / eV / 1.25
(a) (b) (c)
Fig. S1 Peak positions and FWHMs of simulated C1s XPS of graphene with different molecular weight. (a) C62H20.(b) C100H26.(c) C146H32.
(a) (b) (c)
(d) (e) (f)
Fig. S2 Simulated C1s XPS spectra of structures shown in Fig. 2 before applying asymmetric Voigt function.(a) Graphene terminated with hydrogen atoms. (b) Two pentagons. (c) Four pentagons. (d) Six pentagons. (e) Eight pentagons. (f) Twelve pentagons without hydrogen atoms (fullerene).C1 indicates carbon atoms on hexagons whichbonded with carbon atoms. C2 indicates carbon atoms bonded with hydrogen atoms. C3 indicates carbon atoms on pentagons.
(a) (b)
(c)
Fig. S3Actual C1s spectra of graphite and C60 and simulated C1s spectra of graphene and C60 using asymmetricVoigt-type with different of values of m and α.(a) C1s spectra of graphene (graphite). Black line: Simulated C1s spectrum of graphene using asymmetric Voigt-type lineshape (m = 0.95, α = 0.27). Red line: Actual C1s spectrum of graphite.(b) C1s spectra of C60. Black line: Simulated C1s spectrum of C60 using asymmetric Voigt-type lineshape (m = 0.80, α = 0). Red line: Actual C1s spectrum of C60. (c) Proposed values of m and α for applying simulated C1s spectrum of each structure in Fig. 2.
Fig. S4Mulliken charge distribution of graphene terminated with hydrogen atoms. C1 indicates carbon atoms which bond with carbon atoms. C2 indicatescarbon atoms bonded with hydrogen atoms.
(a) (b)
Fig. S5Mulliken charge distribution of graphene with two pentagons. (a) An optimized structure.Two pentagons are identical in structures. (b) A magnified image of (a) and charge distribution of one pentagon.
(a)
Fig. S6Mulliken charge distributions of isolated pentagons and connected pentagons. (a) Two isolated pentagons. (b) Two connected pentagons.(c) Eightconnected pentagons.Red circle: One pentagon. Blue circle: Two carbon atoms bonded each other in two connected pentagons.
(a) (b)
Fig. S7 Optimized structure and simulated XPS spectrum of graphene with one STW defect. (a) Optimized structure. All the edges were terminated with hydrogen atoms (white sphere). C1 indicates carbon atoms on hexagons which bonded with carbon atoms. C2 indicatescarbon atoms bonded with hydrogen atoms. C3 indicates carbon atoms on pentagons (pink spheres). C4 indicates carbon atoms on heptagons (blue-colored spheres). (b)Simulated and normalized C1s XPS spectrum using asymmetric Voigt-type lineshapes. Simulated original spectra are shown asbold lines. Peaks originating from carbon atoms on hexagonswhich bonded with carbon atoms (C1), carbon atoms bondedwith hydrogen atoms (C2),carbon atoms on pentagons(C3), and carbon atoms on heptagons (C4)are shown as thin, dashed,dotted, and gray lines, respectively. Values of mand α(Fig. S3c, SM) for graphene were applied to the spectrum.