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1 This journal is The Royal Society of Chemistry 13 Supplementary Information for Chemical Interaction and Imaging of Single /Graphene Sheet Studied by Scanning Transmission X-ray Microscopy and X-ray Absorption Spectroscopy Jian Wang*, Jigang Zhou*, Yongfeng Hu, and Tom Regier Canadian Light Source Inc., University of Saskatchewan, Saskatoon, SK S7N X, Canada Contents (supplementary figures and table) Fig. S1: C K-edge STXM chemical imaging of individual /N-rmGO sheets on a holey carbon film coated TEM grid. Fig. S: N K-edge STXM chemical imaging of individual /N-rmGO sheets on a holey carbon film coated TEM grid. Fig. S3: Co L-edge STXM chemical imaging of individual /N-rmGO sheets on a holey carbon film coated TEM grid. Fig. S: Correlation analysis for STXM chemical imaging. Fig. S: Co K-edge XANES spectra of /N-rmGO and NP together with the linear combination fit of the spectra. Table S1: Linear combination fitting coefficients and fitting quality (χ ) of Co K-edge XANES spectra of /N-rmGO and NP fitted by the normalized reference spectra of CoO, Co O 3 and NP. 1

2 Thickness (nm) Absorbance (nm -1 ) Absorbance This journal is The Royal Society of Chemistry 13.3 C 1s. C 1s. N-rmGO.3.1 Graphene elemental X-ray absorption N-rmGO 1. (d) nm (e) 1.9 Graphene sheet cross-section thickness profile Distance ( m) (f) Composite map nm.7 nm Figure S1 C K-edge STXM chemical imaging of individual /N-rmGO sheets on a holey carbon film coated TEM grid, linearly scaled reference spectrum of N-rmGO (spectrum scaled to the calculated graphene elemental X-ray absorption profile of 1 nm thick material, assuming graphene density is.1 g/cm 3, same as that of graphite); reference spectrum of holey carbon obtained at a pure region on the sample; thickness map of N-rmGO, the vertical grey scale represents the material thickness in nm, the enclosed white dotted lines indicate the regions of interest, i.e. a folded graphene sheet; (d) cross-section thickness profile along the red dotted arrow in ; (e) map of holey carbon, the vertical grey scale represents the intensity ratio to the reference spectrum; (f) colour composite map, red color: N-rmGO, green color: holey carbon; the enclosed white dotted lines indicate the regions of interest.

3 Absorbance (nm -1 ) This journal is The Royal Society of Chemistry 13 Pre-Edge (39-39 ev).1 od Max. Abs. (3-37 ev). od nm nm N 1s: N-rmGO Thickness 17. nm.1 (d) N 1s.1.9 /N-rmGO nm Figure S N K-edge STXM chemical imaging of individual /N-rmGO sheets on a holey carbon film coated TEM grid, N 1s pre-edge averaged optical density (od) image from 39 to 39 ev; N 1s averaged od image at the maximum absorption from 3 to 7 ev; N- rmgo thickness map derived from the N 1s, i.e. maximum absorption image subtracts preedge image, then scaled by the edge-jump (difference of the pre-edge and the absorption maximum, i.e..1 od nm -1 ) of (d) /N-rmGO linear reference spectrum (nm -1 ) at the N 1s. The enclosed white dotted lines indicate the regions of interest, i.e. a folded graphene sheet; (d) was obtained from the absolute absorption spectrum of /N-rmGO, i.e. Fig. c, divided by the thickness of the sample region of interest (. nm) from which the spectrum was obtained. 3

4 Absorbance (nm -1 ) Absorbance This journal is The Royal Society of Chemistry 13. Co p. Co p Co + rich.. elemental X-ray absorption Co + rich (d). (e) nm 1.3 (f) nm Composite map nm. nm Figure S3 Co L-edge STXM chemical imaging of individual /N-rmGO sheets on a holey carbon film coated TEM grid, linearly scaled reference spectra of Co + rich and stoichiometric (spectra scaled to the calculated elemental X-ray absorption profile of 1 nm thick material, d =.11 g/cm 3 ); reference spectrum (i.e. absorption baseline) of holey carbon at the Co L-edge; and (d) thickness maps of stoichiometric and Co + rich respectively, the vertical grey scales represent the material thickness in nm; (e) map of holey carbon, the vertical grey scale represents the intensity ratio to the reference spectrum; (f) colour composite map, red color: Co + rich, green color: holey carbon, blue color: stoichiometric. The enclosed white dotted lines in, (d) and (f) indicate the regions of interest, i.e. a folded graphene sheet.

5 N 1s: N-rmGO Thickness (nm) This journal is The Royal Society of Chemistry 13 1 y =.x -.7 R = C 1s: N-rmGO Thickness (nm) Co3O Thickness (nm) C 1s: N-rmGO Thickness (nm). (d) N 1s: N-rmGO Thickness (nm). (e) y = 1.x - 1. R = Co rich Co3O Thickness (nm) y =.x - 1. R =. Co rich Co3O Thickness (nm) Co3O Thickness (nm) N 1s: N-rmGO Thickness (nm) C 1s: N-rmGO Thickness (nm) Figure S Correlation analysis for images from Fig. 3a to 3d of the main text, correlation plot between N-rmGO thickness derived at the C 1s and N 1s edges, i.e. Fig. 3a versus Fig. 3b; and correlation plots between Co3O and the N-rmGO thickness derived at the C 1s and N 1s, respectively, i.e. Fig. 3c versus Fig. 3a and 3b respectively; (d) and (e) correlation plots between Co+ rich Co3O and the N-rmGO thickness derived at the C 1s and N 1s, respectively, i.e. Fig. 3d versus Fig. 3a and 3b respectively. The red dashed lines in, and plots are fitted trendlines labelled with linear relationship equations and the correlation coefficients.

6 Normalized (E) This journal is The Royal Society of Chemistry Co K-edge 1... /N-rmGO /N-rmGO fit /N-rmGO Co valence fit NP NP Co valence fit Figure S Co K-edge XANES spectra of /N-rmGO and NP together with the linear combination fit of the spectra. Red line: /N-rmGO XANES spectrum, black dashed line: /N-rmGO spectrum fitted by the normalized reference spectra of CoO, Co O 3 and NP (for reference spectra see Figure in the main text), red dashed line: /N-rmGO spectrum Co valence fitted by the normalized reference spectra of CoO and Co O 3, blue line: NP XANES spectrum, blue dashed line: NP spectrum Co valence fitted by the normalized reference spectra of CoO and Co O 3. All fitting coefficients are listed in Table S1. Table S1 Linear combination fitting coefficients and fitting quality (χ ) of Co K-edge XANES spectra of /N-rmGO and NP fitted by the normalized reference spectra of CoO, Co O 3 and NP. Normalized Reference Spectra CoO Co O 3 NP /N-rmGO fit.131(.).(.).9(.).931 /N-rmGO Co valence fit.31(.9).9(.9).197 NP Co valence fit.311(.9).9(.9).99 N.B.: values in the brackets are the fitting errors. χ