Supporting Information. Dual Route Hydrogenation of the Graphene/Ni. Interface

Transcription

1 Supporting Information. Dual Route Hydrogenation of the Graphene/Ni Interface Daniel Lizzit, Mario I. Trioni, Luca Bignardi,, Paolo Lacovig, Silvano Lizzit,, Rocco Martinazzo, and Rosanna Larciprete, Elettra-Sincrotrone Trieste S.C.p.A., AREA Science Park, S.S. 14 km 163.5, Trieste, Italy CNR- Institute of Molecular Science and Technologies (ISTM), via Golgi 19, Milano, Italy Università degli Studi di Milano, Dip. di Chimica, via Golgi 19, Milano, Italy CNR-Institute for Complex Systems (ISC), via dei Taurini 19, Roma, Italy present address: Dep. of Physics, University of Trieste, via Valerio 2, Trieste, Italy 1

2 LEED pattern of Gr/Ni(111) Fig.S 1: LEED pattern taken at 75 ev on the Gr/Ni(111) suaface. The pattern shows the six sharp diffraction spots characteristic of the crystalline structure of monolayer graphene on Ni(111). The graphene diffraction spots overlap those of the substract due to the similar lattice periodicity. Np spectroscopy Figure S2 shows the Np spectra measured on Ni(111) and Gr/Ni(111) before and after the exposure to hydrogen. For a better evaluation the spectra have been normalized to have the same peak intensity. The comparison between the spectra measured on clean Ni(111) and Gr/Ni(111) demonstrates that the presence of the graphene layer determines a shift of 190 mev to higher BE of the main peak, whose FWHM decrease from 1.22 to 1.10 ev. The changes in the spectral line shape can be mainly attributed to the contribution of the first layer atoms, that, due to the interaction with graphene, is shifted to higher BE with respect to the bare metal surface. The Np spectra measured on Gr/Ni(111) after the exposure to 0.7 KL of hydrogen reveals an additional tiny BE shift ( 40 mev) due to the increased graphene interaction with the substrate, since some C atoms approach the Ni surface after the chemisorption of H atoms on graphene. After the exposure to 34 KL of hydrogen, corresponding to the fully H-intercalated interface with the metal surface covered by H atoms and decoupled from graphene, the Np peak appears up-shifted by 190 mev with 2

3 Fig.S 2: Comparison between the Np spectra taken on Ni(111) and Gr/Ni(111) before and after the exposure to hydrogen; for a better evaluation the spectra were normalized to have the same peak intensity. respect to the clean Ni(111). The same shift is observed for the Ni(111) surface saturated with hydrogen at 130 K, indicating that H adsorption induces the same BE shift in the Np spectrum, independently from the presence of the decoupled graphene cover. This BE shift is by chance equivalent of that observed for Gr/Ni(111). C1s line shape The C1s spectrum measured on as-grown Gr/Ni(111) might exhibit, on the left-side of the main peak C 0, a shoulder S which might have null (left panel in Figure S3) or considerable intensity 1 (right panel in Figure S3) even if graphene is grown in the same conditions (C 2 H 4 precursor, gas pressure, substrate cleaning procedure, growth temperature and rate) on the same Ni(111) crystal. The shoulder has been related to Gr regions where the interaction with the Ni substrate is, for some reasons, decreased and therefore has been attributed to rotated domains where the Gr-Ni interaction is lower, 2 and more recently to the presence of residual NiC 2 carbide islands, 3 that lift graphene with respect to the surrounding regions, where it lies directly on the Ni surface. 3

4 Fig.S 3: C1s spectra showing only the C 0 main peak (left) and also the presence of the shoulder S (right). In the experimental runs carried out to study the hydrogenation of Gr we have grown Gr/Ni(111) samples with and without the shoulder in their pristine C1s spectra, but could not appreciate any meaningful influence on the H chemisorption or intercalation. In the whole article we show only results obtained on Gr/Ni(111) samples, whose C1s spectra showed shoulder of null or negligible intensity. However, when carrying out the hydrogenation in the presence of the shoulder we did not observed any notable difference with respect to the findings here described. 4

5 Reversibility Figure S4 compares the C1s spectra measured on the pristine Gr/Ni(111) surface with those measured on the same surface after the hydrogenation uo to the saturation of the chemisorption phase (d=0.7 KL) and after thermal annealing to 700 K. The perfect similarity of the line shapes taken before and after the hydrogenation-dehydrogenation cycle demonstrates that the H atoms chemisorbed on graphene can be removed in a fully reversible way. Fig.S 4: C1s spectra taken on the pristine Gr/Ni(111) surface and on the same surface after the hydrogenation at the saturation of the chemisorption phase (d=0.7 KL) and after H 2 desorption by thermal annealing at 700 K. 5

6 C1s core level shifts and adsorption energies Table 1: The whole set of C1s core level shifts (CLSs) and average H adsorption energies (Eads ) calculated for the different clusters considered. 1H fcc TOP-FCC H fcc meta H fcc meta i1 i1 7H fcc meta i6 TOP-BRIDGE 1H top-hcp H ortho-brid i H top-fcc 5H fcc meta i H fcc meta 4H fcc meta i1 1H top H fcc meta References 1. Larciprete, R.; Colonna, S.; Ronci, F.; Flammini, R.; Lacovig, P.; Apostol, N.; Politano, A.; Feulner, P.; Menzel, D.; Lizzit, S. Self-Assembly of Graphene Nanoblisters 6

7 Sealed to a Bare Metal Surface. Nano Lett. 2016, 16, Patera, L. L.; Africh, C.; Weatherup, R. S.; Blume, R.; Bhardwaj, S.; Castellarin- Cudia, C.; Knop-Gericke, A.; Schloegl, R.; Comelli, G.; Hofmann, S.; Cepek, C. In Situ Observations of the Atomistic Mechanisms of Ni Catalyzed Low Temperature Graphene Growth. ACS Nano 2013, 7, Africh, C.; Cepek, C.; Patera, L. L.; Zamborlini, G.; Genoni, P.; Menteş, T. O.; Sala, A.; Locatelli, A.; Comelli, G. Switchable Graphene-Substrate Coupling through Formation/Dissolution of an Intercalated Ni-Carbide Layer. Sci. Rep. 2016, 6,