Supporting Information: Electronic and Chemical Properties of Donor ...
Supporting Information: Electronic and Chemical Properties of Donor, Acceptor Centers in Graphene Mykola Telychko,†,‡ Pingo Mutombo,† Pablo Merino,¶ Prokop Hapala,† Martin Ondr´aˇcek,† Fran¸cois C. Bocquet,§,k Jessica Sforzini,§,k Oleksandr Stetsovych,† ˇ ∗,† Martin Vondr´aˇcek,⊥ Pavel Jel´ınek,∗,† and Martin Svec Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnick´a 10, CZ-16200 Prague, Czech Republic, Charles University, Faculty of Mathematics and Physics, V Holeˇsoviˇck´ach 2, Praha 8, Czech Republic, Max Planck Institute for Solid State Research, Heisenberg Strasse 1, 70569 Stuttgart, Peter Gr¨ unberg Institut (PGI-3), Forschungszentrum J¨ ulich, 52425 J¨ ulich, Germany, J¨ ulich-Aachen Research Alliance (JARA); Fundamentals of Future Information Technology, 52425 J¨ ulich, Germany, and Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 10, CZ-18228 Prague, Czech Republic E-mail: [email protected]; [email protected]
∗
To whom correspondence should be addressed Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnick´a 10, CZ-16200 Prague, Czech Republic ‡ Charles University, Faculty of Mathematics and Physics, V Holeˇsoviˇck´ach 2, Praha 8, Czech Republic ¶ Max Planck Institute for Solid State Research, Heisenberg Strasse 1, 70569 Stuttgart § Peter Gr¨ unberg Institut (PGI-3), Forschungszentrum J¨ ulich, 52425 J¨ ulich, Germany k J¨ ulich-Aachen Research Alliance (JARA); Fundamentals of Future Information Technology, 52425 J¨ ulich, Germany ⊥ Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 10, CZ-18228 Prague, Czech Republic †
1
Controllability of the B,N doping The graphene samples were prepared with different B,N dopant concentrations. We were able to control the doping levels by deliberately changing the preparation parameters. We performed more than 30 doping experiments in which either N or B was doped separately or together and evaluated the concentration of five selected samples. The standard deviation arising from the randomness of the dopant distribution is below 0.02% with 0.95 confidence level for all calculated concentrations.
Figure S1: Large-scale constant current STM scans of the four samples with different concentrations of the a),b) B dopants and c),d) N dopants.
In the case of B, the amount of the precursor present on the surface before the annealing reflects in the concentration of the substitutional dopants found in the graphene. However,
2
there are strong indications that the B atoms diffuse to the subsurface region, thus reducing greatly the initial amount of B precursor on the surface (XPS data, not shown here). In the Figure S1a,b we show two example STM images of different samples with B-dopant concentrations 0.05% and 0.11%. For N, the intensity and duration of the ion flux during the implantation process is directly related to the amount of substitutional N dopants in graphene after the thermal stabilization. The Figure S1c,d depicts two concentrations of N dopants on the surface, 0.16% and 0.27%. A considerable fraction of the meta N-dopant configurations is detected at the sample with 0.27% concentrations.
Figure S2: Filled and empty state STM scan of the B,N co-doped graphene with the individual features distinguished. The fact, that the dopants are very stable at high temperatures and thus the N-doping can be executed after the end of the B-doping, allows to control the doping levels independently. Nevertheless, the controllability has certain limitations. As the amount of N and B dopants increases, some new formations emerge. The Figure S2 shows an example, where the doping levels reached 0.68% of N and 0.11% of B (evaluated before the N-doping). We can identify here the expected single N and B dopants plus the meta N-dopants, however a few para 3
N-dopants and some new objects appear, which are likely to be made up of individual N and B dopants, given the high purity of the doping processes. The influence of such formations on the electronic structure of graphene is, at the present moment, unclear. In all the STM measurements, we never observed an indication of a pyrrole or pyridinelike defects being present; however we cannot fully exclude their existence. Especially at higher concentrations, as shown, a number of features appear, that have to be identified yet. Also, the N-doped samples just after the ion implantation but before the high temperature stabilization give broad core-level components in the photoemission spectroscopy, as shown in the Figure S3. After the annealing, the spectral components become visibly sharper, which suggests a recovery of spurious defects in graphene created during the N-ion implantation and reduction of the number of different features on the surface.
Figure S3: N1s photoemission spectrum after exposing the sample to the flux 100 eV N+ ions for 40 min. Red and blue spectra were taken before and after thermal stabilisation.
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Scanning tunneling spectroscopy on the dopants For the B-dopants and their surrounding, we have performed a detailed STS measurements. STS spectra are shown in the Figure S4. Similarly to the case of N-doping, 1 the STS curves taken on graphene surrounding the dopant has two dips at around zero bias and -0.35 V, the fingerprints of the epitaxial graphene on SiC(0001). 2,3 On the other hand, in the vicinity of the B-dopant, a massive increase of the differential conductance in the filled states is observed, suggesting presence of high density of electrons of energy -0.35eV below the Fermi level. The position of this differential current onset may vary with the tunneling distance. Therefore it does not necessarily reflect the exact position of the corresponding electronic state.
Figure S4: Experimental STS taken at different positions over the B dopant and its vicinity as shown at the inset image.
References 1. Telychko, M.; Mutombo, P.; Ondr´aˇcek, M.; Hapala, P.; Bocquet, F. C.; Kolorenˇc, J.; ˇ Vondr´aˇcek, M.; Jel´ınek, P.; Svec, M. Achieving High-Quality Single-Atom Nitrogen Dop5
ing of Graphene/SiC(0001) by Ion Implantation and Subsequent Thermal Stabilization. ACS Nano 2014, 8, 7318–7324. 2. Joucken, F.; Tison, Y.; Lagoute, J.; Dumont, J.; Cabosart, D.; Zheng, B.; Repain, V.; Chacon, C.; Girard, Y.; Botello-M´endez, A. R. et al. Localized State and Charge Transfer in Nitrogen-Doped Graphene. Phys. Rev. B 2012, 85, 161408. 3. Zhao, L.; He, R.; Rim, K. T.; Schiros, T.; Kim, K. S.; Zhou, H.; Guti´errez, C.; Chockalingam, S. P.; Arguello, C. J.; P´alov´a, L. et al. Visualizing Individual Nitrogen Dopants in Monolayer Graphene. Science 2011, 333, 999–1003.
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∗
To whom correspondence should be addressed Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnick´a 10, CZ-16200 Prague, Czech Republic ‡ Charles University, Faculty of Mathematics and Physics, V Holeˇsoviˇck´ach 2, Praha 8, Czech Republic ¶ Max Planck Institute for Solid State Research, Heisenberg Strasse 1, 70569 Stuttgart § Peter Gr¨ unberg Institut (PGI-3), Forschungszentrum J¨ ulich, 52425 J¨ ulich, Germany k J¨ ulich-Aachen Research Alliance (JARA); Fundamentals of Future Information Technology, 52425 J¨ ulich, Germany ⊥ Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 10, CZ-18228 Prague, Czech Republic †
1
Controllability of the B,N doping The graphene samples were prepared with different B,N dopant concentrations. We were able to control the doping levels by deliberately changing the preparation parameters. We performed more than 30 doping experiments in which either N or B was doped separately or together and evaluated the concentration of five selected samples. The standard deviation arising from the randomness of the dopant distribution is below 0.02% with 0.95 confidence level for all calculated concentrations.
Figure S1: Large-scale constant current STM scans of the four samples with different concentrations of the a),b) B dopants and c),d) N dopants.
In the case of B, the amount of the precursor present on the surface before the annealing reflects in the concentration of the substitutional dopants found in the graphene. However,
2
there are strong indications that the B atoms diffuse to the subsurface region, thus reducing greatly the initial amount of B precursor on the surface (XPS data, not shown here). In the Figure S1a,b we show two example STM images of different samples with B-dopant concentrations 0.05% and 0.11%. For N, the intensity and duration of the ion flux during the implantation process is directly related to the amount of substitutional N dopants in graphene after the thermal stabilization. The Figure S1c,d depicts two concentrations of N dopants on the surface, 0.16% and 0.27%. A considerable fraction of the meta N-dopant configurations is detected at the sample with 0.27% concentrations.
Figure S2: Filled and empty state STM scan of the B,N co-doped graphene with the individual features distinguished. The fact, that the dopants are very stable at high temperatures and thus the N-doping can be executed after the end of the B-doping, allows to control the doping levels independently. Nevertheless, the controllability has certain limitations. As the amount of N and B dopants increases, some new formations emerge. The Figure S2 shows an example, where the doping levels reached 0.68% of N and 0.11% of B (evaluated before the N-doping). We can identify here the expected single N and B dopants plus the meta N-dopants, however a few para 3
N-dopants and some new objects appear, which are likely to be made up of individual N and B dopants, given the high purity of the doping processes. The influence of such formations on the electronic structure of graphene is, at the present moment, unclear. In all the STM measurements, we never observed an indication of a pyrrole or pyridinelike defects being present; however we cannot fully exclude their existence. Especially at higher concentrations, as shown, a number of features appear, that have to be identified yet. Also, the N-doped samples just after the ion implantation but before the high temperature stabilization give broad core-level components in the photoemission spectroscopy, as shown in the Figure S3. After the annealing, the spectral components become visibly sharper, which suggests a recovery of spurious defects in graphene created during the N-ion implantation and reduction of the number of different features on the surface.
Figure S3: N1s photoemission spectrum after exposing the sample to the flux 100 eV N+ ions for 40 min. Red and blue spectra were taken before and after thermal stabilisation.
4
Scanning tunneling spectroscopy on the dopants For the B-dopants and their surrounding, we have performed a detailed STS measurements. STS spectra are shown in the Figure S4. Similarly to the case of N-doping, 1 the STS curves taken on graphene surrounding the dopant has two dips at around zero bias and -0.35 V, the fingerprints of the epitaxial graphene on SiC(0001). 2,3 On the other hand, in the vicinity of the B-dopant, a massive increase of the differential conductance in the filled states is observed, suggesting presence of high density of electrons of energy -0.35eV below the Fermi level. The position of this differential current onset may vary with the tunneling distance. Therefore it does not necessarily reflect the exact position of the corresponding electronic state.
Figure S4: Experimental STS taken at different positions over the B dopant and its vicinity as shown at the inset image.
References 1. Telychko, M.; Mutombo, P.; Ondr´aˇcek, M.; Hapala, P.; Bocquet, F. C.; Kolorenˇc, J.; ˇ Vondr´aˇcek, M.; Jel´ınek, P.; Svec, M. Achieving High-Quality Single-Atom Nitrogen Dop5
ing of Graphene/SiC(0001) by Ion Implantation and Subsequent Thermal Stabilization. ACS Nano 2014, 8, 7318–7324. 2. Joucken, F.; Tison, Y.; Lagoute, J.; Dumont, J.; Cabosart, D.; Zheng, B.; Repain, V.; Chacon, C.; Girard, Y.; Botello-M´endez, A. R. et al. Localized State and Charge Transfer in Nitrogen-Doped Graphene. Phys. Rev. B 2012, 85, 161408. 3. Zhao, L.; He, R.; Rim, K. T.; Schiros, T.; Kim, K. S.; Zhou, H.; Guti´errez, C.; Chockalingam, S. P.; Arguello, C. J.; P´alov´a, L. et al. Visualizing Individual Nitrogen Dopants in Monolayer Graphene. Science 2011, 333, 999–1003.
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