Tuning the electronic structure of graphene by molecular dopants ...
Tuning the electronic structure of graphene by molecular dopants: Impact of the substrate Christos Christodouloua‡,, Angelos Giannakopoulosb‡, Giovanni Ligorioa, Martin Oehzelta,c, Melanie Timpela, Jens Niederhausena, Luca Pasqualid,e,f, Angelo Gigliae, Khaled Parvezg, Klaus Mülleng, David Beljonneb*, Norbert Kocha* and Marco V. Nardi a a
Humboldt-Universität zu Berlin, Institut für Physik, Brook-Taylor-Straße 6, 12489 Berlin,
Germany b
Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, 7000,
Mons, Belgium c
Helmholtz-Zentrum Berlin für Materialen und Energie GmbH, Albert Einstein Strasse 16,
12489, Berlin, Germany d
University of Modena e Reggio Emilia, Engineering Department. “E. Ferrari”, Via
Vigolese 905, 41125, Modena, Italy e
f
IOM-CNR, Area Science Park, SS 14 Km, 163.5, 34149, Basovizza, Tieste, Italy Department of Physics, University of Johannesburg, PO Box 524, Auckland Park, 2006,
South Africa g
Max Planck Institute für Polymerforschung, Ackermanweg 10, 55128, Mainz, Germany
corresponding authors: [email protected], [email protected]
STRUCTURAL INFORMATION (DFT Calculations) In our theoretical study an F6TCNNQ molecule was physisorbed on graphene (G) in vacuum and graphene-on-copper (G/Cu). The molecule is shown in Figure 1 in the manuscript and in Figure S1 here. The bond lengths are displayed in the figure and equivalent bonds with same bond lengths are indicated with same color dots. After interaction with graphene and graphene-oncopper the molecular structure slightly changes. Figures S2 and S3 show the F6TCNNQ molecule with the differences in the bond lengths, ∆r, indicated in the cases, a) between the charged molecule and the neutral molecule in the gas phase, and b) between the physisorbed molecule on graphene and the neutral molecule in the gas phase. After interaction, in particular, the C-N bond length in the cyano groups decreases by 0.01A while the C-CN bonds connecting the cyano groups to the core of the molecule increase by 0.03A. No differences in bond lengths are observed for F6TCNNQ physisorbed on graphene in vacuum and on graphene-on-copper. Comparison between figures S2 and S3 show that the molecular structure that is obtained after physisorption is very similar with the structure of the charged molecule in the gas phase. Figures S4 and S5 show the side views of the F6TCNNQ molecule physisorbed on graphene and graphene-on-copper. The molecule lies 3.21A over graphene, while the Nitrogen atoms of the cyano groups are slightly closer to graphene, 3.16A. The molecule adopts a quasi-planar conformation. In the case of the graphene covered copper, F6TCNNQ lies slightly closer to graphene, at a distance of 3.18A and the molecule slightly bends (the nitrogen atoms of the cyano groups are 0.15A closer to the surface with respect to the core of the molecule). Nevertheless, in both cases the plane of the molecule is parallel to the plane of graphene, and no tilting is observed. Graphene lies 2.98A over the top layer of copper. DIFFERENTIAL CHARGE DENSITY PLOT In VASP, the information about the electron density of a system is saved as a large matrix in the CHGCAR file. In order to produce the Differential Charge Density (DCD) plot of a system (adsorbent + adsobate) one needs the electron density matrices of the full system (CHGCARsystem) and the two subsystems (CHGCARadsorbent and CHGCARadsorbate). These files are produced by single point (sp) calculations (with all atoms frozen), one for the system as a whole, one for the adsorbent (one keeps only the substrate and removes the adsorbent) and one for the adsorbate (one removes the substrate and keeps the adsorbent). Atoms in the case of sp calculations of adsorbent and adsorbate should be in the same positions as in the system. After these three files are obtained, the CHGCAR with the differential electron desity is obtained as CHGCAR_diff = CHGCARsys – CHGCARadsorbent – CHGCARadsorbate. Finally, the Plane Average DCD is calculated through the CHGCAR_diff file.
Figure S1. The chemical structure of the molecular acceptor F6TCNNQ in a neutral state. The bond lengths are displayed. Equivalent bonds are marked with same color dots.
Figure S2. F6TCNNQ molecule with the differences in the bond lengths between the charged and neutral state in the gas phase.
Figure S3. F6TCNNQ molecule with the differences in the bond lengths between the physisorbed molecule and the neutral state in the gas phase.
Figure S4. Side view of F6TCNNQ molecule physisorbed on graphene in vacuum.
Figure S5. Side view of F6TCNNQ molecule physisorbed on graphene-on-copper.
Humboldt-Universität zu Berlin, Institut für Physik, Brook-Taylor-Straße 6, 12489 Berlin,
Germany b
Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, 7000,
Mons, Belgium c
Helmholtz-Zentrum Berlin für Materialen und Energie GmbH, Albert Einstein Strasse 16,
12489, Berlin, Germany d
University of Modena e Reggio Emilia, Engineering Department. “E. Ferrari”, Via
Vigolese 905, 41125, Modena, Italy e
f
IOM-CNR, Area Science Park, SS 14 Km, 163.5, 34149, Basovizza, Tieste, Italy Department of Physics, University of Johannesburg, PO Box 524, Auckland Park, 2006,
South Africa g
Max Planck Institute für Polymerforschung, Ackermanweg 10, 55128, Mainz, Germany
corresponding authors: [email protected], [email protected]
STRUCTURAL INFORMATION (DFT Calculations) In our theoretical study an F6TCNNQ molecule was physisorbed on graphene (G) in vacuum and graphene-on-copper (G/Cu). The molecule is shown in Figure 1 in the manuscript and in Figure S1 here. The bond lengths are displayed in the figure and equivalent bonds with same bond lengths are indicated with same color dots. After interaction with graphene and graphene-oncopper the molecular structure slightly changes. Figures S2 and S3 show the F6TCNNQ molecule with the differences in the bond lengths, ∆r, indicated in the cases, a) between the charged molecule and the neutral molecule in the gas phase, and b) between the physisorbed molecule on graphene and the neutral molecule in the gas phase. After interaction, in particular, the C-N bond length in the cyano groups decreases by 0.01A while the C-CN bonds connecting the cyano groups to the core of the molecule increase by 0.03A. No differences in bond lengths are observed for F6TCNNQ physisorbed on graphene in vacuum and on graphene-on-copper. Comparison between figures S2 and S3 show that the molecular structure that is obtained after physisorption is very similar with the structure of the charged molecule in the gas phase. Figures S4 and S5 show the side views of the F6TCNNQ molecule physisorbed on graphene and graphene-on-copper. The molecule lies 3.21A over graphene, while the Nitrogen atoms of the cyano groups are slightly closer to graphene, 3.16A. The molecule adopts a quasi-planar conformation. In the case of the graphene covered copper, F6TCNNQ lies slightly closer to graphene, at a distance of 3.18A and the molecule slightly bends (the nitrogen atoms of the cyano groups are 0.15A closer to the surface with respect to the core of the molecule). Nevertheless, in both cases the plane of the molecule is parallel to the plane of graphene, and no tilting is observed. Graphene lies 2.98A over the top layer of copper. DIFFERENTIAL CHARGE DENSITY PLOT In VASP, the information about the electron density of a system is saved as a large matrix in the CHGCAR file. In order to produce the Differential Charge Density (DCD) plot of a system (adsorbent + adsobate) one needs the electron density matrices of the full system (CHGCARsystem) and the two subsystems (CHGCARadsorbent and CHGCARadsorbate). These files are produced by single point (sp) calculations (with all atoms frozen), one for the system as a whole, one for the adsorbent (one keeps only the substrate and removes the adsorbent) and one for the adsorbate (one removes the substrate and keeps the adsorbent). Atoms in the case of sp calculations of adsorbent and adsorbate should be in the same positions as in the system. After these three files are obtained, the CHGCAR with the differential electron desity is obtained as CHGCAR_diff = CHGCARsys – CHGCARadsorbent – CHGCARadsorbate. Finally, the Plane Average DCD is calculated through the CHGCAR_diff file.
Figure S1. The chemical structure of the molecular acceptor F6TCNNQ in a neutral state. The bond lengths are displayed. Equivalent bonds are marked with same color dots.
Figure S2. F6TCNNQ molecule with the differences in the bond lengths between the charged and neutral state in the gas phase.
Figure S3. F6TCNNQ molecule with the differences in the bond lengths between the physisorbed molecule and the neutral state in the gas phase.
Figure S4. Side view of F6TCNNQ molecule physisorbed on graphene in vacuum.
Figure S5. Side view of F6TCNNQ molecule physisorbed on graphene-on-copper.
