Limits...
Graphene on ferromagnetic surfaces and its functionalization with water and ammonia.

Böttcher S, Weser M, Dedkov YS, Horn K, Voloshina EN, Paulus B - Nanoscale Res Lett (2011)

Bottom Line: In this article, an angle-resolved photoelectron spectroscopy (ARPES), X-ray absorption spectroscopy (XAS), and density-functional theory (DFT) investigations of water and ammonia adsorption on graphene/Ni(111) are presented.ARPES and XAS data of the H2O (NH3)/graphene/Ni(111) system give an information regarding the kind of interaction between the adsorbed molecules and the graphene on Ni(111).The presented experimental data are compared with the results obtained in the framework of the DFT approach.

View Article: PubMed Central - HTML - PubMed

Affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany. dedkov@fhi-berlin.mpg.de.

ABSTRACT
In this article, an angle-resolved photoelectron spectroscopy (ARPES), X-ray absorption spectroscopy (XAS), and density-functional theory (DFT) investigations of water and ammonia adsorption on graphene/Ni(111) are presented. The results of adsorption on graphene/Ni(111) obtained in this study reveal the existence of interface states, originating from the strong hybridization of the graphene π and spin-polarized Ni 3d valence band states. ARPES and XAS data of the H2O (NH3)/graphene/Ni(111) system give an information regarding the kind of interaction between the adsorbed molecules and the graphene on Ni(111). The presented experimental data are compared with the results obtained in the framework of the DFT approach.

No MeSH data available.


(Central panel) Photoemission intensity map shows the modification of the valence band of the graphene/Ni(111) system at the Γ point upon adsorption of water molecules (partial water-pressure p = 5 × 10-8 mbar; t is the deposition time). (Upper panel) Photoemission intensity profiles are shown for several time-points demonstrating the main photoemission features: Ni 3d states, graphene π states, and water-induced states (I and II). (Right panel) Photoemission intensity profiles as a function of water deposition time (t) taken at particular binding energies: red solid line, blue solid circles, and green open squares show intensity profiles at 7, 8.3, and 10 eV of the binding energies, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211271&req=5

Figure 2: (Central panel) Photoemission intensity map shows the modification of the valence band of the graphene/Ni(111) system at the Γ point upon adsorption of water molecules (partial water-pressure p = 5 × 10-8 mbar; t is the deposition time). (Upper panel) Photoemission intensity profiles are shown for several time-points demonstrating the main photoemission features: Ni 3d states, graphene π states, and water-induced states (I and II). (Right panel) Photoemission intensity profiles as a function of water deposition time (t) taken at particular binding energies: red solid line, blue solid circles, and green open squares show intensity profiles at 7, 8.3, and 10 eV of the binding energies, respectively.

Mentions: In order to study the growth modes of water or ammonia, the time sequences of the photoemission maps around the Γ point of the Brillouin zone (sampling angle of ±10° with respect to the normal emission) were recorded. The extracted photoemission intensity map showing the modification of the valence band at the Γ point of the graphene/Ni(111) system upon adsorption of water molecules (t is the deposition time) is shown in Figure 2 (central panel). Photoemission intensity profiles for several time-points demonstrating the main photoemission features of spectra [Ni 3d states, graphene π states, and water-induced states (I and II)], as well as intensity profiles as a function of water deposition time (t) taken at particular binding energies (red solid line, blue solid circles, and green open squares show intensity profiles at 7, 8.3, and 10 eV of the binding energies, correspondingly) are shown in the upper and right panels, respectively. The behavior of the water-related photoemission features, I and II, allows us to conclude that island-type growth of water on graphene/Ni(111) takes place: (i) These features start to grow simultaneously at t = 130 s, but slopes of the intensities growth are different; (ii) After t = 170 s, the intensity of feature I decreases via the exponential law, and there is a small plateau for the feature II (first ML is complete); (iii) At t = 230 s, when the thickness of deposited water is more than 2ML, probably, the structural phase transition takes place--formation of ice. Since ice is an insulator, the rapid decrease of the photoemission intensities of the Ni-related features and the shift of some states to higher binding energies can be explained by the formation of an insulating thin film of ice on top of the graphene/Ni(111) system. The delay in starting of the growth of the water-related photoemission features is somewhat puzzling (130 s until the first water-related signal appears in the spectra), but this delay could be because some clustering centers on the graphene/Ni(111) surface are necessary to allow water growth process to start. As soon as sufficient numbers of such centers are formed, the process of growth is accelerated. The general trend in the observation of the ammonia-related photoemission features in the similar experiments is the same. In subsequent XAS and ARPES experiments, the thicknesses of water and ammonia layers were chosen to be 1/3-1/2 of the ML (as discussed above with regard to the structure).


Graphene on ferromagnetic surfaces and its functionalization with water and ammonia.

Böttcher S, Weser M, Dedkov YS, Horn K, Voloshina EN, Paulus B - Nanoscale Res Lett (2011)

(Central panel) Photoemission intensity map shows the modification of the valence band of the graphene/Ni(111) system at the Γ point upon adsorption of water molecules (partial water-pressure p = 5 × 10-8 mbar; t is the deposition time). (Upper panel) Photoemission intensity profiles are shown for several time-points demonstrating the main photoemission features: Ni 3d states, graphene π states, and water-induced states (I and II). (Right panel) Photoemission intensity profiles as a function of water deposition time (t) taken at particular binding energies: red solid line, blue solid circles, and green open squares show intensity profiles at 7, 8.3, and 10 eV of the binding energies, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211271&req=5

Figure 2: (Central panel) Photoemission intensity map shows the modification of the valence band of the graphene/Ni(111) system at the Γ point upon adsorption of water molecules (partial water-pressure p = 5 × 10-8 mbar; t is the deposition time). (Upper panel) Photoemission intensity profiles are shown for several time-points demonstrating the main photoemission features: Ni 3d states, graphene π states, and water-induced states (I and II). (Right panel) Photoemission intensity profiles as a function of water deposition time (t) taken at particular binding energies: red solid line, blue solid circles, and green open squares show intensity profiles at 7, 8.3, and 10 eV of the binding energies, respectively.
Mentions: In order to study the growth modes of water or ammonia, the time sequences of the photoemission maps around the Γ point of the Brillouin zone (sampling angle of ±10° with respect to the normal emission) were recorded. The extracted photoemission intensity map showing the modification of the valence band at the Γ point of the graphene/Ni(111) system upon adsorption of water molecules (t is the deposition time) is shown in Figure 2 (central panel). Photoemission intensity profiles for several time-points demonstrating the main photoemission features of spectra [Ni 3d states, graphene π states, and water-induced states (I and II)], as well as intensity profiles as a function of water deposition time (t) taken at particular binding energies (red solid line, blue solid circles, and green open squares show intensity profiles at 7, 8.3, and 10 eV of the binding energies, correspondingly) are shown in the upper and right panels, respectively. The behavior of the water-related photoemission features, I and II, allows us to conclude that island-type growth of water on graphene/Ni(111) takes place: (i) These features start to grow simultaneously at t = 130 s, but slopes of the intensities growth are different; (ii) After t = 170 s, the intensity of feature I decreases via the exponential law, and there is a small plateau for the feature II (first ML is complete); (iii) At t = 230 s, when the thickness of deposited water is more than 2ML, probably, the structural phase transition takes place--formation of ice. Since ice is an insulator, the rapid decrease of the photoemission intensities of the Ni-related features and the shift of some states to higher binding energies can be explained by the formation of an insulating thin film of ice on top of the graphene/Ni(111) system. The delay in starting of the growth of the water-related photoemission features is somewhat puzzling (130 s until the first water-related signal appears in the spectra), but this delay could be because some clustering centers on the graphene/Ni(111) surface are necessary to allow water growth process to start. As soon as sufficient numbers of such centers are formed, the process of growth is accelerated. The general trend in the observation of the ammonia-related photoemission features in the similar experiments is the same. In subsequent XAS and ARPES experiments, the thicknesses of water and ammonia layers were chosen to be 1/3-1/2 of the ML (as discussed above with regard to the structure).

Bottom Line: In this article, an angle-resolved photoelectron spectroscopy (ARPES), X-ray absorption spectroscopy (XAS), and density-functional theory (DFT) investigations of water and ammonia adsorption on graphene/Ni(111) are presented.ARPES and XAS data of the H2O (NH3)/graphene/Ni(111) system give an information regarding the kind of interaction between the adsorbed molecules and the graphene on Ni(111).The presented experimental data are compared with the results obtained in the framework of the DFT approach.

View Article: PubMed Central - HTML - PubMed

Affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany. dedkov@fhi-berlin.mpg.de.

ABSTRACT
In this article, an angle-resolved photoelectron spectroscopy (ARPES), X-ray absorption spectroscopy (XAS), and density-functional theory (DFT) investigations of water and ammonia adsorption on graphene/Ni(111) are presented. The results of adsorption on graphene/Ni(111) obtained in this study reveal the existence of interface states, originating from the strong hybridization of the graphene π and spin-polarized Ni 3d valence band states. ARPES and XAS data of the H2O (NH3)/graphene/Ni(111) system give an information regarding the kind of interaction between the adsorbed molecules and the graphene on Ni(111). The presented experimental data are compared with the results obtained in the framework of the DFT approach.

No MeSH data available.