Tailoring the electronic properties of graphene by functionalization: Insights through optical and electron spectroscopy
Zusammenfassung der Projektergebnisse
In the course of this DFG project, we have carried out the spectroscopic investigation of graphane and functionalized mono- and few-layered graphene (FLG) in order to gain a deeper understanding of the influence of various dopants on the electronic properties of graphene layers. Functionalization was carried out with the following methods: (1) evaporation of alkali and alkaline earth metals onto graphene and intercalation into the graphene/substrate interface, (2) deposition of organic molecules onto the graphene surface and (3) reversible hydrogenation of graphene by exposure to a beam of atomic hydrogen. Especially the last point turned out to be a promising way due to the partial sp3 character and the possibility of using hydrogenated graphene (also known as graphane) as a transistor material. Graphane is a very recently discovered form of graphene but with atomic hydrogen bound to the carbon atoms. This results in a change of the hybridization from sp2 to sp3 which is reversible depending on the number of adsorbed hydrogen atoms. So far, the electronic properties of graphane were investigated with transport measurements, clearly indicating the formation of an energy gap, which is relevant regarding possible applications in the field of transistors or sensors. Therefore one main topic of this project was to determine the quasiparticle dispersion of graphane and functionalized graphene with ARPES and the phonon dispersion with high resolution EELS. In this context we studied the influence of the hydrogen content on the electronic properties of graphane since the hybridization change from sp2 to sp3 is tunable by reversible hydrogenation. Afterwards the theoretical description of the experimental data within TB, LDA and GW calculations was performed. The graphene samples that we measured were highly crystalline layers grown by precipitation on SiC and by chemical vapor deposition on Ni(111) surfaces. A big success of this part of the project results was that we managed to get a title page of "Adv. Matt.", a leading journal in the field. In the latter part we concentrated on the effects of alkali metal doping of graphene. We found that the Fermi Level of graphene can be shifted by over 1.3 eV resulting in a strong electron-phonon interaction. This electron-phonon interaction manifests as a kink in quasiparticle spectrum as measured by ARPES. We have experimented with various alkali metal dopants and alkaline earth metals (K, Li, Rb, Cs, Ca, Ba) in order to study the influence of the dopant. For the more interesting of these dopants we have measured the full quasiparticle dispersion by ARPES and determined the electron-phonon coupling constants. In a more recent work we have determined from ARPES data the Eliashberg function, which is the central quantity for a coupled electron-phonon system. This is of central importance to the field of superconductivity in GICs and possibly graphene.
Projektbezogene Publikationen (Auswahl)
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(2010) Quasi-freestanding and single-atom thick layer of hexagonal boron nitride as a substrate for graphene synthesis. Physical Review B, Vol. 82. 2010, Iss. 7, 075415.
Usachov, D., Adamchuk, V., Haberer, D., Grüneis, A., Sachdev H., Preobrajenski, D., Vyalikh, D.V.
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(2010) Tunable band gap in hydrogenated quasi-free-standing graphene. Nano Letters, Vol. 10.2010, Issue 9, pp. 3360–3366.
Haberer, D; Vyalikh, D. V; Taioli,S. ; Dora,B; Farjam, , M. ; Fink,J. ; Marchenko, D; Pichler, T. ; Ziegler,K. ; Simonucci,S.; Dresselhaus,M. S. ; Knupfer,M. ; Büchner, B.; Grüneis, A.
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(2011) 'Graphene Epitaxy by Chemical Vapor Deposition on SiC', Nano Letters, Vol. 11. 2011, Issue 4, pp. 1786–1791.
Strupinski, W., Grodecki, K., Wysmolek, A., Stepniewski, R., Szkopek,T., Gaskell, P.E., Grüneis, A., Haberer, D., Bozek, R., Krupka, J., Baranowski, J. M.
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(2011) Direct observation of a dispersionless impurity band in hydrogenated graphene. Physical Review B, Vol. 83.2011, Issue 16 , 165433.
Haberer, D., Petaccia, L., Farjam, M., Taioli, S., Jafari, S.A., Nefedov, A., Zhang, W., Calliari, L., Scarduelli, G., Dora, B., Vyalikh, D.V., Pichler, T., Woll, Ch., Alfe, D., Simonucci, S., Dresselhaus, M.S., Knupfer, M., Buchner, B., Grüneis, A.
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(2011) Effect of hydrogen adsorbates on the quasiparticle spectra of graphene. Physical Review B, Vol. 83. 2011, Issue 19, 193411.
Farjam, M., Haberer, D., Grüneis, A.
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(2011) Electronic properties of hydrogenated quasi-free-standing graphene. physica status solidi (b), Vol. 248. 2011, Issue 11, pp. 2639–2643.
D. Haberer, L. Petaccia, Y. Wang, H. Quian, M. Farjam, S. A. Jafari, H. Sachdev, A. V. Federov, D. Usachov, D. V. Vyalikh, X.Liu, O. Vilkov, V. K. Adamchuk, S.Irle, M. Knupfer, B. Buchner, A. Grüneis
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(2011) Evidence for a New Two-Dimensional C 4 H-Type Polymer Based on Hydrogenated Graphene. Advanced Materials, Vol. 23. 2011, Issue 39, pp. 4497–4503.
Haberer, D., Giusca, C. E., Wang, Y., Sachdev, H., Fedorov, A. V., Farjam, M., Jafari, S. A., Vyalikh, D. V., Usachov, D., Liu, X., Treske, U., Grobosch, M., Vilkov, O., Adamchuk, V. K., Irle, S., Silva, S. R. P., Knupfer, M., Büchner, B., Grüneis, A.
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(2011) Evidence for a New Two-Dimensional C4H-Type Polymer Based on Hydrogenated Graphene', Advanced Materials, Vol. 23. 2011, Issue 39, pp. 4497–4503.
Haberer, D., Giusca, C. E., Wang, Y., Sachdev, H., Fedorov, A. V., Farjam, M., Jafari, S. A., Vyalikh, D. V., Usachov, D., Liu, X., Treske, U., Grobosch, M., Vilkov, O., Adamchuk, V. K., Ire, S., Silva, S. R. P., Knupfer, M., Büchner, B., Grüneis, A.
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(2011) Nitrogen-Doped Graphene: Efficient Growth, Structure, and Electronic Properties. Nano Letters, Vol. 11. 2011, Issue 12, pp. 5401–5407.
Usachov, D., Vilkov, O., Grüneis, A., Haberer,D., Fedorov,A., Adamchuk,V. K., Preobrajenski, A. B., Dudin,P., Barinov,A., Oehzelt,M., Laubschat,C., Vyalikh,D. V.
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(2012) Probing Local Hydrogen Impurities in Quasi-Free-Standing Graphene ', ACS Nano (2012) , 6 (12), pp 10590
Scheffler, M., Haberer, D., Petaccia, L., Farjam, M., Schlegel, R., Baumann, D., Hänke, T., Grüneis, A., Knupfer, M., Hess, C., Büchner, B.
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(2013) Anisotropic Eliashberg function and electron-phonon coupling in doped graphene. Physical Review B, Vol. 88. 2013, Issue 8, 081401.
D. Haberer, L. Petaccia, A. V. Federov, D. V. Vyalikh, M. Knupfer, B. Buchner, A. Grüneis
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(2013) Anisotropic eliashberg function and electronphonon coupling in doped graphene’. Phys. Rev. B Rapid, 88:081401, Aug 2013
D. Haberer, L. Petaccia, A. V. Fedorov, C. S. Praveen, S. Fabris, S. Piccinin, O. Vilkov, D. V. Vyalikh, A. Preobrajenski, N. I. Verbitskiy, H. Shiozawa, J. Fink, M. Knupfer, B. Büchner, and Grüneis, A.
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(2013) Synthesis and electronic properties of chemically functionalized graphene on metal surfaces’. Journal of Physics: Condensed Matter, Vol. 25. 2013, Number 4: 043001.
Grüneis, A.
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(2013), Kinetic Isotope Effect in the Hydrogenation and Deuteration of Graphene. Advanced Functional Materials, Vol. 23. 2013, Issue 13, pp. 1628–1635.
Paris, A., Verbitskiy, N. I., Nefedov, A., Wang, Y., Fedorov, A. V., Haberer, D., Oehzelt, M., Petaccia, L., Usachov, D., Vyalikh, D. V., Sachdev, H., Wöll, C., Knupfer, M., Büchner, B., Calliari, L., Yashina, L. V., Irle, S., Grüneis, A.
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(2014) Observation of a universal donor-dependent vibrational mode in graphene’, Nature Communications 5, 3257 (2014)
Fedorov,A. V., Verbitskiy, N.I., Haberer, D., Struzzi, C. , Petaccia,L. , Usachov,D.U. , Vilkov,O.Y., Vyalikh, D.V., Fink,J., Knupfer, M., Büchner, B. , Grüneis, A.
