Thin films of molecular organic semiconductors are attracting much interest for use in electronic and optoelectronic applications. The electronic properties of these materials and their interfaces are therefore worth investigating intensively1,2,3, particularly the degree of electron delocalization that can be achieved2,4. If the delocalization is appreciable, it should be accompanied by an observable electronic band dispersion. But so far only limited experimental data on the intermolecular dispersion of electronic states in molecular materials is available5,6,7,8, and the mechanism(s) of electron delocalization in molecular materials are also not well understood. Here we report scanning tunnelling spectroscopy observations of an organic monolayer film on a silver substrate, revealing a completely delocalized two-dimensional band state that is characterized by a metal-like parabolic dispersion with an effective mass of m* = 0.47me, where me is the bare electron mass. This dispersion is far stronger than expected for the organic film alone7, and arises as a result of strong substrate-mediated coupling between the molecules within the monolayer.
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Dimitrakopoulos, C. D. & Malenfant, P. R. L. Organic thin film transistors for large area electronics. Adv. Mater. 14, 99–117 (2002)
Karl, N. Charge carrier transport in organic semiconductors. Synth. Met. 133–134, 649–657 (2003)
Cahen, D., Kahn, A. & Umbach, E. Energetics of molecular interfaces. Mater. Today 8, 32–41 (2005)
Sun, Y., Yunqi, L. & Daoben, Z. Advances in organic field-effect transistors. J. Mater. Chem. 15, 53–65 (2005)
Gensterblum, G. et al. Experimental evidence for 400-meV valence band dispersion in solid C60 . Phys. Rev. B 48, 14756–14759 (1993)
Hasegawa, S. et al. Intermolecular energy-band dispersion in oriented thin films of bis(1,2,5-thiadiazolo)-p-quinobis(1,3-dithiole) by angle-resolved photo-emission. J. Chem. Phys. 100, 6969–6973 (1994)
Yamane, H. et al. Intermolecular energy-band dispersion in PTCDA multilayers. Phys. Rev. B 68, 033102(4) (2003)
Koch, N. et al. Evidence for temperature-dependent electron band dispersion in pentacene. Phys. Rev. Lett. 96, 156803(4) (2006)
Glöckler, K. et al. Highly ordered structures and submolecular scanning tunneling microscopy contrast of PTCDA and DM-PBDCI monolayers on Ag(111) and Ag(110). Surf. Sci. 405, 1–20 (1998)
Witte, G. & Wöll, C. Growth of aromatic molecules on solid substrates for applications in organic electronics. J. Mater. Res. 19, 1889–1916 (2004)
Forrest, S. R. Ultrathin organic films grown by organic molecular beam deposition and related techniques. Chem. Rev. 97, 1793–1896 (1997)
Möbus, M., Karl, N. & Kobayashi, T. Structure of perylene-tetracarboxylic-dianhydride thin films on alkali halide crystal substrates. J. Cryst. Growth 116, 495–504 (1992)
Li, J. T., Schneider, W. D., Berndt, R. & Crampin, S. Electron confinement to nanoscale Ag islands on Ag(111): A quantitative study. Phys. Rev. Lett. 80, 3332–3335 (1998)
Kraft, A. et al. Lateral adsorption geometry and site-specific electronic structure of a large organic chemisorbate on a metal surface. Phys. Rev. B 74, 041402(R) (2006)
Norskov, J. K. Chemisorption on metal surfaces. Rep. Prog. Phys. 53, 1253–1295 (1990)
Jung, M. et al. The electronic structure of adsorbed aromatic molecules: Perylene and PTCDA on Si(111) and Ag(111). J. Molec. Struct. 293, 239–244 (1993)
Zou, Y. et al. Chemical bonding of PTCDA on Ag surfaces and the formation of interface states. Surf. Sci. 600, 1240–1251 (2006)
Eremtchenko, M., Schaefer, J. A. & Tautz, F. S. Understanding and tuning the epitaxy of large aromatic adsorbates by molecular design. Nature 425, 602–605 (2003)
Ando, T., Fowler, A. B. & Stern, F. Electronic properties of two-dimensional systems. Rev. Mod. Phys. 54, 437–672 (1982)
Kröger, J. et al. Surface state electron dynamics of clean and adsorbate-covered metal surfaces studied with the scanning tunnelling microscope. Prog. Surf. Sci. 80, 26–48 (2005)
Hauschild, A. et al. Molecular distortions and chemical bonding of a large π-conjugated molecule on a metal surface. Phys. Rev. Lett. 94, 036106(4) (2005)
Rurali, R., Lorente, N. & Ordejón, P. Comment on ‘Molecular distortions and chemical bonding of a large π-conjugated molecule on a metal surface’. Phys. Rev. Lett. 95, 209601 (2005)
Hauschild, A. et al. Reply to “Comment on ‘Molecular distortions and chemical bonding of a large π-conjugated molecule on a metal surface’.”. Phys. Rev. Lett. 95, 209602 (2005)
Kaufman, D. L., Kosztin, I. & Schulten, K. Expansion method for stationary states of quantum billiards. Am. J. Phys. 67, 133–141 (1999)
The work was financially supported by the Deutsche Forschungsgemeinschaft. Author Contributions R.T. and S.S. conducted the experiments and prepared the figures. A.L., in the context of her B.Sc. thesis, participated in the analysis of the data on the delocalized state. F.S.T. and R.T. wrote the paper. R.T., S.S. and F.S.T. discussed the experiments, the data analysis, and the manuscript intensively at all stages of the work.
Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.
This file contains background information on the structure of the PTCDA/Ag(111) interface (section a), additional data supporting an important conclusion of the main text (section b), and simulated wave functions of two-dimensional confined states for comparison with our data. (PDF 186 kb)
About this article
Cite this article
Temirov, R., Soubatch, S., Luican, A. et al. Free-electron-like dispersion in an organic monolayer film on a metal substrate. Nature 444, 350–353 (2006). https://doi.org/10.1038/nature05270
The Journal of Physical Chemistry Letters (2021)
Electronic Properties of 6,13-Diazapentacene Adsorbed on Au(111): A Quantitative Determination of Transport, Singlet and Triplet States, and Electronic Spectra
The Journal of Physical Chemistry C (2020)
New Journal of Physics (2020)
Quasi-One-Dimensional Free-Electron-Like States Selected by Intermolecular Hydrogen Bonds at the Glycine/Cu(100) Interface
Chinese Physics Letters (2020)
Physical Review B (2020)