Filling of carbon nanostructures
Endohedrally doped (filled) nanostructures display a doping method unique to cage molecules and cylinders in which an ion (or ions) are encaged inside the carbon framework of a fullerene molecule or a nanotube.
These hybrid-systems represent a complete new type of matter. They are described by the symbol for the encapsulated atom and the fullerene molecule's formula separated by the @ sign, which signals the endohedral nature of the complex, for example La@C82. Endohedral fullerenes containing metal ions (socalled metallofulleres) could act as vehicles to transport poisonous atoms, can be used as MRI markers in medicine and can be used to stabilize and passivate reactive species. Moreover N containing metallofullerenes can be used as containers for atomic Nitrogen and can be used as ESR standard. Metal filled nanotubes can act as nonreactive passivated nanomagnets. Last but not least so-called peapods (fullerenes filled into SWCNT) e.g. C60@SWCNT) represent a hybrid system of fullerenes and single wall carbon nanotubes (SWCNT) with intriguing new properties.
In the IFW we span a wide range of activities. On the one hand we are working on the production and purification and separation and spectroelectrochemical characterization of endohedral fullerenes as well as on the production and analysis of the magnetical properties of metal filled MWCNT and on the formation of fullerene peapods. On the other hand we concentrate on the analysis of the electronic optical and vibronic properties of these systems in our Spectroscopy Group using high energy spectroscopy (EELS, PES, XAS) and optical spectroscopy (IR, UVVIS, Raman) as probes. We have been busy investigating the electronic and vibronic structure of endohedral fullerenes and filled SWCNT. Our aim is to understand the interaction between the encapsulated ion and its host cage/tube. As mentioned above, an important parameter here is the interplay between charge transfer and covalent interaction from the metal ion to the fullerene molecule or nanotube.
Examples:
Endohedral Fullerenes:
- Tm@C82: Tm is one of the rare earth metals (a lanthanide) and is normally trivalent in the solid state - i.e. it has three valence electrons and thus an electronic configuration of [Xe] 4f12 6s2 5d1. We have investigated Tm@C82 using photoemission (PES, see Figure 1), electron energy-loss (EELS) and x-ray absorption spectroscopy (XAS). All of these data taken together offer conclusive proof that the Tm in Tm@C82 has 13 4f electrons in the ground state and thus is divalent. The charge transfer is purely ionic and formally Tm2+@C822-. This shows the possibility of the stabilization of encaged metal ions in unusual valence states.
- Trimetalnitride Fullerenes : This system represents another example of an hybridsystem containing two species which are both not stable alone. However, upon formation of the endofullerene the C80 cage with Ih symmetry and the trimetalnitride units such as Sc3N, Tm3N, Dy3N, ... are stabilized. We analysed the interplay between charge transfer and covalent interaction in this system using XAS. From a comparison with multiplett calculations including charge transfer it was shown that Sc is trivalent and the effective valency of Sc(III) is 2.4 leaving a charge transfer of six electrons to the C80 cage. This shows the importance of the covalent interaction between the Sc3N unit and the C80 cage. Recent results on the systems containing rare earth trimetalnitrides, such as Tm3N and Dy3N confirmed this observation.
Filled SWCNT:
- C60@SWCNT: C60 peapods represent new hybridsystems of fullerenes and SWCNT. One important question is guest host interaction as well as the filling rate on a bulk scale. Using bulk sensitive EELS we have shown that pristine peapods are weakly interacting van der Waals systems with a filling ratio up to 78%
- Upon intercalation there is a competitive charge transfer to the SWCNT and to the fullerene cage. At highest intercalation level a metallic singly bonded C606- polymer is stabilized within the SWCNT.
These results and more additional information in the selected papers listed below. If you'd like a copy of any of these publications or want more information about our work, please contact Thomas Pichler.
Literature:
- R. Pfeiffer, H. Kuzmany, T. Pichler, H. Kataura, Y. Achiba, M. Melle-Franco, F. Zerbetto
Electronic and mechanical coupling between guest and host in carbon peapods
Physical Review B 69 (2004) Nr. 3, S. 35404/1-7 - F. Simon, H. Kuzmany, H. Rauf, T. Pichler, J. Bernardi, H. Peterlik, L. Korecz, F. Fueloep, A. Janossy
Low temperature fullerene encapsulation in single wall carbon nanotubes: synthesis of N@C60@SWCNT
Chemical Physics Letters 383 (2004) Nr. 3-4, S. 362-367 - X. Liu, T. Pichler, M. Knupfer, J. Fink and H. Kataura
Electronic properties of potassium-intercalated C60 peapods
Phys. Rev. B 69, 075417 (2004) - T. Pichler, A. Kukovecz, H. Kuzmany, H. Kataura, Y. Achiba
Quasicontinuos electron and hole doping in C60 peapods
Phys. Rev. B 67, (2003) 125416 - H. Kuzmany, R. Pfeiffer, Ch. Kramberger, T. Pichler, X. Liu, M. Knupfer, J. Fink, H. Kataura, Y. Achiba, B.W. Smith and D.E. Luzzi
Analysis of the concentration of C60 fullerenes in single wall carbon nanotubes
Appl. Phys. A 76, 449 (2003) - H. Kuzmany, A. Kukovecz, C. Kramberger, T. Pichler, M. Holzinger, H. Kataura
Exohedral and endohedral functionalization of single wall carbon Nanotubes
Synthetic Metals 135-136 (2003), S. 791-793 - X. Liu, T. Pichler, M. Knupfer, J. Fink and H. Kataura
Determination of the filling factor of C60 peapods by electron energy-loss spectroscopy in transmission
Synth. Met. 135-136, 715 (2003) - L. Alvarez, T. Pichler, P. Georgi, T. Schwieger, H. Peisert, L. Dunsch, Z. Hu, M. Knupfer, J. Fink, M.S. Golden, P. Bressler and M. Mast
Electronic state of pristine and intercalated Sc3N@C80 metallofullerene
Phys. Rev. B 66, 035107 (2002) - X. Liu, T. Pichler, M. Knupfer, M.S. Golden, J. Fink, H. Kataura, Y. Achiba, K. Hirahara, S. Iijima
Filling factors, structural, and electronic properties of C60 molecules in single-wall carbon nanotubes
Physical Review B 65 (2002) Nr. 4, S. 45419/1-6 - T. Pichler, H. Kuzmany, H. Kataura, Y. Achiba
Metallic polymers of C60 inside single-walled carbon nanotubes
Physical Review Letters 87 (2001) Nr. 26, S. 267401/1-4 - T. Pichler, Z. Hu, C. Grazioli, S. Legner, M. Knupfer, M. S. Golden, J. Fink, F. M. F. de Groot, M. R. C. Hunt, P. Rudolf, R. Follath, Ch. Jung, L. Kjeldgaard, P. A. Brühwiler, M. Inakuma and H. Shinohara
Proof for trivalent Sc ions in Sc2@C84 from high energy spectroscopy
Phys. Rev. B 62, 13196 (2000) - T. Pichler, J. Winter, C. Crazioli, M.S. Golden, M. Knupfer, P. Kuran, U. Kirbach, L. Dunsch, and J. Fink
The electronic structure of potassium intercalated Tm@C82
Synth. Metals 103, 2470 (1999) - T. Pichler, M. Knupfer, M.S. Golden, T. Böske, J. Fink, U. Kirchbach, P. Kuran, L. Dunsch, C.H. Jung
The metallofullerene Tm@C82: isomer-selective electronic structure
Appl. Phys. A 66, 281 (1998) - T. Pichler, M. S. Golden, M. Knupfer, J. Fink, U. Kirbach, P. Kuran, and L. Dunsch
Monometallofullerene Tm@C82: proof of an encapsulated divalent Tm ion by high energy spectroscopy
Phys. Rev. Lett. 79, 3026 (1997)
IFF / Electronic and optical Properties || Last update 5. December 2006 || Author: T. Pichler